Nervous System - Spinal Reflexes and Control of Movement

Question 1

skeletal muscle structure

Answer 1

1. skeletal muscles
2. skeletal muscle fibers
3. muscle fascicle

Question 2

skeletal muscles

Answer 2

• muscles connected to the skeleton

- muscle fibers contain myofibrils, organized in sarcomeres

Question 3

myofibrils

Answer 3

• bundles of contractile proteins called myosin and actin

Question 4

skeletal muscle fibers

Answer 4

elongated cylindrical multinucleate cells

- connective tissues surround muscle fibres and nerves that innervate them

Question 5

muscle fascicle

Answer 5

bundle of skeletal muscle fibers

Question 6

spinal nerve

Answer 6

• connected to the spinal cord by a dorsal root

- mixed nerve (carries both sensory and motor info)

Question 7

fibers in a dorsal root

Answer 7

sensory

Question 8

fibers in a ventral root

Answer 8

motor

Question 9

types of muscle fibers

Answer 9

1. extrafusal fibers

2. intramural fibers

Question 10

extrafusal muscle fibers

Answer 10

• majority of skeletal muscle fibers
• generate force to move or rigidly fix body parts
• innervated by efferent motor fibers (alpha motor neurons)

Question 11

intrafusal muscle fibers

Answer 11

• specialized fibers (muscle spindle)
• inform CNS about muscle length and its rate of change
• innervated by both sensory and motor nerves
  - afferent sensory fibers Ia, II
  
  • efferent motor fibers: gamme motor neuron

Question 12

muscle spindle

Answer 12

• spindle-shaped organ
• composed of intrafusal muscle fibers
• intramural muscle fibers are arranged in // with extrafusal muscle fibers
• detect muscle stretch

Question 13

types of intrufsal muscles fibers

Answer 13

1. nuclear bag fibers

2. nuclear chain fibers

Question 14

co-activation of the gamma and alpha motor neurons

Answer 14

co-activation of the gamma efferents occur to maintain muscle spindle sensitive to changes in muscle length, even as the muscle contracts and shortens

Question 15

events occurring when a muscle is stretched

Answer 15

1. muscle stretched
2. extrafusal muscle fibers lengthened
3. intrafusal muscle fibers lengthened
4. sensory afferent fibrs (Ia/II) are activated
5. alpha motoneurons are activates (innervate extrafusal fibres)
6. muscle contracts
7. gamma motoneurons are co-activated (innervate intrafusal fibers)

Question 16

purpose of muscle spindle reflexes

Answer 16

operate to return muscle to its resting length after has been shortened or lengthened

Question 17

principles of the skeletal muscle (5)

Answer 17

1. motor unit
2. motoneuron pool
3. size principle
4. population code
5. frequency code

Question 18

neuromuscular junction

Answer 18

a chemical synapse formed by the contact between a motor neuron and a muscle fiber

Question 19

junction: pre-synaptic cell, type of synapse, neurotransmitter, class of receptors, type of receptor, post-synaptic cell

Answer 19

1. alpha motor neuron
2. chemical
3. acetylcholine
4. ionotropic
5. nicotinic
6. muscle fiber

Question 20

motor end plate = neuromuscular junction

Answer 20

• motor neurons typically branch to innervate multiple muscle fibers
• each branch ends in a neuromuscular junction or motor end plate
• motor end plate consists of a number of terminal enlargements of the nerve (terminal buttons)

Question 21

terminal buttons

Answer 21

• terminal enlargements of nerve

- make up motor end plate

Question 22

motor unit

Answer 22

• single motoneuron and the muscle fibers it innervates

- alpha motor neuron (lower motor neuron) and the set of muscle fibers it innervates

Question 23

producing more force

Answer 23

1. activation of more motor neurons
2. activation of more muscle fibers
3. produces more force

Question 24

motor neuron pool

Answer 24

• set of alpha motor neurons innervating fibers within the same muscle

Question 25

where are lower motor neurons located?

Answer 25

ventral horn of the spinal cord

Question 26

where are upper motor neurons located?

Answer 26

cortex of the brain

Question 27

gradation of muscle force | 3 points

Answer 27

muscle force can vary from delicate control to maximum activation 1. size principle 2. population code 3. frequency code

Question 28

size principle

Answer 28

- successive engagement of larger populations of motor units occurs according to their size - smaller motor units (with smaller motoneurons) recruited first - large motor units are recruited last

Question 29

population code

Answer 29

- successively larger fractions of the motor units are engaged - encodes the strength of the muscle force

Question 30

frequency code

Answer 30

- motor units activated with higher frequencies | - increases the muscle force but also increases its duration

Question 31

somite

Answer 31

body segment

Question 32

dermatome

Answer 32

- skin part supplied by a single spinal nerve | - enabling the clinician to determine the level of a lesion of the spinal cord or nerve roots

Question 33

myotome

Answer 33

- muscle part of a body segment | - controlled by areas of the motor cortex adjacent to the sensory cortex

Question 34

spinal reflex

Answer 34

- stereotyped muscular response to a specific sensory stimulus - "hard wired" - reflection of the stimulus onto the musculature - may be suppressed or enhanced, but not eliminated - no conscious deliberation

Question 35

reflex arc

Answer 35

type of conduction pathway that allows impulses to travel in only one direction

Question 36

reflex arc components (5)

Answer 36

1. receptor 2. sensory (afferent) neuron 3. integration center 4. motor (efferent) neuron 5. effector

Question 37

spinal reflexes (4)

Answer 37

1. myotatic 2. inverse myotatic 3. withdrawal 4. crossed-extensor

Question 38

myotatic reflex

Answer 38

- muscle stretch reflex (knee-jerk reflex = patellar reflex) - monosynaptic - causes muscle contraction in response to muscle stretch - involves muscle spindles which detect stretch)

Question 39

inverse myotatic reflex

Answer 39

- golgi tendon reflex (clasp-knife reflex) - disynaptic - causes muscle relaxation in response to muscle contraction - prevents damage to muscles due to excessive force production

Question 40

withdrawal reflex

Answer 40

- flexor-withdrawal reflex - polysynaptic - occurs in response to painful or noxious stimulus - causes movement of limbs towards the body (activates flexors, inhibits extensor) (pain afferent fibers)

Question 41

crossed-extensor reflex

Answer 41

- activate to maintain balance in response to pain - polysynaptic - limb on opposite side of stimulus extended (flexion on ipsilateral side, extension on contralateral side) (pain afferent fibers)

Question 42

motor control

Answer 42

- posture and movement depend on a combination of: - voluntary actions controlled by higher brain centers - involuntary reflexes coordinated by the spinal cord (spinal cord reflexes + central pattern generators)

Question 43

all reflexes and voluntary control of muscles act through their effect on what type of motorneurons

Answer 43

lower motoneurons

Question 44

major descending motor pathways

Answer 44

- higher control of muscles originates in the cerebrum and is coordinated with inputs and from other parts of the brain - descending tracts contain axons that make contact with the lower motor neurons and help control them

Question 45

how descending tracts are named

Answer 45

- first from their point of origin and secondly from their termination ex. rubrospinal tract, ventral corticospinal tract