Muscle Physiology

Muscle Structure and Function

• Smooth muscle fibers contract like a wave (peristalsis) in response to nerve impulse, hormonal stimulation, or stretching.
• Smooth muscles contract slowly and can remain contracted for long periods of time, and relax slowly.
• Smooth muscles make up the walls of hollow organs such as the stomach, esophagus, small intestines, blood vessels, and respiratory passageways.

Cardiac Muscle

• Cardiac muscle is also known as myocardium or heart muscle.
• It is made up of cells joined by intercalated discs, which are capable of fast impulse transmission.
• Cardiac muscle contracts and relaxes automatically without conscious control, pumping blood at a rate of 60-100 times per minute.

Skeletal Muscle

• Skeletal muscle consists of muscle cells (fibers) that are grouped together in bundles called fascicles.
• Muscle cells are called myocytes, and muscle fibers are composed of myofibrils, which are made up of sarcomeres linked in series.
• The sarcomere is the functional unit of the muscle where contraction occurs.
• Actin and myosin are the force-generating proteins of the sarcomere that work together to produce movement.

Properties of Muscles

• Contractility: the ability to contract or get shorter.
• Excitability: responsiveness to stimuli.
• Conductivity: the ability to conduct electrical charge.
• Extensibility: the ability to stretch without rupture.
• Elasticity: the ability to return to their original shape after contraction or extension.

Muscle Contraction

• Muscle contraction involves the sliding of actin past myosin, generating muscle tension.
• Myosin pulls on actin to shorten the sarcomere, producing movement.

Types of Muscle Contraction

• Muscle tone: a state of partial contraction responsible for posture.
• Isotonic contractions: the tone of the muscle remains the same, but the muscle gets shorter in length.
• Isometric contractions: the tone of the muscle increases, but the length of the muscle stays the same.

Effects of Exercise on Muscles

• Increased capillaries in muscles, increased protein filaments, and increased glycogen storage.
• Muscle hypertrophy: increased muscle size and strength.
• Vasodilation: increased blood flow and decreased resistance, leading to a drop in blood pressure.
• Strengthening of the heart and improvement in respiration.

Action of Muscles

• Prime mover or agonist: provides most force for a given muscle action.
• Antagonist: has opposite action of agonist, producing the opposite movement.
• Synergist: muscles that aid agonists or prime movers, helping to stabilize joints.
• Fixator: specialized synergist that helps to fix the position of the bone being moved.

Muscles of the Body

• Muscles of the head produce facial expressions, speech, and chewing.
• Muscles of the neck, such as the sternocleidomastoid and trapezius, are important for flexing and turning the head.
• Muscles of the upper extremities, such as the latissimus dorsi, pectoralis major, and deltoid, are involved in movements of the arm and shoulder.
• Muscles of the forearm and hand, such as the biceps brachii and triceps brachii, are involved in flexion and extension of the forearm.
• Muscles of the trunk, such as the intercostal muscles and diaphragm, are involved in respiration.
• Muscles of the abdomen and pelvis, such as the rectus abdominis and external oblique, are involved in compressing the abdomen and bending the vertebral column.
• Muscles of the lower extremities, such as the gluteus maximus and quadriceps femoris, are involved in movements of the thigh and leg.

Muscular Disorders

• Atrophy: wasting or decrease in size brought about by lack of use.
• Spasm: sudden, painful, involuntary muscle contraction.
• Strains: muscle injury caused by overuse or overstretching.
• Sprains: more severe than strains, involving twisting of a joint with partial rupture to the muscle and tendon.

Effects of Aging on Muscles

• Decrease in size and strength of all muscles.
• Decrease in skeletal muscle size, strength, and endurance.
• Decrease in skeletal muscle elasticity and flexibility.
• Decrease in exercise tolerance and ability to recover from muscle injury.

