SECTION 6 - ORGANISMS RESPOND TO CHANGES IN THE ENV, NERVOUS COORDINATION AND MUSCLES, HOMEOSTASIS. Flashcards
1
Q
DEFINE A STIMULUS? AND WHAT CELLS DETECT (THESE CHANGES
A
A STIMULUS IS DETECTABLE CHANGE IN THE ENVIRONMENT. THESE CHANGES CAN BE DETECTED BY CELLS, KNOWN AS RECEPTORS.
2
Q
HOW DO ORGANISMS INCREASE THEIR CHANCE OF SURVIVAL?
A
BY RESPONDING TO STIMULI VIA DIFFERENT RESPONSE MECHANISMS
3
Q
DEFINE THE TERM TROPISM?
A
TROPISM IS THE TERM GIVEN TO WHEN PLANTS RESPOND, VIA GROWTH, TO STIMULI.
4
Q
tropisms can be eitehr ___ or ___
A
positive or negative. positive meaning plants grow towards the stimulus, and negative meaning growing away from the stimulus.
5
Q
plants respond to what type of stimulus?
A
light and gravity
6
Q
what are tropisms controlled by?
A
specific growth factors and one key example (i need to know) is indoleacetic acid (IAA)
7
Q
whats the specifc growth factor IAA? and where is it made?
A
IAA is a type of auxin can can control cell elongation in shoots and inhibit growth of cells in the roots. ITS MADE in the tip or the roots and shoots but can diffuse to other cells.
8
Q
phototropism is the term given to the tropisms where what?
A
phototropism is the term given to the tropisms where the plant is responding to light.
9
Q
whats positve phototropism?
A
when shoots of a plant grow and bend towards light, as light is needed for the LDR in photosynthesis. this is positive phototropism
10
Q
how does positive phototropism work? (give the benefit in the end)
A
Shoot tip cells produced IAA, causing cell elongation
the IAA diffuses to other cells
if there is a unilateral light (light coming from one direction), the IAA will diffuse towards the shaded side (away from the light source) of the shoot, resulting in a higher concentraton of IAA in the shaded side (side not receiving)
As a result of there being a higher concentration of IAA in the shaded side of the shoot, the shaded side elongates more, resulting in the plant bending towards the light source (away from gravity), to photosynthesise.
11
Q
why dont roots require light? instead what do they do to the plant?
A
because roots dont photosynthesise. they must anchor (hold it firmly) deep in the soil.
12
Q
how does negative phototropism work? (give the benefit in the end)
A
in the roots, a high concentration of IAA inhibits cell elongation.
causing root cells to elongate more on the lighter side and so the root bends away from the light (towards gravity), increasing the chance of roots growing into the soil where they are able to absorb water and mineral ions.
this is negative phototropism.
13
Q
how does positive and negative geotropism/gravitotropism work?
A
positive geo/gravitotropism: cells in the tip of the root produce IAA.
IAA diffuses from the upper side of the root to the lower side of the root due to gravity
hence casuing a higher concentration of IAA in the lower side of the root.
AS IAA inhibits elongation of the root cells, and there is a higher conc of IAA on the lower side, the cells on the lower side elongate less than the cells on the upper side, (cells in the upper side of the root elongate more), causing the root to bend downwards towards the force of gravity.
negative geo/gravitotropism: IAA will diffuse from the upper side to the lower side of the shoot.
in shoots, the greater concentration of IAA on the lower side of the shoot increases the cell elongation in the lower side and hence causes more cell elongation to happen in the lower side of the shoot than the upper side, as a result the shoot grows upwards, away from gravity.
14
Q
define a reflex?
A
rapid, automatic response to a stimulus.
15
Q
a reflex arc is made up of 3 neurones. give them
A
sensory neurone
relay neurone
motor neurone
16
Q
taxes and kinesis are simple responses which help do what?
A
help keep organisms within the favourable conditions of their environment (eg, light, moisture, chemicals)
17
Q
define taxes?
A
where an organism will move its entire body towards a favourable stiumulus or away from an unfavourable stimulus. (directional). when an organism moves towards a stimulus this is positive phototaxis.
and when it moves away from a stimulus thats negative phototaxis
18
Q
define kinesis?
A
of an organism where an increase in the rate of movement/speed and the rate it changes direction in response to a stimulus. the rate depends on the stimulus intensity - the more unfavourable the stimulus, the greater the rate.. this continues until it reaches favourable conditions. (kineses are hence not directional)
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19
Q
what does stimulation of a receptor mean?
A
the receptor has detected a stimulus AND has responded to it by sending a nerve impulse for eg, to the brain.
Think of it like this analogy:
Imagine a doorbell button is the receptor.
The stimulus is your finger pressing the button.
The stimulation of the receptor is the moment the button gets pushed.
That causes a signal (ding-dong) to be sent (like a nerve impulse to the brain).
20
Q
as we know, receptors detect stimuli (detectable changes in the env). each receptor only responds to specific stimuli and this stimulation of a receptor leads to the establishment of what?
A
a generator potential which can cause a response.
21
Q
what are the 3 receptors
A
Pacininian Corpuscle (
Rods
cones
22
Q
whats a pacinian corpuscle?
