Introduction to the Nervous System

Overview

The nervous system is a complex network responsible for monitoring, integrating, and responding to internal and external stimuli. It is essential for maintaining homeostasis and coordinating bodily functions.

• Monitoring: Detects changes in the environment through sensory receptors.

• Integration: Processes and interprets sensory input, making decisions about appropriate responses.

• Response: Initiates actions by activating muscles or glands (effectors).

Major Divisions of the Nervous System

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord, located within the dorsal body cavity. It serves as the main control center for processing information and directing responses.

• Brain: Responsible for higher functions such as thought, memory, and emotion.

• Spinal Cord: Conducts signals to and from the brain and controls reflex activities.

Peripheral Nervous System (PNS)

The PNS includes all neural tissue outside the CNS, such as nerves, ganglia, and sensory receptors. It connects the CNS to limbs and organs.

• Nerves: Bundles of axons transmitting signals.

• Ganglia: Clusters of neuron cell bodies in the PNS.

• Receptors: Specialized structures that detect stimuli.

Functional Divisions of the PNS

Sensory (Afferent) Division

This division transmits sensory information from receptors to the CNS.

• Somatic Sensory: Carries information from skin, skeletal muscles, and joints.

• Visceral Sensory: Carries information from internal organs (viscera).

Motor (Efferent) Division

This division carries motor commands from the CNS to effectors (muscles and glands).

• Somatic Motor: Controls voluntary movements by innervating skeletal muscles.

• Autonomic Motor (ANS): Regulates involuntary activities by innervating cardiac muscle, smooth muscle, and glands.

Key Functions of the Nervous System

• Monitoring Environments: Sensory receptors detect changes in both internal and external environments.

• Integration: The CNS processes sensory input and determines the appropriate response.

• Coordinating Responses: The nervous system initiates voluntary and involuntary actions to maintain homeostasis.

Example: Drinking Water

• Sensory Input: Receptors in the hand detect the presence of a glass.

• Integration: The brain processes this information and decides to pick up the glass.

• Motor Output: Motor neurons stimulate muscles in the arm to grasp and lift the glass.

Summary Table: Divisions of the Nervous System

Key Terms

• Neuron: The basic functional unit of the nervous system, specialized for transmitting electrical impulses.

• Effector: A muscle or gland that carries out the response to a nervous system command.

• Receptor: A structure that detects changes in the environment and initiates a nerve impulse.

• Afferent: Conducting toward the CNS (sensory).

• Efferent: Conducting away from the CNS (motor).

Additional info:

• The autonomic nervous system (ANS) is further divided into sympathetic and parasympathetic divisions, which have opposing effects on target organs.

• Neuroglia (glial cells) support and protect neurons but do not conduct impulses.