Nervous System Structure and Function: Study Notes for Lab Exam #3

Nervous System Structure and Function

Overview of the Nervous System

The nervous system is a complex network responsible for coordinating body activities by transmitting signals to and from different parts of the body. It is composed of specialized cells called neurons and supporting cells known as neuroglia.

• Central Nervous System (CNS): Consists of the brain and spinal cord. It processes information and coordinates activity throughout the body.

• Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS. It connects the CNS to limbs and organs.

Neurons: Structure and Function

Neurons are the fundamental units of the nervous system, specialized for the transmission of electrical and chemical signals.

• Cell Body (Soma): Contains the nucleus and organelles; responsible for metabolic activities.

• Dendrites: Branch-like extensions that receive signals from other neurons.

• Axon: A long projection that transmits electrical impulses away from the cell body.

• Axon Terminals: The endpoints where neurotransmitters are released to communicate with other cells.

• Myelin Sheath: An insulating layer (formed by Schwann cells in the PNS or oligodendrocytes in the CNS) that increases the speed of impulse transmission.

• Nodes of Ranvier: Gaps in the myelin sheath that facilitate rapid signal conduction via saltatory conduction.

Example: The image above shows a model of a neuron, highlighting the cell body, dendrites, axon, and myelin sheath.

Neuroglia (Glial Cells)

Neuroglia are supporting cells that provide structural and metabolic support to neurons.

• Astrocytes: Maintain the blood-brain barrier and provide nutrients to neurons.

• Oligodendrocytes: Form myelin sheaths in the CNS.

• Schwann Cells: Form myelin sheaths in the PNS.

• Microglia: Act as immune cells within the CNS.

Signal Transmission in Neurons

Neurons communicate through electrical impulses (action potentials) and chemical signals (neurotransmitters).

• Resting Membrane Potential: The difference in electrical charge across the neuron's membrane at rest, typically around -70 mV.

• Action Potential: A rapid change in membrane potential that travels along the axon. Initiated when the membrane depolarizes beyond a threshold.

• Saltatory Conduction: In myelinated axons, action potentials jump from one node of Ranvier to the next, increasing conduction speed.

Equation:

$V_m = V_{in} - V_{out}$

Where $V_m$ is the membrane potential, $V_{in}$ is the potential inside the cell, and $V_{out}$ is the potential outside the cell.

Classification of Neurons

Neurons can be classified based on structure and function.

• Structural Classification:

  • Multipolar: Many dendrites, one axon (most common in CNS).

  • Bipolar: One dendrite, one axon (found in sensory organs).

  • Unipolar: Single process that splits into two branches (sensory neurons in PNS).

• Functional Classification:

  • Sensory (Afferent) Neurons: Transmit impulses from receptors to CNS.

  • Motor (Efferent) Neurons: Carry impulses from CNS to effectors (muscles/glands).

  • Interneurons: Connect sensory and motor neurons within the CNS.

Summary Table: Neuron Types and Functions

Type	Structure	Function	Location
Multipolar	Many dendrites, one axon	Motor, interneurons	CNS
Bipolar	One dendrite, one axon	Sensory	Retina, olfactory epithelium
Unipolar	Single process splits into two	Sensory	PNS

Additional info: The provided images and notes are consistent with the study of nervous tissue, neuron structure, and function, which are core topics in Anatomy & Physiology courses.