Topic 5 - Homeostasis
Brain, eye, endocrine, CNS
nervous system (brain, eyes, reflexes) and the endocrine system (menstrual cycle, contraception, infertility treatments).
Homeostasis
- Our bodily conditions must be kept steady, even when the external environment changes. This is important because our cells and
enzymes need the right conditions to function properly.
- Homeostasis is all about the regulation of conditions inside the body to maintain a stable internal environment, in response to
internal and external changes.
- We have many automatic control systems in our bodies, including nervous and hormonal communication systems. There are control
systems that control our body temperature, our blood glucose level and our water content.
- Each automatic control system is made up of 3 main components that work together: cells called receptors, coordination centres
(brain, spinal cord, pancreas) and effectors.
Negative Feedback
- The mechanism negative feedback is used by our
automatic control systems to keep our internal
environment stable, when the level of something (e.g.
water or temp) gets too high/low, our body uses it to
bring it back to normal
- This process is all automatic.
The Nervous system
Stimuli
- Organisms need to respond to stimuli (changes
in the environment) to survive. A single-celled organism
can just respond to its environment, but the cells of a
multicellular organism must communicate with each
other first.
- As multicellular organisms have evolved, they
developed nervous and hormonal communication
systems.
Receptors and Effectors
- Receptors are cells that detect stimuli, e.g. taste
receptors on the tongue and sound receptors in the ears.
- They can form part of large complex organs, e.g.
the retina of the eye is covered in light receptor cells.
- Effectors respond to nervous impulses and
bring about a change, e.g. muscles and glands. They
respond in different ways - muscles contract in response
to a nerve impulse, whereas glands secrete hormones.
The CNS
- The central nervous system is a coordination centre, which receives info from the receptors and then coordinates a response, which is
carried out by effectors. Only large animals like mammals and birds have complex nervous systems, simple animals like jellyfish don’t -
everything they do is a reflex response.
Synapses
- The connection between 2 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.
Reflexes
- They are rapid, automatic responses to certain stimuli that don’t involve the conscious part of
the brain, they reduce the chances of getting injured.
- Example: If a bright light is shined in our eyes, our pupils automatically get smaller so less light
gets into the eye, stopping any damage. Or if we get a shock, we release the adrenaline
hormone, our body doesn’t wait for us to decide we’re shocked.
- The passage of info in a reflex (receptor to effector) is called a reflex arc.
Reflex Arc
- The neurones in reflex arcs go through the spinal cord or an unconscious
part of the brain.
- When a stimulus is detected by receptors, impulses are sent along a sensory
neurone to the CNS.
- When the impulses reach a synapse between a sensory and 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 and motor neurones,
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, e.g. a
muscle, which then contracts and moves the hand away. It's quicker than a
normal response, because you don’t have to think about it.
Reaction Time
- It's the time it takes to respond to a stimulus, often less than a second. It can be affected by factors like age, gender, drugs etc.
Practical for Reaction Time
Caffeine is a drug that can speed up a person’s reaction time, and its effect on reaction time can be measured like this:
1. The person being tested should sit with their arm resting on the edge of a table, which stops their arm
moving up or down.
2. Hold a ruler vertically between their thumb and forefinger, making sure the zero end is level with their
thumb. Then let go without any warning.
3. The person being tested should try to catch the ruler asap, as soon as they see it fall.
4. Reaction time is measured by the number of the ruler where it’s caught, the further down it's caught
(higher the number), the slower their reaction time.
5. Repeat the test many times and calculate the mean distance that the ruler fell. From the mean distance
we can work out the reaction time in seconds.
6. The person being tested should then have a caffeinated drink, like cola, and after 10 minutes repeat these steps.
7. The variables need to be controlled to make sure it's a fair test, e.g. the same person should be used to catch the ruler each time, the
same hand should always be used, the ruler should always be dropped from the same height, the person being tested has not had any
caffeine (or anything that could affect their reaction time) before the experiment.
It can be measured by computer
- Simple computer tests can also be used to measure reaction time, for example someone has to click the mouse as soon as they see a
stimulus on the screen, like a box changing colour.
- Computers give a more precise reaction time because they remove the possibility of human error. Also the computer gives it in
milliseconds, so gives a more accurate measurement.
- Using a computer also removes the possibility that the person being tested can predict when to respond, in the ruler experiment the
person could predict when the tester is going to drop the ruler by his body language.
The Brain is Responsible for Complex Behaviours
1. The brain is a part of the CNS, along with the spinal cord.
2. It’s made up of billions of interconnected neurons.
3. The brain is in charge of all complex behaviours, in controls and coordinates everything we do.
Brain, eye, endocrine, CNS
nervous system (brain, eyes, reflexes) and the endocrine system (menstrual cycle, contraception, infertility treatments).
