Understanding the Nervous System: Components and Health

The Central Nervous System: Brain and Spinal Cord

The Central Nervous System (CNS), comprising the brain and spinal cord, receives information to process and control bodily functions.

The Brain

Located within the braincase, the brain is divided into two hemispheres. Its outermost part, the gray matter, has convolutions (gyri) and grooves (sulci). This area receives information and develops responses. The innermost zone is white matter.

The Cerebellum

Situated below the brain, the cerebellum is also divided into two hemispheres and features convolutions. It coordinates movements such as walking and maintains balance.

The Medulla Oblongata (Bulb)

This vital part links the encephalon with the spinal cord. It controls automatic bodily functions, including respiration and heart rate.

The Spinal Cord

Housed inside the vertebral column, the spinal cord has outer white matter and inner gray matter. It serves as the nervous pathway through which messages ascend to the brain and descend from it. It also gives rise to 31 pairs of spinal nerves and is responsible for spinal reflexes, such as withdrawing a hand from a hot object.

The Peripheral Nervous System

The Peripheral Nervous System (PNS) is a network of nerves that transmit information to the CNS and carry orders to organs. It is formed by:

• Cranial Nerves: Emerging from the encephalon.
• Spinal Nerves: Emerging from the spinal cord, connecting to CNS organs.

Classification by Nerve Function

• Sensory Nerves: Transmit information from organisms to the CNS.
• Motor Nerves: Transmit orders from the CNS to muscles and organs.

Somatic Nervous System

Nerves in this system connect to skeletal muscles, controlling voluntary actions.

Autonomic (Vegetative) Nervous System

Nerves connect to viscera (internal organs) and the CNS. Its function regulates involuntary organs like the heart and stomach. Organs receive orders through two types of nerves:

• Sympathetic Nervous System: Generally stimulates activity.
• Parasympathetic Nervous System: Generally inhibits activity, and vice versa.

The Neuron: Fundamental Unit of the Nervous System

The neuron is the fundamental unit of the nervous system, transmitting messages in the form of nerve impulses.

Structure of the Neuron

A neuron consists of a cell body or soma, which contains the nucleus, cytoplasm, and extensions. These extensions are of two types:

• Dendrites: Short, branching extensions that receive impulses.
• Axon: A long, unbranched extension that transmits impulses away from the cell body.

The axon is often protected by myelin. Myelinated axons and nerve fibers are grouped in bundles that form nerves.

Neuron Operation

Nerve impulses enter through dendrites and exit through the axon. Pulses are transmitted between neurons via the synapse. The transmission of impulses through the nervous system occurs via chemical messengers called neurotransmitters. Lesions to neurons can sometimes be irreversible.

Alterations in the Nervous System

The nervous system can be affected by various conditions, leading to different types of alterations:

Organic Disorders

These involve physical alterations in the organs of the Nervous System. Examples include:

• Trauma: Irreversible damage to the brain and spinal cord due to physical blows.
• Thrombosis or Obstruction: A blockage or rupture (e.g., stroke) that causes the death of neurons due to lack of blood supply.

Infectious Diseases

These are caused by pathogens affecting the nervous system. A common example is Meningitis, which affects the CNS.

Degenerative Diseases

These involve the progressive breakdown of nervous tissue. The most well-known is Alzheimer's disease.

Psychiatric Illnesses

These conditions affect mental health and can have both psychological and organic components. Examples include anxiety and depression. Certain drugs can also affect both psychological and organic aspects of the nervous system.

Understanding Alzheimer's Disease

Alzheimer's disease involves the destruction of nervous tissue in the brain's cortex. This leads to symptoms such as memory loss, difficulty in speech, and an inability to recognize familiar people, pictures, and sounds.