Ch 13 PNS Flashcards
Provides links from and to world outside body
All neural structures outside brain
PNS
the awareness of changes in the internal and external environment
sensation
the conscious interpretation of those stimuli
perception
part of sensory system serving body wall and limbs
somatosensory system
sensory integration receives inputs from
Exteroceptors, proprioceptors, and interoceptors
Levels of neural integration in sensory systems:
receptor, circuit, perceptual
sensory receptors
receptor level
processing in ascending pathways
circuit level
processing in cortical sensory areas
perceptual level
Specialized to respond to changes in stimuli
sensory receptors
awareness of stimulus
sensation
interpretation of meaning of stimulus
perception
Classification of Receptors based on
Type of stimulus they detect
Location in body
Structural complexity
respond to touch, pressure, vibration, and stretch
mechanoreceptors
sensitive to changes in temperature
thermoreceptors
respond to light energy (e.g., retina)
photoreceptors
respond to chemicals (e.g., smell, taste, changes in blood chemistry)
chemoreceptors
sensitive to pain-causing stimuli (e.g., extreme heat or cold, excessive pressure, inflammatory chemicals)
nociceptors
Respond to stimuli arising outside body
Receptors in skin for touch, pressure, pain, and temperature
Most special sense organs
exteroceptors
Respond to stimuli arising in internal viscera and blood vessels
Sensitive to chemical changes, tissue stretch, and temperature changes
Sometimes cause discomfort but usually unaware of their workings
interoceptors
Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles
Inform brain of one’s movements
proprioceptors
Tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and muscle sense Modified dendritic endings of sensory neurons
simple receptors for general senses
Vision, hearing, equilibrium, smell, and taste
receptors for special senses
simple receptors for general senses are split into
Either nonencapsulated (free) or encapsulated
Abundant in epithelia and connective tissues
Most are nonmyelinated, small-diameter group C fibers; distal endings have knoblike swellings
Respond mostly to temperature and pain; some to pressure-induced tissue movement; itch
nonencapsulated (free) nerve endings
Cold receptors (10–40°C); in superficial dermis Heat receptors (32–48°C); in deeper dermis Outside those temperature ranges, nociceptors activated pain
thermoreceptors
Player in detection – vanilloid receptor
Ion channel opened by heat, low pH, chemicals, e.g., capsaicin (red peppers)
Respond to:
Pinching, chemicals from damaged tissue, capsaicin
nociceptors
Tactile (Merkel) discs
Hair follicle receptors
nonencapsulated
light touch receptors
joint position and motion
Joint kinesthetic receptors
stretch in tendons
tendon organs
muscle stretch
muscle spindles
deep continuous pressure
Bulbous corpuscles (Ruffini endings)
deep pressure and vibration
Lamellar (Pacinian) corpuscles
discriminative touch
Tactile (Meissner’s) corpuscles
Twelve pairs of nerves associated with brain
cranial nerves
Sensory nerves of smell
Run from nasal mucosa to olfactory bulbs
Pass through cribriform plate of ethmoid bone
Purely sensory (olfactory) function
I Olfactory Nerves
Arise from retinas; really a brain tract
Pass through optic canals, converge and partially cross over at optic chiasma
Optic tracts continue to thalamus, where they synapse
Purely sensory (visual) function
II Optic Nerves
Fibers extend from ventral midbrain through superior orbital fissures to four of six extrinsic eye muscles
Function in raising eyelid, directing eyeball, constricting iris (parasympathetic), and controlling lens shape
III Oculomotor Nerves
Fibers from dorsal midbrain enter orbits via superior orbital fissures to innervate superior oblique muscle
Primarily motor nerve that directs eyeball
IV Trochlear Nerves
Largest cranial nerves; fibers extend from pons to face
Three divisions
Ophthalmic (V1) passes through superior orbital fissure
Maxillary (V2) passes through foramen rotundum
Mandibular (V3) passes through the foramen ovale
Convey sensory impulses from various areas of face (V1) and (V2)
Supply motor fibers (V3) for mastication
V Trigeminal Nerves
Fibers from inferior pons enter orbits via superior orbital fissures
Primarily a motor nerve, innervating lateral rectus muscle
VI Abducens
Fibers from pons travel through internal acoustic meatuses, and emerge through stylomastoid foramina to lateral aspect of face Chief motor nerves of face with 5 major branches Motor functions include facial expression, parasympathetic impulses to lacrimal and salivary glands Sensory function (taste) from anterior two-thirds of tongue
VII Facial
Afferent fibers from hearing receptors (cochlear division) and equilibrium receptors (vestibular division) pass from inner ear through internal acoustic meatuses, and enter brain stem at pons-medulla border
Mostly sensory function; small motor component for adjustment of sensitivity of receptors
Formerly auditory nerve
VIII Vestibulocochlear
activate skeletal muscle
somatic reflexes
activate visceral effectors
autonomic reflexes
Integration center in spinal cord
Effectors are skeletal muscle
spinal somatic reflexes
to smoothly coordinate skeletal muscle, nervous system must receive proprioceptor input regarding
Length of muscle
From muscle spindles
Amount of tension in muscle
From tendon organs
Maintains muscle tone in large postural muscles, and adjusts it reflexively
stretch reflex
Causes muscle contraction in response to increased muscle length
stretch reflex
how does the stretch reflex work
Stretch activates muscle spindle
Sensory neurons synapse directly with motor neurons in spinal cord
motor neurons cause stretched muscle to contract
all stretch reflexes are ________ and _______
monosynaptic and ipsilateral
