How Do We Move?

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

List the function properties of muscle.

Answer 2

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

Question 3

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

Answer 3

• epimysuim: surrounds a whole muscle.
• perimysium: surrounds a group of muscle fibres.
• endomysium: surrounds individual muscle fibres.

Question 4

What is a muscle fascicle?

Answer 4

A group of muscle fibres.

Question 5

What is the role of tendons in skeletal muscle.

Answer 5

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

Question 6

Describe the generalised structure of a skeletal muscle cell.

Answer 6

• 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 7

Name the components of thin myofilaments.

Answer 7

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

Question 8

Name the components of thick myofilaments.

Answer 8

Myosin.

Question 9

Why is calcium essential to the process of muscle contraction?

Answer 9

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

Question 10

What are the main reasons why ATP is essential to the process of muscle contraction.

Answer 10

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

Question 11

How do muscles vary the amount of tension they produce?

Answer 11

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

Question 12

Define a motor unit.

Answer 12

• A motor neuron and the muscle fibres innervated by its axon.
• can contain a hundred to thousands of muscle (cells) fibres.

Question 13

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

Answer 13

• 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 14

What is concentric contraction?

Answer 14

Overcomes opposing resistance and muscle shortens. Tension is greater than load.

Question 15

What is eccentric contraction?

Answer 15

Tension maintained but muscle lengthens. Tension is less than load.

Question 16

What are the components of the neuromuscular junction?

Answer 16

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

Question 17

What is excitation-contraction coupling?

Answer 17

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 18

Describe the various conventions by which muscles are named.

Answer 18

• 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.

Question 19

Explain how a muscles action is determined.

Answer 19

• 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.