Co ordination of response Flashcards
what do receptor cells do
send signals via either the nervous system or the hormonal system to the brain or spinal cord
what is CNS
the brain and spinal cord
what is PNS
all of the nerves in the body
how is information sent through nervous system
in the form of electrical impulses known as neurones
what are hormone/chemical messengers produced by and carried by
chemical substances produced by endocrine glands and carried by the blood
what do hormones do
transmit information from one part of an organism to another and bring about change by altering the activity of one or more specific target organs
why are hormones used to control functions that don’t need instant responses
Hormones are slower in action than nerve impulses
what do endocrine glands do
secrete hormones directly into the blood
how can endocrine glands be stimulated
by the action of another hormone or by the arrival of a nerve impulse
what is found in all types of neurones
axon
axon terminal containing nerve endings
cell body
what is the structure of an axon
long fibre
what does cell body contain
nucleus and other cellular structures
what does nerve ending at the axon terminal allow
neurones to connect to and receive impulses from other neurones, forming a network for easy communication
what does myelinated mean
axon is insulated by a fatty layer known as the myelin sheath
what is a myelin sheath made up of
specialised cells known as Schwann cells which wrap themselves around the axon
what are nodes of ranvier
uninsulated gaps between the Schwann cells
how do electrical impulses moved in myelinated cells
jump from one node to the next, speeding up impulse transmission
in non myelinated neurones is the axon insulated by Schwann cells
no, the impulse travels more slowly as it moves through the entire length of the axon
what does sensory neurone do
carry impulses from receptors to the brain and spinal cord in the CNS
where are relay neurones found
found entirely within the CNS and connect sensory and motor neurones
what do motor neurones do
carry impulses from the CNS to effector muscles or glands
describe structure of motor neurone
A large cell body at one end that lies within the spinal cord or brain
highly-branched dendrites extending from the cell body, providing many connections with the axon terminals of other neurones
structure of relay neurone
Short neurones with axons and highly branched dendrites
structure of sensory neurones
A cell body that branches off in the middle of the axon
The dendrites are attached to a receptor cell
The section of neurone that links the axon terminal with the cell body is known as a dendron
The section of neurone that connects the cell body with the CNS is the axon
what does CNS do
acts as a coordinating centre for the impulses that arrive from the receptors, determining which part of the body needs to respond and sending out a new set of impulses along motor neurones
what does motor neurone do
send impulses to the effectors to bring about a response
what do circular muscles contract to do
constrict the pupil, limits the amount of light entering the eye and prevents damage to the retina
what do radial muscles do
contract to dilate the pupil, maximises the amount of light entering the eye, improving vision
charge inside a resting (transmitting no impulses) axon and why?
always has a negative electrical potential compared to outside the axon
The difference in charge between the inside and outside of the neurone is due to different numbers of ions on each side of the neurone cell surface membrane
- membrane is polarised
-70mv
what two factors contribute to establishing and maintaining resting potential
The active transport of sodium ions and potassium ions
A difference in membrane permeability to sodium and potassium ions
what do sodium potassium pumps in cell surface membrane and what does this do
use ATP to actively transport sodium ions (Na⁺) out of the axon and potassium ions (K⁺) into the axon
The two types of ions are pumped at an unequal rate; for every 3 sodium ions that are pumped out of the axon, only 2 potassium ions are pumped in
This creates a concentration gradient across the membrane for both sodium ions and potassium ions
why can potassium ions inside neurone diffuse out at a faster rate
The neurone membrane is less permeable to sodium ions than potassium ions
This results in more positive ions on the outside of the neurone than on the inside, generating a negative charge inside the neurone in relation to the outside
at what point is neurone membrane polarised
Once resting potential is reached
what needs to happen to membrane for a nerve impulse in neurone to be initiated and how does that occur.
