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Physiology Exam I Study Guide
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  • Which brain structures are listed as core components of the CNS overview map?

    • Brain stem
    • Thalamus
    • Hypothalamus
    • Basal nuclei
    • Cerebellum
    • Cerebral cortex (4 lobes)
    • Homunculus
    • Language centers
    • Limbic system
    • Neurotransmitter dynamics
    cns anatomy

  • What connection does the hypothalamus have according to the systems map?

    Hypothalamus controls ANS

    hypothalamus ans

  • Name three sensory receptor types mentioned in the PNS & Sensory section.

    • Merkel
    • Pacinian
    • Meissner
    pns receptors

  • How are sensory receptor adaptation types categorized in the overview?

    Adaptation is categorized as tonic vs. phasic

    sensory adaptation

  • Which pain fiber types are listed in the PNS & Sensory section?

    • A-delta
    • C fibers
    pain sensory

  • What exception to typical autonomic structure is noted in the ANS section?

    Adrenal medulla exception

    ans adrenal

  • Which autonomic receptors are named in the ANS overview?

    • Nicotinic
    • Muscarinic
    • Adrenergic
    ans receptors

  • How does the ANS control pupil size according to the Vision section?

    Parasympathetic constricts pupil; sympathetic dilates pupil

    vision ans

  • Which ear-related system shares cranial nerve VIII with the cochlea?

    Vestibular system (CN VIII shared with cochlea)

    hearing vestibular

  • Which vestibular organs detect linear vs. rotational acceleration?

    • Utricle & saccule detect linear
    • Semicircular canals detect rotational
    vestibular balance

  • How does olfaction relate to other brain systems in the chemosensation section?

    Olfaction projects heavily to limbic system

    olfaction limbic

  • What are key components of GI motility listed in the systems map?

    • Mastication
    • Swallowing
    • Peristalsis
    • Gastric mixing
    • Segmentation
    • MMC
    • Haustral contractions
    • Defecation
    gi motility

  • What does the systems map say about enteric nervous system function?

    Enteric NS can function independently

    enteric gi

  • Which GI secretory cells or components are specifically named in the GI Secretion & Absorption section?

    • Parietal cells (gastric acid)
    • Bile
    • Pancreatic secretions
    • Brush border enzymes
    gi secretion

  • What feedback loop involving hormones is mentioned in the GI Secretion & Absorption section?

    Gastrin → somatostatin feedback loop

    gi hormones

  • What structural feature is described as critical for intestinal absorption?

    Surface area (villi/microvilli) critical for absorption

    absorption gi

  • What is 'gray matter' in the CNS?

    • Gray matter: regions of cell bodies and dendrites (cortical surface, deep nuclei)
    neuroanatomy graymatter

  • What is 'white matter' in the CNS?

    • White matter: myelinated axon tracts deep to cortex
    neuroanatomy whitematter

  • What are 'basal nuclei' and how do they relate to 'basal ganglia'?

    • Basal nuclei: cell clusters lateral to thalamus in CNS; 'ganglia' is an older term used for PNS clusters
    basalnuclei neuroanatomy

  • What structures make up the diencephalon as listed?

    • Diencephalon: thalamus and hypothalamus, sitting above the midbrain
    diencephalon neuroanatomy

  • What are 'association areas' in the cerebral cortex?

    • Association areas: cortical regions that integrate multiple inputs for higher-order processing
    cortex association

  • Which structures comprise the brain stem and their primary role?

    • Brain stem: medulla, pons, midbrain; control vital autonomic functions and connect spinal cord with higher brain
    brainstem autonomic

  • What is the primary role of the thalamus?

    • Thalamus: primary sensory relay station that actively filters, prioritizes, and modulates incoming and outgoing signals
    thalamus sensory

  • What is the cerebellum's main function?

    • Cerebellum: coordinates movement timing and precision; attaches posteriorly to the brain stem
    cerebellum motor

  • What is the primary function of the occipital lobe?

    • Occipital lobe: initial visual processing; receives input from lateral geniculate nucleus of thalamus
    occipital vision

  • What is the primary function of the temporal lobe?

    • Temporal lobe: initial auditory processing; also involved in memory (hippocampus nearby)
    temporal hearing

  • What is the primary function of the parietal lobe?

    • Parietal lobe: somatic and visceral sensory processing; houses the sensory homunculus
    parietal sensory

  • What is the primary function of the frontal lobe?

    • Frontal lobe: voluntary motor control, speech, and planning; houses the motor homunculus
    frontal motor

  • What is the sensory homunculus principle?

    • Sensory homunculus: areas with highest receptor density get the largest cortical representation in parietal cortex
    homunculus sensory

  • What is the motor homunculus principle?

    • Motor homunculus: areas requiring the finest control get the largest cortical representation in frontal cortex
    homunculus motor

  • What is meant by lateralization of sensory/motor signals?

    • Lateralization: most sensory and motor signals cross so the right brain controls the left body and vice versa
    lateralization neurophysiology

  • How do the cerebral hemispheres communicate?

    • Corpus callosum: the structure through which the hemispheres communicate
    corpuscallosum connectivity

  • Where is Broca's area located and what is its primary function?

    • Left frontal lobe
    • Formation of spoken language; controls speech muscles
    neuroanatomy broca

  • What deficit results from damage to Broca's area?

    • Expressive aphasia — comprehension intact but cannot produce speech
    aphasia language

  • Where is Wernicke's area located and what is its primary function?

    • Left temporal-parietal
    • Language comprehension (spoken, written, tactile/braille)
    neuroanatomy wernicke

  • What deficit results from damage to Wernicke's area?

    • Receptive aphasia — can speak but cannot understand language
    aphasia language

  • What does neuroplasticity allow after early-life language-area damage?

    • Analogous areas on the right hemisphere can sometimes assume language function
    neuroplasticity language

  • What is the primary role of the basal nuclei and its key neurotransmitter?

    • Inhibit unwanted muscle tone/movements; ensure smooth purposeful activity
    • Key neurotransmitter: Dopamine
    basalnuclei motor

  • What clinical dysfunction results from basal nuclei problems?

    • Movement disorders (e.g., Parkinson's — tremors, rigidity)
    movement parkinsons

  • What are the primary roles of the hypothalamus?

    • Master autonomic/endocrine regulator: temperature, hunger, thirst, fluid balance, sleep-wake, pituitary control
    hypothalamus homeostasis

  • What functions are associated with the limbic system and which neurotransmitters are involved?

    • Emotion regulation, behavioral drives, memory formation
    • NE, dopamine, serotonin
    limbic emotion

  • What clinical issues are linked to limbic system dysfunction and targeted by SSRIs/SNRIs/MAOIs?

    • Mood disorders
    psychiatry mood

  • How is neurotransmitter action terminated at the synapse?

    • (1) Reuptake into the presynaptic neuron, or (2) Enzymatic degradation (e.g., monoamine oxidase)
    synapse neurotransmitter

  • How do SSRIs and MAO inhibitors alter synaptic neurotransmitter levels?

