CH 16 Flashcards
Sensory receptor
a structure specialized to detect a stimulus.
Sense organs
Accessory tissues may include:
nerve tissue surrounded by other tissues that enhance response to a certain type of stimulus.
-added epithelium, muscle, or connective tissue.
Transduction
the conversion of one form of energy to another.
- conversion of stimulus energy (light, heat, touch, sound, etc.) into nerve signals.
- ex’s: sense organ or gasoline engine.
Sensation
a subjective awareness of the stimulus.
-Most sensory signals delivered to the CNS produce no conscious sensation.
(pH and body temp require no conscious awareness)
Sensory receptors transmit 4 kinds of info:
- modality
- location
- intensity
- duration
Modality
type of stimulus or the sensation it produces.
-vision, hearing, taste.
Labeled line code
all action potentials are identical. Each nerve pathway from the sensory cells to the brain is labeled to identify its origin, and the brain uses these labels to interpret what modality the signal represents.
Location
encoded by which nerve fibers are issuing signals to the brain.
receptive field
rea that detects stimuli for a sensory neuron.
- vary in size- fingertip vs. skin on back.
- TWO POINT DISCRIMINATION
Sensory projection
brain identifies site if stimulation.
Projection pathways
the pathways followed by sensory signals to their ultimate destination in the CNS.
Intensity
encoded in 3 ways
- which fibers are sending signals.
- how many fibers are doing so.
- how fast these fibers are firing.
Duration
how long the stimulus lasts
-change in firing frequency over time.
Sensory adaptation
if stimulus is prolonged, the firing of the neuron gets slower over time, and we become less aware of the stimulus.
Phasic receptor
generat a burst of action potentials when first stimulated, then quickly adapt and sharply reduce or stop signaling even tough the stimulus continues.
-smell, hair movement, and cutaneous pressure.
Tonic receptor
adapt slowly, generate nerve signals more steadily
-proprioreceptors
Proprioreceptors
body position, muscle tension, and joint motion.
Classification of receptors by MODALITY
thermoreceptors, photoreceptors, nociceptors, chemoreceptors, and mechanoreceptors.
classification of receptors by ORIGIN OF STIMULI
- exteroreceptors: detect external stimuli.
- interpreceptors: detect internal stimuli.
- proprioceptors: sense body position and movements.
classification of receptors by DISTRIBUTION:
- general senses: widely distributed.
- special senses: limited to head (vision, hearing, equilibrium, taste and smell)
Unencapsulated nerve endings
dendrites not wrapped in connective tissue
free nerve endings, tactile discs, hair receptors
free nerve endings
- for pain and temp
- skin and mucous membrane.
tactile discs
- for light touch and texture.
- associated with Merkel cells a base of epidermis.
hair receptors
- wrap around base of hair follicle.
- monitor movement of hair
encapsulated nerve endings
- dendrites wrapped by glial cells to CT
- connective tissue enhances sensitivity or selectivity of response.
(tactile corpuscles, Krause end bulbs, lamellar corpuscles, bulbous corpuscles)
Tactile (messier) corpuscles
- light touch and texture
- dermal papillae of hairless skin
Krause end bulbs
tactile; in mucous membranes
Lamellar (pacinian) corpuscles
Phasic
- deep pressure, stretch, tickle, and vibration.
- periosteum of bone, and deep dermis of skin.
Bulbous (Ruffini) corpuscles
Tonic
-heavy touch, pressure, joint movements, and skin stretching.
somatosensory projection pathways (SPP)
from the receptor to final destination in the brain, most somesthetic signals travel by way of 3 neurons.
First-order neuron (afferent) (SPP)
- from body, enter the dorsal horn of spinal cord via spinal nerves.
- from head, enter pons and medulla via cranial nerve.
- touch, pressure, and proprioception on large, fast, myelinated axons.
- heat and cold on small, unmyelinated, slow fibers.
Second-order neuron (SPP)
- decussation to opposite side of spinal cord, medulla, or pons.
- end in THALAMUS, except for proprioception, which ends in cerebellum.
third-order neuron
thalamus to primary somesthetic cortex of cerebellum
Pain
discomfort cause by tissue injury or noxious stimulation, and typically leading to evasive action.
