Download Human Anatomy & Physiology I

Chapter 12
Somatic Senses and
Special Senses
Copyright 2010, John Wiley & Sons, Inc.
Special Senses





Smell (olfaction)
Taste (gustation)
Vision
Balance
Hearing
Copyright 2010, John Wiley & Sons, Inc.
General Senses: Somatic and Visceral

Somatic





Tactile: touch, pressure, vibration
Thermal (warm, cold)
Pain
Proprioception (joint, muscle position sense;
movements of limbs, head)
Visceral: internal organ conditions
Copyright 2010, John Wiley & Sons, Inc.
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
Copyright 2010, John Wiley & Sons, Inc.
Characteristics

Perception: conscious awareness


Occurs in cerebral cortex
Adaptation: decreased receptor response
during prolonged stimulation


Decreased perception
Adaptation speed varies with receptor


Rapid adaptation: pressure, touch, smell
Slow adaptation: pain, body position, chemical levels in
blood
Copyright 2010, John Wiley & Sons, Inc.
Sensory Receptors: Structural Types

Free nerve endings


Encapsulated nerve endings


Pain, thermal, tickle, itch, some touch receptors
Touch pressure, and vibration
Separate, specialized cells


Hair cells in inner ear
Photoreceptors in retina of eye
Copyright 2010, John Wiley & Sons, Inc.
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






Copyright 2010, John Wiley & Sons, Inc.
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
Copyright 2010, John Wiley & Sons, Inc.
Tactile Sensations

Touch, pressure, vibration


Encapsulated mechanoreceptors
Itch and tickle

Free nerve endings
Copyright 2010, John Wiley & Sons, Inc.
Touch

Rapidly adapting receptors for touch



Meissner corpuscles
Hair root plexuses: detect hair movement
Slowly adapting receptors for touch

Type I mechanoreceptors: Merkel discs or tactile
discs


Surface receptors: in epidermis
Type I mechanoreceptors: Ruffini corpuscles

Deep in dermis and tendons
Copyright 2010, John Wiley & Sons, Inc.
Pressure and Vibration

Pressure




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
Copyright 2010, John Wiley & Sons, Inc.
Structure and Location of Sensory Receptors
Copyright 2010, John Wiley & Sons, Inc.
Itch and Tickle

Itch: chemical stimulation of free nerve
endings


Bradykinin from inflammation response
Tickle: from free nerve endings and pacinian
corpuscles


Tickle requires stimulus from outside of self
Effects of attempts to tickle oneself are blocked by
signals to/from cerebellum
Copyright 2010, John Wiley & Sons, Inc.
Thermal Sensations

Two kinds of thermoreceptors

Cold receptors: 10˚–40˚ C (50–105˚ F)


Warm receptors: 32˚–48˚ C (90–118˚ F)



Located in epidermis
Located in dermis
Both adapt rapidly but continue slow signals
during prolonged stimulus
Outside these ranges: nociceptors detect
pain
Copyright 2010, John Wiley & Sons, Inc.
Pain Sensations

Nociceptors




Free nerve endings in every tissue except brain
Can respond to any excessive stimulus
Minimal adaptation
Types of pain

Fast pain: acute, sharp pain


Slow pain: chronic, burning, aching, throbbing


Well localized
More diffuse (not localized)
Referred pain is visceral pain displaced to
surface
Copyright 2010, John Wiley & Sons, Inc.
Distribution of Referred Pain
Copyright 2010, John Wiley & Sons, Inc.
Proprioception (Kinesthesia)

Awareness of


Sites of receptors





Muscles (muscle spindles)
Tendons (tendon organs)
Joint kinesthetic receptors (synovial joints)
Inner ear (hair cells): head position
Tracts to



Body position, movements, weight of objects
Somatosensory area of cerebral cortex and
Cerebellum
Slight adaptation
Copyright 2010, John Wiley & Sons, Inc.
Functional Areas of the Cerebrum
Copyright 2010, John Wiley & Sons, Inc.
Special Senses





Smell (olfaction)
Taste (gustation)
Vision
Balance
Hearing
Copyright 2010, John Wiley & Sons, Inc.
Smell: Olfaction


Site of olfactory receptors
 In mucosa of superior region of nose
Three types of olfactory cells
 Olfactory receptors



