PM&R BOARD FLASHCARDS/EMG
QUESTIONS AND ANSWERS WITH
SOLUTIONS 2024
4 key things to describe in EMG report - ANSWER - location\n- duration\n- severity\n- prognosis
What is the basic functional element of the neuromuscular system? - ANSWER the motor unit
What are the 7 components of the motor unit (from proximal to distal)? - ANSWER - anterior horn cell\n-
nerve root\n- spinal nerve\n- plexus\n- peripheral nerve\n- neuromuscular junction\n- muscle fiber
Where is the alpha-motor neuron located? - ANSWER cell body of the motor nerve; located in the
anterior horn of the spinal cord
What regulates the characteristics of the motor unit? - ANSWER The alpha motor neuron
What is the innervation ratio? - ANSWER The amount of muscle fibers belonging to an axon
Do muscles with stronger/grosser movements have a higher or lower innervation ration? - ANSWER
Higher (more muscle fibers per axon)
What is the relationship between innervation ratio and force generated by a muscle? - ANSWER Higher
innervation ratio = greater force
What is a typical innervation ratio for a muscle in the leg? - ANSWER 600 muscle fibers : 1 neuron
What is a typical innervation ratio for a muscle around the eye? - ANSWER 1 muscle fiber : 1 neuron
Define the neuromuscular junction - ANSWER The location in the motor unit where electrical AP is
converted to chemical energy to initiate a a muscle action potential.
,What type/category of motor neurons can can EMG study? - ANSWER Alpha motor neurons (Ia fibers)
What are the 2 general ways that alpha motor neurons are further described? - ANSWER - size\n-
physiology
What order are alpha motor neurons recruited? - ANSWER In order of the size of the motor unit (smaller
muscle fibers first)
The sequential activation of motor units allowing for smooth increase in contractile force is described by
what principle? - ANSWER Henneman Size Principle
Alpha motor neurons innervate ______ - ANSWER extrafusal fibers (skeletal muscle)
Gamma motor neurons innervate ______ - ANSWER intrafusal fibers (muscle spindle)
Beta motor neurons innervate _____ - ANSWER intrafusal and extrafusal fibers (skeletal muscle and the
muscle spindle)
What are extrafusal fibers? - ANSWER skeletal muscle
What are intrafusal fibers? - ANSWER muscle spindle fibers
4 basic characteristics of type I muscle fibers - ANSWER - smaller cell body\n- thinner diameter axon\n-
lower innervation ratio\n- slower twitch muscle
4 basic characteristics of type II muscle fibers - ANSWER - larger cell body\n- thicker diameter axon\n-
higher innervation ratio\n- faster twitch muscle
What is the Henneman size principle? - ANSWER A smaller alpha motor neuron has a lower threshold of
excitation causing it to be recruited first. Larger alpha motor neurons have larger thresholds causing
them to be recruited when more force is needed.