Other Muscle-Related Concepts

• Oxygen debt: the inability to deliver enough oxygen to the muscles during strenuous exercise, leading to muscle fatigue.
• Sphincter: a muscular ring that tightly regulates an opening, such as the urethral sphincter, anal sphincter, or pyloric sphincter.
• All or none: the principle that a muscle is either fully stimulated to contract or not at all.

Muscle Structure and Function

• Smooth muscle fibers contract like a wave (peristalsis) in response to nerve impulse, hormonal stimulation, or stretching.
• Smooth muscles contract slowly and can remain contracted for long periods of time, and relax slowly.
• Smooth muscles make up the walls of hollow organs such as the stomach, esophagus, small intestines, blood vessels, and respiratory passageways.

Cardiac Muscle

• Cardiac muscle is also known as myocardium or heart muscle.
• It is made up of cells joined by intercalated discs, which are capable of fast impulse transmission.
• Cardiac muscle contracts and relaxes automatically without conscious control, pumping blood at a rate of 60-100 times per minute.

Skeletal Muscle

• Skeletal muscle consists of muscle cells (fibers) that are grouped together in bundles called fascicles.
• Muscle cells are called myocytes, and muscle fibers are composed of myofibrils, which are made up of sarcomeres linked in series.
• The sarcomere is the functional unit of the muscle where contraction occurs.
• Actin and myosin are the force-generating proteins of the sarcomere that work together to produce movement.

Properties of Muscles

• Contractility: the ability to contract or get shorter.
• Excitability: responsiveness to stimuli.
• Conductivity: the ability to conduct electrical charge.
• Extensibility: the ability to stretch without rupture.
• Elasticity: the ability to return to their original shape after contraction or extension.

Muscle Contraction

• Muscle contraction involves the sliding of actin past myosin, generating muscle tension.
• Myosin pulls on actin to shorten the sarcomere, producing movement.

Types of Muscle Contraction

• Muscle tone: a state of partial contraction responsible for posture.
• Isotonic contractions: the tone of the muscle remains the same, but the muscle gets shorter in length.
• Isometric contractions: the tone of the muscle increases, but the length of the muscle stays the same.

Effects of Exercise on Muscles

• Increased capillaries in muscles, increased protein filaments, and increased glycogen storage.
• Muscle hypertrophy: increased muscle size and strength.
• Vasodilation: increased blood flow and decreased resistance, leading to a drop in blood pressure.
• Strengthening of the heart and improvement in respiration.

Action of Muscles

• Prime mover or agonist: provides most force for a given muscle action.
• Antagonist: has opposite action of agonist, producing the opposite movement.
• Synergist: muscles that aid agonists or prime movers, helping to stabilize joints.
• Fixator: specialized synergist that helps to fix the position of the bone being moved.

Muscles of the Body

• Muscles of the head produce facial expressions, speech, and chewing.
• Muscles of the neck, such as the sternocleidomastoid and trapezius, are important for flexing and turning the head.
• Muscles of the upper extremities, such as the latissimus dorsi, pectoralis major, and deltoid, are involved in movements of the arm and shoulder.
• Muscles of the forearm and hand, such as the biceps brachii and triceps brachii, are involved in flexion and extension of the forearm.
• Muscles of the trunk, such as the intercostal muscles and diaphragm, are involved in respiration.
• Muscles of the abdomen and pelvis, such as the rectus abdominis and external oblique, are involved in compressing the abdomen and bending the vertebral column.
• Muscles of the lower extremities, such as the gluteus maximus and quadriceps femoris, are involved in movements of the thigh and leg.

Muscular Disorders

• Atrophy: wasting or decrease in size brought about by lack of use.
• Spasm: sudden, painful, involuntary muscle contraction.
• Strains: muscle injury caused by overuse or overstretching.
• Sprains: more severe than strains, involving twisting of a joint with partial rupture to the muscle and tendon.