    • SSRIs: block reuptake, prolong presence in cleft; MAO inhibitors: block enzymatic breakdown
    pharmacology antidepressants

  • Why do many current drugs have broad side effect profiles regarding neurotransmitter systems?

    • Current drugs are not highly pathway-specific, explaining broad side effects
    pharmacology sideeffects

  • What historical procedure illustrates the prefrontal cortex's role in personality and planning?

    • Prefrontal lobotomies reduced initiative and personality traits
    prefrontal clinicalpearl

  • What does the term afferent neuron mean?

    • Afferent: Neurons carrying information TOWARD the CNS
    neuroanatomy afferent

  • What does the term efferent neuron mean?

    • Efferent: Neurons carrying information AWAY from the CNS
    neuroanatomy efferent

  • What are interneurons?

    • Interneurons: Most numerous CNS neurons; connect afferent to efferent pathways
    neuroanatomy interneurons

  • Define a neuron's receptive field.

    • Receptive field: Area of body surface that, when stimulated, changes a neuron's firing
    sensory receptive_field

  • What is lateral inhibition in sensory systems?

    • Lateral inhibition: Neural mechanism that sharpens spatial localization by suppressing surrounding inputs
    sensory lateral_inhibition

  • What is a nociceptor?

    • Nociceptor: Specialized receptor for detecting painful or potentially damaging stimuli
    sensory nociceptor

  • How do sensory receptors encode stimulus magnitude?

    • Stimulus magnitude is encoded by the frequency of action potentials, not their size
    sensory encoding

  • How do receptors transduce stimuli into electrical signals?

    • All receptors transduce stimuli by opening ion channels (typically Na⁺ influx → depolarization)
    sensory transduction

  • Contrast tonic and phasic receptor adaptation.

    • Tonic: Slowly adapting; keep firing while stimulus persists.
    • Phasic: Rapidly adapting; fire at stimulus onset/offset only
    sensory adaptation

  • Name the main peripheral mechanoreceptor types and one key feature each.

    • Free nerve endings: pain, temperature, crude touch; most widespread.
    • Merkel's disks: light sustained touch; slowly adapting.
    • Meissner's corpuscles: light touch, texture; rapidly adapting.
    • Pacinian corpuscles: vibration, deep pressure; rapidly adapting.
    • Ruffini endings: deep pressure, stretch; slowly adapting.
    sensory receptors

  • What determines acuity in touch perception?

    • Acuity depends on receptive field size and lateral inhibition; small fields = high acuity (e.g., fingertips), large fields = low acuity (e.g., back)
    sensory acuity

  • What is the function of lateral inhibition in sensory perception?

    Suppresses signals from surrounding areas to accentuate the precise stimulus location.

    sensory lateral_inhibition

  • How do somatic afferents differ from visceral afferents in conscious perception?

    Somatic afferents are generally accessible to conscious perception; visceral afferents are subconscious.

    afferents somatic visceral

  • Why can visceral pain be poorly localized and referred to somatic sites?

    Because visceral and somatic afferents converge in the spinal cord, producing poorly localized and referred pain.

    visceral_pain referred_pain

  • Give an example of referred visceral pain mentioned in the notes.

    Heart attack pain felt in the left arm.

    referred_pain example

  • Compare the speed and typical sensation of A-delta fibers versus C fibers.

    • A-delta fibers: Fast; sharp, localized pain
    • C fibers: Slow; dull, diffuse, aching pain
    pain_pathways a-delta c-fibers

  • What are the myelination and typical triggers for A-delta and C fibers?

    • A-delta fibers: Lightly myelinated; triggered by mechanical and thermal stimuli
    • C fibers: Unmyelinated; polymodal (mechanical, thermal, chemical)
    nociceptors myelination

  • Which chemical mediator from tissue injury is given as an example that stimulates chemical nociceptors?

    Bradykinin.

    chemical_mediators bradykinin

  • Which neurotransmitters are involved in CNS processing of pain according to the notes?

    Substance P and glutamate.

    cns neurotransmitters pain

  • Name the endogenous peptides that suppress pain transmission in the spinal cord.

    Enkephalins and endorphins.

    endogenous_opioids pain_control

  • How do enkephalins and endorphins affect pain and when does their production increase?

    They diminish but do not eliminate pain; production increases during stress, exercise, and acupuncture.

    pain_control physiology

  • What is a preganglionic fiber in the autonomic nervous system?

    • The first neuron in an autonomic efferent pathway
    • Originates in the CNS and ends at a ganglion
    autonomic neurons

  • What is a postganglionic fiber in the autonomic nervous system?

    • The second neuron in an autonomic efferent pathway
    • Projects from the ganglion to the target organ via varicosities
    autonomic neurons

  • Define a ganglion in the peripheral nervous system.

    • A cluster of neuron cell bodies in the PNS where preganglionic fibers synapse on postganglionic neurons
    autonomic anatomy

  • What receptor type mediates transmission at all autonomic ganglia?

    • Nicotinic receptor: ACh receptor at ALL autonomic ganglia; activated by nicotine
    receptors autonomic

  • Which receptor type mediates parasympathetic effects at target organs?

    • Muscarinic receptor: ACh receptor at parasympathetic target organs
    receptors parasympathetic

  • What receptors mediate sympathetic target organ responses?

    • Adrenergic receptors: Norepinephrine/epinephrine receptors at sympathetic targets (alpha and beta subtypes)
    receptors sympathetic

  • What does 'dual innervation' mean?

    • An organ receives both sympathetic and parasympathetic input that often have opposing effects
    autonomic concepts

  • What is tonic regulation in autonomic control?

    • Control by varying the level of constant background activity from one division to regulate an organ
    autonomic regulation

  • State the key distinction between 'automatic' and 'autonomic'.

    • 'Automatic' is unconscious but can be voluntarily overridden; 'autonomic' is involuntary, non-conscious regulation that cannot be willfully controlled
    terminology autonomic

  • What is the high-yield rule about the number of neurons in autonomic efferent pathways?

    • All autonomic efferent pathways consist of exactly two neurons: preganglionic → ganglion → postganglionic → target organ
    autonomic pathway

  • List the main structural and neurotransmitter differences between sympathetic and parasympathetic pathways.

    • Preganglionic fiber: Sympathetic short, Parasympathetic long
    • Postganglionic fiber: Sympathetic long, Parasympathetic short
    • Ganglion location: Sympathetic near spinal cord, Parasympathetic near/within target
    • Pre→Post NT: ACh on nicotinic (both)
    • Post→Target NT: Sympathetic NE on adrenergic; Parasympathetic ACh on muscarinic
    sympathetic parasympathetic

  • Are sympathetic and parasympathetic actions always stimulatory or inhibitory?

    • No; sympathetic is not always stimulatory and parasympathetic is not always inhibitory. Effects depend on the organ and the balance between the systems
    autonomic function

  • What is 'dual innervation' in autonomic control?

    Both sympathetic and parasympathetic divisions innervate an organ and produce opposing effects; the outcome is a balance between them.

    autonomic innervation

  • Give an example of dual innervation in the bronchioles.

    Sympathetic stimulation dilates bronchioles; parasympathetic stimulation constricts bronchioles.

    autonomic respiratory

  • How does dual innervation affect GI motility?

