Body Ecyclopedia - NERVOUS SYSTEM

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articlemostwanted - The nervous system is the body's main control system. It is made up of the CENTRAL NERVOUS SYSTEM (or CNS) and a network of NERVES that extend from the CNS to all parts of the body. The nervous system manages both voluntary activities, such as walking and talking, and spontaneous activities, such as breathing, which you make no conscious choices about.

PARTS OF THE SYSTEM

The CNS consists of the brain and spine. The remainder of the nervous system, called the peripheral nervous system, consists of nerves. These include 12 pairs of nerves that branch from the brain (cranial nerves) and 31 pairs that branch from the spinal cord (spinal nerves).
NEURONS

The nervous system consists of billions of neurons (afferent neuron). A nerve cell has a cell body, arms called dendrites, and a long predicting fibre, the axon. Electrical signals-- as much as 2,500 per second-- can pass along axons. They can also jump in between neurons by means of chemicals that pass throughout the gaps in synapses (neuron junctions).

PARTS OF THE BRAIN

The main parts of the brain are the big folded cerebrum, the brainstem, which forms a stalk at the foot of the brain, the cerebellum behind it, and central structures, such as the thalamus.

NERVES

lemari asam berkualitas - Nerves are made up of packages of the axons of nerve cells. A few of these bring info picked up by sensory receptors around the body to the CNS for processing. Other axons bring messages from the CNS to muscles, causing motion, or to the body's glands, causing the release of hormonal agents. Numerous axons are surrounded by a protective sheath including a fatty substance called myelin. This acts to insulate the axons electrically.

NERVE STRUCTURE

Most nerves include several axon packages, called fascicles. The speed at which specific nerves transmit signals varies depending on their thickness and whether or not their axons have myelin sheaths; fatter, myelinated axons transmit signals much faster, at as much as 350 kph (218 miles per hour).

CENTRAL NERVOUS SYSTEM

The CNS has two primary tasks. It has to process information, both about the outside world (obtained by organs such as the eyes) and about the inside of the body (gotten by internal receptors). It likewise needs to create reactions such as movement that will secure and keep the body. Some activity within the CNS is quite simple REFLEX (automatic) activity. But much of its activity, especially in the brain's cerebrum, is complex and mindful.

FUNCTIONS OF THE CEREBRAL CORTEX

The cortex (external layer) of the cerebrum has lots of functions. Various locations of the cortex are associated with processing or evaluating sensory information, sending out signals to direct muscle movements, or in other activities such as reasoning, memory, or creative thought.

SPINAL CORD

The spine's primary function is to transfer information in between the brain and spinal nerves. It is likewise associated with some reflex activity. Its grey matter is comprised of the cell bodies of neurons. Its white matter contains axons (neuronal fibres). These are arranged into groups called systems and bring signals up and down the cord.

REFLEXES

In its simplest sense, a reflex is an emergency reaction of the nervous system to a threat such as a hot object touching the skin. In a wider sense, reflexes are automatic responses to a vast array of scenarios in the body and are vital to lots of internal activities, such as the heart beat. A department of the nervous system called the autonomic nervous system remains in total control of these internal activities.

EASY REFLEX ACTION

In a basic reflex, details passes from the area impacted, in this case the finger, to the main nervous system (red path). This sets off an instant reaction, in this case the contraction of a muscle (blue path) to withdraw the finger. Here, the reflex action involves just 2 nerves and the spinal cord. Nevertheless, a signal likewise passes to the brain, which registers the pain.

source: factmonster