IIa fibers synapse with interneurons that inhibit motor neurons of antagonistic muscles
reciprocal inhibition
positive stretch reflex indicate
Sensory and motor connections between muscle and spinal cord intact
Strength of response indicates degree of spinal cord excitability
if peripheral nerve damage or ventral horn injury
hypoactive or absent
if lesions of corticospinal tract
hyperactive
Initiated by painful stimulus Causes automatic withdrawal of threatened body part Ipsilateral and polysynaptic Protective; important Brain can override
flexor reflex
Occurs with flexor reflexes in weight-bearing limbs to maintain balance
Consists of ipsilateral withdrawal reflex and contralateral extensor reflex
crossed extensor reflex
Elicited by gentle cutaneous stimulation
Depend on upper motor pathways and cord-level reflex arcs
superficial reflexes
most common superficial reflexes
Plantar reflex
Abdominal reflex
Damage to motor cortex or corticospinal tracts and abnormal response
babinskis sign
Test integrity of cord from L4 through S2
Stimulus – stroke lateral aspect of sole of foot
Response – downward flexion of toes
plantar reflex
Test integrity of cord from T8 through T12
Cause contraction of abdominal muscles and movement of umbilicus in response to stroking of skin
Vary in intensity from one person to another
Absent when corticospinal tract lesions present
abdominal reflexes
what are the special senses
Vision Taste Smell Hearing Equilibrium
what percent of the body’s sensory receptors in eye
70
what are the three layers of the wall of the eye
Fibrous
Vascular
Inner
Internal cavity filled with fluids called
humors
Lens separates internal cavity into what
anterior and posterior segments
Outermost layer of eye; dense avascular connective tissue
Two regions
fibrous layer
two regions of fibrous layer are what
sclera and cornea
Opaque posterior region
Protects, shapes eyeball; anchors extrinsic eye muscles
Continuous with dura mater of brain posteriorly
sclera
Transparent anterior 1/6 of fibrous layer
Bends light as it enters eye
Sodium pumps of corneal endothelium on inner face help maintain clarity of cornea
Numerous pain receptors contribute to blinking and tearing reflexes
cornea
Middle pigmented layer
Three regions
vascular layer
what are the three regions of the vascular layer
choroid, ciliary body, and iris
Posterior portion of uvea; contains blood vessels
Supplies blood to all layers of eyeball
Brown pigment absorbs light to prevent light scattering and visual confusion
choroid
Ring of tissue surrounding lens
Smooth muscle bundles control lens shape
Capillaries of processes secrete fluid
Ciliary zonule (suspensory ligament) holds lens in position
ciliary body
Colored part of eye
iris
central opening that regulates amount of light entering eye
pupil
Originates as outpocketing of brain
Delicate two-layered membrane
inner layer/retina
outer layer of inner layer
Single-cell-thick lining
Absorbs light and prevents its scattering
Phagocytosis of photoreceptor cell fragments
Stores vitamin A
pigmented layer
Signals spread from photoreceptors to bipolar cells to ganglion cells
Ganglion cell axons exit eye as optic nerve
Transparent
Composed of three main types of neurons
inner layer of retina
neural layer
what are the types of neurons in neural layer
Photoreceptors, bipolar cells, ganglion cells
Site where optic nerve leaves eye
Lacks photoreceptors
optic disc/blind spot
two types of photoreceptors
rods and cones
Dim light, peripheral vision receptors
More numerous, more sensitive to light than cones
No color vision or sharp images
Numbers greatest at periphery
rods
Vision receptors for bright light
High-resolution color vision
Macula lutea exactly at posterior pole
cones
Tiny pit in center of macula with all cones; best vision
fovea centralis
The lens and ciliary zonule separate eye into two segments
anterior and posterior segments
Transmits light Supports posterior surface of lens Holds neural layer of retina firmly against pigmented layer Contributes to intraocular pressure Forms in embryo; lasts lifetime
vitreus humor
posterior segment contains ______ ______
vitreus humor
Anterior segment composed of two chambers
posterior and anterior chambers
between cornea and iris
anterior chamber
between iris and lens
posterior chamber
Anterior segment contains
aqueous humor
blocked drainage of aqueous humor increases pressure and causes compression of retina and optic nerve blindness
glaucoma
Biconvex, transparent, flexible, and avascular
Changes shape to precisely focus light on retina
Two regions:
lens
two regions of lens
lens fibers(bulk of lens) and lens epithelium
(clouding of lens) consequence of aging, diabetes mellitus, heavy smoking, frequent exposure to intense sunlight
cataracts
Eyes best adapted for _______ _______
distant vision
close vision Requires eye to make active adjustments using three simultaneous processes
Accommodation of lenses
Constriction of pupils
Convergence of eyeballs
Changing lens shape to increase refraction
Near point of vision
accomodation
loss of accommodation over age 50
presbyopia
Accommodation pupillary reflex constricts pupils to prevent most divergent light rays from entering eye
constriction
Medial rotation of eyeballs toward object being viewed
convergence
Focal point in front of retina, e.g., eyeball too long
Corrected with a concave lens
nearsightedness
myopia
farsightedness
Focal point behind retina, e.g., eyeball too short
Corrected with a convex lens
hyperopia
Unequal curvatures in different parts of cornea or lens
Corrected with cylindrically ground lenses or laser procedures
astigmatism
smell
olfaction
taste
gustation
Chemoreceptors respond to chemicals in _____ ______
aqueous solution
olfactory sensory neurons have ______ ______ _____
unusual bipolar neurons
how many odors can humans distinguish
10,000
how many smell genes active in nose?