    Parasympathetic activity increases GI motility while sympathetic activity decreases it.

    autonomic gastrointestinal

  • What is 'tonic regulation' in autonomic control?

    Only one autonomic division innervates the target and regulation occurs by varying a constant background activity.

    autonomic regulation

  • Provide an example of tonic regulation involving vascular smooth muscle.

    Vascular smooth muscle is innervated only by sympathetic fibers: baseline sympathetic tone causes vasoconstriction; ↑ activity causes more constriction; ↓ activity causes vasodilation.

    autonomic vascular

  • How is resting heart rate regulated by autonomic tone?

    Parasympathetic tone is dominant at rest; high vagal tone keeps heart rate low and increases in heart rate occur mainly by parasympathetic withdrawal.

    autonomic cardiac

  • Name one exception where ATP functions in autonomic neurotransmission.

    ATP can act as a sympathetic neurotransmitter by binding receptors (not for energy transfer).

    autonomic exceptions

  • What is an exception to the usual parasympathetic neurotransmitter?

    Some parasympathetic fibers release nitric oxide instead of acetylcholine.

    autonomic exceptions

  • What are autoreceptors in autonomic neurons?

    Norepinephrine and acetylcholine can bind to the releasing neuron to modulate their own activity via autoreceptors.

    autonomic receptors

  • How does the adrenal medulla differ from the typical postganglionic sympathetic pathway?

    Preganglionic sympathetic fibers release acetylcholine onto chromaffin cells, which secrete epinephrine into the blood, effectively replacing the postganglionic neuron.

    autonomic adrenal

  • Why can nicotine produce both GI stimulation and mild bronchodilation?

    Nicotine activates nicotinic receptors at both sympathetic and parasympathetic ganglia, producing simultaneous parasympathetic and sympathetic effects.

    pharmacology clinical

  • What is a photoreceptor in the retina?

    A light-sensitive cell in the retina (rod or cone) that transduces light into an electrical signal.

    vision photoreceptor

  • What is the fovea?

    The central retinal pit containing only cones and representing the highest acuity point.

    vision fovea

  • What is the macula?

    The area around the fovea with high cone density and some rods.

    vision macula

  • Define accommodation of the eye.

    The process of changing lens shape to focus on near versus far objects.

    vision accommodation

  • What is meant by transduction in vision?

    Converting one energy form to another, specifically light into an electrical signal.

    vision transduction

  • What role does cyclic GMP (cGMP) play in photoreceptors in the dark?

    cGMP is a second messenger that keeps Na⁺ channels open in photoreceptors in the dark.

    vision cgmp

  • Describe the main light path through the eye and which structure does most refraction.

    Light passes through cornea → pupil → lens → focuses on retina (image inverted). The cornea is responsible for most light refraction; the lens fine-tunes focus.

    vision lightpath

  • What are the actions and autonomic controls of the circular (sphincter) iris muscle?

    It constricts the pupil (miosis) and is controlled by the parasympathetic system; tropicamide (a cholinergic antagonist) blocks it leading to dilation.

    vision iris

  • What are the actions and autonomic controls of the radial (dilator) iris muscle?

    It dilates the pupil (mydriasis) and is controlled by the sympathetic system; phenylephrine (an α-adrenergic agonist) activates it causing dilation.

    vision iris

  • What is the clinical rationale for combining tropicamide and phenylephrine in dilation drops?

    Tropicamide relaxes the circular muscle by blocking parasympathetic input, while phenylephrine contracts the radial muscle by mimicking sympathetic input, together producing pupil dilation.

    vision pharmacology

  • What does the pupillary light reflex assess?

    It assesses brainstem and occipital cortex function.

    vision reflex

  • How do ciliary muscle states affect lens shape for near versus distance vision?

    Contracted ciliary muscles produce a round lens for near vision; relaxed ciliary muscles produce a flat lens for distance vision.

    vision accommodation

  • Compare rods and cones in light sensitivity and color.

    Rods are extremely sensitive and function in dim light, providing grayscale only; cones require higher intensity light and provide color vision with red, green, and blue subtypes.

    vision photoreceptors

  • Where are rods predominantly located in the retina?

    • Periphery
    vision retina rods

  • Where are cones concentrated in the retina?

    • Fovea
    • Macula
    vision retina cones

  • What is the typical wiring ratio of many rods to bipolar cells and its consequence?

    • Many rods → one bipolar cell (convergent)
    • Consequence: lower acuity, higher sensitivity
    vision wiring rods

  • What is the typical wiring relationship of cones to bipolar cells and its consequence?

    • Often 1:1 with bipolar cells
    • Consequence: higher acuity, lower sensitivity
    vision wiring cones

  • Explain rod bleaching and dark adaptation time

    • Rods oversaturate in bright light (bleach)
    • Dark adaptation for rods: 5–15 minutes
    • Requires vitamin A
    vision rods adaptation

  • Why can dim stars vanish when looked at directly?

    • Foveal cones can't detect low-intensity light; rods (more sensitive) are absent from fovea
    vision rods fovea

  • In darkness, what is the cGMP level and photoreceptor membrane state?

    • cGMP: high
    • Na+ channels: open
    • Photoreceptor: depolarized
    • Neurotransmitter release: high (tonic)
    • Retinal form: cis-retinal
    phototransduction vision dark

  • In light, what happens to cGMP, Na+ channels, and photoreceptor state?

    • cGMP: low (broken down by phosphodiesterase)
    • Na+ channels: closed
    • Photoreceptor: hyperpolarized
    • Neurotransmitter release: decreased
    • Retinal: trans-retinal
    phototransduction vision light

  • What is the key enzyme cascade in phototransduction after retinal activation?

    • Retinal → transducin → phosphodiesterase → ↓cGMP
    • Recovery requires energy to convert trans-retinal back to cis
    phototransduction cascade vision

  • Describe the main visual signal pathway to cortex

    • Photoreceptors → bipolar cells → ganglion cells → optic nerve → primary visual cortex (occipital lobe)
    visualpathway neuroanatomy vision

  • How do lateral and medial visual fields project across hemispheres?

    • Lateral visual field: stays ipsilateral
    • Medial visual field: crosses contralaterally
    vision visualfields neuroanatomy

  • What is the basis of depth perception described in the notes?

    • Binocular vision: each eye sees a slightly different perspective; the brain integrates them
    vision depth binocular

  • What visual condition causes central vision loss due to macula damage?

    • Macular degeneration: degeneration of retinal tissue in the macula → central vision loss
    clinical macula vision

  • What causes a cataract and how is it treated?

    • Cataract: lens protein buildup → cloudy lens
    • Treated by replacing with an artificial lens
    clinical cataract vision

  • What does LASIK do to correct vision?

    • Reshapes the cornea to correct refractive errors
    clinical lasik vision

  • What are the three middle ear bones and their primary function?

    • Malleus, incus, stapes
    • Function: amplify sound
    hearing ossicles

  • What structure seals the cochlea and receives vibrations from the stapes?

