Muscular System

Types and Characteristics of Muscle Tissue

The human body contains three main types of muscle tissue, each with distinct structural and functional properties.

• Skeletal Muscle: Voluntary, striated, attached to bones, responsible for body movement.

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

• Smooth Muscle: Involuntary, non-striated, found in walls of hollow organs (e.g., intestines, blood vessels), controls movement of substances within these organs.

Key Functions: Movement, posture maintenance, joint stabilization, and heat generation.

Muscle Attachments and Connective Tissue Sheaths

Muscles attach to bones via tendons and aponeuroses. Connective tissue sheaths organize and protect muscle fibers:

• Epimysium: Surrounds entire muscle.

• Perimysium: Surrounds bundles of muscle fibers (fascicles).

• Endomysium: Surrounds individual muscle fibers.

Example: The biceps brachii is enveloped by epimysium, with fascicles wrapped in perimysium and each fiber in endomysium.

Anatomy of a Muscle Fiber

Muscle fibers are specialized cells with unique structures for contraction.

• Sarcolemma: Plasma membrane of muscle fiber.

• Sarcoplasm: Cytoplasm containing myofibrils, mitochondria, and glycogen.

• Myofibrils: Contractile elements composed of sarcomeres.

Neuromuscular Junction and Muscle Stimulation

The neuromuscular junction is the site where a motor neuron stimulates a muscle fiber.

• Motor Neuron: Releases neurotransmitter acetylcholine (ACh).

• Action: ACh binds to receptors on sarcolemma, initiating muscle contraction.

Sliding Filament Theory of Contraction

Muscle contraction occurs when actin and myosin filaments slide past each other.

• Steps: Calcium ions bind to troponin, exposing binding sites on actin. Myosin heads attach and pull actin filaments inward.

• Equation:

Energy for Muscle Contraction

Muscle contraction requires ATP, produced by cellular respiration in mitochondria.

• Sources: Creatine phosphate, anaerobic glycolysis, aerobic respiration.

• Example: During intense exercise, muscles rely on anaerobic glycolysis, leading to lactic acid buildup.

Muscle Fatigue and Soreness

Fatigue occurs when muscles cannot maintain contraction due to lack of ATP or accumulation of metabolic byproducts.

• Causes: Oxygen deficit, lactic acid accumulation, ionic imbalances.

• Soreness: Microtears in muscle fibers and inflammation.

Motor Units and Muscle Tone

A motor unit consists of a motor neuron and all the muscle fibers it innervates.

• Muscle Tone: Continuous, passive partial contraction of muscles.

• Tetany: Sustained muscle contraction due to rapid stimulation.

Muscular System Disorders

Common disorders affecting the muscular system include:

• Fibrillation: Rapid, irregular muscle contractions.

• Muscular Dystrophy: Genetic disorder causing progressive muscle weakness.

• Myalgia: Muscle pain.

• Myasthenia Gravis: Autoimmune disorder causing muscle weakness.

• Myoma: Muscle tumor.

Nervous System

Functions and Divisions of the Nervous System

The nervous system coordinates body activities through electrical and chemical signals.

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Nerves outside the CNS.

Neuroglia and Neurons

Neuroglia support and protect neurons. Neurons transmit electrical impulses.

• Types of Neuroglia: Astrocytes, oligodendrocytes, microglia, ependymal cells (CNS); Schwann cells, satellite cells (PNS).

• Neuron Structure: Cell body, dendrites, axon.

• Myelin: Insulating layer that increases impulse speed.

Neuron Classification

Neurons are classified by shape and function.

• Shape: Unipolar, bipolar, multipolar.

• Function: Sensory (afferent), interneuron, motor (efferent).

Action Potential and Synapses

Action potentials are rapid changes in membrane potential that transmit signals along neurons.

• Depolarization: Na+ influx.

• Repolarization: K+ efflux.

• Hyperpolarization: Excess K+ outflow.

• Equation:

• Synapse: Junction between neurons; can be electrical or chemical.

Neurotransmitters

Neurotransmitters are chemicals that transmit signals across synapses.

• Excitatory: Glutamate, acetylcholine.

• Inhibitory: GABA, glycine.

• Neuropeptides: Enkephalins, endorphins (modulate pain and mood).

Central Nervous System (CNS)

Regions and Organization

The CNS consists of the brain and spinal cord, organized into white and gray matter.

• White Matter: Myelinated axons.

• Gray Matter: Neuron cell bodies and unmyelinated fibers.

Brain Anatomy and Functions

The brain is divided into several regions, each with specialized functions.

• Cerebrum: Higher cognitive functions, motor and sensory areas.

• Diencephalon: Thalamus, hypothalamus, epithalamus; regulates sensory input, hormones, and homeostasis.

• Brain Stem: Midbrain, pons, medulla oblongata; controls vital functions.

• Cerebellum: Coordinates movement and balance.

Ventricles and Meninges

The brain contains four ventricles filled with cerebrospinal fluid (CSF), protected by three meninges.

• Meninges: Dura mater, arachnoid mater, pia mater.

• CSF: Cushions brain, circulates nutrients, removes waste.

Neuronal Pathways and Homeostasis

Neuronal pathways transmit signals within the CNS, maintaining homeostasis.

• Ascending Pathways: Carry sensory information to the brain.

• Descending Pathways: Transmit motor commands from the brain.

• Types of Neurons: Sensory, motor, interneurons.

Homeostatic Imbalances

Imbalances in the nervous system can lead to disorders such as stroke, multiple sclerosis, and spinal cord injury.

• Example: Disruption of CSF flow can cause hydrocephalus.

Additional info: Some explanations and examples have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.