Fundamentals of Neurology: Structure and Function of the Nervous System

Function of the Nervous System

Overview of Nervous System Functions

The nervous system is a complex network responsible for controlling and coordinating all bodily functions. It acts as both a control center and a communication network, integrating voluntary and involuntary activities to maintain homeostasis.

• Control: The brain serves as the central command, integrating all body functions.

• Communication Network: Nerve pathways relay information throughout the body, ensuring rapid and precise responses.

• Controls Movement: Voluntary actions (e.g., skeletal muscle movement) and involuntary actions (e.g., breathing, glandular release).

• Homeostatic Control: Regulates hormonal influence, immune response, temperature, and other vital processes.

Table: Major Functions of the Nervous System

Control	Communication Network
"Brain" integrates all body functions	Nerve "highways" relay information
Controls Movement	Homeostatic Control
Skeleton (voluntary), Breathing (involuntary), Glandular release	Hormonal influence, Immune response, Temperature regulation

Divisions of the Nervous System

Central vs. Peripheral Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each division has distinct structures and functions.

• Central Nervous System (CNS): Composed of the brain and spinal cord. Responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Connects the CNS to somatic and visceral body parts. Includes cranial nerves (CN) and spinal nerves.

Key Pathways

• Sensory (Ascending/Afferent): Carries information toward the brain.

• Motor (Descending/Efferent): Carries commands away from the brain to effectors.

Neurons: Structure and Properties

Special Properties of Neurons

Neurons are the primary functional cells of the nervous system, specialized for rapid communication.

• Irritability: Ability to respond to stimuli.

• Propagation of Impulses: Ability to conduct electrical impulses along their membrane.

Functional Classification of Neurons

• Sensory Neurons: Receive sensory stimuli from the environment and within the body. Example: Unipolar neurons.

• Motor Neurons: Control effector organs such as muscles and glands.

• Interneurons: Found in the CNS; connect sensory and motor neurons, facilitating communication.

• Neurosecretory Neurons: Specialized to synthesize and secrete hormones.

Types of Nerve Cells

Neurons and Glial Cells

Nerve tissue consists of two main cell types: neurons and glial cells. Each plays a unique role in nervous system function.

• Neurons:

  • Polarize/repolarize to transmit signals

  • Release neurotransmitters

  • Multipolar (motor), Unipolar (somatic sensory), Bipolar (special sensory)

• Glial Cells:

  • Supportive cells, highly mitotic

  • Astrocytes: Form the blood-brain barrier

  • Microglia: Act as immune cells (macrophage equivalent)

  • Ependymal Cells: Produce cerebrospinal fluid (CSF)

  • Schwann Cells/Oligodendrocytes: Form myelin in PNS/CNS respectively

Neuroglia

Definition and Importance

Neuroglia (or glial cells) are non-neuronal cells that provide structural and functional support to neurons. They are essential for the development, maintenance, and protection of nervous tissue.

• Outnumber neurons by at least 10:1, but are much smaller

• Occupy about 50% of nerve tissue volume

• Four basic types based on morphology and function:

1. Astrocytes (Astroglia): Maintain the blood-brain barrier, provide structural support

2. Oligodendrocytes: Myelinate CNS axons, provide structural framework

3. Microglia: Brain's immune cells, remove debris and pathogens

4. Ependymal Cells: Line ventricles, produce and circulate CSF

Table: Neuroglial Cell Types and Functions

Cell Type	Location	Function
Astrocytes	CNS	Blood-brain barrier, support
Oligodendrocytes	CNS	Myelinate axons
Microglia	CNS	Immune defense
Ependymal Cells	CNS	Produce CSF
Satellite Cells	PNS	Support neuron cell bodies
Schwann Cells	PNS	Myelinate axons

Additional info:

• Neurons are classified by structure (multipolar, unipolar, bipolar) and function (sensory, motor, interneuron, neurosecretory).

• Glial cells are essential for neuron survival, repair, and metabolic support.

• Myelination increases the speed of nerve impulse conduction via saltatory conduction.