Spinal Movement

Question 1

How are motor systems organized?

Answer 1

Hierarchically

Question 2

What are coordinated movements produced by?

Answer 2

Spatial and temporal patterns on muscle contractions ordered by the brain and spine

Question 3

What are the two parts of motor control?

Answer 3

1) Spinal cord -> contains motor programs
2) Brain -> controls spinal motor programs

Question 4

What are spinal nerves?

Answer 4

Mix of sensory and motor

Question 5

What are the two types of muscles?

Answer 5

Smooth (inner gated by ANS fibers) and Striated

Question 6

Do muscles pull or push on a joint?

Answer 6

Pull

Question 7

What direction to flexors and extensors pull on a joint?

Answer 7

Opposite directions in order to antagonize each other

Question 8

What are the 3 groups of muscles that act on joints?

Answer 8

Axial, proximal, distal

Question 9

What do axial muscles control?

Answer 9

Trunk movement, posture

Question 10

What do proximal muscles control?

Answer 10

Shoulder, elbow, pelvis, knee

Question 11

What do distal muscles control?

Answer 11

Hands, feet, and digit movements

Question 12

What are somatic muscles innervated by?

Answer 12

Somatic motor neurons (pretty tricky huh?)

Question 13

Where are somatic motor neurons found?

Answer 13

Ventral horn of the spinal cord (lower motor neurons)

Question 14

What do lower motor neurons do?

Answer 14

Directly command muscle contraction

Question 15

Where are somas of upper motor neurons?

Answer 15

The brain

Question 16

What do upper motor neurons provide?

Answer 16

Input to lower motor neurons

Question 17

What does damage to UMNs cause?

Answer 17

Spasticity/Hypertonia

Question 18

What does damage to LMNs cause?

Answer 18

Paralysis

Question 19

What is meant by “limb enlargements”?

Answer 19

The spinal cord sections of muscles in the ventral horn are not even and are bigger the more skeletal muscle there is somewhere (ex. Lumbar section of spine has much larger ventral horns for the legs)

Question 20

Where do motor neurons controlling flexors lie relative to extensors?

Answer 20

Dorsal

Question 21

Where do motor neurons that control axial muscles lie relative to distal muscles?

Answer 21

Medial

Question 22

What are two categories of LMNs?

Answer 22

Alpha and gamma

Question 23

What do alpha neurons innervate?

Answer 23

Extrafusal muscle fibers

Question 24

What do gamma LMNs innervate?

Answer 24

Intramural muscle fibers

Question 25

What do alpha motor neurons do?

Answer 25

- branch and innervate many fibers over a wide area - triggering generation of force by muscles

Question 26

What is a motor unit?

Answer 26

An alpha neuron and all the muscles fibers it innervates

Question 27

What is a motor neuron pool?

Answer 27

All alpha motor neurons that innervate a single muscle

Question 28

What are the 2 types of muscle fibers?

Answer 28

Red and white

Question 29

What are red muscle fibers?

Answer 29

Slow twitch, fatigue resistant, shit ton of mitochondria, myoglobin, and capillaries

Question 30

What are white muscle fibers?

Answer 30

Sparse in mitochondria, anaerobic metabolism, contrast and fatigue fast, FAST TWITCH

Question 31

What are the 3 types of motor units?

Answer 31

Slow, fast fatigue resistant, fast fatigable

Question 32

What are slow motor units?

Answer 32

Small, innervated by small alpha motor neurons, resistant to fatigue, red muscle, important for sustained muscle contraction

Question 33

What are fast fatigue resistant motor unites?

Answer 33

Intermediate size, innervated by intermediate sized alpha neurons, generate TWICE the force of slow motor units

Question 34

What are fast fatiguable motor units?

Answer 34

Large motor units, innervated by LARGE alpha motor neurons, pale muscles, brief bursts

Question 35

What are the two ways to control force of muscle contraction in a fine way?

Answer 35

Varying firing rate of AMNs and the size principle

Question 36

How does varying the firing rates of AMNs work?

