1
Q
what is the mammalian nervous system composed of
A
the central nervous system and peripheral nervous system
2
Q
what is the cns and what does it consist of
A
- specialised concentration of nerve cells that process incoming information, sends impulses through motor neurones and carries impulses to effectors
consists of :
- brain and spinal cord
- relay (intermediate neurones)
- it has unmyelinated neurones
3
Q
what is the pns and what does it consist of
A
neurones not in the CNS that spread throughout the body
- autonomic : not under conscious control
- sympathetic : ganglia close to CNA (neurotransmitter is noradrenaline)
- parasympathetic : gangalia far from CNA, neurtransmitter is acetylcholine
- voluntary : under concious control
4
Q
what are the 4 main locations of the brain and what are their functions
A
- the medulla oblongata : control breathing and heart rate
- the cerebellum : controls balance and coordination of movement
- cerebrum : initates movement and voluntary behaviour
- hypothalamus : temperature regulaiton ( thermoregulation) and osmoregulation
5
Q
what are the three main neurones and what are their functions
A
- Motor neurons : are involved in transmitting electrical signals from the central nervous
system to muscles and glands in the body. - sensory neurons : transmit impulses from receptors to the central nervous system
- relay neurons : which are located within the central nervous system, are involved in
transming the electrical impulses from sensory neurons to motor neurons.
6
Q
what is the resting potential of a neuron
A
the electrical potential difference across the plasma membrane when the cell is in a non-excited state
the value -70 mV is known as the resting potential
7
Q
what helps the resting potential be generated as well as maintained and how does it do this
A
the sodium-potassium pump, which moves sodium ions out of the neuron and potassium ions into the neuron.
This creates an electrochemical gradient as the concentraon of sodium
ions is higher outside the cell because the membrane is not permeable to sodium ions .
However, the potassium ions diffuse back out due to the presence of potassium ion
channels . As a result, the outside of the cell is positively charged due to the imbalance of
positively charged ions.
8
Q
explain the whole process of action potential being reached
A
when neuron receives an impulse : sodium channels on the dentrites open, leading to the movement of Na+ ions into the cell –> DEPOLARISATION
- if depolarisation reaches THRESHOLD potential (-55mV), it activates vol-gated sodium ions channels causing an ACTION POTENTIAL
- after v-g Na+ ion channels close, v-g K+ ions leave the cell –>REPOLARISATION
- outward diffusion of K+ ions causes HYPERPOLARISATION (too many K+ ions leave the membrane) then the v-g K+ ions close
- finally, sodium-potassium pump returns the cell to resting membrane potential (after refractory period – sodium ions enter the cell)
- REFRACTORY PRTIOD - period in an action potential where the axon cant be depolarisated to initiate a new action potential –> limit the frequency of action potentials and ensures action potentials are discrete and only travel in one direction
9
Q
what is the difference between absolute refractory period and relative refractory period
A
arp : sodium ion channels are blocked and its impossible for another action potential to be generated
rrp : sodium ions channels are not blocked, but potassium ion channels are still open and effectively is raised
10
Q
why is the speed of transmission along myelinated axons greater than along non-myelinated axons
A
- myelin sheath serves as an insulator of axons and dendrons, produced by Schwann cells.
- SALTATORY CONDUCTION : where action potential jumps between gaps in the cells of the myelin sheath (NODES OF RANVIER). this is because the myelin sheath is impermeable.
nerve impulses jump over the myelin sheath rather than travel through it, making the distance to the axon terminal shorter. This occurs due to the large proportion of fatty substances that make up the myelin sheath.
