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South Tuen Mun Government Secondary School Biology Revision Note 11 Nervous coordination: Stimulus Receptor Sensory nerve Central nervous system Motor nerve Effector Response Structure and types of nerve cells (neurons) Sensory neurone Motor neurone Cell bodies outside the spinal cord Cell bodies inside the spinal cord Longer dendron Shorter dendron Shorter axon Synapse Longer axon Spinal cord – for reflex action, to transmit nerve impulse to the brain In spinal cord, white matter (made up of nerve fibre) surrounds the grey matter (made up of nerve fibre and cell bodies) Brain : cerebrum – for nervous coordination : receive nerve impulse from different sense organs and determine our voluntary action Sensory area - receives impulses from different receptors Motor area - sends out impulses to effectors Association area - collects information from different impulses and helps to produce a suitable response cerebellum – for muscle coordination and balancing of the body medulla oblongata – controls reflex action and involuntary actions e.g. breathing rate, heart beat rate In cerebrum and cerebellum, the grey matter surrounds the white matter; while in medulla oblongata, white matter surrounds the grey matter Reflex action : The response of reflex action is fast to reduce injury because the distance is short; it does not involve cerebrum; it is inborn and stereotyped (same stimulus always give the same response). Reflex action Voluntary action not involve the cerebrum always involve the cerebrum automatic, unconscious, involuntary conscious and voluntary faster response relatively slow stereotyped response varied Chemical coordination - hormones Stimulus Receptor endocrine gland Blood target organ response - Hormones are produced by ductless gland (known as endocrine gland) and secreted into the blood capillary (its secretion will increase when there is a specific stimulation) - Blood carries the hormones around the body - Specific target organ(s) take(s) up the specific hormones, other organs are NOT affected - The hormones stimulate the target organ(s) to produce a specific response : normally regulating the rate of certain reaction (response) Example of hormonal control: Insulin Insulin is a hormone which regulates the blood glucose level. (a) Insulin is made by the Islet of Langerhans in pancreas. The Islet of Langerhans is richly supplied with blood capillary. So the insulin is secreted into the blood capillary. (b) When the blood glucose level is high, (STIMULUS) the secretion of insulin by pancreas (RECEPTOR + ENDOCRINE GLAND) increases. (c) The blood carries the insulin around the body. (d) Liver cells and skeletal muscle cells (TARGET ORGANS) take up insulin. (e) More insulin (in liver cells and muscles cells) increases the uptake of glucose by the cells, the conversion of glucose into glycogen for storage, the breakdown of glucose into carbon dioxide and water, and decreases the conversion of fat, protein to glucose. (f) Therefore the blood glucose level is decreased. (RESPONSE) This is a negative feedback mechanism. Chemical coordination Nervous coordination Nature of message Chemical (hormones) Electrical along the neurone and chemical across synapse Route of transmission Blood in blood capillary Nerve cells Areas of responses Widespread Localized Speed of transmission Relatively slower Faster Duration of effect Relatively long-lasting Shorter