The Nervous System

The nervous system is a fundamental part of humans. It carries out the follow functions: -The detection of changes within or outside the body. -To process the information. -After information is processed, the system will initiate the response.

Two Parts

The first part of the nervous system is the brain and spinal cord. This is referred to the central nervous system or CNS for short.

The second part is the peripheral nervous system. This is made up of pairs of nerves, which originate from the brain and spinal cord. The PNS consists of sensory neurons, which carry impulses from receptors, and motor neurones that carry impulses away from the CNS to effectors.

The role of the CNS is to process the information and to initiate the required response. Effectors are able to bring about the response. These effectors can be a majority of specific parts of the body such as muscles or glands. The sensory receptors act as transducers converting the chemical energy into electrical energy. The electrical impulses traveling along the nerves are called nerve impulses.

The Reflex Arc

The simplest type of response from the nervous system is the reflex arc. An example is when you touch something really hot with your hand and there is an automatic reflex that immediately withdraws your hand.

This is described as a rapid and involuntary response that has been brought about from the nervous impulses by an initiated stimulus. The process is described as involuntary due to the brain having no involvement in the process of the reflex. It is served as a general protective function.

There are many terms that are involved in the withdrawal reflex. The following are involved: - Stimulus – A hot surface - Receptor – Temperature receptors within the skin. - Sensory Neurone – This sends an impulse to the spinal cord. - Relay Neurone – Connects the sensory neurone to a motor neurone. - Motor Neurone – This sends an impulse to an effector such as a muscle. - Response – The muscle contracts moving the stimulus from hot surface.


Neurones are specialised cells that have been adapted to rapidly carry nerve impulses from one location of the body to another location of the body. There are three types of these specialised cells. These are: - Sensory Neurones – These bring the impulses from the sensory organs or receptors and transmit them into the CNS. - Motor Neurones – These types of neurones carry impulses from the CNS to the effector neurones. - Connector Neurones – These type of neurones receive the impulses from the sensory neurones or any other type of intermediate neurones. And connects them to the motor neurones.

Nerve Impulses

The associated charge that is associated with the typical nerve impulse has a very small charge at around 50 millivolts. Due to new technology, these nerve impulses can be measured with apparatus with is very sensitive to small impulse changes.

Resting Potential

Resting potential is the negative value that indicates that inside the system is negative in respect with the outside. This is known as polarised at this stage. The following brings about resting potential: - Two ions, sodium and potassium, is actively transported against its concentration gradient across the membrane by active transport. - This process involves the sodium-potassium exchange pumps. These maintain the uneven concentration of the sodium and potassium ions across the membrane. - Sodium gates open and sodium ions are transported out of the axon by the sodium pump. - Sodium gates close opening up the potassium gates allowing the potassium pumps to pump potassium into the axon. - Two potassium’s in, three sodium’s out.


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