Anatomy/Physiology
Chapter 10: Special Senses
I
II
Sensory Functions--define sensations and their importance
1)
sensation--awareness of the external or internal environment
2)
vital for survival and maintaining homeostasis
Sensory Pathways
A
Receptors
1)
stimulus specific--each type of receptor has a low threshold for one type of stimulus (change in
environment strong enough to cause a nerve impulse) and a high threshold for all other stimuli
2)
sensory adaptation--threshold rises after continuous stimulation
3)
classification by sensitivity:
(a)
mechanoreceptors--detect mechanical or physical change
(i)
touch, muscle tension, hearing, equilibrium, blood pressure
(b)
thermoreceptors--temperature change
(c)
nociceptors--pain
(d)
photoceptors--light, only in retina
(e)
chemorecptors--chemicals dissolved in fluids, smell, taste, O2 and CO2
B
1)
C
III
General sensory pathways
first, second, and third order neurons
(a)
1st--receptor to spinal cord
(b)
2nd--conducts towards the thalamus
(c)
3rd--conducts to cerebral cortex for processing
Special Sensory Pathways
1)
location and variations--complex receptors like eyes and ears may have more than three neurons,
impulses travel along cranial nerves
General Senses
A
Touch and Pressure--mechanoreceptors within skin
1)
Meissner's corpuscles--touch, small, oval capsule of C.T. skin of fingers, palms, soles, lips,
external genitals
2)
Merkel's discs--fine touch, dendrites in epidermis
3)
Pacinian corpuscles--pressure, knoblike ending sensory neuron w/ C.T. , looks like an onion
B
Temperature--maybe free nerve endings in skin, stimulated by temp. changes, extremes produce
pain (less than 10 C, greater than 45 C)
C
Pain
1)
importance--protection, informs brain of homeostatic imbalance requiring immediate attention
2)
detection--free nerve ending that respond to chemicals released by damaged cells or restricted
blood flow
3)
visceral pain--receptors located in walls of visceral organs, respond to widespread disturbances ,
>>cramps, heartburn, headaches, uterine cramps
4)
referred pain--visceral pain that is "referred" to a location on the skin because of shared nerve
pathways
D
1)
Body Position
proprioceptors--mechanoreceptors that provide info. on body position by detecting muscle
contraction, tendon tension, joint position, and head position
2)
muscle spindles--specialized muscle fibers associated w/ sensory neurons, stimulated by muscle
stretch
3)
tendon organs--2 or more sensory neurons w/ dendrites embedded in C.T. capsule, stimulated by
tendon tension
IV
Special Senses
A
Smell
1)
general--olfaction, detected by 1000's of chemorecptors located in upper wall of the nasal
cavities, together w/ other cells form olfactory organs
2)
olfactory receptor--neurons embedded within mucous membrane, surrounded by columnar
epithelial cells
(a)
olfactory hair--free dendrites that extend into mucus layer
3)
olfactory pathway
(a)
structure--dendrite stimulated by chemical dissolved in mucus, action potential travels down
axon through cribriform plate into cranial cavity, transmitted to neurons in olfactory bulb (cranial
nerve I) and on to frontal lobe of cerebral cortex
(b)
function--protection, emotional response, memories
B
Taste
1)
structure of taste organs--taste buds (gustation organs) located on surface of tongue within
papillae, consist of receptors cells (gustatory cells) surrounded by supportive epithelial cells, free ends
have microvilli called taste hairs that extend through an opening in taste bud known as a taste pore
2)
four primary tastes--sweet, sour, bitter, salty
3)
gustatory pathway--dissolved chemicals cause A.P. in sensory neurons at base of gustatory cells,
A.P. travels down cranial nerves to medulla oblongata, relayed by thalamus to cerebral cortex
C
Sight
70% of sensory receptors are the photoreceptors
1)
accessory organs-(a)
structure and function of
(i)
eyelids, eyelashes and conjunctiva
(a)
eyelids protect anterior surfaces of eyes
(b)
4 layers--thin skin, skeletal muscle, C.T. , inner mucous membrane called conjunctiva
(c)
conjunctiva secretes mucus to moisten and lubricate eyeball
(ii)
lacrimal apparatus
(a)
secretes tears w/ antibacterial enzyme, collected in lacrimal canals, pass into
nasolacrimal ducts
(iii)
(a)
2)
extrinsic muscles
6 skeletal muscles that move eyeballs
structure of the eye
(a)
fibrous tunica
(i)
sclera--white of eye, provides shape and protects inner parts
(ii)
