Bio 373

midterm 1

What is physiology?

the science of the function of living systems

What is homeostasis?

the maintenance of a relatively stable internal environment (especially ECF)

\-oscillation around a set point

Who is Walter Cannon?

the father of physiology

coined the term "homeostasis"

What is the difference between local and reflex control?

Local control = cells near site of change initiate response

Reflex control = cells at a distant site control response

What is negative feedback?

stabilizes variable (correction in opposite direction of change)

What is feedforward mechanism?

control anticipates change

What is positive feedback?

reinforces stimulus (NOT homeostatic)

What are the 3 ways cells can communicate long range?

endocrine - chemical released in blood and distributed throughout the body

neural - electrical signal travels down neuron then becomes chemical which travels to target cell

neuroendocrine - electrical signal travels travel down neuron then becomes chemical signal that is secreted into the blood

What determines what type of receptors ligands will interact with?

chemical properties of the ligands

surface receptor = hydrophillic/lipophobic/water soluble

intracellular receptor = hydrophobic/lipophillic/water insoluble

How can cells change their response to different signals?

change receptor number or sensitivity

increase = increase expression of gene that codes for receptor or increase expression of receptor proteins on cell surface

decrease = internalize surface receptors

change receptor sensitivity = phosphorylation

How is a GPCR activated?

\-signal molecule binds to receptor and causes conformational change

\-activates G protein by exchanging GDP for GTP

\-when GTp binds alpha subunit+GTP dissociates from the B and gamma subunits

\-G alpha subunit turns itself off by hydrolizing GTP

What affect does Cholera Toxin have on the inactivation of G alpha subunit?

\-blocks GTP hydrolysis (GTPase activity)

\-results in persistent activation of adenylate cyclase

What are Cannon's Postulates?

\-the nervous system has a role in maintaining the 'fitness' of the internal environment

\-some systems under tonic control

\-some systems are under antagonistic control

\-one chemical signal can have different effects in different tissues

Specificity of neural vs. endocrine control

neural = single target cell or limited number of adjacent target cells

endocrine = exposed to all cells but only those which receptors response

Nature of signal for neural vs. endocrine control

neural = electrical signal that turns chemical (neurotransmitter)

endocrine = chemical signals

Speed of neural vs. endocrine control

neural = very rapid

endocrine = much slower than neural responses

Duration of action in neural vs. endocrine control

neural = usually very short

endocrine = longer than neural responses

Coding for stimulus intensity in neural vs endocrine control

neural = each signal is identical in strength. Increase intensity by increasing frequency

endocrine = intensity proportional to amount of hormone secreted

What are the evolutionary trends in the nervous system?

bilateral symmetry -\> cephalization -\> consolidation of PNS -\> nerves -\> ventral nerve cord -\> dorsal nerve cord -\> spinal cord -\> increasing role of forebrain

Describe the development of the Human CNS

4 weeks: anterior end of neural tube specialized into 3 regions (forebrain, midbrain, hindbrain) and spinal cord

6 weeks: neural tube differentiates into major brain regions present at birth

forebrain -> diencephalon, cerebrum

midbrain

hindbrain -> medulla oblongata, cerebellum, and pons

11 weeks: growth of cerebrum much more rapid than that of other regions

birth: cerebrum covers most of other brain regions; convoluted surface due to rapid growth in confined space

What structures provide protection and support for CNS?

\-surrounded by bony cage: cranium

\-3 layers of connective tissues: meninges

\-fluid between layer: cerebrospinal fluid

What are the meninges?

layers of connective tissue that surround the brain and spinal cord

dura mater = outermost layer

arachnoid mater = middle layer

pia mater = innermost layer

Describe the fluid filled cavities in the CNS

\-ventricles within the brain and hollow central canal within the spinal cord

\-2 lateral ventricles and 2 descending ventricles that extend through in brain stem

\-CSF in ventricles continuous with fluid in central canal of spinal cord

\-CSF is secreted by the choroid plexus within each ventricle (choroid plexuses produce \~500mL of CSF/day)

Extracellular fluids of the CNS

1. interstitial fluid - surrounds neurons and glial cells
2. plasma - within cerebral blood vessels
3. cerebrospinal fluid - within ventricular system and bathes external surfaces of the brain between meninges (removed and replaced \~4 times per day)

Plasma vs. CSF

CSF has:

* lower K+, Ca2+, HCO3-, glucose, pH
* similar Na+
* very low protein, no blood cells (presence of elevated protein or blood cells collected from CSF indicates infection)

Glial cells of the CNS

1. oligodendrocytes - form myelin sheaths within CNS "white matter"
2. microglia - immune cell lineage
3. astrocytes - regulate local ECF by releasing chemicals (numerous in the brain)
4. ependymal cells - creates barrier between compartments (decide what ends up in CSF)

What are the special features of the cerebral vasculature?

