VII- LMN Flashcards
motor unit consists of
a motor neuron + all skeletal muscle fibers it innervates
determines the innervation ratio and strength of contraction
LMN location
in spinal cord @ ventral/anterior horn
types of LMN to skeletal muscle
- alpha motor
- gamma motor
direct innervation
lateral LMNs inn
distal muscles
also have short distance circuit/interneurons unilateral
medial LMN inn
proximal muscles
also have long distance interneurons/circuit neurons that project bilateral
size principle
as synaptic drive in ventral horn inc = smaller size LMN reach activation threshold first
-if activity continues then recruitment occurs in order of cell body size
myotatic reflex
shows reciprocal inhibition so when patellar tendon hit extensors are activated + flexors inhibited
Ia afferents excited alpha motor neuron for quads + 1a inhibitory interneuron to hammies
reverse myotatic reflex
polysynaptic reflex via Ib afferents
-interneurons activated to inhibit the contracted/tensed muscle + activate antagonist muscle
flexor withdrawal
polysynaptic reflex/crossed extensor resp
-flexors contract and inhibit extensors + opposite limb extends to support
primary functions of golgi tendon organ
monitor surface tension/contraction strength to maintain muscle tone
primary function of muscle spindle
monitor changes in muscle length and velocity of change
-quick changes by Ia fibers or prolonged stretches by Ia/II
flexors =
distal
extensors are ventral
categories of motor units
- slow fibers- type 1 for long, posture
- fast fatigable fibers- type 2b for rapid forceful movements
- fast fatigue resistant fibers- 2a for moderate force/time
smaller LMNs have
larger input resistance
alpha-gamma coactivation
same motor inputs affect alpha and gamma
-allows gamma to control sensitivity/gain of muscle spindle regardless of length
