Joints, Muscle, and Nervous System: ANP Study Notes

Joints and Articulations

Classification of Joints

Joints, or articulations, are locations where two or more bones meet. They are classified by both their function (degree of movement) and their structure (type of tissue connecting the bones).

• Synarthrosis: Immovable joints. Examples: Sutures of the skull, gomphosis (tooth in socket), synostosis (fused bones).

• Amphiarthrosis: Slightly moveable joints. Examples: Syndesmosis (distal tibia-fibula), symphysis (pubic symphysis).

• Diarthrosis: Freely moveable joints. All synovial joints fall into this category.

Structural Types:

• Fibrous: Suture, gomphosis, syndesmosis

• Cartilaginous: Synchondrosis, symphysis

• Bony: Synostosis

• Synovial: Complex, freely moveable joints

Types of Synovial Joints

Synovial joints are characterized by a joint cavity filled with synovial fluid, articular cartilage, and a joint capsule. They allow various types of movement:

• Plane (Gliding) Joints: Slight, monaxial movement (e.g., intercarpal joints)

• Hinge Joints: Angular, monaxial movement (e.g., elbow, knee)

• Pivot Joints: Rotation, monaxial (e.g., atlantoaxial joint)

• Condylar Joints: Angular, biaxial (e.g., metacarpophalangeal joints)

• Saddle Joints: Angular, biaxial (e.g., thumb carpometacarpal joint)

• Ball-and-Socket Joints: Angular, circumduction, rotation; triaxial (e.g., shoulder, hip)

Joint Structures and Functions

• Articular Cartilage: Hyaline cartilage covering bone surfaces; smooth, low friction, distributes load, absorbs shock, avascular, and aneural.

• Fibrocartilage: Pads (e.g., menisci) between opposing surfaces in a joint.

• Bursae: Fluid-filled sacs reducing friction between tendons/ligaments and other tissues.

• Synovial Membrane: Lines joint cavity, produces synovial fluid for lubrication.

Joint Movements

• Abduction: Movement away from the midline (frontal plane).

• Adduction: Movement toward the midline (frontal plane).

• Extension: Increases angle between bones (sagittal plane).

• Hyperextension: Extension beyond anatomical position.

• Dorsiflexion: Upward movement of foot/toes.

• Plantar Flexion: Downward movement of foot/toes (tip-toe).

Skeletal Muscle Structure and Function

Functions of Skeletal Muscle

• Produce skeletal movement

• Support soft tissues

• Maintain blood flow

• Move materials along internal passageways

• Stabilize body temperature

Muscle Fiber Anatomy

• Sarcolemma: Cell membrane of muscle fiber; conducts electrical signals.

• Sarcoplasmic Reticulum (SR): Stores and releases Ca2+ to control contraction.

• Sarcomere: Functional unit of muscle contraction, defined by Z-lines.

Regions of the Sarcomere and Their Changes During Contraction

Region	Description	Change During Contraction
Z-line	Boundary of sarcomere	Move closer together
I-band	Only actin	Shortens
A-band	Length of myosin	Stays the same
H-zone	Only myosin (center)	Shortens/disappears
M-line	Holds myosin together	Stays in center

Muscle Contraction: Excitation-Contraction Coupling

1. Action potential reaches T-tubule

2. SR releases Ca2+

3. Ca2+ binds troponin

4. SR reabsorbs Ca2+

5. Ca2+ levels in sarcoplasm drop

6. Muscle relaxes

Neuromuscular Junction

• Synapse between motor neuron and muscle fiber

• Neurotransmitter: Acetylcholine (ACh)

• Function: Initiates muscle contraction

Muscle Energy Systems

• Creatine Phosphate: Rapidly regenerates ATP for short, intense activity

• Rigor Mortis: Post-mortem muscle stiffening due to lack of ATP

Muscle Disorders

• Myasthenia Gravis: Autoimmune loss of ACh receptors; causes weakness

• Polio: Viral attack on motor neurons; causes paralysis

Nervous System Structure and Function

Functions of the Nervous System

• Sensory Function: Detects stimuli and sends information to CNS

• Integrative Function: Processes and interprets information in CNS

• Motor Function: Sends commands to effectors (muscles, glands, adipose tissue)

Divisions of the Nervous System

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

• Peripheral Nervous System (PNS): All nerves outside CNS

• Somatic Nervous System: Voluntary control of skeletal muscles

• Autonomic Nervous System (ANS): Involuntary control of smooth/cardiac muscle, glands, adipose tissue

Autonomic Nervous System Divisions

• Sympathetic: "Fight or flight"; increases heart rate, dilates pupils, slows digestion

• Parasympathetic: "Rest and digest"; slows heart rate, increases digestion

Neuron Types and Structure

• Anaxonic: No obvious axon; found in brain/sense organs

• Bipolar: One dendrite, one axon; special senses

• Unipolar: Fused dendrite and axon; sensory neurons in PNS

• Multipolar: Many dendrites, one axon; most common, all motor neurons

Structure	Function
Dendrites	Receive signals
Cell Body (Soma)	Processes information
Axon	Sends electrical impulses
Myelin Sheath	Insulates, speeds conduction
Nodes of Ranvier	Allow jumping of action potential
Axon Terminals	Release neurotransmitters
Synapse	Communication point

