Topic 2.2: Physiology of the Neuron

Overview

The physiology of neurons is central to understanding how the nervous system functions. Neurons are specialized cells responsible for receiving, propagating, and transmitting nerve impulses. This topic covers the structure of neurons, their unique properties, and the mechanisms underlying their electrical activity and synaptic transmission.

Structural Regions of the Neuron

Neurons have distinct regions, each associated with specific functions in the transmission of nerve impulses.

• Receptive Region: Includes dendrites and the cell body (soma). Responsible for receiving signals from other neurons.

• Conducting Region: The axon, which propagates electrical impulses away from the cell body.

• Secretory Region: The axon terminals, where neurotransmitters are released to communicate with other cells.

Example: Dendrites receive input, the axon conducts the action potential, and the axon terminals release neurotransmitters at the synapse.

Special Properties of Neurons

• Extreme Longevity: Neurons can live for over 100 years if adequately nourished.

• Amitotic: Most neurons do not divide after development. Damage to neurons is often permanent.

• High Metabolic Rate: Neurons require continuous supply of oxygen and glucose to function.

Definition: Amitotic means the cell does not undergo mitosis (cell division).

Neuron Structure

• Cell Body (Soma): Contains the nucleus and organelles; site of biosynthetic activity.

• Dendrites: Short, branched extensions that increase surface area for receiving signals.

• Axon: Long process that conducts impulses; may branch into many axon terminals.

Additional info: The cell body contains rough endoplasmic reticulum (Nissl bodies), Golgi apparatus, and mitochondria for energy and protein synthesis.

Neuron Processes and Terminology

• Tract: Bundle of nerve processes in the central nervous system (CNS).

• Nerve: Bundle of nerve processes in the peripheral nervous system (PNS).

• Nucleus: Cluster of neuron cell bodies in the CNS.

• Ganglion: Cluster of neuron cell bodies in the PNS.

Functional Regions and Their Roles

• Receptive Region: Dendrites and soma; receive and integrate incoming signals.

• Conducting Region: Axon; generates and propagates action potentials.

• Secretory Region: Axon terminals; release neurotransmitters into the synaptic cleft.

Key Questions

• Where are action potentials generated? At the axon hillock.

• In what direction do action potentials travel? From the axon hillock toward the axon terminals.

• How many neurons can a single neuron receive from or transmit to? Each neuron can receive input from thousands of other neurons and transmit to thousands more.

Additional info:

Neurons are highly interconnected, forming complex networks that enable sophisticated processing and integration of information.