A
pressure receptor (detect changes in pressure) located deep in skin, mainly in fingers and feet
23
Q
what does the Pacinian corpuscle consist of (structure wise)
A
pacinian corpuscle contains a sensory neurone which has special chanel proteins in its plasma membrane
24
Q
the membranes of the pacinian corpuscle have special channel proteins as mentioned, what are they? and what does it mean for them to have these special channels
A
stretch-mediated sodium channels. what this means is that when these proteins have pressure applied to them, they are stretched and deformed, hence opening the Na+ ion channel allowing na+ ions to enter the sensory neurone.
25
for eg, when pressure is applied to the finger, what happens?
the neurone plasma membrane in the pacinian corpuscle deep in the skin of the finger, will be stretched and deformed, opening/widening the na+ channel, hence allowing Na+ ions to diffuse into the sensory neurone (in the pacinian corpuscle), leading to the establishment of a generator potential, which if it is strong enough to reach the threshold, an action potential is established.
26
whats the resting potential?
the potential difference across the membrane of the neurone when its not transmitting an impulse. it has been measured at apporx -70mV.
27
how is a resting potential achieved?
via a carrier protein in the membrane of the neurone callued a sodium/potassium dump which actively transport 3na+ ions out of the cell for every 2k+ ions in the cell.
hence creating a conc gradient of ions. maintaining a higher conc of na+ ions outside of the cell and a higher conc of K+ ions inside the cell.
A small number of ions also move through the membrane by facilitated diffusion through specific chanel proteins. there are more channel proteins specific to K+ ions than there are for na+ ions.
the net result of these ion movements is that there are more positive ions outside the neurone than inside, leading to the resting potential of -70mV.f
28
define the action potential, and how/when is it inititated?
the action potential is the change in potential difference across the membrane of the axon. the action potential is initiated when the neurone is stimulated by a receptor. Na+ ion channels in the membrane open allowing Na+ ions to diffuse into the axon down a conc gradient. resulting in a higher conc of positive ions inside the axon than outside of it, leading to depolarisation of the membrane.
laeding to the action potential of approx 40mV.
an action potential occuring in one part of the axon, causes na+ ion channels to open in the next part of the membrane causing the action potential to move along the axon in a wave of depolarisation.
29
when can a stimulus only produce an action a potential?
if its greater than a minimum level called the threshod value.
30
define the generator potential?
receptors respond to a simulus, causing na+ ion channels to open which causes the potential diff across the membrane to be more positive. this is the generator potential.
31
the size of the generator potential depends on what?
the strength of the stimulus.
32
if the generator potential exceeds the threshhold value, then what happens?
large numbers of na+ ion channels open in the membrane of the sensory neurone and an action potential of the same size is generated, (regardless of how large the stimilus is)
33
if the generator potential is below the threshold value, what occurs?
the na+ ion channels remain closed. this is called the all or nothing principle.
34
info about the size of the stimulus is conveyed by what?
the frequency of impulses.
35
describe the process of repolarisaiton? state whats the refractory period, and explain why its important
once the membrane has been depolarised it must be repolarised back to the resting potential to enable further action potentials to be conveyed if necessary.
this is done by closing na+ ion channels and opening k+ ion channels in the membrane of the axon allowing k+ ions to diffuse out of the axon down a conc gradient.
this results in more positive ions being outside the axon than inside hence reforming the resting potential.
for a short period after repolarisation the k+ ion channels and the na+ ion channels remain closed. during this time the axon cannot be depolarised and therefore no impulse can pass. this is the refractory period which is important because:
each action potential is kept discrete, meaning there is no overlapping of action potentials.
36
where do receptors initate electrical impulses, which then what happens?
receptors initiate electrical impulses in sensory neurones which carry the impulse to a coordinator (spinal cord in an unconscious reflex or the brain in a conscious response)
in the coordinator, an intermediate neurone connects the sensory neurone with the appropriate motor neurone.
the motor neurone carries the impulse to an effector, either a muscle which responds by contracting or a gland which responds by secreting a chemical.
37
give the structural features of a mediated motor neurone AND GIVE A DIAGRAM OF HOW IT LOOKS LIKE.
a mediated motor neurone consists of the following features:
Cell body - containing the organelles. proteins and neurontransmitter chemicals are made here.
Dendrons - extensions of the cytoplasm of the cell body which conduct impulses towards the cell body, dendrons are sub-divided into dendrites which receive impulses from other neurones and carry action potentials to surrounding cells.
Axons - extensions of the cytoplasm of the cell body which conduct impulses away from the cell body (conductive long fibre that carries nervous impulses along the motor neurone)
Myelin sheath - a layer that electrically insulates the axon formed by cells called Schwann cells. Layers of membranes surround the axon which prevent the movement, of charged, water soluble ions as its a lipid.
