PPT Notes Chapter 13 Flashcards
Structure of a Nerve
Cordlike organ of the PNS
Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
Connective tissue coverings include:
Endoneurium—loose connective tissue that encloses axons and their myelin sheaths
Perineurium—coarse connective tissue that bundles fibers into fascicles
Epineurium—tough fibrous sheath around a nerve
Classification of Nerves
Most nerves are mixtures of afferent and efferent fibers and somatic and autonomic (visceral) fibers
Pure sensory (afferent) or motor (efferent) nerves are rare
Types of fibers in mixed nerves:
Somatic afferent and somatic efferent
Visceral afferent and visceral efferent
Peripheral nerves classified as cranial or spinal nerves
Ganglia
Contain neuron cell bodies associated with nerves
Dorsal root ganglia (sensory, somatic) (Chapter12)
Autonomic ganglia (motor, visceral) (Chapter14)
Regeneration of Nerve Fibers
Mature neurons are amitotic
If the soma of a damaged nerve is intact, axon will regenerate
Involves coordinated activity among:
Macrophages—remove debris
Schwann cells—form regeneration tube and secrete growth factors
Axons—regenerate damaged part
CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration [ALS involvement]
Cranial Nerves
Twelve pairs of nerves associated with the brain
Most are mixed in function; two pairs are purely sensory
Each nerve is identified by a number (Ithrough XII) and a name
I: The Olfactory Nerves
Arise from the olfactory receptor cells of nasal cavity
Pass through the cribriform plate of the ethmoid bone
Fibers synapse in the olfactory bulbs
Pathway terminates in the primary olfactory cortex
Purely sensory (olfactory) function
II: The Optic Nerves
Arise from the retinas
Pass through the optic canals, converge and partially cross over at the optic chiasma
Optic tracts continue to the thalamus, where they synapse
Optic radiation fibers run to the occipital (visual) cortex
Purely sensory (visual) function
III: The Oculomotor Nerves
Fibers extend from the ventral midbrain through the superior orbital fissures to the extrinsic eye muscles
Functions in raising the eyelid, directing the eyeball, constricting the iris (parasympathetic), and controlling lens shape
IV: The Trochlear Nerves
Fibers from the dorsal midbrain enter the orbits via the superior orbital fissures to innervate the superior oblique muscle
Primarily a motor nerve that directs the eyeball
V: The Trigeminal Nerves
Largest cranial nerves; fibers extend from pons to face
Three divisions
Ophthalmic (V1) passes through the superior orbital fissure
Maxillary (V2) passes through the foramen rotundum
Mandibular (V3) passes through the foramen ovale
Convey sensory impulses from various areas of the face (V1) and (V2), and supplies motor fibers (V3) for mastication
VI: The Abducens Nerves
Fibers from the inferior pons enter the orbits via the superior orbital fissures
Primarily a motor, innervating the lateral rectus muscle
VII: The Facial Nerves
Fibers from the pons travel through the internal acoustic meatuses, and emerge through the stylomastoid foramina to the lateral aspect of the face Chief motor nerves of the face with 5 major branches Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands Sensory function (taste) from the anterior two-thirds of the tongue
VIII: The Vestibulocochlear Nerves
Afferent fibers from the hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from the inner ear through the internal acoustic meatuses, and enter the brain stem at the pons-medulla border
Mostly sensory function; small motor component for adjustment of sensitivity of receptors
IX: The Glossopharyngeal Nerves
Fibers from the medulla leave the skull via the jugular foramen and run to the throat
Motor functions: innervate part of the tongue and pharynx for swallowing, and provide parasympathetic fibers to the parotid salivary glands
Sensory functions: fibers conduct taste and general sensory impulses from the pharynx and posterior tongue, and impulses from carotid chemoreceptors and baroreceptors
X: The Vagus Nerves
The only cranial nerves that extend beyond the head and neck region
Fibers from the medulla exit the skull via the jugular foramen
Most motor fibers are parasympathetic fibers that help regulate the activities of the heart, lungs, and abdominal viscera
Sensory fibers carry impulses from thoracic and abdominal viscera, baroreceptors, chemoreceptors, and taste buds of posterior tongue and pharynx
XI: The Accessory Nerves
Formed from ventral rootlets from the C1–C5 region of the spinal cord (not the brain)
Rootlets pass into the cranium via each foramen magnum
Accessory nerves exit the skull via the jugular foramina to innervate the trapezius and sternocleidomastoid muscles
XII: The Hypoglossal Nerves
Fibers from the medulla exit the skull via the hypoglossal canal
Innervate extrinsic and intrinsic muscles of the tongue that contribute to swallowing and speech
The Eye and Vision
70% of all sensory receptors are in the eye
Nearly half of the cerebral cortex is involved in processing visual information!