cornea--anterior, transparent part of F.T., allows light in, lacks blood vessels
(b)
vascular tunica
(i)
choroid--light absorbing membrane that lines inner surface of sclera, reduces reflection of
light
(ii)
ciliary body--smooth muscle fiber that connects to lens and holds it in place
(iii)
iris--colored part of eye, contraction of muscle fibers controls amount of light passing
through pupil
(iv)
lens--transparent cytoplasm, located behind iris and pupil, focuses light
(a)
accommodation --a change in the shape of the lens as it focuses from near to far or vis
versa
(c)
cavities of the eye
anterior chamber--between cornea and iris
(i)
(ii)
posterior chamber--between iris and lens, both filled w/ aqueous humor
(iii)
posterior cavity--behind lens, , filled w/ vitreous humor
(iv)
aqueous and vitreous humor
aqueous--clear, watery, recycled through blood stream
vitreous--thick, gel-like fluid that supports structure of eye
(a)
(b)
(d)
nervous tunic
(i)
retina--thin, fragile layer of light sensitive neurons, lines posterior wall of eyeball, detects
light and transports nerve impulses to optic nerve
(a)
rod cells--detect small levels of light
(b)
cone cells--color sensitive, require more light
(c)
bipolar neurons--middle level of N.T., transmit message to inner layer
(d)
ganglion cells--inner layer of N.T., long axons converge to form Optic nerve
(e)
optic disc--blind spot where optic nerve leaves eye
(f)
macula lutea--area lateral to optic disc, contains concentration of cone cells called the
fovea centralis, area of highest visual acuity
(ii)
pathway of light through the eye
(a)
light is refracted (bent) as it passes from air thru cornea, aq. humor, lens, and vitreous
humor
(b)
only the lens changes refractive ability (accommodation)
(c)
myopia--"nearsighted" lens focuses images in front of retina
(d)
hyperopia--"farsighted" lens focuses images behind retina
(iii)
physiology of vision--light sensitive pigments (rhodopsin in rods) in rods and cones break
apart when they absorb light energy, triggering a series of reactions that increases cell permeability
and causes an A.P. Pigments are resynthesized for next light ray
(iv)
visual pathway--rods and cones>>bipolar cells>>ganglion cells>>optic nerve>>cross at
optic chiasm>>thalamus (some eye reflexes) >>cerebral cortex (visual cortex in occipital lobes)
>>interpretation of signals
(e)
Glaucoma and Interocular Pressure
Hearing
D
1)
production of sound--disturbance of air in the form of waves, stimulate receptors in ear causing an A.P.
(a)
outer ear
(i)
auricle--external part of ear, "the ear"
(ii)
auditory canal--channels sound trapped by auricle to the eardrum
(b) middle ear
(i)
tympanic cavity--lies between inner tympanic membrane and outer wall of inner ear, contains
three auditory ossicles
(ii)
Eustachian tube--allows air to pass between tympanic cavity and throat, equalizes pressure, route
of infections from mouth to middle ear
(iii) tympanic membrane--separates middle and inner ears, connects to the malleus, vibrates in
response to sound
(iv) auditory ossicles--smallest bones in body
(a)
malleus (hammer), incus (anvil), staples (stirrup)form bridge between tym. membrane and
inner ear, transmits sound vibration to the oval window into the cochlea
(c)
inner ear
(i)
bony labyrinth structure--series of canals within temporal bone, lined by membranous labyrinth,
filled w/ perilymph and endolymph
(ii)
regions
(a)
semicircular canals--3 loops at right angles, maintain equilibrium
(b) vestibule chamber between semicircular canals and cochlea, equilibrium
(c)
cochlea--resembles coiled snail, divided into two compartments called scala vestibuli and
scala tympani, contains the organ of Corti which is the site of sound receptors
(d)
summary of hearing--sound waves vibrate tympanic mem. >>vibrates auditory
ossicles>>vibrates perilymph of scala tympani>>increases pressure on endolymph > >vibrates basilar
membrane>>bends hair cells of the organ of Corti> >hair cells release neurotransmitter if stimulus great
enough>>A.P. down cranial nerve VII
(e)
auditory nerve pathway--hair cells passes impulse to cochlear nerve>>joins w/ vestibular nerve
to form cranial nerve VIII>>to medulla oblongata, switches sides>>to midbrain>>relayed by thalamus to
temporal lobe of cerebral cortex
2)
equilibrium
(a)
static equilibrium--sensation of body position, info. to maintain posture, receptors located in
vestibule
(i)
