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Biology A level > Communication and Homeostasis > Flashcards

Communication and Homeostasis Flashcards

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1
Q

Name the neurone structures

A

Cell body, Dendrons, Axon, Schwann cells, Myelin sheath, Nodes of Rnaveir

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2
Q

What are dendrons

A

Carry nerve impulses towards the cell body

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3
Q

What is an axons

A

Single long fibre that carries nerve impulses away from the cell body

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4
Q

What are Schwann cells

A

Cells that surround axon by wrapping around many times, protecting it and providing electrical insulation

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5
Q

What is a myelin sheath

A

Forms covering of axon and made of membranes of Schwann cells, rich in myelin

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6
Q

What are nodes of ranveir

A

Gaps between adjacent Schwann cells where there is no myelin sheath
Gaps are 2-3um and occur every 1-3mm

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7
Q

What is a Pacinian corpuscle

A

Rings of connective tissue wrapped around the end of a sensory neurone
Pressure against the skin deforms the connective tissue and pushes it against the nerve ending

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8
Q

What is a reflex action

A

An automatic, involuntary and rapid response to a stimulus

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9
Q

What is the purpose of a nerve cell body

A

They are involved in the production of neurotransmitters and proteins

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10
Q

What are the roles of the synapses in the nervous system

A

Ensure impulses are unidirectional
Allow an impulse from 1 neurone to reach multiple other neurones - creating a number of simultaneous responses
Allows impulses from different neurones to feed into the same synapse - resulting in one response

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10
Q

Why does Ach need to be recycled

A

To avoid Na+ continuously diffusing into the postsynaptic membrane and causing multiple action potentials to fire off

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10
Q

What is a cholinergic synapse

A

A synapse that uses the neurotransmitter acetylcholine (Ach)

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11
Q

What is the resting potential

A

-70mV

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12
Q

What is the threshold potential

A

-50 mV

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13
Q

What is the action potential peak

A

+40 mV

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14
Q

What are endocrine glands

A

Groups of cells specialised to secrete hormones directly into the bloodstream

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15
Q

What hormone do alpha cells secrete

A

Glucagon

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16
Q

What hormone do Beta cells secrete

A

insulin

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17
Q

What are the features of a good communication systen

A

Spans whole body
Cell communication
Specific
Rapid
Short and long term

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18
Q

What is the neuronal signalling system

A

A network of interconnecting neurones that produce rapid responses to changing stimuli

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19
Q

What is a hormonal signalling system

A

Uses the blood to transport hormones from endocrine glands to target organs. Can be used to produce longer term responses

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20
Q

What is homeostasis

A

The act of maintaining a constant internal environment despite external changes

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21
Q

What are endo and ectotherms

A

Endotherms - warm blooded
Ectotherms - cold blooded

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22
Q

What are the advantages and disadvantages of ectotherms

A

+ Uses less food in respiration
+ Greater proportion of energy used for growth

  • less active in cooler temps
  • may not be capable of activity in winter months
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23
Q

What are the advantages of Endotherms

A

+ Constant, optimal body temp
+ Activity possible even when cool
+ Can inhabit colder parts of the planet

  • Energy used up to maintain constant temp
  • More food required
  • Less energy used in growth
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24
Q

How do endotherms monitor the temperature of their blood

A

Peripheral temperature receptors in the skin monitor the temperature in the extremities and feed information to the thermoregulatory centre in hypothalamus
Acts as an early warning system

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25
Q

What is vasodilation and vasoconstriction

A

Stimulated by nervous signals from hypothalamus; smooth muscle in the arterioles and pre-capillary sphincter muscles at skin surface relax or contract to dilate or constrict
Inc vessel diameter = inc blood flow to skin = inc amount of heat lost by radiation to air

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26
Q

How does sweating work

A

Stimulated directly by motor neurones from hypothalamus
Water in sweat evaporated from skin surface. The high latent heat of vaporisation causes heat energy to be lost

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27
Q

How do hair and fathers regulate temp

A

Too cold: erector muscles contract to raise hair/feathers trapping air to use as an insulator
Too hot: erector muscles relax, feathers/hair lie flat. insulation reduced so more heat loss by radiation

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28
Q

What does the hypothalamus stimulate when temp is too low

A

Stimulates thyroid and adrenal glands to releases thyroxine and adrenaline to increase metabolic activity - leading to more exogenic reactions and more heat being releases
Involuntary muscle spasm (shivering) causes more respiration - more heat release