Nodes of Ranvier - junctions between adjacent Schwann Cells where the axon is exposed allowing movement of ions. (gaps between myelin sheath)
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38
the photoreceptors, Rods and cones are found where?
in the human retina
39
rods can only process images in what?
black and white
40
to create a generator potential, the pigment of rod cells (rhodopsin) must ......
must be broken down by light energy
41
the pigment of rod cells (rhodopsin) can detect what and why?
can detect light at very low intensities as many rod cells connect to one sensory neurone. this is called retinal convergence
42
retinal convergence (when the pigment of rod cells can detect light at low intensities because many rods cell connect to one sensory neurone) provides what (the downside of it)
low visual acuity, which is when the brain cannot distinguish between the separate sources of light that stimulted it.
43
cones process images in ....
colour
44
the 3 types of cone cells contain what?
there are 3 types of cone cells and each of them contain a different type of iodopsin pigment (red, green and blue), and they all absorb different wavelengths of light.
45
what gives off the different colours we see?
depending on the proportion of red, green or blue cone cells that will give the different colours (not just red, green and blue).
46
iodoposin is only broken down when....? and why? and what property as a result of this do cone cells give off
if there is a high light intensity, so action potentials can only be generated with enough light. (i.e you can only see in colour when there is enough light presence).This is because 1 cone cells connects to one sensory/bipolar cell. therefore cones can only respond to high light intensity. which is why we can't see colour when its dark.
AS EACH CONE CELL IS CONNECTED TO ONE BIPOLAR/SENSORY CELL, THE BRAIN CAN DISTINGUISH BETWEEN
47
the distribution of rods and cone cells is .....
uneven in the retina
48
light is focused by the lens on the ____, which will receive what type of light intensity?
light is focused by lens on the fovea, which will receive the highest intensity of light
49
most cone cells are located near ____?
the fovea because light is focused by lens on the fovea, which is an adv as cone cells detect light at high intensities and the fovea receives the highest intensity of light (rod cells are further away)
50
why are rod cells found further away from the fovea
because rod cells detect light at low light intensities, hence will be further away
51
cardiac muscle is ____. and what does that mean? ( in terms of contraction)
cardiac muscle is myogenic, meaning it contracts on its own accord, but the rate of contraction is controlled by a wave of electrical activity.
52
whats known as the pacemaker and where is it found
the sinoatrial node (SAN) is located in the right atrium and is known as the pacemaker as it sets the pace for which the heart beats at.
53
where is the atrioventricular node located?
between the right atrium and left ventricle
54
whats the bundle of His
the tissues which run through the septum
55
whats the purkyne
fibres in the walls of the ventricles
56
how does the control of the heart rate take place (process)
the SAN releases a wave of depolarisation across the atria, causing it to contract
AVN releases another wave of depolarisation when the first wave reaches it. a non-conductive layer (of tissue) between the atira and ventricles prevents the wave of depolarisation travellind down to the ventricles.
instead the bundle of His, conducts the wave of depolarisation down the septum and up the pyrkyne fibres
as a result there is a short delay before the ventricles contract, whilst the AVN transmits the second waves of depolarisation.
This is an adv as it allows enough time for the atria to pump all the blood into the ventricles.
finally the cells repolarise and the cardiac muscles relaxes.
57
what part in the brain controls the heart rate via the autonomic nervous system (meaning its automatic control with no concsiousness, (i.e you cant control it))?
medulla oblongata
58
what are the 2 parts of the nervous system that influence the heart rate?
Sympathetic nervous sytem (heart rate is increased via this sytem)
parasympathetic system (heart rate is decreased via this system)
59
if impulses travel through the sympathetic nervous system (since there is more heart rate) what does this say about the frequency of waves of depolarisation released by the SAN. do the same for when impulses travel via the parasympathetic nervous system.
if impulses travel via the sympathetic nervous sytem,that will cause the SAN to release the waves of depolariszation more frequently hence increasing the heart rate.
if impulses travel via the parasympathetic nervous sytem,that will cause the SAN to release the waves of depolariszation less frequently hence decreasing the heart rate.
60
what 2 stimuli change the heart rate? and these stimuli are detected by which receptors? where are these receptors found?
PH and Blood pressure. chemo receptors and pressure receptors detect these stimuli respectfully and both receptors are found in the (walls of the) aorta and carotid artery.
61
why does the ph of blood decrease during times of high respiratory periods? and why does the excess acid need to be removed?
due to the production of co2 (in aerboic respiration) and lactic acid ( in anaerobic respiration). excess acid must be removed from the blood rapidly to prevent enzymes denaturing.
62
how is the removal of excess acid from the blood achieved?
removal of excess acid from the blood is achieved by increasing the heart rate, meaning more impulses are sent to the SAN via the sympathetic nervous system, causing CO2 to diffuse out, into the alveoli more rapidly.
63
what affect does high blood pressure have to the walls of the arteries? and hence how does the blood pressure get reduced? (how do u decrease its heart rate as thats how u counteract high blood pressure)
if the blood pressure is too high this can damage the walls of the arteries. to reduce the blood pressure this results in more impulses being sent to the SAN via the parasympathetic system to decrease the heart rate.
64
if the blood pressure is too low, there may be insuffiecient supply of oxygenated blood to respiring cells and removal of waste. how do you resolve this? (i.e how do you increase the heart rate as that is how u counteract low blood pressure)
this results in more impulses being sent to the SAN via the sympathetic system to increase the heart rate.
