ME03 - Motor System 1 - SC, Cortex, Brainstem Flashcards
Neural pathways that control the sequence and pattern of muscle contractions
Distributed throughout brain and spinal cord
Motor System
What constitutes a MOTOR UNIT?
Consists of a single motor neuron and the muscle fibers that it innervates
For fine control, a single motor neuron innervates only a few muscle fibers. True or False
True, Example: Eye Muscle
For larger movements, a single motor neuron may innervate thousands of muscle fibers. True or False?
True, Example: Postural Muscles/Axial Muscles
Force of muscle contraction is graded by recruitment of additional motor units
Graded Response - Size Principle of Muscle
What principle is applied in “As additional motor units are recruited, more motor neurons are involved and more tension is generated”
Size Principle of Muscle
2 Types of Motor Neurons
Alpha Motor Neurons | Gamma Motor Neurons
o Innervate extrafusal skeletal muscle fibers
o Action potentials in _ motor neurons lead to action potentials in the extrafusal muscle fibers they innervate, which results in contraction
Alpha Motor Neurons
o Innervate specialized intrafusal muscle fibers
o Adjust the sensitivity of the muscle spindles
Gamma Motor Neurons
2 Types of Muscle Fibers
Extafusal Fibers | Intrafusal Fibers
o Make up the bulk of muscle
o Innervated by alpha motor neurons
o Provide the force for muscle contraction
Extrafusal Fibers
o Smaller than extrafusal muscle fibers
o Are innervated by gamma motor neurons
o Encapsulated in sheaths to form muscle spindles
o Are too small to generate significant force
Intrafusal Fibers
Mnemonic for Motor Neuron Fiber
AEGIS (Alpha Motor - Extrafusal | Gamma Motoe - Intrafusal)
Central role in skeletal muscle control
Cell bodies are topographically arranged within the ventral horn of the spinal cord
Axons innervate skeletal muscle fibers
Alpha Motor Neurons
Cell bodies of Alpha Motor Neuron receive numerous synaptic connections from:
o proprioceptors
o higher levels of the CNS including the brainstem, basal ganglia, cerebellum, and motor cortex
Topographic Arrangement of muscles of the trunk
Medial
Topographic Arrangement of muscles of the extremities
Lateral
Topographic Arrangement of limb flexors
Dorsal
Topographic Arrangement of limb extensors
Ventral
Cells responsible for the synapse with the pool of motor neurons when stimulated
Renshaw Cells»_space; predominantly inhibitory
bring about recurrent or feedback inhibition
NTs involved in the muscle contraction
Glycine - inhibitory | Strignin - cause prolonged muscle contraction
What type of synaptic arrangement is exemplified by Renshaw cells?
One to Many
What neurotransmitter is released by Renshaw cells?
Glycine
What type of neuronal circuit is exemplified by Renshaw cells?
Divergent