Communication and homeostasis Module 5

Question 1

What’s a stimulus?

Answer 1

Any change in the internal or external environment

Question 2

What do receptors do?

Answer 2

Detect specific stimuli

Question 3

What are effectors?

Answer 3

Cells that bring about a response to a stimulus, to produce an effect

Question 4

Example of cell signalling between adjacent cells?

Answer 4

Cells in the nervous system communicate secreting chemicals called nuerotransmiters, which send signals to adjacent cells such as nerve cells or muscle cells

Question 5

Example of cell signalling between long distant cells?

Answer 5

Hormonal system, releases chemicals called hormones which travel in the blood and act on distant cells

Question 6

What is homeostasis and why is it important?

Answer 6

Homeostasis, is the maintenance of a constant internal environment

Provides right condition for cells to function

Question 7

Describe a homeostatic systems response to a change via negative feedback?

Answer 7

Receptors detect when a level is too high or too low, and the information is communicated to effectors via the nervous system or hormonal system

The effectors respond to counteract the change - bringing the level back to normal

= negative feedback mechanism

Question 8

Can negative feedback mechanisms cope with huge changes?

Answer 8

NO

Question 9

What do sensory neurons do?

Answer 9

Transmit nerve impulses from receptors to the central nervous system (brain and spinal cord)

Question 10

What do relay neurons do?

Answer 10

Transmit nerve impulses between sensory neurons and motor neurons

Question 11

What do motor neurons do?

Answer 11

Transmit nerve impulses from the CNS to the effectors

Question 12

Describe the general story from stimulus to response?

Answer 12

Stimulus

Receptors

Sensory neuron takes information to CNS where it’s processed and decides what response is required

Motor neurons to effectors

Response

Question 13

What does the nervous system send information as?

Answer 13

Nerve impulses

Question 14

Why are sensory receptors known as tranducers?

Answer 14

They convert Stimulus energy (eg.light, chemical) into the form of nerve impulses

Question 15

Describe how sensory receptors convert stimulus energy into nerve impulses?

Answer 15

When a Nervous system receptor is in it’s resting state, there’s a difference in charge between the inside and the outside of the cell - so there’s a voltage across the membrane which is known as potential difference

This potential difference is generated by ion pumps and ion channels

The potential difference when a cell is at rest is called the resting potential

When a stimulus is detected, the cell membrane is excited and becomes more permeable, allowing more ions to move in and out of the cell - altering the potential difference

The change in potential difference due to a stimulus is called the generator potential

A bigger stimulus excites the membrane more, causing a bigger movement of ions and a bigger change in potential difference = larger generator potential

If the generator potential is large enough (reaches the threshold level) it will trigger an action potential (nerve impulse) along a neurone

Question 16

Describe the mechanoreceptor pacinian corpuscles?

Answer 16

They detect mechanical stumuli, eg pressure and vibrations

They are found in your skin, and contain the end of a sensory neuron called a sensory nerve ending, which is wrapped in lots of layers of connective tissue called lamellae

When a Pacinan corpuscle is stimulated, the lamellae are stimulated, the lamellae are deformed, and press on the sensory nerve ending

Causing deformation of the stretch mediated sodium channels in the sensory neurons cell membrane

So the Sodium ion channels open and the sodium ions diffuse into the cell, creating a generator potential which if passes the threshold will cause an action potential

Question 17

What do dendrons / dendrites do?

Answer 17

Carry nerve impulses towards the cell body

Question 18

What do axons do?

Answer 18

Carry nerve impulses away from the cell body

Question 19

Structure of a sensory neuron in direction of the impulse?

Answer 19

Connects to receptor cells via dendrites, which then goes on to one long dendron which connects to the cell body

Then one short axon carries impulses from the cell body to the CNS

Question 20

Describe the structure of a relay neuron in direction of the impulse?

Answer 20

Have many short dendrites that carry nerve impulses from the sensory neurons to the cell body

And many short axons that carry nerve impulses from the cell body to motor neurons

Question 21

Describe the structure of a motor neuron in the direction of the impulse?

Answer 21

Have many short dendrites that carry nerve impulses from the CNS, to the cell body

And one long axon, which carries the nerve impulses from the cell body to effector cells

Question 22

Describe how neuron cell membranes are polarised at rest?

Answer 22

The outside of the membrane is more positively charged compared to the inside, as there more positive ions outside than in = polarised as difference in charge

Resting potential = -70mV

The resting potential is created and maintained by Sodium Potassium pumps (SOPI, 2 Sodium out, 3 Potassium in)

Sodium can’t diffuse back in, as there are no ion channels for it, but there are potassium ion channels so the K+ ions diffuse back out

Making it more positive on the outside than the inside

Question 23

Describe the process of a neuron cell membrane becoming depolarised when stimulated and an action potential being generated?

