Lecture three - Introduction to Motor Control

Question 1

Need to know the terms:
Dorsal
Ventral
Rostral
Caudal
Anterior
Posterior

Question 2

What is one argument for why we have a nervous system?

Answer 2

To facilitate movement through our environment.
The tadpol larva to sea squirt adult is one example of when something no longer needs to move through their environment their nervous system is no longer needed.

Question 3

What is Locked in Syndrome?

Answer 3

Occurs when there is damage to the pons area of the brain stem which leads to complete paralysis, including lung function. Cognitive function remains intact. Normal wake and sleep function.
Some people can move their eyes, which can allow them to communicate.

Question 4

What is Blindsight?

Answer 4

When there has been damage to the primary visual rendering people unable to consciously see, but they are able to tell when objects move or where they are in space, or even colour (Type I) or ‘feel’ when objects have moved (type II).

Question 5

What are the three types of muscle in the body?

Answer 5

1. Smooth muscle, such as digestive system, arteries, and reproductive organs.
2. Striated muscle, such as skeletal muscle.
3. Cardiac muscle, which the heart is made of.

Question 6

How many skeletal muscles are there in the body?

Answer 6

640.

Question 7

What is a muscle called if it moves a limb toward the body when it contracts?

Answer 7

Flexsor (agonist), e.g. bicep.

Question 8

What is a muscle called if it moves a limb away from the body when it contracts?

Answer 8

Extensor (antagonist).

Question 9

What are the two types of muscle contraction?

Answer 9

1. Isometric
2. Isotonic

Question 10

What is difference in length and tone of muscle between when performing an isometric or isotonic contraction?

Answer 10

An isometric contraction occurs when the the length of the muscle stays the same but the tone changes. An example would be holding a heavy box (biceps).

An isotonic contraction occurs when the tone of a muscle stays the same despite the length of the muscle changing. This happens when you pick something up or put something down (biceps).

Question 11

What are the two types of isotonic contractions?

Answer 11

Eccentric - when the tone of the muscle stays the same but the muscle is lengthening. e.g. bicep when putting something down.

Concentric - when the tone of the muscle stays the same, but the muscle is shortening. e.g bicep when picking something up.

Question 12

How do muscles receive messages from the brain?

Answer 12

Alpha motor neurons.

Question 13

How many alpha motor neurons innervate a single motor fibre?

Answer 13

Only one.

Question 14

Where are alpha motor neurons located?

Answer 14

In the spinal cord.

Question 15

A single alpha motor neuron can innervate many muscle fibres through its branches and terminals. What is the alpha motor neuron and the muscle fibres it innervates called?

Answer 15

A motor unit.

Question 16

Would alpha motor neurrons that innervate muscles responsible for fine motor movement have connections more muscle fibres than if it were innervating a muscle responsible for gross moto movements?

Answer 16

No. Fine motor movement requires less muscle fibres therefore the alpha motor neuron innervating the fibres would be connected to fewer muscle fibres.

Question 17

What are muscle fibres?

Answer 17

Muscle fibres are single muscle cells.

Question 18

what is the structure of a muscle fibre/cell?

Answer 18

Muscle fibres have myofibrils, which run the length of the fibre and are made of thick and thin filaments. Myofibtrils are the contracting part of the cell. They are what give muscle fibres a striated appearance.

The myofibrils are coated in the sarcoplasmic reticulum. This serves the same function as the endoplasmic reticulum in other cells - transports and sorts proteins - also stores calcium.

T-tubules, which are extensions of the membrane that pentrate/invaginate into the muscle fibre. They are surrounded by sarcoplasmic reticulum.

Question 19

What is the role of t-tubules in muscle fibres?

Answer 19

T-tubules carry the action potential from the neuromascular junction into the cell and the myofibrils.

Question 20

Where is the nucleus of a muscle fibre/muscle cell located?

Answer 20

It is embedded in the membrane of the cell.

Question 21

What is the membrane of a muscle cell called?

Answer 21

Sarcolemma.

Question 22

What is Sliding Filament Theory?

Question 23

Briefly describe how a muscle contraction occurs once an action potential is generated at the muscle membrane.

Answer 23

Once action potential reaches the neuromascular synapse, after travelling down the axon of an alpha motor neuron, achetylcholine is released into the synapse, which binds to ion-gated channels on the muscle cell/muscle fibre, which causes the influx of sodium. This influx causes an electrical impulse which travels across the muscle membrane, down the hollow t-tubules. The electrical impulse causes the release of calcium from the sarcoplasmic reticulum. Calcium shifts proteins that prevent actin and myocin from touching. Myocin binds to actin and then unbinds and binsd again, this “ratched” action causes sliding of actin and myosin closer together, i.e. the shortening of a sarcomere, which is the unit of actin and myosin, repeating functional units of which make up myofibrils.

Question 24

What is a contraction caused by a single action potential at the level of the muscle fibre?

Answer 24

A twitch.

Question 25

What is a twitch?

Answer 25

A twitch is the shortening of a single muscle cell/fibre that is caused by an action potential from an alpha motor neuron.

Question 26

When a muscle contracts, are all fibres twitching?

Answer 26

No. The number of fibres twitching depends on the force and duration of the muscle contraction.

Question 27

What are extrafusal muscle fibres?

Answer 27

They are muscle fibres that are innervated by alpha motor neurons.

Question 28

What are intrafusal muscle fibres?

Answer 28

Intrafusal muscle fibres are surrounded by extrafusal muscle fibres. Multiple intrafusal muscle fibres surrounded by a sheath make up a muscle spindle.
Muscle spindles sense the lengthening of extrafusal muscle fibres regulate contraction of the muscle to ensure it does not get damage. i.e. if the muscle is lengthening then the muscle spindles will send messages to the alpha motor neurons to get the extrafusal fibres to twitch to protect the muscle from lengthening too much.

Question 29

What is the difference between efferent and afferent neural messages?

Answer 29

Effluent neural signals are from the brain to the periphery.
Affluent neural signals from from the periphery to the brain.

Question 30

What is a REFLEX ARC when it comes to intrafusal and extrafusal muscles?

Answer 30

A reflex arc is what happens when the intrafusal muscle fibres sense that the muscle is stretching and so it sends excitatory messages via the afferent sensory axons it is innervated by directly to the aplha-motor neuron that innervates the extrafusal muscle fibres of that particular muscle causing them to twitch/causing the muscle to contract to protect it from tearing.

Question 31

What are the neurons called that innervate intrafusal muscle fibres?

Answer 31

1a afferent neurons.

Question 32

Briefly describe the role of the muscle spindle in the patellar reflex.

Answer 32

The muscle spindle, consisting of intrafusal muscle fibres, senses the lengthening of the quadriceps due to the lengthening of the patellar tendon. This causes signals to be sent to alpha motor neurons in the spinal cord to insight contraction of the quadricep and inhibition of hamstring contraction, in turn preventing over-extension of the quadricep.

Question 33

Blue ringed octopuses and puffer fish contain tetrodotoxin. How does this toxin cause paralysis?

Answer 33

Tetrodotoxin prevents sodium from entering the muscle membrane and allowing the transmission of the action potential. This means that the muscle cannot contract, leading to paralysis.

Question 34

What nociceptor fibres induce the sharp, quick pain we feel when we get say a slap to the face?

What nociceptor fibres produce a dull, aching pain, such as from a bruised arm?

Answer 34

A-delta fibres.

C-fibres.

Question 35

Are A-delta and C-fibres myelinated.

Answer 35

A-delta fibres are myelianted. They need to send their signals quickly. Myelination aids in faster signal transduction.

C-fibres are unmyelinated.