Download CH 16 Sense Organs A aand P 2016

CH 16
sense organs
general senses
hearing & equilibrium
chemical senses,
vision
general properties
- a stimulus stimulates a receptor  which sends
impulses  via transduction to an effector
- transduction = the changing of one form of energy
into another (touch to electrical)
- sense organs transmit 4 types of information
- modality = type of stimulus (labelled line code)
- location = receptive field, sensory projections,
projection pathways –
- intensity = how many fibers are firing and firing frequency
- duration = phasic (quickly adapts) or tonic (adapts slowly)
types of receptors (modality)
thermoreceptors = respond to heat and cold
photoreceptors = respond to light
nociceptors = respond to pain, tissue injury, or situations
that may cause damage
chemoreceptors = respond to chemicals, smell and taste
mechanoreceptors = vibrations, touch, pressure, tension
they make you aware of your
internal and external environment
receptors by origin of stimulus
exteroceptors = sense things outside the body
interoceptors = senses arise from internal organs and tissues
proprioceptors = position, body movements, muscles, joints,
tendons
general (somatosensory & somesthetic) = simple receptors, widely
distributed receptors for senses we are aware of & others
we do not perceive consciously
special senses = limited to the head, use cranial nerves, and sense
arises from complex organs
general senses (simple structures)
unencapsulated
- free nerve endings = skin, mucus membranes, warm, cold, pain
- tactile corpuscles (discs) = Merkels discs for light touch, sense
textures, edges, and shapes, star shaped cells with projections
- peritrichial (hair receptors) = fiber curls about hair follicle and
responds to movement of the hair and quickly adapt
encapsulated
- Meisners tactile corpuscles = phasic, light touch, texture, in skin
- Krauses end bulbs = mucous membranes of lips and tongue, conjunctiva,
and epineurium of large nerves - thermoreceptors
- Pacinian lamellar corpuscles = phasic, deep touch, stretch, tickle, and
vibration, periosteum of bone, joint capsules, viscera and genitalia
- bulbous Raffini corpuscles = tonic, heavy touch, pressure, joints, skin, in
dermis, subcutaneous tissue and joint capsules
somatosensory projections & pathways
- initial injury causes sharp pain by fast myelinated fibers
- rate is from 12 to 30 m/sec
- followed by unmyelinated slow fibers at 0.5 to 2.0 m/sec
- longer lasting dull diffuse pain cause bradykinin release
pathways
- head and neck to brainstem to cortex and cerebellum
- below neck spinothalamic, spinoreticular, to reticular
formation to hypothalamus to limbic to emotional
response to be checked by cerebellum and cerebrum
- gracile fasciculus to spinocerebellar tract to thalamus to
cortex and cerebellum
modulation for pain
- mental and physical state affects perception
- endogenous opioids in CNS are analgesics (enkephalins,
endorphins, & dynorphins)
- endogenous opioids are secreted by CNS (midbrain gray
matter), pituitary, GI tract, other organs
- they are neuromodulators by spinal gating to stop nerve
fibers for pain at the posterior horn from firing
- this affect is the result of descending analgesic fibers and
mechanical stimulation of the injured area
pain modulation parthway
- nociceptor stimulates 2nd order nerve fiber causing it to
release subP
- 2nd order nerve fiber signals up spinothalamic tract to thalamus
- thalamus relays info through 3rd order neurons to cerebral cortex
where it is perceived as pain
- hypothalamus and cerebrum feed info to midbrain for integration
- midbrain sends signals down to reticular formation of medulla
- medulla sends descending serotonin analgesic fibers through the
reticulospinal tract to the posterior horns of the cord
- these synapse & feed inhibitory enkephalins to 2nd order cord pain fibers
- at higher levels presynaptic inhibition can take place in the medulla
by blocking release of subP
the chemical senses
taste, smell, sound, equilibrium, vision
- taste = gustation, tastants interact with about 4000 taste buds
- buds are found on the tongue, inside cheeks, soft palate,
pharynx, and epiglottis
- there are 4 types of taste buds (papillae)
1. fungiform = mushroom shape, 3 buds at apex, tip & sides of tongue
2. foliate = in kids, gone by 3, near molars and premolars on tongue
3. circumvallate = large, V at rear of tongue, 7-12 but 50% of all buds,
250 buds on each papillae surrounded by a deep trench
4. filiform = tiny spikes & no taste buds, most abundant papillae on
human tongue with no role in taste
tongue anatomy
support cells = look like taste cells but no sensory role
