Anatomy and Physiology of Muscle Contraction and Structure

Key Terminology of the Human Body

Receptor

Part of the body that receives signals from the environment or other cells and transmits information.

Stimulus

A signal that results in changes in the body.

Feeling

The ability to notice or feel physical sensations.

Eyebrow

A row of hair above the eye.

Eyelash

Small hair on our eyelids which protects our eyes.

Bactericide

A substance that kills bacteria.

Cavity

A hole, for example in bones or teeth.

Temporal Bone

One of a pair of bones forming part of the sides and base of the skull.

Vibration

A small movement, which the body can sense.

Texture

The structure or substance of something and how it feels.

Pressure

Applying force to something.

Pain

A sensation you feel when you are hurt.

Saliva

A colorless liquid which mixes with food in your mouth when you chew.

Flavour

The part of a substance that the senses of taste and smell detect.

Calcium

A mineral in the body; it is essential for cells and bones, and for muscle contraction.

Spongy

Full of tiny holes, like a sponge.

Calcify

To become hard like bone.

Suture

A rigid joint where two bones meet.

Ligament

Connective tissue that joins bones together.

Bone Marrow

Soft tissue that fills the cavities in bones.

Tendon

Tissue that attaches muscle to other body parts.

Agonist

A muscle that creates a particular movement.

Antagonist

A muscle that works against an agonist in order to help control movement.

Muscle Structure and Function

Muscles are made up of groups of muscle bundles (musculos atados), which themselves are made up of groups of elongated (estirado) muscle fibers.

Muscle bundles, as well as the whole muscle, are wrapped in a protective covering. When they join up, the protective coverings form **tendons**. This is the point where the muscles meet the bones. Tendons are very resistant to stretching, and for this reason, when a muscle **contracts**, the movement is transmitted to the bone.

The Mechanism of Muscular Contraction

Muscles contract by becoming shorter. A motor nerve acts on a muscle, and the muscle cells use energy to contract. This energy is obtained from **aerobic respiration** in the cells, which requires a source of energy and oxygen.

Muscle Coordination: Agonists and Antagonists

For muscle contraction to produce the desired movement, various muscles must be coordinated at the same time. Muscles that coordinate to make a specific movement are called **agonist muscles**. **Antagonist muscles** act against agonists: when one contracts, the other relaxes. This is the case with the biceps and the triceps, which move the forearm bones.

Muscle Shapes

Depending on their shape, muscles can be:

• Fusiform (long)
• Flat
• Circular (or sphincters)

Example: Biceps and Triceps Action

The **biceps** moves the forearm towards the upper arm. The antagonist muscle, the **triceps**, moves the forearm away from the upper arm.