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Communication And Homeostasis Flashcards

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1
Q

What is homeostasis

A

The maintenance of the body’s internal conditions when the external environment is changing

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2
Q

Why is homeostasis important

A

Maintenance of optimal conditions for enzyme action and cell function

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3
Q

What factors does homeostasis control

A

Conc of glucose in blood
Conc of respiratory gases
Blood water potential
Waste products (o2 , urea)
Blood pH
Body temperature

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4
Q

What two systems are involved in homeostasis

A

Endocrine system

Nervous system

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5
Q

What does the nervous system consist of

A

Central nervous system (CNS)

Periphery nervous system (PNS)

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6
Q

What does the CNS consist of

A

Brain

Spinal cord

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7
Q

What does the periphery nervous system consist of

A

All the nerves in the body

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8
Q

What is a hormone

A

A hormone is a chemical substance produced by an endocrine gland and carried by the blood

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9
Q

What is a gland

A

A gland is a group of cells which produces and releases one or more substances

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10
Q

Why does the blood glucose level need to be controlled

A

Because it affects the water potential if the blood and availability of respiratory substrates for cells

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11
Q

What is negative feedback

A

A feedback loop which helps to return the change back to the original levels

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12
Q

Positive feedback

A

When a stimulus produced a response which causes the factor to deviate from its normal range

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13
Q

What is an endotherm

A

An organism which have physiological mechanisms to control body temp

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14
Q

What is an exotherm

A

An organism which relies on behavioural characteristics to control body temp

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15
Q

What is the endotherm response to a low body temperature

A

Vasoconstriction - muscles of arteriole walls contract, so arterioles near skin constrict and allow less blood to flow near skin capillaries and direction of blood flow is directed to deeper vessels to reduce the heat lost to environment

Increased metabolic rate - most metabolic actions are exothermic so provide warmth to body. In cold environments the hormone thyroxine increases basal metabolic rate increasing heat production in body

Shivering

Erection of hairs - erector muscles in skin contract causing hairs to rise and heat to be trapped between air over skins surface

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16
Q

Why can ectotherms survive with less food

A

Because less energy and nutrients is wasted in heat regulation and so more nutrients and energy is used for growth and repair

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17
Q

Why do aquatic ectotherms have a more stable body temperature

A

Because the water has a high specific heat capacity which means it’s temperature remains relatively stable

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18
Q

What is a neurone

A

A specialised cell which carries electrical impulses around the body

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19
Q

What features are found in a neurone?

A

Long fibre called an axon

Cell body which contains a nucleus and other cell structures

The end of an axon called an axon terminal which has many nerve endings

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20
Q

What do the nerve endings at the axon terminal allow neurones to do

A

Connect to other neurones which receive impulses from axon terminal which forms a network for easy communication

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21
Q

What insulates neurones

A

Myelin sheath

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22
Q

What is a myelin sheath made of

A

Schwann cells

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23
Q

What are the gaps between myelinated parts of the neurone called

A

Nodes of ranvier

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24
Q

Why are neurones with myelin sheath faster at transporting impulses than non myelinated neurones

A

Myelinated neurones cause the impulses to jump from one node to the next so less time is wasted transferring the impulse from one neurone to the next as it doesn’t have to pass down the whole axon

