Anatomy & Physiology Study Guide: Chapters 5-8

Skeletal System

Functions of the Skeletal System

The skeletal system provides the framework for the body, supports and protects organs, enables movement, stores minerals, and produces blood cells.

• Support: Provides structural support for the entire body.

• Protection: Shields vital organs (e.g., skull protects the brain, rib cage protects the heart and lungs).

• Movement: Serves as levers for muscles to act upon.

• Mineral Storage: Stores calcium and phosphorus.

• Blood Cell Production: Houses bone marrow for hematopoiesis.

Types of Bones and Bone Classification

Bones are classified by shape and structure:

• Long bones: Longer than they are wide (e.g., femur, humerus).

• Short bones: Cube-shaped (e.g., carpals, tarsals).

• Flat bones: Thin and broad (e.g., skull, ribs, sternum).

• Irregular bones: Complex shapes (e.g., vertebrae, pelvis).

• Sesamoid bones: Embedded in tendons (e.g., patella).

Example: The femur is a long bone, providing leverage and supporting body weight.

Structure of Compact and Spongy Bone

• Compact bone: Dense, forms the outer layer of bones, provides strength.

• Spongy bone (cancellous): Porous, found at the ends of long bones and inside flat bones, contains red marrow.

Location: Compact bone is found in the diaphysis of long bones; spongy bone is found in the epiphyses and inside flat bones.

Bone Cells and Their Functions

• Osteoblasts: Build new bone matrix.

• Osteocytes: Mature bone cells, maintain bone tissue.

• Osteoclasts: Break down bone matrix for remodeling and calcium release.

Endochondral Ossification

Endochondral ossification is the process by which bone forms from cartilage templates, primarily in long bones.

• Epiphyseal plate: Growth plate where new bone is produced during childhood and adolescence.

• Process: Cartilage is gradually replaced by bone tissue.

Bone Remodeling and Nutrients

• Bone remodeling: Ongoing replacement of old bone tissue by new bone tissue.

• Key nutrients: Calcium, vitamin D, phosphorus, and protein are essential for bone health.

Hormonal Regulation of Bone Growth

• Growth hormone: Stimulates bone growth.

• Parathyroid hormone (PTH): Increases blood calcium by stimulating osteoclasts.

• Calcitonin: Lowers blood calcium by inhibiting osteoclasts.

Types of Joints

• Fibrous joints: Immovable (e.g., sutures of the skull).

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

• Synovial joints: Freely movable (e.g., knee, shoulder).

Most movable type: Synovial joints. Examples: Ball-and-socket (shoulder), hinge (elbow).

Muscular System

Functions of the Muscular System

The muscular system enables movement, maintains posture, and produces heat.

• Movement: Skeletal muscles contract to move bones.

• Posture: Continuous muscle contractions maintain body position.

• Heat production: Muscle activity generates heat for temperature regulation.

Structure of a Muscle Cell (Muscle Fiber)

• Sarcolemma: Cell membrane of a muscle fiber.

• Sarcoplasm: Cytoplasm of a muscle fiber.

• Myofibrils: Rod-like units containing contractile proteins (actin and myosin).

• Sarcomere: Functional unit of contraction.

Neuromuscular Junction

The neuromuscular junction is the synapse between a motor neuron and a muscle fiber, where nerve impulses trigger muscle contraction.

• Neurotransmitter: Acetylcholine (ACh) is released to stimulate muscle contraction.

Muscle Contraction: Sliding Filament Theory

• Calcium ions: Released from the sarcoplasmic reticulum, bind to troponin, exposing binding sites on actin.

• ATP: Provides energy for myosin heads to attach, pivot, and detach from actin filaments.

• Result: Sarcomeres shorten, causing muscle contraction.

Equation for ATP hydrolysis:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$

Muscle Relaxation and Repolarization

• Repolarization: Restoration of the resting membrane potential after contraction.

• Calcium reuptake: Calcium ions are pumped back into the sarcoplasmic reticulum.

Nervous System

Components of the Nervous System

• Central nervous system (CNS): Brain and spinal cord.

• Peripheral nervous system (PNS): Nerves outside the CNS.

Neurons and Neuroglia

• Neuron: Basic functional unit; transmits electrical impulses.

• Neuroglia: Support, protect, and nourish neurons (e.g., astrocytes, oligodendrocytes, Schwann cells).

Structure of a Neuron

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

• Dendrites: Receive signals from other neurons.

• Axon: Transmits impulses away from the cell body.

Graded Potential and Action Potential

• Graded potential: Local change in membrane potential; varies in size.

• Action potential: Rapid, all-or-none electrical impulse along the axon.

• Depolarization: Influx of Na+ ions makes the inside of the cell less negative.

• Repolarization: Efflux of K+ ions restores negative membrane potential.

Equation for membrane potential:

$V_m = V_{in} - V_{out}$

Synapse and Neurotransmission

• Synapse: Junction between two neurons or a neuron and effector cell.

• Neurotransmitters: Chemical messengers (e.g., acetylcholine, dopamine) released into the synaptic cleft.

Reflex Arc

• Components: Receptor, sensory neuron, integration center, motor neuron, effector.

• Function: Enables rapid, involuntary responses to stimuli.

Major Brain Structures and Functions

• Cerebrum: Higher brain functions (thought, memory, voluntary movement).

• Cerebellum: Coordination and balance.

• Brainstem (medulla, pons, midbrain): Autonomic functions (breathing, heart rate).

• Thalamus: Sensory relay station.

• Hypothalamus: Homeostasis, hormone regulation.

Spinal Cord and Nerves

• White matter: Myelinated axons; transmits signals up and down the spinal cord.

• Gray matter: Neuron cell bodies; processes information.

• Spinal nerves: 31 pairs; connect the CNS to the body.

Autonomic Nervous System

• Sympathetic division: Prepares body for "fight or flight".

• Parasympathetic division: Promotes "rest and digest" activities.

Special Senses

Olfaction (Smell)

• Receptors: Olfactory receptors in the nasal cavity.

• Pathway: Olfactory nerve transmits impulses to the olfactory cortex in the brain.

Vision

• Receptors: Rods and cones in the retina.

• Pathway: Optic nerve transmits impulses to the visual cortex in the occipital lobe.

Hearing and Equilibrium

• Receptors: Hair cells in the cochlea (hearing) and vestibular apparatus (balance).

• Pathway: Vestibulocochlear nerve transmits impulses to the auditory cortex.

Touch and Other Senses

• Receptors: Mechanoreceptors, thermoreceptors, nociceptors in the skin and tissues.

Summary Table: Types of Joints

Type of Joint	Structure	Mobility	Example
Fibrous	Dense connective tissue	Immovable	Sutures of skull
Cartilaginous	Cartilage	Slightly movable	Intervertebral discs
Synovial	Joint cavity with synovial fluid	Freely movable	Knee, shoulder

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