taste cells = banana shape epithelial cells with sensory hair cells, 7-10
days until replaced
taste hairs = sensory receptors for tastants
taste pore = pit into which chemicals descend
basal cells = stem cells but may also have an integrative function
sensory nerve = carry info to brainstem, thalamus, cerebrum,
olfactory area
synaptic vesicles = taste cells are not neurons but release
neurotransmitters to activate sensory nerve
what makes up a taste
salty = Na and K
sour = acids
umami = meat, amino acids
sweet = many organics, flowering plants
bitter = alkaloids
- taste cells release neurotransmitters
- Info via facial nerve (VII) from 1st 2/3 of tongue
- info via glossopharyngeal from posterior 1/3 of tongue
- vagus form palate, epiglottis, & pharynx
- all to solitary nucleus in medulla oblongata
- 2nd order to hypothalamus and amygdala
- projections to tahalamus-insula-postcentral gyrus= taste
- taste signals to orbitofrontal cortex and integrated with input
from eyes and nose and forms a conclusion about the
taste and emotional acceptance of the food
Smell (olfaction)
odorant – travels to olfactory mucosa – binds to receptor on
olfactory hairs – hairs synapse with to glomerulus cells (each
type for a specific odor) – integration laterally and vertically –
mitral and tufted cells form nerve fibers - travelling into
olfactory bulb primary olfactory cortex, thalamus, and
hypothalamus
some cells have nociceptor functions and identify noxious or
painful substances or are hyperstimulated by others providing
the sensation of pain (ammonia, chlorine menthol are noxious
but capsaicin overstimulates)
- as the eyes see more the sense of smell diminishes
- olfactory hairs in humans 5 cm2 but cats have 20 cm2
- women are more sensitive than men
- most humans can identify 2000 -4000 odors but some 10,000
- some animals have as many as 12,000 receptor types
- humans have about 350 different receptor types for odors
hearing (auditory, vibrations, equilibrium)
- pitch = treble or base
- human ear can hear from about 20 to 20,000 Hz (cps)
- <20 = infrasonic and >20,000 = ultrasonic
- best hearing 1500 to 5000 Hz most loss at 250 to 2100
- loudness = intensity = amplitude = dB = decibels
- outer, middle, inner ear
outer ear
- helix, external acoustic meatus, antitragus, lobule
- carries vibrations to tympanic membrane
- ear canal contains guard hairs, cerumen, low pH, lysosomes,
waterproof epithelium, ceruminous & sebaceous glands
middle ear
- tympanic cavity and membrane, innervated by branches of
the vagus (X) and trigeminal nerves (IV), contains the
auditory ossicles (3 bones which transmit vibrations in
the air into liquid pressure against inner ear nerve cells)
inner ear
- temporal bone labyrinth lined by membranous canals filled
with perilymph and surrounded by endolymph
- the 3 ossicles are the smallest bones of the body
- in order to function they are kept in position by muscles
and ligaments
- these function to protect the inner ear from too loud sounds
- protects the oval window
- auditory canal = the opening from the exterior to the
tympanic membrane, where you should not put a q tip
- auditory tube = canal which joins the middle ear to pharynx
- malleus, incus, stapes are the 3 ossicles
- vibrations as high and low pressure variations enter the
external acoustic meatus
- as they strike the tympanic membrane the muscles reduce
the affect upon the oval window
- malleus in and out, affects incus, which moves the stapes in
and out
- which causes the perilymph of the inner ear to move which in
turn moves cochlear hair cells which initiate nerve
impulses eventually to the vestibulocochlear nerve
(cranial nerve VIII)
vestibule = contains the labyrinth for equilibrium,
cochlea = contains the labyrinth for hearing
modiolus = circular bone in which the labyrinths exist
spiral organ (Corti) = within the cochlear duct is the spiral
made up of hair and supporting cells and membranes
whose function is to allow the hair cells to act as
receptors for different frequencies which will be
interpreted as sound
inner hair cells = single row of about 3,500 medial hair cells,
outer hair cells = three rows of about 20,000 hair cells
arranged as Vs each with about 100 hair cells
sensory coding
-the ability to differentiate loudness (amplitude)
- and pitch (frequency)
- soft sounds = slight amplitude and limited
stimulation of cochlear hair cells
- louder sounds = larger amplitude, higher frequency
of firing & stimulation of more cochlear hair cells
- proximal end (base)of cochlea narrow and stiff hairs
for high pitch
- distal end (apex) 5X wider, more flexible, low pitch
-each time a sound wave passes down the cochlea the
perilymph moves like a wave and moves the inner
