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# Human Nervous System ## Neurones and Motor Neurones **Key Points** * Neurones are the basic units of the human nervous system. * All neurones have a cell body, dendrites, an axon, and synapses. Many human neurones also have an insulating myelin sheath. * Sensory neurones carry impulses fr...

# Human Nervous System ## Neurones and Motor Neurones **Key Points** * Neurones are the basic units of the human nervous system. * All neurones have a cell body, dendrites, an axon, and synapses. Many human neurones also have an insulating myelin sheath. * Sensory neurones carry impulses from sensory receptors to the CNS. * Motor neurones carry impulses from the CNS to effectors such as muscles and glands. * Relay neurones link sensory and motor neurones in the CNS. * Nerves are bundles of hundreds or thousands of neurones. ## The Structure of a Motor Neuron * Each motor neuron is a single cell. * The cell body is located in the CNS. * Dendrites: receive impulses from other neurones. * Axon: carries impulses away from the cell body. * Myelin sheath: insulates the axon. * Synapse: the junction between the axon terminals of one neuron and the dendrites of another (or an effector). ## The Structure of a Relay Neurone * Relay neurones are found in the CNS. * Their function is to link sensory and motor neurones directly, without involving any conscious thought. These rapid responses allow you to avoid danger. They are called reflex responses. ## Questions 1. State the function of neurones. 2. State the characteristics of all neurones. 3. a. Draw and label a sensory neurone and a motor neurone. b. Give three differences in the structure and function of sensory and motor neurones. **Diagram Description:** The diagram shows a detailed structure of a motor neuron, highlighting its components like the cell body, dendrites, axon, myelin sheath, and axon terminals. Another diagram illustrates relay neurons and the direction of nerve impulses. Labels are provided for various parts of the neurons. A key is also provided to help identify different features of neurons.