Class 1 : Muscles, bones & joints

Question 1

Define muscle tissue.

Answer 1

Muscle is a contractile tissue of the body, derived from the mesodermal layer of embryonic gem cells.

They are responsible for all types of body movements and make up about 40-50% of total adult BW.

Question 2

Name the proprieties of muscle tissue (4).

Answer 2

1. Excitability/irritability (ability to receive and respond to a stimulus)
2. Contractibility (causes fibers to contract/shorten when stimulated)
3. Elasticity (muscle’s ability to return to its original length when tension is released)
4. Extensibility (muscle’s ability of being streched or extending in length in response to the contraction of opposing muscle fibers)

Question 3

There are 3 ways to classify muscles, what are they ?

Answer 3

According to :

1. Control (volontary/involuntary)
2. Microscopic anatomy (smooth/striated)
3. Association (Skeletal/visceral/cardiac)

Question 4

What are the types of muscles tissues (3) and differences between them?

Answer 4

Smooth : no striations, one central nucleus, contracts slowly, under involuntary control, 2 layers of opposing fibers, found in the viscera/blood vessels.

Skeletal : striated, peripheral nuclei, contracts rapidly, voluntarily and found in every muscles that is in contact w/ bones.

Cardiac : striated (not as much as skeletal), central nucleus, contracts rapidly, under involuntary control, non branched **and found in the heart.

Question 5

Name 5 specificities about the cardiac muscle.

Answer 5

1. Cardiac muscle is only found in the heart, arranged in thick bundles.
2. Muscle fibres are striated, short and thick, and they only have 1 central nucleus.
3. Adjacent muscle fibers are joined together at gap junctions called intercalated discs.
4. Cardiac muscle contracts rhythmically throughout its lifespan and does not become fatigued
5. Cardiac muscle is myogenic (its own pacemaker)- the built-in rhythm is termed autorhythmicity.

Question 6

Name 5 specificities of smooth muscles.

Answer 6

1. Small, spindle-shaped
2. One central nucleus
3. No connective tissue covering
4. Has thin and thick filaments, but no sarcomeres
5. Cells are usually arranged into sheets of opposing fibres forming a longitudinal and a circular layer : contraction of the opposing layers causes peristalsis.

Question 7

Name 3 specificities of skeletal muscle.

Answer 7

1. Fibres are multinucleated
2. Nuclei are peripherally located
3. Fibres are non branching

Question 8

A skeletal muscle as 2 or more attachments. What are the attachments sites called ?

Answer 8

Origin: Attachement on the less movable bone.

Insertion: Attachement on the more movable bone.

In limb muscles, origin usually lies proximal to insertion.

Question 9

The fleshy part of the muscle is referred to as :

Answer 9

Belly

Question 10

Define tendon.

Answer 10

Thick rope-like structure (of connective tissue) that attaches muscle to bone, cartilage or ligaments.

White, shiny & glazed colour.

Question 11

Define aponeurosis.

Answer 11

Connective tissue that serves the same fonction as tendons (i.e. connects muscle to bone) but specifically for flattened muscles.

It is very thin and delicate compared to tendon, and transparent.

Also acts as a shock absorber. Much less subject to injury than tendon.

Question 12

Define Raphe.

Answer 12

Connective tissue : interdigitation of the tendinous ends of fibres of flat muscles.

Structure forming the fused ends of 2 flat muscle sheets.

Question 13

Name the different types of skeletal muscles according to shape (7).

Answer 13

1. Flat muscles
2. Pennate muscles
3. Fusiform muscles
4. Convergent muscles
5. Quadrate muscles
6. Circular/sphincteric muscles
7. Multiheaded/multibellied muscles

Question 14

Describe flat muscles and give an example.

Answer 14

Broad, relatively thin, sheetlike muscleFlat muscles have parallel fibres often with aponeurosis

e.g. muscle of the anterolateral wall of abdomen such as external/internal obliques.

Question 15

Describe fusiform muscles and give an example.

Answer 15

Fusiform muscle are spindle shaped muscles with a round thick belly(or bellies) and tapered ends.

E.g. Bicep brachii.

Question 16

Define circular or sphincteric muscles and give an exemple.

Answer 16

They surround a body opening or orifice, constricting it when contracted.

Eg. Orbicularis oculi , Orbicularis oris

Question 17

Define quadrate muscles and give an example.

Answer 17

They have 4 equal sides.

The rectus abdominis is a quadrate muscle and so is pronator quadratus in the forearm.

Question 18

What are pennate muscles ?