Most of the eye is protected by a cushion of fat and the bony orbit
Accessory Structures of the Eye
Protect the eye and aid eye function Eyebrows Eyelids (palpebrae) Conjunctiva Lacrimal apparatus Extrinsic eye muscles
Eyebrows
Overlie the supraorbital margins
Function in
Shading the eye
Preventing perspiration from reaching the eye
Eyelids
Protect the eye anteriorly
Palpebral fissure—separates eyelids
Lacrimal caruncle—elevation at medial commissure; contains oil and sweat glands
Tarsal plates—internal supporting connective tissue sheet
Levator palpebrae superioris—gives the upper eyelid mobility
Eyelashes
Nerve endings of follicles initiate reflex blinking
Lubricating glands associated with the eyelids
Tarsal (Meibomian) glands
Sebaceous glands associated with follicles
Ciliary glands between the hair follicles
Conjunctiva
Transparent membrane
Palpebral conjunctiva lines the eyelids
Bulbar conjunctiva covers the white of the eyes
Produces a lubricating mucous secretion
Lacrimal Apparatus
Lacrimal gland and ducts that connect to nasal cavity
Lacrimal secretion (tears)
Dilute saline solution containing mucus, antibodies, and lysozyme
Blinking spreads the tears toward the medial commissure
Tears enter paired lacrimal canaliculi via the lacrimal puncta
Drain into the nasolacrimal duct
Extrinsic Eye Muscles
Six straplike extrinsic eye muscles
Originate from the bony orbit
Enable the eye to follow moving objects
Maintain the shape of the eyeball
Four rectus muscles originate from the common tendinous ring; names indicate the movements they promote
Two oblique muscles move the eye in the vertical plane and rotate the eyeball
Structure of the Eyeball
Wall of eyeball contains three layers
Fibrous
Vascular
Sensory
Internal cavity is filled with fluids called humors [aqueous, vitreous]
The lens separates the internal cavity into anterior and posterior segments (cavities)
Fibrous Layer
Outermost layer; dense avascular connective tissue
Two regions: sclera and cornea
Sclera
Opaque posterior region
Protects and shapes eyeball
Anchors extrinsic eye muscles
Cornea:
Transparent anterior 1/6 of fibrous layer
Bends light as it enters the eye
Sodium pumps of the corneal endothelium on the inner face help maintain the clarity of the cornea
Numerous pain receptors contribute to blinking and tearing reflexes
Vascular Layer (Uvea)
Middle pigmented layer
Three regions: choroid, ciliary body, and iris
Choroid region
Posterior portion of the uvea
Supplies blood to all layers of the eyeball
Brown pigment absorbs light to prevent visual confusion
Ciliary body
Ring of tissue surrounding the lens
Smooth muscle bundles (ciliary muscles) control lens shape
Capillaries of ciliary processes secrete fluid into the anterior segment.