1. astrocyte foot processes- secrete paracrine factors that promote tight junction formation
2. tight junctions- prevent solute movement between endothelial cells

Describe the blood-brain 'barrier'

\-lipid soluble molecules cross readily (o2, co2)

\-hydrophillic substances (ions, amino acids, peptides, proteins) will only cross if specific transporters/carriers are present in endothelial cells of capillaries within CNS

\-considerations for drugs that are and are not wanted to reach the CNS: antihistamines and treating diseases of the CNS

What are the metabolic needs of the CNS?

1. oxygen requirement- neurons are "obligate aerobes' (require O2 to functions) so O2 readily crosses the blood brain barrier
2. glucose requirement- capillaries of CNS express high levels of glucose transporters to provide adequate levels of glucose (brain responsible for 1/2 body's glucose consumption)
3. vaculature to deliever O2 and glucose- approximately 15% of cardiac output received by the brain

Describe the spinal cord

\-major path for information flow between CNS, skin, joints and muscles

\-contains neural networks involved in locomotion

\-divided into 4 regions (cervical, thoracic, lumbar, sacral) each of which is divided into 4 segments

\-each segment gives rise to a pair of spinal nerves

Describe the segments of the spinal cord

1. white matter (myelinated axons) - consists of ascending and descending tracts
2. -ascending tracts: dorsal columns (fine touch, proprioception, vibration) or spinothalamic (pain,temp, crude touch)
3. -descending tracts: corticospinal tracts (voluntary movement)
4. grey matter (synapse + cell bodies) - consists of sensory and motor nuclei

Where does sensory info enter spinal cord?

dorsal root -\> dorsal horn gray matter

Where does motor (efferent) info leave the spinal cord?

ventral horn gray matter -\> ventral root

What is a spinal reflex?

\-spinal reflex initiates response without input from the brain (integrating center within spinal cord)

\-still sends feedback to the brain

Describe the brain stem

\-medulla pons and midbrain

\-oldest most primitive part of the brain

\-organized much like the spinal cord (most cranial nerves originate here)

\-contains nuclei associated with reticular formation (diffuse network of neurons involved in processes such as arousal/sleep, muscle tone, coordination of breathing, blood pressure)

What is the function of the midbrain?

coordination of eye movement, visual and auditory reflexes

What is the function of the medulla?

1. gray matter involved in control of many involuntary functions (blood pressure, breathing, swallowing, vomiting)
2. white matter - ascending somatosensory tracts, descending corticospinal tracts
3. site of deccusation for most neurons in corticospinal tract

What is the function of the pons?

relay station between cerebrum and cerebellum (also works with medulla to coordinate breathing)

Describe the cerebellum

2nd largest structure in the brain

coordinates movement

Describe the diencephalon

located between brain stem and cerebrum


1. thalamus - relays and integrates sensory info from lower parts of the CNS, ears, eyes, motor info from cerebellum
2. hypothalamus - homeostasis: contain centers that drive behavior related to hunger, thirst and influences autonomic responses, endocrine systems
3. pituitary gland - regulated by hypothalamus
4. pineal gland - secretes hormone melatonin (involved in circadian and seasonal rhythms)

Describe the cerebrum

\-site of higher brain functions

\-each cerebral hemisphere divided into 4 lobes (parietal, temporal, frontal, occipital)

\-groove = sulcus

\-convolution = gyrus (raised parts)

\-degree of folding not related to higher processing

How is the cerebrum organized?