65
whats the reason for why there is a resting potential? and why is it negative
when a neurone is not conducting any impulse due to there being no stimulus, and hence there is a difference between the electrical charge inside and outside of the neurone (pd across the membrane). then this is known as the resting potential.
there are more positive ions, of na+ and k+ outside compared to inside the AXON, hence the inside of the neurone is more negative. giving a pd value of -70mV
66
how is the resting potential maintained?
Sodium-Potassium Pump:
Actively transports 3 Na⁺ ions out of the axon and 2 K⁺ ions in.
Requires ATP because ions are moved against their concentration gradients.
Concentration Gradient:
Creates a higher concentration of Na⁺ outside the cell and a higher concentration of K⁺ inside the cell.
Ion Movement via Channel Proteins:
The membrane is more permeable to K⁺ ions than Na⁺ ions, due to more potassium channel proteins.
K⁺ ions diffuse out of the neuron via facilitated diffusion, following their concentration gradient.
Resting Potential:
More K⁺ ions leave the neuron than Na⁺ ions enter, creating a negative charge inside the cell.
This results in the resting membrane potential of -70mV, meaning the inside of the neuron is 70 millivolts more negative than the outside when at rest.
67
define action potential?
when the neurones voltate increases beyond thethreshold, to generate a nervous impulse, to travel along the motor neurone and to be sent to the effector.
68
an increase in voltage, or _______, is due to what?
an increase in voltage or depolarisation is due to the inside of the neurone becoming more permeable to na+
69
once an action potential is generated it moves along the axon like what?
a mexican wave
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70
if the motor neurone wasnt myelinated, what affect would this have on where action potentials form and how is this a harm.
the action potential would form at every single position in the axon, as there would be no myelin sheaths present, hence it would take longer for all the action potetials to reach the end of the axon (axon terminal)
71
whats the all or nothing principle? and why is it important for animals?
if the depolarisation does not exceed -55V (THRESHOLD), an actional potential and impulse arent produced. (Nothing)
any stimulus that does trigger depolarisation -55V will (i.e exceeds it) will always peak at the same max voltage (ALL)
bigger stimuli increase the frequency of action potentials. this is the principle.
important as it makes sure that animals can only respond to large enough stimuli rather than responding to every slight change in the env.
72
whats repolarisation
this is what happens after an action potential is reached, where in order to get the membrane back to the resting potential this happens:
the Na+ ion channels close and the K+ ion channels open in the membrane of the axon allowing k+ ions to diffuse out of the axon down a conc gradient
this reults in more positive ions being outside the axon than inside hence forming the resting potential.
73
74
whats the refractory period. and give 3 reasons why its important
for a short period after repolarisation the k+ and na+ ion channel remain closed. during this time the axon cannot be depolarised and hence no impulse can pass. this is the refractory period
this is important for 3 reasons:
it ensures that discrete impulses are produced. action potentials cant be generated immediately after another hence this makes sure that each are produced separately. (no overlapping of action potentials)
it ensures that action potentials travel in one direction. this stops the action potential from spreading out in 2 directions which would prevent a response.
it limits the number of impulse trasnmission, preventing over reaction to a stimulus.
75
what are the 3 factors that affect the speed of conduction in the axon of the neurone
myelination resulting in saltatory conduction
AXON DIAMETER
TEMPERATURE
76
whats saltatory conduction?
Saltatory conduction is when the action potential "jumps" from one node of Ranvier to the next along a myelinated axon.
The myelin sheath, formed by multiple layers of Schwann cell membranes, acts as an electrical insulator.
Because the myelin prevents ion movement across the membrane, as a result, depolarisation cannot occur in the myelinated regions.
Therefore, the action potential can only occur at the nodes of Ranvier, which are unmyelinated gaps between adjacent Schwann cells.
The impulse effectively "jumps" from node to node, rather than moving continuously along the axon.
This allows the action potential to travel much faster compared to conduction in unmyelinated axons, where waves of depolarisation must happen along the entire membrane.
77
the wider the diameter of the axon, the ... and why?
faster the speed of conductance in the axon. this is because the wider the diameter, the less leakage of ions takes place, hence depolarisation is maintained as a higher conc of mainly na+ ions remain in the axon, hence the action potential travels faster.
78
give the 2 reasons why a higher temperature increases the speed of conductance in the axon?
1) higher temp means ions will have more ke, and hence diffuse faster
2) the enzymes involved in respiration to provide the atp needed for the sodium-potassium pump will work faster. hence there is more atp for active transport in the sodium-potassium pump which actively transports 3 Na⁺ out and 2 K⁺ in to restore ion gradients after each action potential.
Faster ion gradient restoration means the neuron can repolarise more quickly and be ready to conduct the next impulse sooner. As a result, the speed of nerve impulse conduction increases.
79
define synapses?
the gaps between the end of the axon of one neurone and the dendrite of another one
80
when the action potential reaches the end of the neurone, how does it reach the next neurone and be generated again? (more general simple answer)
neurotransmitters (chemicals) diffuse across the synapse, hence generating the action potential in the next neurone.