saccule and utricle--two sacs connected by a duct, contain flat regions of special cells known
as macula (supporting cells and hair cells)
(ii)
otoliths--calcium carbonate crystals resting in gel above macula, movement of head causes
otoliths to move>>gel moves>>hair cells bend and produce A.P. down C.N. VII
(b)
dynamic equilibrium--rapid movement of head, info. to balance head and body, receptors in 3
semicircular canals
(i)
ampulla--expanded region at end of each canal, contains cristae, the sense organ which
contains gel and mass of hair cells called cupula, movement causes cupula to move>>bends hair
cells>>A.P. down C.N.VIII to cerebellum
V
Integrative Functions
ability of nervous system to process and interpel sensory info. before
cerebral cortex, involves thought,
memory, emotions
sending out response, mainly in
A
Functional regions of the cerebral cortex
1)
sensory areas--lg. no. of neurons that receive and interpret sensory impulses
(a)
general sensory area--parietal lobe behind central sulcus, mainly receptors from skin
(b)
somasthethetic association area--behind GSA, impulses from thalamus and GSA, interprets
nature of sensation, stores memories
(c)
visual area--occipital lobe, impulses from eyes and visual assoc. area
(d)
auditory area--temporal lobe, info. from ears,
(e)
gustatory area--parietal lobe, taste
(f)
olfactory area--temporal lobe, smell
2)
Association areas
(a)
functions--recognize, analyze, and initiate a response to sens. info., include learning, reasoning,
memory storage and recall, language ability, consciousness
(b)
location--frontal and temporal lobes
(c)
gnostic area--integrates all sensory info. into conscious thought or understanding, activates
proper motor response
3)
Motor areas
(a)
general--located in frontal lobes in front of central sulcus, receive impulses from assoc. areas for
initiation of motor response, muscle groups represented by degree of control needed, not size of group
(b)
primary motor area--located in front of central sulcus in frontal lobe, control groups of muscles
(c)
(d)
premotor area--in front of PMA; impulses from PMA, cerebellum, and basal ganglia;
>>controlled, coordinated, precise, learned movements like writing, typing, sewing
(e)
motor speech area--Broca's area, controls speech muscles
B
Thought and memory--most complex functions in human body, involves billions of neurons in assoc. area
of brain,
1)
thought--conscious understanding of idea, image projected within brain or symbols in the form of
language, involves millions of neurons and impulses, originates from sensory input
2)
memory--recall of past experiences including thoughts, enables learning to occur which allows us to
avoid making the same mistake
(a)
brain centers responsible for memory include areas where mem. resides and areas where it is
integrated; these areas have been identified through research: integration centers in the diencephalon,
limbic system, basal ganglia, and hippocampus
(b)
short vs. long term memory--short is brief, does not return, involves changes in strength of
synaptic connections; long lasts for years, associated w/ memories, requires growth of new synaptic
connections within brain
C
Emotions: the Limbic system
1)
parts of cerebral cortex, basal gang., hypothalamus, thalamus, and brain stem; responsible for
emotions or feelings; contains network of neurons that connect higher and lower brain; receive and integrate
info. from variety of stimuli>>complex responses
VI
Motor Functions
A
Motor origins
1)
spinal cord--integration center in gray matter, generate reflexes, little
integration
2)
brain stem--nuclei of medulla oblongata, pons, and midbrain; generate
visceral reflexes like coughing and sneezing; little integration
3)
basal ganglia--grey matter within cerebrum, integrate semivoluntary
movements like laughing and walking
4)
cerebellum--integration centers within grey matter, equilibrium, posture,
balance; stimulate skeletal muscle
5)
hypothalamus--involuntary integration; autonomic N.S. smooth muscle,
cardiac muscle, glands
6)
cerebral cortex--highest level of integration; motor impulses requiring
thought, memory, coordination, precision
B
How much of your mind do you use?
C
Motor pathways
1)
reflex and autonomic--covered in Chapter 9
2)
somatic pathways--conduct voluntary motor impulses from motor areas
of brain to skeletal muscle
(a)
pyramidal pathways--(upper motor neuron)--from cerebral cortex to
spinal cord or cranial nerve