-important since it helps protect us
diabetic neuropathy
lost in diabetes mellitus
Nociceptors (pain)
two types proving different pain sensations
- fast pain
- slow pain
fast pain
travels myelinated fibers at 12 to 30 m/s
sharp, localizza, stabbing pain perceived with injury
slow pain
travels unmyelinated fibers at 0.5 to 2 m/s.
longer-lasting, dull, diffuse feeling
somatic pain
from skin, muscles, and joints.
visceral pain
from the viscera
-streatch, chemical irritants, or ischemia of viscera (poorly localize) (fetal position)
Bradykinin
most potent pain stimulus known.
- makes us aware of injury and activates cascade or reaction that promote healing.
- histamine, prostaglandin, and serotonin also stimulate nociceptors.
Pain signals from head: first order neuron
cell bodies in dorsal and root ganglion of spinal nerves or cranial nerves V, VII, IX, X
Pain signals from head: second order neurons
decussate and send fibers up spinothalamic tract or through medulla to thalamus.
-gracile fasciculus carries visceral pain signals.
Pain signals from head: third order neurons
from thalamus reach post central gyrus of cerebrum
Pain signals from neck down
travel by way of three ascending tracts.
- spinothalamic tract
- spinoreticular tract
- gracile fasciculus
Spinothalamic tract
most significant pain pathway.
-carries most somatic pain signals.
Spinoreticular tract
carries pain signals to reticular formation.
-activate visceral, emotional, and behavioral reactions to pain.
Gracile fasciculus
carries signals to the thalamus for visceral pain.
Referred pain
pain in viscera often mistakenly thought to come from the skin or other superficial site.
- results from convergence of neural pathways in CNS.
- Brain “assumes” visceral pain is coming from skin. (brain cannot distinguish source)
- heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 to T5.
Analgesic (pain-relieving)
mechanisms of CNS just beginning to be understood.
-tied to receptor sites for opium, morphine, and heroin in the brain.
Enkephalins
Endorphins and dynorphins:
two analgesic oligopeptides with 200 times the potency of morphine.
-larger analgesic neuropeptides discovered later.
Endogenous opioids
internally produced opium like substances.
-enkephalins, endorphins, dynorphins.
CNS modulation of pain
secreted by the CNS, pituitary gland, digestive tract, and other organs.
Neuromodulators
can block the transmission of pain signals and produce feelings of pleasure and euphoria.
Spinal gating
stops pain signals at the posterior horn of the spinal cord.
- descending analgesic fibers aride in brainstem.
- travel down the spinal cord in the reticulospinal tract.
- block pain signals from traveling up the cord to the brain.
normal pain pathway
- nociceptor stimulates second-orer nerve fiber.
- substance P
- second order fiber transmits signal up the spinothalamic tract tot he thalamus.
- thalamus relays signals though third order neurons to the cerebral cortex where one becomes conscious of the pain.
Another pathways of spinal gating
rubbing or massaging injury.
-rubbing stimulates mechanoreceptors which stimulates spinal interneurons to secrete enkephalins that inhibit second-order pain neurons
ICE?
Gustation (taste)
4,000 taste buds mainly on tongue
-inside cheeks , and on soft paw;te, parynx, and epiglottis
Lingual papillae
- Filiform
- foliate
- fungiform (3)
- vallate (circumvallate) (250)
Filiform
no taste buds
- important for food texture.
- cats
foliate
no taste buds
- weakly developed in humans.
- present in infants
fungiform (3)
at tips and sides of tongue
vallate (circumvallate) (250)
at rear of tongue
taste cells
have a tuft of apical microvilli (taste hairs) that serve as receptor surface for taste molecules (tastants)
taste pores
pit in which the taste hairs project
taste hairs are ________ not neurons.
epithelial cells
basal cells
stem cells that replace taste cells every 7 to 10 days
produced by metal ions (sodium and potassium)
salty
associated with carbohydrates and other foods of high caloric value
sweet
acids such as in citrus fruits
sour
associated with spoiled foods and alkaloids such as nicotine, caffeine, quinine, and morphine, (low threshold)
bitter
“meaty” taste of amino acidic chicken or beef broth
Umami
taste is influence by food texture, aroma, temperature, and appearance
frontal lobe
mouth feel
detected by branches of lingual nerve in papillae
hot peppers stimulates ______ (pain) not taste buds
free nerve endings
regional differences in taste sensations on tongue
tip is most sensitive to sweet (licking, salivating), edges to salt and sour and rear to bitter.
