Download Note 11

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