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:

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:

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

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