Ciliary zonule (suspensory ligament) holds lens in position
Iris
The colored part of the eye
Pupil—central opening that regulates the amount of light entering the eye
Close vision and bright light—sphincter pupillae (circular muscles) contract; pupils constrict
Distant vision and dim light—dilator pupillae (radial muscles) contract; pupils dilate
Changes in emotional state—pupils dilate when the subject matter is appealing or requires problem-solving skills
Sensory Layer: Retina
Delicate two-layered membrane
Pigmented layer
Outer layer
Absorbs light and prevents its scattering
Stores vitamin A for use by photoreceptor cells
Neural layer
Photoreceptor: transduce light energy
Cells that transmit and process signals: bipolar cells, ganglion cells, amacrine cells, and horizontal cells
The Retina
Ganglion cell axons
Run along the inner surface of the retina
Leave the eye as the optic nerve
Optic disc (blind spot)
Site where the optic nerve leaves the eye
Lacks photoreceptors
Photoreceptors
Rods
More numerous at peripheral region of retina, away from the macula lutea
Operate in dim light
Provide indistinct, fuzzy, non color peripheral vision
Cones
Found in the macula lutea; concentrated in the fovea centralis
Operate in bright light
Provide high-acuity color vision
Blood Supply to the Retina
Two sources of blood supply
Choroid supplies the outer third (photoreceptors)
Central artery and vein of the retina supply the inner two-thirds
Internal Chambers and Fluids
The lens and ciliary zonule separate the anterior and posterior segments
Posterior segment contains vitreous humor that:
Transmits light
Supports the posterior surface of the lens
Holds the neural retina firmly against the pigmented layer
Contributes to intraocular pressure
Anterior segment is composed of two chambers
Anterior chamber—between the cornea and the iris
Posterior chamber—between the iris and the lens
Anterior segment contains aqueous humor
Plasma like fluid continuously filtered from capillaries of the ciliary processes
Drains via the scleral venous sinus (canal of Schlemm) at the sclera-cornea junction
Supplies nutrients and oxygen mainly to the lens and cornea but also to the retina, and removes wastes
Glaucoma: compression of the retina and optic nerve if drainage of aqueous humor is blocked
Lens
Biconvex, transparent, flexible, elastic, and avascular
Allows precise focusing of light on the retina
Cells of lens epithelium differentiate into lens fibers that form the bulk of the lens
Lens fibers—cells filled with the transparent protein crystallin
Lens becomes denser, more convex, and less elastic with age
Cataracts (clouding of lens) occur as a consequence of aging, diabetes mellitus, heavy smoking, and frequent exposure to intense sunlight
Light
Our eyes respond to visible light, a small portion of the electromagnetic spectrum
Light: packets of energy called photons (quanta) that travel in a wavelike fashion
Rods and cones respond to different wavelengths of the visible spectrum
Refraction and Lenses
Refraction
Bending of a light ray due to change in speed when light passes from one transparent medium to another
Occurs when light meets the surface of a different medium at an oblique angle
Light passing through a convex lens (as in the eye) is bent so that the rays converge at a focal point
The image formed at the focal point is upside-down and reversed right to left
Focusing Light on the Retina
Pathway of light entering the eye: cornea, aqueous humor, lens, vitreous humor, neural layer of retina, photoreceptors
Light is refracted
At the cornea
Entering the lens
Leaving the lens
Change in lens curvature allows for fine focusing of an image
Focusing for Distant Vision
Light rays from distant objects are nearly parallel at the eye and need little refraction beyond what occurs in the at-rest eye
Far point of vision: the distance beyond which no change in lens shape is needed for focusing; 20 feet for emmetropic (normal) eye
Ciliary muscles are relaxed
Lens is stretched flat by tension in the ciliary zonule
Focusing for Close Vision
Light from a close object diverges as it approaches the eye; requires that the eye make active adjustments
Close vision requires
Accommodation—changing the lens shape by ciliary muscles to increase refractory power
Near point of vision is determined by the maximum bulge the lens can achieve
Presbyopia—loss of accommodation over age 50
Constriction—the accommodation pupillary reflex constricts the pupils to prevent the most divergent light rays from entering the eye
Convergence—medial rotation of the eyeballs toward the object being viewed
Problems of Refraction
Myopia (nearsightedness)—focal point is in front of the retina, e.g. in a longer than normal eyeball
Corrected with a concave lens
Hyperopia (farsightedness)—focal point is behind the retina, e.g. in a shorter than normal eyeball
Corrected with a convex lens
Astigmatism—caused by unequal curvatures in different parts of the cornea or lens
Corrected with cylindrically ground lenses, corneal implants, or laser procedures
Functional Anatomy of Photoreceptors
Rods and cones
Outer segment of each contains visual pigments (photopigments)—molecules that change shape as they absorb light
Inner segment of each joins the cell body
Rods
Functional characteristics
