MUSCLE

Muscles

Anatomy of a Muscle

• A muscle is a soft tissue that is attached to bones and helps in movement of the body.
• It is a long, cylindrical, and multinucleated structure.
• The muscle is composed of muscle fibers which are the building blocks of muscles.
• A muscle fiber is a long, cylindrical cell that is the basic unit of muscle tissue.
• Each muscle fiber has many nuclei and is bound by a membrane called the sarcolemma.

Structure of a Muscle

• A muscle is composed of three main parts: the epimysium, the perimysium, and the endomysium.
• The epimysium is the outermost layer of the muscle and is composed of dense connective tissue.
• The perimysium is the layer of connective tissue that surrounds a bundle of muscle fibers.
• The endomysium is the layer of connective tissue that surrounds each individual muscle fiber.

Types of Muscles

• Skeletal muscles are attached to bones and are responsible for voluntary movements.
• Smooth muscles are found in the walls of hollow organs such as the digestive tract, blood vessels, and airways.
• Cardiac muscles are found in the heart and are responsible for pumping blood throughout the body.

Action of a Muscle

• When a muscle contracts, the sarcomeres within the muscle fibers shorten.
• The contraction of the muscle fibers results in the movement of the bones to which the muscle is attached.
• The action of a muscle can be described as follows:
  1. Muscle contraction → sarcomere shortening → muscle fiber shortening → muscle shortening → bone movement.

Blood Supply to a Muscle

• The blood supply to a muscle is provided by the arteries that branch off from the aorta.
• The arteries then branch into smaller arterioles and finally into capillaries where the exchange of oxygen and nutrients takes place.
• The venous blood from the muscle is collected in the venules and then passes into the veins.

Lymph Drainage from a Muscle

• The lymph drainage from a muscle is through the lymphatic vessels that collect the lymph from the capillaries.
• The lymph is then passed into the lymph nodes where it is filtered and cleansed.
• The filtered lymph then passes into the lymphatic ducts and eventually into the bloodstream.

Nerve Supply to a Muscle

• The nerve supply to a muscle is provided by the motor nerves that branch off from the spinal cord.
• The motor nerves then branch into smaller nerve fibers that innervate the muscle fibers.
• The contraction of the muscle is initiated by the release of neurotransmitters from the nerve terminals.

Development of a Muscle

• The development of a muscle occurs through the process of myogenesis.
• Myogenesis is the process by which the mesenchymal cells differentiate into muscle fibers.
• The muscle fibers then aggregate to form a muscle.
• The development of a muscle is as follows:
  1. Mesenchymal cells → myoblasts → myotubes → muscle fibers → muscle.

Muscle Fibers

• A muscle fiber is a long, cylindrical cell that is the basic unit of muscle tissue.
• Each muscle fiber has many nuclei and is bound by a membrane called the sarcolemma.
• The muscle fiber is composed of many myofibrils that are the contractile units of the muscle.
• The myofibrils are made up of actin and myosin filaments that slide past each other to produce muscle contraction.

Myofibrils

• A myofibril is the contractile unit of a muscle fiber.
• The myofibril is composed of many sarcomeres that are the functional units of the muscle.
• The sarcomeres are made up of actin and myosin filaments that slide past each other to produce muscle contraction.
• The myofibrils are arranged in a parallel fashion to each other to produce the maximum amount of force.

Sarcomere

• A sarcomere is the functional unit of a muscle fiber.
• The sarcomere is composed of actin and myosin filaments that slide past each other to produce muscle contraction.
• The actin filaments are attached to the Z-disks and the myosin filaments are attached to the M-line.
• The contraction of the sarcomere is initiated by the release of calcium ions from the sarcoplasmic reticulum.

Muscle Contraction

• Muscle contraction is initiated by the release of calcium ions from the sarcoplasmic reticulum.
• The calcium ions then bind to the troponin-tropomyosin complex to expose the myosin binding site.
• The myosin heads then bind to the actin filaments and undergo a power stroke to produce muscle contraction.
• The contraction of the muscle is as follows:
  1. Calcium ion release → troponin-tropomyosin complex binding → myosin binding site exposed → myosin heads bind to actin → power stroke → muscle contraction.

Muscle Relaxation

• Muscle relaxation is initiated by the removal of calcium ions from the sarcoplasmic reticulum.
• The calcium ions then bind to the troponin-tropomyosin complex to cover the myosin binding site.
• The myosin heads then detach from the actin filaments to produce muscle relaxation.
• The relaxation of the muscle is as follows:
  1. Calcium ion removal → troponin-tropomyosin complex binding → myosin binding site covered → myosin heads detach from actin → muscle relaxation.

