Human Nervous System: Structure, Function, and Disorders

Central Nervous System

Cerebrum

The cerebrum interprets information sent by sensory receptors, regulates muscle activity, and is involved in emotional and intellectual processes. It has two hemispheres joined by the corpus callosum, which is made up of neuron axons. The cerebrum also has a superficial layer of gray matter called the cerebral cortex.

Thalamus and Hypothalamus

The thalamus and hypothalamus produce hormones and control the endocrine system.

Cerebellum

The cerebellum controls motor coordination, posture, and balance. It has two hemispheres and a central zone.

Brainstem

The brainstem connects the brain to the spinal cord. It includes the medulla oblongata, which regulates blood pressure, heartbeat, and respiration.

Hemispheric Specialization

There are functional differences between the two hemispheres:

• Left Hemisphere: Spoken language, written language, numeric ability, scientific ability, and control of the right-hand side of the body.
• Right Hemisphere: Spatial perception, musical ability, artistic ability, emotions and feelings, imagination, and control of the left-hand side of the body.

Spinal Cord

The spinal cord is nervous tissue that runs through the spine. It extends from the medulla oblongata down to between the first and second lumbar vertebrae. The spinal cord connects the brain to the peripheral nervous system and controls many reflex actions in which the brain does not participate.

Disorders of the Nervous System

Vascular Diseases

Vascular diseases affect the blood vessels in the brain and are more frequent in elderly people. Certain diseases, such as hypertension, and addictive substances (tobacco, alcohol, drugs) can increase the risk.

Stroke or Cerebrovascular Event

A stroke happens when a cerebral vessel gets blocked or breaks. Blood flow to the brain is reduced and can cause neuronal death, leading to loss of strength, confusion, difficulty speaking, and paralysis on one side of the face.

Neurodegenerative Diseases

Neurodegenerative diseases involve the destruction of neurons in one or more areas of the brain. They are more frequent in elderly people.

• Alzheimer's Disease: Characterized by forgetfulness, changes in behavior, memory loss, and spatial and temporal disorientation.
• Parkinson's Disease: Symptoms include tremor or shaking, impaired balance, muscle stiffness, and slowed movement.

Spinal Cord Injuries

• Paraplegia: Paralysis of the legs, typically resulting from injury in the thoracic or lumbar area.
• Tetraplegia: Paralysis of the legs and arms, typically resulting from injury in the cervical area.

Peripheral Nervous System (PNS)

The PNS is composed of nerves, which are groups of axons from different neurons bound together and protected by connective tissue.

• Sensory Nerves: Transmit impulses from the receptors to the central nervous system.
• Motor Nerves: Transmit impulses from the CNS to effectors.
• Mixed Nerves: Contain both sensory and motor nerves that transmit impulses in both directions.

Cranial Nerves

There are 12 pairs of cranial nerves distributed around the head, neck, and limbs. They are divided into the respiratory, digestive, and circulatory systems.

Spinal Nerves

There are 31 pairs of spinal nerves that connect the spinal cord with the torso and limbs. They are divided into cervical, thoracic, lumbar, sacral, and coccygeal nerves.

Somatic Nervous System

The somatic nervous system connects the receptors to the CNS and the CNS to the skeletal muscles.

• Voluntary Actions: A stimulus is detected, travels to the spinal cord and cerebrum, and the effector organ carries out the response.
• Reflex Actions: A stimulus is detected by the receptor and travels to the spinal cord, bypassing the brain for a faster response.