the motor system (1)

Question 1

what are the two types of muscle?

Answer 1

1. skeletal/striate - moves bones, limbs and axis of the body.
2. smooth - regulates body function

Question 2

how are muscles organised?

Answer 2

1. muscle is attached to the bone by the tendon
2. muscle is made up of cells - large cells are called muscle fibres.
3. muscle fibres contain myofibrils which contain the active component to move.

Question 3

what are the 2 types of myofibril?

Answer 3

• actin

- myosin

Question 4

what does the sarcomere do?

Answer 4

is within the myofibril.
borders are defined by zbands.
contains actin and myosin
sarcomere is where muscle contractions occur

Question 5

what substance is released when an action potential occurs in the muscle fibre?

Answer 5

calcium

Question 6

what happens when calcium is released into the sarcomere?

Answer 6

myosin moves over the actin. the myosin heads touch the actin which pulls the actin towards the centre. this pulls the z-bands closer, making the sarcomere smaller.

Question 7

where is calcium stored?

Answer 7

the sarcoplasmic reticulum

Question 8

you only see muscle contraction when..

Answer 8

there has been an action potential

Question 9

which is the only type of neuron to innervate muscle cell?

Answer 9

alpha motor neuron

Question 10

where is the cell body of the alpha motor neuron found?

Answer 10

in the ventral horn of the spinal cord.

- butterfly shape made of grey matter in the center.

Question 11

what happens at the neuromuscular junction?

Answer 11

the alpha motor neuron synapses with the muscle fibre.

- there is a specialised junction here called the end-plate

Question 12

what does the end-plate in the neuromuscular junction contain?

Answer 12

acetylcholine receptors

Question 13

what is a motor unit?

Answer 13

the complex of one alpha motor neuron and the muscle fibres it innervates

Question 14

what is good about small motor units?

Answer 14

gives very fine control as only a small group of muscles are moving.

Question 15

where does the action potential in the alpha motor neuron begin?

Answer 15

the axon hillock in the ventral horn of the spinal cord.

Question 16

how do action potentials occur in alpha motor neurons?

Answer 16

1. starts at axon hillock in ventral horn and is propagated down the axon.
2. at the axon terminal, the influx of calcium causes acetylcholine to be released.
3. acetylcholine binds with cholinergic receptors at the end-plate.
4. the binding of this causes sodium channels to open which depolarises the membrane of the muscle. (end-plate potential)
5. the end plate potential develops into an action potential in the muscle fibre.

Question 17

what are the 4 ways in which we control the strength of contraction through spinal control?

Answer 17

1. the AMN gets feedback about muscle activity
2. skin sensory
3. receives input from antagonist muscle
4. the renshaw cell

Question 18

how does the alpha motor neuron get feedback from the muscle about activity?

Answer 18

• muscle spindle

- golgi tendon organ

Question 19

what does the muscle spindle do?

Answer 19

• gives us information about stretch

- also called the intrafusal muscle fiber

Question 20

what does the intrafusal muscle fiber do (muscle spinal)

Answer 20

• sends info about stretch via 1a nerve - dorsal root

-

Question 21

the muscle spindle only increases its activity when..

Answer 21

stretched

Question 22

what is the spindle reflex?

Answer 22

has to coordinate the agonist and antagonist muscles (excitation of one and inhibition of the other)
- is MONOSYNAPTIC

Question 23

what does the golgi tendon organ do?

Answer 23

gives info about tension in the tendon

Question 24

what is the renshaw cell?

Answer 24

a collateral to the AMN.

- makes sure that the muscle doesnt become over active.