    • Oval window
    • Role: membrane sealing cochlea; receives vibrations from stapes
    cochlea ovalwindow

  • How do hair cells transduce mechanical bending into neurotransmitter release?

    • Bending opens mechanically gated channels → \(K^+\) enters → depolarization → \(Ca^{2+}\) channels open → neurotransmitter released onto afferent neurons
    haircells transduction

  • What happens when hair cell stereocilia bend in the opposite direction?

    • Hyperpolarization of hair cell → decreased neurotransmitter release
    haircells polarization

  • What is tonic activity in hair cells?

    • A steady baseline firing rate maintained even in silence
    haircells tonic

  • How does tonic activity help auditory encoding?

    • Baseline firing lets the system detect bidirectional changes and distinguish sound from other mechanical stimulation
    audition encoding

  • Describe the transmission pathway of sound from air to hair cells.

    • Sound wave → tympanic membrane vibrates → malleus → incus → stapes → oval window → cochlear fluid → basilar membrane → hair cells
    pathway transmission

  • How is pitch encoded along the basilar membrane?

    • Location-dependent stiffness: base (proximal) = high frequency; apex (distal) = low frequency
    pitch basilar

  • According to the text, what determines perceived pitch?

    • Which hair cells fire (their location), not action potential frequency
    pitch encoding

  • How is loudness encoded in the auditory system?

    • By net change in action potential frequency from baseline tonic rate; greater bending → larger change → perceived as louder
    loudness encoding

  • What is the clinical significance of fluid in the middle ear?

    • Middle ear should not contain fluid normally; fluid presence typically indicates infection
    clinical infection

  • What is the function of the Eustachian tube related to hearing?

    • Connects middle ear to pharynx to equalize pressure
    eustachian pressure

  • What is conduction deafness?

    Hearing loss caused by a mechanical defect before the hair cells (e.g., eardrum, ossicles, fluid).

    hearing conduction

  • What are common causes of conduction deafness?

    • Eardrum problems
    • Ossicle defects
    • Abnormal middle ear fluid
    conduction causes

  • What treatments improve conduction deafness prognosis?

    • Artificial cochleae
    • Hearing aids
    conduction treatment

  • What is neural (sensorineural) deafness?

    Hearing loss due to damage at or beyond the hair cells, affecting the neural pathway.

    hearing sensorineural

  • How does repair potential compare for sensorineural versus conduction deafness?

    Sensorineural deafness is more difficult to repair than conduction deafness.

    treatment repair

  • Which frequencies does age-related hearing loss (presbycusis) primarily affect?

    High frequencies.

    presbycusis frequency

  • Which part of hearing is preferentially damaged by loud noise?

    High-frequency regions are preferentially damaged by loud noise.

    noise damage

  • What is the vestibular system?

    Inner ear structures detecting head position and movement; shares CN VIII with cochlea

    vestibular anatomy

  • What do the utricle and saccule detect?

    Head tilt (position) and linear acceleration/deceleration

    vestibular otolith

  • How do the utricle and saccule transduce linear acceleration or tilt?

    Gravity/inertia shifts otolith mass, bending embedded hair cells in the cupula

    transduction otolith

  • What do the semicircular canals detect?

    Rotational movement in three-dimensional axes (x, y, z)

    vestibular semicircular

  • What is the transduction mechanism for the semicircular canals?

    Head rotation moves bone before fluid; lagging endolymph bends hair cells causing signal

    transduction semicircular

  • What is the cupula in vestibular organs?

    A gelatinous mass containing embedded hair cells in vestibular organs

    structure vestibular

  • What is nystagmus?

    Involuntary, abnormal eye movements caused by disrupted vestibular input

    clinical nystagmus

  • Which cranial nerve carries vestibular signals?

    The vestibular branch of CN VIII (vestibulocochlear nerve)

    neuroanatomy cnviii

  • What clinical test assesses utricle and saccule function?

    Head tilt test

    clinical testing

  • How does sensory integration produce dizziness after conflicting inputs?

    The brain coordinates vestibular, visual, and proprioceptive inputs; conflict (e.g., spinning then stopping) causes nystagmus and dizziness

    physiology integration

  • What common causes of vestibular disorders are mentioned?

    Infections or fluid imbalance causing conflicting sensory information and dizziness

    pathology vestibular

  • What is a chemoreceptor?

    A receptor activated by specific chemicals binding to it.

    chemosensation receptors

  • Which receptor type mediates sweet, bitter, and umami tastes?

    G protein-coupled receptors (GPCRs) using intracellular signaling cascades.

    taste gpcr

  • How is salty taste transduced at the receptor level?

    Direct Na+ entry through ion channels; Na+ is most effective, K+ less so.

    taste salty

  • How is sour taste detected by receptors?

    Direct stimulation of ion channels by H+ (protons) caused by acidity.

    taste sour

  • What characterizes bitter taste receptors and their significance?

    Many GPCR receptor types; evolutionarily linked to avoiding toxic alkaloids.

    taste bitter

  • What does the umami taste receptor respond to?

    GPCRs that respond to amino acids, especially glutamate (MSG).

    taste umami

  • Are taste receptors localized to specific tongue regions?

    No; taste receptors are scattered across the tongue and the 'tongue map' is oversimplified.

    taste distribution

  • Describe the main olfactory pathway from epithelium to brain.

    Chemoreceptive cilia in olfactory epithelium → olfactory bulb via mitral cells and glomeruli.

    olfaction pathway

  • How many distinct odors can humans detect and how does receptor count compare to dogs?

    Humans detect 100,000+ distinct odors from ~hundreds of receptor types; dogs have over 10,000 receptor types.

    olfaction detection

  • Why is smell strongly linked to memory and emotion?

    A large portion of olfactory input projects to the limbic system, linking smell with memory and emotion.

    olfaction limbic

  • What is the vomeronasal organ and what does it detect?

    A specialized organ in sinuses that detects pheromones affecting physiology and behavior subconsciously.

    vomeronasal pheromones

  • Does the vomeronasal organ produce conscious smell perception?

    No; it does not produce conscious smell perception but affects mood and attraction subconsciously.

    vomeronasal perception

  • What can cause olfactory hallucinations and why are they clinically useful?

    Mental illness or lesions causing inappropriate neuronal stimulation; they have diagnostic utility.

    clinical olfaction

  • What commonly causes taste or smell loss such as after COVID infection?

    Interference with neural transmission rather than direct receptor cell death.

    clinical anosmia

  • How does receptor density for taste change across individuals and age?

    Receptor density changes with age and varies between individuals, which may explain childhood taste aversions.

    taste variation

  • What is the primary function of the gastrointestinal (GI) system?

    Transfer nutrients, water, and electrolytes from food into the body's internal environment.

    gi function

  • What are the four major processes of the GI system?

    • Motility
    • Secretion
    • Digestion
    • Absorption
    gi processes

  • Define peristalsis in the GI tract.

    Sequential contraction of circular muscle behind a bolus plus longitudinal shortening ahead, propelling contents forward.

    motility peristalsis

  • What is segmentation and where is it the main motility during meals?

    Alternating contractions that mix contents without net propulsion; main small intestine motility during meals.

    motility segmentation

  • What are slow waves in GI smooth muscle and what generates them?

