Fundamentals of the Nervous System: Structure and Function

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Nervous System Overview

Divisions of the 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 specialized structures and functions.

Central Nervous System (CNS): Consists of the brain and spinal cord. Responsible for processing and integrating information.
Peripheral Nervous System (PNS): Includes all neural tissue outside the CNS. Subdivided into sensory (afferent)motor (efferent)

PNS Subdivisions

Sensory Division: Transmits sensory information from receptors to the CNS.
- Visceral sensory division: Carries signals from organs.
- Somatic sensory division: Carries signals from skin, muscles, and joints.
Motor Division: Transmits commands from the CNS to effectors.
- Visceral motor division (Autonomic Nervous System): Controls involuntary functions.
  - Sympathetic division: Prepares body for 'fight or flight'.
  - Parasympathetic division: Promotes 'rest and digest' activities.
- Somatic motor division: Controls voluntary movements of skeletal muscles.

Functional Organization: Sensory and Motor Pathways

Sensory (afferent) neurons carry information to the CNS, while motor (efferent) neurons carry commands from the CNS to muscles and glands.

Afferent (Sensory) Pathways: Skin and other receptors send signals to the spinal cord and brain.
Efferent (Motor) Pathways: CNS sends signals to muscles and glands to elicit responses.

Neurons: Structure and Function

Parts of a Neuron

Neurons are the basic functional units of the nervous system. They have specialized structures for receiving, processing, and transmitting information.

Dendrites: Receive incoming signals from other neurons.
Cell body (Soma): Contains the nucleus and organelles; integrates signals.
Axon: Conducts electrical impulses away from the cell body.
Axon terminals: Release neurotransmitters to communicate with other cells.
Myelin sheath: Insulates the axon, increasing the speed of impulse transmission.

Types of Neurons

A neurons: Large, fast-conducting, myelinated fibers.
B neurons: Smaller, myelinated fibers with intermediate conduction speed.
C neurons: Small, unmyelinated fibers; slowest conduction.

Neuroglia (Glial Cells)

Major Types and Functions

Neuroglia support and protect neurons. Different types are found in the CNS and PNS.

Cell Type	Main Function
Astrocyte	Support neurons, maintain blood-brain barrier, regulate ion balance
Microglia	Phagocytosis of debris and pathogens
Ependymal cell	Line ventricles, produce and circulate cerebrospinal fluid
Oligodendrocyte	Form myelin sheaths in CNS
Schwann cell	Form myelin sheaths in PNS
Satellite cell	Support neurons in PNS ganglia
Myelin	Insulates axons, increases conduction speed

Electrical Signaling in Neurons

Resting Membrane Potential

Neurons maintain a polarized membrane at rest, with different ion concentrations inside and outside the cell.

Na+ (Sodium): Higher concentration outside the cell.
K+ (Potassium): Higher concentration inside the cell.

The resting membrane potential is typically around .

Action Potential Phases

Depolarization: Na+ channels open, Na+ enters the cell, making the inside more positive.
Repolarization: K+ channels open, K+ leaves the cell, restoring negative charge inside.
Hyperpolarization: K+ channels remain open longer, making the inside even more negative than resting potential.

Propagation of Action Potentials

Continuous Conduction: Occurs in unmyelinated axons; action potential moves along every part of the membrane.
Saltatory Conduction: Occurs in myelinated axons; action potential 'jumps' from one node of Ranvier to the next, increasing speed.

Neuronal Communication

Synapses and Neurotransmitters

Neurons communicate at specialized junctions called synapses. The presynaptic neuron releases chemical messengers called neurotransmitters that bind to receptors on the postsynaptic cell.

Synapse: Site of communication between two neurons or a neuron and an effector cell.
Presynaptic neuron: Releases neurotransmitter.
Postsynaptic neuron: Receives neurotransmitter.

Types of Neurotransmitters

Biogenic amines: Examples include dopamine, norepinephrine, serotonin.
Amino acids: Examples include glutamate, GABA, glycine.
Peptides: Examples include endorphins, substance P.

Example: Synaptic Transmission

An action potential arrives at the axon terminal of the presynaptic neuron.
Neurotransmitter is released into the synaptic cleft.
Neurotransmitter binds to receptors on the postsynaptic membrane, causing a response.

Additional info: The notes infer the basic organization and function of the nervous system, including the role of glial cells and the mechanisms of electrical and chemical signaling. The table of glial cells was completed based on standard academic knowledge.