Anatomy & Physiology Study Guide: Skeletal, Muscular, Nervous, and Sensory Systems

Skeletal System

Functions of the Skeletal System

The skeletal system provides the framework for the body and serves several essential functions.

• Support: The skeleton supports the body and maintains its shape.

• Protection: Bones protect vital organs, such as the brain (skull) and heart/lungs (rib cage).

• Movement: Bones act as levers for muscles to produce movement.

• Mineral Storage: Bones store minerals, especially calcium and phosphorus.

• Blood Cell Production: Hematopoiesis occurs in the red bone marrow.

• Fat Storage: Yellow bone marrow stores fat.

Bone Types and Structure

Bones are classified by shape and internal 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., sternum, skull).

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

Bone tissue is organized into two main types:

• Compact Bone: Dense, smooth, and forms the outer layer of bones. Contains osteons (Haversian systems) as its structural units.

• Spongy Bone: Made of trabeculae and has open spaces. Contains red or yellow bone marrow.

Bone Anatomy and Physiology

• Periosteum: A tough, fibrous membrane covering the outer surface of bones, containing nerves and blood vessels.

• Osteoblasts: Cells responsible for bone formation.

• Osteocytes: Mature bone cells maintaining bone tissue.

• Osteon: The structural and functional unit of compact bone.

• Lamellae: Concentric rings of bone matrix within osteons.

Bone Growth and Repair

• Epiphyseal Plate: Responsible for bone growth during childhood.

• Fracture Repair: Begins with hematoma formation, followed by callus formation, and remodeling.

• Periosteum: Plays a role in bone repair and growth.

Calcium Regulation

• Parathyroid Hormone (PTH): Increases blood calcium levels by stimulating bone resorption.

• Calcitonin: Lowers blood calcium levels by inhibiting bone resorption.

Joints

Classification of Joints

Joints, or articulations, are points where two or more bones meet. They are classified by structure and function.

• Fibrous Joints: Immovable (e.g., sutures in the skull).

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

• Synovial Joints: Freely movable, characterized by a joint cavity, articular cartilage, and synovial fluid.

Synovial Joint Types

• Hinge Joint: Allows flexion and extension (e.g., elbow).

• Ball-and-Socket Joint: Allows movement in all directions (e.g., hip, shoulder).

• Pivot Joint: Allows rotation (e.g., radius and ulna).

• Plane Joint: Allows sliding movements (e.g., intercarpal joints).

• Saddle Joint: Allows movement in two planes (e.g., thumb).

Joint Movements

• Flexion: Decreases the angle of a joint.

• Extension: Increases the angle of a joint.

• Supination: Rotation of the palm upward.

• Pronation: Rotation of the palm downward.

• Circumduction: Circular movement of a limb.

Muscular System

Muscle Types and Properties

Muscle tissue is classified into three types:

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

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

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

Key properties of skeletal muscle:

• Responsiveness (excitability): Ability to respond to stimuli.

• Contractility: Ability to shorten forcibly.

• Extensibility: Ability to be stretched.

• Elasticity: Ability to return to original length.

Muscle Structure and Contraction

• Functional Unit: The sarcomere is the basic contractile unit of skeletal muscle.

• Actin and Myosin: Protein filaments involved in muscle contraction.

• Sliding Filament Model: Myosin heads form cross-bridges and pull actin filaments to slide past each other, causing contraction.

• Acetylcholine: Neurotransmitter essential for muscle contraction.

• Acetylcholinesterase: Enzyme that breaks down acetylcholine to stop muscle contraction.

Nervous System

Organization and Function

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

• CNS: Brain and spinal cord; processes and integrates information.

• PNS: Cranial and spinal nerves; transmits signals to and from the CNS.

Main functions:

• Sensory Input: Detects changes inside and outside the body.

• Integration: Processes and interprets sensory input.

• Motor Output: Responds by activating muscles or glands.

