Nervous System Organization and Resting Membrane Potential (RMP)

Cellular Environment Maintenance

The nervous system maintains distinct environments inside and outside cells, crucial for electrical signaling. This is achieved through selective permeability of the plasma membrane and active transport mechanisms.

• Selective permeability: Cell membranes allow certain ions to pass while restricting others, maintaining concentration gradients.

• Active transport: The Na+-K+ ATPase pump moves sodium out and potassium into the cell, using ATP.

• Homeostasis: Ensures optimal conditions for nerve function.

Ion Channels and Na+-K+ ATPase Pump

These proteins are essential for generating the resting membrane potential and action potentials.

• Na+-K+ ATPase: Maintains high K+ inside and high Na+ outside the cell.

• Leak channels: Allow passive movement of ions, especially K+, contributing to RMP.

• Voltage-gated channels: Open in response to changes in membrane potential, crucial for action potentials.

Gradients and Permeability

Ion movement is determined by concentration gradients, electrical gradients, and membrane permeability.

• Concentration gradient: Difference in ion concentration across the membrane.

• Electrical gradient: Difference in charge across the membrane.

• Permeability: How easily ions cross the membrane.

• Direction of ion movement: Determined by the combined effect of these gradients.

Structural and Functional Classification of Neurons and Glial Cells

• Neurons: Specialized for transmitting electrical signals. Classified by structure (multipolar, bipolar, unipolar) and function (sensory, motor, interneuron).

• Glial cells: Support neurons. Types include astrocytes, oligodendrocytes (CNS), Schwann cells (PNS), microglia.

Parts of the Neuron

• Dendrites: Receive signals.

• Cell body (soma): Integrates signals.

• Axon: Conducts action potentials.

• Axon terminals: Transmit signals to other cells.

CNS vs. PNS

• CNS (Central Nervous System): Brain and spinal cord; contains neurons and glial cells like astrocytes and oligodendrocytes.

• PNS (Peripheral Nervous System): Nerves outside CNS; contains Schwann cells and satellite cells.

Action Potential Phases Graph

• Phases: Resting, depolarization, repolarization, hyperpolarization.

• Graph: Shows membrane potential changes over time.

Nervous System – Action Potential (AP)

Key Terms

• Depolarization: Membrane potential becomes less negative.

• Repolarization: Membrane potential returns to resting value.

• Hyperpolarization: Membrane potential becomes more negative than resting.

Action Potential Graph

• Resting phase: Stable negative potential.

• Depolarization: Rapid rise due to Na+ influx.

• Repolarization: K+ efflux restores negativity.

• Hyperpolarization: Temporary overshoot.

Long-Distance Signal Propagation

• Axons: Conduct action potentials over long distances.

• Myelination: Increases speed via saltatory conduction.

Effects of Channel or Pump Perturbation

• Na+ or K+ channel dysfunction: Alters action potential shape and propagation.

• Na+-K+ pump inhibition: Gradually disrupts RMP and AP generation.

Myelination Effects

• Loss of myelin: Slows or blocks AP propagation (e.g., multiple sclerosis).

Refractory Periods

• Absolute refractory period: No new AP can be generated; Na+ channels inactivated.

• Relative refractory period: AP possible with stronger stimulus; K+ channels still open.

Nervous System – Synapses

Chemical Synapse Communication

Neurons communicate via synapses, where neurotransmitters are released and bind to receptors on the next cell.

• Neurotransmitter release: Triggered by Ca2+ influx.

• Receptors: Determine response in postsynaptic cell.

• Clearance: Removal of neurotransmitter by reuptake, degradation, or diffusion.

Disturbance Effects

• Impaired release: Reduces signal transmission.

• Receptor dysfunction: Alters cell response.

• Impaired clearance: Prolongs or disrupts signaling.

Nervous System – Sensory Physiology

Information Flow

• Sensory input: Detected by receptors.

• Integration: Processed in CNS.

• Motor output: Response generated.

Sensory Transduction

• Sensory neurons: Convert stimuli into action potentials.

• Specialized receptors: Photoreceptors, mechanoreceptors, chemoreceptors, etc.

Types of Receptors

• Photoreceptors: Detect light.

• Mechanoreceptors: Detect touch, pressure.

• Chemoreceptors: Detect chemicals.

• Thermoreceptors: Detect temperature.

Photoreceptor Function

• Opsins: Light-sensitive proteins.

• Channel changes: Affect neurotransmitter release.

• Light level changes: Modify receptor activity.

Nervous System – Motor Control

Somatic vs. Autonomic Nervous System

• Somatic: Controls voluntary skeletal muscle.

• Autonomic: Regulates involuntary functions (heart, glands).

Neuromuscular Junction (NMJ)

• Structure: Synapse between motor neuron and muscle fiber.

• Events: Acetylcholine release, receptor activation, muscle contraction.

Channel, Enzyme, and Pump Effects

• Channel dysfunction: Impairs muscle contraction.

• Enzyme inhibition: Alters neurotransmitter breakdown.

• Pump failure: Disrupts ion gradients, affecting contraction.

Muscle Types Comparison

Contractile and Regulatory Protein Effects

• Disturbance: Alters contraction strength and rhythm.

• Ca2+ role: Essential for contraction in skeletal and cardiac muscle.

Sliding Filament Theory

• Explanation: Muscle contraction occurs as actin and myosin filaments slide past each other, powered by ATP.

Nervous System – Motor Control and Autonomic Nervous System (ANS)

Somatic vs. Autonomic Nervous System

• Somatic: Voluntary control.

• Autonomic: Involuntary control; includes sympathetic and parasympathetic divisions.

Sympathetic vs. Parasympathetic Activation

• Sympathetic: Activated during stress ('fight or flight').

• Parasympathetic: Activated during rest ('rest and digest').

Neurotransmitters/Hormones

• Sympathetic: Releases norepinephrine and epinephrine.

• Parasympathetic: Releases acetylcholine.

Receptor Differences

Example: During exercise, the sympathetic nervous system increases heart rate and blood flow to muscles.

Additional info: The resting membrane potential is typically around -70 mV, calculated using the Nernst equation: Action potentials are all-or-none events, and their propagation depends on the integrity of ion channels and myelin sheaths.