3 regions of cerebral gray matter:


1. basal ganglia - coordination of movement
2. limbic system - linking emotion/fear with higher cognitive functions
3. cerebral cortex

What are the functional areas of the cerebral cortex

1. sensory areas - sensory input translated into perception (awareness)
2. motor areas - control skeletal muscles
3. association areas - integrate info from sensory and motor areas

Describe the primary motor cortex

\-on ridge just anterior to central sulcus

\-cell bodies of descending 'upper' or 'first order' motor neurons

Describe the primary somatosensory cortex

\-on ridges just posterior to central sulcus

\-terminals of ascending sensory pathways from skin, musculoskeletal system, viscera (info about touch, pain, pressure, temperature, body position)

Where are cortex's for special senses?

special senses have devoted regions (ex. visual cortex, auditory cortex)

Who is Wilder Penfield?

developed the Montreal procedure

\-having patient lay awake and probed different area of their brain (mapped the brain)

\-burnt toast

How does information travel on sensory pathway?

stimulus -\> receptor tranduces stimulus into intracellular signal (usually change in Em) -\> APs travel along afferent neuron -\> info reaches subcorticol integrating/relay centres (thalamus, medulla) -\> information reaches appropriate regions in cortex (only becomes conscious when processing reaches cortex)

How do sensory receptors vary?

1. free nerve endings - cutaneous receptors for pain, temp, crude touch
2. receptors with nerve endings enclosed in connective tissue capsules - Pacinian corpuscle (vibration)
3. specialized receptor cell that release neurotransmitter onto sensory neuron - special senses, hair cell in inner ear

What are the different types of sensory receptors?

chemoreceptors - O2, pH, glucose, smell, taste

mechanoreceptors - pressure (baroreecptors), cell stretch (osmoreceptors), vibration, acceleration, sound, touch

photoreceptors - photons of light

thermoreceptors - varying degrees of heat

What is are the adequate stimuli of each receptor type?

each sensory receptor has an adequate stimulus... type of energy to which it best responds

thermo - increased temp

mechano - deformations of membrane that open ion channels

photoreceptors - light

What is receptor potential?

change in membrane potential

Describe receptive fields

\-somatosensory and visual neurons are activated by stimuli that fall within a certain physical area
\-at least 2 afferent neurons in pathway to CNS


1. first order (primary) sensory neuron - directly associated with stimuli
2. second order (secondary) sensory neuron - relays info from first neuron
\-receptive fields often determined by neurons further up the pathway (sensory input can then be gathered by more than one primary sensory neuron)
\-several primary neurons converge into a secondary neuron
\-convergence allows summation (creates larger receptive fields)

What is the problem with convergence of sensory neurons?

no 2-point discrimination:

\-2 stimuli fall within same receptive field and only 1 signal goes to the brain = perceived as a single point

\-smaller receptive fields = better 2 point discrimination (activate different pathways to the brain and perceived as distinct stimuli)

How is sensory info integrated in the CNS?

\-olfactory pathways from nose projected through olfactory bulb to olfactory cortex

\-most sensory pathways (hearing, taste, vision, somatic) project to thalamus which modifies and relays info to cortical centres

\-equilibrium pathways project primarily to the cerebellum (some to thalamus)

\-visceral sensory info most integrated in brain stem and spinal cord (usually does not reach conscious processing)

How are different sensations distinguished if all stimuli are converted to APs?

CNS must be able to decode: \n -type of stimulus: modality \n -location \n -intensity \n -duration

What is labelled line coding?

adequate stimulus for that receptor type -> brain associates information from that receptor type with that modality

ex. touch receptors - perceived as touch

How is location of sensory stimulus coded for?

\-location is coded according to which receptive fields are activated (touch receptors in specific part of body project to certain area in somatosensory cortex)

\-special senses are different (ex. hair cells respond to different frequencies but no receptive fields relating to location of sound source)

What is lateral inhibition?

\-primary neuron response is proportional to stimulus strength \n -pathway closest to the stimulus inhibits neighbours \n -inhibition of lateral neurons enhances perception of stimulus (better localization)

How is stimulus intensity coded for?

1. # of receptors activated (population coding)

\-different thresholds for stimulation among groups of receptors

\-with low intensity stimulus most sensitive (lowest threshold) receptor recruited first

\-as stimulus intensifies, more receptors activated


2. frequency of APs coming from individual receptor cells

\-frequency of APs increases with stimulus intensity until a max. is reached

How is stimulus intensity and duration coded for?

