A&P I Final Study Guide: Joints, Muscular System, and Nervous System

Joints

Structural and Functional Classification of Joints

Joints, or articulations, are connections between bones that allow for varying degrees of movement. They can be classified by the type of tissue binding the bones (structural) or by the amount of movement they permit (functional).

• Structural Classification:

  • Fibrous Joints: Bones are joined by dense connective tissue; no joint cavity. Examples: sutures (skull), syndesmoses (distal tibiofibular joint), gomphoses (teeth in sockets).

  • Cartilaginous Joints: Bones are joined by cartilage; no joint cavity. Examples: synchondroses (epiphyseal plates), symphyses (pubic symphysis).

  • Synovial Joints: Bones are separated by a fluid-filled joint cavity; most movable type. Examples: shoulder, knee.

• Functional Classification:

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

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

  • Diarthroses: Freely movable joints (e.g., most synovial joints).

Joint Description

• Fibrous Joints: Bones are held together by dense fibrous connective tissue. Types include:

  • Sutures: Found between skull bones; immovable.

  • Syndesmoses: Bones connected by ligaments; slightly movable (e.g., distal tibiofibular joint).

  • Gomphoses: Peg-in-socket joints (e.g., teeth in alveolar sockets).

• Cartilaginous Joints: Bones are united by cartilage. Types include:

  • Synchondroses: Hyaline cartilage unites bones (e.g., epiphyseal plates).

  • Symphyses: Fibrocartilage unites bones (e.g., pubic symphysis, intervertebral discs).

• Synovial Joints: Characterized by a joint cavity filled with synovial fluid. Key features:

  • Articular cartilage covers bone ends.

  • Joint (articular) cavity contains synovial fluid.

  • Articular capsule encloses the cavity.

  • Synovial fluid lubricates and nourishes cartilage.

  • Reinforcing ligaments and nerves/blood vessels present.

Types of Synovial Joints

Type	Movement	Example
Plane	Gliding	Intercarpal joints
Hinge	Flexion/Extension	Elbow
Pivot	Rotation	Proximal radioulnar joint
Flexion/Extension, Abduction/Adduction	Wrist
Saddle	Flexion/Extension, Abduction/Adduction	Thumb (carpometacarpal joint)
Ball-and-Socket	All movements	Shoulder, hip

Types of Joint Movements

• Origin: The fixed attachment point of a muscle.

• Insertion: The movable attachment point of a muscle.

• Movements: Flexion, extension, abduction, adduction, rotation, circumduction, pronation, supination, inversion, eversion, elevation, depression, opposition.

Examples of Synovial Joints

• Jaw (Temporomandibular Joint): Modified hinge joint; allows opening/closing and side-to-side movement.

• Shoulder (Glenohumeral Joint): Ball-and-socket; greatest range of motion.

• Elbow: Hinge joint; allows flexion and extension.

• Knee: Largest, most complex; primarily a hinge, with some rotation.

• Hip: Ball-and-socket; stable, supports body weight.

Muscular System

Overview of Muscle Tissue

Muscle tissue is specialized for contraction and is essential for movement, posture, joint stability, and heat production.

• Skeletal Muscle: Striated, voluntary, attached to bones.

• Cardiac Muscle: Striated, involuntary, found in heart.

• Smooth Muscle: Non-striated, involuntary, found in walls of hollow organs.

• Functions: Movement, maintaining posture, stabilizing joints, generating heat.

Skeletal Muscle Structure

• Connective Tissues: Epimysium (surrounds muscle), perimysium (surrounds fascicles), endomysium (surrounds fibers).

• Muscle Fiber Parts:

  • Sarcolemma: Muscle cell membrane.

  • Sarcoplasm: Cytoplasm of muscle fiber.

  • Myofibrils: Contractile elements containing sarcomeres.

  • Sarcoplasmic Reticulum: Stores calcium ions.

  • T-tubules: Invaginations of sarcolemma for signal transmission.

