4. Nerves And Homeostasis Flashcards
What is a stimulus?
A change in your environment (which you may need to react to).
What are the five sense organs?
1) Eyes
2) Ears
3) Nose
4) Tongue
5) Skin
What are receptors?
Groups of cells which are sensitive to stimuli.
What do receptors do?
They convert the stimulus energy into electrical impulses.
Are sense organs the same as receptors?
No, sense organs usually contain the receptors (e.g. The eye contains light receptors)
What receptors do the eyes contain and what stimulus are they sensitive to?
Light receptors - sensitive to light
What receptors do the ears contain and what stimulus are they sensitive to?
Sound receptors - sensitive to sound
Balance receptors - sensitive to changes in position
What receptors does the nose contain and what stimulus are they sensitive to?
Smell receptors - sensitive to chemical stimuli
What receptors does the tongue contain and what stimulus are they sensitive to?
Taste receptors - sensitive to chemical stimuli
What receptors does the skin contain and what stimulus are they sensitive to?
Touch receptors - sensitive to touch, pressure, pain and temperature change.
What are some examples of stimuli?
- Light
- Sound
- Touch
- Pressure
- Pain
- Chemical
- A change in position or temperature
Are light receptors cells the same as normal cells?
Yes, they have a nucleus, cytoplasm and cell membrane.
What does the CNS consist of?
The brain and spinal cord ONLY.
What does CNS stand for?
Central Nervous System
How is a stimulus processed?
- Receptor cells detect a stimulus
- Information as electrical impulses is sent to the coordination centres in the CNS via a neurone
- A response is coordinated in the brain
- A neurone transmits instructions to the effectors
What are neurones?
Nerve cells which carry signals around the body.
What is a sensory neurone?
Nerve cells that carry signals from the receptors to the CNS.
What is a relay neurone?
Nerve cells that carry signals from sensory neurones to motor neurones.
What is a motor neurone?
Nerve cells that carry signals from the CNS to the effector muscles or glands.
What is an effector?
Muscles and glands which respond to a stimulus.
How do muscles respond to a stimulus?
They contract.
How do glands respond to a stimulus?
They secrete chemicals (hormones).
What are control systems?
Automatic control systems help to keep conditions constant by responding to stimuli.
What are the parts of a control system?
Receptors -> Coordination centres -> Effectors
What is the fastest way for the body to respond to a stimulus?
Reflex reactions. They are quicker than normal responses, since you don’t have to think about the response.
What is the connection between two neurones called?
A synapse.
What is a synapse?
The connection between two neurones.
How is a nerve signal transmitted across a synapse?
Chemicals, which diffuse across the gap.
How fast is transmission across a synapse?
It is slower than in the neurones, because the diffusion takes time.
What are reflexes?
Automatic, rapid responses to certain stimuli.
What are reflex reactions used for?
To reduce the chance of injury.
Give an example of a reflex reaction.
If someone shines a bright light in your eye, your pupils automatically get smaller to stop the eye being damaged.
What is the path of a reflex reaction called?
A reflex arc.
Describe a reflex arc.
1) Stimulus is detected by the receptors
2) Impulse is sent along sensory neurone
3) Impulse passes across a synapse to relay neurone as chemical signal
4) Impulse travels along relay neurone
5) Impulse passes across a synapse to motor neurone as chemical signal
6) Impulse reaches effector and a response happens
Does a reflex arc go through the CNS?
Yes, the neurones gone through the spinal cord or an unconscious part of the brain.
Compare a reflex reaction and a normal response or behaviour.
Both pass through the CNS, except the reflex reaction doesn’t go to a conscious part of the brain.
What is the brain made of?
Billions of interconnected neurones.
What behaviours is the brain in charge of?
Complex behaviours.
What are the 3 parts of the brain?
- Cerebral cortex
- Medulla
- Cerebellum
Where is the cerebral cortex?
Top, outer part of the brain. (Pg 45 diagram)
Where is the medulla?
Bottom, near the spinal cord. In front of the cerebellum. (Pg 45 diagram)
Where is the cerebellum?
Back, bottom, behind the spinal cord and medulla. (Pg 45 diagram)
What is the cerebral cortex responsible for?
Consciousness, intelligence, memory and language.
What is the medulla responsible for?
Unconscious activities - e.g. Breathing and heart rate
What is the cerebellum responsible for?
Muscle coordination (movement).
What 3 methods can be used to study the brain?
1) Studying patients with brain damage
2) Electrically stimulating the brain
3) MRI scans
How can studying patients with brain damage be used to study the brain?