81
temps beyond the opt of 37 can do what to the speed of conduction in the axon?
decrease it
82
Describe how an action potential is generated in the postsynaptic membrane after neurotransmitter release? and how is this process UNIDIRECTIONAL. an eg of this that i need to know is the choligernic synapse, where the neurotransmitter is acetylcholine.what prevents acyetylcholine from being permanently bound to the receptor
An action potential reaches the axon terminal and arrives at the synaptic knob. depolarisation of the synaptic knob leads to the opening of ca2+ ion channels, hence allowing ca2+ ions to diffuse into the synaptic knob.
vesicles containing neurotransmitter move towards and fuse with the presynaptic membrane. the neurotransmitter as a result is then released to the synaptic cleft.
since the neurotransmitters released are of high concentration they diffuse, down the conc gradient, across the synaptic cleft, into the post synaptic membrane. the neurotransmitter is complementary in shape to the receptors on the surface of the post-synaptic membrane, and hence bind to the receptors.
this causes the Na+ ion channels on the post-synaptic membrane to open and na+ diffuse in. if enough na+ ions to diffuse in to the point where it exceeds the -55mV threshold, the post-synaptic neurone becomes depolarised, and eventually generating an action potential.
once the action potential is generated the neurotransmitter is released from the receptor. the na+ ion channel closes and the post synaptic neurone restablishes resting potential. the neurotransmitter is transported back into the presynaptic neurone/membrane where its recycled.
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THe overall process is unidirectional because:
the vesicles containing the neurotransmitters are only found in the presynaptic neurone
because of the conc gradient present across the synaptic cleft, diffusion of neurotransmitters occurs always from the pre to the post synaptic neurone.
the receports are only complementary in shape to the neurotransmitters in the membrane of the post synaptic neurone.
aceytylcholine when binding to the receptor dont remain perm bound because if they remained perm banned, the na+ ion channel would remain open and hence an action potential would be continually triggered and hence triggering contiually a response even though no stimulus is present anymore.
to prevent acetylcholine from permanently binding to the receptor, an enzyme is used to break down acetylcholine into choline and acetate which can then be reabsorbed into the presynaptic neurone and be reused.
83
define summation? and give the 2 methods which it is done by?
rapid build up of neurotransmitters in the synapse to help generate an action potential which is done by 2 methods. spatial or temporal summation.
spacial summation: this is when many different neurones collectively trigger a new action potential by combining the neurotransmitter they release to the same post synaptic neurone in order to exceed the threshold value. the different neurones collectively release enough neurotransmitters in order for enough of the na+ ion channel to open on the post synaptic neurone.
temporal summation: unlike spatial, this is when u have 1 presynaptic neurone relseasing neurotransmitter repeatedly over a short period of time to add up until enough conc/amount of neurotransmitter is bound to the receptor on the post synaptic membrane so that many na+ ion channels can open, so that more na+ ions can diffuse in enough to exceed the threshold value.
84
what are inhibitory synapses/what do they do?
An inhibitory synapse is a type of synapse where the neurotransmitter released makes it less likely that an action potential will be generated in the postsynaptic neuron.
HERES HOW:
The presynaptic neuron releases an inhibitory neurotransmitter (e.g. GABA or glycine).
This binds to receptors on the postsynaptic membrane.
Instead of opening Na⁺ channels, it opens Cl⁻ (chloride ion) channels or K⁺ (potassium ion) channels.
Cl⁻ ions diffuse in (making inside more negative), or K⁺ ions diffuse out.
This causes hyperpolarisation of the postsynaptic membrane (membrane potential becomes more negative than -70 mV).
The membrane is now further from threshold, so it’s less likely an action potential will occur.
85
define a neuromuscular junction?
this is a synapse that occurs between a motor neurone and a muscle and is very similar to a synaptic junction.
86
GIVE THE SIMILARITIES AND DIFFERENCES BETWEEN THE NEUROMUSCULAR JUNCTION AND THE CHOLIGERNIC SYNAPSE?
S: BOTH ARE UNIDIRECTIONAL, AS THE NEUROTRANSMITTER RECEPTORS ARE ONLY FOUND IN THE POST SYNAPTIC MEMBRANE.
D:
neuromuscular junction will only be excitatory, meaning it will only generate the response, whereas a choligernic synapse could be excitatory or inhibitory as a response can be generated through the generationof an action potential, or an action potential could not be genereated for eg when using inhibitory synapses (using chloride ions etc) where an action potential is not generated and hence a response aint generated.
the neuromuscular junctionconnects motor neurone to muscles, whereas the choligernic synapse is a synapse which occurs between any 2 neurones. which could be sensory, relay or motor.
the neuromuscular junction is always the end point for the action potential (as it causes a muscle contraction, not another action potential in a neuron), whereas with choligernic synapses, a new action potential is generated in the next neurone. (Neuromuscular junction: end of the neuron line → causes muscle response (no more neurons after this).
Cholinergic synapse between neurons: passes the signal forward by triggering a new action potential in the next neuron.)
with neuromuscular junction, acetyl choline binds to receptors on muscle fibre membranse, whereas with choligernic synapses, acetyl choline binds to receptors on the post synaptic membrane.
