Chapter 10: Muscle Tissue

Properties and Functions of Muscle Tissue

Muscle tissue is specialized for contraction and is essential for movement, posture, and heat production in the body. There are three main types: skeletal, cardiac, and smooth muscle.

• Properties of muscle tissue: Excitability, contractility, extensibility, and elasticity.

• Functions of skeletal muscle: Movement, posture maintenance, joint stabilization, and heat generation.

Types of Muscle Tissue

The three types of muscle tissue differ in structure, function, and location.

• Skeletal muscle: Voluntary, striated, attached to bones.

• Cardiac muscle: Involuntary, striated, found in the heart.

• Smooth muscle: Involuntary, non-striated, found in walls of hollow organs.

Development and Structure of Muscle Fibers

Muscle fibers develop from myoblasts during embryonic development and have specialized components for contraction.

• Myoblasts: Embryonic cells that fuse to form muscle fibers.

• Skeletal muscle fiber components: Sarcolemma, sarcoplasm, myofibrils, sarcoplasmic reticulum, T-tubules.

Sarcomere Structure and Contraction

The sarcomere is the functional unit of muscle contraction, composed of actin and myosin filaments.

• Sliding filament theory: Muscle contraction occurs as actin filaments slide over myosin filaments, shortening the sarcomere.

• Contraction cycle: Involves cross-bridge formation, power stroke, detachment, and reactivation.

Neuromuscular Junction and Action Potentials

The neuromuscular junction is the site where a motor neuron stimulates a muscle fiber, leading to contraction.

• Components: Synaptic terminal, synaptic cleft, motor end plate.

• Neurotransmitter: Acetylcholine (ACh) is released, binds to receptors, and initiates an action potential in the muscle fiber.

• Enzyme: Acetylcholinesterase breaks down ACh to terminate the signal.

Muscle Contraction Physiology

Muscle contraction is regulated by calcium ions, ATP, and the interaction of actin and myosin.

• Excitation-contraction coupling: The process linking the action potential to muscle contraction.

• Factors affecting contraction: Frequency of stimulation, number of fibers activated, muscle fiber length.

Muscle Tension and Motor Units

Muscle tension depends on the number of motor units recruited and the frequency of stimulation.

• Motor unit: A motor neuron and all the muscle fibers it innervates.

• Summation: Increased frequency of stimulation leads to greater tension.

• Complete tetanus: Maximum tension with no relaxation between stimuli.

Isotonic and Isometric Contractions

Muscle contractions can be classified based on whether the muscle changes length or not.

• Isotonic contraction: Muscle changes length (concentric: shortens, eccentric: lengthens).

• Isometric contraction: Muscle tension increases, but length remains the same.

Energy Sources for Muscle Contraction

Muscle fibers use ATP, creatine phosphate, and other metabolic pathways to generate energy for contraction.

• ATP: Immediate source of energy.

• Creatine phosphate: Rapidly regenerates ATP.

• Anaerobic glycolysis and aerobic respiration: Provide sustained energy.

Muscle Fatigue and Recovery

Fatigue occurs when muscles can no longer contract efficiently, and recovery involves metabolic processes.

• Causes of fatigue: Depletion of energy reserves, accumulation of lactic acid.

• Recovery period: Includes removal of lactate, replenishment of oxygen, and restoration of ATP.

Types of Skeletal Muscle Fibers

Skeletal muscle fibers are classified based on contraction speed and metabolic properties.

• Red fibers (slow-twitch): High endurance, aerobic metabolism.

• White fibers (fast-twitch): Rapid contraction, anaerobic metabolism.

• Intermediate fibers: Properties between red and white fibers.

Effects of Exercise, Hormones, and Aging

Exercise, hormones, and aging influence muscle structure and function.

• Aerobic exercise: Increases endurance, capillary supply.

• Anaerobic exercise: Increases muscle size and strength.

• Hormones: Influence muscle growth and metabolism.

• Aging: Leads to decreased muscle mass and strength.

Cardiac and Smooth Muscle

Cardiac and smooth muscle have unique structural and functional characteristics.

• Cardiac muscle: Intercalated discs, rhythmic contractions.

• Smooth muscle: Spindle-shaped cells, slow contractions.

• Comparison: Skeletal muscle is voluntary and striated; cardiac is involuntary and striated; smooth is involuntary and non-striated.

