Motor System and Reflexes Flashcards
Where is the primary motor cortex located?
precruciate and postcruciate gyri and the rostral suprasylvian gyrus
What are the motor tracts of the primary motor cortex?
lateral and ventral corticospinal tract
What are precise and refined voluntary control of extremities controlled by?
the contralateral side of the cerebrum
What percentage of motor fibers from the corticospinal tract terminate in cervical segments?
50
What percentage of motor fibers from the corticospinal tract terminate in thoracic segments?
30
What percentage of motor fibers from the corticospinal tract terminate in lumbosacral segments?
20
What are interneurons?
local circulatory neurons mediating signals between neurons
What are the type of interneurons?
excitatory, inhibitory, and renshaw cells
What do excitatory internuerons release?
Ach and glutamate
What do inhibitory interneurons release
GABA and glycine
What do renshaw cells release?
glycine
What does tetanus toxin do?
prevents the release of GABA and glycine from inhibitory and renshaw cells
What are the types of spinal motor neurons?
alpha motor neurons and visceral motor neurons
What are the alpha motor neurons located in and what type of motor neuron is it?
extrafusal muscles; lower motor neuron
What are the visceral motor neurons located in?
smooth and cardiac muscles
What is a motor unit?
a motor neuron and all of the muscle fibers it innervates
What do motor units do?
generate appropriate contractile force of muscles needed for any given task
What do upper motor neurons control?
lower motor neurons in the brain stem and spinal cord mostly via interneurons
What do lower motor neurons innervate?
directly innervate muscles - skeletal, smooth, and cardiac
What is a spinal reflex?
A relatively simple, stereotyped motor response to sensory input of sufficient intensity
What is the myotatic reflex?
a reflex that induces stretching of the target muscle by tapping the associated tendon
What nerve does the quadriceps reflex test the function of?
the femoral
What cord segments does the quadriceps test?
L4-L6
What muscle does the quadriceps reflex test test?
the quadriceps femoris
What is the reflex pathway for the quadriceps reflex test?
muscle spindle to primary sensory neuron to motor neuron to skeletal muscle to golgi tendon organ
What type of neurons does the reflex circuit use?
sensory, interneuron, and motor
What are some spinal reflexes other than the myotatic reflex?
flexor (or withdrawal) reflex, crossed extensor reflex, perineal reflex
How must the animal be positioned for the flexor/withdrawal reflex?
lateral recumbency
How is the flexor or withdrawal reflex executed?
A stimulus to the foot triggers a flexion of the limb
How must the animal be positioned for the crossed exensor reflex?
the animal must be standing
How is the crossed extensor reflex executed?
Flex one limb, the opposite limb extends to support the increased weight on that limb
How does the perineal reflex work?
Contraction of the anal sphincter and tail flexion in response to tactile stimulation of the perineum
What nerves does the perineal reflex test test?
pudendal and caudal nerves
What cord segments does the perineal reflex test test?
S1-S3
What muscle does the perineal reflex test the function of?
anal sphincter and flexion tail muscles
What is motor neuron disease classified by?
any disease that directly affects the function of motor neurons (perikarya and/or axons)
