Muscle Function and Anatomy

2

Characteristics of Muscles

· Muscle cells are elongated (muscle cell = muscle fiber)

· Contraction of muscles is due to the movement of microfilaments

· All muscles share some terminology· Prefix myo refers to muscle

· Prefix mys refers to muscle

· Prefix sarco refers to flesh

The Muscular System

· Muscles are responsible for all types of body movement

· Three basic muscle types are found in the body· Skeletal muscle

· Cardiac muscle

· Smooth muscle

Classifications of

Muscles

Skeletal Cardiac Smooth

Cardiac muscle tissue

• Makes up myocardium of heart• Unconsciously (involuntarily) controlled• Microscopically appears striated• Cells are short, branching & have a single nucleus• Cells connect to each other at intercalated discs

Smooth (visceral) muscle tissue

• Makes up walls of organs & blood vessels• Tissue is non-striated & involuntary• Cells are short, spindle-shaped & have a single nucleus• Tissue is extremely extensible, while still retaining

ability to contract

Skeletal muscle tissue

• Associated with & attached to the skeleton• Under our conscious (voluntary) control• Microscopically the tissue appears striated • Cells are long, cylindrical & multinucleate

• Are the prime movers of the human body. They produce forces under the control of the nervous system. Man has 645 skeletal muscles of many shapes and sizes

• Muscles are situated across joints and are attached at two or more points to bony levers.

• Each muscle is well adapted to provide an appropriate range, direction and force of contraction to meet the requirements.

Skeletal muscles

Properties of Skeletal Muscles

• Irritability: is the ability of the muscle to respond to stimulus.

• Contracility: is the capacity of the muscle to produce tension between it’s ends.

• Relaxation: is the opposite of contraction and is the giving up of tension.

• Distensibility: is the ability of the muscle to be stretched or lengthened up to a

certain limit by an outside force; e.g. pull of an antagonist muscle, of gravity or

by an opponent. The muscle suffers no harm so long as it is not stretched beyond

its physiological limits.

• Elasticity: is the ability of the muscle to recoil to its original length when an

outside force is removed unless it has been overstretched.

Function of the skeletal Muscles

• Create the force responsible for human movement and positioning of the bony segments of the body.

• Give shape to body segments.

• Form supportive walls.

Classification of Muscles:1. According to the shape and fascicular architecture:

• Parallel: spindle.• Oblique: e.g. pennate.• Spiral: Supinator.

• The muscles designed for strength are of pennate type & the ones designed for speed have parallel fibers.

Parallel muscles (range of motion1. Flat (rectus abdominus)2. Fusiform (biceps)3. Strap (sartorius)4. Radiate (trapezius)5. Sphincter

Pennate (force)1. Unipennate (biceps femoris)2. Bipennate (rectus femoris)3. Multipennate (deltoid)

Shape of Muscles and Fiber Arrangement Strap

Sphinter

Muscle Shapes

Muscle Shapes

2) According to the myoglobin content:

• Red: contain more red fibers and they are responsible for movement, which require slow action for a long time e.g antigravity muscles.

• White: contain more white fibers and they are responsible for movement, which require rapid action for a short time.

3) According to the type of contractile activity:

a. Tonic muscles (stabilizers): for continuous low level of contractile activity which is required to maintain a given posture.

b. Phasic muscle (mobilizers): for rapid (fast twitch) activity which is required when changing from one position to another.

4) According to general limb appearance:

Contractors: those muscles pull the body into approximation of the fetal position/ midline e.g. flexor adductors and medial rotators.

Expanders: those muscles which expand or open up the body e.g.

extensors. Abductors and lateral rotators.

5) According to the relative magnitude of their stabilizing

and rotatory components (muscle attachments):

Spurt: mainly rotator muscles which have their origin away from the joint and their insertion near to the joint e.g. biceps muscle.

Shunt: mainly stabilizer muscles which have origin near the joint and their insertion away from the joint e.g. brachio-radialis.

6) According to the orientation of the line of pull to the joint structure:

e.g. flexors, extensors, abductors and adductors• The muscle located anterior to a joint may be extensor (knee

joint) or may be flexor (elbow joint).• The possible axes of motion are determined by the structure of

the joint itself.

7) According to the number of joints over which the muscle crosses:

– One joint muscle ( e.g. vastus mediales).– Two joint muscle( e.g. rectus femoris).– Multi-joint muscle ( e.g. finger flexors).

8) According to the type of muscle action or function (their interaction in joint movement):

• One action of the joint is not only the responsibility of one muscle but it is the responsibility of different groups of muscles, which can be classified as follows:

Agonists, antagonists, synergists, fixators.

FIBRE TYPES OF SKELETAL MUSCLE

• 2 types of muscle fibres:

– Fast twitch

– slow twitch

due to speed at which they contract.

Slow twitch fibresType 1:

• Red in colour – have good blood supply.• Dense network of blood vessels.• Suited to endurance work.• Slow to fatigue.• Contain many mitochondria

to make them more efficient

at producing energy using

oxygen.

Mitochondria – energy-producing

organelles with in cells.

Fast twitch fibresType 2:

• Contract twice as fast and

are thicker in size.• Poor blood supply.• Whiter in appearance:

– due to lack of oxygen.

• Fatigue fairly quickly.• Suitable for: producing fast,

powerful actions such as sprinting & lifting heavy weights.

Fast twitch fibres:

• Within the group of fast twitch fibres there are 2 types: 2A & 2B.