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25
Why does the non myelinated neurone take longer to transport impulses
Because the impulse has to carry down the whole axon
26
What does the sensory neurone do
Carries impulses from receptors to CNS
27
What do relay neurones do
Connect sensory and motor neurones in the CNS
28
What do motor neurones do
Carry impulses from CNS to effectors
29
What are the features of a motor neurone
Motor neurones have: a large cell body at one end which lies within spinal cord or brain A nucleus always in the cell body Many branched dendrites which provide a large surface area for the axon terminals and other neurones
30
What are the features of a relay neurone
Short but branched axons and dendrites
31
What are the features of a sensory neurone
A cell body branching off in the middle of the cell A single long dendron which carries impulses to the cell body And a single long axon which carries impulses away from cell body
32
What are transducers
Something which converts energy from one form to another in an electrical impulse
33
What are pacinian corpuscles an example of
A mechanoreceptor
34
Where are pacinican corpuscles found
In the feet, fingers, joints, tendons , ligaments
35
What do pacinian corpuscles respond to changes in
Pressure
36
Describe how a pacinian corpuscle functions
No pressure Stretch mediated sodium channels are too narrow so sodium remains outside membrane. This helps maintain resting potential Pressure applied Layers distorted causing stretch mediated sodium channels to open. Sodium ions enter axon of sensory neurone Generator potential established Influx of sodium ions changes the potential of the axon which causes depolarisation of the membrane. If enough generator potential produced an action potential will be established and nerve impulse moves along axon
37
What is between the layers of pascilian corpuscles
Positively charged Na+ ions
38
What does the resting potential mean
The inside of the neurone is more negative than the outside
39
What is the resting potential
-70mV
40
What maintains the resting potential in neurones
Sodium-potassium pumps actively pump 3Na+ ions out of the neurone for every 2k+ pumped in (therefore outside more positive) Potassium channels which makes the membrane more permeable to potassium ions than sodium ions Anions inside the cytoplasm which are negative
41
What are the stages of an action potential
Stimulus Depolarisation Depolarisation Hyperpolarisation Resting potential
42
Describe in detail the process of generating an action potential
Stimulus - stimulus detected resulting in sodium channels opening. This causes some Na+ ions to diffuse into the neurone making it slightly more positive inside. This generated a small potential difference. Depolarisation - once the potential difference created meets the threshold of about -40mV, an action potential is generated and voltage gated sodium channels open causing a huge influx of sodium ions down the electrochemical gradient into the neurone making it more positive compared to the outside. This triggers more sodium channels to open. Once depolarisation meets a threshold of about +30mV, the sodium channels close and the voltage gated potassium channels open. This causes an influx of potassium ions out of the neurone making it more negative than the outside of the neurone. This returns the potential difference back to resting potential. However as the voltage gated potassium channels close slowly, it results in hyperpolarisation where the potential difference becomes more negative than the resting potential. The resting potential is later restored due to the sodium-potassium pump.
43
What is the refractory period
A period during hyperpolarisation when the sodium ion channels are closed (during depolarisation) and the potassium ion channels are closed (during hyperpolarisation) and the axon is ‘recovering and unresponsive’
44
Where does the refractory period begin
When repolarisation starts and when resting potential is re-established
45
Why is the refractory period important
Stops action potentials merging into one Ensures ‘new’ action potentials generated ahead rather than behind original action potential so impulses can only travel in one direction
46
What is the speed of conduction determined by
Myelination Diameter of axon Temperature
47
Why do myelinated areas have a faster speed of conduction
Because they contain Schwann cells This means that myelin areas cannot be depolarised and therefore action potentials cannot be generated as myelin blocks the diffusion of sodium and potassium ions Therefore the action potential is only generated through saltatory conduction where the action potential ‘jumps’ between nodes of ranvier
48
Why do thicker axons have a higher speed of conduction
Thicker axons have a large surface area for the diffusion of ions. This increases the rate of diffusion of sodium and potassium ions through protein channels which increases the rate of depolarisation and action potentials Thicker axons also have greater volume of cytoplasm which reduces their electrical resistance so an action potential can push into next section faster
49
How does temperature affect the rate of conductivity
