Download Unit 11 - Perry Local Schools

Unit 11
Somatic Senses and Special Senses
Objectives:
Overview of Sensations
 Definition of Sensation
 Characteristics of Sensations
 Types of Sensory Receptors
General Senses: Somatic and Visceral
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Somatic
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Tactile: Touch, Pressure, Vibration
Thermal (warm, cold)
Pain
Proprioception
Visceral: Internal organ conditions
Definition of Sensation
Conscious or subconscious awareness of
change in external or internal environment
Requires


1.
2.
3.
4.
Stimulus
Sensory receptor
Neural pathway
Brain region for integration
Characteristics

Perception: Conscious awareness

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Occurs in cerebral cortex
Adaptation: Decreased receptor response during
prolonged stimulation
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Decreased perception
Adaptation speed varies with receptor

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Rapid adaptation: Pressure, Touch, Smell
Slow adaptation: Pain, Body position, Chemical levels in blood
Sensory Receptors: Structural Types

Free nerve endings

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Encapsulated nerve endings

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Pain, thermal, tickle, itch, some touch receptors
Touch pressure, and vibration
Separate, specialized cells

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Hair cells in inner ear
Photoreceptors in retina of eye
Sensory Receptors: Functional Types

Mechanoreceptors
Cell deformation: Stretching or bending
 Touch, Pressure, Vibration
Thermoreceptors: Temperature
Nociceptors: Pain
Photoreceptors: Light
Chemoreceptors: Taste, Smell
Osmoreceptors
 Osmotic pressure of body fluid
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Objectives:
Somatic Senses
 Tactile Sensations
 Thermal Sensations
 Pain Sensations
 Proprioceptive Sensations
Somatic Senses


Somatic receptors in skin, mucous membranes,
muscles, tendons, and joints
Distributed unevenly: Dense concentration of
receptors in very sensitive areas


Fingertips, Lips, Tip of tongue
Include tactile, thermal, pain, proprioceptive
Tactile Sensations

Touch, pressure, vibration


Encapsulated mechanoreceptors
Itch and tickle

Free nerve endings
Touch

Rapidly adapting receptors for touch
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Meissner corpuscles
Hair root plexuses: Detect hair movement
Slowly adapting receptors for touch

Type I Mechanoreceptors: Merkel discs or Tactile discs

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Surface receptors: In epidermis
Type I Mechanoreceptors: Ruffini corpuscles

Deep in dermis and tendons
Pressure and Vibration

Pressure

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Pacinian (lamellated) corpuscles: Layers like onion
Rapid adapting
Widely distributed: In dermis, subcutaneous, around
joints, tendons, muscles, periosteum
Vibration


Response to rapidly repetitive stimuli
Receptors: Meissner and Pacinian
Structure and Location of Sensory Receptors
Copyright 2010, John Wiley & Sons, Inc.
Itch and Tickle

Itch: Chemical stimulation of Free nerve endings

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Bradykinin from inflammation response
Tickle: From Free nerve endings and Pacinian
corpuscles
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Tickle requires stimulus from outside of self
Effects of attempts to tickle oneself are blocked by
signals to/from cerebellum
Thermal Sensations

Two kinds of Thermoreceptors
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Cold receptors: 10˚– 40˚ C (50 – 105˚ F)

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Warm receptors: 32˚– 48˚ C (90 – 118˚ F)
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Located in epidermis
Located in dermis
Both adapt rapidly but continue slow signals during
prolonged stimulus
Outside these ranges: Nociceptors detect pain
Pain Sensations
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Nociceptors
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Free nerve endings in every tissue except brain
Can respond to any excessive stimulus
Minimal adaptation
Types of pain
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Fast pain: acute, sharp pain
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Slow pain: chronic, burning, aching, throbbing
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Well localized
More diffuse (not localized)
Analgesic drugs – Block formation of chemicals that
stimulate nociceptors
Referred pain is visceral pain displaced to surface
Distribution of Referred Pain
Copyright 2010, John Wiley & Sons, Inc.
Proprioception (Kinesthesia)

