lecture 11 Flashcards
describe afference of the PNS
- cutaneous receptor, free nerve ending, abdominal viscera, etc. receives sensory information from stimuli
- information is passed back to sc via rami, then spinal nerve, then dorsal root to the dorsal horn
describe efference of the PNS
- information from the spinal cord (ventral horn) is passed to body via the ventral root, spinal nerve, then rami
- usually innervate skeletal muscle
what is the difference btwn rami and root?
- dorsal/ventral root only carry afferent/efferent information, rami do both (more information flow)
- rami are larger
cutaneous receptors are the _____ response to _____?
primary afferent response to mechanical stretch
with cutaneous receptors, mechanical stretch energy is converted into ________ so it can be sent as a signal to the brain
electrical energy
describe how the conversion of mechanical stretch to electrical energy works
stretch allows Na to flow into the cell, converting mechanical energy to a chemical signal
what are the 4 sensory receptors attributes
- intensity
- modality
- duration
- location
describe intensity as a receptor attribute
discharge of receptor increased with stimuli
describe modality as a receptor attribute
percept is constant for a given receptor
doesn’t matter how the receptor is stimulated, it always sends the same signal to the brain - e.g. sound, vision
describe duration as a receptor attribute
receptors may be slowly adapting (one large signal then consistent little signals) or rapidly adapting (one large signal)
describe location as a receptor attribute
perception is confined to the receptor’s location
what are the two types of cutaneous receptors?
nonencapsulated and encapsulated
what are the subtypes of nonecapsulated cutaneous receptors?
free nerve endings, hair follicle receptors, markel’s discs
where are free nerve endings, what is their modality, and what is their adaptation (duration)?
- glaborous and nonglaborous skin (dermis)
- pain, temperature, touch, pressure
- varies
where are hair follicle receptors, what is their modality, and what is their adaptation (duration)?
- nonglaborous skin (dermis)
- touch
- rapid
where are Merkel’s discs, what is their modality, and what is their adaptation (duration)?
- glaborous and nonglaborous skin (dermis)
- touch
- slow
what are the subtypes of encapsulated cutaneous receptors?
- Meissener’s Corpuscle
- Pacinian Corpuscle
- Ruffini Ending
where are Meissener’s Corpuscles, what is their modality, and what is their adaptation (duration)?
- glaborous skin (dermis)
- touch
- rapid
where are Pacinian Corpuscles, what is their modality, and what is their adaptation (duration)?
- glaborous and nonglaborous skin (hypodermis)
- pressure/vibration
- very rapid (imp for vibration)
where are Ruffini Endings, what is their modality, and what is their adaptation (duration)?
- glaborous and nonglaborous skin (hypodermis)
- stretch
- slow
describe the receptive feild of Meissener’s Corpuscles (rapidly adapting)
small (only exists at point of contact)
describe the receptive feild of Pacinian Corpuscles (rapidly adapting)
larger area than Meissener’s, but most sensitive at point of contact
describe the receptive feild of Ruffini Endings (slowly adapting)
generally larger area than Merkel’s, but are similar in orientation to that of the corpuscle
describe the receptive feild of Merkel’s discs (slowly adapting)
smaller than Ruffini endings (only rlly exists at point of contact)
describe cutaneous receptive feilds in general, moving from the hand, to the arm, to the back
- hand: small, close together, massive density
- arm: larger, farther apart, less dense
- back: massive receptive fields, farther apart, way less dense
what is a dermatome?
area of skin that sends signals to the brain for a given spinal nerve
is there an overlap of sensory fields?
yes - btwn adjacent spinal nerves
are there differences between dermatomes and peripheral nerves?
yes (don’t need to know explicit differences, just know that they exist)
what is a motor unit?
1 motor neuron + innervated muscle fibres
what are the basic features of a motor unit?
- many motor neurons innervate each muscle
- each motor neuron targets only one muscle
- each muscle fibre is only innervated by one motor neuron
- when a motor neuron fires, all its muscle fibres contract
axons of terminal motor neurons synapse onto:
the junctional folds of the sarcolemma of the muscle fibre at motor end plate
what is the motor neuron neurotransmitter?
Ach
what are myotomes?
groups of muscles innervated by one spinal nerve
what are the components of a muscle spindle?
has:
- intrafusal muscular fiber
- extrafusal muscle fibers
- capsule
describe intrafusal muscule fibers
associated with capsule, has afferents
describe extrafusal muscle fibers
generate force
desribe the capsule
connective tissue surrounding the muscle spindle
what do alpha motor neurons innervate?
extrafusal muscle fibers - supply power
what do gamma motor neurons innervate?
intrafusal muscle fibers
what do gamma motor neurons contain?
primary afferent and secondary afferent axons
primary afferent axons increase with muscle:
velocity
secondary afferent axons increase with muscle:
length
if gamma neurons fire, what happens to primary and secondary afferents?
they become even more responsive to stretch for extreme/small muscle movements
what is a golgi tendon organ?
tree-like sensory ending enclosed in a spindle-like connective tissue capsule (axon sits btwn collagen fibers of the muscle)
how do golgi tendon organs generate an impulse?
pulling on collagen fibers pinches the axon, generating an impulse
how do golgi tendon organs discharge in terms of muscle force
they discharge proportional to muscle force
describe (in simple terms) an action potential
- Na enters the axon in response to stimulus (initiates action potential)
- K leaves the axon (terminates action potential)
describe myelin sheath
- for the PNS: schwann cells
- for the CNS: oligodendrocytes
- insulates axon, speeds up conduction
- underlying axons have no channels
describe nodes of ranvier
- gap btwn myelin sheath
- where membrane channels are located
- action potential propogation jumps btwn nodes
larger axons have (faster/slower) transmission?
faster
unmyelinated axons have (faster/slower) transmission?
slower
why are neurons unmyelinated if myelination speeds condution time?
because its important to have some slow neurons too
summarize the neuron fiber types
- BIGGER: alpha motor neurons/msucle spindle primary endings/golgi tendon organs
- BIG: gamma motor neurons/muscle secondary afferent (meissner, merkel, pacinian, etc.)
- MED: sharp pain, cold, some touch
- SMALL: slow pain (when damage is done just need to be aware), heat, itch, some touch
-most ones we covered are myelinated except some smaller bare nerve endings for temperature and pain
