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Nervous System 1 A neurotransmitter, i.e. a chemical compound (substance) that transmits a nerve impulse from one neuron (nerve) to another. It is found at the synapse and is discharged after transmission of the impulse. In nerve impulse transmission a stimulus must be of a certain 'size' (threshold) before it will be transmitted. If a stimulus exceeds the threshold all will be transmitted and if the stimulus does not exceed the threshold nothing will be transmitted. Long appendage coming from cell body of nerve cell (neuron). Conducts impulses away from cell body. Controls activities of neurons (nerve cell). Contains Nissl's granules (composed of RNA and used in protein synthesis), nucleus and mitochondria and produces a neurotransmitter. A mass of nerve cells (nervous tissue) which co-ordinates the activities of an animal. In vertebrates it is composed of the brain and spinal cord. acetylcholine all or nothing law axon cell body central nervous system (CNS) Outer layer of the cerebral hemispheres. Composed of grey matter. cerebral cortex That part of the human brain found above the pons and medulla oblongata. It is made up of two halves, the cerebral hemispheres, which are connected together by a band of nerve fibres – the corpus callosum. It is responsible for movement, sensations, learning, memory, intelligence and emotions. cerebrum Tightly bundled nerve fibres that join the two cerebral hemispheres of the brain. corpus callosum A process (a piece sticking out) of the cell body of a neuron, which transmits impulses towards the cell body. dendron Pairs of projections arise from the spinal cord; these are called spinal roots of which there are two types. Which one has a swelling, and carries sensory neurons into the spinal cord? Carries messages from the central nervous system (CNS) to effectors. Cell body located at end of axon, inside CNS, e.g. motor neurons. dorsal root efferent neuron Found in the spinal cord and brain. Consists of nerve cell bodies and dendrites. grey matter Chemical change transmitted along a nerve fibre, which brings about a response in an effector (muscle or gland). impulse Page 1 of 3 Neurons that carry messages from one or more sensory neurons to motor neurons. They are found within the central nervous system. interneurons Drug used in the treatment of Parkinson’s disease. It is converted into dopamine by the body. levodopa Membranes surrounding the brain and spinal cord. meninges Lipid covering formed by the Schwann cells of neuron. Insulation on dendrites or axons of neurons. Speeds up impulse transmission. myelin sheath Chemical change transmitted along a neuron that brings about a response in an effector. nerve impulse Bony projection from a vertebra for muscle attachment. neural spine Nerve cell. Bundles of these form nervous tissue. All are basically similar in structure. Each consists of one axon, one or more dendrons, neurotransmitter vesicles (pouches) and a nucleus contained in the cell body. A myelin sheath and Schwann cells may also be present. There are three types: sensory, motor and inter... neuron Constriction of myelin sheath on the axon to separate Schwann cells on some neurons. Speeds up impulse transmission. node of Ranvier Loss of feeling and movement due to damage to a nerve cord or the central nervous system. paralysis All nerves outside the central nervous system (CNS), i.e. all nerves except the brain and spinal cord. They carry messages to and from the CNS. peripheral nervous system (PNS) Nerve cell that carries the impulse (message) away from the synapse. postsynaptic neuron A structure that receives and transmits a stimulus; touch, smell, taste, pain, etc. receptor The pathway from the point of stimulation to the responding effector. It has five components. The stimulus is picked up by a receptor (1), that sends the message along an afferent (sensory) neuron (2), to the spinal cord (3). The reply to this stimulus is sent from the spinal cord along an efferent (motor) neuron (4), to an effector (muscle or gland) (5). reflex arc Cell found around the axon of a neuron – secretes the myelin sheath. Schwann cell Page 2 of 3 Afferent neuron. Pick up and carry messages from sense organs (receptors) to the central nervous system (CNS). Cell body at end of a short branch to one side of the axon, outside CNS. sensory neuron Any change in the environment (internal or external) that causes a cell or organism to respond. stimulus Neurotransmitter swelling. A swelling at the end of an axon. synaptic knob / terminal button The minimum limit/level at which a stimulus is perceptible or generated. threshold Pairs of projections arise from the spinal cord. These are called spinal roots of which there are two types. Which type carries motor neurons away from the spinal cord? ventral root Page 3 of 3