Awareness of

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Sites of receptors
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Muscles (muscle spindles)
Tendons (tendon organs)
Joint kinesthetic receptors (synovial joints)
Inner ear (hair cells): head position
Tracts to
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Body position, movements, weight of objects
Somatosensory area of cerebral cortex and
Cerebellum
Slight adaptation
Functional Areas of the Cerebrum
Copyright 2010, John Wiley & Sons, Inc.
Objectives:
Special Senses
 Olfaction: Sense of Smell
Special Senses
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Smell (Olfaction)
Taste (Gustation)
Vision
Balance
Hearing
Smell: Olfaction
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Site of olfactory receptors
 In mucosa of superior region of nose
Three types of olfactory cells
1. Olfactory receptors


2.
Supporting cells

3.
Consist of olfactory hairs with chemoreceptors
These are first order neurons of olfactory pathway
Epithelial cells: Support, Protect
Basal cells: Stem cells that produce new
neurons (receptors) throughout life. Rare!
Smell:
Olfaction
Copyright 2010, John Wiley & Sons, Inc.
Stimulation of Receptors


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Genetic evidence: 100’s of primary odors exist
Binding of chemical odorants stimulates receptor
Recognition of 10,000 odors from combination of
primary receptor input
Rapid adaptation by 50% in 1 second
Olfactory Pathway
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First-order neurons
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Olfactory receptors are neurons in nasal mucosa
Axons form olfactory nerves (Cranial nerve I)
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Second-order neurons
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Extend through cribriform plate into cranium to olfactory bulb
Neuron cell bodies in olfactory bulb
Olfactory tract: Axons extend from olfactory bulb to
cerebral cortex (Temporal lobe)
Limbic system: Emotional response to odors
Olfactory
Receptors
Copyright 2010, John Wiley & Sons, Inc.
Objectives:
Special Senses
 Gustation: Sense of Taste
Taste: Gustation
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Five primary tastes: Salt, Sweet, Sour, Bitter, and
Umami
Perception of what is called “Taste” includes
olfactory input
Receptors in 10,000 taste buds
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Located on tongue, pharynx, epiglottis
In structures called Papillae
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Vallate (posterior)
Fungiform (all over)
Filiform: Touch receptors only
Taste:
Gustation
Copyright 2010, John Wiley & Sons, Inc.
Taste: Gustation
Copyright 2010, John Wiley & Sons, Inc.
Structure of Taste Bud

Contains 3 types of Epithelial cells
1.
2.
Supporting cells that surround
Gustatory receptor cells

3.
Gustatory hair projects from receptor through taste pore
Basal cells

Stem cells that produce supporting cells that develop into
receptor cells (10-day life span)
Taste: Gustation
Copyright 2010, John Wiley & Sons, Inc.
Stimulation of Taste Receptors

Sequence of events
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Tastant dissolves in saliva 
Enters taste pore  contacts gustatory hair 
Electrical signal produced 
Causes gustatory cell to release neurotransmitter
That activates dendrites of first-order neurons
Adaptation occurs within minutes
Different tastes arise from activation of different
groups of taste neurons
Gustatory Pathway
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Cranial nerves transmit impulses
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Facial (CN VII) from Anterior of tongue
Glossopharyngeal (CN IX) from Posterior
Vagus (CN X) from Pharynx, Epiglottis
To medulla oblongata
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 Thalamus  Primary gustatory area of cerebral
cortex
 Limbic system or hypothalamus
Objectives:
Special Senses
 Vision: Sense of Sight
Vision: Eyes
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Accessory structures
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Eyebrows, eyelashes: Protection
Eyelids: Protection and Lubrication (blinking)
Extrinsic muscles: Move eyeball
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Superior, Inferior, Lateral and Medial rectus
Superior and Inferior oblique
Lacrimal apparatus: Produces tears
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Lysozyme – Bacteria killing enzyme in tears
Lacrimal glands  lacrimal ducts  surface of upper eyelid 
surface of eye 
Lacrimal canals  lacrimal sac  nasolacrimal duct  nasal
cavity
Vision: Eyes
Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball
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First layer: Fibrous tunic
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Anteriorly: Cornea (clear, colorless)
Posteriorly: Sclera (“white of eye”)
Second layer: Vascular tunic consists of
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Choroid: Lines most of internal surface of eye
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Ciliary body consists of
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Contains blood vessels that nourish the eye
Ciliary processes: Secrete aqueous humor
Ciliary muscles: Changes lens shape for focusing
Iris: Pigmented part of eye (blue, brown, green)
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Smooth muscle that dilates or constricts pupil
Pupil: Hole for passage of light
Layers of Eyeball
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Third layer: Retina—composed of 2 layers
1.
Neural layer: Outgrowth of brain
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2.
Photoreceptor layer: Rods and Cones
Bipolar cell layer
Ganglion cell layer: Axons of neurons form optic nerve (CN II)
that exits eye at Optic disc (“blind spot” - no rods/cones)
Pigmented layer: Helps absorb stray light