87
whats a choligernic synapse?
A cholinergic synapse is a type of synapse where the neurotransmitter acetylcholine (ACh) is used to send the signal from one neuron to the next (or to a muscle cell).
88
whats myofibrils?
long thread-like structure made up of fused cells that share nuclei and cytoplasm,known as sarcoplasm (muscle cells version of cytoplasm - sarcoplasm is the gel-like substance that fills the space inside the muscle cell(myofiber) like in cytoplasms of other cells), and there is a high number of mitochondria ( as atp is needed for respiration for the muscle contraction)
89
muscle fibres are made up of what? and myofibrils are made up of what? to form what?
milions of myofibrills which collectively bring about the force to cause movement.
myfibrils are made up of 2 key protein, myosin and actin, that form a sarcomere.
(A sarcomere is the basic functional unit of a muscle fiber (or muscle cell), and it's where the actual contraction of the muscle happens.) - (Sarcomeres are repeated along the length of myofibrils.)
90
what region in a sarcomere, highlights the A band?
length of the myosin and remains constant.
91
what region in a sarcomere, highlights the H zone? and what occurs to the length of the H zone when muscle contracts?
where myosin is present by itself ( no overlapping of actin present). length of H zone decreases when muscle contracts as when muscle contraction takes place, actin slides in towards the centre of the sarcomere, the M-line.
92
what region in a sarcomere, highlights the I band? and what occurs to the length of the I band when muscle contracts?
where Actin is only present. length of the I band decreases when muscle contracts as the actin again slides in towards the centre of the sarcomere, the M-line.
93
what does the Z lines represent? and what happens to Z lines when muscle contracts?
the start and the end of 1 sarcomere. DURing contraction, the Z line becomes closer together aswell as actin slides in.
94
give the diagram showing the sarcomere, with all its bands, and showing what happens post contraction. show diagram on microscope aswell.
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95
give the sliding filament theory (how a muscle contracts)
Action potential being produced in the muscle, stimulates a reponse (muscle contraction)
this is done by ca+ ions being released by the sarcoplasm, which causes tropomyosin protein (the protein covering the actin binding sites) to move and hence uncover the actin binding sites, leaving them exposed.
As a result, ADP + PI attach to the myosin head which binds and attaches to the actin binding site, forming a cross bridge, creating tension, which then causes the actin filament to be pulled and slide along the myosin .
as a result ADP + pi molescule are then released.
ATP is then formed which then binds to the myosin head, causing it to change shape slightly hence causing it to detach from the actin molecule
Calcium ions are then released form the sarcoplasm which activates enzyme ATPase (in the sarcoplasm) to hydrolyse ATP into ADP + pi releasing sufficient energy for the myosin head to return to its og position.
process repeats (as long as calcium ions remain high and muscle remains stimulated by the nervous system)
2 diagrams showing all this here:
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EWEIh9Bv9UZMjW46SfpKWcEBoMbD16NpK84RoCd6MecKSw?e=jZKGNQ
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for the sliding filament theory (for a muscle to contract) to occur, what do u need?
active muscles need a high conc of ATP.
the chemical phosphocreatine, which is stored in muscles, assists this by providing phosphate to regenerate ATP from ADP.
97
compare the structure, location of where they are found and general properties for both Slow-twitch fibres and Fast-twitch fibres.
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define homeostasis
the maintenance of a constant interval environment. importatn in maintaining:
a stable core temp
stable blood PH in relation to enzyme activity
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constant levels are controlled by a certain principle. state the name of it and expand on it.
constant levels are controlled by a principle called negative feedback. - A DEVIATION from a set level causes events to happen which reverse the change - bringing levels back to those set.
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when does blood glucose conc increase and decrease (in terms of what u do )
increases - ingestion of food or drink containing carbs.
decreases - following excercise or if you have not eaten
101
what does the pancreas do, what does it have.
pancreas detects changes in the blood glucose levels, within the pancreas islet of Langerhans cells are present, these cells release insulin and glucagon to bring blood glucose level back to normal.
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when is insulin released vs when is glucagon released?
insulin is released when blood glucose level are too high, hence insulin causes a decrease in blood glucose levels.
Glucagon is released when blood glucose levels are too low. it causes an increase in blood glucose levels.
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what is adrenaline released by and when?
adrenaline is released by adrenal glands when ur body anticipates danger and this results in more glucose being released from hydrolysis of glycogen in the liver.
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how do blood glucose levels restore to normal after blood glucose level increase. (glycogenesis). what does insulin also do interms of exces glucose being converted ....
if blood glucose levels become too high (due to absorbing glucose in small intestine):
the increase is detected by beta cells in the islets of Langerhands of the pancrease.
these beta cells release insulin into the blood.
insulin binds to specific receptors in the membranse of liver cells.
liver cells respond by increasing their permeability to glucose by transporting protein channels into the membrane (so more glucose can enter the cells), and activating enzymes to convert glucose into glycogen. a process called glycogenesis.
insulin also causes the liver to convert excess glucose into fats to be stored in adipose tissue under the skin.