activate second messenger systems
sugars, alkaloids, and glutamate bind to receptors which activates G proteins and second messenger systems within the cell.
depolarize cells directly
sodium and acids penetrate cells and depolarize directly
______ nerve collects sensory info from taste buds over anterior 2/3 of tongue
facial
______nerve from posterior 1/3 of tongue
glossopharyngeal
______nerve from taste buds of plate, pharynx, and epiglottis.
vagus
Spicy?
trigeminal nerve
-doesn’t decrease over time.
olfaction
sense of smell
all fibers reach ______ in medulla oblongata
solitary nucleus
-have to be able to salivate
post central gyrus
parietal lobe
amygdala
gratification & aversion
olfactory cells
- neurons
- head bears 10 to 20 cilia (olfactory hairs)
- binding sites for odorant molecules and nonmotile
- basal end of each cell become axon
axons collect into small fascicles and leave cranial cavity through the cribriform foramina in the _____bone
ethmoid
fascicle are collectively regarded as cranial nerve ___
1
olfactory receptors adapt ____
quickly
some odorants act on nociceptors of the trigeminal nerve:
ammonia, menthol, chlorine, and capsaicin of hot peppers (smelling salts)
-stimulate pain receptors which stimulate RAS which stimulates cerebral cortex.
dormitory effect
females that get on the same cycle
ovulating women’s vaginal secretion contain pheromones called ______ , that have been shown to raise mens testosterone levels.
copulines
secondary destinations
hippocampus, amygdala, hypothalamus, insula, and oritofrontal cortes.
-identify odors, integrate smell with taste, perceive flavor, evoke memories and emotional responses
hearing
a response to vibrating air molecules
-liquids, solids
equilibrium
the sense of motion, body orientation, and balance.
Sound
nay audible vibration of molecules
- a vibrating object pushes on air molecules
- air molecules hitting eardrum cause it to vibrate.
Pitch
our sense of whether a sound is high or low.
- determmined by frequency: cycles per second (hertz HZ)
- speech is 1,500-5,000 Hz, hearing is most sensitive.
- hearing loss with age is 250 to 2,050 Hz.
infrasonic
frequencies below 20Hz (elephants)
ultrasonic
frequencies above 20,000 Hz (bats)
loudness
the perception of sound energy, intensity, or amplitude of the vibration,
- decibels (dB)
- prolonges exposure to sounds >90 dB can cause damage (cochlia-inner hair cells)
- speech 60 dBs
Outer ear
- tympanic membrane (eardrum)
- auricle (pinna)-funnels sound waves.
- Auditory canal or external acoustic meatus: -guard hairs (keep stuff out) -cerumen(wax)
functions?
- anti-microbial
- water repellent
- keeps tympanic membrane moist
middle ear
Tympanic membrane (eardrum) closes the inner end of the auditory canal. -tympanic cavity: contains auditory ossicles.
auditory (eustachian) tube
middle ear*
connects middle-ear cavity to nasopharynx.
- opens when swallowing or yawning (planes)
- eustachian tube
- otits media
Auditory ossicles
helps with transfer of mechanic energy.
- malleus
- incus
- stapes
- stapedius and tensor tympani muscles attach to stapes and malleus (metallica)
Sound travels well through ____ more _____ the better.
solid; dense
middle-ear infection
-otits media
- fluid accumulates in tympanic cavity producing pressure, pain, and impacted hearing.
- can spread leading to meningitis.
- can cause fusion of ear ossicles and hearing loss.
- children have shorter eustachian tubes.
- Tympanostomy
tympanostomy
lancing tympanic membrane and draining fluid from tympanic cavity.
Bony labyrinth
passageways in temporal bone
membranous labyrinth
- filled with ENDOLYMPH
- floating in PERILYMPH
fleshy tubes lining bony labyrinth
- similar to intracellular fluid
- similar to cerebral spinal fluid
labyrinth
vestibule and 3 semicircular ducts
cochlea
organ of hearing
Scala vestibuli
superior chamber
- filled with perilymph
- begins at oval window and spirals to apex
Scala tympani
inferior window
- filled with perilymph
- beings at apex and ends at round window
scala media
triangular middle chamber
-filled with endolymph
organ of corti
acoutic organ that converts vibrations into nerve impulses