and outer hair cells
- as the hair cells move they pull on the prior cell and open an
ion gate which allows K to rapidly flow down the
concentration gradient and depolarize the hair cell
- as the wave moves away the basilar membrane hair cells
bend back and move in the opposite direction and the
cells repolarize
- during depolarization the hair cells release a neurotransmitter
which stimulates the sensory dendrites of nerve fibers
sound – vibration – perilymph movement – hair cells
depolarize/repolarize – initiate sensory impulse – to medulla –
pons sends motor impulses to hair cells – which shorten and
make basilar membrane less or more flexible – this allows hair
cells to be more sensitive – and allows brain to – to better
differentiate between frequencies
also
pons sends efferents – to IHC – to inhibit some cells – so areas
of most and least sensitivity can be differentiated
hair cells nerve fibers – to spiral ganglion – to cochlear nerve –
joins vestibular nerve fibers – becomes cranial nerve VIII – goes
to cochlear nuclei – which goes to the pons – where binaural
hearing or comparison from left and right ears takes place also to inferior colliculi – then 3rd order to thalamus – 4th order
to primary auditory cortex – to temporal lobe – to perceive
sound – much decussation along the way
at the same time
branches of the vestibulocochlear nerve (VIII) as well as V and
VII send efferents back to the tensor tympani and stapedius
muscles to allow for better discrimination
equilibrium – original function of the ear
- vestibular apparatus – 3 semicircular canals with 2 chambers
- static equilibrium such as the orientation of the head when
the body is still
- semicircular duct measures active events such as motion,
linear, angular, rotation
- ducts are filled with endolymph, and hair cells
- anterior saccules are vertically oriented
- posterior saccules are horizontally oriented
- medial duct is at a 30 degree angle
As you turn or bend your head etc.
the endolymph in the semicircular canals
does not move as fast as the motion of the head and
it causes the hairs in the ampulla to bend
which initiates impulses to
the aural areas and cerebellum
- the impulses synapse with sensory fibers of the vestibular nerve
fibers which merges with the cochlear nerve and then VIII
- which leads to 4 vestibular nuclei in the pons and medulla
- they communicate with each other to learn about position and
motion of the body
- then send info to the cerebellum, thalamus, and vestibulospinal
tract to control balancebalance
- thalamus sends reverberating fibers back to the postcentral
gyrus and transitional zone between the primary sensory and
motor cortex
- thalamus also sends info to III, IV, and VI for compensating eye
movements, and the reticular system for control of blood
pressure and breathing as posture changes
vision
the perception of a small part
of the electromagnetic spectrum
from 400 to 700 nm (nanometers)
your eye
eyebrows = communication
palpebral = eyelids, protection, wet, sweep, medial and lateral
canthi, orbicularis oculi muscles, tarsal plate with 20-25
tarsal glands which secrete oil that coats the eye and
reduces evaporation
eyelashes = guard hairs, blink reflex
conjunctiva = transparent mucous membrane, covers anterior
eyeball, except cornea, prevent drying, rich BV supply
lacrimal apparatus = almond sized glands in frontal bones at the
superior lateral corner with 10-14 short ducts to the surface of
the conjunctiva
- tears contains nutrients, lubricants, and antimicrobial
lysosomes
- tears collect in the medial commissure, and flow into the
lacrimal punctum at the corner of the eyes
- which connect to the lacrimal canaliculi which drain into the
lacrimal sac which drains into the nasolacrimal duct
- and washes the tears into the inferior meatus of the nasal
cavity, so runny eyes equals runny noses
- the eye has 6 extrinsic muscles
- these attach to the walls of the orbit
- and to the eyeball
- these muscles are used to move the eyeball
- there are 4 rectus (straight) muscles(sup,inf, med, lat)
- and 2 oblique (slanted) muscles (sup, inf)
- superior oblique innervated by trochlear nerve IV
- lateral rectus is innervated by abducens VI
-the rest if the muscles are innervated by oculomotor III
superior, inferior, medial, and lateral rectus muscles originate from a
shared circular tendinous ring on the posterior wall of the orbit and
inserts on the anterior eyeball just behind the white of the eye and move
the eyeball up, down, medially, and laterally
Superior oblique starts on the medial wall of the orbit, travels through a
fibrocartilage ring (trochlea) and inserts on the superolateral part of the eyeball.