\-receptor potential strength and duration vary with stimulus -receptor potential is integrated at the trigger zones -duration of a series of APs is proportional to duration of the stimulus -neurotransmitter release varies with pattern of APs arriving at the axon terminal -some receptors adapt to sustained stimuli


1. tonic receptors - slowly adapting, respond throughout stimulus
2. phasic receptors - rapidly adapt to a sustained stimulus and turn off

Merkel's disk

cutaneous sensory receptor \n location: superficial \n receptive field: small \n adaptation: slow (tonic) \n function: sustained touch/pressure, texture

Meissner's corpuscle

cutaneous sensory receptor \n location: superficial \n receptive field: small \n adaptation: fast (phasic) \n function: beginning and end of fine touch/pressure

Ruffini's corpuscle

cutaneous sensory receptor \n location: deep \n receptive field: large \n adaptation: slow (tonic) \n function: sustained gross touch/vibration/stretch

Pacinian corpuscle

cutaneous sensory receptor \n location: deep \n receptive field: large \n adaptation: fast (phasic) \n function: beginning and end of gross touch/vibration

Free Nerve Endings

cutaneous sensory receptor \n location: variable \n receptive field: variable \n adaptation: variable \n function: pain, temperature, hair movement

Nociception

\-found in many tissues (not just skin) \n -"pain" is a sensation rather than a stimulus \n -nociception is mediated by free nerve endings expressing ion channels that respond to a variety of strong stimuli (chemical/mechanical/thermal) \n -pain (eg. due to tissue injury) is mediated via release of local chemicals (K+, histamine, prostaglandins, serotonin, substance P): can either directly activate nociceptors or sensitize them (inflammation) \n -mediated by Transient Receptor Potential (TRP) channels

Transient Receptor Protein (TRP) channels

\-mediate a wide variety of sensations including pain, heat/warmth, cold, some tastes, pressure, vision, osmotic pressure, stretch

\-relatively non-selective ion channels

Somatic pain

\-information from nociceptors can follow many different pathways


1. spinal reflexes
2. ascending pathways to cerebral cortex (info also sent to limbic system and hypothalamus)
\*emotional reactions
\*autonomic responses (sweating, vomiting, nausea)

\-different types of pain travel on different fibre types

Describe the conduction velocities of different fibre types

1. alpha motor neurons = fastest
\-myelinated
\-diameter = largest
\-function: innervates extrafusal muscle fibres, afferent from muscle spindle, afferent from Golgi tendon organ
2. cutaneous mechanoreceptors (fine touch)
\-myelinated
\-diameter = medium
3. free nerve endings of crude touch/pressure, fast pain, temp and innervates intrafusal muscle fibres (gamma)
\-myelinated
\-diameter = small
4. slowest = slow pain, itch, temp
\-unmyelinated
\-diameter = small

How are neural reflexes classified?

1. according to effector
\-skeletal muscle (controlled by somatic motor neurons)
\-smooth and cardiac muscle, glands, adipose tissue (controlled by autonomic neurons)
2. according to integrating centre
\-spinal reflexes, 'cranial' reflexes
3. innate (inborn) vs. conditioned (learned)
4. number of neurons in pathway
\-monosypnaptic (only afferent and efferent neurons): somatic motor reflexes only
\-polysynaptic (eg. autonomic reflexes, involving interneurons)

Autonomic (visceral) reflexes

\-some are spinal reflexes (can often be modulated via signals from higher centers and inhibition by higher centres can be a learned response) \n -others integrated in the brain (hypothalamus, thalamus, brain stem) \n -emotional stimuli can be converted into visceral responses

Skeletal muscle reflexes

\-monitor: proprioception (position of limbs in space relative to other body parts) and effort exerted in lifiting/holding objects \n -integrating centre = CNS (via networks of excitatory or inhibitory neurons) \n -efferent pathway: somatic motor neurons (alpha motor neurons) \n -effectors: contractile skeletal muscle fibres (extrafusal muscle fibres)

Proprioceptors

\-receptors that sense changes in joint movements, muscle length, muscle tension, and send info the CNS \n -depending on appropriate response, CNS activates motor neurons to make motor units contract or activates inhibitory interneurons to make muscles relax \n -examples of proprioceptors: muscle spindles (muscle stretch), Golgi tendon organs (muscle tension), joint receptors (distortions as bones are repositioned)