Chapter 11: The Muscular System

Muscle Organization and Classification

Muscles are organized based on fascicle arrangement, which affects their function and strength.

• Fascicle arrangements: Parallel, convergent, pennate, circular.

• Examples: Biceps brachii (parallel), deltoid (multipennate).

Levers and Bones

Bones act as levers, and muscles provide the force for movement.

• Lever classes: First-class, second-class, third-class.

• Mechanical advantage: Ratio of output force to input force.

• Examples: Neck (first-class), calf (second-class), biceps (third-class).

Origins, Insertions, and Actions

Muscle attachment sites determine movement and function.

• Origin: Fixed attachment.

• Insertion: Movable attachment.

• Action: Movement produced by muscle contraction.

Muscle Interactions

Muscles interact as agonists, antagonists, synergists, and fixators.

• Agonist: Prime mover.

• Antagonist: Opposes the agonist.

• Synergist: Assists the agonist.

• Fixator: Stabilizes origin.

Naming Muscles

Muscles are named based on location, shape, size, direction, number of origins, and action.

• Examples: Rectus abdominis (direction), deltoid (shape), biceps brachii (number of origins).

Chapter 12: Nervous Tissue

Functions and Organization of the Nervous System

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

• Functions: Sensory input, integration, motor output.

• Divisions: Central nervous system (CNS), peripheral nervous system (PNS).

• PNS subdivisions: Somatic, autonomic, enteric.

• Autonomic subdivisions: Sympathetic, parasympathetic.

Neurons and Neuroglia

Neurons are the functional units of the nervous system; neuroglia support and protect neurons.

• Neuron structure: Cell body, dendrites, axon.

• Types of neurons: Anaxonic, bipolar, unipolar, multipolar.

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

Action Potentials and Synaptic Transmission

Neurons communicate via action potentials and synapses.

• Resting potential: Difference in charge across the membrane; typically -70 mV.

• Action potential: Rapid change in membrane potential due to ion movement.

• Refractory period: Time during which a neuron cannot fire another action potential.

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

Neurotransmitters and Receptors

Neurotransmitters are chemicals that transmit signals across synapses.

• Types: Acetylcholine, biogenic amines, amino acids, neuropeptides.

• Receptors: Ionotropic (direct), metabotropic (indirect via second messengers).

Integration and Modulation

Neuronal integration involves summation and modulation of signals.

• Summation: Spatial and temporal summation of postsynaptic potentials.

• Inhibition vs. facilitation: Inhibition decreases likelihood of action potential; facilitation increases it.

• Presynaptic regulation: Axoaxonic synapses can modulate neurotransmitter release.

Selected Key Terms (Bonus Section)

Definitions of selected terms relevant to muscle and nervous tissue:

• Axoaxonic synapse: A synapse between the axon of one neuron and the axon of another.

• Axon terminal: The end of an axon where neurotransmitters are released.

• Cerebral blood flow: The blood supply to the brain, essential for neural function.

• Effector organ: An organ that responds to neural stimulation (e.g., muscle or gland).

• Excitable membrane: A membrane capable of generating action potentials.

• Extrinsic muscle: A muscle that originates outside the part it moves.

• Fascicle: A bundle of muscle fibers.

• Fusiform: Spindle-shaped muscle with parallel fibers.

• Gliosis: Proliferation of glial cells in response to injury.

• G-protein coupled receptor: A receptor that activates intracellular signaling via G-proteins.

• Hippocampus: A brain region involved in memory and learning.

• Lateral excursion: Side-to-side movement (e.g., jaw).

• Mechanical advantage: The efficiency of a lever system.

• Norepinephrine: A neurotransmitter involved in arousal and autonomic function.

• Repetitive strain injury: Injury from repeated motion or stress.

• Rigor mortis: Stiffening of muscles after death due to lack of ATP.

• Simple machine: A device that changes the direction or magnitude of a force (e.g., lever).

• Sphincter: A circular muscle that controls passage through an opening.

• Titin: A large protein that stabilizes thick filaments in muscle.

• Urogenital triangle: An anatomical region of the pelvis.

Additional info:

• For equations related to muscle contraction, the force generated by a muscle can be described as: where F is force, m is mass, and a is acceleration.

• Resting membrane potential equation: where V_m is membrane potential, and E_{K^+} is the equilibrium potential for potassium ions.