Answer 23

The stimulus excites the neuron cell membrane, causing Na+ ion channels to open, to membrane has become more permeable to Na+ ions, so they diffuse into the neuron down a electrochemical gradient. making the inside of the neuron less negative

If the potential difference reaches the threshold (around -55mV), voltage gated Na+ channels open. More Na+ ions diffuse into the neurone.

This is positive feedback

At a potential difference of around -+30mV, the Na+ ion channels close and voltage gated K+ ion channels open. The membrane is now more permeable to K+, so they diffuse out down a concentration gradient.

This is repolarisation- and is a negative feedback process

Hyperpolarsiation - K+ ion channels are slow to close, so there is a slight overshoot, where too many K+ ions diffuse out of the nueron, the potential becomes more negative than the resting potential (less than 70mV)

Resting potential - the ion channels are reset, the SOPI pumps returns the membrane to it’s resting potential

Question 24

What’s a positive feedback mechanism do?

Answer 24

Amplify a change from the normal level

Question 25

Example of positive feedback in the blood?

Answer 25

When you have a wound, platelets are activated which releases a chemical that activates more platelets, which forms a blood clot at the site

Question 26

Describe how the action potential moves along the neuron as a wave of depolarisation?

Answer 26

When an action potential happens, some of the sodium ions that enter the neuron diffuse sideways This causes sodium ion channels in the next region of the neuron to open and Na+ ions to diffuse into that part This causes a wave of depolarisation to travel along the nuerone The wave moves away from the parts of the membrane in the refractory period, because these parts can't fire an action potential

Question 27

What is the refractory period?

Answer 27

After an action potential the neurone cell membrane can't be excited again straight away, as channels are recovering

Question 28

What does a bigger stimulus cause?

Answer 28

More frequent impulses to the brain, (not a larger voltage)

Question 29

In the peripheral system, what are myelinated nuerones?

Answer 29

Nuerones with a myelin sheath made up of schwann cells which is an electrical insulator Between the Schwann cells are tiny patches of bare membrane called the nodes of ranvier, Na+ ion channels are concentrated here

Question 30

Why do action potentials go faster in myelinated neurones?

Answer 30

Depolarisation only occurs at the nodes of ranvier (where sodium ions can get through the membrane), The neurons cytoplasm conducts enough electrical charge to depolarise the next node, so the impulse jumps from node to node This is called salatory conduction and it's really fast

Question 31

How does an impulse travel along a non-myelinated nueron?

Answer 31

The impulse travels along the whole length of the axon membrane

Question 32

What's a synapse?

Answer 32

The junction between a neuron and another nueron, or between a neuron and an effector cell

Question 33

What's the tiny gap between the cells at a synapse called?

Answer 33

Synaptic cleft

Question 34

What does the presynaptic neuron have a swelling called and what does it contain?

Answer 34

Has a swelling called a synaptic knob, which contains synaptic vesicles filled with chemicals called neurotransmitters

Question 35

What happens when an action potential reaches the end of a nuerone?

Answer 35

Causes neurotransmitters to be released into the synaptic cleft, they then diffuse across the postsynaptic membrane and bind to specific receptors

Question 36

What's the pre synaptic and post synaptic membrane?