    Regular depolarization/repolarization cycles in smooth muscle, generated by interstitial cells of Cajal (ICC).

    physiology slow_waves

  • When do smooth muscle contractions occur relative to slow waves?

    Contraction occurs only when slow waves reach threshold; additional depolarization increases the number of action potentials.

    physiology slow_waves

  • How is a 'sphincter' defined in the GI context?

    A ring of circular smooth muscle regulating passage between GI regions (more accurate term than 'valve').

    anatomy sphincter

  • What is the migrating motor complex (MMC)?

    Strong interdigestive peristaltic sweeps that occur between meals.

    motility mmc

  • What composes the enteric nervous system and its capability?

    Intrinsic nerve plexuses (myenteric and submucosal) that can function independently of the CNS.

    neuro enteric

  • What three systems make up the Regulatory Triad controlling GI function?

    • Intrinsic nerve plexuses
    • Autonomic nervous system (ANS)
    • GI hormones
    regulation gi

  • What types of receptor feedback inform GI regulation?

    • Mechanoreceptors (distension)
    • Chemoreceptors (meal composition)
    • Osmoreceptors (fluid balance)
    receptors gi

  • List the GI wall layers from outside to inside.

    • Serosa (visceral peritoneum)
    • Muscularis externa (outer longitudinal + inner circular, with myenteric plexus)
    • Submucosa (with submucosal plexus)
    • Mucosa (mucous membrane + lamina propria + muscularis mucosa)
    • Lumen
    anatomy layers

  • What is the mesentery and one of its functions?

    Connective tissue sheets with blood vessels that attach GI structures to the peritoneal wall, preventing bowel telescoping and knotting.

    anatomy mesentery

  • What are the main roles of the mouth in digestion?

    • Mastication
    • Tongue positioning
    • Voluntary control with tongue proprioception largely unconscious reflex
    digestion mouth

  • How does swallowing transition from voluntary to involuntary control?

    Swallowing is voluntary in the mouth/pharynx then becomes involuntary at the pharynx; the epiglottis closes the airway and the UES & LES regulate entry/exit.

    swallowing pharynx

  • Which neural center controls involuntary phases of swallowing?

    The brain stem controls involuntary aspects of swallowing.

    neuro swallowing

  • Describe the main mixing functions of the stomach.

    Stomach mixes food via peristaltic waves + churning, exhibits receptive relaxation before food arrives, and the pyloric sphincter meters chyme into the duodenum.

    stomach motility

  • What phases regulate stomach activity and their primary triggers?

    • Cephalic: sight/smell/thought/chewing
    • Gastric: food in stomach (stretch + protein)
    • Intestinal: chyme in duodenum (acid, fat, protein)
    stomach phases

  • What effects occur during the gastric phase of stomach regulation?

    During the gastric phase there is ↑ acid, ↑ pepsinogen, ↑ motility, and gastrin release from G cells.

    gastric hormones

  • How does the intestinal phase affect gastric emptying?

    The intestinal phase slows gastric emptying and decreases acid while releasing CCK & secretin.

    intestinal hormones

  • What are the two main motor patterns of the small intestine and when do they occur?

    • Segmentation: during meals for mixing and absorption
    • MMC (migrating motor complex): between meals (90-120 min cycles) to sweep residue and prevent bacterial overgrowth
    smallintestine motility

  • What are the primary motor patterns of the large intestine and their functions?

    • Haustral contractions: haustral churning to aid water reabsorption
    • Mass movements: push content toward the rectum
    largeintestine motility

  • Outline the neural control and sequence leading to defecation.

    Rectal distension activates sensory afferents → internal anal sphincter relaxes (involuntary) → urge to defecate; the external anal sphincter remains under voluntary control.

    defecation control

  • What commonly causes constipation according to the notes?

    Constipation often results from excessive water removal in the colon (dehydration).

    constipation colon

  • What is a parietal cell and what does it secrete?

    • Parietal cell: stomach cell producing HCl via H+/K+-ATPase
    gi cells parietal

  • What is a chief cell and what does it secrete?

    • Chief cell: stomach cell producing pepsinogen, activated to pepsin by low pH
    gi cells chief

  • Write the chemical sequence used by parietal cells to generate acid.

    \(CO_2 + H_2O \rightarrow \text{carbonic acid (via carbonic anhydrase)} \rightarrow H^+ + HCO_3^-\); H^+ is pumped by H+/K+-ATPase into the lumen

    gi physiology acid

  • What is the 'alkaline tide' after meals?

    • Alkaline tide: temporary rise in blood HCO3⁻ after meals as parietal cells export bicarbonate into plasma
    gi acid-base alkaline

  • How does chloride contribute to gastric acid formation?

    • Chloride shift: Cl⁻ follows basolateral exchange to combine with H⁺ in the lumen forming HCl
    gi physiology chloride

  • How does the gastric mucus layer protect the epithelium?

    • Mucus layer embedded with bicarbonate protects epithelium from acid
    gi protection mucus

  • How do NSAIDs increase risk of acid-induced ulceration?

    • NSAIDs reduce prostaglandins → thin the mucus layer → increased risk of acid-induced ulceration
    gi drugs nsaids

  • How does H. pylori increase gastric acid secretion?

    • H. pylori colonizes mucus, lowers somatostatin from D cells → increased gastrin → increased acid
    gi pathogen hpylori

  • What is a micelle and what is its role in digestion?

    • Micelle: aggregate of bile salts surrounding fat droplets, enabling lipase access
    gi lipids micelle

  • What are brush border enzymes and their function?

    • Brush border enzymes: enzymes on microvilli surface that perform final digestion of disaccharides and peptides
    gi enzymes brushborder

  • What is a chylomicron and its role after fat absorption?

    • Chylomicron: lipoprotein particle carrying absorbed fats from enterocytes into lymphatics
    gi lipoprotein chylomicron

  • Which stimuli activate parietal cells according to the table?

    • Parietal cell stimuli: Gastrin, histamine, ACh
    gi cells stimuli

  • Which stimuli activate chief cells according to the table?

    • Chief cell stimuli: Gastrin, ACh
    gi cells chief

  • What do G cells secrete and what stimulates them?

    • G cells: secrete gastrin; stimulated by peptides in lumen and distension
    gi cells gcell

  • What do D cells secrete and what stimulates them?

    • D cells: secrete somatostatin (inhibitory); stimulated by low pH via feedback
    gi cells dcell

  • What is the primary function of goblet cells in the GI tract?

    • Goblet cells: produce mucus barrier; secretion is continuous and increases with irritation
    gi cells goblet

  • What cells produce gastrin and what stimuli increase its release?

    • G cells (stomach)
    • Stimuli: peptides and distension
    gi hormone

  • What are the main effects of gastrin on gastric cells?

    • Increases parietal cell acid secretion
    • Increases chief cell pepsinogen release
    gi gastric

  • Which hormone is released by I cells and what triggers its release?

    • CCK from I cells (duodenum)
    • Trigger: fat & protein in duodenum
    gi hormone

  • List the main actions of CCK on the digestive system.