Muscle spindles

\-each spindle consists of 3-12 intrafusal muscle fibres (arranged in parallel to extrafusal muscle fibres) \n -most sensitive to muscle stretch (increased length) \n -tonically active, sending stream of APs even at rest \n -mediate stretch reflexes (introduces contraction when muscle is stretched, tends to maintain muscle at constant length) \n -unloaded when muscle shortens unless tightened up by intrafusal muscle fibres (alpha-gamma coactivation) \n -alpha MN innervates extrafusal \n -gamma MN innervates intrafusal

Explain how a stretch reflex works

\-muscle stretched \n -increased firing from sensory neuron associated with spindle \n -increased firing of alpha motor neuron to biceps \n -biceps contracts \n -increased firing of inhibitory interneuron \n -decreased firing of alpha motor neuron to triceps (reciprocal inhibition) \n -antagonist muscle relaxes

Golgi Tendon Organ

\-between fibres and tendon (in series with muscle fibres) \n -whether isotonic or isometric, contraction of muscle causes tendon and GTO to stretch (most sensitive to isometric contraction) \n -relatively insensitive to muscle stretch \n -monitors tension (force of contraction)

What are the purposes of skeletal muscle reflexes?

1. stretch reflex (sensor: muscle spindle - change in length)
\-maintenance of posture
\-positional info to CNS (usually includes reciprocal inhibition)
2. monitoring muscle tension (sensor: Golgi tendon organ)
\-eg. maintaining constant grip on a paper cup
3. withdrawal reflex (sensor: pain receptors)
\-get away from pain, ideally while maintaining posture and balance (usually involves reciprocal inhibition and crossed extensor reflex)

How is control of movement integrated?

1. muscle reflex
\-primarily driven by external stimuli
\-inherent (vs. learned), rapid
\-mostly handled at the level of the spinal cord and brain stem with modulation by higher centres
2. voluntary movement
\-most complex, integrated in cerebral cortex
\-learned movements can improve with practice (become subconscious)

How are voluntary movements coordinated?

1. sensory inputs- sensory cortex, motor cortex
2. planning and decision making- prefrontal cortex, motor association areas, basal ganglia, thalamus
3. coordination and timing- input from cerebellum
4. execution- corticospinal tract to skeletal muscles
5. execution- brain stem, spinal cord
6. continuous feedback to sensory cortex

Parkinson's disease

\-results from death of dopamine secreting neurons in a particular region of basal ganglia \n -motor symptoms include tremor at rest, slowness of movement, rigidity (increased muscle tone) and many non-motor effects \n -main treatment is replacing dopamine with L-dopa (able to cross the blood-brain barrier

Olfaction (smell)

\-the only sensory modality that does not go through the thalamus; does not cross the midline \n -the only special sense for which the sensory cell itself is the neuron that carries the info to the CNS \n -much more important in other species than humans (closely linked with taste and emotion/memory)

Olfactory Receptor Neurons (OLNs)

\-bipolar neurons (replaced every \~60 days) \n -dendrites end in non-motile cilia which express odorant receptor proteins \n -axons go through gaps in cribiform plate; synapse on 2nd order neurons \n -odorant receptor proteins are GPCRs, form one of the largest gene families in vertebrates (3/5% of genome) \n (1000s of different types of receptors)

Coding of Olfactory 'Quality'

\-each ORN expresses only one type of odorant receptor protein \n BUT \n -each receptor can recognize more than one odorant \n -each odorant can stimulate more than one receptor \n \n -subsequent processing en route to olfactory cortex (input of 100s of olfactory neurons in combination is then interpreted as a particular odour)

Structure and Odour perception

\-small organic compounds that are simple enough to go up in the air \n -different sturctures have different odours

Gustation (taste)

combination of 5 basic tast

combination of 5 basic tastes:


1. sweet (carbs -> energy)
2. sour (H+)
3. salty (Na+)
4. bitter (many compounds -> possible toxicity)
5. umami (glutamate, some nucleotides -> protein)
\-taste receptor cells are non-neural epithelial cells (frequently come into contact with chemicals so replaced every 10 days)

Taste buds

\-number of taste buds per papillae depends on type (circumvallate, foliate, fungiform) can be 1000-2000 \n -each taste bud contains 50-150 taste receptor cells \n -supporting epithelial cell secrete fluid into lumen of taste pore

The myth of the chemotopic tongue map

-we can taste all flavours around our tongue, but some tastes more concentrated in certain areas