Skeletal Muscle Contraction

• Neuromuscular Junction: Site where motor neuron stimulates muscle fiber via acetylcholine release.

• Excitation-Contraction Coupling: Sequence linking action potential to muscle contraction via calcium release.

• Cross-Bridge Cycle: Myosin heads bind to actin, perform power stroke, detach, and reset using ATP.

Motor Units, Summation, and Types of Contractions

• Motor Unit: A motor neuron and all muscle fibers it innervates.

• Muscle Twitch: Response of a muscle to a single stimulus; phases: latent, contraction, relaxation.

• Isometric Contraction: Muscle tension without length change.

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

Energy for Contraction

• ATP Regeneration:

  1. Direct phosphorylation by creatine phosphate

  2. Anaerobic glycolysis

  3. Aerobic respiration

• EPOC (Excess Post-exercise Oxygen Consumption): Increased oxygen intake after exercise to restore metabolic conditions.

• Muscle Fatigue: Inability to contract despite stimulation, often due to ATP depletion.

Smooth Muscle vs Skeletal Muscle

• Smooth Muscle: Spindle-shaped, single nucleus, no striations, involuntary.

• Skeletal Muscle: Long, cylindrical, multinucleate, striated, voluntary.

• Unitary Smooth Muscle: Contracts as a single unit (e.g., digestive tract).

• Multi-unit Smooth Muscle: Fibers contract independently (e.g., iris of eye).

Muscular Anatomy

• Main Axial Muscles: Muscles of head, neck, trunk (e.g., sternocleidomastoid, rectus abdominis).

• Main Appendicular Muscles: Muscles of limbs (e.g., biceps brachii, quadriceps femoris).

Fundamentals of the Nervous System

General Functions of the Nervous System

The nervous system is responsible for sensory input, integration, and motor output.

• Divisions:

  • Central Nervous System (CNS): Brain and spinal cord; integration and control center.

  • Peripheral Nervous System (PNS): Cranial and spinal nerves; communication lines.

Neuroglia

• Types and Functions:

  • Astrocytes: Support neurons, maintain blood-brain barrier.

  • Microglia: Phagocytic defense cells.

  • Ependymal Cells: Line ventricles, produce cerebrospinal fluid.

  • Oligodendrocytes: Form myelin in CNS.

  • Schwann Cells: Form myelin in PNS.

  • Satellite Cells: Support PNS neurons.

Neuron Structure and Classification

• Parts of a Neuron: Cell body (soma), dendrites (receive signals), axon (transmits signals), axon terminals.

• Classification:

  • By Structure: Multipolar, bipolar, unipolar.

  • By Function: Sensory (afferent), motor (efferent), interneurons.

• Myelin Sheath: Insulates axons, increases conduction speed; formed by oligodendrocytes (CNS) and Schwann cells (PNS).

Cell Membrane Potential

• Polarization: Resting membrane potential is maintained by ion gradients and selective permeability.

• Action Potential: Rapid depolarization and repolarization of membrane; all-or-none event.

• Propagation: Action potentials travel along axon; faster in myelinated fibers (saltatory conduction).

• Refractory Periods:

  • Absolute: No new action potential possible.

  • Relative: Stronger stimulus needed for new action potential.

• Comparison: Myelinated axons conduct impulses faster than unmyelinated axons.

Synaptic Transmission

• Chemical Synapse: Neurotransmitter released from presynaptic neuron binds to receptors on postsynaptic cell, causing excitatory or inhibitory potentials.

• Excitatory vs Inhibitory Potentials: Excitatory depolarize membrane; inhibitory hyperpolarize.

• Neuronal Organization: Converging, diverging, reverberating, and parallel after-discharge circuits.

Central Nervous System

Overview of the Central Nervous System

• Components: Brain and spinal cord.

• Major Brain Regions: Cerebrum, diencephalon, brain stem, cerebellum.

