Lecture 8

Question 1

Muscle?

Answer 1

Tissue with the ability to contract and relax

Question 2

Tendon?

Answer 2

Tough band of fibrous connective tissue that connects muscle to bone

Question 3

Ligament?

Answer 3

Attaches bone to bone

Question 4

How many skeletal muscles are there in the human body?

Answer 4

Approximately 650

Question 5

How many surface (anatomical) muscles are there in the human body?

Answer 5

Over 150

Question 6

Are muscles attached to 2 different bones of the skeleton?

Answer 6

Yes, one attachment is fixed and called the origin and the other called the insertion is drawn towards the origin

Question 7

Muscles tend to work in groups or sets, so how are they arranged in antagonistic pairs?

Answer 7

• Flexor closes a joint

- Extensor opens a joint

Question 8

Epimysium?

Answer 8

A loose connective tissue sheath that is bound to each muscle

Question 9

Muscle composition?

Answer 9

• Each muscle is composed of bundles of fascicles
• Each fascicle is composed of many muscle fibers
• Each fiber is composed of smaller fibers called myofibers
• The myofibers contain the contractile apparatus – the sarcomere

Question 10

What are three muscle types?

Answer 10

Skeletal muscle:
- Attached to bones

Cardiac muscle:
- Walls of the myocardium

Smooth muscle:
- Organs

Question 11

Striated Muscle?

Answer 11

• Voluntary muscle i.e. under direct nervous control

- Low endurance muscle

Question 12

What is the structure of the muscle fibres in striated muscles?

Answer 12

• Hexagonal
• Nuclei on outside (peripheral)
• Fibres generally have the same size
• Polynucleated

Question 13

How are muscle biopsies done?

Answer 13

Wide-bore Needle inserted into muscle, and a small ‘tube’ of muscle removed

Question 14

Cardiac muscle?

Answer 14

• Only in the heart
• A type of striated muscle but related to smooth muscle
• Involuntary muscle
• High endurance muscle

Question 15

What is the structure of the muscle fibres in cardiac muscles?

Answer 15

• Intercalated discs (gap junctions)
• 1- 2 nuclei per cell
• Centrally placed nuclei
• Innervated by the pace maker

Question 16

Smooth Muscle?

Answer 16

• Lines the digestive tract, bronchus and blood vessels
• Involuntary muscle i.e. not under direct nervous control
• High endurance muscle

Question 17

What is the structure of the muscle fibres in smooth muscles?

Answer 17

• 1 centrally placed nucleus per cell
• No striations
• Sustained contraction

Question 18

What is a motor unit?

Answer 18

The functional unit of skeletal muscle is the motor unit (MU)

Question 19

What is a motor unit composed of?

Answer 19

• A single motor neuron

- The group of muscle fibres innervated by it

Question 20

Why must some motor neurons innervate more than one fibre?

Answer 20

Bc there are considerably more muscle fibres than there are motor neurons

Question 21

What does the number of muscle fibres per motor unit vary according to?

Answer 21

• The fineness of the control required

- Fewer muscle fibres per motor unit leads to increased dexterity and vice versa

Question 22

Neuromuscular Junction (NMJ)?

Answer 22

• Also known as the motor endplate
• The connection between the muscle fibre and its motor neuron
• The membranes of the nerve and muscle cells come into close contact
• One NMJ per fibre

Question 23

What happens when muscle fibre is stimulated at the NMJ?

Answer 23

It contracts; this is an “all-or-nothing” response

Question 24

When is there maximal contraction?

Answer 24

When all MUs are firing tog

Question 25

What are the two ways that muscles contract?

Answer 25

1. Isometric contraction ‘same length’ 2. Isotonic contraction ‘same tension’

Question 26

Isometric contraction?

Answer 26

- The length of the muscle does not change - The tension on the muscle increases - Muscle contracts but doesn't shorten

Question 27

Isotonic Contraction?

Answer 27

- The muscle length changes | - The tension remains constant

Question 28

Two types of Isotonic contraction?

Answer 28

Concentric – Muscle shortens | Eccentric – Muscle lengthens

Question 29

Concentric Isotonic Contraction?

Answer 29

- Force generated by the muscle is greater than the load to be lifted - Muscle shortens in length

Question 30

Eccentric Isotonic Contraction?

Answer 30

- Force generated by the muscle is less than the load applied to it - Muscle lengthens as it contracts

Question 31

When/why do Eccentric Isotonic Contractions happen?

Answer 31

- Also occur to slow joint movement - Muscles undergoing heavy eccentric loading suffer greater damage when overloaded leading to greater muscle necrosis - Principle behind body building - Muscles are approximately 10% stronger during eccentric contractions than during concentric contractions

Question 32

Three phases to muscle contraction?

Answer 32

- Latent period (0.005 sec) between the stimulus and first visible reaction - Contraction period (0.04 sec) when the muscle shortens - Relaxation period (0.05 sec) the muscle returns to its original length - After initial stimulation there is a short period during which muscle will not respond to further stimulus called the Refractory period (0.002 sec)

Question 33

How does summation happen (general)?

Answer 33

- Muscle can respond to a second stimulation while still contracting - Stimulation at frequency shorter than the twitch time results in the second stimulus being superimposed on the first - This results in a greater shortening of the muscle (summation)

Question 34

What are two different ways in which summation can occur?

Answer 34

1. By increasing the number of motor units involved - called multiple motor unit summation (recruitment) 2. By increasing the rate of contraction of individual motor units - called wave summation - In practice both these occur together during contraction helped by the asynchronous firing of the motor units

Question 35

Tetanization?

Answer 35

- As the impulse frequency increases the twitches become superimposed upon one another in wave summation (10 pulses/sec) - Eventually increasing stimulus causes the successive contractions to fuse together in a state of maximal contraction called tetanus (>40 pulses/sec) - Upon tetanization further increased stimulation will only result in very slight shortening

Question 36

Is the action equal at both the insertion and the origin?

Answer 36

Yes

Question 37

What is one thing that muscles don't do?

Answer 37

Push, they can only contract

Question 38

What does the muscle or its nerve respond with when it is stimulated by a single electric shock?

Answer 38

A quick twitch