The Nervous System

Overview and Control Functions

The nervous system is the primary control and communication center of the body, coordinating rapid responses to internal and external stimuli. It works alongside the endocrine system, which controls body functions more slowly via hormones.

• Endocrine System: Regulates body processes through hormones released into the bloodstream.

• Nervous System: Utilizes nerves and neurotransmitters to transmit signals quickly throughout the body.

The nervous system is divided into two main anatomical divisions:

• Central Nervous System (CNS): Consists of the brain and spinal cord. It is responsible for integrating, processing, and coordinating sensory data and motor commands.

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

General Functions of the Nervous System

Functional Organization

The nervous system performs three essential functions to maintain homeostasis and respond to the environment:

• Sensory Input: The process of receiving information from both inside and outside the body and transmitting it to the CNS. Sensory (afferent) neurons are responsible for this function.

• Integration: The CNS processes and interprets sensory input, determining the appropriate response.

• Motor Output: The CNS sends signals to effector organs (muscles or glands) to elicit a response. Motor (efferent) neurons carry out this function.

Example: When you touch a hot object, sensory neurons send a signal to the CNS, which processes the information and sends a motor command to withdraw your hand.

Nervous Tissue

Cell Types in Nervous Tissue

Nervous tissue is specialized for communication and consists of two main types of cells:

• Neurons ("Nerve Cells"): Specialized cells that conduct electrical impulses, enabling rapid communication throughout the body.

• Neuroglia (Glial Cells): Supporting cells that provide structural and metabolic support to neurons.

Glial Cells of the Central Nervous System (CNS)

Types and Functions

Glial cells, or neuroglia, are non-neuronal cells that maintain homeostasis, form myelin, and provide support and protection for neurons in the CNS. The main types include:

• Astrocytes: Star-shaped cells that anchor neurons to blood vessels, maintain the blood-brain barrier, and regulate the extracellular environment.

• Oligodendrocytes: Form the myelin sheath around axons in the CNS, which increases the speed of electrical signal transmission.

• Microglial Cells: Act as phagocytes, cleaning up debris and ingesting damaged or dead neurons.

• Ependymal Cells: Line the ventricles of the brain and the central canal of the spinal cord; involved in the production and circulation of cerebrospinal fluid (CSF).

Additional info: In the Peripheral Nervous System (PNS), Schwann cells form the myelin sheath, and satellite cells support neuron cell bodies.

Summary Table: Glial Cells of the CNS

Key Terms and Concepts

• Neuron: The functional unit of the nervous system, capable of generating and transmitting electrical signals.

• Neuroglia: Non-neuronal cells that support, protect, and nourish neurons.

• Myelin Sheath: A fatty layer that insulates axons, increasing the speed of nerve impulse conduction.

• Blood-Brain Barrier: A selective barrier formed by astrocytes and endothelial cells that protects the brain from harmful substances in the blood.