Effects of Aging on Muscles

• Decrease in size and strength of all muscles.
• Decrease in skeletal muscle size, strength, and endurance.
• Decrease in skeletal muscle elasticity and flexibility.
• Decrease in exercise tolerance and ability to recover from muscle injury.

Other Muscle-Related Concepts

• Oxygen debt: the inability to deliver enough oxygen to the muscles during strenuous exercise, leading to muscle fatigue.
• Sphincter: a muscular ring that tightly regulates an opening, such as the urethral sphincter, anal sphincter, or pyloric sphincter.
• All or none: the principle that a muscle is either fully stimulated to contract or not at all.

Muscle Types and Characteristics

• Smooth muscle fibers contract in a wave-like manner (peristalsis) and respond to nerve impulses, hormonal stimulation, and stretching.

• They contract slowly and can remain contracted for long periods, relaxing slowly.

• Smooth muscles make up the walls of hollow organs, such as the stomach, esophagus, and blood vessels.

• Cardiac muscle (myocardium) is composed of cells joined by intercalated discs, allowing for fast impulse transmission and simultaneous contraction.

• It contracts and relaxes automatically without conscious control, typically 60-100 times per minute.

• Skeletal muscle consists of muscle cells (fibers) bundled into fascicles, surrounded by perimysium and epimysium.

• Muscle cells are called myocytes, and muscle fibers are composed of myofibrils, which are made up of sarcomeres linked in series.

Muscle Contraction and Relaxation

• Muscle contraction involves the sliding of actin past myosin, generating muscle tension.
• Myosin pulls on actin to shorten the sarcomere, resulting in muscle contraction.
• The nervous system stimulates skeletal muscle contraction, which is usually fast and relaxes quickly.

Muscle Properties

• Contractility: the ability to contract or get shorter.
• Excitability: responsiveness to stimuli.
• Conductivity: the ability to conduct electrical charge.
• Extensibility: the ability to stretch without rupture.
• Elasticity: the ability to return to original shape after contraction or extension.

Muscle Structure and Function

• Motor nerves carry signals to muscles to facilitate movement and function.
• The neuromuscular junction is the point at which a motor nerve meets a muscle cell.
• An axon or nerve fiber meets the muscle fiber, releasing acetylcholine (a neurotransmitter) across the synapse, causing muscle contraction.

Muscle Contraction Types

• Muscle tone: a state of partial contraction responsible for maintaining posture.
• Isotonic contractions: muscle tone remains the same, but the muscle shortens in length.
• Isometric contractions: muscle tone increases, but muscle length remains the same.

Effects of Exercise on Muscles

• Increased capillaries, protein filaments, and glycogen storage in muscles.
• Muscle hypertrophy (size and strength increase).
• Vasodilation and increased blood flow, leading to decreased blood pressure.
• Strengthening of the heart and increased blood circulation to the lungs.

Muscle Actions and Functions

• Prime mover (agonist): provides the most force for a given muscle action.
• Antagonist: has the opposite action of the agonist.
• Synergist: muscles that aid the agonist by stabilizing joints.
• Fixator: specialized synergist that helps to fix the position of the bone being moved.

Muscles of the Body

• Muscles of the head: produce facial expressions, speech, and chewing.
• Muscles of the neck: flex and turn the head.
• Muscles of the upper extremities: adduct, rotate, and flex the arm.
• Muscles of the trunk: support respiration, flex and rotate the vertebral column.
• Muscles of the lower extremities: flex, rotate, and extend the leg.

Muscle Disorders and Aging

• Atrophy: wasting or decrease in muscle size due to lack of use.
• Spasm: sudden, painful, involuntary muscle contraction.
• Strains: muscle injury caused by overuse or overstretching.
• Sprains: twisting of a joint with partial rupture of the muscle and tendon.
• Effects of aging on muscles: decreased size, strength, and endurance, with reduced flexibility and exercise tolerance.

Learn about the characteristics and functions of smooth muscle fibers and cardiac muscle, including their contraction mechanisms and locations in the body.