The Brain and Cranial Nerves

The Brain and Cranial Nerves

One of the most complex and fascinating things in the human body is the brain. The body is "capable of almost everything, but it would not be possible, without the brain receiving information, and analyzing the information."

The brain is aware of its surroundings, via input from the spinal cord and cranial nerves. Cranial nerves with sensory functions allow us to smell and see. Nerves with both motor and sensory functions are responsible for everything from tasting and chewing, to breathing and the heating of your heart. Many of the little things we take for granted are also made possible by cranial nerves.

Solving problems, feeling hungry, laughing. Each of these activities occurs in a different region of the brain. The portion of the central nervous system is contained in the cranium. About one hundred billion neurons and ten to fifty trillion neuralgia make up the brain. In adults, the brain has a mass of about three pounds.

The four major parts of the brain are the Brain Stem, Cerebellum, Diencephalons, and the Cerebrum.

The brain stem is continuous with the Spinal Cord and consists of the Meclulla Oblongata, Pons, and the Mid Brain.

Posterior to the Brain Stem is the Cerebellum. Superior to the Brain Stem is the Diencephalon. The Diencephalons consists mainly of the Thalamus and Hypothalamus.

Supported on the Diencephalon of the Brain Stem, the Cerebrum which is the largest part of the brain.

Since the brain does not store oxygen, it needs a constant flow to prevent it shutting down.

Blood flows to the brain mainly via, the internal Caroticl and Vertebral Arteries. The internal Tugular Veins return blood from the head to the heart.

In adults, the brain is only two percent of the total body weight, but it consumes about two percent of the oxygen and glucose used at rest.

When activity of neurons and neuralgia increases in a region of the brain, blood flow to that area also increases. Even a brief slowing of brain blood flow may cause unconsciousness.

Typically an interruption in blood flow for one or two minutes impairs neuronal function. Should total deprivation of oxygen incur for about four minutes, perminate damage can occur. Because virtually no glucose is stored in the brain, the supply of glucose also must be continuous. If the blood entering the brain has a low level of glucose, mental confusion, dizziness, convulsions, and loss of consciousness may occur.

The blood brain barrier protects brain cells from harmful substances, as well as, pathogens, by preventing passage of many substances from blood into brain tissue.

Tight junctions seal together the enclothelial cells of brain capillaries, which also are surrounded by a thick basement membrain. The process of many astrocyties pressing up against the capillaries is known as the Astrocyties Process. This process selectively passes some substances from the blood to the neurons, at the same time, inhibiting the passage of others.

A few water soluble substances, like glucose, cross the brain blood barrier by active transport. Other substances like creatinine, vrea, and most ions, cross very slowly. Other substances and protions, including most antibiotic drugs, do not pass at all from the blood into brain tissue. Trauma, certain toxins, and inflammation, can all cause a breakdown of the Brain blood barrier.

The cranium and the Cranial Meniges surround and protect the brain. The Cranial meninges are continuous with the Spical meninges. Both have the same basic structure.

Cerebrospinal fluid is a clear, colorless, liquid that protects the brain and spinal cord against chemical and physical injuries. It also carries oxygen, glucose, and other needed chemicals from the flood to neurons, and neurogla.

The brain stem is the part of the brain between the spinal cord and the Diencephalon. The brain stem is made up of three structurally and functionally connected regions. These regions are the Medulla Oblongata, the Pons, and the Midbrain.

The Medulla Oblongata is a continuation of the Spinal cord. The Medulla contains white matter that is sensory and motor tracts. These tracts extend between the spinal cord and other parts of the brain.

The Pons lies directly superior to the Medulla. Like the Medulla, the Pons is a bridge that connects parts of the brain with one another.

The midbrain extends fro the Pons to the Diencephalon. The Midbrain contains both tracts and nuclei. The interior art of the midbrain contains a pair of tracts called Cerebral Pedunctis. They contain axons of corticospinal corticopontine and corticobolbar motor neurons. These conduct nerve impulses from the cerebrum to the spinal cord, medulla, and pons.

The posterior part of the midbrain is called the tectum. The Tectum contains four rounded elecations, two superior, and two inferior. The two superior elevations are known as the superior culliculi. They serve as reflex centers for certain visual activities. The two inferior elevations, the inferior colliculi, are aprt of the auditory pathway, relaxing impulses from the receptors for hearing in the ear to the thalamus.

The Cerebellum is the second largest part of the brain. The cerebellum occupies the inferior and posterior aspects of the cranial cavity. The Diencephalon extends from the brain stem to the cerebrum. It includes the thalamus, hypothalmas, epithalamus, and subthalmus.

The twelve cranial nerves are responsible for a variety of things. Some of these nerves bring information from the sense organ to the brain, other cranial nerves control muscles. Then we have cranial nerves that are connected to glands or internal organs such as the heart and lungs.

Cranial Nerve I - The Olactory Nerve. This nerve has only a special sensory component. Special sensory is the sense of smell or olfaction.

Cranial Nerve II - The Optic Nerve. The optic nerve has only a social sensory component, this special sensory conveys visual information from the retina.

Cranial Nerve III - The Oculomotor Nerve. This nerve consists of two components with distinct functions. The somatic motor supplies four of the six extraocular muscles of the eye and the levator palpebroce superioris muscle of the upper eyelid.

The visceral motor through

the parasyimpathetic innervations of the constrictor pupil and ciliary's muscles. The visceral motor component is in the papillary light so by reflex your pupil will

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