The inferior oblique starts at the inferior medial wall of the orbit and inserts at the
inferolateral part of the eyeball.
the eyeball has 3 tunics (coverings)
fibrosa = sclera, the white of the eye, cornea, made of collagen
and stratified squamous epithelium anteriorly and simple
squamous posteriorly, Na and H2O pumped out to prevent
swelling, anterior tissue rich in stem cells for rapid healing
vasculosa = uvea, middle layer, choroid, ciliary body (muscular
ring about the lens and secretes the aqueous humor), iris
(controls the diameter of the pupil, gives color to your eye),
pupil (opening to allow light in)
interna = retina and optic nerve
optical components of the eye
- transparent parts which allow light to pass through
- include cornea, aqueous humor, lens, vitreous body, & retina
- light can pass straight through or be bent or be blocked
- ciliary body makes aqueous humor and secretes it into the
anterior chamber between cornea and iris
- lens is made up of transparent flattened lens cells and is
supported by a ring called the suspensory ligament
attached to the ciliary body
- vitreous body (humor) is a transparent jelly that fills the vitreous
chamber behind the lens
neural component of the eye
- retina is an outgrowth of the diencephalon (optic vesicles)
- macula lutea and fovea centralis (most finely detailed images)
has about 4,000 small cones and no rods, high resolution,
no convergence, 1:1:1 (cone – bipolar – ganglion)
- optic disc is an path for blood vessels, a blind spot
- visual filling means the brain fills in the missing information
- saccades - the eye is always flickering, fastest moves of body
- photopupillary reflex – ANS reflex – pupillary dilator (sym) &
constrictor (parasym) – result 5X light
refraction = change in direction of light beam
emmetropia = focus 20 ft away is a relaxed eye
near response = convergence, constriction, accommodation
convergence = both eyes move to focus on an object
constriction = reduce spherical aberration
accommodation = ciliary muscles change shape of lens
 = far vision,  = close vision
the retina (sensory transduction)
sclera – outer layer of eyeball, dense collagenous CT+BV+nf
choroid – dark vascular layer at back of retina
pigment layer – stops stray light from hitting retina
rods – receptor cells for black & white vision, not a neuron 130
cones – receptor cells for color vision, not a neuron 6.5
rod and cone nuclei = synapse with bipolar and horizontal cells
bipolar cells = 1st order neurons
horizontal cells = integration of visual info
ganglion cells = 2 different types (visual & light)
glial cells = support and hold in place all cells
ganglion cells = 2nd order neurons, form the optic nerve,
receive info from bipolar cells and amarcine cells, some
ganglion cells are photosensitive and send light info to
brainstem for control of circadian rhthyms
amacrine cells = integrate info from bipolar cells which received
info from rods, cones, and horizontal cells and feed this info to
ganglion cells
- light to retina – energy to chemical change
- chemical to electrical change – electrical signal – synapse
- integration and convergence
- passage to brain
rod/cone – bipolar – ganglion – optic nerve – optic chiasma –
hemi decussation – lateral geniculate of thalamus – optic
radiation to primary visual cortex of occipital
but
some photosensitive ganglion cells send info to superior
colliculus (extrinsic muscle reflexes) and pretectal midbrain
(pupillary reflexes)
color vision – 3 cones – blue(420) – green(531) – red(558)
color is an integration of all 3 cones
color blindness – lack of 1 of the opsins (usually sex linked)
nocturnal = rods only
diurnal = rods and cones
stereoscopic vision
provides depth perception
less than 100 feet focuses lateral to the fovea
greater than 100 feet focuses medial to the fovea
about 100 feet focuses on the fovea
action of light on rhodopsin
1) light enters eye
2) rhodopsin energized
3) cis-retinal becomes trans retinal
4) opsin on energized trans form initiates cGMP breakdown and
5) sends signals through optic nerve
6) trans retinal breaks down into opsin and retinal
7) trans retinal reverts enzymatically back to cis form
8) opsin and cis retinal combine back to regenerate rhodopsin