11
Q
describe and explain the cholinergic synapse
A
- when action potential happens : presynaptic neurone depolarized, causing CALCIUM ION CHANNELS TO OPEN (allow calcium ions to enter the neuron by diffusion)
- presence of calcium ions in the neuron causes FUSION OF SYNAPTIC VESICLES filled with neurotransmitter (eg. acetylcholine) with the presynaptic membrane
- then this gets released into synaptic cleft by exocytosis
- neurotransmitter diffuses actros synaptic cleft to the post synaptic neurone
- the neurotransmitter binds to the receptors located in the postsynaptic membrane and either :
★ stimulate opening of CATION CHANNELS - enable sodium ions to enter – membrane depolarise – trigger another action potential – excitatory post-synapthic potential
★ stimulate opening of ANION CHANNELS - enable sodium ions to enter the neuron – hyperpolarisation — more difficult to trigger a new action potential – inhibitory post-synaptic potential
12
Q
what does nicotine do to nerovus system
A
mimics effect of acetylcholine and trigger release of dopamine…high doses : bind to and blocks acetylcholine receptors
13
Q
what does lidocaine do to the nervous system
A
blocks voltage gated Na+ ion channels
14
Q
what does cobra venom do to nervous system
A
binds to and blocks acetylcholine receptors - lower heartrate to point of death
15
Q
what is the definition of homeostasis
A
maintenance of a state of dynamic equilibriym
16
Q
what are 3 things homeostasis controls
A
controls the internal environment of body
- temp
-pH
-water levels
17
Q
what is a negative feedback loop
A
when something in the body becomes too high, so the body responds and performs a mechanism which would counteract that change and return the levels to normal
18
Q
what is a positive feedback loop
A
when something in the body increases, it will trigger the increase of another substance
19
Q
why is maintaining temp so important
A
- Important because if the temp is not maintained a person could die from hypo or hyperthermia
20
Q
what happens in an environment that is too cold
A
enzymes will not function so metabolic reactions cannot occur, and the body cannot function
21
Q
what happens in an environment that is too hot
A
enzymes will denature so metabolic reactions cannot occur and the body cannot function
22
Q
what does the body do when it is too hot
A
- Sweating: sweat evaporates which cools the body
- Vasodilation – more blood flows near the skin surface and heat is lost from the blood
23
Q
what does the body do when it is too cold
A
- Shiver: muscles contract rapidly to generate heat
- Vasoconstriction - less blood flows near the skin surface and less heat is lost from the blood (does not warm the body, but it will prevent further heat loss)
- Hair on the skin stands upright and heat is trapped on the skin surface
24
Q
why is maintaing pH so important
A
- Extreme pH: enzymes will denature so metabolic reactions cannot occur and the body cannot function
- After respiration, tissues release CO2 into the blood
- CO2 dissolves in the plasma forming H2CO3
- H2CO3 H+ + HCO3-
- This equilibrium buffers the blood
25
why is osmoregulation so important
* ADH – antidiuretic hormone controls how much water is lost in the urine
* Too much water: cells will lyse
* Too little water: cells will shrivel
26
what is the endocrine system
the release of hormones by endocrine glands directly into the blood
27
what are the two ways hormones can work
o Method 1: Can attach to receptors and trigger the release of a secondary messenger (g-protein). The secondary messenger will activate ATP and convert it to cAMP (cyclic AMP) and specific enzymes will be activated in a cell and that will produce a response
o Method 2: hormones can enter a cell directly and bind to transcription factors
Transcription factors control transcription of DNA to mRNA and therefore hormone action on them means that protein synthesis is affected
28
what is chemical control in plants carried out by
by growth factors (plant hormones – they aren’t true hormones)
auxins, gibberellins and cytokinins
29
why are plant hormones not true hormones
because hormones are something that are secreted into the blood stream (plants do not have blood)
30
what are the functions of auxin
cell elongation, suppression of lateral bus (grows taller but not wider)
promotes root and shoot growth
31
how does auxin promote root growth
o The shoot has directional growth towards the sun and away from gravity (positively phototropic and negatively geotropic)
o The roots have directional growth away from the sun and towards gravity (negatively phototropic and positively geotropic)
32
how does auxin cause cell elongation