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29
Q

What are sensory receptors

A

A specialised cell or sensory neurone ending that can detect changes in the environment and may generate a nerve impulse as a result of a stimulus
They are tranducers

30
Q

What are tranducers

A

Convert energy in one form to electrical energy in the form of a nerve impulse

31
Q

How does a Na+/K+ pump work

A

3 Na+ are actively transported out, 2 K+ are transported in - this creates a charge imbalance

32
Q

How is an action potential generated

A

A stimulus is detected, causing some Na+ channels to open. Charge increases from -70 to a threshold potential (-50mV) causing all voltage gated Na+ channels to open - this is known as depolarisation
At the AP peak, Na+ gates close and K+ gates open - repolarisation
Then it undergoes a refractory period in which K+ gates close - hyperpolarisation
Na+/K+ pumps restore resting potential

33
Q

Why is there a refractory period

A

To ensure each AP is unique

34
Q

What is the transmission of an action potential in an unmyelinated neurone

A

Na+ diffuses into neurone through a channel
There is a localised high concentration of Na+ inside the neurone
Na+ diffuses along the inside of the neurone
Na+ gate opens due to depolarisation
There is a series of local circuits

35
Q

How does transmission of AP happen in a myelinated neurone

A

Ionic exchanges occur only at Nodes of Ranvier. Na+/K= cant diffuse through myelin
There are elongated local currents
Action potential jumps from one node to the next in a process called saltatory conduction

36
Q

What are the advantages of having a myelin sheath

A

Insulates
Speeds up transmission
Fewer channels needed

37
Q

What effects the speed of an impulse

A

Axon diameter - inc diameter = inc speed
Temperature - inc temp = int diffusion = inc speed
Too high a temp = denaturing of channels

38
Q

What are the parts of a synapse

A

Axon, synaptic vesicles, synaptic cleft, neurotransmitter, receptor, dendrites

39
Q

What is a synapse

A

Where two neurones meet but dont touch

40
Q

What happens when an AP reaches a cholinergic synapse

A

AP arrives at presynaptic bulb
Voltage gated Ca2+ channels in presynaptic bulb open - Ca2+ diffuses in
Synaptic vesicles containing acetylcholine move to and diffuse with presynaptic membrane
Ach is released by exocytosis and diffuses across synaptic cleft
Ach binds to receptor site on Na+ channel receptors on postsynaptic membrane
Na+ channels open - Na+ diffuses into postsynaptic neurone
Generator potential produced - if it reaches threshold potential an AP will fire

41
Q

How is the recycling of acetylcholine done

A

Ach is broken down by hydrolytic enzyme acetylcholinesterase
Ach is hydrolysed into ethanoic acid and choline - both diffuse back across synaptic cleft and re-enter presynaptic bulb
ATP from mitochondria is used to reform Ach

42
Q

Why is ach recyckes

A

To stop sodium ions from continuously diffusing into postsynaptic membrane - stops multiple APs from firing

43
Q

What are the features of synapse

A

Spatial summation
Temporal summation
1 pre converges into many post
many pre converge into one post
Unidirectional
Filters out low level stimuli
Acclimatisation
Summations
inhibition

44
Q

What is spatial summation

A

Many presynaptic neurones share 1 synaptic cleft + postsynaptic neurone
together they release enough neurotransmitters to create AP

45
Q

What is temporal summation

A

1 presynaptic neurone releases neurotransmitters many times over a short period
AP is sent if neurotransmitter exceeds threshold value

46
Q

How are synapses involved in inhibition

A

Cl- channels in postsynaptic membrane
If these open, Cl- flows into postsynaptic neurone - causing hyperpolarisation
Harder to achieve an action potential

47
Q

What are exocrine glands?

