Nervous Communication and Homeostasis

Question 1

The peripheral nervous system

Answer 1

made up of neurones that connect the CNS to the rest of the body has two different systems the somatic nervous system and the autonomic nervous system.

Question 2

The somatic nervous system

Answer 2

controls conscious activities e.g running and playing video games.

Question 3

The autonomic nervous system

Answer 3

controls unconscious activities e.g digestion.Its got two different divisions that have opposite effects on the body the sympathetic nervous system and parasympathetic nervous system.

Question 4

The sympathetic nervous system

Answer 4

gets body ready for action.Its the ‘fight or flight’ system

Question 5

The parasympathetic nervous system

Answer 5

calms the body down.The ‘rest and digest’ system.

Question 6

What is a tropism

Answer 6

a plants growth response to an external stimulus.

Question 7

Are shoots negatively or positively gravitropic?

Answer 7

negatively gravitropic they grow upwards

Question 8

Are roots negatively or positively gravitropic?

Answer 8

positively gravitropic they grow downwards

Question 9

How does IAA work in phototropism?

Answer 9

IAA moves to the more shaded parts of the shoots and roots, IAA concentration increases on the shaded side, cells elongate and the shoot bends towards the light.

In roots the IAA concentration increases on the shaded side, growth is inhibited so the shoot bends away from the light.

Question 10

What are auxins effects on shoots and roots?

Answer 10

Auxins stimulate growth of shoots by cell elongation.

High concentrations of auxins in roots inhibit growth.

Question 11

How does IAA work in gravitropism?

Answer 11

• IAA moves to the underside of shoots and roots.
• In shoots IAA concentration increases on the lower side making cells elongate and the shoot grow upward.
• IAA concentrations increase on the lower side meaning growth is inhibited so the root grows downwards.

Question 12

What is taxes?

Answer 12

The organisms move away or toward a directional stimulus e.g light.

Question 13

What is kineses?

Answer 13

The organisms movement is affected by a non-directional stimulus e.g humidity
For example in high humidity woodlice move slowly and turn less frequently so they stay where they are whereas in low humidity they move faster and turn more often.

Question 14

How do receptors trigger an action potential?

Answer 14

• 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, this alters the potential difference.
• The change in potential difference is called the generator potential.
• If the generator potential reaches the threshold level it will activate an action potential.

Question 15

The Pacinian Corpuscle

Answer 15

• Pacinian corpuscle contains the end of a sensory neurone it is wrapped in lots of layers of connective tissue called lamellae.
• Pressure causes the the lamellae to become deformed and press on the sensory nerve ending.
• This causes the sensory nerve ending to membrane to stretch, deforming the stretch mediated sodium ion channels, causing them to open.
• Sodium ions diffuse into the cells generating a generator potential.

Question 16

Where are the photoreceptor cells located?

Answer 16

The photoreceptor cells are found on the retina.

Question 17

What is the fovea?

Answer 17

An area of the retina that contains lots of photoreceptors

Question 18

Why is there a blind spot?

Answer 18

It is where the optic nerve leaves the eye there aren’t any photoreceptor cells here so not it is not sensitive to light.

Question 19

How do photoreceptors convert light into an electrical impulse?

Answer 19

• Light enters the eyeshots the photoreceptors and is absorbed by light sensitive optical pigment.
• The light bleaches the pigments, causing a chemical change and altering the membrane permeability to sodium ions.
• A generator potential is created and if it reaches the threshold, a nerve impulse is sent along a bipolar neurone.
• Bipolar neurones connect the photoreceptors to the optic nerve which takes the imputes to the brain.
• Two types of photoreceptors rods and cones, which contain different pigments.

Question 20

Rod Cells:

Answer 20

• Only give information in black and white.
• mainly found in the peripheral parts of the retina.
• Very sensitive to light.This is because many rods join one neurone, so many weak generator potentials can combine and reach the threshold to trigger an action potential.
• Rods give low visual acuity because many rods join the same neurone which means light from two points close together can’t be told apart.

Question 21

Cone Cells:

Answer 21

• Give information in colour
• Found packed together in the fovea.
• There a three different types of cone cell, each containing a different optical pigment, red-sensitive, green-sensitive and blue sensitive when they’re stimulated in different proportions you see different colours.
• Less sensitive to light as only one cone joins one neurone so it takes more light to reach the threshold.
• High visual acuity because cones are close together and one cone joins one neurone.When light from two points hits two cones it triggers two different action potentials so the points can be distinguished as separate.