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how do blood glucose levels restore to normal after blood glucose level decrease.(glycogenolysis)
and give the process and how it works of when glycogen reserves are empty after severe fasting , and hence the liver cells produce new glucose from where?
blood glucose levels decrease
the decrease is detected by alpha cells in the islets of Langerhands of the pancreas.
these alpha cells release glucagon
glucagon binds to specifc receptors in the membrane of liver cells.
liver cells respond by activating enzymes to hydrolyse the glycogen back into glucose. a process called glycogenolysis.
in times of stress or excitement, adrenaline is also released from the adrenal glands, which also causes glycogenolysis.
if glycogen reserves are empty after severe fasting the liver cells will produce new glucose from:
lactic acid from anaerobic respiration in muscles
glycerol from fatty acid breakdown
amino acids from body proteins (only in prolonged fasting)
this process is called gluconeogensis and is also controlled by glucagon. -
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Glucagon increases blood glucose in multiple ways. the 1st messenger model is when glucagon attaches to protein receptors on the surface of target cells (liver cells) whats the second messenger model? and what type of hormones use second messengers to do what?
Glucagon increases blood glucose in the following ways:
some hormones like glucagon and adrenlaine use second messengers to cause a response in a target cell.
THE hormone (glucagon) (1st messenger) binds to a protein receptor on the membrane of the target (liver cell to form a hormone receptor complex. (glucagon receptor complex)
2nd Messenger Model:
When glucagon binds it causes a protein to be activated into adenylate cyclase and this enzyme converts ATP into a molecule called Cylic AMP (cAMP). cAMP (cAMP is the 2nd messanger) activates an enzyme, protein kinase (from its inactive form), that can hydrolyse glycogen into glucose.
same second messenger model occurs with adrenaline where adrenaline attaches to receptors on the surfaces of target cells. this cause a protein to be activated and hence convert atp into cAMP.
cAMP activates an enzyme that can hydrolyse glycogen into glucose.
https://merchanttaylorsschools-my.sharepoint.com/:w:/g/personal/tofoma_merchanttaylors_com/EaNHapX80MxHjp-Dp3E0zgkB25W_p54cn2HPkZnm5lOUmA?e=8wsYZ2
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define gluconeogensis?
creating of glucose from other molecules like amino acid and glycerol in the liver.
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whats diabetes?
a disease caused by an inability to control blood glucose levels
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During diabetes, glucose remains in the blood and is not absorbed by cells so cells lack glucose for respiration leading to weight loss and fatigue. The glucose in the blood does what to the water potential and what affect does that have on cells resulting in what? Also why does urine contain glucose?
the glucose in the blood hence lowers the water potentials causing water to move out of the cells by osmosis, resulting in thirst and urine production.
urine contains glucose due to incomplete reabsorption in the kidneys.
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type 1 and type 2 diabetes
type 1: (insulin dependent)
pancreas is unable to produce insulin in response to high blood glucose levels
treated byregular injections of insulin
type 2: (insulin independent)
insulin is produced but the cells of the body fail to respond to it.
treated by reducing the amount of soluble sugar and carbs in the diet, and by increasing exercise.
111
Osmoregulation (The control of the water potential of body fluids) occurs in the nephrons in the kidneys. whats a nephron?
the functional unit of the kidney is the nephron.
nephrons are long tubulues surrounded by capillaries and there are around 1 mil per kidney
the blood is filtered here to remove waste and selectively reabsorb useful substances back into the blood.
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give the 5 structures i must know in the nephron and give the diagram.
Renal (Bowmans) capsule
proximal convoluted tubule (PCT)
Loop of Henle
Distal convoluted Tubule (DCT)
Collecting duct
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where does the formation of glomerular filtrate (aka ultrafiltration) occur and how does it work?
specifically between the glomerulus and the renal bowmans capsule.
how it works:
Blood enters the afferent arteriole (wider) and leaves via the efferent arteriole (narrower), creating high hydrostatic pressure in the glomerulus.
This pressure forces small molecules out of the blood and into the Bowman’s capsule.
what gets filtered is: ✅ Water
✅ Glucose
✅ Urea
✅ Ions (e.g. Na⁺, Cl⁻)
❌ Large proteins and blood cells (too big)
Filtrate passes through:
1.)Endothelium of capillaries
2.)Basement membrane (filters based on size)
3.)Podocyte layer of Bowman’s capsule (has filtration slits)
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where does selective reabsorption occur?
occurs in the proximal convoluted tubule (PCT) (here 85% of the golmerulus filatrate is reabsorbed back into the blood, leaving urea and excess mineral ions behind)
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give adaptations of the cells lining the PCT and for what reason?
PCT cells have many microvilli, to provide a large surface area for reabsorption
PCT cells also have lots of mitochondria to provide energy for active transport
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Selective reabsorption process
How glucose is reabsorbed:
Co-transport with sodium ions:
Na⁺ actively transported out of PCT cells into blood, creating a lower conc of na+ ions in the PCT.
due to the conc gradient, Na⁺ diffuses from filtrate into PCT cells via carrier proteins, pulling glucose in with it.
Glucose then diffuses from the PCT epithelial cell into the blood (facilitated diffusion).
