Ch 5 - EDX: Anatomy & Physiology Flashcards
Where is the cell body of a motor neuron located?
Anterior (ventral) horn of the SC
Where is the cell body of a sensory neuron?
Located in dorsal root ganglion outside the SC in intervertebral foramen
What is an axon?
Projection from sensory or motor neurons that propagate current flow and transport nutrition
Where do axons of motor neurons project?
Projects axons distal
Where do axons of a sensory neuron project?
Bipolar cells with 2 axons
1 projects proximal and one distal
What is the innervation ratio?
Amount of muscle fibers innervated by one axon
What is the innervation ratio of a muscles of gross movement?
High
The higher the ratio the higher the force
ex) 600 muscle fibers to one axon in leg
What is a myotome?
Group of muscles innervated by one spinal segement
What is a dermatome?
Sensory innervation of one spinal segment
What is a NMJ?
Sites where electric impulse along an axon converts to a chemical rxn and translated to an electrical impulse at postsynaptic mem to initiate a muscle fiber action potential (AP)
What is a motor unit?
Anterior horn cell Motor nerve axon Peripheral nerve NMJ Muscle fibers
What is the Henneman size principle?
Smaller alpha motor neuron has low threshold for excitation and is recruited first in voluntary contraction
(Large recruited for greater contractile force)
Describe Type I muscle fibers
Small cell body
Thin diameter axon
Low innervation ratio
Slow twitch muscle fibers
Describe Type II muscle fibers
Large cell body
Thick diameter axon
High innervation ratio
Fast twitch muscle fibers
What type of fibers does EDX evaluate?
Ia (large, myelinated) fibers