Muscle Tone

• Muscle tone is the continuous contraction of the muscle that is necessary for posture and movement.
• The muscle tone is maintained by the continuous contraction and relaxation of the muscle fibers.
• The muscle tone is regulated by the nervous system through the release of neurotransmitters.

Muscle Fatigue

• Muscle fatigue is the decrease in the ability of the muscle to contract over time.
• The muscle fatigue is caused by the accumulation of metabolic byproducts such as lactic acid and the depletion of energy stores.
• The muscle fatigue is regulated by the nervous system through the release of neurotransmitters.

Muscle Atrophy

• Muscle atrophy is the wasting away of the muscle due to disuse or disease.
• The muscle atrophy is caused by the loss of muscle fibers and the decrease in muscle protein synthesis.
• The muscle atrophy is regulated by the nervous system through the release of neurotransmitters.

Muscle Hypertrophy

• Muscle hypertrophy is the increase in the size of the muscle due to exercise or injury.
• The muscle hypertrophy is caused by the increase in muscle protein synthesis and the accumulation of muscle fibers.
• The muscle hypertrophy is regulated by the nervous system through the release of neurotransmitters.

Muscle Spasm

• Muscle spasm is the involuntary contraction of the muscle that can be caused by injury or disease.
• The muscle spasm is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle spasm is regulated by the nervous system through the release of neurotransmitters.

Muscle Strain

• Muscle strain is the injury to the muscle that can be caused by overuse or trauma.
• The muscle strain is caused by the tearing of muscle fibers and the disruption of normal muscle function.
• The muscle strain is regulated by the nervous system through the release of neurotransmitters.

Muscle Cramp

• Muscle cramp is the involuntary contraction of the muscle that can be caused by electrolyte imbalance or muscle fatigue.
• The muscle cramp is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle cramp is regulated by the nervous system through the release of neurotransmitters.

Muscle Spasticity

• Muscle spasticity is the increased muscle tone that can be caused by injury or disease.
• The muscle spasticity is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle spasticity is regulated by the nervous system through the release of neurotransmitters.

Muscle Weakness

• Muscle weakness is the decrease in the ability of the muscle to contract.
• The muscle weakness is caused by the disruption of normal muscle function and the decrease in muscle protein synthesis.
• The muscle weakness is regulated by the nervous system through the release of neurotransmitters.

Muscle Pain

• Muscle pain is the sensation of pain that can be caused by injury or disease.
• The muscle pain is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle pain is regulated by the nervous system through the release of neurotransmitters.

Muscle Injury

• Muscle injury is the damage to the muscle that can be caused by trauma or overuse.
• The muscle injury is caused by the tearing of muscle fibers and the disruption of normal muscle function.
• The muscle injury is regulated by the nervous system through the release of neurotransmitters.

Muscle Repair

• Muscle repair is the process of repairing damaged muscle tissue.
• The muscle repair is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle repair is regulated by the nervous system through the release of neurotransmitters.

Muscle Regeneration

• Muscle regeneration is the process of regenerating new muscle tissue.
• The muscle regeneration is caused by the proliferation of satellite cells and the release of growth factors.
• The muscle regeneration is regulated by the nervous system through the release of neurotransmitters.

Muscle Remodeling

• Muscle remodeling is the process of changing the shape and size of the muscle.
• The muscle remodeling is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle remodeling is regulated by the nervous system through the release of neurotransmitters.

Muscle Plasticity

• Muscle plasticity is the ability of the muscle to adapt to changing demands.
• The muscle plasticity is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle plasticity is regulated by the nervous system through the release of neurotransmitters.

Muscle Adaptation

• Muscle adaptation is the process of adapting to changing demands.
• The muscle adaptation is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle adaptation is regulated by the nervous system through the release of neurotransmitters.

Muscle Sarcopenia

• Muscle sarcopenia is the loss of muscle mass and strength that occurs with aging.
• The muscle sarcopenia is caused by the decrease in muscle protein synthesis and the increase in muscle protein breakdown.
• The muscle sarcopenia is regulated by the nervous system through the release of neurotransmitters.

Muscle Wasting

• Muscle wasting is the loss of muscle mass and strength that can be caused by disease or injury.
• The muscle wasting is caused by the decrease in muscle protein synthesis and the increase in muscle protein breakdown.
• The muscle wasting is regulated by the nervous system through the release of neurotransmitters.

Muscle Hypertrophy

• Muscle hypertrophy is the increase in muscle size and strength that can be caused by exercise.
• The muscle hypertrophy is caused by the increase in muscle protein synthesis and the accumulation of muscle fibers.
• The muscle hypertrophy is regulated by the nervous system through the release of neurotransmitters.

Muscle Atrophy

• Muscle atrophy is the wasting away of the muscle that can be caused by disuse or disease.
• The muscle atrophy is caused by the loss of muscle fibers and the decrease in muscle protein synthesis.
• The muscle atrophy is regulated by the nervous system through the release of neurotransmitters.

