the nervous system

• The nervous system is made up of nervous tissue.
• Nervous tissue consists of nerve cells called neurones.
• A relay neurone transmits nerve impulses from the sensory neurone to the motor neurone.
• Relay neurones are found within the central nervous system.
• A sensory neurone transmits nerve impulses from the sense organs or receptors to the central nervous system.
• Nerve impulses travel from the sensory neurone to the motor neurone along nerve fibres.
• Motor neurones transmit nerve impulses from the central nervous system to the effectors.
• A sense organ or receptor is a type of sensory neurone.
• A muscle fibre is a type of effector neurone.
• The structure of a motor neurone includes a cell body which contains a nucleus, cytoplasm, cell membrane and organelles.
• The cell body of a motor neurone is irregular in shape.
• The nerve fibre is a strand of cytoplasm extending from the cell body of a motor neurone.
• The structure of a sensory neurone includes a circular cell body, one long nerve fibre extending towards the receptor and a short nerve fibre extending towards the relay neurone in the central nervous system.
• The cell body of a sensory neurone is the site where sensory information is processed.
• Nerve impulses cannot directly cross from one neurone to the next due to the tiny space between them.
• Nerve impulses are transmitted across a synapse by chemicals released by the neurones.
• A living organism is able to react to changes in its surroundings. Any change in the environment that causes an organism to react is called a stimulus (plural: stimuli).

  An organism's reaction to a stimulus is called a response

  The ability to respond to a stimulus is termed sensitivity or irritability.
• The components of the human nervous system include the central nervous system (CNS) which consists of the brain and the spinal cord, and the peripheral nervous system (PNS) which consists of the cranial nerves, the spinal nerves and the sense organs.
• The sense organs in humans receive stimuli through receptors found in them and inform the central nervous system of any change in the surroundings, by producing electrical signals or messages called nerve impulses.
• Nerves transmit nerve impulses from the receptors to the central nervous system, and from there to the effectors.
• Receptors detect changes in the environment (receive stimuli), while the effectors respond to the processed stimuli.
• Nerve impulses are transmitted by neurones to and from the central nervous system.
• The spinal cord and the brain are parts of the central nervous system.
• The brain is contained within the skull which protects it.
• From the brain, the spinal chord runs down the back of the body.
• The spinal cord passes through the vertebral column (backbone) which protects it.
• Spinal nerves connect the spinal cord to various parts of the body.
• Like all nerves, spinal nerves are composed of bundles of nerve fibres.
• Spinal nerves emerge at intervals along the length of the spinal cord.
• As the spinal nerve leaves the spinal cord, it progressively subdivides into branches supplying nerve fibres to various parts of the body.
• Relay neurones may synapse with the sensory neurones and then transmit nerve impulses up the spinal cord to the brain, enabling us to feel sensations.
• Relay neurones may transmit nerve impulses about a voluntary action from the brain, down the spinal cord.
• In the spinal cord, relay neurones may synapse with the sensory neurones and motor neurones.
• Relay neurones transmit nerve impulses from the sensory neurones to the motor neurones in a reflex action.
• The spinal nerve contains both sensory and motor neurones, making it a 'mixed' nerve.
• Damage to the spinal cord can paralyse a person from neck down, leaving them unable to move any part of their body except for their head.
• Advances in computer and biomedical engineering technologies offer hope for rehabilitation of paralysed individuals.
• Biomedical engineers and neuroscientists have been experimenting with brain implant technology to stimulate specific muscles in the arm and hand of a paralysed person, creating an artificial neural loop that bypasses the damaged spinal cord.
• The results of these early studies have been promising, with the victim being able to perform simple actions like holding simple objects and even self-feeding.
• While there is still a lot to do, this emerging field could change the lives of millions of people who are paralysed.