Comprehensive Study Notes: Nervous System and Muscles & Muscle Tissue

Nervous System

Overview and Organization

The nervous system is responsible for receiving stimuli, integrating information, and coordinating responses via effectors. It is divided into central and peripheral components, each with sensory and motor functions.

• Homeostatic Reflex Circuit: Involves receptors (stimulus detection), control/integration centers, and effectors (response organs).

• Organization:

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

  • PNS (Peripheral Nervous System): All neural tissue outside CNS

  • Divisions:

    • Sensory Division: Afferent pathways

    • Motor Division: Efferent pathways, including autonomic (sympathetic and parasympathetic) and somatic systems

Types of Cells

• Neurons: Primary signaling cells

• Supporting Cells (Neuroglia):

  • Schwann cells & satellite cells: Found in PNS

  • CNS Neuroglia: Oligodendrocytes, astrocytes, microglia, ependymal cells

Nerve Structure

• Layers: Endoneurium, perineurium, epineurium

• Fascicles: Bundles of axons

• Mixed nerves: Contain both sensory and motor fibers

Neurophysiology

Neurophysiology focuses on how neurons transmit signals via electrical impulses and synaptic communication.

• Types of Channels:

  1. Passive (leakage) channels

  2. Active/gated channels:

     • Ligand (chemically) gated

     • Voltage gated

     • Mechanically gated

Graded Local Potentials & Action Potentials

Neurons communicate via graded potentials and action potentials, which are changes in membrane voltage.

• Resting Membrane Potential: The baseline electrical charge across the membrane, typically -70 mV.

• Action Potential: Rapid change in membrane potential due to ion movement.

Key Phases:

• Depolarization: Na+ influx

• Repolarization: K+ efflux

• Hyperpolarization: Excess K+ outflow

Typical Values:

• Resting potential: -70 mV

• Threshold: -55 mV

• Peak: +30 mV

• Depolarization: -70 to +30 mV

• Repolarization: +30 to -90 mV

• Hyperpolarization: -90 mV

Equation for Nerve Impulse Speed:

$\text{Conduction velocity} = \frac{\text{distance}}{\text{time}}$

Factors Affecting Speed:

• Myelination (faster conduction)

• Axon diameter (larger = faster)

Synaptic Transmission

• Types of Synapses: Electrical and chemical

• Neurotransmitters: Acetylcholine, norepinephrine, dopamine, etc.

Classification of Neurons

• Structural: Multipolar, bipolar, unipolar

• Functional: Sensory (afferent), motor (efferent), association (interneurons)

Muscles & Muscle Tissue

Muscle Characteristics

Muscle tissue is specialized for contraction and movement. There are three main types, each with unique features and functions.

• Types of Muscle:

  1. Skeletal

  2. Cardiac

  3. Smooth

• Functional Characteristics: Contractility, excitability, extensibility, elasticity

Skeletal Muscle

• Gross Anatomy: Muscle parts, attachments (origin/insertion), strength, and movement

• Microscopic Anatomy:

  • Myofibrils: Contractile units

  • Sarcomeres: Functional units, composed of actin and myosin filaments

  • Sarcoplasmic reticulum: Stores Ca2+

  • T-tubules: Conduct impulses

Sliding Filament Theory

Describes how muscles contract by actin and myosin filaments sliding past each other.

• ATP binds to myosin, allowing it to detach from actin

• Myosin head pivots, pulling actin filament

• Cycle repeats as long as Ca2+ and ATP are present

Muscle Contraction

• Phases: Latent period, contraction period, relaxation period

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

• Muscle Twitch: Single contraction event

Energy for Contraction

• Sources of ATP:

  • Direct phosphorylation (creatine phosphate)

  • Anaerobic glycolysis

  • Aerobic respiration

Equation for ATP Production:

$\text{Glucose} + 6\,\text{O}_2 \rightarrow 6\,\text{CO}_2 + 6\,\text{H}_2\text{O} + 36\,\text{ATP}$

Muscle Fiber Types

• Slow-twitch (Type I): Endurance, fatigue-resistant

• Fast-twitch (Type II): Rapid, powerful contractions, fatigue quickly

Smooth and Cardiac Muscle

• Cardiac Muscle: Found only in the heart, involuntary, striated

• Smooth Muscle: Found in walls of hollow organs, involuntary, non-striated

Summary Table: Muscle Types Comparison

Feature	Skeletal Muscle	Cardiac Muscle	Smooth Muscle
Location	Attached to bones	Heart	Walls of hollow organs
Control	Voluntary	Involuntary	Involuntary
Striations	Present	Present	Absent
Contraction Speed	Fast	Intermediate	Slow

Example: Skeletal muscles are used for voluntary movements such as walking, while cardiac muscle is responsible for pumping blood, and smooth muscle controls the movement of food through the digestive tract.

Additional info: Some details, such as the full list of neurotransmitters and the complete mechanism of muscle contraction, were expanded for academic completeness.