Coordination and response IGCSE 0610

• The nervous system is made up of the central nervous system (CNS) and peripheral nervous system (PNS).
• Nervous system
• A nerve impulse is an electrical signal that passes along nerve cells called neurons.
• A bundle of neurons is known as a nerve.
• The human nervous system consists of the Central nervous system (CNS) and the peripheral nervous system.
• The human nervous system allows for coordination and regulation of body functions.
• The human nervous system has two types of actions/responses: voluntary and involuntary.
• Voluntary action is one where you make a conscious decision to carry out a particular action, it starts with the brain.
• Involuntary action does not involve the brain and you are not aware of it until you have completed it, such as a knee-jerk reaction.
• Involuntary action occurs due to sensation and is very fast, automatic and protective.
• There are three types of neurons: sensory, relay, and motor.
• Sensory neurons carry an impulse from sense organs to the CNS.
• Relay neurons are found inside the CNS.
• Motor neurons carry impulses from CNS to effectors (muscles or glands).
• Neurons have a long fibre called an axon.
• The axon is insulated by a fatty sheath with uninsulated sections along it called nodes.
• Neurons connect to many other neurons and receive impulses from them.
• Neurons have to transfer the impulse but they are unable to since there is a tiny gap in between them.
• The junctions or gaps between neurons is called a synapses.
• The electrical impulse is carried along the first axon.
• The membrane of the first neuron is called the pre synaptic membrane.
• This impulse triggers the release of chemicals called neurotransmitters from vesicles.
• These neurotransmitters diffuse into the gap (the gap is called synaptic cleft).
• There are receptors on the end of the other neuron, the neurotransmitters bind with the receptor molecules on the membrane of the other neuron.
• The membrane of the second neuron is called the postsynaptic membrane.
• This stimulates the second neuron to generate an electrical impulse.
• There are no light-sensitive cells at all in the area where the optic nerve attaches to the retina, and so it is known as the blind spot.
• The glands are collectively known as the endocrine system.
• In bright light the pupil constricts in order to prevent too much light entering the eye and damaging the retina.
• There are three types of cones, each sensitive to different types of light (RGB).
• The retina contains light receptors, some sensitive to light of different colours.
• The cornea allows light in.
• The iris refracts light.
• When an object is far, ciliary muscles relax, causing the lens to become thinner and light to be refracted less.
• The fovea is an area on the retina, where almost all of the cone cells are found.
• Adrenaline is the hormone secreted in ‘fight or flight’ situations and its effects include increasing breathing, pulse rate, dilating pupils, increasing information sent to the brain, increasing blood glucose concentration, and diverting blood flow towards muscles and away from non-essential parts.
• When an object is close, ciliary muscles contract, causing the lens to become fatter and light to be refracted more.
• Photoreceptors detect change in the environment (light) and radial muscles relax, causing the pupil to constrict.
• The pupil reflex protects the retina from damage and in dim light the pupil dilates in order to allow more light in.
• Changes in accommodation are brought about by ciliary muscles.