Taste transduction

1. ligands activate TRCs
2. various intracellular pathways are activated
3. Ca2+ signal triggers exocytosis (sour H+) or ATP formation (sweet, bitter, umami)
4. neurotransmitter (sour H+) or ATP (sweet, bitter, umami) released
5. primary sensory neuron fires; APs sent to the brain
\-sweet, bitter, umami ligands believed to be GPCRs
\-ultimately release ATP as signal molecule

Taste pathway

1. taste info travels through many cranial nerves to medulla
2. thalamus
3. gustatory complex

Signal transduction in hair cells (hearing)

1. normal position = some ion channels open, tonic rate of APs
2. bent to the right = more ion channels open, cation entry depolarizes cell, increased frequency of APs
3. bent to the left = channels closed, less cation entry hyperpolarizes cell, no APs

Sound waves

\-pattern in air pressure (amplitude and frequency) \n -amplitude = volume \n -frequency = pitch

Sound transmission through the ear

1. sound wave strike tympanic membrane and become vibrations
2. sound wave energy is transferred to the 3 bones of the middle ear (malleus, incus, stapes) which vibrate
3. the stapes is attatched to the membrane of the oval window. Vibrations of the oval window create fluid waves within the cochlea
4. the fluid waves push on the flexible membranes of the cochlear duct. Hair cells bend and ion channels open, creating an electrical signal that alters neurotransmitter release
5. neurotransmitter release onto sensory neurons creates APs that travel through the cochlear nerve to the brain
6. energy from the waves transfers across the cochlear duct into the tympanic duct and is dissipated back into the middle ear and the round window

Cochlea

\-perilymph (similar to plamsa- high Na+, low K+) \n -endolymph (similar to ICF- low Na+, high K+) \n -cochlear duct contains the Organ of Conti (sensory hair cells and support cells)

Neural coding for pitch - place code hypothesis

\-sound wave trigger activity at different places along the cochlea's basillar membrane and are perceived as different pitches 'tonographic map' \n \*waves travel along cochlea, hair cells in areas that bend the most at a given frequency encode that pitch \n \*'labelled line' based on which hair cells are stimulated \n -this explanation based on the anatomy of the ear \n -dominated for over 100 years \n -distance from stapes (farther = low frequency)

Neural coding for pitch - temporal code hypothesis

\-frequency of sound wave determines frequency of APs travelling along auditory nerve, perceived as pitch (location along basillar membrane irrelevant) \n -eg. low frequency -> slow waves along basillar membrane -> low firing rate of primary sensory neurons -> perceived as low pitch sound \n -problem: we can hear pitches at 20,000 Hz but we cannot transmit APs at this frequency

Current hypothesis for coding of pitch

\-groups of neurons working as a team (with staggered firing rates) carry the temporal code \n \*pooled neural response interpreted as pitch \n -place coding also plays a role (which region hair cells along the basillar membrane are stimulated) \n -relative importance of place and temporal coding depends on pitch (low pitches -> temporal coding, high pitches -> place coding)

Neural pathways for auditory information

1. primary auditory neurons project from the cochlea to the medulla
2. from the medulla, secondary sensory neurons project to 2 higher nuclei (one ipsilateral - on the same side of the body and one contralateral - on the opposite side). Splitting info into 2 ascending tracts means that each side of brain receives info from both ears

3a. ascending tracts synapse in midbrain and thalamus before projecting to the auditory complex

3b. collateral pathways take info to cerebellum and reticular formation


4. brain accounts for time difference between sides to create 3D representation of sound source (tell which side sound is coming from)

Hearing loss

1. conductive
\-no transmission through either external or middle ear (issues with wax or fluid in middle ear- can usually be repaired)
2. central
\-damage to neural pathways between ear and cerebral cortex or damage to the cortex itself (ex stroke) -uncommon
3. sensorineural
\-damage to structures of inner ear
\-eg. death of hair cells due to loud noise
\-common in youth and elderly
\-hair cells cannot yet be replaced in mammals

Equilibrium - vestibular apparatus

1. dynamic component - movement of the body through space
2. static component - position of head
\-integrated with info from other sensory systems (muscle + joint proprioceptors and vision)
\-like hearing, detected by hair cells lining fluid-filled (endolymph) chambers

* otolith organs- utricle, saccule -> linear acceleration and head position
* 3 semicircular canals- rotational acceleration (superior, posterior, horizontal)