    • Increases pancreatic enzyme release
    • Causes gallbladder contraction
    • Slows gastric emptying
    gi cck

  • Which hormone do S cells release and what stimulates it?

    • Secretin from S cells (duodenum)
    • Stimulus: acid in duodenum
    gi secretin

  • What are the primary effects of secretin on the pancreas and stomach?

    • Increases pancreatic bicarbonate
    • Inhibits gastric acid
    gi secretin

  • What triggers somatostatin release and what does it inhibit?

    • Released by D cells (stomach/duodenum) in response to low pH / feedback
    • Inhibits gastrin, histamine, acid, pancreatic enzymes
    gi somatostatin

  • What do pancreatic acinar and duct cells produce?

    • Acinar cells: digestive enzymes (proteases, amylase, lipase)
    • Duct cells: bicarbonate-rich fluid to neutralize acidic chyme
    pancreas secretion

  • Which hormones drive pancreatic bicarbonate and enzyme release?

    • Secretin drives bicarbonate release
    • CCK drives enzyme release
    pancreas hormone

  • What are the main functions of bile and the gallbladder?

    • Bile salts emulsify fats to form micelles aiding lipase action
    • Gallbladder stores and concentrates bile; contracts via CCK
    bile digestion

  • How are glucose and galactose absorbed across the apical membrane?

    • Secondary active transport with Na+ via SGLT1
    absorption carbohydrate

  • How is fructose absorbed by enterocytes?

    • Facilitated diffusion via GLUT5 (no energy required)
    absorption carbohydrate

  • How are single amino acids transported into enterocytes?

    • Secondary active transport with Na+ (similar mechanism to glucose)
    absorption protein

  • How are dipeptides and tripeptides absorbed and processed intracellularly?

    • Absorbed via H+-coupled transporter (PepT1) and broken down intracellularly
    absorption peptides

  • In what form are fats absorbed and how are they transported after re-esterification?

    • Absorbed as monoglycerides + fatty acids by simple diffusion after micelle delivery
    • Re-esterified → chylomicrons → lymphatics
    absorption lipids

  • How is intestinal surface area maximized and how often is the lining replaced?

    • Surface area: circular folds → villi → microvilli
    • Intestinal lining replaced every ~3 days
    intestinal anatomy

  • Where do brush border enzymes perform final digestion of disaccharides and peptides?

    • At the microvilli surface (brush border enzymes perform final digestion)
    digestion brushborder

  • How does loss of intestinal surface area (eg, flattened villi) affect nutrient absorption?

    • It causes major drops in absorption
    gi absorption

  • What is the mechanism by which lactase deficiency causes diarrhea?

    • Unabsorbed lactose creates an osmotic load → osmotic diarrhea
    gi physiology

  • What is the primary effect of orlistat on digestion and vitamins?

    • Blocks pancreatic lipase → fat malabsorption and loss of fat-soluble vitamins
    pharmacology gi

  • How do GLP-1 agonists affect appetite, gastric emptying, and fat absorption?

    • Reduce appetite and slow gastric emptying; minimal effect on fat absorption
    pharmacology gi

  • What does the hepatic portal vein deliver to the liver first?

    • ALL absorbed nutrients (first-pass metabolism)
    liver physiology

  • What feature of hepatic sinusoidal capillaries enables exchange with hepatocytes?

    • Large gaps in sinusoidal capillaries allow free exchange with hepatocytes
    liver microanatomy

  • How is bilirubin handled by the liver?

    • Bilirubin is excreted in bile
    liver metabolism

  • What is the liver's role in cholesterol balance compared with dietary intake?

    • Cholesterol is mainly synthesized by the liver; dietary intake is a minor contributor
    liver metabolism

  • How does the sympathetic nervous system affect heart rate?

    Increases heart rate (but primarily controlled by parasympathetic withdrawal).

    autonomic cardio

  • How does the parasympathetic nervous system affect heart rate at rest?

    Decreases heart rate (dominant at rest due to vagal tone).

    autonomic cardio

  • Which autonomic division primarily increases cardiac contractility?

    The sympathetic division primarily increases contractility.

    autonomic cardio

  • What effect do sympathetic and parasympathetic systems have on bronchioles?

    Sympathetic: dilation. Parasympathetic: constriction.

    autonomic respiratory

  • Compare sympathetic and parasympathetic effects on GI motility.

    Sympathetic: decreases GI motility. Parasympathetic: increases GI motility.

    autonomic gi

  • How do sympathetic and parasympathetic systems affect pupil size and which muscles are involved?

    Sympathetic: dilation (radial muscle). Parasympathetic: constriction (circular muscle).

    autonomic vision

  • What is the sympathetic effect on most blood vessels?

    Sympathetic constriction (tonic — only sympathetic control of vessels).

    autonomic vascular

  • Describe the difference in salivation between sympathetic and parasympathetic activation.

    Sympathetic: thick, viscous saliva. Parasympathetic: watery, copious saliva.

    autonomic gi

  • How do autonomic divisions control the bladder during filling and voiding?

    Sympathetic: relaxation for filling. Parasympathetic: contraction for voiding.

    autonomic urogenital

  • What stimuli activate free nerve endings and what is a key fact about them?

    Detect pain, temperature, crude touch; adaptation varies; they are the most widespread receptor.

    sensory receptors

  • What do Merkel's disks detect and how do they adapt?

    Detect light sustained touch; adapt slowly (tonic) for continuous pressure monitoring.

    sensory receptors

  • What stimuli do Meissner's corpuscles detect and what is their adaptation type?

    Detect light touch and texture; adapt rapidly (phasic) and are abundant in fingertips.

    sensory receptors

  • What do Pacinian receptors detect and how do they adapt?

    Detect vibration and deep pressure; adapt rapidly (phasic) and detect changes only.

    sensory receptors

  • What stimuli do Ruffini endings detect and how do they adapt?

    Detect deep pressure and stretch; adapt slowly (tonic) for sustained deformation.

    sensory receptors

  • What triggers gastrin release and what is its primary action?

    Triggered by peptides and stomach distension; increases acid and pepsinogen secretion.

    gi hormones

  • What triggers CCK release and what are its main actions?

    Triggered by fat and protein; increases pancreatic enzymes, causes gallbladder contraction, and decreases gastric emptying.

    gi hormones

  • What triggers secretin release and what is its primary action?

    Triggered by acid in the duodenum; increases pancreatic HCO₃⁻ and decreases acid.

    gi hormones

  • What is the primary effect of somatostatin released from D cells in low pH?

    Inhibits gastrin, gastric acid, and digestive enzyme secretion (acts as a systemic brake).

    gi hormone

  • In dim light, which photoreceptor type is most sensitive?

    Rods are highly sensitive in dim light.

    vision rods

  • Which photoreceptor type mediates color vision and which colors are indicated?

    Cones mediate color vision: red, green, and blue.

    vision cones

  • Compare acuity and wiring between rods and cones.

    • Rods: low acuity due to convergent wiring
    • Cones: high acuity due to 1:1 wiring
    vision acuity

  • Where are rods and cones primarily located on the retina?

