Introduction to the Nervous System and Nervous Tissue: Overview and Anatomical Divisions

Introduction to the Nervous System and Nervous Tissue

Overview of the Nervous System

The nervous system is a complex network that controls our perception and experience of the world. It is responsible for directing voluntary movement and serves as the seat of consciousness, personality, learning, and memory. Alongside the endocrine system, the nervous system regulates many aspects of homeostasis, including:

• Respiratory rate

• Blood pressure

• Body temperature

• Sleep/wake cycle

• Blood pH

These regulatory functions are essential for maintaining the body's internal balance and responding to environmental changes.

Anatomical Divisions of the Nervous System

Central Nervous System (CNS)

The central nervous system (CNS) consists of the brain and spinal cord:

• Brain: Composed of billions of nerve cells called neurons, the brain is protected by the bones of the skull. It is the primary organ for processing information and coordinating responses.

• Spinal Cord: Begins at the foramen magnum and continues through the vertebral foramina from the first cervical to the first or second lumbar vertebra. The spinal cord contains millions of neurons (fewer than the brain) and enables the brain to communicate with most of the body below the head and neck.

Peripheral Nervous System (PNS)

The peripheral nervous system (PNS) includes all nerves outside the protection of the skull and vertebral column:

• Nerves: Bundles of axons from neurons, along with blood vessels and connective tissue. Nerves carry signals to and from the CNS and are classified based on their origin or destination.

• Cranial Nerves: 12 pairs of nerves that travel to or from the brain.

• Spinal Nerves: 31 pairs of nerves that travel to or from the spinal cord.

These divisions allow for the organization and specialization of nervous system functions throughout the body.

Visual Representation

Figure 11.1 illustrates the structure of the nervous system, showing the CNS (brain and spinal cord) and the PNS (cranial nerves and spinal nerves with their branches).

Key Terms Defined

• Neuron: The basic functional cell of the nervous system, specialized for transmitting electrical and chemical signals.

• Axon: A long, slender projection of a neuron that conducts electrical impulses away from the cell body.

• Homeostasis: The maintenance of a stable internal environment within the body.

Example

When you touch a hot surface, sensory nerves in the PNS detect the stimulus and send a signal to the CNS, which processes the information and sends a motor response back through the PNS to move your hand away.