Functional Anatomy

Muscle Belly

The central large part of the muscle, which is responsible for contracting and generating force

Epimysium

The outer connective tissue layer that surrounds the entire muscle belly. It helps protect the muscle and provides structure.

Fascicle

A bundle of muscle fibres within the muscle, grouped together by the perimysium.

Perimysium

The connective tissue surrounding each fascicle, providing structure and a conduit for nerves and blood vessels.

Muscle Fibre (Myocyte)

These are individual muscle cells that make up a fascicle. They are elongated, multinucleated cells capable of contracting.

Endomysium

The connective tissue that surrounds each individual muscle fibre. It provides support and helps transport nutrients and waste.

Myofibril

These are thread like structures within muscle fibre. They contain the actin and myosin filaments that allow muscle contractions.

Effect of gym on muscle fibre size

Myocytes increase in size as a result of strength or resistance training.

Concentric Contraction

Movement is in the opposite direction to gravitational pull. Muscle shortens

Concentric Contraction example

Bicep Curl, lifting the weights up (Curling towards you)

Eccentric Contraction

Movement is in the same direction as gravitational pull. Muscle Lengthens

Eccentric Contraction Example

Bicep Curl lengthening the muscle and moving it back to the resting position

Isometric Contraction

Muscle contracts, but no movement occurs. No change in muscle length. Has the greatest potential for force generation, as maximum number of crossbridge can be attached to the actin simultaneously.

Isometric Contraction example

Holding a plank

Actin

Thin protein filament attached to the Z line

Z - Line

Found at either end of the sarcomere. The Z-lines come closer together during concentric contractions and spread further apart during eccentric contractions.

Cross Bridges

Tiny projections from myosin filaments that attach to actin filaments. This pulls the actin filament towards the midline, making the H-zone shorten. Shortens the sarcomere and creates movement.

H - Zone

Space between the filaments which either gets longer or shorter as the sarcomere changes length.

I - Band

The light band that contains the thin actin filament. In a relaxed muscle, the thin filaments don’t completely overlap the myosin. In a thick filament, there is a prominent I-band.

A - Band

Contains both thick and thin filaments and is the centre of the sarcomere that spans the H-zone.

Sliding Filament Theory Step 1.

A neurochemical stimulation releases calcium from the sarcoplasmic reticulum in to the sarcomere.

Sliding Filament Theory Step 2

This causes the Actin filaments to reveal bonding sites for the myosin head.

Sliding Filament Theory Step 3

Myosin heads bind to Actin filaments, creating a cross bridge.

Sliding Filament Theory Step 4

Breakdown of ATP releases energy to stimulate the myosin cross bridges to pull the actin filaments towards the mid-line.

Sliding Filament Theory Step 5

This results in the shortening of the sarcomere as the actin and myosin filaments slide over each other, causing the Z lines to come closer together and the H zone to shorten.

Sliding Filament Theory Step 6

Shortening each sarcomere shortens the myofibril, resulting in the shortening of the muscle fibres and movement occurs.S

Sliding Filament Theory Step 7

Cross bridges attach and re-attach at different times to create movement and maintain tension.

Sliding Filament Theory Step 8

The process keeps repeating if the neural impulse is present or the muscle relaxes if the neural impulse ends.

Brain

Sends messages in the form of action potential to the spinal cord. Receives messages delivered from the spinal cord and analyses them to determine next actions.

Spinal Cord

Responsible for the transmission of messages between the brain and muscle.

Motor Neurons

Receives the message from the spinal cord and delivers it to the target muscle, causing movement to occur.

Sensory Neurons

Send messages back to the brain via spinal cord.

3 Key Functions

Receive information and pass it on to the brain, the brain determines and suitable response and the brain sends commands to the muscle to carry out a selected response.

Central Nervous System

Comprises the brain and spinal cord.

Peripheral Nervous System

The remainder of the nervous system.

Sensory Division

Carries messages from the body and environment to the spinal cord and Brain

Motor Division

Carries messages from the body and environment to the spinal cord and brain.

Motor Neuron

A cell within the nervous system that transmits impulses/signals to other nerve cells/muscles.

Dendrites

Acts as an antenna to detect the impulse from the sensory receptors and then deliver it to the cell body.

Cell body

Contains the nucleus which directs neurons activities and sends the message to the axon.

Axon

Transmits the message away from the neuron.

Motor Unit

The motor neuron and the fibres it activates. Related to size of the movement, number of units required and size of the action potential.

Small movements

Precise movement, small number of fibres, small motor unit, small action potential

Large movments

Large movement, gross motor skill, many fibres required, large motor unit, large action potential

Motor Unit Recruitment

Refers to increasing the number of motor units firing to increase the force being generated. Motor units are recruited on order depending on exercise intensity. Force can be increased in 2 ways: increasing the number of motor units or increasing impulse frequency.

All or None Principle

When a motor unit receives stimulation that exceeds the threshold, all the muscle fibres associated will contract to their maximum potential. If this threshold isn’t met, the muscle will not activate.

Force Velocity

The relationship between force production and velocity of movement. Muscles can create a larger force with a decrease in velocity. It’s easier to lift a heavier weight than a lighter one.

Force Length

The amount of muscle force that can be produced at varying muscle lengths. Maximum force comes from a muscle at it’s normal relaxed length.