Chapter 11: The Nervous System – Structure and Function

Nervous System Overview

Introduction to the Nervous System

The nervous system is the master controlling and communicating system of the body. It is responsible for regulating and coordinating all body activities by transmitting signals between different parts of the body.

• Sensory input: Monitoring internal and external stimuli.

• Integration: Interpretation and processing of sensory input.

• Motor output: Initiating a response to stimuli by activating effector organs (muscles and glands).

Organization of the Nervous System

Central Nervous System (CNS)

The CNS consists of the brain and spinal cord. It serves as the integration and command center, processing information and issuing instructions.

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

• Spinal cord: Conducts signals to and from the brain; responsible for reflexes.

Peripheral Nervous System (PNS)

The PNS includes all neural structures outside the CNS: paired spinal and cranial nerves. It links all parts of the body to the CNS and carries messages to and from the CNS.

• Spinal nerves: Carry impulses to and from the spinal cord.

• Cranial nerves: Carry impulses to and from the brain.

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

Functional Divisions of the PNS

Sensory (Afferent) Division

The sensory division transmits impulses from sensory receptors to the CNS.

• Somatic afferent fibers: Carry impulses from skin, skeletal muscles, and joints.

• Visceral afferent fibers: Carry impulses from visceral organs (organs within the ventral body cavity).

Motor (Efferent) Division

The motor division transmits impulses from the CNS to effector organs (muscles and glands).

• Somatic nervous system: Known as the "voluntary nervous system"; controls skeletal muscles via somatic motor nerve fibers. Allows conscious control of movement.

• Autonomic nervous system (ANS): Known as the "involuntary nervous system"; regulates smooth muscle, cardiac muscle, and glands via visceral motor nerve fibers. Subdivided into sympathetic and parasympathetic branches.

Histology of Nerve Tissue

Principal Cell Types

• Neurons: Excitable cells that transmit electrical signals. They are the structural and functional units of the nervous system.

• Neuroglia (glial cells): Supporting cells that surround and wrap neurons. They provide structural support, insulation, and aid in the health and maintenance of neurons.

Supporting Cells: Neuroglia

Neuroglia, or glial cells, are essential for the proper functioning of neurons. They:

• Insulate neurons to speed up action potential (AP) conduction.

• Promote health and growth of neurons.

• Provide structural support and maintain the extracellular environment.

Summary Table: Organization of the Nervous System

Division	Main Components	Function
Central Nervous System (CNS)	Brain, Spinal Cord	Integration, command, processing
Peripheral Nervous System (PNS)	Cranial nerves, Spinal nerves, Ganglia	Communication between CNS and body
Sensory (Afferent) Division	Somatic and Visceral afferent fibers	Transmit sensory input to CNS
Motor (Efferent) Division	Somatic and Autonomic nervous systems	Transmit motor output from CNS to effectors

Key Terms and Definitions

• Neuron: A nerve cell; the basic building block of the nervous system.

• Neuroglia (Glial cells): Non-neuronal cells that provide support and protection for neurons.

• Afferent: Conducting toward a center; sensory.

• Efferent: Conducting away from a center; motor.

• Somatic: Relating to the body, especially as distinct from the mind.

• Autonomic: Involuntary or unconscious; relating to the autonomic nervous system.

Example: Functional Pathway

• A person touches a hot object (stimulus).

• Sensory receptors in the skin send an impulse via afferent fibers to the CNS.

• The CNS processes the information and sends a response via efferent fibers to the muscles (effectors), causing the hand to withdraw.