Question 22

Neurones at rest:

Answer 22

• In a neurones resting state the outside of the membrane is positively charges compared to the inside.
• This means the membrane is charged.THe voltage across the membrane at rest is called the resting potential and its about -70mV
• The resting potential is created and maintained by sodium potassium pumps and potassium ion channels.
• The sodium potassium pump moves sodium ions out of the neurone but the membrane isn’t permeable to sodium ions so they can’t diffuse back in, this creates an electrochemical gradient because there are more positive sodium ions outside the cell than inside.
• The sodium potassium pump also moves potassium ions in the neurone but the membrane is permeable to potassium ions so the diffuse back out.
• This makes the outside of the cell positively charged compared to the inside.

Question 23

Describe the action potential:

Answer 23

1) Stimulus- this excites the neurone cell membrane, causing sodium ion channels to open.The membrane becomes more permeable to sodium, so sodium ions diffuse into the neurone down the electrochemical gradient.This makes the inside of the neurone less negative.
2) Depolarisation- if the potential difference reaches the threshold, more sodium ion channels open.More sodium ions diffuse rapidly into the neurone.
3) Repolarisation- at a potential difference of around +30mV the sodium ion channels close and potassium ion channels open.The membrane is more permeable to potassium so potassium ions diffuse out of the neurone down the potassium ion concentration gradient.This starts to get the membrane back to its resting potential.
4) Hyperpolaroisation - potassium ion channels are slow to close so there’s a slight overshoot where too many potassium ions diffuse out of the neurone.The potential difference becomes more negative than the resting potential.
5) Resting potential- the ion channels are reset.The sodium-potassium pump returns the membrane to its resting potential and maintains it until the membrane is excited by another stimulus.

Question 24

Explain the wave of depolarisation

Answer 24

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

Question 25

The refractory period

Answer 25

• During the refractory period the ion channels are recovering and can’t be opened.
• So the refractory period acts as a time delay between one action potential and the next this means action potentials don’t overlap, theres a limit to the frequency at which nerve impulses can be transmitted and action potentials can only travel in one direction.

Question 26

Explain how action potentials have an all or nothing nature:

Answer 26

• Once a threshold is reached an action potential will always fire with the same charge in voltage no matter how big the stimulus is.
• If the threshold isn’t reached an action potential won’t fire.
• A bigger stimulus won’t cause a bigger action potential but will cause them to fire more frequently.

Question 27

Myelination

Answer 27

• Some neurones have a myelin sheath
• It is an electrical insulator
• In the peripheral nervous system the sheath is made up of Schwann cells
• Between the Schwann cells there are tiny patches of bare membrane called nodes of Ranvier. Sodium ion channels are concentrated at the nodes.
• In a myelinated neurone, depolarisation only happens at the nodes of Ranvier.
• The neurones cytoplasm conducts enough charge to depolarise the next node so the impulse jumps from node to node.
• This is called saltatory conduction and its really fast.
• In a non myelinated neurone the impulse travels the whole length of the axon membrane so its slower than saltatory conduction.

Question 28

Axon Diameter

Answer 28

Action potentials are conducted quicker along axons with bigger diameters because there’s less resistance to the flow of ions than in an axon with a smaller diameter.With less resistance, depolarisation reaches other parts of the neurone cell membrane much quicker.

Question 29

Temperature in neurones

Answer 29

The speed of conduction increases as the temperature increases too, because ions diffuse faster.The speed only increases to 40 degrees as proteins begin to denature and speed decreases.

Question 30

Explain how synapses work:

Answer 30

1) An action potential arrives at the synaptic knob of the presynaptic knob.
2) The action potential stimulates voltage gated calcium ion channels in the presynaptic neurone to open.
3) Calcium ions diffuse into the synaptic knob
4) This influx of calcium ions causes synaptic vesicles to move towards the presynaptic membrane.They then fuse with the presynaptic membrane.
5) The vesicles release a neurotransmitter acetylcholine into the synaptic cleft.
6) ACh diffuses across the synaptic cleft and binds to specific cholinergic receptors on the postsynaptic membrane.
7) This causes sodium ion channels to open in the postsynaptic neurone
8) The influx of sodium ions causes depolarisation.An action potential is generated if the threshold is reached.
9) ACh is removed from the synaptic cleft so the response doesn’t keep happening.Its broken by an enzyme called acetylcholinesterase and the products are reabsorbed by the presynaptic neurone to make more acetylcholine.

Question 31

Excitatory neurotransmitter

Answer 31

depolarise the postsynaptic membrane making it fire an action potential, if the threshold is reached.

Question 32

Inhibitory neurotransmitters

Answer 32

hyper polarise the postsynaptic membrane, preventing it from firing an action potential.

Question 33

Summation

Answer 33

the effect of neurotransmitter released from many neurones is added together.

