Module 3

Question 1

List the functions of muscle.

Answer 1

• movement of the body.
• maintenance of posture.
• respiration.
• production of body heat.
• communication.
• constriction of organs and vessels.
• contraction of the heart.

Question 2

Describe the function properties of muscle.

Answer 2

• contractility.
• excitability.
• extensibility.
• elasticity.

Question 3

What are the types of muscle tissue in the body, where are they used and what tasks do they carry out?

Answer 3

1) Skeletal muscle (voluntary)
- Makes up 40% of the body weight
- Responsible for locomotion, respiration, posture, mastication, facia; expressions
- Generally attached to the bone (facial expression- muscles attached to underlying connective tissue)
2) Smooth muscle (involuntary)
- Found in hollow organs and tubes
- E.g. bronchioles, gut, blood vessels, iris of eye
3) Cardiac muscle
- Found only on the heart
- To move blood
- Creates pressure differential in heart chambers to move blood along

Question 4

Skeletal

Answer 4

location : attached to bone

cell shape : long cylindrical fibres

nucleus : multiple located peripherally

special cell to cell : none

striations : yes

control : vol and invol (reflex)

not capable of spontaneous contr

function : body movement

• Banding that goes across fibre caused by arrange of structures within giving striated appearance
• Always innervated by nervous system

Question 5

cardiac

Answer 5

location : heart

cell shape : cylindrical and bramched

nucleus : single, central

special cell-cell attachments : intercalated disks joins cells to one another

striations : yes

control : invol

capable of spontaneous cont : yes

function : pump blood

• Striated like skeletal
• Nucleus in middle like smooth but is circular

Question 6

smooth

Answer 6

location : walls of hollow organs, blood vessels, glands, eyes, skin

cell shape : spindle shaped

nucleus : single, central

special cell-cell : gap junctions join some visceral smooth muscle cells together

striations : no

control : involuntary

capable of spont : yes

function : movement food, pupil size, blood vessel diameter

• Usually stimulated by hormones

Question 7

How are different types of muscle tissue controlled?

Answer 7

Involuntary – smooth and cardiac

Voluntary – skeletal

Question 8

Name the connective tissue layers found in and around skeletal muscle.

Answer 8

Epimysium

• Surrounds a whole muscle
• Composed of dense collagenous connective tissue

Perimysium
- Surrounds a group of muscles fibres; each group called a fascicle

Endomysium
- Surrounds individual muscle fibres

Question 9

What is a muscle fascicle?

Answer 9

Group of muscle fibres

Question 10

What is the role of tendons in skeletal muscles?

Answer 10

Transferring the force created by the shortening of the muscle through the tendon then to bones.

Question 11

Describe the generalised structure of a skeletal muscle cell.

Answer 11

• sarcolemma (plasma membrane).
• sarcoplasm (cytoplasm).
• multiple nuclei at periphery.
• lots of mitochondria.
• myofibrils (cylindrical organelles with sarcoplasm).
• sarcoplasmic reticulum (=smooth endoplasmic reticulum).
• transverse (T) tubule.

Question 12

Briefly explain how muscles accomplish movements.

Answer 12

Muscles, their tendons and bones act together as lever systems to move either parts of the body or the whole body
- As a muscle contracts it creates tension on the tendons and pulls the bony points of attachment closer to one another
- Movement is determined by relative positions of
 Bone
 Joint
 Muscles - main

Question 13

Name the components of thick and thin myofilaments. Explain the main roles of each of the components of myofilaments and how they achieve this.

Answer 13

Thick:
Myosin: heads can bend at hinge region, which allows binding to the active sites on the actin molecules to form cross-bridges

Thin:

• actin: has a binding site for myosin.
• tropomyosin: covers the binding sites on actin.
• troponin: contains a binding site for calcium (Ca).

Question 14

Why is calcium essential to the process of muscle contraction?

Answer 14

It triggers contraction by reaction with regulatory proteins that in the absence of calcium prevent interaction of actin and myosin.

Question 15

Give two main reasons why ATP is essential to the process of muscle contraction.

Answer 15

Required for the bending of myosin heads and the release of myosin from actin.

Question 16

How do muscles vary the amount of tension they produce? (in your answer define a motor unit and explain its role in varying tension within a muscle)

Answer 16

1. Increasing or decreasing frequency of nerve impulses = SUMMATION.
2. Recruiting more or removing motor units =RECRUITMENT.

Question 17

What is meant by isometric muscle contraction, and how does it differ from an isotonic contraction?

Answer 17

• isometric: no movement (holding contraction), tension generated equals load.
• isotonic is when tension is greater than the load but isometric is when tension is NOT greater than the load.

Question 18

What is the difference between concentric and eccentric contraction of a muscle and explain what is occurring between the thick and thin filaments in each?

Answer 18

Concentric - Overcomes opposing resistance and muscle shortens. Tension is greater than load.
Eccentric - Tension maintained but muscle lengthens. Tension is less than load.

Question 19

What are the components of the neuromuscular junction?

Answer 19

• pre-synaptic terminal.
• synaptic cleft.
• postsynaptic membrane (or motor end plate).

Question 20

Describe the events that occur at the neuromuscular junction to transmit and action potential from the postsynaptic neuron on to the scarolemma.

Answer 20

• Action potential causes calcium voltage gated channels to open allowing calcium to flow into the presynaptic terminal
• Causing the synaptic vesicles to move and fuse with the cell membrane of the presynaptic terminal, releasing neurotransmitters known as acetylcholine into the synapse
• As its released into the synapse it moves very quickly by diffusion rto receptor
• Sodium channels open – sodium flows into muscle cell

Question 21

What is excitation-contraction coupling and explain the events that occur during this process.

Answer 21

The sequence of events from an action potential on the surface of the muscle cell to the interaction of the myofilaments (mechanisms whereby action potentials on the sarcolemma lead to actin and myosin interaction).

Question 22

Explain how a muscle’s action in determined by which joints are crossed, relative position of the muscle to the joint, line of pull, and the bony attachments.

Answer 22

• if a muscle crosses a joint it will act upon it.
• line of pull (muscle fasicle/fibre direction).
• bony attachments: many have 2 or more attachments, shortening of muscle brings points together.

Question 23

Describe the various conventions by which muscles are named.

Answer 23

• by shape.
• by number of heads (where two or more muscle bellies share a common tendon).
• by direction of fibres.
• by region or attachment.
• by action.
• some other reason.