Nervous Tissue Structure

• Neuron: The basic functional unit of the nervous system.

• Glial Cells: Support and protect neurons (e.g., astrocytes, Schwann cells).

• Fascicle: Bundle of nerve fibers surrounded by perineurium.

• Nerve: Bundle of axons in the PNS.

Signal Transmission and Action Potentials

• Action Potential: Rapid change in membrane potential that travels along the neuron.

• Sodium-Potassium Pump: Restores resting potential by pumping sodium out and potassium into the cell.

• Synapse: Junction between two neurons; neurotransmitters are released to transmit signals.

Key equation for the sodium-potassium pump:

• $3\text{Na}^+ \text{(out)} : 2\text{K}^+ \text{(in)}$

Divisions of the Nervous System

• Somatic Division: Voluntary control of skeletal muscles.

• Autonomic Division: Involuntary control of organs; includes sympathetic ("fight or flight") and parasympathetic ("rest and digest") divisions.

Central Nervous System (CNS)

Brain Structures and Functions

• Homunculus Map: Represents the relative amount of neurons and receptors in body parts.

• Primary Somatic Sensory Area: Receives impulses from sensory receptors.

• Hypothalamus: Regulates body temperature, water balance, and metabolism.

• Reticular Activating System: Controls wakefulness and consciousness.

• Commissural Fibers: Connect left and right hemispheres of the brain.

Cerebrospinal Fluid (CSF)

• Function: Provides cushioning and buoyancy to the brain, and removes waste products.

• Circulation: Ependymal cells help circulate CSF in the CNS.

Meninges

• Layers (outermost to innermost): Dura mater, arachnoid mater, pia mater.

Peripheral Nervous System (PNS)

Nerves and Plexuses

• Nerve: Bundle of axons in the PNS.

• Brachial Plexus: Serves the skin and muscles of the shoulder and neck.

• Spinal Nerves: 31 pairs in humans.

Cranial Nerves

• Abducens (VI): Controls lateral eye movement.

• Optic (II): Carries visual information to the brain.

Autonomic Nervous System

Divisions and Functions

• Sympathetic Division: Responsible for "fight or flight" responses; increases heart rate, dilates pupils, inhibits digestion.

• Parasympathetic Division: Responsible for "rest and digest"; slows heart rate, stimulates digestion.

• Craniosacral Outflow: Parasympathetic fibers originate from cranial and sacral nerves.

Sensory System

Special Senses

• Five Special Senses: Smell, taste, touch, balance, hearing.

• Rods: Photoreceptors in the retina for dim light vision.

• Accommodation: The ability of the eye to adjust to focus on near or distant objects.

• Retina: Image is inverted and reversed compared to the actual object.

Visual Pathways

• Pathway of Impulses: Retina → Optic nerve → Optic chiasma → Optic tract → Thalamus → Optic cortex.

Joint Type	Movement	Example
Hinge	Flexion/Extension	Elbow
Ball-and-Socket	All directions	Hip, Shoulder
Pivot	Rotation	Radius/Ulna
Plane	Sliding	Intercarpal joints
Saddle	Two planes	Thumb

Muscle Type	Control	Location
Skeletal	Voluntary	Attached to bones
Cardiac	Involuntary	Heart
Smooth	Involuntary	Walls of organs

Division	Function	Example
Somatic	Voluntary control	Skeletal muscle movement
Autonomic	Involuntary control	Heart rate, digestion
Sympathetic	"Fight or flight"	Emergency response
Parasympathetic	"Rest and digest"	Relaxation, digestion

Example: The sodium-potassium pump is essential for restoring the resting membrane potential after an action potential in neurons. It actively transports three sodium ions out of the cell and two potassium ions into the cell, maintaining the electrochemical gradient necessary for nerve impulse transmission.

Additional info: Some explanations and tables have been expanded for clarity and completeness based on standard Anatomy & Physiology curriculum.