Neurones and hormones and homeostatis

Question 1

Why do multicellular organisms need communication systems?

Answer 1

To increase their chance of survival by responding to changes in the internal and external environment.

Question 2

How do adjacent cells communicate?

Answer 2

Secrete chemicals called neurotransmitters which send signals to adjacent cells.

Question 3

How do distant cells communicate?

Answer 3

Cells release hormones into the blood which travel and act as signals to distant cells. Cell surface receptors allow cells to recognise the chemicals involved in cell signalling

Question 4

What is the difference between receptors and effectors?

Answer 4

Receptors detect stimuli
Effectors bring about a response to a stimulus

Question 5

What is the difference between negative and positive feedback?

Answer 5

Negative feedback reverses any change in the internal environment to return it to optimal level
Positive feedback increases any change detected by receptors so does not lead to homeostasis

Question 6

Do endotherms maintain body temperature?

Answer 6

They maintain body temperature within strict limits and their internal temperature is independent of their external body temperature

Question 7

Do ectotherms maintain body temperature?

Answer 7

Their body temperature fluctuates with external temperatures

Question 8

How do endotherms maintain body temperature?

Answer 8

Physiologically:
- sweat glands in skin
- hairs on skin (lie flat or stand up)
- Arterioles ( dilate and constrict)
- Liver cells (increase/reduce rate or metabolism)
- skeletal muscles (shivering)
Behavioural:
-move into sun/shade
- increase/decrease exposed surface area

Question 9

What are the benefits of endotherms maintaining body temperature?

Answer 9

Constant optimal temperature, activity is possible even when cool, inhabit colder parts of the planet

Question 10

What are the negatives to endotherms maintaining body temperature?

Answer 10

Energy is used up to maintain constant temperature, more food required, less energy used in growth

Question 11

How do endotherms monitor their body temperature?

Answer 11

Peripheral temperatures in the skin monitor the temperature in the extremeties and feed the information to the thermoregulatory centre in the hypothalamus in the brain

Question 12

What are the advantages of ectotherms not regulating their internal body temperature?

Answer 12

Use less food in respiration, need less food, greater proportion of energy used for growth

Question 13

What are the disadvantages of ectotherms not regulating their internal body temperature?

Answer 13

Less active in cooler temperatures, may not be capable of activity in winter months

Question 14

What do sensory receptors do?

Answer 14

They convert the energy of a stimulus into electrical energy. They act as transducers - something that converts one form of energy into another

Question 15

How do receptors that communicate information via the nervous system work?

Answer 15

When the nervous system receptor is resting theres a difference in charge between the inside and outside of the cell. This means there is a voltage/ potential difference across the membrane. This is the resting potential and is -70mV. When a stimulus is detected the cell membrane allows more ions to move in and out of the cell changing the potential difference - this causes the generator potential. If the generator potential crosses the threshold level of -55mV it will activate the action potential

Question 16

Describe the sequence of events known as the action potential.

Answer 16

• Stimulus - excites the neuron cell membrane causing sodium ion channels to open. Sodium ions diffuse into the neuron making the inside of the neuron more positive
• Depolarisation - if potential difference reaches the threshold (-55) voltage gated sodium ion channels open and more sodium ions diffuse into the membrane. This is positive feedback
• Repolarisation - at a a potential difference of around 30mv sodium ion channels close and voltage gated potassium ion channels open. Potassium ions diffuse out of the neurone. This starts to get the membrane back to its resting potential. This is negative feedback.
• Hyperpolarisation - potassium ion channels are slow to close so there is a slight overshoot where too many potassium ions diffuse out of the neurone. The potential difference becomes more negative than the resting potential.
• Resting potential - ion channels are reset until the membrane is excited by another stimulus

Question 17

What is meant by the term all or nothing response?

Answer 17

If the depolarisation is not great enough to reach the threshold then an action potential and hence an impulse are not produced

Question 18

How is an action potential transmitted in an unmyelinated neurone?

