Nervous System and Action Potentials Notes

Functions of the Nervous System

• Communication: All functions in the body involve communication through electrical signals.

• Control and Coordination: Regulates body systems and responds to external stimuli.

• Integration of Information: Processes sensory input for perception and response.

Divisions of the Nervous System

• Central Nervous System (CNS): Comprises the brain and spinal cord, responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Includes all nerves outside the CNS, facilitating communication between the CNS and the rest of the body.

Somatic vs. Autonomic Nervous Systems

• Somatic Nervous System: Controls voluntary movements via skeletal muscles.

• Autonomic Nervous System: Regulates involuntary functions, further divided into:

  • Sympathetic: Prepares body for 'fight or flight' response.

  • Parasympathetic: Promotes 'rest and digest' activities.

CNS vs. PNS Functions

• CNS: Analyzes sensory data; coordinates response.

• PNS: Transmits sensory information to CNS; carries out responses from CNS to target organs.

Neuron Structure and Function

• Main Components:

  • Cell Body: Contains nucleus; integrates signals.

  • Dendrites: Receive incoming signals.

  • Axon: Transmits impulses away from the cell body.

• Types of Neurons:

  • Sensory Neurons: Transmit sensory information to CNS.

  • Motor Neurons: Transmit commands from CNS to muscles or glands.

  • Interneurons: Connect sensory and motor neurons.

Neuroglial Cells

• Support Cells in CNS:

  • Astrocytes: Support neurons; regulate blood flow.

  • Oligodendrocytes: Form myelin sheath around CNS axons.

  • Microglia: Immune defense for the CNS.

• Support Cells in PNS:

  • Schwann Cells: Form myelin sheath around PNS axons.

  • Satellite Cells: Support neuron cell bodies in ganglia.

Resting Membrane Potential (RMP)

• Definition: The electrical charge difference across a resting neuron's membrane; typically around -70 mV.

• Establishment:

  • Maintained by K+ leak channels and the Na+/K+ pump.

  • Higher concentration of Na+ and Cl- outside; K+, proteins, and PO4^-3 inside.

Neural Excitability and Action Potentials

• Process:

  • Depolarization: Na+ channels open; interior cell becomes positive.

  • Repolarization: Na+ channels close; K+ channels open; interior returns to negative.

  • Afterpotential: Period where K+ continues to leave, making membrane potential more negative.

• Types of Potentials:

  • Graded Potential: Localized changes that can summate but do not propagate far.

  • All-or-None Principle: Once threshold is reached, action potential occurs fully.

Conduction Velocity

• Factors:

  • Myelination increases speed (saltatory conduction) as impulses jump between Nodes of Ranvier.

  • Unmyelinated axons conduct impulses more slowly by depolarizing each segment sequentially.

Synapses

• Components:

  • Pre-synaptic terminal, membrane, post-synaptic membrane, and synaptic cleft.

  • Types:

  • Electrical Synapse: Direct electrical signal transfer; less common.

  • Chemical Synapse: Uses neurotransmitters to transmit signals.

• Neurotransmitter Removal:

  • Mechanisms: Enzymatic breakdown, re-absorption, or diffusion away.

Reflex vs. Reaction

• Reflection: An automatic, rapid response to stimuli, typically involving a reflex arc (e.g., withdrawal reflex).

• Reaction: A conscious, voluntary response which may take longer to process through the CNS.

Compendium Questions for Review

1. Functions of the nervous system?

2. Difference between CNS and PNS?

3. Roles of somatic, autonomic, and enteric divisions?

4. Components of a neuron?

5. Differences between sensory, motor, and interneurons?

6. Neuroglial cells in the CNS and PNS?

7. Definition of resting membrane potential?

8. Voltage differences on either side of the membrane?

9. Changes in RMP when a neuron is stimulated?

10. Conduction velocity differences between myelinated and unmyelinated cells?

11. Processes occurring at the synapse?

12. Main parts of a reflex arc?

13. Difference between reflex and reaction?