Answer 36

``` Pre = before the synapse Post = after the synapse ```

Question 37

What happens when the neurotransmitters bind to receptors on the post synaptic membrane?

Answer 37

They might trigger an action potential (in a neuron) Cause muscle contraction (in a muscle cell) Cause a hormone to be secreted from a gland cell

Question 38

Describe exactly in 3 main steps how neurotransmitters transmit nerve impulses between neurones?

Answer 38

An action potential arrives at the synaptic knob of the presynaptic neurone The action potential stimulates voltage gated Ca2+ in the presynaptic neuron to open Ca2+ diffuses into the synaptic knob The influx of calcium ions into the synaptic knob, causes the synaptic vesicles to move to the presynaptic membrane, they then fuse with the presynaptic membrane The vesicles release the neurotransmitter into the synaptic cleft via exocytosis The nuerotransmitter diffuses across the synaptic cleft and binds to specific receptors on the post synaptic membrane Causing Na+ ion channels in the postsynaptic neuron to open The influx of Na+ in the postsynaptic membrane causes depolarisation. An action potential on the postsynaptic membrane is generated if the threshold is achieved Neurotransmitter is removed from synaptic cleft so the response doesn't keep happening

Question 39

What's synaptic divergence?

Answer 39

When one nuerone connects to many neurones information can be dispersed to different parts of the body

Question 40

What's synaptic convergence?

Answer 40

When many nuerones connect to one nuerone, information can be amplified So stimuli may arrive from different sources

Question 41

What's spatial summation, and how does it finely tune the nervous response?

Answer 41

When neurones converge, the small amount of neurotransmitter released from each nuerone can be enough altogether to reach the threshold potential in the postsynaptic neurone and trigger an action potential

Question 42

What's temporal summation, and how does it finely tune the nervous response?

Answer 42

Where 2 or more nerve impulses arrive in quick sucession from the same presynaptic neurone. which makes the action potential more likely, as more neurotransmitter has been released

Question 43

What do synapses make sure on the direction of transmitions?

Answer 43

That they only go one way

Question 44

What is the hormonal system made up of?

Answer 44

Endocrine glands and hormones

Question 45

What are endocrine glands?

Answer 45

Groups of cells that are specialised to secrete hormones

Question 46

Whar are hormones?

Answer 46

Chemical messengers | They are either proteins or steriods

Question 47

How can endocrine cells be stimulated to secrete hormones?

Answer 47

Change of concentration of a specific substance | Or electrical impulses

Question 48

How do hormones travel around the body?

Answer 48

They diffuse into the blood

Question 49

Describe a very basic story of hormones acting on the liver target cells?

Answer 49

Stimulus- low blood glucose concentration Receptors on pancreas cells detect the low blood glucose concentration The pancreas releases the hormone glucagon into the blood Effector step - Target cells in the liver which have specific receptors to the hormone, detect the glucagon, and convert glycogen into glucose Response - Glucose is released into the blood, so glucose concentration increases

Question 50

Describe the process of adrenaline acting as the first messenger on cells?

Answer 50

Adrenaline binds to specific receptors on the cell membrane When adrenaline binds it activates an enzyme in the membrane called adenylyl cyclase Activated adenylyl cyclase, catalsyes the production of a second messenger called cyclic AMP (cAMP) from ATP cAMP activates a cascade of enzyme controlled reactions, which makes more glucose available to the cell, by catalysing the breakdown of glycogen into glucose

Question 51

Describe where adrenal glands are found, and their structure?

Answer 51

They are endocrine glands, found just above the kidneys Each adrenal gland has an outer part called the cortex and an inner part called the medulla

Question 52

Function of the cortex in the adrenal glands?

Answer 52

Secretes steroid hormones such as cortisol and aldosterone when you are stressed Effects of these are: Stimulating the breakdown of proteins and fats into glucose, increasing 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 53

Describe the function of the medulla in the adrenal glands?

Answer 53

Secretes catechloamine (modified amino acid) hormones such as adrenaline and noradrenaline when you stressed Effects are: Increase in heart and breathing rate Cuasing cells to break down glycogen into glucose Constricting some blood vessels, so that blood is diverted to the brain and muscles

Question 54

Where is the pancreas found?

Answer 54

Bellow the stomach

Question 55

Describe what islets of langerhan are and their function?

Answer 55

They are areas of the pancreas that contain endocrine tissue, and are found in clusters around blood capillaries, so they can secrete hormones directly into the blood They are made up of Alpha cells that secrete a hormone called glucagon And beta cells which secrete a hormone called insulin Which both help to control blood glucose concentration

Question 56

Describe what an ectotherm is an their 4 features?

Answer 56

Reptiles and fish Can't control their body temperature internally - so they control their body temperature by changing their behaviour So their internal temperature is dependent on their external temperature Activity levels depend on the external temperature more active in higher temps and less active in lower temps They have a variable metabolic rate, and they generate very little heat themselves

Question 57

Describe what an endotherm is and 4 features of them?

Answer 57

