Biology & Neuroscience

Central and Peripheral Nervous System

The nervous system is divided into two main parts: the Central Nervous System (CNS) and the Peripheral Nervous System (PNS). Each plays a distinct role in processing and transmitting information throughout the body.

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

• Peripheral Nervous System (PNS): Composed of all nerves outside the CNS. Connects the CNS to limbs and organs, serving as a communication relay.

Example: The CNS processes information received from the PNS, such as touch or pain, and sends out instructions for movement or response.

Functions of the Nervous System

The nervous system is essential for receiving, processing, and responding to information from the environment and the body.

• Input: Receives information from sensory organs (e.g., eyes, skin).

• Processing: Integrates new sensory input with past experiences to make decisions.

• Output: Guides actions and responses, such as moving a hand away from a hot surface.

Example: Waking up to an alarm involves sensory input (sound), processing (recognizing the alarm), and output (turning off the alarm).

Cells of the Nervous System

Neuron

Neurons are the primary cells of the nervous system responsible for transmitting electrochemical signals.

• Definition: A nerve cell that sends and receives signals via electrical impulses and chemical neurotransmitters.

• Function: Communication within the nervous system, enabling sensation, thought, and movement.

Glial Cell

Glial cells support neurons by providing nourishment, insulation, and structural support.

• Definition: Non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons.

• Function: Support, nourish, and insulate neurons; involved in immune defense within the nervous system.

Example: Oligodendrocytes are a type of glial cell that form the myelin sheath in the CNS.

The Structure of the Neuron

Major Components of a Neuron

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

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

• Soma (Cell Body): Contains the nucleus; receives incoming signals from dendrites and passes them on.

• Axon: A long fiber that carries signals away from the soma toward other neurons or muscles.

• Myelin Sheath: Fatty layer covering the axon; increases the speed of signal transmission (up to 120 meters/second).

• Terminal Buttons: Endings of the axon that form junctions with other neurons and release neurotransmitters.

Example: The direction of signal travel in a neuron is from dendrites → soma → axon → terminal buttons.

Direction of Signal Transmission

Neural signals travel in one direction: from the dendrites, through the soma, along the axon, and out the terminal buttons.

• Signal Pathway: Dendrites → Soma → Axon → Terminal Buttons

• Neurotransmitter Release: At the terminal buttons, chemical messengers are released to communicate with other neurons or target cells.

Additional info: The myelin sheath is produced by oligodendrocytes in the CNS and Schwann cells in the PNS. Nodes of Ranvier are gaps in the myelin sheath that facilitate rapid signal conduction via saltatory conduction.

Summary Table: Neuron vs. Glial Cell

Additional info: Glial cells also play roles in immune defense and maintaining the blood-brain barrier.