Answer 36

- a single AMN AP causes a muscle twitch - sustained contraction requires CONTINUED stimulation - # of and freq of APs increases

Question 37

How does increasing the # of active MUs change the force produced by a muscle?

Answer 37

INCREASES it

Question 38

What happens when you switch the alpha motor neuron controlling a muscle?

Answer 38

The muscle changes phenotype (ex. Making a fast motor neuron a slow one will make the muscle it innervates slow)

Question 39

What are the 3 major sources of input of AMNs?

Answer 39

DRG neurons (innervate muscle spindle), upper motor neurons (in brain stem and motor cortex), and interneurons (Biggest input, can excite or inhibit)

Question 40

What are muscle spindles?

Answer 40

8-10 intrafusal fibers arranged parallel to extrafusal fibers inside belly of muscle

Question 41

What type of sensory axons wrap around the muscle fibers?

Answer 41

1a

Question 42

What are muscle spindles specialized in?

Answer 42

Detecting changes in muscle length

Question 43

What do muscle spindles contain that make them sensitive to stretch?

Answer 43

Mechanosensitive ion channels

Question 44

What is the stretch reflex used to test?

Answer 44

If nerves and muscles are in tact

Question 45

Describe the stretch reflex dumb

Answer 45

In dumb terms: - ur holding a cup thats getting heavier from pouring - your muscles send info from the spindle to the spine which it then messages back saying to inhibit your tricep (your extensor) and excite your bicep (your flexor)

Question 46

Describe the stretch reflex smart

Answer 46

- monosynaptic reflex arc - stretching a muscle spindle increases 1a activity - the 1a detects a stretch and sends info to alpha motor neuron to contract that muscle

Question 47

What are gamma motor neurons?

Answer 47

LMNs that innervate INSIDE muscle spindles

Question 48

What are intrafusal fibers?

Answer 48

Skeletal muscle within the fibrous capsule (the purple thing of the muscle spindle)

Question 49

What is the gamma motor neurons main job?

Answer 49

Keep the muscle spindle taut (not loose)

Question 50

What is a gamma motor neuron activated?

Answer 50

When the spindle is limp after the muscle contracts

Question 51

What are golgi tendon organs?

Answer 51

Strain gauges meant to protect muscles from overload and help fine motor acts

Question 52

Where are golgi tendon organs found?

Answer 52

Between muscles and the tendon

Question 53

What innervates golgi tendon organs?

Answer 53

1b sensory axons

Question 54

How are 1b sensory axons activated in golgi tendon organs?

Answer 54

Inside the golgi tendon organs are collagen fibrils which get more tense with muscle contraction, these fibrils squeeze 1b sensory axons and cause their mechanosensitive channels to open

Question 55

What is a golgi tendon organs NORMAL function?

Answer 55

Regulate muscle tension within an optimal range to not overload a muscle

Question 56

What do the 1b sensory axons branch to into the spine?

Answer 56

Inhibitory interneurons in the ventral horn which inhibit the muscle the 1b sensory axons were tensed by

Question 57

What are the main differences between muscle spindles and golgi tendon organs?

Answer 57

Muscle spindles - parallel to muscle fibers - 1a axons - detect muscle LENGTH Golgi - in series of muscle fibers - 1b axons - detect muscle TENSION

Question 58

During passive stretch (think cup) which one is more important?

Answer 58

Spindles

Question 59

During active contraction, which one is more important?

Answer 59

Golgi

Question 60

What basic reflexes do inhibitory interneurons do?

Answer 60

Contracting one muscle group and relaxing another

Question 61

What do excitatory interneurons mediate?

Answer 61

The flexor withdrawal reflex

Question 62

What is the flexor withdrawal reflex?

Answer 62

Withdraws a limb, slower than stretch, Adelta nociceptive axons enter spinal chord and active interneuron which excited AMNs to withdraw the limb

Question 63

Where is the program for walking located?

Answer 63

Spine