Osseous Tissue (Chapter 6)

Functions of Bone

Bones serve multiple essential functions in the human body, providing structural support, protection, and facilitating movement.

• Support: Framework for the body, supporting soft tissues.

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

• Movement: Acts as levers for muscles.

• Mineral Storage: Reservoir for calcium and phosphate.

• Blood Cell Production: Hematopoiesis occurs in red marrow.

• Fat Storage: Yellow marrow stores triglycerides.

Bone Types: Comparison

Bones are classified by shape and internal structure.

• Long Bones: Longer than wide (e.g., femur, humerus).

• Flat Bones: Thin, often curved (e.g., skull, sternum).

• Compact Bone: Dense, forms outer layer; provides strength.

• Spongy Bone: Porous, found at ends of long bones and inside flat bones; contains red marrow.

Bone Structure

The bone matrix is composed of organic and inorganic components.

• Hydroxyapatite: Inorganic mineral, provides hardness. Formula:

• Collagen: Organic protein fibers, provide flexibility and tensile strength.

Bone Cells

Four main types of bone cells regulate bone formation and resorption.

• Osteoprogenitor Cells: Stem cells that differentiate into osteoblasts.

• Osteoblasts: Bone-forming cells; synthesize bone matrix.

• Osteocytes: Mature bone cells; maintain bone tissue.

• Osteoclasts: Bone-resorbing cells; break down bone matrix.

Medullary Cavity

The central cavity of long bones contains marrow.

• Red Marrow: Site of blood cell production; found in diploë (spongy bone of flat bones).

• Yellow Marrow: Stores fat; found in adult long bones.

Load Bearing

Bones are adapted to bear mechanical loads, distributing stress through their structure.

Bone Formation

Bone formation involves several processes:

• Calcification: Deposition of calcium salts.

• Ossification: Formation of bone tissue.

• Endochondral Ossification: Bone develops from cartilage model; involves primary and secondary ossification centers, epiphyseal cartilage, articular cartilage, and growth plate closure.

• Appositional Growth: Increase in bone diameter.

• Intramembranous Ossification: Formation of "dermal" bones (e.g., skull); occurs directly from mesenchymal tissue.

Blood Supply to Long Bone

Long bones receive blood through specialized vessels.

• Nutrient Artery & Vein: Enter through nutrient foramina.

• Metaphyseal Arteries & Veins: Supply metaphysis and epiphysis.

Exercise Effects on Bone

Physical activity stimulates bone remodeling and increases bone density.

Hormone Effects and Calcium Homeostasis

Hormones regulate bone metabolism and calcium levels.

• Sex Hormones: Influence bone growth; deficiency can lead to osteoporosis.

• Skeleton as Calcium Reserve: Stores and releases calcium as needed.

• Calcium Homeostasis: Maintained by parathyroid hormone (PTH) and calcitonin.

Low Blood Calcium:

• PTH released → osteoclast activation → decreased Ca2+ excretion by kidneys → increased intestinal absorption → rise in blood Ca2+

High Blood Calcium:

• Calcitonin released → osteoclast inactivation → osteoblast activation → increased Ca2+ excretion by kidneys → decreased intestinal absorption → drop in blood Ca2+

Bone Fractures

Fractures are classified by their characteristics and location.

• Simple vs. Compound: Simple (closed), compound (open).

• Transverse: Perpendicular to bone axis.

• Displaced: Bone fragments not aligned.

• Compression: Bone crushed.

• Spiral: Twisting force.

• Epiphyseal: Involves growth plate.

• Comminuted: Bone broken into several pieces.

• Greenstick: Partial fracture, common in children.

• Colles: Distal radius fracture.

• Pott’s: Ankle fracture.

Repair of Fractures: Involves stages and formation of external callus.

Joints (Chapter 8)

Articulations

Joints, or articulations, connect bones and allow movement.

• Synarthroses: Immovable joints (e.g., sutures).

• Amphiarthroses: Slightly movable joints (e.g., intervertebral discs).

• Diarthroses (Synovial Joints): Freely movable; classified by type:

  • Hinge: Elbow, knee.

  • Pivot: Atlas/axis.

  • Ball-and-Socket: Shoulder, hip.

  • Gliding: Carpals.

  • Saddle: Thumb.

  • Compound: Multiple bones involved.

Synovial Joint Structure

Synovial joints have a joint cavity, articular cartilage, synovial membrane, and supporting ligaments.

Joint Injuries

• Cartilage Tears: Damage to meniscus or discs.

• Sprains: Ligament injury.

• Dislocations: Bone forced out of joint.

• Bursitis and Tendonitis: Inflammation of bursae or tendons.

• Arthritic Conditions: Joint inflammation and degeneration.

Abnormal Spine Curvatures

• Scoliosis: Lateral curvature.

• Kyphosis: Excessive thoracic curvature.

