Lecture 7: Spinal Cord, Control of Motor Function Flashcards
What do Renshaw cells do?
Receive collateral branches from alpha motor neurons and results in lateral inhibition
What neurons are capable of spontaneous activity and are 30x as numerous as anterior motor neurons?
Interneurons
What apparatus detects changes in muscle length via stimulation of sensory fibers in region of intrafusal fibers?
Muscle spindle
Stimulation of sensory fibers from central region of intrafusal fibers results from?
Lengthening of muscle and contraction at ends of intrafusal fibers
T/F: Dynamic stretch reflex opposes sudden changes to muscle length.
True
T/F: Static reflex causes muscle contraction to remain constant.
True
Gamma-_____ motor neurons excite nuclear bag intrafusal fibers and Gamma-_____ motor neurons excite nuclear chain intrafusal fibers.
Gamma-dynamic
Gamma-static
What is the function of the posterior motor cortex?
Make sure the motor cortex signal is what the body actually wants to happen
Input signals enter the motor cortex in layers…?
2-4
TQ: Upper motor neurons are entirely within the _____.
CNS
Lower motor neurons are made up of _____.
Alpha motor neurons
75-85% of upper motor neurons decussate in _____, the rest decussate near _____.
Pyramidal system
Synapse
The lateral corticospinal tract is made up of fibers that have crossed in the _____ and supply _____ levels of spinal cord.
Medulla
All
The anterior corticospinal tract is made up of fibers that cross near the _____ and supply _____.
Synapse
Neck and Upper limbs
TQ: Which neurons pass through an internal capsule?
Upper motor neurons
Tertiary sensory neurons?
TQ: What is the pathway of the corticospinal tract?
Site of origin–>internal capsule–>medullary pyramids–>x in lower medulla–>lateral columns of spinal cord
Which cells send collaterals back to the cortex?
Giant pyramidal cells (Betz)
What are 2 major functions of the coritcospinal tract?
1) add speed and agility to conscious movements (especially of hand)
2) provide a high degree of motor control (movement of fingers)
TQ: What do corticospinal tract lesions cause?
Reduced muscle tone
Clumsiness
Weakness
Not complete paralysis
What does the corticobulbar tract innervate?
The head
Where does the rubrospinal tract decussate?
Lower brain stem
What 3 tracts make up the extrapyramidal system?
Rubrospinal
Vestibulospinal
Reticulospinal
What do lesions of the rubrospinal tract cause?
Impaired distal arm & hand movement & intention tremors
What is the vestibulospinal tract mainly involved with and what does it synapse with?
Maintenance of upright posture, LMNs
