Homeostasis and Response
Homeostasis
Homeostasis:
- The body has to maintain certain conditions in the body in order to Negative Feedback
survive. Nervous system
o Blood glucose concentration – you need to have enough glucose
The brain
in your blood for your cells to respire. Not enough would leave
you with insufficient energy, and too much would send you into The eye
a coma. Correcting vision defects
o Body temperature – too hot or cold, and your enzymes
Control of body temperature
wouldn’t be able to control your cellular reactions.
o Water balance – too little or too much would kill you. Hypothermia and hyperthermia
- The maintenance of these factors is called homeostasis. This is the The endocrine system
detection of changes to these conditions and responses to return the Controlling blood glucose
body to normal. These changes are automatic, and you don’t know that
Diabetes
they are happening.
Kidneys
Negative Feedback:
- The internal maintenance is done by negative feedback. When the level Kidney failure
of something gets too high or too low, your body uses negative feedback Hormones in human
to bring it back to normal. reproduction
1. Receptor detects a stimulus – level is too high
2. The coordination centre receives and processes the information, Controlling fertility
then organises a response. Adrenaline and thyroxine
3. The effector produces a response, which counteracts the Plant hormones
change and restores the optimum level, the level decreases.
Uses of plant hormones
- This is the same but opposite when the level is too low.
- The effectors will carry on producing responses for as long as they’re stimulated by the coordination
centre. This might cause the opposite problem – making the level change too much, but the receptor
detects if the level becomes too different and negative feedback starts again.
- This process is automatic.
Nervous System:
- The nervous system controls its voluntary and involuntary actions and is responsible for transmitting
and receiving impulses in different parts of its body. It is comprised of the Central Nervous System
- Receptors in your body detect a change inside or outside the body à Your central nervous system
coordinates your body’s response à Effectors cause a response by moving part of your body or
secreting a hormone.
Sense Organ Stimuli
- All messages sent along nerves are electrical. These are
generated by cells called receptors and travel to your brain Sight Eyes Light
and/or spinal cord. Many different types of receptors Hearing Ears Sound (and position of
measure and respond to different stimuli. head)
Taste Tongue Chemicals in food
- There are 3 types of neurones or nerve cells in the nervous
system: Smell Nose Chemicals in air
o Sensory neurones – carry impulses from the Touch Skin Touch, pressure,
temperature, pain and
receptor to the spinal cord or the brain.
itch
1
, o Relay neurones – carry impulses through the spinal cord to the brain and from the brain back
along the spinal cord.
o Motor neurones – take impulses from the spinal cord to an effector.
- Electrical impulses cannot pass from neuron to neuron. When an impulse reaches the end of a neuron,
a neurotransmitter is released. This chemical diffuses across the gap between this neuron and the next
and initiates an impulse in the second neuron. This gap is called a synapse.
- Stimulus à Receptor à Sensory Neurones à Relay Neurones à Motor Neurones à Motor
Neurones à Effector à Response
- Reflexes are rapid, automatic responses 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.
1. The neurones in reflex arcs go through the spinal cord or an unconscious part of the brain.
2. When a stimulus (e.g. a bee sting) is detected by the receptors, impulses are sent along a
sensory neuron to a relay neuron in the CNS.
3. When the impulses reach a synapse between the sensory neuron and the relay neuron, they
trigger chemicals to be released. These chemicals cause impulses to be sent along the relay
neuron.
4. When the impulses reach a synapse between the relay neurone and a motor neurone, the
same thing happens. Chemicals are released and cause impulses to be sent along the motor
neuron.
5. The impulses then travel along the motor neuron to the effector (usually a muscle).
6. The muscle then contracts and moves your hand away from the bee.
7. Because you don’t have to think about the response, it’s quicker than normal responses.
The Brain:
- The brain is made up of billions of interconnected neurons. The brain is in charge of all of our complex
behaviours. It controls and coordinates everything you do.
- Different regions of the brain carry out different functions:
o Cerebral cortex – the outer wrinkly bit, responsible for consciousness, intelligence, memory and
language
o Medulla oblongata – part above the spinal cord, controls unconscious activities like breathing
and heartbeat.
o Cerebellum – the back part of the brain, responsible for muscle coordination.
o Spinal cord
- The study of the brain is called neuroscience, and it first began in ancient Egypt. Drilling holes in the
skull (trepanning) was thought to cure mental disorders in early cultures.
- Ancient Greek physician Hippocrates was the first to believe that senses and intelligence were related
to the brain; previously thought that the heart was the source of consciousness.
- Work of French surgeon Paul Broca helped better understand the structure and how the brain works –
best known for his work on part of the frontal lobe of cerebral cortex, now known as Broca’s area;
found that people with speech problems had lesions (abnormal growths) on this part and proved
different areas of the brain have different functions.
- More recent studies focus on patients with brain damage; parts of their brain have been electronically
stimulated to start neurons sending impulses; these impulses are then looked at using an MRI scanner.
- Almost all animals can change their behaviour as a result of experiences; your behaviour is determined
by your brain function, so scientists believe that changes in behaviour result from changes in the brain.
