Muscles and Movement

Muscles

A muscle is a tissue composed of cells capable of contracting and exerting force. Muscles work in conjunction with the skeleton to facilitate movement and locomotion.

Role of muscles in movement

1. The skeleton alone cannot bring about movement; muscles attached to bones play a vital role.
2. Movement, such as bending or straightening of the arm, involves two sets of muscles:
   1. Biceps: Located above the humerus, responsible for bending the arm.
   2. Triceps: Located at the back of the humerus, responsible for straightening the arm.

Antagonistic pairs:

1. Muscles work in pairs with opposing actions.
2. For bending, the flexor (biceps) contracts, and the extensor (triceps) relaxes.
3. For straightening, the triceps contract while the biceps relax.
4. This coordinated action is termed antagonistic movement.

Muscles are attached to bones via tendons, which are strong, inelastic fibers.

Types of muscles

Skeletal muscle (voluntary muscle):

1. Attached to bones of the skeleton.
2. Made up of long fibers and also called striated muscles due to their striped appearance.
3. Controlled by will (voluntary).
4. Capable of rapid contraction and relaxation but fatigues quickly.

Function: Responsible for the movement of limbs and skeletal parts.

Cardiac muscle (involuntary muscle):

1. Found only in the heart.
2. Made of branching fibers forming an interconnected network.
3. Contraction occurs involuntarily and continuously without fatigue.
4. Function: Pumps blood throughout the body.

Smooth muscle (involuntary muscle):

1. Found in the walls of internal organs (e.g., intestines, blood vessels).
2. Non-striated and involuntary.
3. Function: Moves substances through organs (e.g., peristalsis in the alimentary canal).

Muscle properties

1. Contractility: Ability to shorten and tighten, causing movement.
2. Elasticity: Ability to return to original shape after stretching.
3. Flexibility: Muscles can stretch during relaxation.
4. Fatigue: Skeletal muscles tire quickly after prolonged use.

Skeletal muscle

These are muscles which are attached to bones of the skeleton. They are made up of long fibres and cover the skeleton. They are also known as striated or voluntary muscles because they are controlled by the will. Skeletal muscles can contract and relax quickly but get fatigued quickly.

Functions

Skeletal muscles are concerned with movement of the limbs and parts of the skeleton.

Smooth muscle

These are muscles found on the wall of internal organs.

1. Such internal organs are alimentary canal, bladder, uterus, sperm ducts and blood vessels.
2. Smooth muscles are controlled by the involuntary nervous system, meaning they cannot contract at will. So they are involuntary muscles.
3. Smooth muscles contract slowly and they get fatigued relatively slowly.

Functions of smooth muscle

• Smooth muscles contract and relax to facilitate movement in various organs.
• Example: Peristalsis in the alimentary canal, which moves food and other materials through the digestive system.

Cardiac muscle

Location: Found only in the heart.

Structure: Composed of muscle fibres that branch and interconnect, forming a network.

Unique features:

1. Fatigue resistance: Cardiac muscles can contract and relax throughout life without becoming fatigued.
2. Involuntary contraction: Their contractions occur without stimulation from the nervous system, making them involuntary muscles.

Function:

• The rhythmic contraction and relaxation of cardiac muscles pump blood throughout the body, maintaining circulation and oxygen supply.

Muscle and movement

The skeleton alone cannot facilitate locomotion or the movement of body parts such as the arms, fingers, and jaws. Movement is made possible by the interaction between muscles and bones.

The bending and straightening of the arm involve two sets of muscles located above and below the humerus (the bone of the upper arm).

1. Biceps: Located above the humerus, the biceps are responsible for bending the arm.
2. Triceps: Located at the back of the upper arm, the triceps are responsible for straightening the arm.

How the muscles work

1. Bending the arm: This is achieved by the contraction of the biceps (flexor muscle), which pulls the forearm up. The triceps (extensor muscle) relaxes to allow this movement.
2. Straightening the arm: This is achieved when the triceps contracts (extensor muscle), and the biceps relaxes. The contraction of the triceps pulls the forearm back, straightening the arm.

Antagonistic pairs

1. Muscles that work in opposition to each other are called antagonistic pairs. For example, the biceps and triceps are antagonistic muscles because they work together to bring about movement, but they perform opposite actions (one contracts while the other relaxes).
2. The antagonistic action of muscles is necessary for continuous, controlled movement.

Tendons

Muscles are attached to bones at both ends by strong, inelastic fibres called tendons. These tendons facilitate the transfer of force from muscles to bones, enabling movement.

Muscle contraction

1. For a muscle to contract, energy is required. This energy is derived from respiration and it is found in the muscle cells in the form of ATP.
2. During muscle contraction ATP is broken down to ADP, thereby releasing the energy. The released energy is used to cause the muscle tissue to contract.

Muscle cramps

Muscle cramps are sudden, involuntary contractions of muscles or groups of muscles, which may cause the affected tissue to become hard and knotted. Cramps in skeletal muscles often occur after prolonged exercise, such as swimming, or due to a lack of salt in the body.

Relief: Stretching and warming the affected muscles can help to relieve the cramp.

Causes of muscle cramps

1. Dehydration: Lack of adequate fluids in the body.
2. Lack of magnesium: Low magnesium levels can affect muscle function.
3. Muscle fatigue: Overuse or strain of muscles during exercise.
4. Excessive exercise: Overworking the muscles without proper rest or recovery.

Prevention of muscle cramps

1. Stretching muscles more often: Regular stretching can help maintain flexibility and reduce the risk of cramps.
2. Regular physical exercise: Staying active and engaging in regular physical activity helps keep muscles conditioned.
3. Taking salt through a solution of water: Ensuring the body has enough electrolytes, such as sodium, can help prevent cramps related to salt depletion.