Nervous System Overview

Main Divisions of the Nervous System

The nervous system is responsible for coordinating and integrating bodily functions through electrical and chemical signaling. It is divided into two main components:

• Central Nervous System (CNS): Consists of the brain and spinal cord. This is where integrative and interpretive functions take place.

• Peripheral Nervous System (PNS): Composed of nerves and sensory organs that connect the CNS to the rest of the body.

Key Structures:

• Brain: The primary organ for processing and interpreting sensory information and directing responses.

• Spinal Cord: Conveys information to and from the brain and generates basic patterns of locomotion. It can produce reflexes independently of the brain.

• Nerves: Bundles of axons that transmit signals between the CNS and the body.

• Sensory Organs: Specialized structures for detecting environmental stimuli.

Reflexes

A reflex is the body's automatic response to a stimulus, often mediated by the spinal cord without direct involvement of the brain. For example, the knee-jerk reflex is triggered by a doctor using a mallet.

• Reflex Arc: The neural pathway involved in a reflex action.

• Example: Knee-jerk reflex, withdrawal from pain.

Peripheral Nervous System (PNS)

Functions and Components

The PNS transmits information to and from the CNS and regulates movement and the internal environment.

• Afferent Neurons: Carry signals towards the CNS to be integrated (sensory input).

• Efferent Neurons: Carry signals away from the CNS to stimulate muscles or glands (motor output).

Efferent Components of the PNS

The PNS has two efferent components:

• Motor System: Carries signals to skeletal muscles; actions can be voluntary or involuntary.

• Autonomic Nervous System: Regulates smooth and cardiac muscles; generally involuntary.

• Enteric Nervous System: Exerts direct, partially independent control over the digestive tract, pancreas, and gallbladder.

Divisions of the Autonomic Nervous System

The autonomic nervous system is further divided into:

• Sympathetic Division: Regulates arousal and energy generation; responsible for the "fight-or-flight" response.

• Parasympathetic Division: Promotes calming and a return to "rest-and-digest" functions; has antagonistic effects on target organs compared to the sympathetic division.

Glial Cells (Glia)

Types and Functions

In addition to neurons, the nervous system includes glial cells, which nourish, support, and regulate neurons.

• Schwann Cells: Form the myelin sheath in the PNS, which insulates axons and speeds up signal transmission.

• Oligodendrocytes: Form myelin in the CNS.

• Astrocytes: Participate in the formation of the blood-brain barrier, restricting entry of most substances into the brain.

• Other Functions: Glia are involved in maintaining homeostasis, providing nutrients, and modulating synaptic activity.

Comparison Table: CNS vs. PNS and Glial Cell Types

Summary of Nervous System Divisions

Additional info: The notes reference figures (48.3, 49.3, etc.) which likely illustrate these concepts, such as neural pathways, reflex arcs, and glial cell functions. For exam preparation, students should be familiar with the structure and function of each nervous system division, the roles of glial cells, and the basic mechanisms of reflexes and signal transmission.