    • Rods: retinal periphery (absent in fovea)
    • Cones: concentrated in fovea and macula
    vision retina

  • Which deep brain structure acts as a sensory relay and active filter?

    Thalamus functions as a sensory relay and active filter.

    thalamus cns

  • What role and key neurotransmitter are associated with the basal nuclei?

    Basal nuclei inhibit unwanted movements and use dopamine as a key neurotransmitter.

    basal movement

  • What are the main functions of the hypothalamus?

    Autonomic and endocrine master control of temperature, hunger, and thirst.

    hypothalamus homeostasis

  • Contrast A-delta fibers and C fibers in pain transmission.

    • A-delta: fast, sharp localized pain, lightly myelinated, mechanical/thermal
    • C fibers: slow, dull diffuse pain, unmyelinated, polymodal
    pain fibers
Study Notes

Physiology Exam I — Condensed Study Notes

Overview

  • Scope: CNS & brain structure, peripheral sensory physiology, autonomic nervous system (ANS), special senses (vision, hearing, vestibular, chemosensation), GI motility, secretion, digestion, absorption.
  • Study tip: focus on functions, pathways, key cell types, and clinical correlations.

1. CNS & Brain Structure — Essentials

Key terms

  • Gray matter: neuron cell bodies/dendrites; white matter: myelinated axon tracts.
  • Basal nuclei (basal ganglia): inhibit unwanted movements; key NT = dopamine.
  • Diencephalon: thalamus (sensory relay/filter) + hypothalamus (autonomic/endocrine master).

Brain stem & cerebellum

  • Brain stem (medulla, pons, midbrain): vital autonomic centers and conduit for tracts.
  • Cerebellum: timing and coordination of movement.
  • Thalamus actively filters/prioritizes sensory signals to cortex.

Cerebral cortex (four lobes)

  • Occipital: primary visual cortex (LGN input).
  • Temporal: auditory processing, memory association.
  • Parietal: somatic/visceral sensation; sensory homunculus (face/hands large).
  • Frontal: voluntary motor, planning, motor homunculus (fine control areas large).
  • Lateralization: motor/sensory decussate; hemispheres connected via corpus callosum.

Language centers

  • Broca (left frontal): speech production — damage → expressive aphasia.
  • Wernicke (left temporal-parietal): comprehension — damage → receptive aphasia.
  • Neuroplasticity: early lesions can shift function contralaterally.

Limbic system & hypothalamus

  • Limbic: emotion, memory; NTs include NE, DA, 5-HT.
  • Hypothalamus: temperature, hunger/thirst, circadian, pituitary control.

Synaptic NT dynamics (clinical relevance)

  • Termination by reuptake or enzymatic degradation (e.g., MAO).
  • Drugs (SSRIs, MAOIs) modify synaptic NT levels and have broad side effects.

2. PNS & Sensory Physiology

Core concepts

  • Sensory neurons encode stimulus intensity by AP frequency; receptor cells transduce stimuli to ion flux.
  • Receptive field size and lateral inhibition determine spatial acuity.
  • Tonic receptors fire continuously during stimulus; phasic receptors fire at onset/offset.

Major receptor types (functional summary)

  • Free nerve endings: pain/temperature/crude touch; variable adaptation.
  • Merkel: sustained light touch (slow-adapting).
  • Meissner: light touch/texture (rapid-adapting); fingertips.
  • Pacinian: vibration/deep pressure (rapid-adapting); layered corpuscle.
  • Ruffini: stretch/deep pressure (slow-adapting).

Acuity & two-point discrimination

  • Small receptive fields (fingertips, lips) → high acuity; lateral inhibition sharpens localization.

Pain pathways

  • A-delta fibers: lightly myelinated, fast, sharp/localized pain.
  • C fibers: unmyelinated, slow, dull/aching, polymodal.
  • Endogenous opioids (enkephalins, endorphins) reduce spinal pain transmission (stress/exercise effect).

3. Autonomic Nervous System (ANS)

Architecture & receptors

  • All autonomic efferent pathways: preganglionic neuron → ganglion → postganglionic neuron → target.
  • Nicotinic receptors: at all autonomic ganglia (ACh).
  • Muscarinic receptors: parasympathetic targets (ACh).
  • Adrenergic receptors (α, β): sympathetic targets (NE/Epi).

Sympathetic vs Parasympathetic (summary)

  • Sympathetic: short preganglionic, long postganglionic; ganglia near spinal cord; post → NE (mostly).
  • Parasympathetic: long preganglionic, short postganglionic; ganglia near/within organ; post → ACh (muscarinic).
  • Adrenal medulla: preganglionic sympathetic → chromaffin cells → secrete epinephrine into blood (exception).
  • High-yield: neither system is exclusively excitatory/inhibitory; effect depends on receptor type.

Regulation patterns

  • Dual innervation: opposing actions produce balance (e.g., bronchioles, heart rate via vagal tone).
  • Tonic regulation: single-division control by altering baseline firing (e.g., most blood vessels).
  • Exceptions: ATP or NO can be neurotransmitters; autoreceptors modulate release.

4. Vision (special senses)

Optics & pupil control

  • Light path: cornea → pupil → lens → retina (image inverted; cortex corrects).
  • Cornea provides most refraction; lens adjusts focus (accommodation): contracted ciliary muscle → round lens (near); relaxed → flat lens (far).
  • Iris muscles: circular/sphincter (parasympathetic → constrict), radial/dilator (sympathetic → dilate).
  • Pupillary reflex tests brainstem integrity.

Photoreceptors: rods vs cones (quick)

  • Rods: high sensitivity (dim light), grayscale, peripheral retina, convergent wiring → low acuity, dark adaptation 5–15 min.
  • Cones: color vision (R/G/B), concentrated at fovea/macula, often 1:1 with bipolar cells → high acuity.

Phototransduction (concise)

  • In dark: high cGMP keeps Na+ channels open → photoreceptor depolarized → tonic NT release.
  • In light: photon converts cis-retinal → trans-retinal → activates transducin → phosphodiesterase ↓cGMP → Na+ channels close → hyperpolarization ↓NT release.
  • Recovery requires energy to reisomerize retinal to cis form.

Mathematical/chemical summary: - \(\(\mathrm{CO_2 + H_2O \xrightarrow{CA} H_2CO_3 \leftrightarrow H^+ + HCO_3^-}\)\) (used later in parietal cells section).

Visual pathways

  • Photoreceptor → bipolar cell → ganglion → optic nerve → optic chiasm (nasal fibers cross) → lateral geniculate → visual cortex. Binocular disparity → depth perception.

Clinical notes

  • Macular degeneration → central vision loss; cataract → cloudy lens treatable by replacement; LASIK reshapes cornea.

5. Hearing

Mechanics & encoding

  • Sound: alternating air compression/rarefaction. Pitch = frequency; loudness = amplitude.
  • Transmission: tympanic membrane → ossicles (malleus, incus, stapes) → oval window → cochlear fluids → basilar membrane.
  • Basilar membrane tonotopy: base = high frequency; apex = low frequency.