Very sensitive to dim light
Best suited for night vision and peripheral vision
Perceived input is in gray tones only
Pathways converge, where as many as 100 rods feed one ganglion cell, resulting in fuzzy and indistinct images
Cones
Functional characteristics
Need bright light for activation (have low sensitivity)
Have one of three pigments that furnish a vividly colored view
Nonconverging pathways, by virtue of each cone cell having its own “personal” bipolar cell, result in detailed, high-resolution vision
Excitation of Cones
Method of excitation is similar to that of rods
There are three types of cones, named for the colors of light absorbed: blue, green, and red
Intermediate hues are perceived by activation of more than one type of cone at the same time
Color blindness is due to a congenital lack of one or more of the cone types
Signal Transmission in the Retina
Photoreceptors and bipolar cells only generate graded potentials (EPSPs and IPSPs)
Light hyperpolarizes photoreceptor cells, causing them to stop releasing the inhibitory neurotransmitter glutamate
Bipolar cells (no longer inhibited) are then allowed to depolarize and release neurotransmitter onto ganglion cells
Ganglion cells generate APs that are transmitted in the optic nerve
Light Adaptation
Occurs when moving from darkness into bright light
Large amounts of pigments are broken down instantaneously, producing glare
Pupils constrict
Dramatic changes in retinal sensitivity: rod function ceases
Cones and neurons rapidly adapt
Visual acuity improves over 5–10 minutes
Dark Adaptation
Occurs when moving from bright light into darkness
The reverse of light adaptation
Cones stop functioning in low-intensity light
Pupils dilate
Rhodopsin accumulates in the dark and retinal sensitivity increases within 20–30 minutes
Visual Pathway
Axons of retinal ganglion cells form the optic nerve
Medial fibers of the optic nerve decussate at the optic chiasma
Most fibers of the optic tracts continue to the lateral geniculate body of the thalamus
The optic radiation fibers connect to the primary visual cortex in the occipital lobes
Other optic tract fibers send branches to the midbrain, ending in superior colliculi (initiating visual reflexes)
Depth Perception
Both eyes view the same image from slightly different angles Depth perception (three-dimensional vision) results from cortical fusion of the slightly different images
Retinal Processing
Several different types of ganglion cells are arranged in doughnut-shaped receptive fields
On-center fields
Stimulated by light hitting the center of the field
Inhibited by light hitting the periphery of the field
Off-center fields have the opposite effects
These responses are due to different receptor types for glutamate in the “on” and “off” fields
Thalamic Processing
Lateral geniculate nuclei of the thalamus
Relay information on movement
Segregate the retinal axons in preparation for depth perception
Emphasize visual inputs from regions of high cone density
Sharpen contrast information
Cortical Processing
Two areas in the visual cortex
Striate cortex (primary visual cortex)
Processes contrast information and object orientation
Prestriate cortices (visual association areas)
Processes form, color, and motion input from striate cortex
Complex visual processing extends into other regions
Temporal lobe—processes identification of objects
Parietal cortex and postcentral gyrus—process spatial location
Chemical Senses
Taste and smell (olfaction)
The chemoreceptors respond to chemicals in aqueous solution
May be inhaled vapors
Sense of Smell
The organ of smell—olfactory epithelium in the roof of the nasal cavity
Olfactory receptor cells—bipolar neurons with radiating olfactory cilia
Bundles of axons of olfactory receptor cells form the filaments of the olfactory nerve (cranial nerve I)
Supporting cells surround and cushion olfactory receptor cells
Basal cells lie at the base of the epithelium
Physiology of Smell
Dissolved odorants bind to receptor proteins in the olfactory cilium membranes
A G protein mechanism is activated, which produces cAMP as a second messenger
cAMP opens Na+ and Ca2+ channels, causing depolarization of the receptor membrane that then triggers an action potential
Olfactory Pathway
Olfactory receptor cells synapse with mitral cells in glomeruli of the olfactory bulbs
Mitral cells amplify, refine, and relay signals along the olfactory tracts to the:
Olfactory cortex
Hypothalamus, amygdala, and limbic system
Sense of Taste
Receptor organs are taste buds
Found on the tongue
On the tops of fungiform papillae
On the side walls of foliate papillae and circumvallate (vallate) papillae
Structure of a Taste Bud
Flask shaped 50–100 epithelial cells: Basal cells—dynamic stem cells Gustatory cells—taste cells Microvilli (gustatory hairs) project through a taste pore to the surface of the epithelium
Taste Sensations
There are five basic taste sensations
Sweet—sugars, saccharin, alcohol, and some amino acids
Sour—hydrogen ions
Salt—metal ions
Bitter—alkaloids such as quinine and nicotine
Umami—amino acids glutamate and aspartate
Physiology of Taste
In order to be tasted, a chemical:
Must be dissolved in saliva
Must contact gustatory hairs
Binding of the food chemical (tastant)
Depolarizes the taste cell membrane, causing release of neurotransmitter
