Chapter 9: The Muscular System

Types of Muscle Tissue

The human body contains three main types of muscle tissue, each with distinct characteristics and functions.

• Skeletal Muscle: Voluntary, striated muscle attached to bones; responsible for movement and posture.

• Cardiac Muscle: Involuntary, striated muscle found only in the heart; responsible for pumping blood.

• Smooth Muscle: Involuntary, non-striated muscle found in walls of hollow organs; controls movement of substances within these organs.

Example: Skeletal muscles such as the biceps brachii enable arm flexion, while cardiac muscle contracts rhythmically to circulate blood.

Voluntary Muscles

Voluntary muscles are those under conscious control, primarily skeletal muscles.

• Function: Enable movement, posture, and facial expressions.

• Control: Regulated by the somatic nervous system.

Muscle Structure

• Epimysium: Outer layer of connective tissue surrounding the entire muscle.

• Fascicle: Bundle of muscle fibers within the muscle.

• Sarcoplasmic Reticulum: Specialized endoplasmic reticulum that stores and releases calcium ions for muscle contraction.

• T Tubules: Invaginations of the sarcolemma that help transmit action potentials into the muscle fiber.

• A Band: Dark band containing thick (myosin) filaments.

• I Band: Light band containing thin (actin) filaments.

• Sarcomere: The functional unit of muscle contraction, defined as the region between two Z lines.

Additional info: The arrangement of A and I bands gives skeletal and cardiac muscle their striated appearance.

Neuromuscular Junction

The neuromuscular junction is the synapse between a motor neuron and a skeletal muscle fiber.

• Function: Transmits nerve impulses to muscle fibers, triggering contraction.

• Key Components: Axon terminal, synaptic cleft, motor end plate.

Myofilaments: Myosin and Actin

Myofilaments are the contractile proteins within muscle fibers.

• Myosin: Thick filament responsible for pulling actin during contraction.

• Actin: Thin filament that slides past myosin to shorten the sarcomere.

Sliding Filament Theory Equation:

Origin and Insertion

Muscles attach to bones at two points:

• Origin: The fixed attachment point.

• Insertion: The movable attachment point.

Example: The biceps brachii originates at the scapula and inserts on the radius.

Major Muscles: Location and Function

• Sternocleidomastoid: Neck muscle; rotates and flexes the head.

• Temporalis, Masseter, Frontalis: Muscles of the head; involved in chewing and facial expressions.

• Diaphragm: Main muscle of respiration; separates thoracic and abdominal cavities.

• Gastrocnemius, Soleus: Calf muscles; involved in plantar flexion of the foot.

• Hamstring Group: Posterior thigh muscles; flex the knee and extend the hip.

• Gluteus Maximus: Buttock muscle; extends and rotates the hip.

• Triceps Brachii: Posterior arm muscle; extends the elbow.

• Biceps Brachii: Anterior arm muscle; flexes the elbow.

• Brachioradialis, Brachialis: Forearm muscles; assist in elbow flexion.

• Latissimus Dorsi, Trapezius, Deltoid, Pectoralis Major: Muscles of the back, shoulder, and chest; responsible for various arm and trunk movements.

• Abdominal Wall Muscles: Support trunk movement and protect internal organs.

Chapter 10: Muscle Tissue and Muscle Physiology

Muscle Contraction Mechanism

Muscle contraction occurs through the interaction of actin and myosin filaments, regulated by calcium ions and ATP.

• Steps:

  1. Action potential arrives at neuromuscular junction.

  2. Calcium ions released from sarcoplasmic reticulum.

  3. Myosin binds to actin, forming cross-bridges.

  4. ATP hydrolysis powers the sliding of filaments.

  5. Muscle shortens (contracts).

Equation for ATP Hydrolysis:

Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Central and Peripheral Nervous System

The nervous system is divided into two main parts:

• Central Nervous System (CNS): Consists of the brain and spinal cord; processes and integrates information.

• Peripheral Nervous System (PNS): Includes all nerves outside the CNS; transmits signals between the CNS and the rest of the body.

Autonomic Nervous System: Subdivision of the PNS that controls involuntary functions (e.g., heart rate, digestion).

Neurons and Neuroglia

Neurons are the functional cells of the nervous system, while neuroglia support and protect neurons.

• Neurons: Transmit electrical impulses; consist of cell body, dendrites, and axon.

• Neuroglia: Provide structural support, nutrition, and insulation for neurons.

Example: Astrocytes (a type of neuroglia) maintain the blood-brain barrier.

Key Terms Table

Additional info: Students should review figures and tables in their textbook for visual understanding of muscle and nervous system anatomy.