Mammals, birds Control body temperature internally via homeostasis, and also by behaviour Their internal temperature is less affected by the external temperatures Their activity level is not dependent on the external temperature They have a constantly high metabolic rate and they generate a lot of heat from metabolic reactions

Question 58

3 mechanisms to reduce body temperature?

Answer 58

Sweating Hairs lie flat Vasodilation

Question 59

Describe how Sweating reduces body temperature?

Answer 59

More sweat is secreted from sweat glands when the body is too hot, the water evaporates and takes heat away from the body

Question 60

Describe how hairs lying flat reduces body temperature?

Answer 60

When it's hot erector pill muscles releax, so the hairs lie flat, less air is trapped, so less insulation and heat can be more easily lost

Question 61

Describe how vasodilation reduces body temperature?

Answer 61

Arterioles near the surface of the skin dilate, more blood flows through the capillaries in the surface layers of the dermis, so more heat is lost from the skin by radiation, and the temperature is lowered

Question 62

4 mechanisms which increase body temperature?

Answer 62

Shivering Hairs stand up Vasoconstriction Hormones

Question 63

Describe how shivering increases body temperature?

Answer 63

Muscles contract in spasms, making the body heat up from increased respiration

Question 64

Describe how hairs standing up increases body temperature?

Answer 64

Erector pili muscles contract when it's cold, making the hairs stand up, the traps more air for insulation

Question 65

Describe how vasoconstriction increases body temperature?

Answer 65

When it's cold aterioles near the surface of the skin constrict, so less blood flows through the capillaries, in the surface layers of the dermis. Reducing heat loss

Question 66

Describe how hormones increase body temperature?

Answer 66

Adrenaline and thyroxine increase metabolism so more heat is produced

Question 67

Describe how the hypothalamus controls body temperature in mammals?

Answer 67

The hypothalamus (part of the brain) receives information about the temperature from thermoreceptors ( the ones in the hypothalamus detect internal temperature, and the ones in the skin (peripheral thermoreceptors detect external temperature Thermoreceptors send impulses along sensory neurons to the hypothalamus, which sends impulses along motor neurons to effectors to restore the temperature back to normal (eg . vasodialtion or vasoconstriction)

Question 68

Describe how beta cells from the ilsets of langerhan in the pancrease releasing the hormone insulin, lowers the blood glucose concentration?

Answer 68

Insulin binds to specific receptors on the cell membranes of liver cells and muscle cells It increases the permeability of cell membranes to glucose so the cells take up more glucose Insulin also activates enzymes that convert glucose to glycogen Cells are able to store glycogen in their cytoplasm as an energy source The process of forming glycogen from glucose is called glycogenesis It also increases the rate of respiration of glucose, especially in muscle cells

Question 69

Describe how alpha cells from the islets of langerhans in the pancreas releasing glucagon raises the blood glucose concentration?

Answer 69

Glucagon binds to specific receptors on the cell membranes of liver cells Glucagon activates enzymes that break down glycogen into glucose The process of breaking down glycogen is called glycogenolysis Glucagon also promotes the formation of glucose from fatty acids and amino acids, which is called gluconeogenesis Glucagon also decreases the rate of respiration of glucose in cells

Question 70

What type of process is maintaining blood sugar levels?

Answer 70

Negative feedback

Question 71

Describe how Beta cells secrete insulin when they are depolarised?

Answer 71

When blood glucose concentration is high more glucose enters the beta cells via facilitated diffusion More glucose in a Beta cell causes the rate of respiration to increase, making more ATP The rise in ATP triggers the K+ ion channels in the Beta cell plasma membrane to close This means K+ ions can't can't get through the membrane, so they build up inside the cell This makes the inside of the cell less negative, as there more K+ ions within the cell- so the plasma membrane is depolarised Depolarisation triggers calcium ion channels in the membrane to open, so calcium ions diffuse into the beta cell This causes vesicles containing insulin to fuse with the beta cell plasma membrane, releasing insulin via exocytosis

Question 72

What is type 1 diabetes?

Answer 72

An auto immune disease, in which the body attacks and destroys the beta cells in the islets of langerhans, so the person can't produce any insulin, so blood concentration stays high which can be deadly

Question 73

How do you treat type 1 diabetes?

Answer 73

Regular insulin injections, or a constant insulin pump Can have islet cell transplation

Question 74

What's type 2 diabetes?

Answer 74

When the Beta cells don't produce enough insulin, or when the body's cells don't respond properly to insulin, so the blood glucose concentration is higher than normal Acquired later in life than type 1 and is heavily linked to obesity

Question 75

How is type 2 diabetes treated?

Answer 75

Lifestyle changes Medicine which reduces amount of glucose released by liver, and makes other cells more sensitive to insulin

Question 76

Advantages of having insulin produced by gentically modified bacteria, compared to being extracted from animals?

Answer 76

Cheaper Larger quantities can be produced They make human insulin which is more effective than using pig or cattle insulin- which is more likely to be rejected by immune system or cause an allergic response Ethical and religious reasons

Question 77

How could stem cells be used to cure diabetes?

Answer 77

Could be grown into Beta cells Implanted into pancreas of someone with type 1 diabetes So they can now make insulin as normal