If a small part of the brain is damaged, the effect on the patient can tell you what that part does.
How can electrically stimulating the brain be used to study the brain?
When a part of the brain is stimulated, the effect can be observed and what that part does can be worked out.
How can the brain be stimulated electrically?
By pushing a tiny electrode into the tissue and passing electricity through it.
How can MRI scans be used to study the brain?
An MRI scanner can produce detailed images of the brain’s structures. It can be used to see which parts of the brain are active when a patient is doing a certain activity.
What does an MRI scanner do?
Produces a detailed image of the brain’s structures.
What does MRI stand for?
Magnetic Resonance Imaging
What is homeostasis?
The process of maintaining a constant internal environment.
What are some bodily levels that need to be controlled?
- Ions content
- Water content
- Temperature
- Sugar content
What are bodily levels (e.g. water content) kept constant by?
Automatic control systems.
What are the effectors in homeostasis usually?
Glands
What are hormones and how do they work in homeostasis?
- Chemicals substances secreted by glands
- Carried in blood to other parts of the body, but only affect particular cells (target cells)
How are ions taken into the body?
In food.
What happens when too much of an ion is taken into the body?
The excess needs to be removed.
What are the ways in which ions can be removed from the body?
- Sweat
* In the kidneys (as urine)
What organ regulates ion content?
Kidneys
How is water taken into the body?
Food and drink
How is water lost from the body?
- Sweat
- Breath
- Urine
- Faeces
How do the liver and kidneys work together to remove waste?
- Liver breaks waste products into less harmful products
- Kidney then remove these in the urine
What two main things is the liver responsible for?
Deamination and detoxification (see pg 47)
What is deamination?
The liver breaking down amino acids into ammonia. This ammonia is then converted into urea which can be excreted.
Why must deamination happen?
It gets rid of excess amino acids, which can be damaging if they stay in the body.
What is detoxification?
The liver breaking harmful substances (e.g. alcohol, drugs and unwanted hormones) down into less harmful substances that are then excreted in the urine.
Which substances does the liver break down?
- Amino acids -> Ammonia ( -> Urea)
- Alcohol, drugs and unwanted hormones
- Old blood cells
What does the liver do with old RBCs?
They are removed and the iron in them is stored.
What do the kidneys do?
1) Filter the blood
2) Reabsorb needed products
3) Release urea, excess ions and excess water as urine
What are nephrons?
Filtration units in the kidneys
What are the filters in the kidneys called?
Nephrons
In detail, how are substances absorbed and reabsorbed into the nephrons?
- High pressure is built up
- Small molecules fit through filter and are forced into the nephron
- Larger molecules cannot fit and so stay in the blood
- Useful substances are selectively reabsorbed into the blood (using active transport for sugar and ions)
- Those which are not reabsorbed stay in the kidney and are stored in the bladder
Which molecules are and are not absorbed in the kidneys?
ABSORBED • Water / Salt • Urea • Ions • Amino acids • Ammonia • Sugar NOT ABSORBED • Cells • Protein
Which molecules are reabsorbed and not reabsorbed in the kidneys?
REABSORBED • Sugar • Amino acids • SOME Ions • SOME Water / Salts NOT REABSORBED • Ammonia • Urea • SOME Ions • SOME Water / Salts
How is sugar reabsorbed into the blood from the kidneys?
Using active transport (since it is against the concentration gradient).
How are ions reabsorbed into the blood from the kidneys?
Using active transport (since it is against the concentration gradient).
What happens to molecules which are not reabsorbed from the kidneys?
They continue out of the nephron, into the ureter and down to the bladder as urine.
Why must water concentration in the blood plasma be kept constant?
- Prevents too much water moving into or out of the tissues by osmosis
- Keeps blood pressure constant
What controls the amount of water reabsorbed from the kidney nephrons?
ADH (Anti-diuretic hormone)
What is ADH?
Anti-diuretic hormone
How does ADH work?
It makes the nephrons more permeable so that more water is reabsorbed back into the blood.
What is the coordination centre for water content in the blood?
The brain.
How does the brain control blood water content?
- The brain monitors the water content of the blood
- The brain instructs the pituitary gland to release ADH
- This regulates the blood water concentration
What happens when water content of the blood get too low?
- Brain detects lack of water
- Brain instructs pituitary gland to release more ADH
- Kidneys reabsorb more water
What happens when the water content of the blood gets too high?
- Brain detects excess water
- Brain instructs pituitary gland to release less ADH
- Kidneys reabsorb less water
How does heat affect the urine produced and why?