Question 34

Spatial summation

Answer 34

• Sometimes many neurones connect to one neurone .
• The small amount of neurotransmitter released from each of these neurones can be enough altogether to reach the threshold in the postsynaptic neurone and trigger an action potential.
• If some neurones release an inhibitory neurotransmitter then the total effect of all the neurotransmitters may be no action potential.

Question 35

Temporal Summation

Answer 35

-where two or more nerve impulse arrive in quick succession from the same presynaptic neurone.This makes an action potential more likely because more neurotransmitter is released into the synaptic cleft.

Question 36

Give 5 ways in which drugs affect the action of neurotransmitters at synapses:

Answer 36

1) some drugs are the same shape as neurotransmitters so mimic their action at receptors, meaning more receptors are activated.
2) some drugs block receptors so they can’t be activated, this means fewer receptors are activated can cause paralysis in the muscle.
3) some drugs inhibit the enzyme that breaks down neurotransmitters.This means there are more neurotransmitters in the synapse and for longer.This can lead to loss of muscle control.
4) some drugs stimulate the release of neurotransmitters so more receptors are activated.
5) some drugs inhibit the release the of neurotransmitters from the presynaptic neurone so fewer receptors are activated.

Question 37

What are the two components of muscle antagonistic pairs?

Answer 37

• the contracting muscle- the agonist

- the relaxing muscle- the antagonist

Question 38

Describe the structure of muscles:

Answer 38

• skeletal muscles are made up of large bundles of long muscle fibres
• the cell membrane of the muscle fibre cells is called the sarcolemma
• bits of the sarcolemma fold inwards across the muscle fibre and stick into the sarcoplasm.These folds are called traverse tubules and they help to spread electrical impulses throughout the sarcoplasm and reach all parts of the muscle fibre.
• a network of internal membranes called the sarcoplasmic reticulum runs through the sarcoplasm.The sarcoplasm reticulum stores and releases calcium ions.
• muscle fibres have lots of ATP to provide the energy needed for muscle contraction.
• muscle fibres containment nuclei
• muscle fibres have long cylindrical organelles called myofibrils made up of proteins and are specialised for contraction.

Question 39

Describe myosin and actin filaments:

Answer 39

1) myofibrils contain bundles of thick and thin myofilaments that move past each other.
- thick myosin filaments
- thin actin filaments
2) -dark bands contain thick myosin filaments and some overlapping overlapping thin filaments theses are called A bands
- light bands contain actin filaments only these are called I bands
3) a myofibril is made up of many short units called sarcomeres
4) The ends of each sarcomere are marked with a z line
5) in the middle of each sarcomere there is an M line.The M line is the middle of the myosin filaments.
6) Around the M line is the H zone which only contains myosin filaments.

Question 40

Describe the sliding filament theory:

Answer 40

• myosin and actin filaments slide over each other to make the sarcomeres contract.
• the simultaneous contraction of lots of sarcomeres means the myofibrils and muscle fibres contract
• contracted sarcomeres get shorter, the I band gets shorter, the H zone gets shorter and the A band stays the same length.

Question 41

Explain hoe muscles contract:

Answer 41

1) When an action potential from a motor neurone stimulates a muscle cell, it depolarises the sarcolemma. Depolarisation spreads down the T-tubules to the sarcoplasmic reticulum.
2) This causes the sarcoplasmic reticulum to release stored calcium ions into the sarcoplasm.
3) Calcium ions bind to a protein attached to tropomyosin, causing the protein to change shape.This pulls the tropomyosin out of the actin-myosin binding site on the actin filament.
4) This exposes the binding site, which allows the myosin head to bind.
5) The bond formed when a myosin head binds to to an actin filament is called an actin-myosin cross-bridge.
6) Calcium ions also activate the enzyme ATP hydrolase which hydrolyses ATP to provide energy for muscle contraction.
7) The energy released from ATP causes the myosin head to bend, which pulls the actin filament along in a rowing action.
8) Another ATP molecule provides the energy to break the actin-myosin cross-bridge so the myosin head detaches from the actin filament after its moved.
9) The myosin head then binds to a binding site further along the actin filament and the cycle continues.
10) Many cross bridges form and break rapidly, pulling the actin filament along which shortens the sarcomere.
11) The cycle will continue as long as calcium ions are present.

Question 42

What happens excitation in the muscle stops?

Answer 42

1) When the muscle stops being stimulated calcium ions leave their binding sites and move by active transport back into the sarcoplasmic reticulum.
2) This causes tropomyosin molecules to move back, so they block the actin-myosin sites again.
3) Muscles aren’t contracted because no myosin heads are attached to actin filaments.
4) The actin filaments slide back to their relaxed position, which lengthens the sarcomere.

