Rabu, 20 Maret 2013

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Central Nervous System (CNS) For Human

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2013 Central Nervous System (CNS) For Human Central nervous system includes spinal cord and brain. Brain is protected by skull, while spinal cord is protected by spine or back bone.

Spinal Cord



Based on the cross section, the spinal cord consists of two parts. The outer part is a white mass, composed of a large amount of nerve fibers (axon and dendrite bond) covered by membrane. The inner part is a grey mass whose outer surface has butterfly’s wing-like shape. The end of the “wing” is called horn.

There are 31 pairs of spinal nerves along the spinal cord. The branch of each spinal nerves has a ganglion located at the posterior end. The sensory nerve cell body lies in the ganglion while motor nerve cell body lies at the end of anterior.

The spinal cord has several functions, some of which are as follows
1. Transmitting sensory impulse from peripheral nervous system toward the brain.
2. Transmitting motor impulse from the brain to various effector, such as striated muscle, heart muscle, smooth muscle, and gland.

As a central of reflex movement.
1. Impulse Pathway in Spinal Cord
Sensory nerve fibers conduct impulse from the body toward spinal cord posterior, while in anterior part, the impulse is conducted from spinal cord toward the body.
2. Reflex Movement.
Reflex movement is the simplest nerve activity which includes automatic reaction involving spinal cord or brain. Reflex movement occurs and finishes before the brain recognize the pain.

Brain

The brain fills the skull cavity and weighs 1,4 kg. The brain is composed of smooth nerve tissue and covered by protection membrane called meninges. Meninges comprises of three layers, piameter, arachnoidmeter, and durameter.

The brain structure consists of three parts, fore brain, mid brain, and hind brain.

• Forebrain Forebrain (proencephalom) consist of telencephalon (cerebrum) and diencephalon.

a) Cerebrum (Telencephalon)

Cerebrum is located at the brain posterior and is the largest part of the brain (80% of brain weight). Cerebrum is divided into two parts (hemisphere), left hemisphere and right hemisphere. The outer layers of cerebrum is grey and called cortex, while the inner part is white and called medulla.

Cortex contains a bulk of neuron body cell (pericarion). It has folded structure to expand the surface so that more neuron can be stored. Cortex is also important in limbic system, which is the emotional center around corpus callosum. Corpus callosum is a collection of association fibers which connect left hemisphere and right hemisphere and act as lateral ventricle roof.

Medulla is composed of nerve fibers. In medulla there is part containing neuron perycarion bulge called nucleus. Each hemisphere is divided into four lobes, which are frontal lobes (around forehead), pariental lobes (around frontal fontanelle), temporal lobes (lateral), and occipital lobes (anterior).

b) Diencephalon

Diencephalon lies in front of the midbrain. It includes thalamus, hypothalamus, and infundibulum (hypophysis stem). Thalamus consists of grey substances built by neuron without myelin membrane. It serves as a receiver area of all sensory information, except smell. Thalamus influences cerebrum’s function as well as increasing memory and emotional function.

Hypothalamus lies below the thalamus. It contains neurosecretor cells producing neurohormone. Neurohormone has the function to control pituitary gland. It also controls wide variety of internal processes, such as body temperature, sexual desire, carbohydrate metabolism, hunger, and thirst.

• Midrain
Midbrain and hindbrain function as assistance, distributor, and relay station of impulse. The inner part of midbrain contains cerebrospinal, while the base (optic tectum) is the connector of vision and auditory signal.

• Hindbrain
Hindbrain consist of three parts, cerebellum, pons varolli, and medulla oblongata.

  • Cerebellum consists of two hemispheres and one vermis (center) located in the inferior posterior of  cerebrum. The shape of cerebellum is much like that of cerebrum, but flatter and folded. The surface comprises of grey mass, while the inner part comprises of white mass.
  • Cerebellum is the center of motor regulation, both reflex and conscious motion. It helps cerebrum to control muscle activities and to strengthen impulse transmission to muscle. Cerebellum helps us controlling balance at any time.
  • Pons Varolli Pons varolli (bridge) has encircled structure in the brain stem above the medulla oblongata. Pons contains motor pathway connecting cerebrum cortex with cerebellum cleavages and between medulla and cerebrum. Medulla Oblongata


Medulla oblongata lies at the beginning of brain stem in the base of skull, it is the continuity of with the spinal cord and serves as the cross section site of fibers and controls internal organ activities, for example respiration, heart beat, and digestive muscle.

In medulla oblongata, there are 12 pairs of cranial nerves connected to the brain and are parts of peripheral nervous system. The cranial nerve functions as a rect connection to important organs.
The brainstem is a brain bulge which consists of three parts (start from front), which are midbrain, pons varolli, and medulla oblongata (connective brain or myelin cephalon).

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