Basic/GCSE anatomy of the nervous system

The nervous system is vital to the body in lots of ways. It allows us to detect changes in our environment but additionally the ability to take action. The nervous system is divided into two main sections:

1.The central nervous system-The spinal chord and the brain

2. The peripheral nervous system-All the other neurons that connect to the central nervous system

Special cells called receptors are used by the human body to determine stimuli (changes in the environment) and transmit information to the brain in the form of electrical impulses. Receptors are most commonly located at special organs, these include:

Eye: Receptors here are perceive changes in light

Skin: Receptors here are sense changes in pressure and
temperature

Tongue: Receptors here are determine chemicals in food

Ears: Receptors here are determine changes in sound levels and changes in position (so we can keep our balance)

Nose: Receptors here are responsible for changes in chemicals in the air

When a receptor senses forms of stimuli it sends the information as an electrical signal down nerves (neurons). The brain is then able to gather information about changes in the environment and co-ordinate a response. This response is more rapid and frequently involves effectors.

Effectors

Effectors are muscles/glands that the brain sends commands to via neurones. Any mobile part of the body is an effector as are internal glands: a muscle used to lift your leg up is an effector; a muscle that controls the eye lid is an effector; a gland that releases a hormone into the cardiovascular system is an effector.

Reflex

Most of the time when a receptor senses stimuli it causes an electrical message to travel down the sensory neurone to the central nervous system. Here the brain organises a response (thinking time) and another impulse is sent down down the motor nerve.This in turn sends an electrical message to an effector and the effector produces a response:

Stimuli->Receptor->Sensory neuron->CNS->Motor neuron->Effector->Response

In some cases this response time is too slow and this would lead us to get injured. At these times the system does not include the CNS to speed up the reaction: a receptor detects stimuli and an electrical message goes down the sensory nerve. At this point it sends an electrical impulse down a relay neuron which bypasses the brain and communicates directly with a motor nerve which causes an effector to produce a reaction:
Stimuli->Receptor->Sensory neuron->Relay neuron->Motor neuron-Effector->Response
Though a relay neuron is part of the CNS, this is more quickly as it does not include the thinking time.

Neurone Structure

Nerves are a type of cell that is capable of transmitting electrical impulses. Nerves are involved in the whole nervous system. Without them we couldn't think or move! There are three main types of nerve:

1.Sensory neurons
2.Relay neurons
3.Motor neurons

Despite these three different nerves having different places within the nervous system, they share some central features:

Axon: This is what an electrical impulse travels down

Myelin Sheathe: This insulates the Axon and quickens up the electrical impulse.

Dendrites: These overlap with other neuron dendrites at junctions called synapses. This is where neurones communicate with each other.

Nerve Synapses

Synapses are the area where nerve cells (neurons) pass impulses between each other. The impulse travels down the axon. At the Dendrites (dendrons) it comes to a synapse. The message causes a neurotransmitter to be released across the neurone synapse. The neurotransmitter causes the next nerve cell to pass an impulse along its axon. In this way a nervous impulse can travel all over the body, controlling all sorts of processes and responses.