bio paper 2

• The human nervous system allows the body to respond to stimuli from the environment and coordinate responses.
• The nervous system consists of receptors, effectors, the central nervous system and different types of neurone.
• Electrical impulses are passed between neurones (across the synapse) as chemical neurotransmitter.
• When a rapid response is required, impulses travel along the reflex arc.
• The human nervous system detects stimuli from the external environment, transports the message around the body along neurones and coordinates behavioural changes in the body in response.
• Stimuli (changes in the environment) are detected by receptor cells.
• Different receptors are specialised to detect different types of stimuli, e.g. taste receptors on the tongue, sound receptors in ear, light receptor cells on the retina of the eye.
• Sensory neurones carry electrical impulses from the receptors to the central nervous system (CNS).
• The central nervous system (CNS) consists of the brain and spinal cord.
• A person stands on something sharp by detecting the sharp object with a receptor in the foot, sending an impulse along a sensory neurone to the CNS, passing the impulse along a relay neurone in the CNS to a motor neurone, and carrying the electrical impulse to muscle cells in the leg and foot (effector) causing them to contract, moving the foot away from the sharp object to prevent or limit the amount of damage.
• Neurones are adapted for their function by having a long axon to transport impulses over long distances, being branched at both ends to pass signals easily, and having an axon insulated in a fatty sheath to help impulses travel along quickly.
• Repeat the whole experiment again after the person has had a caffeinated drink to investigate its affect on the reaction time.
• This causes a new electrical impulse to travel along the axon of the second neurone.
• An electrical impulse crosses a synapse by arriving at the end of the first neurone and causing the release of neurotransmitter.
• The neurotransmitter binds to receptors on the second neurone.
• The neurotransmitter diffuses across the gap.
• Repeat this experiment a few times without caffeine to calculate the mean distance which equates to an average reaction time.
• You can perform simple experiments to determine how these factors affect reaction time; this example uses caffeine intake.
• Neurones are specialised to carry electrical nerve impulses around the body: long axon to carry the impulse over long distances, branched at both ends to easily pass signals between them, axon is insulated in a fatty sheath to help the impulse travel quickly.
• Synapses are where two neurones join together and use chemicals to transfer the electrical nerve impulses across the gap between them.
• Effectors receive electrical impulses from the CNS and respond to the stimuli.
• Danger is detected by receptors, and an impulse is sent from receptors, down a sensory neurone to the CNS.
• Neurones bundle together to make nerves.
• The effector produces a quick response to prevent or limit damage, which is involuntary as it does not involve the conscious part of the brain.
• Reaction time is the time taken to respond to a stimulus and can be affected by many factors such as age, stress, drugs and background noise.
• Motor neurones carry electrical impulses from the CNS to effectors.
• An electrical impulse travels along the first neurone to the end, causing the release of chemicals called neurotransmitters into the gap between the neurones.
• Instead of sending signals all the way to the brain, the impulse is sent to a relay neurone in the central nervous system (CNS), quickly sending impulses to effectors to produce a response that will limit or prevent damage.
• Sensory, motor and relay neurones all vary slightly due to their different functions.
• When a person is in danger of becoming injured, the body reacts quickly to prevent or limit the damage through the reflex arc.
• Neurotransmitter diffuses across the gap and binds to receptors on the second neurone, setting off a new electrical impulse that travels along the second neurone.
• An impulse is sent along a relay neurone in the CNS and straight down a motor neurone to an effector.
• Sensory and motor neurones are longer than relay neurones because they have to carry impulses over longer distances.
• The cell body of sensory neurones branches off half way down the axon but the cell bodies of motor and relay neurones is at one end.
• The Central Nervous System (CNS) receives and processes electrical impulses from receptor cells and organises a response.
• breathing is controlled by the medulla oblongata which sends signals down nerves to control muscles involved in breathing