Between choroid and neural layer
Pupil Response to Light
Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball
Copyright 2010, John Wiley & Sons, Inc.
Photoreceptors: Rods and Cones
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Rods: Black-and-white vision; 120 million
Cones: Color sensitive; 6 million cones
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Three types: Sensitive to blue, green or red light
Color vision results from combined input
Cones mostly in Central Fovea in center of Macula
Lutea
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Point of highest visual acuity (sharpness)
Visual pathway
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Photoreceptor cells (rods or cones) 
Bipolar layer 
Ganglion cells; their axons form Optic nerve
Photoreceptors: Rods and Cones
Copyright 2010, John Wiley & Sons, Inc.
Interior of Eyeball
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Two cavities separated by the lens
1.
Anterior cavity filled with Aqueous humor
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2.
Clear, colorless fluid secreted from capillaries in ciliary body
Completely replaced every 90 min
Establishes intraocular pressure, maintains eye shape;
nourishes lens and cornea
Drains into blood in scleral venous sinus (canal of Schlemm)
Vitreous chamber: Filled with gel-like vitreous body
(not replaced)

Holds retina back against choroid
Physiology of Vision: Three Steps
A. Formation of image on retina
B. Stimulation of photoreceptors (rods and cones)
C. Visual pathway: Nerve impulses pass to cerebral
cortex
A. Formation of Image on Retina: Four
Steps
1. Refraction (bending) of light rays to focus them on
retina
2. Accommodation: Change of lens shape to focus
for near (or far) vision
3. Constriction (narrowing) of pupil to control amount
of light entering the eye
4. Convergence of eyeballs: For binocular vision
Step 1: Refraction of Light
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Definition: Bending of light rays as they pass from
medium of one density to another of different
density
75% occurs at cornea; Lens also helps focus light
on retina
Image is inverted but brain adjusts and interprets
distance and size
Step 1: Refraction of Light
Copyright 2010, John Wiley & Sons, Inc.
Step 1: Refraction of Light
Copyright 2010, John Wiley & Sons, Inc.
Step 1: Refraction of Light
Copyright 2010, John Wiley & Sons, Inc.
Step 2: Accommodation

Lens adjusts shape for distance to allow image to
focus on retina
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For distant objects, ciliary muscle relaxes  Flat lens
For closeup vision, ciliary muscle contracts  Fat lens
(rounder = more convex)
Visual disorders

Myopia (nearsightedness): Can see near but not far
objects

Eyeball is too long so lens cannot accommodate enough to
focus images of distant objects onto retina
Step 2: Accommodation
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Visual disorders
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Hyperopia (Farsightedness): Can see far but not near
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Eyeball is too short so lens cannot accommodate enough to
focus images of near objects onto retina
Astigmatism: irregular curvature of cornea or lens
Presbyopia: aging change  loss of elasticity of lens 
farsightedness  reading glasses
These disorders can be corrected with lenses or LASIK
(laser-assisted in situ keratomileusis)
Step 2:
Accommodation
Copyright 2010, John Wiley & Sons, Inc.
Steps 3 and 4: Constriction and Convergence
■
Constriction of pupil
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■
Autonomic (parasympathetic) reflex to prevent
excessive light rays from entering eye
By contraction of circular muscles of iris
Convergence
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Eyes rotate inward for binocular vision
By contraction of extrinsic eye muscles
B. Stimulation of Photoreceptors
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Photoreceptors: Light  neural signal

In rods light is absorbed by a photopigment
(rhodopsin) which splits into opsin + retinal and leads
 receptor potential
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Vitamin A deficiency decreases rhodopsin production and
leads to night blindness.
In cones light is absorbed by 3 opsins  receptor
potential for color vision