THIS IS HOW ALL THE GLUCOSE IS REABSORBED
How water is reabsorbed:
Reabsorbed by osmosis, following the movement of solutes like glucose and Na⁺ into the blood (low water potential is created in blood).
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What type of mechanism does the Loop of Henle use?
A countercurrent multiplier mechanism.
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Which limb of the Loop of Henle is permeable to water
The descending limb.
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Which limb of the Loop of Henle is impermeable to water but actively transports ions
The ascending limb.
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What happens in the descending limb of the Loop of Henle?
Water moves out by osmosis into the salty medulla; the limb is permeable to water.
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Why does the filtrate become more concentrated as it moves down the descending limb?
Because water leaves the filtrate but ions stay in, increasing solute concentration.
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How does the Loop of Henle help the collecting duct reabsorb water?
It creates a salt gradient in the medulla, so water can be drawn out of the collecting duct by osmosis if needed (especially under the influence of ADH).
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the walls of the mitochondria are thicker as they have many mitochondira. why do they have this muitochondira?
to provide energy to actively transport sodium ions out of the ascending limb of the loop of henle into the medulla
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the reabsoroption of water by the DCT (distil convulated tubule) and collecting ducts is controlled by which hormone? and what happens in the process. and whats the outcome?
ADH (antidiuretic hormone)
When you're dehydrated, ADH is released from the pituitary.
ADH makes the walls of the DCT and collecting duct more permeable to water.
So, more water is reabsorbed by osmosis into the salty medulla → blood.
result:
concentated urine is produced.
water is conserved in the body.
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give a table outlining the nephron parts: Bowman’s capsule, PCT, Loop of Henle, and DCT and Collecting duct. and their main function
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what are osmoreceptors
osmoreceptos are receptor cells located in the hypothalamus, which are sensitive to changes in the water potential of the blood.
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define osmoregulation and outline the procedure (control of water absorption)
when kindeys control the water potential of the blood by regulating the amount of water that it reaborbs from the filtrate. Procuedure:
if the water potential of the blood is too low (concentrated blood), action potentials are sent to the pitutiary gland which releases more of the hormone ADH.
ADH travels to the kindey in the blood stream and causes cells lining the collecting duct and the distal convoluted tubule (DCT) to become more permeable to water, hence more water is reabsorbed from the filtrate into the blood, increasing its water potential (negative feedback). Urine will be very concentrated and reduced in volume.
if the water potential of the blood becomes to high, osmorecepors send action potentials to the pitutary gland which releases less ADH.
Less ADH means the cells lining the DCT and collecting duct become less permeable to water hence less water is absorbed from the filrate making the water potential of the blood lower (negative feedback). urine as a result will be more dilute and higher in volume.
128
thermo-receptors in the skin vs in the hypothalamus?
thermo-receptors in the skin monitor the external temp and thermo-receptors in the hypothalamus monitor core (internal) temps.
129
if thermo-receptors detect a deviation (change) from set levels, how do they act?
they send nerve impulses to the thermoregulatory centre in the hypothalamus, which in turn sends a nerve impulse to effectors which respond by reversing the change.
130
when an environment is too cold, what do thermo-receptors do, to cause what?
they send impulses to the heat gain area of the thermoregulatory centre of the hypothalamus.
impulses from the heat gain area are then sent along sympathetic neurones of the autonomic nervous system to:
skeletal muscles - causing them to contract and relax, causing heat from respiration.
arterioles supplying surface capillaries -causing circular muscle in walls to contract, reducing blood flow through them to the skin which cools, reducing heat loss by radiation (vasocontriction)
Muscles connected to hair - which contract raising the hair, hence trapping a layer of insulating air, reducing heat loss by convection.
adrenal glands to release adrenaline which increases resouratuib rates in organs hence generating heat.
131
when an environment is too hot, what do thermoreceptors do to cause what?
they send impulses to heat loss area of the thermoregulatory centre of the hypothalamus.
impulses fro mthe heal loss area are sent along the parasympathetic neurones of the autonomic nervous system to:
sweat glands, causing them to release sweat on the skin surface. the evaporation of the water uses heat energy, hence cooling the skin and therefore cooling the blood.
Arterioles supplying surface capillaries, cuasing circular muscle in walls to relax, increasing blood flow through them to the skin which heatsup, increasing heat loss by radiation (vasodilation).
132
if the temp of the body exceeds 40 degrees, negative feedback systems ____ and positive feedback systems ____.
if the temp of the body exceeds 40 degrees, negative feedback systems _stop___ and positive feedback systems __begins__.
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as positive feedback system begins, what happens to metabolic rates, leading to what?
metabolic rates begin to increasing releasing more heat energy, leading to greater deviations from the set levels and can quickly lead to death.
134
Antagonistic muscle action
A muscle pulls in one direction at a joint and the other muscle pulls in the opposite direction
This is described as antagonistic muscle action
An example of this can be seen in the bicep and tricep of the arm
To raise the lower arm
The bicep contracts and the tricep relaxes
As the bone can't be stretched the arm flexes around the joint
This brings the tricep into its full length so that it can contract again
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diagrams of skeletal muscle and myofibril in it.
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