1000
Activation of olfactory sensory neurons
Dissolved odorants bind to receptor proteins in olfactory cilium membranes
taste buds are _____ ____
receptor organs
what are the five basic sensations of taste
BUSS: bitter, umami, sweet, sour, salt
sugars, saccharin, alcohol, some amino acids, some lead salts
sweet
hydrogen ions in solution
sour
metal ions (inorganic salts)
salty
alkaloids such as quinine and nicotine; aspirin
bitter
amino acids glutamate and aspartate
umami
Possible sixth taste
lipids
tastes/dislikes have
homeostatic value, genetic, and protective
To be tasted, chemicals must
Be dissolved in saliva
Diffuse into taste pore
Contact gustatory hairs
three major areas of the ear
external. inner, middle
hearing only
external(outer), and middle (tympanic)
hearing and equilibrium
internal
composed of Helix (rim); lobule (earlobe)
Funnels sound waves into auditory canal
auricle(pinna)
Short, curved tube lined with skin bearing hairs, sebaceous glands, and ceruminous glands
Transmits sound waves to eardrum
external acoustic meatus(auditory canal)
Boundary between external and middle ears
Connective tissue membrane that vibrates in response to sound
Transfers sound energy to bones of middle ear
tympanic membrane(eardrum)
A small, air-filled, mucosa-lined cavity in temporal bone
Flanked laterally by eardrum
Flanked medially by bony wall containing oval (vestibular) and round (cochlear) windows
middle ear (tympanic cavity)
Three small bones in tympanic cavity
ear ossicles: Malleus, incus, stapes
two major divisions of internal ear
bony labyrinth and membranous labyrinth
Tortuous channels in temporal bone
Three regions
Filled with perilymph – similar to CSF
bony labyrinth
three regions of bony labyrinth
vestibule, semicircular canals, and cochlea
Series of membranous sacs and ducts
Filled with potassium-rich endolymph
membranous labyrinth
Pressure disturbance (alternating areas of high and low pressure) produced by vibrating object
sound
Moves outward in all directions
Illustrated as an S-shaped curve or sine wave
sound wave
Number of waves that pass given point in given time
Pure tone has repeating crests and troughs
frequency
Distance between two consecutive crests
wavelength
Shorter wavelength = what
higher frequency of sound
Perception of different frequencies
Normal range 20–20,000 hertz (Hz)
pitch
Higher frequency = what
higher pitch
Most sounds are mixtures of different frequencies
Richness and complexity of sounds (music)
quality
Height of crests
amplitude
Amplitude perceived as ______
loudness
Severe hearing loss with prolonged exposure above
90dB
Normal range of loudness
0–120 decibels (dB)
Equilibrium receptors in semicircular canals and vestibule
Vestibular receptors monitor static equilibrium
Semicircular canal receptors monitor dynamic equilibrium
vestibular apparatus
Sensory receptors for static equilibrium
One in each saccule wall and one in each utricle wall
Monitor the position of head in space, necessary for control of posture
Respond to linear acceleration forces, but not rotation
Contain supporting cells and hair cells
maculae
Each crista has supporting cells and hair cells that extend into gel-like mass called
ampullary cupula
Sensory receptor for rotational acceleration
One in ampulla of each semicircular canal
Major stimuli are rotational movements
crista ampullares
Bending of hairs in cristae causes
Depolarizations, and rapid impulses reach brain at faster rate
Strange eye movements during and immediately after rotation
vestibular nystagmus
