Structure and function

Anatomical Position 

The erect position of the body with the face directed forward, the arms at the side, and the palms of the hands facing forward, used as a reference in describing the relation of body parts to one another. 

BODY PLANES 

a) Sagittal plane: divides the body into right and left sides.

b) Frontal plane: divides the body into anterior (front) and posterior (back) sections. 

c) Transverse plane: divides the body into top (upper) and bottom (lower) sections.

DIRECTIONAL TERMS 

An anatomical reference system called directional terms is used to identify the location of bones and muscles. The starting point assumes that the body is in the anatomical position. 

Superior — towards the head, above. Superior = skull. 

- E.g. The head is superior to the shoulders.

Inferior — towards the feet, below. Inferior = floor.

- E.g. The feet are inferior to the knees.

Anterior — towards the front. 

 Anterior = A before P. 

- E.g. The nose is anterior to the back of the head.

Posterior — towards the back. Posterior = behind. 

- E.g. The heart is posterior to the sternum.

Medial — towards the midline of the body. Medial = middle. 

- E.g. The sternum is medial to the shoulder.

Lateral — towards the side of the body. Lateral = lats. 

- E.g. The arms are lateral to the chest.

Proximal — towards the body's mass, near the origin. Proximal= proximity.

- E.g. The elbow is proximal to the wrist.

Distal — away from the body's mass. Distal= distant. 

- E.g. The fingers are distal to the hand.

Structure and Function of The Skeletal System

The skeletal system comprises bones, cartilages, ligaments, and other tissues that play vital roles in the human body. Bone tissue, also known as osseous tissue, is a hard, dense connective tissue that forms the majority of the adult skeleton, providing the body's internal support structure. In areas where bones move against each other, such as joints like the shoulder or between vertebrae in the spine, cartilages offer flexibility and smooth surfaces to facilitate movement. Additionally, ligaments, which are dense connective tissues, surround these joints, connecting bones to one another.

Collectively, these components perform the following functions:

- Provides structure for the body 

- Allows for movement

- Protects vital organs

- Produces blood cells (red and white)

- Stores minerals storage (particularly calcium)

- Regulates endocrine

Axial and Appendicular Skeleton

The axial skeleton bones are located along the body's central axis. This includes the bones of the skull, spinal column and rib cage. Whereas, the appendicular skeleton consists of the bones in the limbs and the structures that attach these limbs to the body. The pectoral and pelvic girdles serve as connection points between the limbs and the axial skeleton. The bones in the limbs encompass the long bones of the arms and legs, and the bones of the hands and feet. Additionally, it includes the short bones that make up the wrists and ankles.

Major bones

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Types of bones 

The bones (or skeletal system) form a rigid framework to which muscles and other organs attach. The shape and length of the bone, how it joins to other bones and the location of the bone in the human body will influence what movement that bone is capable of. 

The main types of bones:

1. Flat bones 

2. Long bones 

3. Short bones 

4. Irregular bones

5. Sesamoid bones

Structure of a Bones

Please refer to the image below.

Types of Joints in the Body

A joint is any junction in the body where two bones meet. Joints are often referred to as articulations. The bones are joined together with ligaments which hold the joint in place. Joints, along with the bones and muscles enable movement of the body. Human joints enable our limbs to bend and move.

There are three main types of joints which can be classified according to the range of movement possible at the joint. These are:

Fibrous or immovable joints. This is a joint where no movement is possible.

The bones of the cranium are an example of a fibrous joint as the bones of the cranium are fused together in lines called sutures.

Cartilaginous or slightly moveable joints. These joints allow for rather limited movement. They are bound by very tight ligaments that permit minimal movement. An example of a cartilaginous joint is in the vertebral column where fibrous cartilage between discs allows a limited range of movement.

Synovial or freely moveable joints. These are the most common type of joint in the body and are largely found in the appendicular skeleton. Synovial joints allow for the greatest range of movement depending on the type of synovial joint. The knee joint is an example of a synovial joint. 

There are six different types of synovial joints, each offering a different range of movement, yet they all have some common characteristics. The most important structures in synovial joints are: tendons, ligaments, cartilage and synovial fluid. 

Types of Synovial Joints

Ligaments: are fibrous bands that connect bone to bone. They are designed to maintain joint stability by ensuring there is no excessive movement but at the same time control the degree and direction of movement.

Tendons: are tough inelastic cords that attach muscle to bone. They can assist in strengthening joints where they extend across a joint.

Hyaline (articular) cartilage: acts as the cushioning between the articulating surfaces of the bones. It is a layer of smooth, shiny cartilage that allows the bones to move freely over each other. This cartilage is thicker in leg joints as they are weight-bearing.

Synovial fluid: acts as a lubricant, keeping the joint well-oiled and the moving surfaces apart. No two joints fit perfectly together, so synovial fluid acts as a fluid cushion between them. It also provides nutrition for the cartilage and carries away waste products. This is all contained within the joint cavity.

