Neurophysiology Overview

Neurophysiology Summary

Organization of the Nervous System

  • CNS (Central Nervous System): Structural and functional center.

  • PNS (Peripheral Nervous System): Includes nerve tissues, spinal nerves, cranial nerves.

  • Divided into Afferent (sensory) and Efferent (motor) divisions.

Functional Regions of the Nervous System

  • Somatic Nervous System (SNS): External sense organs, skeletal muscles.

  • Autonomic Nervous System (ANS): Involuntary functions; further divided into Sympathetic and Parasympathetic.

Neurons

  • Basic functional unit; respond to excitation/inhibition.

  • Types: Afferent (toward CNS), Efferent (away from CNS), Mixed (both).

  • Structure: Dendritic zone, cell body, axon hillock, axon, synaptic knobs.

Peripheral Nerve Anatomy

  • Nerves: Bundles of axons; myelin formed by glial cells.

  • Nodes of Ranvier enable rapid electrical impulse propagation (saltatory conduction).

Nerve Fiber Classification

  • Type A: Large, myelinated, fast.

  • Type B: Medium, myelinated, moderate speed.

  • Type C: Small, unmyelinated, slow.

Action Potentials

  • All-or-None Principle: Complete response required if action occurs.

  • Polarization: Resting state (-70 mV normal).

  • Depolarization: Na+ influx leads to action potential; threshold at -50 mV.

  • Repolarization: Returns to resting potential post-peak.

Conduction and Local Anesthetics

  • Local anesthetics inhibit sodium influx via voltage-gated sodium channels.

  • Smaller fibers more sensitive; larger fibers require more anesthetic.

  • Blocks occur in the order of small myelinated -> nonmyelinated -> large myelinated fibers.

  • Large nerve trunks need more anesthetic for effective blockage.