Homeostasis
- Our bodily conditions must be kept steady, even when the external environment changes. This is important because our cells and
enzymes need the right conditions to function properly.
- Homeostasis is all about the regulation of conditions inside the body to maintain a stable internal environment, in response to
internal and external changes.
- We have many automatic control systems in our bodies, including nervous and hormonal communication systems. There are control
systems that control our body temperature, our blood glucose level and our water content.
- Each automatic control system is made up of 3 main components that work together: cells called receptors, coordination centres
(brain, spinal cord, pancreas) and effectors.
Negative Feedback
- The mechanism negative feedback is used by our
automatic control systems to keep our internal
environment stable, when the level of something (e.g.
water or temp) gets too high/low, our body uses it to
bring it back to normal
- This process is all automatic.
The Nervous system
Stimuli
- Organisms need to respond to stimuli (changes
in the environment) to survive. A single-celled organism
can just respond to its environment, but the cells of a
multicellular organism must communicate with each
other first.
- As multicellular organisms have evolved, they
developed nervous and hormonal communication
systems.
Receptors and Effectors
- Receptors are cells that detect stimuli, e.g. taste
receptors on the tongue and sound receptors in the ears.
- They can form part of large complex organs, e.g.
the retina of the eye is covered in light receptor cells.
- Effectors respond to nervous impulses and
bring about a change, e.g. muscles and glands. They
respond in different ways - muscles contract in response
to a nerve impulse, whereas glands secrete hormones.
The CNS
- The central nervous system is a coordination centre, which receives info from the receptors and then coordinates a response, which is
carried out by effectors. Only large animals like mammals and birds have complex nervous systems, simple animals like jellyfish don’t -
everything they do is a reflex response.
Synapses
- The connection between 2 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.
Reflexes
- They are rapid, automatic responses to certain stimuli that don’t involve the conscious part of
the brain, they reduce the chances of getting injured.
- Example: If a bright light is shined in our eyes, our pupils automatically get smaller so less light
gets into the eye, stopping any damage. Or if we get a shock, we release the adrenaline
hormone, our body doesn’t wait for us to decide we’re shocked.
- The passage of info in a reflex (receptor to effector) is called a reflex arc.
Reflex Arc
- The neurones in reflex arcs go through the spinal cord or an unconscious
part of the brain.
- When a stimulus is detected by receptors, impulses are sent along a sensory
neurone to the CNS.
- When the impulses reach a synapse between a sensory and 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 and motor neurones,
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, e.g. a
muscle, which then contracts and moves the hand away. It's quicker than a
normal response, because you don’t have to think about it.
Reaction Time
- It's the time it takes to respond to a stimulus, often less than a second. It can be affected by factors like age, gender, drugs etc.
Practical for Reaction Time
Caffeine is a drug that can speed up a person’s reaction time, and its effect on reaction time can be measured like this:
1. The person being tested should sit with their arm resting on the edge of a table, which stops their arm
moving up or down.
2. Hold a ruler vertically between their thumb and forefinger, making sure the zero end is level with their
thumb. Then let go without any warning.
3. The person being tested should try to catch the ruler asap, as soon as they see it fall.
4. Reaction time is measured by the number of the ruler where it’s caught, the further down it's caught
(higher the number), the slower their reaction time.
5. Repeat the test many times and calculate the mean distance that the ruler fell. From the mean distance
we can work out the reaction time in seconds.
6. The person being tested should then have a caffeinated drink, like cola, and after 10 minutes repeat these steps.
7. The variables need to be controlled to make sure it's a fair test, e.g. the same person should be used to catch the ruler each time, the
same hand should always be used, the ruler should always be dropped from the same height, the person being tested has not had any
caffeine (or anything that could affect their reaction time) before the experiment.
It can be measured by computer
- Simple computer tests can also be used to measure reaction time, for example someone has to click the mouse as soon as they see a
stimulus on the screen, like a box changing colour.
- Computers give a more precise reaction time because they remove the possibility of human error. Also the computer gives it in
milliseconds, so gives a more accurate measurement.
- Using a computer also removes the possibility that the person being tested can predict when to respond, in the ruler experiment the
person could predict when the tester is going to drop the ruler by his body language.
The Brain is Responsible for Complex Behaviours
1. The brain is a part of the CNS, along with the spinal cord.
2. It’s made up of billions of interconnected neurons.
3. The brain is in charge of all complex behaviours, in controls and coordinates everything we do.
