Neurophysiology: Structure and Function of the Neuron

Neurophysiology: Structure and Function of the Neuron

# Dendrites

• Function:

• Receive information from both the internal and external environment of the cell.

• Contain numerous receptors on the membrane.

• Characteristics:

• Short, branched cytoplasmic extensions.

• Each neuron has many dendrites.

• Contain numerous receptors on the membrane to receive information.

# Neuron Cell Body (Soma)

• Function:

• The central processing unit of the neuron.

• Conducts nerve impulses.

• Characteristics:

• Contains numerous Nissl bodies, giving the neuron cell body a gray color.

• Contains fewer organelles than other cells, primarily mitochondria.

• Differences from other cells:

• Contains numerous Nissl bodies, giving the neuron cell body a gray color.

• Note:

• The neuron cell bodies in the central nervous system form the gray matter.

# Axon

• Function:

• Conducts nerve impulses from the cell body to target cells.

• Characteristics:

• May or may not be covered in myelin.

• Myelinated axons are called white matter, which allows for faster nerve impulse conduction.

• Unmyelinated axons are called gray matter, and conduct impulses slower.

• The gaps between Schwann cells on myelinated axons are called nodes of Ranvier.

• Types of Axons:

• A alpha fibers: Conduct motor impulses to skeletal muscles, efferent fibers.

• A gamma fibers: Conduct impulses controlling muscle tone.

• A beta fibers: Conduct tactile sensations.

• A delta fibers: Conduct fast pain sensations.

• B fibers: Pre-ganglionic sympathetic fibers.

• C fibers: Conduct slow pain sensations and crude touch.

• Conduction Characteristics:

• Myelinated axons conduct impulses faster, through “saltatory conduction” across the nodes of Ranvier.

• Unmyelinated axons conduct impulses slower.

• The conduction speed on myelinated axons is proportional to the diameter of the axon.

• The conduction speed on various types of axons decreases in the following order: A alpha > A beta > A gamma > A delta > B > C.

# Synapse

• Structure:

• Presynaptic membrane: Axon terminal of the neuron.

• Synaptic cleft: Space between the pre-synaptic and post-synaptic membranes.

• Post-synaptic membrane: Membrane of the target cell (which can be a neuron, muscle cell, etc.).

• Mechanism of Transmission:

• Nerve impulses reaching the axon terminal trigger the release of neurotransmitters into the synaptic cleft.

• Neurotransmitters act on receptors on the post-synaptic membrane, causing a response in the target cell.

• Involvement of Ca++ ions:

• Ca++ ions enter the axon terminal, triggering the release of neurotransmitters into the synaptic cleft.

• Conditions Affecting Transmission:

• Depletion of neurotransmitters at the axon terminal.

• Reduced intracellular Ca++ concentration.

• Laws of Activity:

• “All-or-none” law: An axon either transmits a complete impulse or no impulse at all.

# Effects of Internal Environment on Neuron Activity

• Acidosis:

• Decreases neuronal excitability.

• Metabolic Alkalosis:

• Increases excitability, potentially leading to seizures.

# Drugs Affecting Neuron Activity

• Inhibition:

• Lidocaine, Seduxen, Propofol.

• Enhancement:

• Caffeine, Theophylline, Theobromine.

# Properties of Neurons

• High Functional Activity: Neurons can respond to high-frequency, rhythmic stimuli.

• Low Excitation Threshold: Neurons can be excited by weak stimuli.

# Related Concepts

• White matter: Collection of neuron cell bodies in the central nervous system.

• Gray matter: Collection of neuron cell bodies in the peripheral nervous system.

• Nerve: Collection of axons in the periphery and dendrites of ganglionic neurons.

• Nerve tract: Collection of axons in the central nervous system within a specific conduction pathway.

• Reflex center: Nervous structures involved in processing information and generating a response.

Conclusion

This article has provided basic knowledge on the structure and function of neurons. Understanding neuronal activity helps us to better comprehend the functioning of the nervous system, as well as to aid in the diagnosis and treatment of neurological disorders.