• Gray Matter: Neuron cell bodies; White Matter: Myelinated axons.

• Ventricles: Lateral, third, and fourth ventricles contain cerebrospinal fluid.

The Brain

• Lobes of Cerebrum: Frontal, parietal, temporal, occipital, insula.

• Grooves: Sulci (shallow), fissures (deep).

• Cerebral Cortex Areas: Sensory, association, motor.

• Hemisphere Dominance: Left (language, logic), right (creativity, spatial).

• Basal Nuclei: Regulate movement.

• Diencephalon: Thalamus (relay), hypothalamus (homeostasis), epithalamus (pineal gland).

• Brain Stem: Midbrain, pons, medulla oblongata; vital functions.

• Cerebellum: Coordinates movement and balance.

• Limbic System: Emotions; Reticular Formation: Arousal.

• Blood Brain Barrier: Selective permeability of brain capillaries.

Protection of the CNS

• Protection: Skull, vertebrae, meninges (dura mater, arachnoid mater, pia mater), cerebrospinal fluid (CSF).

• CSF Formation: Produced by choroid plexus; circulates through ventricles and subarachnoid space.

Spinal Cord

• Structure: Extends from foramen magnum to L1/L2; central gray matter, outer white matter.

• Functions: Conduction, reflexes.

• Pathways: Ascending (sensory), descending (motor).

Peripheral Nervous System and Autonomic Nervous System (ANS)

Peripheral Nervous System Overview

• PNS: Connects CNS to body; includes cranial and spinal nerves.

Sensory Receptors and Sensation

• Receptor Types: Mechanoreceptors, thermoreceptors, photoreceptors, chemoreceptors, nociceptors.

• General vs Special Senses: General (touch, pain), special (vision, hearing, taste, smell, equilibrium).

• Sensation vs Perception: Sensation is awareness; perception is interpretation.

General Senses

• Touch, Pressure, Temperature, Pain: Different receptors for each.

• Pain: Produced by nociceptors; unique in that it adapts little.

• Sensory Adaptation: Decreased response to constant stimulus.

• Stretch Receptors: Monitor muscle/tendon stretch.

Nerves

• Peripheral Nerve Structure: Bundles of axons (fascicles) surrounded by connective tissue.

• Cranial Nerves: 12 pairs; various sensory/motor functions.

• Spinal Nerves: 31 pairs; named by vertebral region.

Reflexes

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

• Autonomic vs Somatic Reflexes: Autonomic (viscera), somatic (skeletal muscle).

• Spinal Reflexes: Stretch, withdrawal, crossed-extensor, etc.

Autonomic Nervous System

• Somatic vs Autonomic Pathways: Somatic (single neuron to skeletal muscle), autonomic (two-neuron chain to viscera).

• Sympathetic Division: "Fight or flight"; thoracolumbar origin.

• Parasympathetic Division: "Rest and digest"; craniosacral origin.

• Neurotransmitters: Acetylcholine (cholinergic), norepinephrine (adrenergic).

• Receptors: Cholinergic (nicotinic, muscarinic), adrenergic (alpha, beta).

Special Senses

Vision

• Eye Structures: Cornea, lens, retina, iris, pupil, optic nerve.

• Photoreceptors: Rods (dim light, black/white), cones (color, detail).

• Visual Pathway: Retina → optic nerve → optic chiasm → thalamus → visual cortex.

Smell and Taste

• Olfaction: Olfactory epithelium in nasal cavity; detects airborne chemicals.

• Gustation: Taste buds on tongue; detects dissolved chemicals.

• Relationship: Smell enhances taste perception.

Hearing and Equilibrium

• Ear Parts: Outer (auricle, canal), middle (ossicles), inner (cochlea, vestibule, semicircular canals).

• Sound Conduction: Sound waves → tympanic membrane → ossicles → cochlear fluids → hair cells.

• Equilibrium: Vestibular apparatus detects static (position) and dynamic (movement) balance.