Nervous System Notes

Nervous System Overview

• A.K. Daemicke

Learning Objectives

• Understand key concepts of:

  • Cell structure, function, and processes

  • Membrane structure and function

  • Transport across membranes

  • Communication systems in animals

  • Structures and functions of the nervous system

Body System Communication

• Human communication systems include:

  • Nervous System: Uses electrochemical signals.

    • Fast, targeted, and short-lived responses.

  • Endocrine System: Uses hormonal signals.

    • Generally slower, wide-spread, and sustained responses.

Functions of the Nervous System

• Sensory Functions: Receive information from sensory receptors.

• Integrative Functions: Analyze and store incoming information.

• Motor Functions: Respond appropriately to incoming stimuli.

Divisions of the Nervous System

• Central Nervous System (CNS):

  • Composed of the brain and spinal cord.

• Peripheral Nervous System (PNS):

  • Comprised of nerves extending from the CNS.

Nervous System Structure

• Neural Components:

  • Sensory Input

  • Integration (Brain and spinal cord)

  • Motor Output through Effectors.

Anatomy of Neural Tissue

Basic Neuron Structure

• Components:

  • Cell Body: Contains nucleus and organelles.

  • Dendrites: Receive information and convey it to the cell body.

  • Axon: Conducts impulses away from the cell body.

  • Axon Terminals: End points for neurotransmitter release.

• Neuronal Classifications:

  • Motor Neurons

  • Interneurons

  • Sensory Neurons

Cell Body Characteristics

• Unable to divide mitotically, affecting its response to injury.

• Longevity: can exceed 100 years.

• High metabolic demand for glucose and oxygen.

• Unique organelles: Nissl bodies, neurofibrils.

Axons

• Structure: Max of two axons per neuron, with side branches called collaterals.

• Function: Conducts impulses away from the cell body.

Axonal Transport

• Methods:

  • Anterograde: From cell body to axon terminals.

  • Retrograde: From axon to cell body.

• Substances transported include organelles, ions, and nutrients.

Myelination

• White Matter: Myelinated nerve fibers, appear white.

  • Function: Speeds up nerve impulse transmission.

• Gray Matter: Unmyelinated nerve fibers, appear gray.

  • Function: Involves processing of information.

Myelin Sheath Structure

• Formed by Schwann cells.

• Nodes of Ranvier: Gaps allowing for rapid impulse conduction.

Cell Membrane Characteristics

• Phospholipid Bilayer: Resting potential where the inside is negative.

• Membrane Potential: Energy within the membrane that keeps opposite charges apart.

Resting Membrane Potential

• Net negative charge inside the cell compared to the outside:

  • Intracellular: High K+, low Na+.

  • Extracellular: High Na+, low K+.

• Ion Gradients: Maintained by ion pumps (Na+/K+ ATPase).

Action Potentials

• Properties:

  • Initiate when threshold potential is reached (-55 mV).

  • Voltage change creates a fast depolarization and repolarization phase.

• Refractory Periods:

  • Absolute: No new action potential possible.

  • Relative: Requires stronger stimulus to initiate.

Saltatory Conduction

• Action potentials jump through myelinated axons through Nodes of Ranvier, speeding transmission.

Communication Process

• Classified as electrochemical:

  • Action Potential Phase: Generates neurotransmitter release.

• Graded Potentials: Changes in membrane potential based on neurotransmitter binding.

  • Determines if threshold potential is reached for firing.

Neurotransmitter Roles

• Excitatory Neurotransmitters (e.g., Glutamate) cause depolarization.

• Inhibitory Neurotransmitters (e.g., GABA) induce hyperpolarization.

• Firing of neuron occurs if depolarization exceeds hyperpolarization.

Neurotransmitter Removal Mechanisms

• Enzymatic degradation, reuptake, diffusion, and action of glial cells.

Anesthetics Mechanism

• Block intracellular sodium channels, preventing Na+ influx and subsequent action potentials, blocking pain signals.