Muscle Tissue and Function

Types and Functions of Muscle

Muscle tissue is specialized for contraction and is essential for movement, posture, and various bodily functions. There are three main types of muscle tissue: skeletal, cardiac, and smooth.

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

• 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.

Key Functions:

• Movement of the body and its parts

• Maintenance of posture

• Stabilization of joints

• Heat production

Structural Organization: Muscle tissue is organized into bundles:

• Epimysium: Surrounds the entire muscle

• Perimysium: Surrounds bundles of muscle fibers (fascicles)

• Endomysium: Surrounds individual muscle fibers

Muscle Anatomy and Attachment

• Muscles attach to bones via tendons.

• Muscle contraction pulls on tendons, moving bones at joints.

• Muscle origin: attachment to stationary bone; insertion: attachment to movable bone.

Microscopic Structure of Skeletal Muscle

• Muscle Fiber: Single muscle cell, multinucleated, contains myofibrils.

• Myofibrils: Composed of repeating units called sarcomeres, the functional unit of contraction.

• Sarcomere: Contains thick (myosin) and thin (actin) filaments.

• Sarcolemma: Plasma membrane of muscle fiber.

• Sarcoplasmic Reticulum: Stores calcium ions necessary for contraction.

• Neuromuscular Junction: Site where motor neuron communicates with muscle fiber.

Muscle Contraction and Control

• Initiated by nerve impulses at the neuromuscular junction.

• Calcium release triggers interaction between actin and myosin, causing contraction.

• ATP is required for both contraction and relaxation.

Muscle Fiber Types

• Slow-twitch (Type I): Fatigue-resistant, used for endurance.

• Fast-twitch (Type II): Fatigue quickly, used for rapid, powerful movements.

Muscle Organization and Movement

• Muscles work in groups: agonists (prime movers), antagonists (oppose movement), synergists (assist movement), and fixators (stabilize origin).

• Muscle actions include flexion, extension, abduction, adduction, rotation, and circumduction.

Axial and Appendicular Muscles

Axial Muscles

Axial muscles support and move the head, neck, and trunk, and protect internal organs.

• Include muscles of the head, neck, vertebral column, and thoracic cage.

• Examples: sternocleidomastoid, erector spinae, intercostals, diaphragm.

Appendicular Muscles

Appendicular muscles move the limbs and stabilize the pectoral and pelvic girdles.

• Include muscles of the shoulder, arm, forearm, hand, hip, thigh, leg, and foot.

• Examples: deltoid, biceps brachii, triceps brachii, gluteus maximus, quadriceps femoris.

Surface Anatomy and Regional Approach

Surface Anatomy

Surface anatomy involves identifying landmarks on the body to locate underlying structures.

• Important for physical examination and clinical assessment.

• Examples: clavicle, scapula, iliac crest, patella.

Regional Anatomy

• Divides the body into regions (e.g., head, neck, thorax, abdomen, limbs) for study.

• Helps in understanding relationships between structures in a specific area.

Nervous System Structure and Function

Overview of the Nervous System

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

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

• Peripheral Nervous System (PNS): Nerves outside CNS; transmits signals to and from CNS.

Neurons and Neuroglia

• Neuron: Functional unit of the nervous system; transmits electrical impulses.

• Neuroglia: Support and protect neurons; include astrocytes, oligodendrocytes, Schwann cells, microglia.

Structure of a Neuron

• Cell body (soma): Contains nucleus and organelles.

• Dendrites: Receive signals from other neurons.

• Axon: Transmits impulses away from cell body.

• Myelin sheath: Insulates axon, increases speed of impulse transmission.

Synaptic Transmission

• Neurons communicate at synapses via neurotransmitters.

• Presynaptic neuron releases neurotransmitter into synaptic cleft; postsynaptic neuron receives signal.

Resting and Action Potentials

• Resting potential: Difference in electrical charge across the neuron's membrane at rest (typically -70 mV).

• Action potential: Rapid change in membrane potential that travels along the axon.

Key Equation:

where is the membrane potential, is the potential inside the cell, and is the potential outside the cell.

Neurotransmitters

• Chemical messengers that transmit signals across synapses.

• Examples: acetylcholine, dopamine, serotonin, norepinephrine.

Reflexes and Reflex Arcs

• Reflex: Rapid, involuntary response to a stimulus.

• Reflex arc: Neural pathway involved in a reflex; includes receptor, sensory neuron, integration center, motor neuron, and effector.

Organization of Nerves and Connective Tissue Layers

Connective Tissue Layers of Nerves

• Endoneurium: Surrounds individual nerve fibers.

• Perineurium: Surrounds bundles of nerve fibers (fascicles).

• Epineurium: Surrounds the entire nerve.

Spinal Cord and Spinal Nerves

• Spinal nerves emerge from the spinal cord and branch to supply the body.

• Each spinal nerve has dorsal (sensory) and ventral (motor) roots.

Summary Table: Muscle and Nerve Connective Tissue Layers

Additional Key Points

• Recall the order of connective tissue layers from smallest to largest for both muscle and nerve.

• Understand the clinical significance of surface anatomy and regional anatomy in assessment and diagnosis.

• Be able to identify major muscles and nerves on diagrams or models.

• Recognize the importance of hydration, exercise, and rest for optimal muscle and nerve function.

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