Motor System

Question 1

alpha motor neurons

Answer 1

large spinal cord neuron that enters through ventral root of spinal cord and terminates in muscles–> results in contraction of muscles

primary interaction between muscles and nervous system

Question 2

motor unit

Answer 2

a single motor neuron and all muscle fibers it innervates.

can add more muscle fibers/connections to increase the contraction of a muscle, but overall, contraction is all or none

Question 3

muscle spindle

Answer 3

embedded in muscles and are sensitive to stretching of muscle

will inhibit antagonist muscle to dampen oscillation

Question 4

antagonist pairs

Answer 4

two muscles that act arounf a single joint

e.g. tricep & bicep

Question 5

basal ganglia and cerebellum

Answer 5

play an important role in modulating action

receive inputs from cortical motor regions(like M1), and send signals back to cortical regions to modulate motor planning and execution

cerebellum also receives sensory input and sends some output to spinal cord for more direct movement control

Question 6

hierarchy of motor system

Answer 6

premotor/supplementary motor cortex –> primary motor cortex (M1) –> brainstem –> spinal cord

cerebellum and brainstem send signals to cortical areas

Question 7

central pattern generators

Answer 7

rhythmic behaviors that generate a pattern of action stored in the spinal cord (e.g. cat treadmills)

muscle spindles have transected connections to contralateral muscle –> causes it them to do the opposite. one stretches, the other contracts

reflexes are still intact, but voluntary movements are not

Question 8

spinal level control of muscles

Answer 8

stretch reflex provides mechanism for automatically adjusting muscle activity

muscle spindles in muscle directly activate alpha motor neurons in spinal cord to send a signal to contract muscle

Question 9

cortical motor regions

Answer 9

can specialize in motor execution, planning specific actions, monitoring the outcome of an action, translating sensory info into action, etc. depending on area

Question 10

which 3 main motor areas send descending neuronal projections to the spinal cord?

Answer 10

primary motor cortex (M1)
-low levels of stimulation will evoke simple muscle contraction

supplementary motor area (SMA)
premotor cortex
-lower density of descending fibers
-densely connected to M1
-involved in cognitive aspects of planning/initiation of complex actions

Question 11

motor homunculus

Answer 11

motor cortical regions organized according to movement of different body parts

larger representation for areas w greater dexterity and sensitivity

Question 12

M1 primary motor cortex

Answer 12

low levels of stimulation evoke simple muscle contraction

deep neuronal projections to spinal cord

code for movement direction

organized according to action pattern & movement planning

Question 13

population vector

Answer 13

the sum of activity of all the neurons pointing to the direction of actual movement (like a dipole moment but for neural firing of direction of movement)

indicates direction of movement up to 300ms prior to movement onset

suggests movement planning occurs in M1