- Heat causes you to sweat, which loses water
- This means more water needs to be reabsorbed into the blood
- Therefore, less water is lost through urine, making the urine more concentrated
How does exercise affect the urine produced and why?
- Exercise causes you to sweat, which loses water
- This means more water needs to be reabsorbed into the blood
- Therefore, less water is lost through urine, making the urine more concentrated
How does water intake affect the urine produced and why?
- Not drinking enough will produce concentrated urine, since there is little excess water that needs to be lost
- Drinking too much will produce dilute urine, since there is a lot of water that needs to be lost
What happens if the kidneys stop working?
Waste substances build up in the blood and you can’t control ion and water levels in the blood. This can lead to death.
What are the two methods of treating kidney failure?
1) Dialysis treatment
2) Kidney transplant
What is dialysis treatment?
Filtering a patient’s blood using a machine instead of the kidneys.
Why does dialysis have to be done regularly?
To keep concentrations of dissolved substances at normal levels and to remove waste.
How does dialysis work?
- Blood flows between partially permeable membranes, surrounded by dialysis fluid.
- Dialysis fluid has the same concentration of ions and glucose as healthy blood.
- This means only waste substances diffuse across the membrane.
- The dialysis fluid is constantly pumped around to maintain a steady concentration gradient.
How often is dialysis treatment required?
Most patients have it 3 times a week for 3-4 hours.
What are the advantages and disadvantages of dialysis treatment?
ADV. • Can keep the patient alive until a donor organ is found • No need for surgery DIS. • Not pleasant experience • Takes a long time and is repetitive • May cause blood clots or infections • Expensive
Where are donor kidneys taken from?
- People who have recently died suddenly
* People who are still alive (since people have two kidneys)
What are the advantages and disadvantages of kidney transplants?
ADV. • One time operation -> Permanent solution • Cheaper in the long term DIS. • Small risk to living donor • Risk of operation • Kidney may be rejected by patient • Long waiting lists for kidneys
Why is maintaining internal body temperature important?
Most enzymes work most efficiently at 37*C. If they cannot catalyse important reactions, it could even result in death.
What part of the brain is responsible for controlling body temperature?
Thermoregulatory centre.
How does the thermoregulatory centre control body temperature?
- It contains receptors that are sensitive to the temperature of the blood flowing through the brain
- It also receives impulses from receptors in the skin
- It then controls the body’s responses
How does the body respond to being too hot?
1) Hairs lie flat
2) Sweat is produced -> Evaporates, removing heat
3) Blood vessels supplying the skin capillaries dilate -> More blood flows close to surface
How does the body respond to being too cold?
1) Hairs stand up on end -> Trap a layer of insulating air
2) No sweat produced
3) Blood vessels supplying skin capillaries constrict -> Less blood flows near surface
4) Shivering -> Heat released from respiration
What are the two hormones involved in blood glucose control?
Insulin and glucagon
How is glucose added and removed from the blood (not by hormones)?
- Added by eating foods -> which are digested.
* Removed by cells -> where it is needed for respiration.
How can excess glucose be stored?
1) As glycogen in the liver and muscles
2) When these stores are full -> As lipid (fat) in the tissues
Which organ monitors blood glucose concentration?
Pancreas
What is the response when blood glucose level gets too high?
- Pancreas detects high level of glucose
- Insulin is secreted into the blood by the pancreas
- Insulin causes more glucose to be taken into liver and muscles, where it is stored as glycogen
- This reduces blood glucose concentration
What is the response when blood glucose level gets too low?
- Pancreas detects low level of glucose
- Glucagon is secreted into the blood by pancreas
- Glucagon encourages glycogen to be converted to glucose and released into the blood
- Blood glucose concentration increases
What is diabetes?
A condition which affects your ability to control your blood sugar level.
What is Type 1 diabetes?
Where the pancreas produces little or no insulin, meaning the blood glucose level can rise so high that it can kill the person.
How can Type 1 diabetes be treated?
- Having a carefully controlled diet and regularly exercising.
- Injecting insulin -> This removes excess glucose
What is Type 2 diabetes?
Where a person becomes resistant to their own insulin, which can cause blood glucose level to rise dangerously high.
How can Type 2 diabetes be treated?
- Having a carefully controlled diet -> Avoiding carbohydrate-rich foods
- Exercise -> Keeps glucose levels low
- Drugs -> Improve responsiveness to insulin
Which type of diabetes is genetic and which can be developed?
Type 1 - Genetic
Type 2 - Can be developed (although partly genetic)
What are some risk factors of developing Type 2 diabetes?
- Obesity
- Diet
- Lack of exercise
- Race
- Genetics
- Age