Answer 18

Muscles whose fibres run obliquely to the line of pull and they resemble a feather.

1. Unipennate : Muscles in which the tendon lies along on side of the muscle & the muscles fibres pass obliquely to it. E.g. Extensor digitorum longus.
2. Bipennate : a muscle in which the tendon lies in the center of the muscle and the muscle fibres pass to it from two sides. E.g. Rectus femoris.
3. Multipennate : arranged as a series of bipennate muscles lying alongside one another (e.g. acromial fibers of the deltoid) OR they may have the tendon lying within its center and the muscle fibers passing to it from all sides converging as they go (e.g. tibialis antierior)

Question 19

What are multiheaded ou multi bellied muslces?

Answer 19

Types of skeletal muscles that have more than one head of attachment or more than one contractile belly respectively.

E.g. Biceps brachii (2 heads) ; triceps brachii (3 heads)

E.g. Digastric and gastrocnemius muscles have 2 bellies.

Question 20

What is a prime mover (Agonist) ?

Answer 20

Muscles responsible for producing a desired movement.

Prime movers brings the insertion towards the origin.

For instance, bicep brachii is the prime mover when it produces flexion at the elbow joint.

Question 21

What is an antagonist ?

Answer 21

Produces the movement opposite to the prime mover.

Usually, the agonist and the antagonist act together so that when the prime mover contracts, it’s antagonist undergoes relaxation.

Therefore, antagonists for one movement can be agonists for another movement.

Question 22

What does it mean when we functionally classify a muscle as a synergist ?

Answer 22

The undesired mvmt at a joint is prevented by synergist so that the prime mover can function properly.

E.g. When clenching the fist, the extensors of the wrist contract as synergist to prevent wrist flexion.

Question 23

How would you describe a fixator muscle ?

Answer 23

A muscle is said to act as a fixator when it contracts to stabilize the origin of the prime mover so that it can act efficiently.

E.g. when throwing a punch : the muscles attaching the shoulder girdle to the trunk (trapezius, pectoralis major) contract as fixator to allow the deltoid to act on the shoulder joint to produce abduction.

Question 24

Where does the nerve enter the muscle and what is the point of the entrance known as ?

Answer 24

The nerve enters the muscle at about midpoint on its deep surface, often near the margin.

The place of entrance is known as the motor point.

This arrangement allows the muscle to move with minimal interference w/ the nerve trunk.

Question 25

What are the four functional categories of muscles?

Answer 25

1. Agonists (prime movers)
2. Antagonists
3. Synergists
4. Fixators

Question 26

Describe tonic contraction.

Answer 26

This refers to muscle tone (tonus). Muscles keep slightly contracted states which does not produce mvmt or active resistance but gives the muscle a certain firmness.

This assists the stability of joints & the maintenance of posture, while keeping the muscle ready to respond to appropriate stimuli.

Question 27

What are the 3 states in which muscle tone is absent ?

Answer 27

1. Sleep
2. Unconscious
3. After a nerve lesion resulting in paralysis

Question 28

What is isotonic contraction ?

Answer 28

Maintains constant tension in the muscle as it changed length.

Isotonic contractions can be either concentric or eccentric.

Question 29

Describe concentric & eccentric contractions.

Answer 29

An isotonic type of contraction in which the muscle shortens while generating force, overcoming resistance.

Eccentric contractions results in the elongation of the muscle while the muscle is still generating force. They can be both volontary (e.g. controlled lowering of heavy weight) and involontary (e.g. weight is too heavy to forearm is lowering while under tension).

Question 30

What is phasic contraction ?

Answer 30

Often when the main muscle of a particular mvmt (prime move) is undergoing a concentric contraction, its antagonist is undergoing a coordinated eccentric contraction.

This is referred to as phasic contraction.

E.g. walking (we contract concentrically to pull our center of gravity forward and then, as it passes ahead of limb, muscles contract eccentrically to prevent a lurching during the transfer of weight of the body).

Question 31

What are isometric contractions?

Answer 31

In contrast to isotonic contractions, isometric contractions generate force without changing the length of the muscle.

Common in the muscles of the hand and the forearm responsable for grip. This would also apply to the muscle contraction required to grip but not move a heavy object prior to lifting it.

Isometric contractions are frequently used to maintain posture.

Question 32

Describe reflexive contractions.

Answer 32

Involuntary contractions ; automatic (reflexive).

For instance, respiratory mvmts of the diaphragm are controlled most of the time by reflexes, stimulated by the level of O2 and CO2 in the blood).

Myotatic reflex (tapping a tendon with a reflex hammer).