Supporting cells


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!
Copyright 2010, John Wiley & Sons, Inc.
Smell:
Olfaction
Copyright 2010, John Wiley & Sons, Inc.
Stimulation of Receptors




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
Copyright 2010, John Wiley & Sons, Inc.
Olfactory Pathway

First-order neurons


Olfactory receptors are neurons in nasal mucosa
Axons form olfactory nerves (cranial nerve I)


Second-order neurons



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
Copyright 2010, John Wiley & Sons, Inc.
Olfactory
Receptors
Copyright 2010, John Wiley & Sons, Inc.
Taste: Gustation



Five primary tastes: salt, sweet, sour,
bitter, and umami
Perception of what is called “taste”
includes olfactory input
Receptors in 10,000 taste buds


Located on tongue, pharynx, epiglottis
In structures called papillae



Vallate (posterior)
Fungiform (all over)
Filiform: touch receptors only
Copyright 2010, John Wiley & Sons, Inc.
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


Supporting cells that surround
Gustatory receptor cells


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)
Copyright 2010, John Wiley & Sons, Inc.
Taste: Gustation
Copyright 2010, John Wiley & Sons, Inc.
Stimulation of Taste Receptors

Sequence of events







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
Copyright 2010, John Wiley & Sons, Inc.
Gustatory Pathway

Cranial nerves transmit impulses




Facial (CN VII) from anterior of tongue
Glossopharyngeal (CN IX) from posterior
Vagus (CN X) from pharynx, epiglottis
To medulla oblongata


 Thalamus  primary gustatory area of cerebral
cortex
 Limbic system or hypothalamus
Copyright 2010, John Wiley & Sons, Inc.
Vision: Eyes

Accessory structures



Eyebrows, eyelashes: protection
Eyelids: protection and lubrication (blinking)
Extrinsic muscles: move eyeball


Superior rectus, inferior rectus, lateral rectus, medial
rectus, superior oblique, inferior oblique
Lacrimal apparatus: produces tears


Lacrimal glands  lacrimal ducts  surface of upper
eyelid  surface of eye 
Lacrimal canals  lacrimal sac  nasolacrimal duct
 nasal cavity
Copyright 2010, John Wiley & Sons, Inc.
Vision: Eyes
Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball

First layer: Fibrous tunic



Anteriorly: cornea (clear, colorless)
Posteriorly: sclera (“white of eye”)
Second layer: Vascular tunic consists of

Choroid: lines most of internal surface of eye


Ciliary body consists of



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)


Smooth muscle that dilates or constricts pupil
Pupil: hole for passage of light
Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball

Third layer: Retina—composed of two layers

Neural layer: outgrowth of brain




Photoreceptor layer: rods and cones
Bipolar cell layer
Ganglion cell layer: axons of neurons here form optic
nerve (CN II) that exits eye at optic disc (“blind spot”
since no rods/cones here)
Pigmented layer: helps absorb stray light

Between choroid and neural layer
Copyright 2010, John Wiley & Sons, Inc.
Pupil Response to Light
Copyright 2010, John Wiley & Sons, Inc.
Layers of Eyeball
Copyright 2010, John Wiley & Sons, Inc.
Photoreceptors: Rods and Cones


Rods: black-and-white vision; 120 million
Cones: color sensitive; 6 million cones



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


Point of highest visual acuity (sharpness)
Visual pathway



Photoreceptor cells (rods or cones) 
Bipolar layer 
Ganglion cells; their axons form optic nerve
Copyright 2010, John Wiley & Sons, Inc.
Photoreceptors: Rods and Cones
Copyright 2010, John Wiley & Sons, Inc.
Interior of Eyeball

Two cavities separated by the lens

Anterior cavity filled with aqueous humor





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
Copyright 2010, John Wiley & Sons, Inc.
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
Copyright 2010, John Wiley & Sons, Inc.
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
Copyright 2010, John Wiley & Sons, Inc.
Step 1: Refraction of Light



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
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 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



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
Copyright 2010, John Wiley & Sons, Inc.
Step 2: Accommodation

Visual disorders

Hyperopia (farsightedness): can see far but not
near




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)
Copyright 2010, John Wiley & Sons, Inc.
Step 2:
Accommodation
Copyright 2010, John Wiley & Sons, Inc.
Steps 3 and 4: Constriction and Convergence
■
Constriction of pupil


■
Autonomic (parasympathetic) reflex to prevent
excessive light rays from entering eye
By contraction of circular muscles of iris
Convergence