In colder temperatures, the sodium and potassium ions have less kinetic energy which means that the rate of facilitated diffusion and therefore generation of an action potential is lower
50
What is a synapse
A junction when two neurones meet
51
What do synapses consist of
Presynaptic knob Synaptic cleft Postsynaptic membrane
52
What are synapses which use acetylcholine described as being
Cholinergic synapses
53
Describe how synapses work to transport the action potential across the gap
An action potential reaches the presynaptic knob. This causes the voltage gated calcium channels to open allowing calcium ions to diffuse into the presynaptic knob. This causes the synaptic vesicles to move and bind to the presynaptic membrane. Then acetylcholine is released by exocytosis. Then acetylcholine diffuses across the presynaptic cleft and binds to the receptions on the sodium ion channels on the post synaptic membrane. This causes the sodium channels to open causing an influx of sodium ions causing a generator potential. If there is enough generator potentials then an action potential is created. The acetyl cholinesterase enzyme breaks down the acetylcholine into acetic acid and choline/ recycled back to presynaptic knob
54
What is the enzyme which breaks down acetylcholine after it has bound to the membrane on the sodium channels on the postsynaptic membrane
Acetylcholinesterase
55
What is acetylcholine broken down into
Ethanoic acid (acetic acid) Choline
56
Why does the presynaptic bulb contain lots of mitochondria and endoplasmic reticulum
Mitochondria - it is an active process so mitochondria involved. ATP also required to form acetylcholine after it has been returned to the presynaptic bulb in the form of acetic acid and choline Endoplasmic reticulum - to pack the synaptic vesicles which contains the neurotransmitter
57
Why is it important that the presynaptic cleft contains acetylcholinesterase
To ensure a constant action potential is not generated
58
Why do synapses only conduct an electrical impulse one way
As neurotransmitters are released on one side and the other side is receptors so chemical transmission can only go in one direction
59
Why are some impulses unable to trigger an action potential
This is because the impulse is too small so only a little acetylcholine is released. This means that only a few voltage gated sodium channels open so few sodium ions diffuse into the membrane and threshold potential is not reached
60
What is summation
Summation is when impulses are added together to produce an action potential
61
What are the advantages of summation
Allows for effect of stimulus to be magnified Combination of different stimuli can trigger a response Avoids nervous system being overwhelmed
62
What is temporal summation
Temporal summation is when multiple impulses arrive in quick succession and added together to produce an action potential
63
What is spatial summation (Spatial = simultaneous and several synaptic knobs)
Spatial summation is when multiple impulses arrive simultaneously at different synaptic knobs which stimulates the same cell body which triggers an action potential
64
What can happen after repeated stimulation of a neurone
It becomes fatigued as the vesicles run out of neurotransmitter. Therefore the synapse no longer responds to stimulus It has become HABITUATED
65
How is habituation a good thing
It prevents over stimulation of an effector which can cause damage
66
What do IPSPs do (inhibitory post synaptic potential)
It decreases the effect of summation to prevent an action potential in the post synaptic neurone
67
What does an EPSP do (excitatory post synaptic potential)
Increases the effect of summation
68
What are the two layers of the adrenal glands
Inner part is the medulla Outer part is the cortex
69
What does the cortex release
The cortex releases steroid hormones - regulates salt conc through aldosterone - regulates metabolism of glucose, proteins and fats to release energy
70
What does the medulla release
The medulla releases adrenaline and noradrenaline
71
Describe how peptide hormones signal to other cells
They are not fat soluble so cannot diffuse through phospholipid bilayer This means they have to bind to a complimentary receptor. This activates a G protein which then activates the enzyme acetyl Cyclase which catalyses the reaction of ATP —-> cAMP (second messenger). Because cAMP is the second messenger it can then go onto either having a direct effect on a target cell or can be used to trigger a cascade of other enzyme reactions
72
What are the three areas in the cortex
Zona glumerulosa Zona fasciculata Zona reticuluaris
73
What is the function of the Zona glomerulosa
Secretes mineralcorticoids such as aldosterone It regulates salt concentration
74
What is the function of the Zona fasciculata
Secretes glucocorticoids like cortisol which regulate starch/carbohydrate metabolism
75
What is the function of the Zona reticularis
Secretes androgens (precursor molecules) which control sex hormones
76
What are 2 things the pancreas secretes
Pancreatic juices to aid digestion Hormones secreted from islets of langerhans into blood
77
What do alpha cells secrete
Glucagon
78
What do beta cells secrete
Insulin
79
What cells do the islets of langerhan contain
Both beta cells and alpha cells

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