The Nervous System

• The nervous system is divided up into two regions. The central nervous system (brain and spinal cord) and the peripheral nervous system (Nerves extending from the brain and spinal cord)
• A stimulus is any change in the environment that may cause a response.
• Stimulus is detected by neurons and sense organs in reception. In transmission, the message is carried along the neurons. Messages are sorted and processed by the CNA in integration. In response, the messages are carried to the effector.
• A neutron is a nerve cell.
• A sensory neuron takes message from a sense organ (eye, ear, skin, tongue) to the CNS.
• Diagram of a sensory neuron.

  
• Motor neurone take messages from the CNS to muscles and glands causing them to respond.
• Diagram of a motor neuron.

  
• An interneuron carries information between the sensory and motor neurons.
• Diagram of the interneuron

  
• Receptors are cells that detect a stimulus.
• Nerve endings connect sensory neurons to receptor cells or sense organ.
• Dendrites are fibers that carry impulses towards the cell body.
• Axons carry impulses away from the cell body.
• Schwann cells make the myelin sheath. This is a rich fat membrane that insulated up electrical impulses.
• Synaptic knobs release chemicals that carry the impulses from one nerve cell to another.
• If a stimulus is not sufficiently strong, the message will not be transmitted. This is called the All or Nothing rule.
• The threshold is the minimum stimulation required to send a message along a neuron.
• A synapse is a region where two neurons come into close contact. A synaptic cleft is a tiny gap between the two neurons.
• Diagram of a synapse.

  
• Electrical impulses cannot cross a synapse. The message is carried by chemicals that are released by the neurotransmitter swellings. They diffuse across the synaptic cleft.
• Gray matter is the part of the CNS that contains cell bodies and has a darker color.
• White matter is the part of the CNS that contains the axons and has a lighter color.
• The brain is divided into three main sections: the cerebrum (concious thought), the thalamus and hypothalamus (processing information and regulation) and the cerebellum (coordination)
• The pituitary “master“ gland secrets hormones that stimulate other glands to release their hormones.
• The medulla oblongata coordinates involuntary, automatic processes e.g. breathing and heartbeat.
• The spinal cord is composed of nerve tissue and is surrounded by protective vertebrae.
• Cross-section of the spinal cord.

  
• Dorsal root carries sensory neurone into the spinal cord. The ventral root carries motor neurons out of the spinal cord.
• The gray matter in the central canal of the spinal cord contains cerebrospinal fluid.
• A reflex action is an automatic, involuntary, unthinking response to a stimulus.
• Reflex actions allow for fast responses to protect the body from damage e.g pulling hand away from hot flame.
• Parkinson’s disease is a nervous system disorder caused by the failure to produce a neurotransmitter called dopamine in the brain.