Chapter 13: Spinal Control of Movement

Question 1

Muscles and neurons that control muscles

Answer 1

motor system

Question 2

role of motor system:

Answer 2

generation of coordinated movements

Question 3

Parts of motor control (2 types of motor programs)

Answer 3

1. spinal cord - control of coordinated muscle contraction
2. brain - modulates control of motor programs in spinal cord

Question 4

types of muscle

Answer 4

smooth, striated

Question 5

Each muscle has hundreds of (), the fused skeletal muscle cells (multiple nuclei). And each fiber is innervated by a single axon branch from the CNS

Answer 5

muscle fibers

Question 6

Inner movement of arms: (1) -> Promoted by (2) muscles

Answer 6

1. flexion
2. flexor

Question 7

outward movement of arms: (1) -> Promoted by (2) muscles

Answer 7

1. extension
2. extensor

Question 8

Groups of Somatic Musculature and Distribution of Lower Motor Neurons

Answer 8

Axial muscles: trunk movement/ maintaining posture

Proximal muscles: shoulder, elbow, pelvis, knee movement/locomotion

Distal muscles: hands, feet, digits (fingers and toes) movement/manipulation of objects

Question 9

(): neurons in the brain that supply input to the spinal cord;

Answer 9

Upper motor neurons

Question 10

Somatic muscles are majorly innervated by (1), whose somas are found in (2)

Answer 10

1. lower motor neurons
2. ventral horn of spinal cord

Question 11

Motor neurons innervating proximal and distal muscles are found mainly in the (1) segments of the spinal cord, whereas those innervating axial muscles are found (2).

Answer 11

1. cervical and lumbar-sacral
2. at all levels

Question 12

Motor neurons controlling flexors lie (dorsal/ventral) to extensors.

Answer 12

dorsal

Question 13

Motor neurons controlling axial muscles lie (lateral/medial) to those controlling distal muscles.

Answer 13

medial

Question 14

() motor neurons directly trigger the generation of force by muscle

Answer 14

Alpha

Question 15

(): motor neuron and all the muscle fibers it innervates

Answer 15

Motor unit

Question 16

(): all the alpha motor neurons that innervate a single muscle

Answer 16

Motor neuron pool

Question 17

The () is one important way the CNS grades muscle contraction

Answer 17

rate of firing of the motor unit

Question 18

Recruiting additional synergistic motor units -> muscles with a large number of small motor units can be ().

Answer 18

more finely controlled by the CNS

Question 19

Inputs to Alpha Motor Neurons (3)

Answer 19

1. sensory input from muscle spindles
2. upper motor neurons in brain
3. spinal interneurons

Question 20

Sensory input from muscle spindles: via (1); provide feedback about (2)

Answer 20

1. stretch receptors
2. muscle length

Question 21

Upper motor neurons in the brain: ()

Answer 21

initiation and control of voluntary movement and will

Question 22

Spinal interneurons can be ()

Answer 22

excitatory or inhibitory

Question 23

types of motor units

Answer 23

fast and slow motor units

Question 24

types of fast motor units (fibers)

Answer 24

fatigue-resistant (FR)
fatigable (FF)

Question 25

(): large number of mitochondria and enzymes for oxidative energy metabolism, slow to contract, can sustain contraction

Answer 25

Red muscle fibers (slow motor unit)

Question 26

(): fewer mitochondria, anaerobic metabolism (no need for O2), contract and fatigue rapidly-escape reflex

Answer 26

Fast motor units (White muscle fibers)

Question 27

(): white fibers with moderate strength and fast contractions

Answer 27

Fatigue-resistant (FR) fast fibers

Question 28

(): fastest, strongest white fibers, but rapidly fatiguing

Answer 28

Fast fatigable (FF) fibers

Question 29

rank strength of contraction of types of motor units

Answer 29

FF > FFR > S

Question 30

() are important for transporting AP towards SR to induce significant Ca2+ release

Answer 30

T-tubules

Question 31

(): division of myofibril into segments (sarcomeres) by disks

Answer 31

Z lines

Question 32

(): two Z lines and myofibril; basic unit of muscle fiber

Answer 32

Sarcomere

Question 33

(): series of bristles anchored to Z lines

Answer 33

Thin filaments

Question 34

(): between and among thin filaments

Answer 34

Thick filaments

Question 35

Muscle contraction occurs when the thin filaments slide along the thick filaments, bringing adjacent Z lines toward one another.

Answer 35

Sliding-Filament Model of Muscle Contraction

Question 36

() allows myosin heads (thick filaments) to bind to actin (thin filament)—myosin heads then pivot, causing filaments to slide.

Answer 36

Ca+ binding to troponin

Question 37

Sensory feedback from muscle spindles—()

Answer 37

stretch receptor (proprioceptors)

Question 38

stretch receptors are specialized for body sense () : how our body is positioned and moving in the space

Answer 38

proprioception

Question 39

() axons -> thickest myelinated axons in the boy -> conduct AP very rapidly

Answer 39

Group I

Question 40

Stretch reflex: muscle pulled results in () as a result

Answer 40

strong and rapid tendency to pull back

Question 41

feedback loop involved in stretch reflex:

Answer 41

Bet. G IA axons and alpha motor neurons

Question 42

Discharge rate of sensory axons of Group 1a: related to ()

Answer 42

muscle length

Question 43

Innervate intrafusal fibers inside muscle spindle (both ends) -> Like a “sensory organ” of muscle

Answer 43

Gamma Motor Neurons

Question 44

Keeps spindle “on air” – sensitive, able to activate Ia axons; Changes set point of the stretch feedback loop

Answer 44

Gamma loop

Question 45

() activation -> decrease Ia activity

Answer 45

Alpha

Question 46

() activation -> increase Ia activity

Answer 46

Gamma

Question 47

Alpha motor neurons can inhibit (1) and stimulate (2) based on sensory input from muscle spindle

Answer 47

1. further muscle stretching 2. contraction

Question 48

During (), muscle spindle is short and “loosened” -> Ia sensory axons cannot be activated -> no AP transmitted

Answer 48

off-air

Question 49

- Gamma motor neurons work on ends of muscle spindle to keep it ()

Answer 49

long and “tight”

Question 50

Additional proprioceptive input—acts like strain gauge— monitors muscle tension.

Answer 50

Golgi Tendon Organs

Question 51

Golgi Tendon Organs exist inside (1), among (2)

Answer 51

1. tendons 2. collagen fibers

Question 52

Golgi Tendon Organs are innervated by () -> deliver signals spinal cord if tendons are stretched

Answer 52

Ib axons

Question 53

Tendons are stretched when muscles are ()

Answer 53

contracted

Question 54

2 types of sensing in the muscle

Answer 54

Spindles in parallel with fibers— sense muscle length Golgi tendon organs in series with fibers – sense muscle tension

Question 55

function of golgi tendon organs is to: regulate () -> Important for the proper execution of fine motor acts

Answer 55

muscle tension within optimal range

Question 56

Golgi tendon organs sense tension in muscle -> fire AP via Ib axons -> stimulate () -> inhibits alpha motor neurons to suppress muscle contraction

Answer 56

inhibitory interneurons

Question 57

Most input to alpha motor neurons mediated by ()

Answer 57

spinal interneurons

Question 58

Variety of synaptic inputs to spinal interneurons; modulate overall activity of motor neurons

Answer 58

Primary sensory axons (e.g. muscle spindles, Golgi tendon organs, etc) Descending axons from brain Collaterals of lower motor neuron axons Other interneurons

Question 59

(): contraction of one muscle set accompanied by relaxation of antagonist muscle

Answer 59

Reciprocal inhibition