2
Homeostasis
Homeostasis:
- The body has to maintain certain conditions in the body in order to Negative Feedback
survive. Nervous system
o Blood glucose concentration – you need to have enough glucose
The brain
in your blood for your cells to respire. Not enough would leave
you with insufficient energy, and too much would send you into The eye
a coma. Correcting vision defects
o Body temperature – too hot or cold, and your enzymes
Control of body temperature
wouldn’t be able to control your cellular reactions.
o Water balance – too little or too much would kill you. Hypothermia and hyperthermia
- The maintenance of these factors is called homeostasis. This is the The endocrine system
detection of changes to these conditions and responses to return the Controlling blood glucose
body to normal. These changes are automatic, and you don’t know that
Diabetes
they are happening.
Kidneys
Negative Feedback:
- The internal maintenance is done by negative feedback. When the level Kidney failure
of something gets too high or too low, your body uses negative feedback Hormones in human
to bring it back to normal. reproduction
1. Receptor detects a stimulus – level is too high
2. The coordination centre receives and processes the information, Controlling fertility
then organises a response. Adrenaline and thyroxine
3. The effector produces a response, which counteracts the Plant hormones
change and restores the optimum level, the level decreases.
Uses of plant hormones
- This is the same but opposite when the level is too low.
- The effectors will carry on producing responses for as long as they’re stimulated by the coordination
centre. This might cause the opposite problem – making the level change too much, but the receptor
detects if the level becomes too different and negative feedback starts again.
- This process is automatic.
Nervous System:
- The nervous system controls its voluntary and involuntary actions and is responsible for transmitting
and receiving impulses in different parts of its body. It is comprised of the Central Nervous System
- Receptors in your body detect a change inside or outside the body à Your central nervous system
coordinates your body’s response à Effectors cause a response by moving part of your body or
secreting a hormone.
Sense Organ Stimuli
- All messages sent along nerves are electrical. These are
generated by cells called receptors and travel to your brain Sight Eyes Light
and/or spinal cord. Many different types of receptors Hearing Ears Sound (and position of
measure and respond to different stimuli. head)
Taste Tongue Chemicals in food
- There are 3 types of neurones or nerve cells in the nervous
system: Smell Nose Chemicals in air
o Sensory neurones – carry impulses from the Touch Skin Touch, pressure,
temperature, pain and
receptor to the spinal cord or the brain.
itch
1
, o Relay neurones – carry impulses through the spinal cord to the brain and from the brain back
along the spinal cord.
o Motor neurones – take impulses from the spinal cord to an effector.
- Electrical impulses cannot pass from neuron to neuron. When an impulse reaches the end of a neuron,
a neurotransmitter is released. This chemical diffuses across the gap between this neuron and the next
and initiates an impulse in the second neuron. This gap is called a synapse.
- Stimulus à Receptor à Sensory Neurones à Relay Neurones à Motor Neurones à Motor
Neurones à Effector à Response
- Reflexes are rapid, automatic responses 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.
1. The neurones in reflex arcs go through the spinal cord or an unconscious part of the brain.
2. When a stimulus (e.g. a bee sting) is detected by the receptors, impulses are sent along a
sensory neuron to a relay neuron in the CNS.
3. When the impulses reach a synapse between the sensory neuron and the relay neuron, they
trigger chemicals to be released. These chemicals cause impulses to be sent along the relay
neuron.
4. When the impulses reach a synapse between the relay neurone and a motor neurone, the
same thing happens. Chemicals are released and cause impulses to be sent along the motor
neuron.
5. The impulses then travel along the motor neuron to the effector (usually a muscle).
6. The muscle then contracts and moves your hand away from the bee.
7. Because you don’t have to think about the response, it’s quicker than normal responses.
The Brain:
- The brain is made up of billions of interconnected neurons. The brain is in charge of all of our complex
behaviours. It controls and coordinates everything you do.
- Different regions of the brain carry out different functions:
o Cerebral cortex – the outer wrinkly bit, responsible for consciousness, intelligence, memory and
language
o Medulla oblongata – part above the spinal cord, controls unconscious activities like breathing
and heartbeat.
o Cerebellum – the back part of the brain, responsible for muscle coordination.
o Spinal cord
- The study of the brain is called neuroscience, and it first began in ancient Egypt. Drilling holes in the
skull (trepanning) was thought to cure mental disorders in early cultures.
- Ancient Greek physician Hippocrates was the first to believe that senses and intelligence were related
to the brain; previously thought that the heart was the source of consciousness.
- Work of French surgeon Paul Broca helped better understand the structure and how the brain works –
best known for his work on part of the frontal lobe of cerebral cortex, now known as Broca’s area;
found that people with speech problems had lesions (abnormal growths) on this part and proved
different areas of the brain have different functions.
- More recent studies focus on patients with brain damage; parts of their brain have been electronically
stimulated to start neurons sending impulses; these impulses are then looked at using an MRI scanner.
- Almost all animals can change their behaviour as a result of experiences; your behaviour is determined
by your brain function, so scientists believe that changes in behaviour result from changes in the brain.
2