Hair cell transduction

  • Stereocilia bending opens mechanically gated channels → K+ influx (endolymph high K+) → depolarization → Ca2+ influx → NT release.
  • At rest hair cells show tonic firing, enabling detection of increases/decreases.
  • Pitch determined by which region of basilar membrane is activated; loudness encoded by change in AP frequency from baseline.

Hearing loss types

  • Conduction deafness: mechanical problems before hair cells (e.g., fluid, ossicle damage) — often aided by hearing aids.
  • Sensorineural (neural): hair cell or neural pathway damage — harder to repair (cochlear implant option sometimes).
  • Presbycusis: age-related high-frequency loss; loud noise preferentially damages high-frequency regions.

6. Vestibular System

Components & functions

  • Utricle & saccule: detect head tilt and linear acceleration via otoliths shifting and bending hair cells.
  • Semicircular canals (3 orthogonal): detect rotational acceleration; fluid inertia bends cupula and hair cells.
  • Signals travel via vestibular branch of CN VIII and integrate with visual and proprioceptive input for balance.

Clinical signs

  • Nystagmus: involuntary eye movements from conflicting vestibular/visual signals (e.g., after spinning).
  • Vestibular disorders: cause dizziness when sensory inputs conflict.

7. Chemosensation (Taste & Smell)

Taste (gustation) — receptors & mechanisms

  • Salty: direct Na+ entry via channels.
  • Sour: direct H+ action on channels.
  • Sweet, Bitter, Umami: GPCR-mediated intracellular cascades (different receptors/subtypes).
  • Taste receptors are distributed across the tongue; receptor density varies by age and individual.

Smell (olfaction)

  • Odorants bind olfactory GPCRs on cilia of olfactory epithelium → mitral cells in olfactory bulb (glomeruli) → strong projection to limbic system (memory/emotion link).
  • Humans detect many odors by combinations of receptor activations; olfaction is highly combinatorial.

Vomeronasal organ (pheromones)

  • Detects pheromones subconsciously; influences physiology/behavior rather than conscious smell.

Clinical pearl

  • Olfactory hallucinations may indicate neural lesions; loss of smell (e.g., viral) often reflects transmission disruption.

8. GI System — Motility (core)

Four GI processes

  • Motility, secretion, digestion, absorption — lumen is physiologically external until absorbed.

Control systems (Regulatory Triad)

  • (1) Enteric nervous system (myenteric & submucosal plexuses) — can act independently.
  • (2) ANS — modulates enteric activity.
  • (3) GI hormones (gastrin, CCK, secretin, somatostatin) — endocrine modulation.

Pacemaker activity

  • Slow waves from interstitial cells of Cajal (ICC) set rhythmic depolarization; contraction occurs when threshold reached and APs fire.

Region-specific motility

  • Mouth: mastication (voluntary).
  • Pharynx/esophagus: swallowing → peristalsis (voluntary → involuntary transition).
  • Stomach: receptive relaxation, mixing, pyloric metering of chyme.
  • Small intestine: segmentation during meals (mixing), MMC between meals (90–120 min) to sweep residues.
  • Colon: haustral contractions and mass movements; water absorption concentrated here.
  • Defecation: rectal distension → internal sphincter relaxes (involuntary), external sphincter voluntary control.

9. GI Secretion, Digestion & Absorption

Parietal cell acid production (succinct)

  • Carbonic anhydrase reaction: \(\(\mathrm{CO_2 + H_2O \xrightarrow{CA} H_2CO_3 \leftrightarrow H^+ + HCO_3^-}\)\)
  • Parietal cells pump \(H^+\) into lumen via \(H^+/K^+-ATPase\); Cl- follows to form HCl. Bicarbonate enters plasma → alkaline tide after meals.
  • Mucus + bicarbonate protect epithelium; NSAIDs reduce prostaglandins → thinner mucus → ulcer risk; H. pylori disrupts feedback.

Key gastric cell types

  • Parietal: HCl secretion (stimulated by gastrin, histamine, ACh).
  • Chief: pepsinogen (activated by low pH).
  • G cells: gastrin release (stimulated by peptides/distension).
  • D cells: somatostatin (inhibitory; responds to low pH).

Important GI hormones (concise)

  • Gastrin (G cells): ↑ acid & pepsinogen.
  • CCK (I cells): fat/protein in duodenum → ↑ pancreatic enzymes, gallbladder contraction, ↓ gastric emptying.
  • Secretin (S cells): acid in duodenum → ↑ pancreatic HCO3-, ↓ gastric acid.
  • Somatostatin (D cells): inhibits gastrin, acid, enzymes (system brake).

Pancreas & bile

  • Pancreatic acinar cells: digestive enzymes (proteases, lipase, amylase); duct cells: bicarbonate (secretin-driven).
  • Bile salts (hepatic) emulsify fats → form micelles to deliver monoglycerides/FA to enterocyte surface; gallbladder stores bile and contracts with CCK.
  • After cholecystectomy bile flows continuously; fat digestion still occurs but timing altered.

Nutrient absorption (key transporters)

  • Glucose/galactose: SGLT1 (Na+-coupled secondary active transport) across apical membrane.
  • Fructose: facilitated diffusion via GLUT5.
  • Amino acids: Na+-dependent transporters; di-/tri-peptides via PepT1 (H+-coupled), cleaved intracellularly.
  • Fats: micelles deliver monoglycerides + FAs → diffuse into enterocytes → re-esterified → packaged into chylomicrons → lymphatics.
  • Surface area: circular folds → villi → microvilli (brush border enzymes for final digestion).

Clinical pearls

  • Flattened villi (celiac) → severe malabsorption.
  • Lactase deficiency → unabsorbed lactose → osmotic diarrhea.
  • Orlistat inhibits pancreatic lipase → fat malabsorption and fat-soluble vitamin loss.
  • GLP-1 agonists: slow gastric emptying and reduce appetite, minimal direct fat absorption effect.

Hepatic portal circulation

  • All absorbed nutrients pass first to the liver via hepatic portal vein (first-pass metabolism). Hepatocytes exchange across sinusoidal capillaries; bilirubin excreted in bile; liver major site of cholesterol synthesis.

Rapid-Review High-Yield Tables (compact)

ANS quick reference

  • Heart rate: sympathetic ↑, parasympathetic ↓ (vagal tone at rest).
  • Bronchioles: sympathetic dilates, parasympathetic constricts.
  • GI motility: sympathetic ↓, parasympathetic ↑.
  • Vessels: mainly sympathetic tonic control.

Pain fibers

  • A-delta: fast, sharp, lightly myelinated.
  • C fibers: slow, dull, unmyelinated.

Photoreceptors (summary)

  • Rods: peripheral, high sensitivity, grayscale, slow dark adaptation (5–15 min).
  • Cones: fovea, color, high acuity, rapid adaptation.

Final study tips

  • Draw pathways (visual, auditory, ANS) and label key synapses and neurotransmitters.
  • Memorize GI hormones with their stimuli and main actions (Gastrin, CCK, Secretin, Somatostatin).
  • Practice clinical scenarios: referred pain, pupillary reflex, vocal aphasias, hearing loss types, and causes of malabsorption.