Question 43

Properties of slow twitch muscle fibres:

Answer 43

• contract slowly
• muscles you use for posture
• good for endurance activities
• can work for a long time without getting tired
• energy’s released slowly through aerobic respiration.Lots of mitochondria and blood vessels supply the muscles with oxygen.
• Reddish in colour because they’re rich in myoglobin

Question 44

Properties of fast twitch muscle fibres:

Answer 44

• muscle fibres that contract very quickly
• muscles you use for fast movement
• good for short bursts of speed and power
• get tired very quickly
• energy’s released very quickly through anaerobic respiration
• whitish in colour because they don’t have much myoglobin.

Question 45

what is homeostasis?

Answer 45

the maintenance of a stable internal environment.

Question 46

where are islets of langerhans found, what are the two types and what do they do?

Answer 46

• Found in the pancreas
• Beta cells- secrete insulin into the blood
• Alpha cells- secrete glucagon into the blood

Question 47

What does insulin do?

Answer 47

• insulin lowers blood glucose concentration when its too high.
• insulin binds specific receptor cells on the cell membrane of liver and muscle cells.It triggers channel protein GLUT4 t move to the membrane.
• it increases the permeability of muscle cells to glucose so the cells take up more glucose
• insulin activates enzymes in liver and muscle cells that convert glucose into glycogen (glycogenesis)
• the cells are able to store glycogen in their cytoplasm as an energy store.
• insulin also increases the rate of respiration of glucose.

Question 48

What does glucagon do?

Answer 48

• glucagon raises blood glucose conc when its too low
• binds to specific receptors on liver cells
• activates enzymes the liver that break down glycogen into glucose (glycogenolysis)
• activates enzymes involved in the formation of glucose from glycerol and amino acids
• decreases the rate of respiration of glucose

Question 49

What does adrenaline do?

Answer 49

• increases blood glucose concentration
• it is a hormone secreted from the adrenal gland when there’s a low concentration of glucose in the blood, when you’re stressed and when you’re exercising
• adrenaline binds to liver cells and triggers the breakdown of glycogen to glucose and inhibits the syntheses of glycogen from glucose.
• it also activates glucose secretion.

Question 50

Describe how adrenaline and glucagon act through a second messenger?

Answer 50

• they bind to receptors that activate an enzyme called adenylate cyclase
• this enzyme when activated converts ATP into a chemical signal called cAMP
• cAMP activates an enzyme called protein kinase A which activates a cascade that breaks sown glycogen into glucose.

Question 51

Explain type 1 diabetes:

Answer 51

• the immune system attacks the beta cells in the islets of langehans so they can’t produce any insulin.
• After eating, the blood glucose level rises and stays high, this is called hyperglycaemia and can result in death if left untreated.
• The kidneys can’t reabsorb all this glucose, so some of its excreted in the urine.
• treated with insulin therapy, need regular insulin injections, the insulin has to be very carefully controlled so there isn’t a dangerous drop in glucose concentration.
• eating regularly and controlling carbohydrate intake avoids a sudden rise in glucose.

Question 52

Explain type 2 diabetes:

Answer 52

• Type 2 diabetes is usually acquired in later life, the beta cells don’t produce enough insulin or when the bodys cells don’t respond to insulin properly.
• cells don’t respond properly to insulin because the receptors on their membranes don’t work properly so the cells don’t take up enough glucose.
• can be treated by diets, exercise, losing weight, glucose lowering medication and even insulin shots can be used.

Question 53

Describe how cardiac muscle controls the regular beating of the heart:

Answer 53

1) the process starts in the SAN, which is in the wall of the right atrium
2) The SAN is like a pacemaker, it sends out regular waves of electrical activity to the atrial walls.
3) this causes the right and left atrium to contract at the same time
4) A band of non-conducting collagen tissue prevents the waves of electricity being passed directly from the atria to the ventricles
5) instead, these waves of electrical activity are transferred from the SAN to the AVN
6) the AVN is responsible for passing the waves of electrical activity on to the bundle of His.But, there’s a slight delay before the AVN reacts, to make sure the atria have emptied before the ventricles contract.
7) The bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity between the ventricles to the apex of the heart.The bundle splits into finer muscle fibres in the right and left ventricle walls called the purine tissue
8) the purine tissue carries the waves of electrical activity into the muscular walls of the right and left ventricles causing them to contract simultaneously from the bottom to the top.

Question 54

What effect does acetylcholine have on heart rate?

Answer 54

slows heart rate

Question 55

What effect does noradrenaline have on heart rate?

Answer 55

increases heart rate