Muscle Structure and Function

Types of Muscle The human body is comprised of 324 muscles Muscle makes up 30-35% (in women) and 42-47% (in men) of

body mass.

Three types of muscle:

Skeletal muscle

Smooth muscle

Cardiac muscle

Characteristics of a Muscle Irritability

Muscles have ability to receive and respond to stimuli (force and electrical)

Contractility Muscle has the ability to shorten

Extendibility Muscle has the ability to lengthen

Elasticity Muscle has the ability to return to normal length

A. Skeletal (Striated) Muscle

Connects the various parts of the skeleton through one or more connective tissue tendons

During muscle contraction, skeletal muscle shortens and moves various parts of the skeleton

Through graded activation of the muscles, the speed and smoothness of the movement can be gradated

Activated through signals carried to the muscles via nerves (voluntary control)

Repeated activation of a skeletal muscle can lead to fatigue

Biomechanics: assessment of movement and the sequential pattern of muscle activation that move body segments

B. Smooth Muscle Located in the blood vessels, the respiratory

tract, the iris of the eye, the gastro-intestinal

tract

The contractions are slow and uniform

Functions to alter the activity of various body

parts to meet the needs of the body at that

time

Is fatigue resistant

Activation is involuntary

C. Cardiac Muscle Has characteristics of both skeletal and

smooth muscle

Functions to provide the contractile

activity of the heart

Contractile activity can be gradated (like

skeletal muscle)

Is very fatigue resistant

Activation of cardiac muscle is

involuntary (like smooth muscle)

a) Muscle b) muscle fibre bundle c) muscle fibre d) myofibril

Components of skeletal muscle

Muscle Fibres Cylinder-shaped cells that make up skeletal muscle

Each fibre is made up of a number of myofilaments

Diameter of fibre (0.05-0.10 mm)

Length of fibre (appr. 15 cm)

Surrounded by a connective tissue sheath called Sarcolemma

Many fibres are enclosed by connective tissue sheath Perimycium to

form bundle of fibres

Each fibre contains contractile machinery and cell organelles

Activated through impulses via motor end plate

Group of fibres activated via same nerve: motor unit

Each fibre has capillaries that supply nutrients and eliminate waste

Muscle Teamwork Agonist (prime mover):

- the muscle or group of muscles producing a desired effect

Antagonist:

- the muscle or group of muscles opposing the action

Synergist: - the muscles surrounding the joint being moved

Fixators:

- the muscle or group of muscles that steady joints closer to the body axis so that the desired action can occur

Bending or straightening of elbow requires the coordinated interplay of the biceps and triceps muscles

Contractile Machinery:

Tendons, origin, insertion In order for muscles to contract, they must be

attached to the bones to create movement

Tendons: strong fibrous tissues at the ends of each muscle that attach muscle to bone

Origin: the end of the muscle attached to the bone that does not move

Insertion: the point of attachment of the muscle on the bone that moves

Muscle Fibre Types

Slow twitch fibres:

Slow Oxidative (Type I)

Fast twitch fibres: Fast Glycolytic (Type IIb) Fast Oxidative Glyc. (Type IIb)

A. Slow Twitch Fibres Suited for repeated contractions during activities requiring a

force output of < 20-25% of max force output

Examples: lower power activities, endurance events

B) Fast Twitch Fibres Significantly greater force and speed generating capability than

slow twitch fibres

Well suited for activities involving high power

Examples: sprinting, jumping, throwing

Glycogen fibresLarge diameter

Oxidative fibres

Small diameter

Capillary blood vessels

Muscle Biopsy