Initiates a generator potential that elicits an action potential
Taste Transduction
The stimulus energy of taste causes gustatory cell depolarization by:
Na+ influx in salty tastes (directly causes depolarization)
H+ in sour tastes (by opening cation channels)
G protein gustducin in sweet, bitter, and umami tastes (leads to release of Ca2+ from intracellular stores, which causes opening of cation channels in the plasma membrane)
Gustatory Pathway
Cranial nerves VII and IX [facial and glossopharyngeal] carry impulses from taste buds to the solitary nucleus of the medulla
Impulses then travel to the thalamus and from there fibers branch to the:
Gustatory cortex in the insula
Hypothalamus and limbic system (appreciation of taste)
Influence of Other Sensations on Taste
Taste is 80% smell
Thermoreceptors, mechanoreceptors, nociceptors in the mouth also influence tastes
Temperature and texture enhance or detract from taste
The Ear: Hearing and Balance
Three parts of the ear External (outer) ear Middle ear (tympanic cavity) Internal (inner) ear External ear and middle ear are involved with hearing Internal ear (labyrinth) functions in both hearing and equilibrium Receptors for hearing and balance Respond to separate stimuli Are activated independently
External Ear
The auricle (pinna) is composed of:
Helix (rim)
Lobule (earlobe)
External acoustic meatus (auditory canal)
Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands
Tympanic membrane (eardrum)
Boundary between external and middle ears
Connective tissue membrane that vibrates in response to sound
Transfers sound energy to the bones of the middle ear
Middle Ear
A small, air-filled, mucosa-lined cavity in the temporal bone
Flanked laterally by the eardrum
Flanked medially by bony wall containing the oval (vestibular) and round (cochlear) windows
Epitympanic recess—superior portion of the middle ear
Pharyngotympanic (auditory) tube—connects the middle ear to the nasopharynx
Equalizes pressure in the middle ear cavity with the external air pressure
Ear Ossicles
Three small bones in tympanic cavity: the malleus, incus, and stapes
Suspended by ligaments and joined by synovial joints
Transmit vibratory motion of the eardrum to the oval window
Tensor tympani and stapedius muscles contract reflexively in response to loud sounds to prevent damage to the hearing receptors
Internal Ear
Bony labyrinth
Tortuous channels in the temporal bone
Three parts: vestibule, semicircular canals, and cochlea
Filled with perilymph
Series of membranous sacs [membranous labyrinth] within the bony labyrinth
Filled with a potassium-rich endolymph
Vestibule
Central egg-shaped cavity of the bony labyrinth
Contains two membranous sacs
Saccule is continuous with the cochlear duct
Utricle is continuous with the semicircular canals
These sacs
House equilibrium receptor regions (maculae)
Respond to gravity and changes in the position of the head
Semicircular Canals
Three canals (anterior, lateral, and posterior) that each define two-thirds of a circle
Membranous semicircular ducts line each canal and communicate with the utricle
Ampulla of each canal houses equilibrium receptor region called the crista ampullaris
Receptors respond to angular (rotational) movements of the head
The Cochlea
A spiral, conical, bony chamber
Extends from the vestibule
Coils around a bony pillar
Contains the cochlear duct, which houses the spiral organ (of Corti) and ends at the cochlear apex
The cavity of the cochlea is divided into three chambers
Scala vestibuli—abuts the oval window, contains perilymph
Scala media (cochlear duct)—contains endolymph
Scala tympani—terminates at the round window; contains perilymph
The scalae tympani and vestibuli are continuous with each other at the helicotrema (apex)
The “roof” of the cochlear duct is the vestibular membrane
The “floor” of the cochlear duct is composed of:
The bony spiral lamina
The basilar membrane, which supports the organ of Corti
The cochlear branch of nerve VIII runs from the organ of Corti to the brain
Properties of Sound
Sound is
A pressure disturbance (alternating areas of high and low pressure) produced by a vibrating object
A sound wave
Moves outward in all directions
Is illustrated as an S-shaped curve or sine wave
Pitch
Perception of different frequencies
Normal range is from 20–20,000 Hz
The higher the frequency, the higher the pitch
Loudness
Subjective interpretation of sound intensity
Normal range is 0–120 decibels (dB)
Properties of Sound Waves
Frequency
The number of waves that pass a given point in a given time
Wavelength
The distance between two consecutive crests
Amplitude
The height of the crests
Transmission of Sound to the Internal Ear
Sound waves vibrate the tympanic membrane
Ossicles vibrate and amplify the pressure at the oval window
Pressure waves move through perilymph of the scala vestibuli
Waves with frequencies below the threshold of hearing travel through the helicotrema and scali tympani to the round window
Sounds in the hearing range go through the cochlear duct, vibrating the basilar membrane at a specific location, according to the frequency of the sound
Resonance of the Basilar Membrane
Fibers that span the width of the basilar membrane are short and stiff near oval window, and resonate in response to high-frequency pressure waves.