Answer 18

1) Na+ diffuses into the neurone through a channel
2) There is a localised high concentration of Na+ inside the neurone
3) Na+ diffuses along the inside of the neurone
4) Na+ gate which was initially closed now opens due to the depolarisation

Question 19

Explain the difference between myelinated and unmyelinated neurones.

Answer 19

In myelinated neurones thay have a myelin sheath which is an electrical insulator made up of schwann cells. The gaps inbetween the schwann cells where there are tiny patches of bare membrane are known as the nodes of ranvier. In a myelinated neurone depolarisation only occurs at the nodes of ranvier as this is where the sodium ions can get through the membrane.
Unmyelinated neurones have a cell body with a nucleus that connects it to other neurones. These are dendrites and dendrons or axons. Dendrites and dendrons carry nerve impulses towards the cell body. Axons carry nerve impulses away from the cell body.

Question 20

What are the structural differences between sensory neurones, relay neurones, and motor neurones?

Answer 20

Sensory - have short dendrites and one long dendron to carry nerve responses from receptor cells to the cell body. Have one short axon that carries nerve impulses from the cell body to the CNS.
Relay - many short dendrites which carry nerve impulses from sensory neurones to the cell body. One axon carries nerve impulses from the cell body to motor neurones
Motor - many short dendrites that carry nerve impulses from the CNS to the cell body. One long axon that carries nerve impulses from the cell body to effector cells.

Question 21

Describe and explain the structure of a synapse.

Answer 21

The tiny gap between the cells in the synapse is called the synaptic cleft. The presynaptic neuron (the one before the synapse) has a swelling called a synaptic knob. This contains synaptic vesicles filled with neurotransmitters.

Question 22

Explain how a synapse works.

Answer 22

When an action potential reaches the end of a neurone it causes neurotransmitters to be released into the synaptic cleft. They diffuse across the postsynaptic membrane and bind to specific receptors. When neurotransmitters bind to receptors they can trigger an action potential, cause muscle contraction or cause a hormone to be secreted.

Question 23

Describe the structure of a cholinergic synapse.

Answer 23

Presynaptic membrane has a synaptic knob that contains vesicles filled with acetylcholine (ACh). Postsynaptic membrane (on a neurone or effector cell) has cholinergic receptors on it.

Question 24

How is a nerve impulse transmitted across a cholinergic synapse?

Answer 24

• An action potential arrives at the synaptic knob of the presynaptic neurone. The action potential stimulates voltage gated calcium ion channels in the presynaptic neurone to open. Calcium ions diffuse into the synaptic knob.
• Influx of calcium ions causes the synaptic vesicles to move to the presynaptic membrane. Vesicles fuse with the membrane and release ACh into the synaptic cleft (exocytosis)
• ACh diffuses across the synaptic cleft and binds to the specific cholinergic receptors on the postsynaptic membrane. This causes sodium ion channels in the postsynaptic neurone to open which causes depolarisation and stimulates an action potential.

Question 25

When ACh has diffused across a cholinergic synapse, what stops more action potentials being generated?

Answer 25

ACh is removed from the synaptic cleft and broken down by the enzyme acetylcholinesterase and the products are reabsorbed by the presynaptic neurone and used to make more ACh

Question 26

What happens in an inhibitory synapse?

Answer 26

Inhibitory neurotransmitters hyperpolarise the postsynaptic membrane preventing the firing of an action potential

Question 27

What happens at an excitatory synapse?

Answer 27

Excitatory neurotransmitters depolarise the postsynaptic membrane making it fire action potentials if the threshold is reached.

Question 28

What are hormones?

Answer 28

Many hormones are proteins or peptides, some are steroids but they are all used as chemical messengers

Question 29

How are hormones secreted?

Answer 29

Hormones are secreted when an endocrine gland is stimulated. Endocrine glands can be stimulated by an electrical impulse but sometimes they are secreted by a change of concentration of a specific substance (sometimes another hormone)

Question 30

Generically how do hormones work?

Answer 30

They diffuse directly into the blood where they are taken around the blood in the circulatory system. They then diffuse out of the blood all over the body but each hormone will only bind to specific receptors for that hormone found on the membrane of target cells.W

Question 31

What is a target tissue?

