Joints and Articulations

Functional and Structural Classification of Joints

Joints, or articulations, are locations where two or more bones meet. They are classified both functionally (by the amount of movement allowed) and structurally (by the type of tissue connecting the bones).

• Synarthrosis: Functional classification; joints allow no motion between bones.

• Amphiarthrosis: Functional classification; joints allow only a small amount of motion.

• Diarthrosis: Functional classification; joints allow a wide range of motion.

• Fibrous joint: Structural classification; bones held together by dense collagenous connective tissue, no synovial cavity.

• Cartilaginous joint: Structural classification; bones held together by cartilage, no synovial cavity.

• Synovial joint: Structural classification; bones have a fluid-filled synovial cavity and are enclosed within an articular capsule.

Types of Fibrous Joints

• Suture: Found between bones of the skull; synarthrosis.

• Gomphosis: Found between teeth and their sockets; synarthrosis.

• Syndesmosis: Bones joined by interosseous membrane or ligament; amphiarthrosis.

Types of Cartilaginous Joints

• Synchondrosis: Bones joined by hyaline cartilage; synarthrosis. Example: Epiphyseal plate in growing long bones.

• Symphysis: Bones connected by fibrocartilaginous pad; amphiarthrosis. Example: Intervertebral discs.

Synovial Joint Structure

• Articular capsule: Double-layered structure enclosing the joint.

• Synovial fluid: Secreted by synovial membrane; provides lubrication, shock absorption, and nutrients.

• Ligament: Dense regular collagenous connective tissue connecting bone to bone; strengthens joint.

• Tendon: Connects muscle to bone; composed of dense regular collagenous connective tissue.

• Bursa: Synovial fluid-filled sac reducing friction between moving parts.

Joint Disorders

• Bursitis: Inflammation of a bursa.

• Arthritis: Inflammation of one or more joints, causing pain and limitation of movement.

• Osteoarthritis: Most common form; associated with aging and wear.

• Rheumatoid arthritis: Autoimmune form.

• Gouty arthritis: Due to uric acid crystal deposits, often in the great toe.

Movements at Synovial Joints

Synovial joints allow various types of movement, classified by the direction and nature of motion.

• Flexion: Decreases the angle between articulating bones.

• Extension: Increases the angle between articulating bones.

• Hyperextension: Extension beyond anatomical position.

• Abduction: Movement away from the midline.

• Adduction: Movement toward the midline.

• Circumduction: Circular movement combining flexion, extension, abduction, and adduction.

• Rotation: Bone pivots around its own axis.

• Reposition: Thumb returns to anatomical position from opposition.

• Depression: Body part moves in an inferior direction.

• Elevation: Body part moves in a superior direction.

• Protraction: Body part moves in an anterior direction.

• Retraction: Body part moves in a posterior direction.

• Inversion: Sole of foot rotates medially.

• Eversion: Sole of foot rotates laterally.

• Dorsiflexion: Foot moves upward, decreasing angle with leg.

• Plantarflexion: Foot moves downward, increasing angle with leg.

• Supination: Palm faces anteriorly (anatomical position).

• Pronation: Palm faces posteriorly.

Types of Synovial Joints

• Pivot joint: Uniaxial; rotation around one axis (e.g., atlantoaxial joint).

• Hinge joint: Uniaxial; convex surface fits into concave depression (e.g., elbow, knee).

• Ball and socket joint: Multiaxial; ball-shaped surface fits into cup-shaped socket (e.g., shoulder, hip).

Muscle Structure and Function

Muscle Roles in Movement

• Agonist (prime mover): Main muscle responsible for movement.

• Synergist: Assists agonist for efficient movement.

• Fixator: Stabilizes bone or joint during movement.

• Origin: Less movable attachment point.

• Insertion: More movable attachment point.

• Abductor: Moves limb away from midline.

• Adductor: Moves limb toward midline.

Muscle Naming and Types

• Serratus: Saw-toothed.

• Vastus: Large.

• Deltoid: Triangular.

• Orbicularis: Circular.

• Oculi: Eye.

• Oris: Mouth.

Muscle Physiology

• Fatigue: Inability to maintain intensity during activity.

• Latent period: Time for action potential to propagate across sarcolemma.

• Tropomyosin: Regulatory protein covering actin's active sites.

• Ligand-gated channels: Open in response to chemical signals.