Longer fibers near the apex resonate with lower-frequency pressure waves
Excitation of Hair Cells in the Spiral Organ
Cells of the spiral organ
Supporting cells
Cochlear hair cells
One row of inner hair cells
Three rows of outer hair cells
Afferent fibers of the cochlear nerve coil about the bases of hair cells
The stereocilia
Protrude into the endolymph
Enmeshed in the gel-like tectorial membrane
Bending stereocilia
Opens mechanically gated ion channels
Inward K+ and Ca2+ current causes a graded potential and the release of neurotransmitter glutamate
Cochlear fibers transmit impulses to the brain
Auditory Pathways to the Brain
Impulses from the cochlea pass via the spiral ganglion to the cochlear nuclei of the medulla
From there, impulses are sent to the
Superior olivary nucleus at the junction of the medulla and pons
Inferior colliculus (auditory reflex center in the midbrain)
From there, impulses pass to the auditory cortex via the thalamus
Auditory pathways decussate so that both cortices receive input from both ears
Auditory Processing
Impulses from specific hair cells are interpreted as specific pitches
Loudness is detected by increased numbers of action potentials that result when the hair cells experience larger deflections
Localization of sound depends on relative intensity and relative timing of sound waves reaching both ears
Homeostatic Imbalances of Hearing
Conduction deafness
Blocked sound conduction to the fluids of the internal ear
Can result from impacted earwax, perforated eardrum, or otosclerosis of the ossicles
Sensorineural deafness
Damage to the neural structures at any point from the cochlear hair cells to the auditory cortical cells
Tinnitus: ringing or clicking sound in the ears in the absence of auditory stimuli
Due to cochlear nerve degeneration, inflammation of middle or internal ears, side effects of aspirin
Meniere’s syndrome: labyrinth disorder that affects the cochlea and the semicircular canals
Causes vertigo, nausea, and vomiting
Equilibrium and Orientation
Vestibular apparatus consists of the equilibrium receptors in the semicircular canals and vestibule
Vestibular receptors monitor static equilibrium
Semicircular canal receptors monitor dynamic equilibrium
Maculae
Sensory receptors for static equilibrium
One in each saccule wall and one in each utricle wall
Monitor the position of the head in space, necessary for control of posture
Respond to linear acceleration forces, but not rotation
Contain supporting cells and hair cells
Stereocilia and kinocilia are embedded in the otolithic membrane studded with otoliths (tiny CaCO3 stones)
Maculae in the utricle respond to horizontal movements and tilting the head side to side
Maculae in the saccule respond to vertical movements
Activating Maculae Receptors
Bending of hairs in the direction of the kinocilia
Depolarizes hair cells
Increases the amount of neurotransmitter release and increases the frequency of action potentials generated in the vestibular nerve
Bending in the opposite direction
Hyperpolarizes vestibular nerve fibers
Reduces the rate of impulse generation
Thus the brain is informed of the changing position of the head
Crista Ampullaris (Crista)
Sensory receptor for dynamic equilibrium
One in the ampulla of each semicircular canal
Major stimuli are rotatory movements
Each crista has support cells and hair cells that extend into a gel-like mass called the cupula
Dendrites of vestibular nerve fibers encircle the base of the hair cells
Activating Crista Ampullaris Receptors
Cristae respond to changes in velocity of rotatory movements of the head
Bending of hairs in the cristae causes
Depolarizations, and rapid impulses reach the brain at a faster rate
Bending of hairs in the opposite direction causes
Hyperpolarizations, and fewer impulses reach the brain
Thus the brain is informed of rotational movements of the head
