Bone, Muscle, and Neural Histology & Physiology: ANP Study Guide

Bone Histology

Structural and Physiological Functions of the Skeleton

The skeleton provides the framework for the body, supports soft tissues, protects internal organs, enables movement, stores minerals, and houses bone marrow for blood cell production.

• Support: Bones form the structural framework for the body.

• Protection: Bones protect vital organs (e.g., skull protects brain, ribs protect heart and lungs).

• Movement: Muscles attach to bones, enabling movement via joints.

• Mineral Storage: Bones store calcium and phosphate.

• Blood Cell Production: Red marrow produces blood cells (hematopoiesis).

• Fat Storage: Yellow marrow stores fat.

General Features of Long and Flat Bones

• Long Bones: Have a diaphysis (shaft), metaphysis (transition), epiphysis (ends), medullary cavity, and articular cartilage.

• Flat Bones: Thin, often curved, with compact bone on the outside and spongy bone (diploë) inside.

Bone Cells and Their Functions

• Osteogenic Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; secrete osteocalcin and build bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; perform osteolysis.

Bone Matrix

The bone matrix consists of organic (collagen fibers) and inorganic (hydroxyapatite crystals) components, providing strength and flexibility.

• Hydroxyapatite: Calcium phosphate mineral giving hardness.

• Collagen: Provides tensile strength.

Compact vs. Spongy Bone

• Compact Bone: Dense, forms outer layer; contains osteons.

• Spongy Bone: Porous, contains trabeculae; houses red marrow.

Bone Ossification

• Intramembranous Ossification: Direct formation of bone from mesenchyme (e.g., flat bones).

• Endochondral Ossification: Bone forms by replacing cartilage (e.g., long bones).

Bone Growth

• Length: Occurs at epiphyseal plate via endochondral ossification.

• Thickness: Appositional growth adds layers to the periosteum.

Calcium Homeostasis and Hormones

• Hypercalcemia: High blood calcium; calcitonin lowers levels.

• Hypocalcemia: Low blood calcium; PTH and calcitriol raise levels.

• Calcitriol: Increases calcium absorption.

• PTH (Parathyroid Hormone): Stimulates osteoclasts.

• Calcitonin: Inhibits osteoclasts.

Bone Fractures

• Stress Fracture: Caused by repeated stress.

• Pathological Fracture: Due to disease.

• Displaced Fracture: Bone ends out of alignment.

• Greenstick Fracture: Incomplete break (common in children).

• Comminuted Fracture: Bone breaks into several pieces.

Skeletal Muscle Histology

Functions and Properties of Skeletal Muscle

• Functions: Movement, posture, joint stabilization, heat production, protection, and support.

• Properties: Excitability, contractility, extensibility, elasticity, conductivity.

Structure of Skeletal Muscle

• Epimysium: Surrounds entire muscle.

• Perimysium: Surrounds fascicles.

• Endomysium: Surrounds individual muscle fibers.

• Muscle Fascicle: Bundle of muscle fibers.

• Muscle Fiber (Cell): Multinucleated, contains myofibrils.

• Aponeurosis: Flat tendon.

Myofilaments and Sarcomere Structure

• Thick Filaments: Composed of myosin.

• Thin Filaments: Composed of F actin, G actin, tropomyosin, troponin.

• Titin: Provides elasticity.

• Sarcomere: Functional unit; contains A band, I band, Z line, M line, H band, zone of overlap.

Motor Units

• Large Motor Units: Many fibers per neuron; for strength.

• Small Motor Units: Few fibers per neuron; for precision.

Neuromuscular Junction

• Axon Terminal: Releases acetylcholine.

• Synaptic Cleft: Gap between neuron and muscle.

• Ach Receptors: Bind acetylcholine.

• Acetylcholinesterase: Breaks down acetylcholine.

Excitability of Muscle Cells

• Transmembrane Potential: Difference in charge across membrane.

• Resting Potential: Baseline charge.

• Depolarization: Change making inside more positive.

• Action Potential: Electrical signal for contraction.

Contraction Physiology and Whole Muscle Contraction

Neuromuscular Junction Excitation

• Action potential arrives at axon terminal.

• Acetylcholine released into synaptic cleft.

• Ach binds to receptors, causing depolarization.

Excitation-Contraction Coupling

• Depolarization triggers calcium release from sarcoplasmic reticulum.

• Calcium binds to troponin, moving tropomyosin and exposing actin sites.

Sliding Filament Model

• Myosin heads bind to actin, pull (power stroke), detach, and repeat.

• ATP is required for detachment and re-cocking of myosin heads.

Muscle Relaxation

• Calcium pumped back into sarcoplasmic reticulum.

• Tropomyosin covers actin sites; contraction ends.

Length-Tension Relationship

The force a muscle can generate depends on its initial length; optimal overlap of actin and myosin produces maximal tension.

Myogram and Muscle Twitch

• Latent Period: Time between stimulus and contraction.

• Contraction Phase: Muscle shortens.

• Relaxation Phase: Muscle returns to resting length.

Summation and Recruitment

• Wave Summation: Increased frequency of stimuli increases contraction strength.

• Recruitment: More motor units activated for stronger contraction.

