Anatomy of the Nervous System

Main Divisions of the Nervous System

The nervous system is divided into two primary components: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each division has distinct structures and functions essential for processing and transmitting information throughout the body.

• Central Nervous System (CNS): Consists of the brain and spinal cord. Responsible for integrating sensory information and coordinating bodily responses.

• Peripheral Nervous System (PNS): Includes cranial and spinal nerves and peripheral ganglia. Connects the CNS to limbs and organs, facilitating communication between the body and the brain.

Functions of the Nervous System

Types of Neurons

Neurons are specialized cells that transmit electrical and chemical signals. They are classified based on their function:

• Sensory Neurons (Afferent): Detect changes in the internal and external environment and carry information from sensory organs to the brain.

• Motor Neurons (Efferent): Control muscle contraction and movement by transmitting information from the brain to the organs and muscles.

• Interneurons: Relay information between sensory and motor neurons, primarily found within the CNS.

Cells of the Nervous System

Glial Cells

Glial cells are non-neuronal cells in the CNS that provide support, protection, and nutrition to neurons. They play crucial roles in maintaining the environment necessary for neuronal function.

• Astrocytes: Provide physical support, regulate the chemical environment, and supply nutrients (such as lactate) to neurons.

• Oligodendrocytes: Produce myelin sheaths around axons in the CNS, which increase the speed of electrical signal transmission.

• Microglia: Act as the immune cells of the CNS, protecting neurons from invading organisms through phagocytosis.

Myelin Sheath: A fatty layer that surrounds and insulates axons, preventing electrical signals from spreading and increasing conduction speed.

Structure of Neurons

Neuron Anatomy

Neurons have specialized structures that enable them to transmit signals efficiently:

• Soma (Cell Body): Contains the nucleus and organelles responsible for the cell's metabolic activities and genetic information.

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

• Axon: A long, slender projection that conducts electrical impulses away from the soma toward other neurons or muscles.

• Axon Terminal (Terminal Button): The endpoint of an axon where neurotransmitters are released to communicate with other cells.

• Myelin Sheath: Insulates the axon and increases the speed of impulse transmission.

• Nodes of Ranvier: Gaps in the myelin sheath where action potentials are regenerated, allowing rapid signal conduction.

Key Structures and Functions

• Synapse: The junction between the axon terminal of one neuron and the dendrite or soma of another, where neurotransmitters are released.

• Neurotransmitter: Chemical messengers released by neurons to transmit signals across the synapse, producing excitatory or inhibitory effects on the postsynaptic cell.

Additional info:

• Action Potential: The rapid change in electrical charge across a neuron's membrane that allows the transmission of nerve impulses. The process involves depolarization and repolarization of the axonal membrane.

• Saltatory Conduction: The process by which action potentials jump from one node of Ranvier to the next, greatly increasing the speed of neural transmission.

• Formula for Resting Membrane Potential:

• Example: Damage to the myelin sheath, as seen in multiple sclerosis, leads to impaired signal transmission and neurological symptoms.