Somatic Nervous System Flashcards
somatic innervartion
skin and MSK system
includes skin, muscle, bone, ligaments, tendons, fascia
somatic sensory innervation
touch, pain and proprioception
somatic motor innervation
skeletal muscle
somatic
innervation of cutaneous and musculoskeletal
visceral
internal structures of of head, thorax, abdomen, pelvic cavity
afferent
input to CNS
Somatosensory & viscerosensory
efferent
output from CNS
motor - muscle & glands
4 categories of SNS
somatic afferent, somatic efferent, visceral afferent, visceral efferent
SA: somatosensation
SE: motorneuron innervation of skeletal msucle
VA: viscerosensation, painful or non-painful, inside head/body
VE: visceromotor, to smooth muscle, glands, organs
What is included at every segment of spinal cord?
somatosensory system (touch/pain/temperature/pain/proprioception), motor system (voluntary/skeletal muscle), reflexes
anterior horn cells receive what from brain
mediating voluntary movement
anterior horn cells receive what from sensory neurons?
mediating reflexes
anterior horn cells recieve what from brain, associated with coordination
mediating non-conscious control of balance & motor condition
upper extremities innervated by what segmental level?
brachial plexus, C5-T1
lower extremities innervated by what segmental level?
lumbosacral plexus, L1-S5
circuitry initial path
motor neuron cell body in ventral horn, axon projects via ventral root to spinal nerve, from spinal nerve to dorsal or ventral rami or named nerve to NMJ
Corticospinal motor system - voluntary movement
2 consecutive neurons
- upper motorneuron in cerebral cortex to brain stem and cross side until at the level of synapse on lower neuron
- lower motorneuron in ventral horn then projects onto the muscle
Projection from upper motor neuron regulate lower motor neuron
both excitatory and inhibitory projections depending on the muscle activation needed
if want something to flex, will use glutamate to excite flexors and then inhibit the extensor with GABA
Cutaneous somatosensory nerve endings
merkel’s touch domes, pacinian corpuscles, meissner’s, ruffini, free nerve endings
fine and discriminative touch used in
hair - motion
merkel’s touch domes (pressure, edges, textures)
Pacinian corpuscles
vibration (even if eyes closed)
Meissner’s
Crude touch with low spatial resolution
tap, flutter, texture
Ruffini
proprioception
skin stretch, joint movement
free nerve endings
pain & temperature
ONLY somatosensory neuron that stops in spinal cord to synapse
muscle spindle
senses stretch
golgi tendon organ
senses contraction
Why are dermatomes clinically important
identify different problems in spine if certain dermatome path followed for region of impact
loss of sensation in single dermatome
single disc herniation and pinched nerve/root
can induce dermatomal pattern of pain/parathesias
common levels of herniation
C5-6 disc & C6 root/nerve
C6-7 disc & C7 root/nerve
L4-5 disc & L4 root/nerve
L5-S1 disc & L5 root/nerve
nerve conduction study
stimulate nerve in one spot and record latency & amplitude in muscles innervated by it
amplitude
height of response
if decreased, means decreased neuronal activity (dead axons or decreased number
velocity
speed of response
mostly affected by loss of myelination
What happens when inputs of neurons converge in spinal cord
visceral and somatic receptors go to same region or level
Stretch reflex (deep tendon reflexes)
mediated by muscle spindles as only stretch is what is sensed in reflexes
Tap on reflex creates mild stretch and detect by sensory neuron around spindle muscle fiber then this neuron fires to release excitatory NT on motor neuron
What level does the knee jerk reaction occur at?
L4, femoral peripheral nerve
3 components of muscle spindle stretch reflex circuitry
muscle spindle, sensory arc, motor arc
muscle spindle
what is stretched, embedded in extrafusal muscle, contains intrafusal muscle fibers
sensory arc
stretch muscle spinfle fibers to activate sensory neurons that are wrapped around intrafusal muscle fibers
motor arc
sensory fiber form excitatory synapse on alpha motorneurons, activate extrafusal muscle contraction and movement
GTO Reflex path
GTO detect tension/contraction, muscle contraction excites sensory neuron, sensory neuron axon projection to inhibitory interneuron, sensory neuron releases NT that excite inhibitory interneuron that releases NT that inhibits motorneuron
Muscle energy using isometric contraction
isometri contract of hypertonic, follow by post isometric relaxation allows refractory period in hyperactive muscle so that motor neuron decreases tension in the golgi tendon organ, allow for manipulation of previosuly too tight muscle
muscle energy using antagonist
use antagonist contraction to engage reciprocal inhibition
if bicep too tight, activate tricep which engages antagonistic relaxation of bicep, allowing for work to then be done on bicep
