neuro quiz 3 Flashcards
most nerves in the PNS have a covering called..
neurilemma - covers Schwann cell and is important in repair
stage 1 PNS repair
degeneration
(chromatolysis - nissl bodies in cell break up, provides metabolic support for regeneration to occur)
&
Wallerian degeneration - damaged axon and myelin disintegrate, neurilemma remain)
(chromatolysis is concurrent w wallerian degeneration)
regeneration - Stage 2 PNS repair
- dependent on Scwhann cells
- they multiply by mitosis and grow to form a regeneration tube
- neurolemma forms tube
- buds of regenerating axons fill tube until axon is fully regrown
- grow at 1-1.5mm per day
- myelin sheath is now grown and covers axon
conditions that must be present for regeneration
- neurons must be located in PNS
- intact cell body
- myelination by functional Schwann cells having a neurolemma
birth of a new neuron from a stem cell
neurogenesis
after an injury, if the ________ is intact and there is a functioning _____ cell, the axon may be repaired
cell body
schwann cell
- temporary interupption of conduction w/o loss of axonal continuity
- everything still intact
- NO wallerian degeneration
- often sensory/motor problems distal to injury
neuropraxia
most mild injury
- damage to axon and myelin
- sensory and motor deficits distal to injury
- no nerve conduction distal to injury
- wallerian deg distal to injury site
- prognosis = good
axonotmesis
- total severance of nerve fiber
- partial or incomplete
- sensory or motor problems and autonomic defects are severe
- no nerve conduction distal to injury site
- wallerian degeneration distal to injury
-sx needed - prognosis = not good
neurotmesis
what temperature are cold receptors (A fibres) activated by
10 & 40
what temp are warm receptors (C fibers) activated by
32 and 48 (90-118)
what temp stimulates pain receptors producing painful sensations
below 10 & 48
what are thermoreceptors
free nerve endings that have receptive fields about 1 mm in diameter on the skin surface
fast pain =
myelinated A fibers
superficial - acute, sharp, pricking
slow pain =
unmyelinated C fibers
excruciating, chronic, burning, aching, throbbing
deeper and internal organs
(toothache)
3 types of proprioceptors
- mm spindles
- GTO
- joint kinesthetic receptors (in synovial joint capsules)
4 events that occur for sensation to arise
- stimulation of a sensory receptor (stimulus occurs within the receptors “receptive field”
- transduction of the stimulus (a sensory receptor converts the energy in the stimulus into a graded potential) it can transduce (convert) only one type of stimulus
- generation of nerve impulses
- integration of sensory input (integrated in cerebral cortex)
what are sensory neurons called that conduct impulses from the PNS to the CNS
first-order neurons
physical stimulus –> transduction –> transmission –> analysis and integration
bare dendrites associated w pain, thermal, tickle, itch, some touch sensations
free nerve endings
dendrites enclosed in connective tissue capsule for pressure, vibration, some touch sensations
encapsulated nerve endings
receptor cells synapse w first order neurons located in retina, inner ear, taste buds of tongue
separate cells
located in blood vessels, viseral organs
monitor conditions internally
not consciously perceived
interoceptors (visceroceptors)
sensitive to stimuli like deformation, stretching, bending of cells
provide sensations of touch, pressure, vibration, proprioception, hearing, equilibrium
monitor stretching of blood vessels and internal organs
mechanoreceptors
detect changes in temperature
thermoreceptors
respond to painful stimuli resulting from physical or chemical damage to the tissue
nociceptors
detect light that strikes the retina of the eye
photoreceptors
detect chemicals in the mouth, nose and body fluids
chemoreceptors
detect osmotic pressure of body fluids
osmoreceptors
(CSF, blood)
encapsulated receptors (slowly adapting) in the dermis, subcutaneous tissue
highly sensitive to stretching
bulbous corpuscles/ ruffini corpuscles
sensory neurons that conduct nerve impulses from somatic sesnory receptors into brainstem or spinal cord
first order neurons
conduct nerve impulses from the brainstem or spinal cord to thalamus
second order
axons of second order neurons decussate as they move through brainstem or spinal cord before ascending into the thalamus
conduct nerve impulses from the thalamus to the primary somatosensory cortex on the same side
third order
each piece of incoming information is combined w other arriving and previously stored information in a process called ..
integration
sensations are made up of
- levels and components of pathways that convey sensory nerve impulses from the body to the brain
- general sensations that result
special senses modalities
smell
taste
vision
hearing
equilibrium / balance
a sensory receptor is a structure of the nervous system that
monitors change in the external or internal environment
where does the process of sensation begin
sensory receptor
what is it called when the generator potential or receptor potential decreases in amplitude during a maintained, constant stimulus
adaptation
this causes the freqeuncy of nerve impulses in the first order neuron to decrease
what are the areas w the highest density of somatic sensory receptors
tip of tongue
lips
fingertips
arise from stimulating the skin surface
ex) pain, thermal, tactile
cutaneous sensations
4 modalities of somatic sensation
- tactile
- thermal
- pain
- proprioceptive
tactile sensations
touch, pressure, vibration, itch, tickle
what tactile sensations are detected by encapsulated mechanoreceptors (A fiber)
touch, pressure, vibration
what tactile sensations are detected by free nerve endings (C fibre)
itch and tickle
2 types of rapidly adapting touch receptors
- Meissner corpuscles
- dermal papillae of hairless skin - hair root plexuses
- free nerve endings wrapped around hair follicles
2 types of slowly adapting touch receptors
- merkel discs
- flattened free nerve endings - ruffini corpuscles
- encapsulated receptors deep in dermis
- sensitive to stretching
receptors that contribute to sensations of pressure include
- meissner corpuscles
- merkel discs
- pacinian corpuscles
receptors for vibration sensations
- meissner - low freq.
- pacinian - higher freq.
receptors for tickle
free nerve endings
where are cold receptors located
stratum basale of epidermis
warm are in dermis
nociceptors
free nerve endings found in every tissue of the body except the brain
the visceral organ involved and the area to which the pain if referred are served by the _____
same segment of the spinal cord
where are proprioceptors found
mm’s (especially postural mm’s)
tendons
golgi tendon reflex steps
- neuron from golgi tendon organ fires
- motor neuron inhibited
- muscle relaxes
- load is dropped
what responds to pressure in the capsules of joints
free nerve endings
ruffini corpuscles
in the connective tissue, what responds to acceleration and deceleration of joints during movement
small Pacinian corpuscles
where are conscious sensations or perceptions integrated
cerebral cortex
when stimulated, dendrites of free nerve endings, encapsulated nerve endings and the receptive part of olfactory receptors produce ……
a generator potential
detect light touch and pressure, located in the skin
merkel cells
sense light touch and low frequency vibrations
in areas of high frequency
meissners corpuscles
detect deep pressure and high frequency vibration
pacinian corpuscles
sense skin stretch and sustained pressure
ruffini endings