H+ ions are actively transported into the cell wall causing low pH --> this makes cell walls more flexible allowing it to stretch and accommodate more water --> therefore more cell expansion (growth)
33
what can auxins be used in
weed killers and rooting powder
34
what are gibberelins and what do they do
they are a plant growth factors
* Stimulate elongation at the cell internodes and promotes lateral growth of the plant
* Stimulates fruit growth
* Stimulates germination
35
how does germination occur
o Seed absorbs water which will activate the embryo embryo secretes gibberelins gibberelins diffuse to the aleurone layer in this layer amylase is produced amylase diffuses into the endosperm layer amylase breaks down starch into glucose (for respiration and growth)
- stimulates flowering
36
what do cytokinins do
* Promote cell division in apical meristems and the lateral buds
* Promotes leaf abscission (falling/dying)
37
what does synergistic mean (to do with plants)
* Synergistic: 2 chemicals work to produce the same effect (e.g. cytokinin work well with ethene to promote leaf abscission – falling)
38
what does antagonistic mean (to do with plants)
: 2 chemicals which have opposing effects (e.g. gibberellins promote later growth while auxin suppresses lateral growth)
39
what are phytochromes
they are pigments
40
what are the two types of phytochrome pigments
o Pr = inactive form, absorbs red light (sunlight)
o Pfr = active form: absorbs far red light (IR light)
41
what happens to phytochromes in the dark
o In the dark: it absorbs the far-red light and is converted from Pfr to Pr
42
what happens. to phytochromes in the light
: it absorbs the normal red light and is converted from Pr to Pfr
43
what are long day plants and do they have more pr/pfr
(plants which survive more in the summer when the days are longer): more Pfr is made which stimulates flowering.
44
what are short day plants
plants (plants which survive more in the winter): The Pfr inhibits flowering, so more pr
45
wht happens to plants which are grown in the dark
* Plants which are grown in the dark (all the phytochrome will be in the form Pr) – they are etiolated
o Tall and thin, fragile stems, small yellow leaves, little root growth
46
how does Pfr act as a transcription factor
It moves through the nuclear pores and binds to the promotor region of the gene and activates transcription growth and development
47
How do phytochromes control photomorphogenesis (development of form and structure of a plant, which is affected by light)?
o The Pr converts to Pfr
o This causes proteins to be localised (fixed in place) in cells
o This causes the transcription of certain genes and phosphorylation of certain proteins
o This affects germination, flowering, circadian rhythm
(Circadian rhythms are physical, mental, and behavioural changes that follow a 24-hour cycle)
48
describe the structure of the human retina
ganglion cells from optic nerve fibre
- bipolar neurones
then photoreceptors
49
name the 2 types of phtoreceptor cells located in the retina
- cone cells
- rod cells
50
where are rod and cone cells located in the retina
rods : evenly distributed around periphery but not in central fovea
cone : mainly central fovea
no photoreceptors at blind spot where ganglion axon fibres form optic nerve
51
explain why rod cells do not generate action potential in the dark
- Na+ enters outer segment of rod cells via non-specific cation channels. active transport of Na + out of inner segment = rod cell is slightly depolarised
- action potential = voltage-gated Ca2+ channels open. Triggers exocytosis of glytamate
- glutamate acts as inhibiotry neurotransmitter to hyperpolarise bipolar neuron
52
explain how rod cells generate an action potential in the light
1. rhodopsin pigment bleaches when it absorbs light and breaks down into opsin and retinal
2. opsin closes cation channels via a hydrolysis reaction. Acion transport of Na+ out of inner segment continues
3. rod cells becomes hyperpolarisation. No glutamate is released, so no inhibitory signals
4. bipolar neuron depolarises
53
describe the pigments in rod and cone cells
rod : rhodopsin absorbs all wavelength of light=tricolour
54
describe the visual acuity of rod and cone cells
rod : many rod cells synapse with 1 bipolar neuron = low resolution
cone : 1 cone cell synapses with 1
55
describe the light sensitivity of rods and cone cells
rods- very sensitive due to spatial summation of subthreshold impulses -- vision is low-light conditions
cone : les sensitive - vision in bright light
56
how is urea produced in the liver
they are called hepatocytes and in these cells, amino acids are converted to urine
57
describe the gross structure of a mammalian kidney
fibrous capsule : protects kidneys
cortex : outer region consists of Bowman's capsule convoluted tubule (tube that curves)