A

Glands that secrete chemicals through ducts onto a surface

48
Q

What are hormones

A

Messenger molecules released by endocrine glands into the blood
Act as signals for target tissues/organs

49
Q

What are some examples of non-steroid hormones

A

Adrenaline
Insulin
Glucagon
ADH

50
Q

What are some examples of steroid hormones

A

Oestrogen
Testosterone

51
Q

What is the difference between steroid and non-steroid hormones

A

Steroid - enter the cell and have a direct effect on the DNA in the nucleus
Non-steroid - dont enter the cell, bind to receptors in the cell surface membranes

52
Q

What is the mechanism of non-steroid hormones

A

hormone = first messenger. As it is hydrophilic it cannot pass through the cell membrane and instead binds to specific receptors on cell surface of target cells
When a hormone binds to a complimentary receptors, a G protein is activated
This activates an enzyme called adenyl cyclase which converts ATP to cAMP
cAMP = second messenger, can act directly on another protein, stimulate transcription or initiate a cascade of enzyme controlled reactions

53
Q

What is the mechanism for steroid hormones

A

Pass through plasma membrane, bind to steroid hormone receptors in cytoplasm or nucleus - forms a hormone-receptor complex
Complex acts as a transcription factor and can facilitate or inhibit the transcription of a specific gene

54
Q

What hormones are produced by adrenal cortex and its function

A

Aldosterone - steroid hormone that controls Na+ and K+ concentrations in blood
Cortisol - steroid hormone that controls metabolism of carbohydrates + proteins in liver

55
Q

What does the adrenal cortex use to produce steroid hormones

A

Cholesterol

56
Q

Where are the adrenal cortex hormones produced

A

Alsosterone - zona glomerulosa
Cortisol - zona fasciculata
sex hormones - zona reticularis

57
Q

What hormone is produced in the Adrenal Medulla

A

Adrenaline and noradrenaline

58
Q

What is the role of adrenaline

A

A peptide hormone that is secreted in response to stress
Relaxes smooth muscle in bronchioles
Increases stroke volume of the heart
Increases heart rate

59
Q

What is the exocrine function and mechanism in the pancreas

A

Secretes enzymes
Pancreatic cells surround tubules which drain into the pancreatic duct (acini)
Pancreatic cells produce pancreatic juice made up of Amylase, trypsinogen, lipase

60
Q

What is the endocrine function of the pancreas

A

Hormones are secreted from the cells in the islets of Langerhans

61
Q

What is an acini

A

Any cluster of cells that resemble a many lobed berry

62
Q

What happens when a raised glucose level is detected

A

Change is detected in beta cells of the islets of Langerhans, beta cells secrete insulin into blood, insulin is detected by receptors on liver and muscle cells
Liver and muscle cells remove glucose from the blood and convert glucose to glycogen (glycogenesis)

63
Q

What is glycogenesis, glycogenolysis, gluconeogenesis

A

glycogenesis = glucose -> glycogen
glycogenolysis = glycogen -> glucose
gluconeogenesis = new glucose made

64
Q

What happens when blood glucose conc falls

A

Detected by alpha cells in islets of Langerhans
Alpha cells secrete glucagon into blood
Glucagon detected by receptors on liver cells

65
Q

How are insulin levels in beta cells regulated

A

Cell membrane had K+ and Ca2+ channels
K+ flows out through channels
When blood glucose conc is high, glucose diffuses into cells
Glucose is metabolised to produce ATP
ATP closes K+ channels
K+ is accumulated, inside becomes less negative
This change opens Ca2+ channels
Ca2+ causes vesicles of insulin to fuse with cell membrane - insulin undergoes exocytosis

66
Q

What is Diabetes mellitus

A

Disease in which the body is no longer able to control blood glucose conc
Pancreas doesnt produce enough insulin or body cannot respond to insulin produce

67
Q

What is it called when there are very high and very low blood glucose conc

A

High - hyperglycaemia
Low - hypoglycaemia

68
Q

What is Type 1 diabetes

A

Patients are unable to produce insulin
Autoimmune response where immune system destroys beta cells
Develops during childhood

69
Q

What is type 2 diabetes and what is it caused by

A

Patients cannot use insulin to control blood glucose levels
caused by insulin resistance or Beta cells not producing enough
Caused by physical inactivity, excess body weight, overeating of refined carbohydrates

70
Q

How do you treat diabetes

A

Type 1 - regular glucose monitoring and insulin injections
Type 2 - regulation of carb intake, exercise, weight loss, drugs, insulin injections

71
Q

What are the sources of insulin

A

extracted from pancreas of pigs, stem cells, genetically engineered bacteria

72
Q

What are the advantages of using genetically modified insulin

A

produced in pure form - less likely to produce allergic reactions
produced in higher quantities
cheaper
less ethical concerns

73
Q

What are the advantages and disadvantages using stem cell therapy to produce insulin

A

+No need for donors
+less likely to be rejected
+no need to inject insulin
- Not fully understood
- Concerns that it may cause tumours
- ethical issues

Biology A level (19 decks)

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