Myelin Sheath Formation

• Formed by Schwann cells (PNS) or oligodendrocytes (CNS)

• Glial cell wraps around axon, forming multiple layers

• Nodes of Ranvier: Gaps between myelinated segments; essential for saltatory conduction

Neuroglia (Glial Cells)

• Support, nourish, insulate, and protect neurons

• Microglia: Phagocytic cells removing debris and pathogens in CNS

• Satellite cells: Support sensory neuron cell bodies in ganglia

Sensory vs. Motor Division

Feature	Sensory Division	Motor Division
Direction	Body → CNS	CNS → Body
Type	Input	Output
Neurons	Sensory (Afferent)	Motor (Efferent)
What it Carries	Sensory Info	Motor Commands
Targets	CNS	Effectors
Subdivisions	Somatic sensory, visceral sensory	Somatic motor, autonomic motor

Synapses: Electrical vs. Chemical

Feature	Electrical Synapse	Chemical Synapse
Speed	Very Fast	Slower
Signal Type	Electrical ions	Chemical neurotransmitters
Direction	Bidirectional	Unidirectional
Gap	None (gap junctions)	Synaptic cleft
Flexibility	Low	High (excite/inhibit)
Common?	Rare	Very common
Found in	Heart, smooth muscle, some brain	Most neuron-neuron/muscle synapses

Calcium Ion (Ca2+) in Neuronal Function

• Triggers neurotransmitter release at synapses

• Contributes to depolarization and modulation of ion channels

• Activates intracellular signaling, gene expression, and synaptic plasticity (learning/memory)

Membrane Channels in Axons

Channel Type	Opens When	Ion Movement	Purpose
Leak Channels	Always open	Na+ in, K+ out	Resting membrane potential
Voltage-gated Na+	Threshold reached	Na+ in	Depolarization
Voltage-gated K+	After Na+	K+ out	Repolarization/hyperpolarization
Voltage-gated Ca2+	AP at terminal	Ca2+ in	Neurotransmitter release
Na+/K+ Pump	Always cycling	3 Na+ out, 2 K+ in	Restore gradients

Sodium-Potassium Pump

• Active transport protein using ATP

• Pumps 3 Na+ out, 2 K+ in

• Maintains resting membrane potential and ion gradients

Equation:

$3\ \mathrm{Na}^+_{\text{(in)}} + 2\ \mathrm{K}^+_{\text{(out)}} + \mathrm{ATP} \rightarrow 3\ \mathrm{Na}^+_{\text{(out)}} + 2\ \mathrm{K}^+_{\text{(in)}} + \mathrm{ADP} + \mathrm{P_i}$

Spinal Cord and Reflexes

Spinal Cord Structure

• Central pathway for sensory and motor signals

• 31 segments: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal

• Spinal nerves: Mixed sensory and motor, formed by merging dorsal (sensory) and ventral (motor) roots

• Conus Medullaris: Tapered end at L1-L2

• Filum Terminale: Connective tissue anchoring cord to coccyx

Spinal Meninges

• Dura Mater: Outermost, tough, protective

• Arachnoid Mater: Middle, web-like, contains CSF in subarachnoid space

• Pia Mater: Innermost, adheres to cord, contains blood vessels

Spaces:

• Epidural Space: Between dura and vertebrae; contains fat and blood vessels

• Subdural Space: Potential space between dura and arachnoid

• Subarachnoid Space: Between arachnoid and pia; contains CSF

Spinal Tap (Lumbar Puncture)

• Performed between L3-L4 or L4-L5 (below spinal cord)

• Needle enters subarachnoid space to collect CSF

Gray and White Matter in Spinal Cord

• Gray Matter: Inner region; contains neuron cell bodies, dendrites, and synapses

• White Matter: Outer region; contains myelinated axons for fast signal conduction

• Horns: Posterior (sensory), anterior (motor), lateral (autonomic)

• Gray Commissures: Connect right and left sides of gray matter

Reflexes and Effectors

• Reflex: Automatic, rapid, involuntary response to stimulus (e.g., withdrawal from pain)

• Effector: Muscle or gland that carries out the response

Posterior Root Ganglia

• Contain cell bodies of unipolar sensory neurons

• Supported by satellite glial cells

Spinal Cord vs. Vertebral Column

• Spinal Cord: Nervous tissue, part of CNS

• Vertebral Column: Bony structure protecting the spinal cord

Major Nerve Plexuses

• Brachial Plexus: Controls upper limb

• Lumbosacral Plexus: Controls lower limb

Additional info: For action potential phases and membrane potential graphs, refer to standard neurophysiology resources (e.g., textbook pages 422-423) for detailed diagrams and explanations.