Summary
Summary Homeostasis and Response
Everything you need to know to get a 9 in this topic
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The conditions inside your body need to be kept steady, even when the external environmentchanges. This is important because your cells need the right conditions in order to function properly,
including the right condition for enzyme action. Homeostasis involves maintain a constant
environment in the body. Processes in the human body that need to be kept the same are
temperature, water levels, oxygen, carbon dioxide levels and blood glucose.
Automatic control systems in our body regulate internal environment- these include both nervous
and hormonal communication system. AUS are made of three main components:
Receptor- detect changes to the internal condition of our body. Detect stimuli
Coordination Centre- (brain, spinal cord, pancreas) receives messages about our internal
condition and take action
Effector- muscles or glands which bring about change to maintain the optimal levels
Stimulus Receptor Coordination Centre Effector Response
Coordination Centres:
Nervous System controls muscles an gland
Endocrine System involves hormones
The nervous system detects and reacts to stimuli. It means that it can react to their surroundings and
coordinate their behaviour.
Motor neurone- send impulses from the CNS (central nervous system) to the effector
Sensory neurone- transmits nerve impulses from the receptor to the CNS
Relay neurone- transmits the impulses from the sensory neurone to the motor neurone
Stimulus is a change in your environment which you may need to react to
Sensory neurons receive information from the receptor cells from sense organs. They pass this
information to the CNS. Messages within the CNS are passed by short relay neurones. Instructions
from the CNS are sent by motor neurones to muscles and glands which react to them.
The CNS consist of the brain and spinal cord. The peripheral nervous system consists of the neutrons
receptors cells and effectors.
The connection between two neurones is called a synapse. The nerve signal is transferred by
chemicals which diffuse across the gap. These chemicals then set off a new electrical signal in the
next neurone.
Reflex and rapid, automatic response to certain stimuli that don’t involve the conscious part of the
brain- they can reduce the chances of being injured. The passage of information in a reflex is called a
reflex arc. Reflexes are designed to allow you to respond to potentially dangerous situation very
quickly. As there is no time to think, the brain does not need to be involved. These action are still
coordinated by the CNS, but by the spinal cord instead.
The neurones in reflex arc go through the spinal cord or through an unconscious part of brain. When
a stimulus (e.g. a painful bee sting) is detected by receptors, impulses are sent along a sensory
neurone to a relay neurone in the CNS. When the impulses reach a synapse between the sensory
neurone and the relay neurone, they trigger chemicals to be released. These chemicals cause
impulses to be sent along the relay neurone. When the impulses reach a synapse between the relay
neurone and motor neurone, the same thing happens. Chemicals are released and cause impulses to
be sent along the motor neurone. The impulses then travel along the motor neurone to the effector.
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