the sensorimotor system: sub-cortical structures (2.7)

Question 1

descending pathways (4)

Answer 1

dorsolateral: corticospinal, corticorubrospinal
ventromedial: corticospinal, cortico-brainstem-spinal

Question 2

corticospinal tract vs corticorubrospinal tract (dorsolateral)

Answer 2

corticospinal: M1 -> medullary pyramids -> decussation -> direct synapse in spinal cord; wrist, hands, fingers, toes
corticorubrospinal: red nucleus -> decussation before medulla; face, arms, legs

Question 3

corticospinal tract vs cortico-brainstem-spinal tract (ventromedial)

Answer 3

corticospinal: ipsilateral directly into spinal cord then branches and innervates interneuron circuits bilaterally in multiple spinal segments
cortico-brainstem-spinal: synapses on various brainstem structures and descends bilaterally, carrying information from both hemispheres

Question 4

dorsolateral vs ventromedial tracts (direct or indirect; synapse; red nucleus?; termination; close or far; function)

Answer 4

dorsolateral: one direct; synapses in brain stem; talks to red nucleus; terminates in one contralateral spinal cord segment, distal muscles; limb movements
ventromedial: one direct; synapses in brain stem; does not talk to red nucleus; proximal muscles; posture and whole body movements

Question 5

motor units

Answer 5

the smallest unit of motor activity; comprises a single motor neuron and all of the individual skeletal muscle fibers it innervates (smaller number of fibers = finer control)

Question 6

acetylcholine

Answer 6

released by motor neurons at neuromuscular junction; activates motor-end-plate on each muscle fiber; causes contraction

Question 7

slow vs fast fibers (motor units)

Answer 7

slow: sustained contraction; near blood; “marathon muscles”; red muscle; ongoing activity
fast: fatigue quickly; far from blood supply; store oxygen and glucose; instantaneous but short-lived power; sprinter muscles

Question 8

flexors vs extensors

Answer 8

flexors: bend or flex a joint
extensors: straighten or extend a joint

Question 9

synergistic vs antagonistic muscles

Answer 9

synergistic: contraction produces same movement (pull in same direction)
antagonistic: two muscles that act in opposition (pull in opposite directions)

Question 10

extrafusal fibers

Answer 10

slow; cause muscle contraction; job is to contract

Question 11

intrafusal fibers

Answer 11

slow; found within muscle spindles; job is to watch (i.e. maintain posture)

Question 12

proprioceptors (2)

Answer 12

muscle spindles: sensitive to changes in muscle length
Golgi tendon: sensitive to changes in muscle tension

Question 13

reflex

Answer 13

an involuntary and nearly instantaneous movement in response to an external stimuli (make muscle go back to normal length)

Question 14

patellar tendon vs withdrawal reflex

Answer 14

patellar tendon: monosynaptic; stretch reflex
withdrawal: polysynaptic; reciprocal innervation (C fiber pain)

Question 15

walking

Answer 15

reflex; an ‘inverted pendulum’ gait in which the body vaults over the stiff limb or limbs with each step

Question 16

motor equivalence

Answer 16

a given movement can be accomplished various ways, using different muscles

Question 17

response chunking

Answer 17

practice combines the central sensorimotor programs that control individual responses into programs that control sequences (chunks) of behavior

Question 18

shifting control to lower levels

Answer 18

can free up higher levels of the system