Understanding the Human Nervous System: Neurons, Brain, and Function

Nervous System: The Body's Control Center

The Nervous System controls, processes, and responds to information, coordinating the body's activities.

Neuron: The Basic Unit of the Nervous System

The neuron is the basic structural unit of the nervous system. Neurons conduct impulses throughout the nervous system and consist of three regions:

• Axon
• Dendrites
• Cell Body

Dendrites and Axons: The Neuron's Extensions

Dendrites are extensions of the neuron that receive impulses and carry them toward the cell body.

The axon is an extension of the neuron that carries impulses away from the cell body toward other neurons, muscles, or glands.

Three Categories of Neurons

Neurons are categorized into three types:

1. Sensory Neurons: Carry impulses from the body to the spinal cord and brain.
2. Interneurons: Located in the brain and spinal cord, they process impulses and pass them to motor neurons.
3. Motor Neurons: Carry impulses away from the brain and spinal cord to a muscle or gland.

Neurons at Rest: Polarization

When a neuron is at rest, or polarized, it is ready to transmit an impulse.

A polarized neuron has more potassium ions (K+) inside the cell than outside, and there are more sodium ions (Na+) outside the cell.

Neuron Depolarization

When a neuron is depolarized, pumps are used to move Na+ ions into the cell and K+ ions out of the cell (3 Na+ for every 2 K+).

The concentration of Na+ ions will increase inside the neuron, and the concentration of K+ ions will increase outside the neuron.

White and Gray Matter

Most axons are surrounded by a white covering of cells called the myelin sheath. This insulates the axon, allowing the movement of ions across its plasma membrane.

Result: The impulse jumps from gap to gap, increasing speed. The myelin sheath gives axons a white appearance.

In the brain and spinal cord, masses of myelinated axons make up white matter.

Myelin in masses of neurons accounts for the grayish color of gray matter in the brain.

Brain: The Control Center

The brain is the control center of the entire nervous system.

Cerebrum

The cerebrum is divided into two hemispheres.

It controls senses, intelligence, language, skeletal muscles, and more.

The outer surface of the cerebrum is the cerebral cortex. This is made up of gray matter and contains folds and grooves, increasing its total surface area, which is linked to the evolution of human intelligence.

Cerebellum

The cerebellum is at the back of the brain and controls balance, posture, and coordination.

Brain Stem

The brain stem is made up of the medulla oblongata, which controls involuntary activities like heart rate and breathing.