Eyes rotate inward for binocular vision
By contraction of extrinsic eye muscles
Copyright 2010, John Wiley & Sons, Inc.
B. Stimulation of Photoreceptors

Photoreceptors: light  neural signal

In rods light is absorbed by a photopigment
(rhodopsin) which splits into opsin + retinal and
leads  receptor potential


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.
Copyright 2010, John Wiley & Sons, Inc.
C. Visual Pathway

Rods or cones  bipolar cells  ganglion
cells (their axons form optic nerve = CN II)




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
Copyright 2010, John Wiley & Sons, Inc.
Physiology of
Vision: Three
Steps
Copyright 2010, John Wiley & Sons, Inc.
Hearing and Equilibrium: Ear Structure

Outer ear: auricle, external auditory canal,
and tympanic membrane (ear drum)


Middle ear: auditory tube (eustachian tube)
and ossicles (bones)


Canal contains hairs and ceruminous glands
Ossicles (malleus, incus, stapes: attached to oval
window)
Inner ear: bony labyrinth + membranous
labyrinth filled with endolymph


Cochlea: sense organ of hearing ,
Vestibule and semicircular canals: organs of
balance
Copyright 2010, John Wiley & Sons, Inc.
Hearing and Equilibrium: Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Inner Ear Structure: Three Regions

Vestibule includes


Semicircular canals: at right angles



Two sacs: utricle and saccule
Contain membranous semicircular ducts
Each ends in a swelling known as ampulla
Cochlea: 3 levels

Cochlear duct: membranous, has endolymph



Contains spiral organ (sensory organ for hearing)
Above: scala vestibuli: ends at oval window
Below: scala tympani: ends at round window
Copyright 2010, John Wiley & Sons, Inc.
Spiral Organ

Sits on basilar membrane



Floor of cochlear duct
Contains supporting cells + hair cells
Hair cells



Covered with jellylike tectorial membrane
Are receptors for auditory sensations
Synapse with sensory neurons in cochlear branch
of vestibulocochlear nerve cranial nerve VIII)
Copyright 2010, John Wiley & Sons, Inc.
Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Inner Ear Structure
Copyright 2010, John Wiley & Sons, Inc.
Physiology of Hearing



Sound waves in air  auditory canal
Tympanic membrane  ossicle movement
 stapes strikes oval window
Pressure waves in perilymph


Pressure waves in endolymph cause




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
Copyright 2010, John Wiley & Sons, Inc.
Malleus Incus
Stapes vibrating Helicotrema
in oval window
Cochlea
Sound waves
Perilymph
3
7
4
5
1
6
2
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
Copyright 2010, John Wiley & Sons, Inc.
Auditory Pathway

Cochlear neurons (in cranial nerve VIII) end
in medulla



On same side: R ear  R side medulla
 Midbrain  thalamus
 Auditory cortex in temporal lobe

Each side of brain receives input from both ears
Copyright 2010, John Wiley & Sons, Inc.
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
Copyright 2010, John Wiley & Sons, Inc.
Static Equilibrium


Sensed in maculae of utricle and saccule
Mechanism



Gravity pulls on otoliths in otolithic membrane
Bends hair cells in otolithic membrane
Triggers nerve impulses in vestibular branch of
vestibulochochlear nerve
Copyright 2010, John Wiley & Sons, Inc.
Static Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Static Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium

Semicircular canals (3)


Cristae in each ampulla contain



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
Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Dynamic Equilibrium
Copyright 2010, John Wiley & Sons, Inc.
Equilibrium Pathways




Axons from vestibular branch
 medulla or cerebellum
Medulla  motor control: eye, head, neck
 Spinal cord tracts for adjusting muscle
tone and postural muscles
Copyright 2010, John Wiley & Sons, Inc.
End of Chapter 12

Copyright 2010 John Wiley & Sons, Inc.
All rights reserved. Reproduction or translation of this
work beyond that permitted in section 117 of the 1976
United States Copyright Act without express permission
of the copyright owner is unlawful. Request for further
information should be addressed to the Permission
Department, John Wiley & Sons, Inc. The purchaser may
make back-up copies for his/her own use only and not
for distribution or resale. The Publishers assumes no
responsibility for errors, omissions, or damages caused
by the use of theses programs or from the use of the
information herein.
Copyright 2010, John Wiley & Sons, Inc.