• Lordosis: Excessive lumbar curvature.

Neural Tissue & Neurophysiology (Chapter 11)

Overview of Nervous System

The nervous system is divided into the central (CNS) and peripheral (PNS) systems.

• CNS: Brain and spinal cord.

• PNS: Nerves and ganglia outside CNS.

Neural Response to Injury

Neurons respond to injury through processes such as Wallerian degeneration, differing between CNS and PNS.

• Wallerian Degeneration: Axon distal to injury degenerates.

• CNS vs. PNS: PNS can regenerate axons; CNS regeneration is limited.

Neurophysiology Overview

Neurons communicate via electrical signals generated by transmembrane potentials.

• Transmembrane Potential: Voltage difference across cell membrane.

ECF vs. ICF Composition

Extracellular fluid (ECF) and intracellular fluid (ICF) differ in ion concentrations.

• ECF: High Na+, low K+.

• ICF: High K+, low Na+.

Electrochemical Gradients

Electrochemical gradients drive ion movement across membranes.

• Chemical Gradient: Difference in ion concentration.

• Electrical Gradient: Difference in charge.

Types of Transmembrane Regulated Channels

• Chemical/Ligand-Gated: Open in response to neurotransmitters.

• Voltage-Gated: Open in response to membrane potential changes.

• Mechanical-Gated: Open in response to physical deformation.

• Leak Channels: Always open; maintain resting potential.

Neural Physiology

• Graded Potentials: Local changes in membrane potential.

• Action Potentials: Rapid, all-or-nothing electrical signals; step-by-step process includes depolarization, repolarization, and hyperpolarization.

• Threshold Potential: Minimum voltage to trigger action potential.

• Resting Membrane Potential: Typically in neurons.

• All-or-Nothing Principle: Action potential occurs fully or not at all.

• Absolute vs. Relative Refractory Periods: Absolute: no new AP possible; relative: AP possible with stronger stimulus.

• Continuous vs. Saltatory Propagation: Continuous: unmyelinated axons; saltatory: myelinated, faster.

• Voltage vs. Chemical Synapses: Voltage: direct electrical; chemical: neurotransmitter-mediated.

• Neurotransmitters: Location and function (e.g., acetylcholine at skeletal muscle synapses).

• Events at Cholinergic Synapse: Ach release, binding, and effect on muscle.

• Synaptic Delay vs. Synaptic Fatigue: Delay: time for neurotransmitter release; fatigue: depletion of neurotransmitter.

• Post Synaptic Potentials: EPSP (depolarization), IPSP (hyperpolarization); ions involved.

• Temporal vs. Spatial Summation: Temporal: repeated signals; spatial: multiple sources.

• Facilitation & Inhibition: Modulation of synaptic activity.

Neural Integration

Neuronal pools integrate signals for complex processing.

Central Nervous System: Brain & Spinal Cord (Chapter 12)

Protection & Support of Brain

The brain is protected mechanically and biochemically by structures and fluids.

• Cerebrospinal Fluid (CSF): Cushions and nourishes brain.

• Glial Cells: Support neurons; types include astrocytes, oligodendrocytes, microglia, ependymal cells.

Functions of Cerebrum

• Motor & Sensory Areas: Control movement and sensation; damage can cause deficits (e.g., aphasia).

• Association Areas: Integrate information.

• Association Fibers: Arcuate (short), longitudinal (long).

• Commissural Fibers: Connect hemispheres.

• Projection Fibers: Connect cortex to lower centers.

• Hemispheric Lateralization: Functional differences between hemispheres.

Functions of Diencephalon

Includes thalamus and hypothalamus; relays sensory information and regulates homeostasis.

Thalamus

• Medial Dorsal, Anterior Nuclear Group, Pulvinar, Medial Geniculate Body, Lateral Geniculate Body: Nuclei involved in sensory relay and processing.

Hypothalamus

• Paraventricular, Supraoptic, Preoptic Nuclei: Regulate endocrine and autonomic functions.

Functions of Mesencephalon

• Midbrain: Visual and auditory reflexes.

• Pons: Relays information; regulates breathing.

• Medulla Oblongata: Controls vital functions (e.g., heart rate).

Brain Networks

• Limbic System: Emotion and memory; includes hippocampus.

• Reticular Activating System: Regulates arousal and consciousness.

Functions of Cerebellum

Coordinates movement and balance.

Higher Order Functions

• Consciousness: Measured by brain waves.

• NREM vs. REM Sleep: Different stages; REM associated with dreaming.

• Memory: Fact (declarative) vs. skill (procedural); short-term vs. long-term; consolidation mechanisms.

Poliomyelitis & ALS

Both diseases involve destruction of specific gray horns in the spinal cord, affecting motor function.

Additional info: Academic context was added to expand brief points into full explanations, including definitions, examples, and tables for clarity.