• Type 2B work when a person is working very close to their maximum intensity, eg. 100 m sprint.

• Type 2A work at a slightly lower intensities but higher intensities than slow twitch, eg. 400 m sprint.

Training Effect on Muscle Fibres:

• Type 1 & type 2B fibres don’t change.• Type 2A can take on characteristics of Type 1 & 2B.

• More endurance training = 2A would develop more endurance.

• More speed training = 2A would develop more speed.

• They don’t change their fibre type.

Training Effect on Muscle Fibres:

• Postural muscles predominantly slow twitch.

• Arms tend to be more fast twitch.

• Legs depends on endurance running or sprinting.

Muscle Terminology

• Origin– proximal attachment– least moveable end– closest to the midline of the body

• Insertion– distal attachment– most moveable end– furthest from the midline of the body

• Action– The movement at the joint when the muscle(s) contract

Anatomy of the Muscular System

• Origin Muscle attachment that remains . fixed

• InsertionMuscle attachment that moves

• ActionWhat joint movement a muscle

producesi.e. flexion, extension, abduction,

etc.

Attachments and Actions of Skeletal Muscles

• Actions depend largely on what the muscles are attached to

• Attachment sites– Origin – an attachment site

for a less movable bone

– Insertion – an attachment site for a more moveable bone

• For muscles to create a movement, they can only pull, not push

• Muscles in the body rarely work alone, & are usually arranged in groups surrounding a joint

• A muscle that contracts to create the desired action is known as an agonist or prime mover

• A muscle that helps the prime mover by stabilizing joints is a synergist

• A muscle that opposes the action of the agonist, therefore undoing the desired action is an antagonist(Relaxes when prime mover contracts)

• Types of muscle action

• Agonists

• Prime movers

• Secondary

movers

•Antagonists •Synergists

•Conjoint

•Stabilizers

•Neutralizers

•Around•The target

joint

•On another joint

•Fixators

Agonist and Antagonist

Antagonist

Agonist

Agonist

Antagonist

• Antagonists:

Muscles which oppose the prime movers as they relax and lengthen

progressively to allow agonists to move.

For every action, there are agonists and antagonists (e.g. Gluteus

maximus is antagonist for iliopsoas).

• Synergists:

Synergists are muscles that work together in a close cooperation as they either contract or relax to modify the action of the agonist.

Their aims are:

1) To make the agonist stronger

2) To eliminate the action of undesired movement.

They may alter the direction of pull and that depends on their power in relation to the agonist muscle.

Types of Synergists:

a) Conjoint:

• They are the two muscles acting together to produce a certain movement which neither of them could produce it alone. They are considered as prime movers of agonists and they are parallel to each other.

• E.g. tibialis anterior and peroneous tertious work together to produce dorsiflexion.

b) Neutralizer:

They are the muscles that neutralize or cancel the undesired action of prime movers.

This is more apparent in two- joint muscles which cross more than one joint and are capable of performing more than one action which are not needed

therefore, the neutralizers must contract to counteract the undesired movement.

Neutralizers for undesired motion on another joint in case of two joint muscles:

• For example: Contraction of the finger flexors to grasp an object also tend to flex the wrist. The unwanted wrist flexion is neutralized by wrist extensors.

• Stabilizers:

Muscles that surround the proximal joint. They contract and

become firm to allow distal joint to move smoothly.

Their contraction is generally isometric (e.g. the rotator cuff muscles all

contribute their opposing tension to support the humeral head against the

glenoid fossa when the arm is moved away from the body and the hand

reaches for an object).

• Fixators:

Muscles which contract in both agonists and antagonists simultaneously

and that occur especially under stress conditions.

The tension will develop inside both groups of muscles to prevent any

degree of freedom. That occurs in normal physiological conditions during

strenuous effort and increased demand (e.g. during standing on one leg).

Types of bodily movements

• Movements can be classified into:

• Passive: Subject is relaxed and movement is performed by any outside force.

• Active: Is volitionally performed or reflex reaction to an external stimulus:

a. Slow or rapid tension movement that involve constant . application of force.

b. Ballistic movement: Movement is initiated by vigorous muscular contraction and completed by momentum.

Types of Muscle Contraction

• Concentric contraction– Length of muscle shortens– Muscle force is greater than the resistance

• Static or Isometric contraction– No change in muscle length– Muscle force is equal to the resistance

• Eccentric contraction– Muscle lengthens– Muscle force is less than the resistance

Lengthens Lengthens

Concentric

Concentric

EccentricEccentric

Eccentric Contraction

• Used to control agonist and prevent over lengthening of the antagonist.

• Example: triceps lowers dumbbell while biceps ’controls’ the triceps activity (action)

• Causes more damage than other types

• Also, results in more muscle soreness.

Determination of Muscle Action

• Muscle location– Origin and insertion– What joint(s) it crosses

• Planes and their actions– Most muscle can not perform opposite actions (e.g.

flexion AND extension)

• Line of pull– Muscles only pull on bones, they do not push bones!– Insertion is pulled towards the origin

Nomenclature

• Muscles are named according to:– Location: pectoralis gluteus, brachial– Size: maximus, minimus, longus, brevis– Shape: deltoid, quadratus, teres– Orientation: rectus– Origin and insertion: sternocleidomastoid,

brachioradialis– Number of heads: biceps, triceps– Function: abductor, adductor, masseter