Muscle Spasticity

• Muscle spasticity is the increased muscle tone that can be caused by injury or disease.
• The muscle spasticity is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle spasticity is regulated by the nervous system through the release of neurotransmitters.

Muscle Weakness

• Muscle weakness is the decrease in the ability of the muscle to contract.
• The muscle weakness is caused by the disruption of normal muscle function and the decrease in muscle protein synthesis.
• The muscle weakness is regulated by the nervous system through the release of neurotransmitters.

Muscle Pain

• Muscle pain is the sensation of pain that can be caused by injury or disease.
• The muscle pain is caused by the abnormal release of neurotransmitters and the disruption of normal muscle function.
• The muscle pain is regulated by the nervous system through the release of neurotransmitters.

Muscle Injury

• Muscle injury is the damage to the muscle that can be caused by trauma or overuse.
• The muscle injury is caused by the tearing of muscle fibers and the disruption of normal muscle function.
• The muscle injury is regulated by the nervous system through the release of neurotransmitters.

Muscle Repair

• Muscle repair is the process of repairing damaged muscle tissue.
• The muscle repair is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle repair is regulated by the nervous system through the release of neurotransmitters.

Muscle Regeneration

• Muscle regeneration is the process of regenerating new muscle tissue.
• The muscle regeneration is caused by the proliferation of satellite cells and the release of growth factors.
• The muscle regeneration is regulated by the nervous system through the release of neurotransmitters.

Muscle Remodeling

• Muscle remodeling is the process of changing the shape and size of the muscle.
• The muscle remodeling is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle remodeling is regulated by the nervous system through the release of neurotransmitters.

Muscle Plasticity

• Muscle plasticity is the ability of the muscle to adapt to changing demands.
• The muscle plasticity is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle plasticity is regulated by the nervous system through the release of neurotransmitters.

Muscle Adaptation

• Muscle adaptation is the process of adapting to changing demands.
• The muscle adaptation is caused by the release of growth factors and the proliferation of satellite cells.
• The muscle adaptation is regulated by the nervous system through the release of neurotransmitters.

1. Classification of Muscle Tissue

   • Skeletal muscle
   • Smooth muscle
   • Cardiac muscle

2. Microscopic Structure of Skeletal Muscle

   • Longitudinal Section (LS)
     • Fibers are multinucleated, cylindrical, and aligned in a parallel fashion
     • Each fiber is surrounded by a thin layer of connective tissue called endomysium
     • Fibers are further grouped into fascicles, which are surrounded by perimysium
     • Fascicles then form muscles, which are surrounded by epimysium
   • Transverse Section (TS)
     • Fibers appear as circular profiles
     • Each fiber is surrounded by a thin layer of connective tissue called endomysium
     • Fibers are further grouped into fascicles, which are surrounded by perimysium
     • Fascicles then form muscles, which are surrounded by epimysium

3. Microscopic Structure of Smooth Muscle

   • LS and TS
     • Fibers are spindle-shaped, uninucleated, and arranged in a wavy or helical pattern
     • Each fiber is surrounded by a thin layer of connective tissue called endomysium
     • Fibers are further grouped into bundles, which are surrounded by perimysium
     • Bundles then form layers, which are surrounded by a thin layer of connective tissue called adventitia

4. Microscopic Structure of Cardiac Muscle

   • LS and TS
     • Fibers are branched, multinucleated, and arranged in a branching pattern
     • Each fiber is surrounded by a thin layer of connective tissue called endomysium
     • Fibers are further grouped into fascicles, which are surrounded by perimysium
     • Fascicles then form layers, which are surrounded by a thin layer of connective tissue called adventitia

Muscle Action Sequence

Muscle action involves the following steps:

1 → Shortening of muscle fibers 2 → Contraction of the sarcomere 3 → Shortening of the sarcomere 4 → Lengthening of the muscle fiber

Muscle Contraction

Muscle contraction involves the following steps:

1 → Initiation of action potential at the neuromuscular junction 2 → Propagation of action potential along the muscle fiber 3 → Excitation-contraction coupling 4 → Contraction of the sarcomere

Muscle Relaxation

Muscle relaxation involves the following steps:

1 → Termination of action potential 2 → Relaxation of the sarcomere 3 → Lengthening of the muscle fiber

Muscle Tension

Muscle tension is generated by the following steps:

1 → Contraction of the sarcomere 2 → Shortening of the sarcomere 3 → Generation of tension in the muscle fiber

Muscle Length

Muscle length is determined by the following steps:

1 → Lengthening of the sarcomere 2 → Relaxation of the sarcomere 3 → Lengthening of the muscle fiber