Muscular System

Key Terms and Structures

The muscular system is composed of specialized cells and structures that enable movement and force generation in the body. Understanding the terminology is essential for mastering muscle physiology.

• Troponin: A protein complex involved in muscle contraction by regulating the interaction of actin and myosin.

• Tropomyosin: A protein that blocks myosin binding sites on actin molecules in resting muscle.

• Actin: A thin filament protein that forms the backbone of the muscle fiber's contractile apparatus.

• Myosin: A thick filament protein with heads that bind to actin, enabling contraction.

• Myofibril: Cylindrical organelles within muscle cells, composed of repeating sarcomeres.

• Myofilament: The filaments of myofibrils, including actin (thin) and myosin (thick).

• Sarcomere: The functional unit of muscle contraction, defined by Z-lines.

• Sarcolemma: The cell membrane of a muscle fiber.

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

• Myoglobin: An oxygen-binding protein in muscle tissue.

• Endomysium: Connective tissue surrounding individual muscle fibers.

• Perimysium: Connective tissue surrounding bundles of muscle fibers (fascicles).

• Lactic Acid: A byproduct of anaerobic metabolism in muscle cells.

• Agonist (Prime Mover): The main muscle responsible for a specific movement.

• Synergist: Muscles that assist the agonist in performing its action.

• Antagonist: Muscles that oppose the action of the agonist.

Role of Acetylcholine, Ca2+, and ATP in Muscle Contraction

Muscle contraction is a complex process involving several key molecules:

• Acetylcholine (ACh): A neurotransmitter released at the neuromuscular junction, triggering muscle fiber depolarization.

• Calcium ions (Ca2+): Released from the sarcoplasmic reticulum, Ca2+ binds to troponin, causing tropomyosin to move and expose binding sites on actin.

• ATP: Provides energy for myosin head movement and detachment from actin.

Equation:

Acetylcholinesterase

Acetylcholinesterase is an enzyme that breaks down acetylcholine in the synaptic cleft, terminating the signal for muscle contraction.

Types of Muscle Contraction

• Isometric Contraction: Muscle tension increases, but length remains the same (no movement).

• Isotonic Contraction: Muscle changes length (shortens or lengthens) while tension remains constant, resulting in movement.

Levers in the Musculoskeletal System

The body uses bones and muscles as levers to facilitate movement. Levers are classified based on the relative positions of the fulcrum, effort, and load.

• First-class lever: Fulcrum between effort and load (e.g., neck muscles).

• Second-class lever: Load between fulcrum and effort (e.g., standing on tiptoe).

• Third-class lever: Effort between fulcrum and load (e.g., biceps curl).

Effect of Resistance Exercise on Muscle Tissue

• Increases muscle fiber size (hypertrophy).

• Enhances strength and endurance.

• Promotes metabolic adaptations.

Functions of the Muscular System

• Movement of the body and its parts.

• Maintenance of posture.

• Heat production.

• Stabilization of joints.

Properties of Muscle Tissue

• Excitability: Ability to respond to stimuli.

• Contractility: Ability to shorten forcibly.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to return to original length.

Types of Muscle Tissue

Classification of Muscles

• By location (skeletal, cardiac, smooth)

• By function (agonist, antagonist, synergist)

• By shape and arrangement (fusiform, pennate, etc.)

Nervous System

Functions of the Nervous System

The nervous system coordinates body activities by transmitting signals between different parts of the body.

• Sensory input

• Integration of information

• Motor output

Central vs. Autonomic Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for processing and integrating information.

• Autonomic Nervous System (ANS): Controls involuntary functions (e.g., heart rate, digestion); subdivided into sympathetic and parasympathetic divisions.

Neurotransmitters and Related Disorders

• Dopamine: Involved in reward, motivation, and motor control.

• Serotonin: Regulates mood, appetite, and sleep.

• Norepinephrine: Influences alertness and arousal.

• Endorphins: Natural painkillers.

• Glutamate: Main excitatory neurotransmitter.

• GABA: Main inhibitory neurotransmitter.

• Parkinson's Disease: Associated with dopamine deficiency.

• Multiple Sclerosis: Autoimmune disorder causing demyelination in the CNS.

• Blood-brain barrier: Selective barrier protecting the brain from harmful substances.

Neuroglia

• Astrocytes: Support neurons, maintain blood-brain barrier.

• Oligodendrocytes: Form myelin sheath in CNS.

• Microglia: Act as immune cells in CNS.

• Schwann cells: Form myelin sheath in PNS.

• Ependymal cells: Line ventricles, produce cerebrospinal fluid.

Bipolar Neurons

• Found in sensory organs (e.g., retina, olfactory epithelium).

• Have one axon and one dendrite.

Peripheral Nerve Stimulation

• The "funny bone" sensation is due to stimulation of the ulnar nerve.

Neural Pathway Sequence

• Effector

• Receptor

• Afferent neuron

• Integration center

• Efferent neuron

Correct order: Receptor → Afferent neuron → Integration center → Efferent neuron → Effector

Essay Topics (Expanded Context)

• Neuromuscular Junction Illustration: Steps include release of acetylcholine, depolarization of muscle fiber, calcium release, actin-myosin interaction, and contraction. Label synaptic cleft, motor end plate, and sarcolemma.

• Multiple Sclerosis: Destruction of myelin sheath disrupts nerve signal transmission, leading to symptoms such as muscle weakness, coordination problems, and sensory disturbances.

• GABA and Alcohol: GABA inhibits neural activity; alcohol enhances GABA's effect, leading to sedation. Chronic alcohol use disrupts normal GABA function, affecting cognition and motor control.

Additional info: Some definitions and explanations have been expanded for clarity and completeness.