Answer 31

A tissue that contains target cells

Question 32

Describe the structure of adrenal glands.

Answer 32

Found just above your kidneys. Have an outer part called the cortex and the inner bit is called the medulla. Prepare the body for flight or fight response.

Question 33

Function of the cortex in an adrenal gland.

Answer 33

Secretes steroid hormones e.g. cortisol when youre stressed. The effects of these hormones involve:
- stimulating the breakdown of proteins and fats into glucose. This increases the amount of energy available so the brain and muscles can respond to the situation
- Increasing blood volume and pressure by increasing the uptake of sodium ions and water by the kidneys
- Supressing the immune system

Question 34

Function of the medulla in the adrenal glands.

Answer 34

Secretes catecholamine hormones e.g. adrenaline and noradrenaline. These act to make more energy available in the short term by increasing heart rate and breathing rate causing cells to break down glycogen into glucose and constricting blood vessels to allow blood to reach the brain and muscles.

Question 35

What are the areas of the pancreas that contain endocrine tissue?

Answer 35

Islets of Langerhans

Question 36

What are the islets of langerhans made up of?

Answer 36

Alpha and beta cells - the alpha cells secrete glucagon and the beta cells secrete insulin to help control the blood glucose concentration

Question 37

How do the different tissues of the pancreas appear under a microscope?

Answer 37

Purple stained cells are beta cells
Pink stained cells are alpha cells
Islets of Langerhans appear as paler patches

Question 38

How is blood glucose concentration regulated?

Answer 38

Insulin - lowers blood glucose by binding to the receptors on cell membranes and making the cells more permeable to glucose so the cells take up more glucose. GLYCOGENESIS: Insulin also activates enzymes that convert glucose into glycogen. Liver and muscle cells then store glycogen in their cytoplasm as an energy source.
Glucagon - raises blood glucose concentration when it is too low. It binds to specific receptors on the cell membranes of the liver cells and activates enzymes that break down glycogen into glucose. This process is called GLYCOGENOLYSIS. Glucagon also promotes the formation of glucose from glycerol and amino acids. This process of forming glucose from non-carbohydrates is called GLUCONEOGENESIS. Glucagon and Insulin are examples of a negative feedback loop

Question 39

Explain how the pancreas is involved in a negative feedback loop to keep a normal blood glucose concentration.

Answer 39

• Pancreas detects high glucose concentration. Beta cells secrete insulin, alpha cells stop secreting glucagon. Insulin then acts to return blood glucose concentration to normal.
• Pancreas detects blood glucose is too low. Beta cells stop secreting insulin, alpha cells secrete glucagon. Glucagon acts to return blood glucose concentration to normal.

Question 40

What are the differences between type 1 and type 2 diabetes mellitus?

Answer 40

Type 1:
- Autoimmune disease
- The body attacks and destroys the beta cells in the islets of langerhans
- People dont produce insulin
- The kidneys cant reabsorb all this glucose so some of it is excreted in urine
Type 2:
- Occurs when beta cells dont produce enough insulin or the body cells dont respond to the insulin
- The cells dont respond properly because the insulin receptors on the membrane dont work so the cells dont take up enough glucose

Question 41

What are the treatments for type 1 diabetes mellitus?

Answer 41

Insulin therapy:
- regular insulin injections throughout the day
- Sometimes an insulin pump
- Some people have islet cell transplantation so their pancreas can produce some insulin

Question 42

What are the treatments for type 1 diabetes mellitus?

Answer 42

Initially managed through lifestyle changes e.g. eating a healthy balanced diet, getting regular exercise and losing weight if you need to
If this doesnt work then some medicine can be prescribed

Question 43

Explain the potential future treatments for diabetes mellitus?

Answer 43

Human insulin can be produced by genetically modified bacteria. This has many benefits including:
- cheaper than extracting from animal pancreas
- larger quantities can be produced
- human insulin is more effective than animal insulin and is less likely to trigger allergic responses
- For ethical reasons genetic modification is better than using animals.

Stem cells could be used as they can potentially be grown into beta cells which can then be implanted into the pancreas. This could cure type 1 diabetes mellitus.