• Size Principle: Small units recruited first, then larger ones.

Types of Contraction

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

• Isometric: Muscle tension without length change.

Muscle Energetics

Metabolic Processes at Rest

• Muscle uses fatty acids and stores ATP, creatine phosphate, and glycogen.

Energy Demands

• Immediate: Phosphagen system (creatine phosphate, myokinase).

• Short-Term: Glycogen-lactate system (anaerobic glycolysis).

• Long-Term: Aerobic respiration (mitochondria, myoglobin).

Muscle Fatigue

• High Intensity, Short Duration: Due to ATP depletion, lactic acid buildup.

• Low Intensity, Long Duration: Due to fuel depletion, electrolyte imbalance.

Oxygen Debt (EPOC)

• Extra oxygen needed after exercise to restore ATP, clear lactic acid (Cori cycle), and replenish myoglobin.

Muscle Fiber Types

• Type I (Slow-Twitch): Endurance, aerobic, rich in myoglobin.

• Type II (Fast-Twitch): Power, anaerobic, less myoglobin.

Exercise Effects

• Resistance Exercise: Causes hypertrophy (muscle growth).

• Endurance Exercise: Increases mitochondria, capillaries.

Neural Histology

Structure and Divisions of the Nervous System

• CNS: Brain and spinal cord.

• PNS: Nerves and ganglia.

Functional Properties of Neurons

• Excitability: Respond to stimuli.

• Conductivity: Transmit signals.

• Secretion: Release neurotransmitters.

Functional Categories of Neurons

• Sensory (Afferent): Carry information to CNS.

• Motor (Efferent): Carry commands from CNS.

• Interneurons: Integrate information within CNS.

Parts of a Neuron

• Dendrites: Receive signals.

• Cell Body: Contains nucleus.

• Axon: Conducts impulses.

• Axon Hillock: Initiates action potential.

• Axolemma: Axon membrane.

• Axoplasm: Axon cytoplasm.

• Telodendria: Axon branches.

• Synaptic Terminals: Release neurotransmitters.

Structural Classes of Neurons

• Anaxonic: No obvious axon.

• Bipolar: One axon, one dendrite.

• Unipolar: Single process.

• Multipolar: Many dendrites, one axon.

Axonal Transport

• Anterograde: From cell body to axon terminal.

• Retrograde: From axon terminal to cell body.

Neuroglial Cells

• CNS: Ependymal cells (produce CSF), microglia (immune), astrocytes (support, blood-brain barrier), oligodendrocytes (myelinate axons).

• PNS: Schwann cells (myelinate axons), satellite cells (support neurons).

Myelin and Nervous Tissue

• Myelin: Insulates axons, speeds conduction.

• Node of Ranvier: Gap in myelin sheath.

• White Matter: Myelinated axons.

• Gray Matter: Cell bodies, dendrites.

Neural Electrophysiology and Synaptic Activity

Membrane Potential and Resting Potential

• Maintained by sodium-potassium pump and leak channels.

• Resting potential typically $-70\ \text{mV}$.

Local Potentials

• Caused by ligand-gated channels.

• Can be depolarizing (EPSP) or hyperpolarizing (IPSP).

Action Potential

• Triggered when threshold is reached.

• All-or-none response.

• Absolute and relative refractory periods control firing.

Propagation of Action Potential

• Continuous Conduction: Unmyelinated axons.

• Saltatory Conduction: Myelinated axons; jumps between nodes of Ranvier.

Synaptic Activity

• Chemical Synapse: Uses neurotransmitters.

• Electrical Synapse: Direct ion flow.

• Cholinergic Synapse: Uses acetylcholine.

• GABA-ergic Synapse: Uses GABA.

• Excitatory Adrenergic Synapse: Uses norepinephrine.

• Neurotransmitter Removal: Diffusion, reuptake, enzymatic degradation.

Neural Integration

• Temporal Summation: Multiple signals in quick succession.

• Spatial Summation: Multiple signals from different locations.

• Neural Pools: Groups of neurons processing information.

Example Table: Comparison of Bone Cells

Cell Type	Function	Location
Osteogenic	Stem cell, forms osteoblasts	Periosteum, endosteum
Osteoblast	Builds bone matrix	Bone surface
Osteocyte	Maintains bone tissue	Lacunae
Osteoclast	Resorbs bone	Bone surface

Example Table: Types of Muscle Contraction

Type	Length Change	Example
Isotonic (Concentric)	Shortens	Biceps curl upward
Isotonic (Eccentric)	Lengthens	Biceps lowering weight
Isometric	No change	Holding weight steady

Example Table: Types of Neurons

Type	Structure	Function
Anaxonic	No axon	Unknown, CNS
Bipolar	One axon, one dendrite	Sensory (retina)
Unipolar	Single process	Sensory (PNS)
Multipolar	Many dendrites, one axon	Motor, CNS

Key Equations

• Resting membrane potential: $V_{\text{rest}} = -70\ \text{mV}$

• Sodium-potassium pump: $3\ \text{Na}^+ \text{out},\ 2\ \text{K}^+ \text{in}$

Additional info: Academic context was added to expand brief terminology and learning objectives into full explanations, tables, and examples for exam preparation.