medulla : inner region consists of collecting ducts, loop of henle, blood vessels
58
what are the blood vessels associated with a nephron
- afferent arteriole from renal artery enters reenal capsule and forms glomerulus
- efferent arteriole branches to form capillary networks that surround tubules
59
what is the glomerulus
branched knot of capillaries which combine to form narrow efferent arterioles
60
what is ultrafiltration
happens in the glomerulus. knot of capillaries under high pressure --> means anything small enough gets squeezed out of the capillary walls and moves to the bowman's capsule
61
what is the difference between the afferent and efferent arteriole
- afferent arteriole is wider than the efferent -> since the blood is moving into a narrower area this is what causes the increased pressure
- efferent arteriole out of the glomerulus and to the rest of the arterioles
62
what is selective reabsorption and where does it happen
- it happens in the proximal convoluted tubule
- of all the substances that had been filtrated out into the filtrate, the useful substances are reabsorbed back into the blood (this is all active transport)
63
what is reabsorbed
- all of glucose
- vitamins
- hormones
- all amino acids are
- some water and some salts will reabsorb by diffusion/osmosis down a concentration gradient
64
does urea get reabsorbed?
no
65
what does the loop of henle conduct
selective reabsorption
66
what is selective reabsorption
The reabsorption of filtered molecules, i.e. H+ Na+, K+, ions from the glomerular filtrate in the tubules to the blood is called selective reabsorption.
67
what part of the glomerulus is permeable to water and which part is impermeable
the descending limb is permeable
the ascending limb is impermeable
68
how does selective reabsorption in the loop of henle take place
Sodium and chloride ions move out of the filtrate in the ascending limb of the loop of Henle into the surrounding medulla region, lowering its water potential
The movement of ions occurs by both diffusion and active transport
Diffusion takes place in the first part of the ascending limb
Active transport occurs in the second part of the ascending limb
The ascending limb of the loop of Henle is impermeable to water, so water is unable to leave the loop here by osmosis
The water potential in the ascending limb increases as it rises back into the cortex due to the removal of solutes and retention of water
The neighbouring descending limb is permeable to water, so water moves out of the descending limb by osmosis due to the low water potential in the medulla created by the ascending limb
The descending limb has few transport proteins in the membranes of its cells, so has low permeability to ions
The water potential of the filtrate decreases as the descending limb moves down into the medulla due to the loss of water and retention of ions
The water and ions that leave the loop of Henle for the medulla make their way into the nearby capillary network
69
what happens in the collecting duct and how does the role of ADH help with the water regulation in the
o The collecting duct passes through the medulla – through the salt bath created by the loop of Henle
o As the collecting duct passes through the low water potential salt bath in the medulla, water leaves the filtrate by osmosis – concentrating the urine and conserving water
o Water diffuses through special water channels in the cell membrane called aquaporins as well as through the phospholipid bilayer
o The number aquaporin channels can be controlled by the hormone ADH, so allowing the amount of water in the urine to be controlled.
70
what happens if there is high ADH
less urine (your body doesnt want to lose too much of water because the conditions are too salty
71
what happens if there is low ADH
more urine (already enough water in the blood so water is ok to secrete out)
walls of the collecting duct are less porous
72
why do kangaroo rats need adaptations
they live in a dry environment so they have to retain lots of water
73
what are the adaptations of the kangaroo rats
behavioural : live in burrows where the temp is lower
physiological : obtain a lot of their water from oxidation reactions rather than sources of drinking water
- long loop of henle
- lots of adh receptors
anatomical : they have lots of juxtamedullary nephrons (this means they have long loops of Henle with long descending limbs - which allows lots of water reabsorption); many microvilli and many mitochondria for effective respiration
74
why is the loop of henle so long
so that the water can be reabsorbed by osmosis (the salty conditions from the sodium and chloride ions from the descending limb makes the water move out by osmosis, so the process takes long)
75
where is adh made
pituitary gland
