Skeletal Muscle Anatomy and Function

Functional Anatomy of Skeletal Muscles

• Skeletal muscles attach to two bones across a joint.
• Muscle contraction results in a pulling force.
• Muscles have two attachment points located on different bones across a joint.
• The origin point is the attachment point to the bone that doesn't move during muscle contraction and is at the proximal end.
• The insertion point is the attachment point to the bone that moves when the muscle contracts and is at the distal end.
• Agonists, or prime movers, facilitate movement through contraction.
• Antagonists are muscles that relax to allow movement.
• In elbow flexion, the Bicep is the agonist, and the Triceps are the antagonist.
• Fixator muscles stabilize a body part, providing stability to the origin for maximal force application.
• Synergist muscles stabilize and control surrounding muscles to assist in smooth, controlled movements.

Functions of the Skeleton

• Provides a framework and shape for the body.
• Serves as attachment points for muscles, enabling movement through leverage.
• The skull protects the brain.
• Ribs protect the heart, lungs, and kidneys.
• The spinal column protects the spinal cord.
• Stores essential minerals like calcium and phosphorus for bone tissue health.
• Produces red blood cells (RBCs) in the bone marrow, especially during childhood and adolescence.

Classification of Joints

• Fibrous joints are immovable.
• Cartilaginous joints are slightly movable.
• Synovial joints are freely movable.

Types of Synovial Joints

• Gliding joints, such as carpals within the wrist, allow for gliding movements.
• Hinge joints, like the knee, permit movement in one plane.
• Pivot joints, such as the radius and ulna, allow for rotational movement.
• Saddle joints, like the carpals of the thumb, enable movement in multiple planes.
• Condyloid joints, such as the joint between carpals of the wrist and radius, allow for oval-shaped movement.
• Ball and socket joints, like the hip, allow for movement in multiple axes.

Functions of the Circulatory System

• Circulates blood throughout the body.
• Transports oxygen, water, and nutrients to cells.
• Transports carbon dioxide and wastes away from cells.
• Maintains body temperature.
• Produces white blood cells.

Characteristics of Skeletal Muscle Tissue

• Excitability is the ability to contract in response to chemical or electrical signals.
• Extensibility is the capacity of a muscle to stretch beyond its normal resting length.
• Contractility is the ability of a muscle to contract or shorten.
• Elasticity is the ability of a muscle to return to its original resting length after being stretched.

Arteries

• Carry blood away from the heart.
• They have thick muscular walls and no valves.
• Blood is under high pressure.
• Blood (except in the pulmonary arteries) is oxygenated.

Veins

• Carry blood toward the heart.
• Veins have thin, collapsible walls.
• Valves are present and blood is under low pressure.
• Blood (except in the pulmonary veins) is de-oxygenated.

Capillaries

• Allow the diffusion of oxygen to tissues and removal of carbon dioxide.
• Consist of very thin walls, only one cell thick.
• They branch from arterioles and venules to form a network.

Systemic Circulation

• Carries blood from the heart to the body tissues and back.

Pulmonary Circulation

• Carries blood from the heart to the lungs for gaseous exchange and back.

Cardiac Output

• Cardiac Output (L/min) = Heart Rate (bpm) + Stroke Volume (ml/beat)
• Heart Rate is the number of heartbeats per minute.
• Stroke Volume is the amount of blood ejected from the left ventricle per beat.
• Cardiac Output is the amount of blood ejected from the heart per minute and can be calculated as HR x SV (L/min).

Functions of the Respiratory System

• Delivers O2 from the atmosphere to the lungs.
• Facilitates gaseous exchange within the lungs.
• Creates speech and facilitates the sense of smell.
• Expels heat and water vapor.

Respiratory System Components

• Air passages include the nasal cavity, mouth, pharynx, larynx, trachea, bronchi, bronchioles, and alveoli.
• Lungs, protected by the sternum, ribs, and vertebral column, contain the bronchi, bronchioles, and alveoli, which are the site of gas exchange.

Gas Exchange

• Occurs via diffusion at two sites: the lungs (alveoli/capillary interface) and the muscles (capillary/muscle interface).

Mechanics of Breathing

• Inspiration involves contraction of intercostals and the diaphragm, increased lung volume, and decreased lung pressure.
• Expiration involves relaxation of intercostals and the diaphragm, decreased lung volume, and increased lung pressure.
• Ventilation is the amount of air inspired and expired in one minute.
• Respiratory rate is the number of breaths per minute.
• Tidal rate is the amount of air breathed in and out in one breath.