Structure and function

Muscles are the only organs in the body with the ability to contract and, therefore, their main function is to provide or cause movement. The muscular system includes skeletal, smooth and cardiac muscle within the body. There are three basic functions that muscle tissue serves through contracting and relaxing. 

Muscles can: 

- Produce movement to walk, run, jump, breathe, digest and excrete

- Provide stabilisation of posture and internal organs

- Generate heat to maintain body temperature

Cardiac muscle is the muscle that makes up the majority of the heart and allows the heart to contract (beat) and pumps blood around the body. It is a non-voluntary muscle and when viewed under a microscope has a striated appearance.

Smooth muscle is a non-voluntary muscle and often forms cylindrical shapes around the outside of internal organs. Examples of organs with smooth muscle include the digestive and circulatory systems where the smooth muscle helps to control the diameter of the intestines, stomach, colon, and blood vessels.

Skeletal muscle is the only voluntary muscle with a striated appearance under the microscope. Skeletal muscles provide the movements we perform every day and usually connect to bone via a tendon across skeletal joints.

Refer to the image below.

Refer to the image below.

Refer to the table below.

How a Muscle Contracts and Relaxes

Neural Stimulation: The process begins with a nerve impulse (action potential) from the brain or spinal cord reaching a motor neuron.

Calcium Release: The nerve impulse causes calcium ions to be released from the sarcoplasmic reticulum (SR), a specialised organelle within muscle cells.

Actin and Myosin Interaction: Calcium ions bind to troponin, a protein that regulates the interaction between actin (thin filaments) and myosin (thick filaments). This binding exposes the actin binding sites.

Cross-Bridge Formation: Myosin heads bind to the exposed actin binding sites, forming cross-bridges.

Power Stroke: The myosin heads use ATP as energy to pull the actin filaments towards the centre of the sarcomere, shortening the muscle fibre.

Relaxation: When the nerve impulse stops, calcium ions are reabsorbed into the SR. Troponin and tropomyosin return to their original positions, blocking the actin binding sites. Myosin heads detach, and the muscle relaxes.

Source: Marieb, E. N., & Hoehn, K. (2016). Human Anatomy & Physiology. Pearson Education.

Types of Muscle Contractions

The Sliding Filament Theory

The sliding filament theory explains how muscles contract. It states that the overlapping actin and myosin filaments slide past each other, shortening the muscle fibre. The actual length of the filaments remains unchanged. The sarcomere is where the sliding filament contraction happens. The Z line is the end of the sarcomere and the M line is the middle.

Source: Welch, A. S., & Wilmore, J. E. (2014). Exercise Physiology. Lippincott Williams & Wilkins.

Motor Neurons:

Motor neurons: Nerve cells that transmit electrical signals from the central nervous system (brain and spinal cord) to muscle fibres.

Neuromuscular junction: The point where a motor neuron and a muscle fibre meet.

Acetylcholine: A neurotransmitter released at the neuromuscular junction that stimulates muscle contraction.

Isotonic vs. Isometric Contractions

Isotonic contraction: A muscle contraction that results in a change in muscle length. Examples include leg curls using weights, performing a push up.

 - Concentric contraction: This occurs when a muscle shortens as it contracts, overcoming external resistance. Examples include lifting a weight or bending your elbow. 

 - Eccentric contraction: This occurs when a muscle lengthens as it contracts, resisting an external force. Examples include lowering a weight or slowly extending your arm after a bicep curl. 

Isometric contraction: A muscle contraction that does not result in a change in muscle length. Examples include holding a heavy object in a fixed position or pushing against a wall.

Sources: Piotrowski, T. E. (2014). Kinesiology: The Scientific Study of Human Movement. McGraw-Hill Education. Human Anatomy & Physiology by Elaine N. Marieb and Katja Hoehn (2016). Pearson Education.

Muscle relationship

Muscle Origin and Insertion

Origin: The fixed attachment point of a muscle.

Insertion: The movable attachment point of a muscle.

Movement: When a muscle contracts, the insertion point moves towards the origin, creating movement. For example, when the biceps brachii contracts, the insertion point (forearm) moves towards the origin (shoulder).

Muscular System - The Interrelationship between the Skeletal and Muscular Systems and Movement

The skeletal and muscular systems work together to enable movement. The skeletal system provides structure and support, while the muscular system contracts to produce force.

Bones: Serve as levers, providing a rigid structure for muscles to pull against.

Joints: Allow for movement between bones, such as flexion, extension, abduction, and adduction.

Ligaments: Attach bone to bone. For example, at the knee joint the femur is attached to the tibia and fibula. As a result this allows for the knee to hinge and allow movement during a jump in netball to intercept the ball.

Tendon: Attach muscle to bone.

Muscles: Contract and relax to produce force, causing bones to move at joints.