, What order do the "neurium" layers go in from outside in? - ANSWER - epineurium\n- perineurium\n-
endoneurium
Define endoneurium - ANSWER Connective tissue surrounding each individual axon and its myelin
sheath
Define perineurium - ANSWER Connective tissue surrounding bundles or fascicles of myelinated and
unmyelinated nerve fibers
What is the purpose of the perineurium? - ANSWER - strengthens the nerve\n- acts as a diffusion barrier
May individual neurons cross from one bundle to another throughout the course of the nerve? -
ANSWER yes
Define epineurium - ANSWER loose connective tissue surrounding the entire nerve that holds the
fascicles together and protects it from compression
Define resting membrane potential - ANSWER the voltage of the axon's cell membrance at rest
What are "leak channels"? - ANSWER Channels that allow K and Na to move passively in and out of the
cell membrane
What is the normal resting membrance potential of an axon? - ANSWER -70 to -90mV
How many K and Na are involved in the K/Na pump? - ANSWER 3Na out for every K in
The resting membrane potential is maintained by the - ANSWER Na/K pump
Most important event in generating an action potential is... - ANSWER sodium conductance
QUESTIONS AND ANSWERS WITH
SOLUTIONS 2024
4 key things to describe in EMG report - ANSWER - location\n- duration\n- severity\n- prognosis
What is the basic functional element of the neuromuscular system? - ANSWER the motor unit
What are the 7 components of the motor unit (from proximal to distal)? - ANSWER - anterior horn cell\n-
nerve root\n- spinal nerve\n- plexus\n- peripheral nerve\n- neuromuscular junction\n- muscle fiber
Where is the alpha-motor neuron located? - ANSWER cell body of the motor nerve; located in the
anterior horn of the spinal cord
What regulates the characteristics of the motor unit? - ANSWER The alpha motor neuron
What is the innervation ratio? - ANSWER The amount of muscle fibers belonging to an axon
Do muscles with stronger/grosser movements have a higher or lower innervation ration? - ANSWER
Higher (more muscle fibers per axon)
What is the relationship between innervation ratio and force generated by a muscle? - ANSWER Higher
innervation ratio = greater force
What is a typical innervation ratio for a muscle in the leg? - ANSWER 600 muscle fibers : 1 neuron
What is a typical innervation ratio for a muscle around the eye? - ANSWER 1 muscle fiber : 1 neuron
Define the neuromuscular junction - ANSWER The location in the motor unit where electrical AP is
converted to chemical energy to initiate a a muscle action potential.
,What type/category of motor neurons can can EMG study? - ANSWER Alpha motor neurons (Ia fibers)
What are the 2 general ways that alpha motor neurons are further described? - ANSWER - size\n-
physiology
What order are alpha motor neurons recruited? - ANSWER In order of the size of the motor unit (smaller
muscle fibers first)
The sequential activation of motor units allowing for smooth increase in contractile force is described by
what principle? - ANSWER Henneman Size Principle
Alpha motor neurons innervate ______ - ANSWER extrafusal fibers (skeletal muscle)
Gamma motor neurons innervate ______ - ANSWER intrafusal fibers (muscle spindle)
Beta motor neurons innervate _____ - ANSWER intrafusal and extrafusal fibers (skeletal muscle and the
muscle spindle)
What are extrafusal fibers? - ANSWER skeletal muscle
What are intrafusal fibers? - ANSWER muscle spindle fibers
4 basic characteristics of type I muscle fibers - ANSWER - smaller cell body\n- thinner diameter axon\n-
lower innervation ratio\n- slower twitch muscle
4 basic characteristics of type II muscle fibers - ANSWER - larger cell body\n- thicker diameter axon\n-
higher innervation ratio\n- faster twitch muscle
What is the Henneman size principle? - ANSWER A smaller alpha motor neuron has a lower threshold of
excitation causing it to be recruited first. Larger alpha motor neurons have larger thresholds causing
them to be recruited when more force is needed.
, What order do the "neurium" layers go in from outside in? - ANSWER - epineurium\n- perineurium\n-
endoneurium
Define endoneurium - ANSWER Connective tissue surrounding each individual axon and its myelin
sheath
Define perineurium - ANSWER Connective tissue surrounding bundles or fascicles of myelinated and
unmyelinated nerve fibers
What is the purpose of the perineurium? - ANSWER - strengthens the nerve\n- acts as a diffusion barrier
May individual neurons cross from one bundle to another throughout the course of the nerve? -
ANSWER yes
Define epineurium - ANSWER loose connective tissue surrounding the entire nerve that holds the
fascicles together and protects it from compression
Define resting membrane potential - ANSWER the voltage of the axon's cell membrance at rest
What are "leak channels"? - ANSWER Channels that allow K and Na to move passively in and out of the
cell membrane
What is the normal resting membrance potential of an axon? - ANSWER -70 to -90mV
How many K and Na are involved in the K/Na pump? - ANSWER 3Na out for every K in
The resting membrane potential is maintained by the - ANSWER Na/K pump
Most important event in generating an action potential is... - ANSWER sodium conductance