In Colorblindness, red or green cones are missing.
C. Visual Pathway

Rods or cones  Bipolar cells  ganglion cells
(their axons form optic nerve = CN II)
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About 50% of these axons cross over to opposite side
of brain in optic chiasm
Axons continue on into optic tract 
 Terminate/synapse in Thalamus 
 Occipital lobes of cerebral cortex


Right brain sees left side of object
Left brain sees right side of object
Physiology of
Vision: Three
Steps
Copyright 2010, John Wiley & Sons, Inc.
Visual Disease/Disorder
• Conjunctivitis – Pinkeye
• Cataracts – Loss of transparency of lens
Ophthalmology – Science that focuses on
eyes and disorders
https://www.youtube.com/watch?v=nBNNg
eHsPxQ
Objectives:
Special Senses
 Hearing & Equilibrium
Hearing and Equilibrium: Ear Structure
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Outer ear:
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Auricle
External auditory canal
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Canal contains hairs and ceruminous glands
Tympanic membrane (ear drum)
Middle ear:
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Eustachian tube
Ossicles
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Malleus, Incus, Stapes
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Inner ear:
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Bony labyrinth + Membranous labyrinth filled with
endolymph
Cochlea: Sense organ of hearing,
Vestibule and semicircular canals: Organs of balance
Hearing and Equilibrium: Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Inner Ear Structure: Three Regions
Vestibule includes
1.

Two sacs: Utricle and Saccule
Semicircular canals: at right angles
2.
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Contain membranous semicircular ducts
Each ends in a swelling known as Ampulla
Cochlea: 3 levels
3.
1.
Cochlear duct: Membranous, has Endolymph

2.
3.
Contains Spiral organ (sensory organ for hearing)
Above: Scala Vestibuli: ends at Oval window
Below: Scala Tympani: ends at Round window
Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Spiral Organ

Sits on Basilar membrane
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Floor of cochlear duct
Contains supporting cells + hair cells
Hair cells
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Covered with jellylike Tectorial membrane
Receptors for Auditory sensations
Synapse with sensory neurons in cochlear branch of
Vestibulocochlear nerve cranial nerve VIII)
Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Physiology of Hearing

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Sound waves in air  Auditory canal
Tympanic membrane  Ossicle movement 
Stapes strikes oval window
Creates pressure waves in Perilymph
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Pressure waves in Endolymph cause
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Conveyed from Scala Vestibuli  Scala Tympani
Hair cells bend against tectorial membrane
Neurotransmitter released to sensory neurons
Pitch (wavelength): Location in cochlea
Volume (loudness): Intensity of waves
Malleus Incus
Stapes vibrating Helicotrema
in oval window
Cochlea
Sound waves
Perilymph
3
7
4
5
1
2
6
9
External auditory
canal
8
Scala
tympani
Scala
vestibuli
Basilar
membrane
8
Spiral organ
(organ of Corti)
Tectorial membrane
Vestibular membrane
Cochlear duct
(contains endolymph)
Tympanic
membrane
Secondary tympanic
membrane vibrating
in round window
Middle ear
Auditory tube
Auditory Pathway

Cochlear neurons (cranial nerve VIII) end in
medulla

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 Midbrain  Thalamus
 Auditory cortex in Temporal lobe


On same side: R ear  R side medulla
Each side of brain receives input from both ears
Tinnitus – ringing in the ears
Physiology of Equilibrium

Static equilibrium: senses position relative to
gravity


As when head is tilted or a car is speeding up or
slowing down
Dynamic equilibrium: senses position in response
to head movement

As in spinning movements
Static Equilibrium


Sensed in Maculae of Utricle and Saccule
Mechanism

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Gravity pulls on otoliths in otolithic membrane
Bends hair cells in otolithic membrane
Triggers nerve impulses in vestibular branch of
Vestibulochochlear nerve (VIII)
Static Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Static Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium

Semicircular canals (3)
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Cristae in each ampulla contain
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At right angles to each other
Hair cells embedded in jellylike cupula
Supporting cells
Mechanism



When head turns, hair cells move
Endolymph lags and bends hair cells
 Nerve impulses in Vestibular branch
Dynamic Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Equilibrium Pathways
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Axons from vestibular branch
 Medulla or Cerebellum
Medulla  motor control: eye, head, neck
 Spinal cord tracts for adjusting muscle tone and
postural muscles