Saraf PusatSaraf TepiSaraf Otonom( Tak Sadar )OTAKSumsum Tulang BelakangCranial ( Serabut Saraf Otak )Spinal ( Serabut Saraf Sumsum T. Belakang )Saraf SimpatisSaraf Parasimpatis

Pelindung(Meninges)

Piameter ( melekat pada otak)Araknoid (antara Durameter & Piameter )Durameter( pada tulang )BagianOtak Besar ( Cerebrum )Otak TengahOtak Depan ( Diensefalon )Otak Kecil ( Cerebellum )Sumsum Lanjutan ( Medulan Oblongata )

Rangsangan Reseptor (alat indra) Neuron Sensorik / Aferen Pusat saraf (otak) Neuron Motorik /Eferen Efektor (otot, kelenjar)Rangsangan Reseptor (alat indra) Neuron Sensorik/Aferen Sumsum Tulang Belakang (Neuron konektor ) Neuron Motorik Efektor

Beside Hormones, mammals also have another methode pf communication within their bodies. This methode is faster and more precise and involves the transmission of electrical signals or impulses along precisely constructed pathways. The cells which carry these signals are called nerve cells or neuronesNervous communication

Figure beside shows the structure of a mamalian neurone. This s a motor neurone which transmits messages from the brain or spinal cord to a muscle or gland. The cell body of motor neurone lies within the spinal cord or brain. The nucleus of a neurone is always in its cell body. Often dark specks can be seen in the cytoplasma. These are groups of ribosomes involved in protein synthesis.

In a motor neurone all but one of these process are relatively short. They conduct impulses towards the cell body and are called Dendrons or Dendrites.

One process is much longer, and conduct impulses away from the cell body. This is called Axon.

Within the cytoplasm of an Axon, all of the usual organelles such as endoplasmic reticulum, Golgi aparatus, and mithocondria.

DendritBadan SelAkson / Neurit Sel

Particularly large numbers of mithocondria are found at the tips the terminal branches of the axon, together with many vesicles containing chemical called Transmitter substance Figure beside, In some neurones, cells called Schwan Cells wrap themselves around the axon all along its length.

Figure beside shows one such cell. Viewed the axon is cut transversely. The schwann cell spiral around, enclosing the axon in many layers of its plasma membrane. This enclosing sheath called Myelin Sheath, is made largely of lipid together with some proteins.

The small, Uncovered areas of axon between schwann cells are called Nodes of Ranvier.

In the human body, a sensory neurone and a motor neurone may from a reflex arc. A reflex arc is pathways along which impulses are carried from receptor to an effector, without involving Conscious regions of the brain. The neurone between the sensory and motor neurone is called an Intermediate neurone, Within the spinal cord, the impulses will also be passed on to other neurons which take the impulses up the cord to the brain. This happens at the same time as the message is traveling along the motor neurone to the effector. The effector therefore responds to the stimulus before there is any voluntary response, involving conscious regions of the brain. This type pof the reaction to a stimulus is called Reflex action. It is a fast, automatic response to a stimulus. Reflex action are very useful way of the responding to danger signals, such as the touch of a very hot object on your skin of the sight of an object flying towards you.aA reflex Arc

Intermediate Neurone

A reflex arc. The spinal cord is shown in transverse section

Neurone transmit impulses as electrical signals. These signals travel very rapidly along the plasma membrane from one end of the cell to the other and are not a flow of electrons like an electric current.Its caused by the very rapid movement of sodium and potassium ions into and out of the axon.

Figure di atas shows myelinated and nonmyelinated nerve tissue.

Figure beside shows myelinatedand nonmyelinated nerve tissue.

In a resting axon, it is found that the inside of the axon always has a slightly negative electrical potential compared with the outside ( Figure 19.30 an 19.31 ).

19. 30 measuring the resting potential of an axon

Explanation!!!!Before touhing the axon, the two electrodes are at the same electrical potential, so the voltmeter shows a potential difference of zero.When one electrode is pushed inside the axon, the voltmeter shows that there is a potential difference between the inside and outside of about -65mV inside with respect to outside.

At Rest, an axon has negative electrical potential inside

Action potentialThis rapid, fleeting change in potential difference accros the membrane is called an Action potential. It is caused by changes in the permentability of the plasm membrne to Na+ and K+.

As well as the sodium potasium pump, there are other channels in the plasm membrane that alow Na+ or K+ to pass through. They open and close depending on the electricl potential ( or voltage ) across the membrane and are therefore said to be Voltage gated channels.

Mechanism First, the electri current used to stimulate the axon causes the opening of the channels in the plasm membrane which allow sodium ions to pass through. As there is a much greater concentration of sodium ions outside the axon than inside, they flood in through the open channels. The now reltively high concentration of positively charged sodium ions inside the axon makes it less negative inside than it was before. The membrane is said to be DEPOLARISED. As sodium ions continue to flood in, the inside of the + 40 mV compared with the outside.At this point, the sodium channels close, so sodium ions stop diffusing into the axon. At the same time, the potasium changnels open. Potassium ions therefore diffuse out of the axon, down their concentration gradient. The outward movement of potassium ions removes positive charge from inside the axon to the outside, thus beginning to return the potential difference to normal. This is called POLARISATIONSo many potassium ions leave the axon that the potential difference across the membrane briefly becomes even more negative than the normal resting potential. The potassium channels then close, and the sodium-potassium pump begins to act again, restoring the normal distribution of sodium and potassium ions across the mebrane nd therefore restoring the resting potential

The brain can therefore interpret the frequency of action potentials arriving along the axon of a sensory neurone and the number of neurones carrying action potential to get inforation about the strength of the stimulus being detected by that receptorr. The nature of the stimulus . Whether it is light, heat, touch, or so on, is deduced from the position of the sensory neurone bringing the information. If the neurone is from retina of the eye, then the brain will interpret the information as meaning light . If for some reason is different stimulus, such as preassure, stimulates a receptor cell in the retina, the brain will still interpret the action potential from this receptor as meaning light. This is way rubbing your eyes when they are shut can caused you to see patrent of life.

Speed conductionFigure 19.36Shows how an action potential is transmitted long myelinated axon. The local circuit that are set up stretch from one node to the next., a distance of 1 -3 mm. this is called Saltatory conduction. It can increase the speed of transmission by up to 50 times that in a nonmyelinated axon of the same diameter. Transmission of an action potential in a myelinated axon. The myelin sheat acts as an insulator, preventing differences in potential across the parts of the axon al surrounded by the sheath. Potential differences can only occur at the nodes of ranvier. The action potential