Muscle Cell Structure

• Sarcoplasm: Muscle cell cytoplasm.

• Sarcolemma: Muscle cell plasma membrane.

• Sarcoplasmic reticulum: Specialized smooth ER storing calcium ions.

• Transverse tubules (T-tubules): Inward extensions of sarcolemma.

• Triad: Combination of T-tubule and two terminal cisternae.

• Thin filament: Composed of actin, troponin, tropomyosin.

• Thick filament: Composed of myosin.

Sarcomere Structure

• Z-disc: Contains structural proteins anchoring thin filaments.

• I-band: Light region with only thin filaments.

• A-band: Dark region with thick filaments and overlapping thin filaments.

• Sarcomere: Functional unit of muscle contraction; extends from one Z-disc to the next.

Neuromuscular Junction and Muscle Contraction

• Neuromuscular junction: Location where neuron communicates with muscle fiber.

• Neurotransmitter: Chemical messenger from neuron to target cell.

• Acetylcholine: Neurotransmitter involved in muscle contraction.

• Acetylcholinesterase: Enzyme degrading acetylcholine in synaptic cleft.

• Axon terminal: End of axon containing synaptic vesicles.

• Synaptic cleft: Space between axon terminal and muscle fiber.

• Motor end plate: Region of muscle fiber plasma membrane with acetylcholine receptors.

Muscle Contraction Cycle

• Crossbridge cycle: Myosin heads bind to actin, pulling thin filaments toward M line.

• Power stroke: Myosin pivots, pulling actin filament.

• Glycolysis: Glucose is split, producing ATP and NADH. Equation:

Nervous System Structure and Function

Divisions of the Nervous System

• Central Nervous System (CNS): Brain and spinal cord.

• Peripheral Nervous System (PNS): Cranial and spinal nerves outside CNS.

Functional Divisions

• Somatic sensory division: Carries signals from skin, muscles, bones, joints, and special senses.

• Visceral sensory division: Carries signals from organs (heart, lungs, stomach, kidneys, bladder).

• Integrative function: CNS processes information to determine response.

• Motor function: Response performed by motor division of PNS.

• Somatic motor division: Voluntary control of skeletal muscle.

• Autonomic nervous system: Involuntary control of thoracic and abdominal viscera.

Neuron Structure and Types

• Cell body: Metabolically active region.

• Neurofibrils: Intermediate filaments providing support.

• Dendrites: Receive input from other neurons.

• Axon hillock: Origin of axon from cell body.

• Axon collaterals: Branches from main axon.

• Telodendria: Small branches at end of axon.

• Axon terminals: Communicate with target cells.

• Axolemma: Axon plasma membrane.

• Multipolar neuron: One axon, multiple dendrites.

• Bipolar neuron: One axon, one dendrite.

• Pseudounipolar neuron: Single process from cell body.

Neuroglia (Glial Cells)

• Oligodendrocytes: Form myelin sheath in CNS.

• Microglia: Phagocytic cells in CNS.

• Ependymal cells: Secrete and circulate cerebrospinal fluid.

• Schwann cells: Form myelin sheath in PNS.

• Satellite cells: Protect cell bodies in PNS.

White and Gray Matter

• White matter: Myelinated axons in brain and spinal cord.

• Gray matter: Unmyelinated axons in brain and spinal cord.

Membrane Potentials and Signal Transmission

• Depolarization: Temporary increase in cell's membrane potential.

• Repolarization: Return to resting membrane potential after depolarization.

• Hyperpolarization: Membrane potential becomes more negative than resting value.

• Saltatory conduction: Rapid conduction in myelinated axons; action potentials jump between nodes of Ranvier.

Synapses and Neurotransmission

• Synapse: Location where presynaptic neuron communicates with target cell.

• Presynaptic neuron: Sends message from axon terminal.

• Postsynaptic neuron: Receives message.

• Excitatory postsynaptic potential (EPSP): Membrane potential becomes less negative, increasing likelihood of action potential.

• Inhibitory postsynaptic potential (IPSP): Membrane potential becomes more negative, decreasing likelihood of action potential.

Cholinergic Synapses

• Cholinergic synapse: Synapse where acetylcholine is the neurotransmitter; found in parasympathetic neurons and some sympathetic neurons.

Table: Joint Types and Their Characteristics

Additional info: Some definitions and examples were expanded for clarity and completeness. Table entries inferred from standard anatomical knowledge.