the membrane needs to be depolarised
when an action potential is generated; lead to the reversal of resting potential from around -70 mV to around +30 mV
what exactly is action potential
rapid movement of sodium ions and potassium ions across the membrane of the axon
An action potential is the potential electrical difference produced across the axon membrane when a neurone is stimulated
when do voltage gated ion channels close
when the membrane is at rest, but they are involved in the generation and transmission of action potentials
what occurs when neurone is stimulated
A small number of sodium ion channels in the axon membrane open
Sodium ions begin to move into the axon down their concentration gradient
This reduces the potential difference across the axon membrane as the inside of the axon becomes less negative
what happens when threshold potential is met (-55)
more sodium ion channels open, leading to a further influx of sodium ions
when is action potential only initiated
if the threshold potential is reached
when is the membrane said to be depolarised and action potential has been generated
Once the charge has been reversed from -70 mV to around +30 mV
what happens as soon as action potential is generated
all the voltage gated sodium channels in this section of membrane close
what is opened after voltage gated sodium channels are closed
Voltage gated potassium channels in this section of axon membrane now open
what does opening of voltage gated potassium channel allow (repolarisation)
diffusion of potassium ions out of the axon down their concentration gradient causing inside of the axon to become negatively charged again, a process known as repolarisation
in resting potential where is it more negative
the inside of the axon always has a negative electrical potential compared to outside the axon
during the refractory period what happens
The membrane is unresponsive to stimulation so a new action potential cannot be generated at this time
This makes the action potentials discrete events and means the impulse can only travel in one direction
what happens when repolarisation ends
The voltage gated potassium channels then close, and the sodium-potassium pumps work to restore resting potential
when can membrane be stimulated again
Only once resting potential is restored
what does depolarisation of membrane at the site of the first action potential cause
hint - The action potential is said to move along the axon in a wave of depolarisation
sodium ions to diffuse along the cytoplasm into the next section of the axon, depolarising the membrane in this new section, and causing voltage gated sodium channels to open
triggers another action potential in this section of the axon membrane
This process then repeats along the length of the axon
why cant sodium ions that diffuse backwards along the membrane initiate a new action potential
due to the hyperpolarised nature of the membrane
when will a impulse be transmitted
if the initial stimulus is sufficient to increase the membrane potential above a threshold potential
how can stimulus size be detected by the brain
as the intensity of a stimulus increases, the frequency of action potentials transmitted along the neurone increases
why is speed of conduction slow in unmyelinated neurones
depolarisation must occur along the whole membrane of the axon
By insulating the axon membrane myelin increases the speed at which action potentials can travel along the neurone
can depolarisation occur in sections of the axon that are surrounded by myelin sheath membrane
depolarisation cannot occur, as the myelin sheath stops the diffusion of sodium and potassium ions
where can action potential occur
at the nodes of Ranvier - the gaps between the Schwann cells that make up the myelin sheath
what is saltatory conduction
Saltatory conduction allows the impulse to travel much faster than in an unmyelinated axon of the same diameter
The action potential therefore appears to ‘jump’ from one node to the next
where do sodium ions diffuse along the axon
within the Schwann cells and the membrane at the nodes of Ranvier depolarises when the sodium ions arrive
how can it be possible to design medication that prevent impulse transmission
drugs may bind to sodium ion channels, preventing them from opening and therefore preventing an influx of
sodium ions when an axon is stimulated
Preventing sodium ion influx prevents membrane depolarisation and an action potential cannot be generated
where are synapses found in sense organs
between sensory receptor cells and sensory neurones
where are synapses found in muscles
between motor neurones and muscle fibres
what is the gap between neurones called
synaptic cleft
what is the neurone before the synapse known as and its structure
presynaptic neurone and has a rounded end known as the synaptic knob
where are neurotransmitters contained
within vesicles in the synaptic knob
explain synaptic transmission
when an action potential arrives at the end of the axon of the presynaptic neurone….
the presynaptic membrane becomes depolarised, causing voltage gated calcium ion channels to open
Calcium ions diffuse into the synaptic knob via calcium ion channels in the membrane
The calcium ions cause vesicles in the synaptic knob to move towards the presynaptic membrane where they fuse with it and release chemical messengers called neurotransmitters into the synaptic cleft by exocytosis
what happens when neurotransmitters diffuse across synaptic cleft
bind with receptor molecules on the postsynaptic membrane; this causes associated sodium ion channels on the postsynaptic membrane to open, allowing sodium ions to diffuse into the postsynaptic cell
what happens if enough neurotransmitter molecules bind with receptors on postsynaptic membrane
an action potential is generated, which then travels down the axon of the postsynaptic neurone
what does generation of action potential depend on
whether or not threshold potential is reached, which in turn depends on the number of action potentials arriving at the presynaptic knob
what does a large amount of neurotransmitters allow at presynaptic knob
many sodium ion channels to open
Many sodium ion channels opening will allow a large influx of sodium ions, increasing the likelihood of threshold being reached
why are neurotransmitters then broken down
to prevent continued stimulation of the postsynaptic neurone
explain movement of Ach after presynaptic vesicles fuse with membrane
diffuse across the synaptic cleft and bind with receptor molecules on the postsynaptic membrane
sodium ions diffuse through and postsynaptic membrane is depolarised ACh is broken down into Acetate and Choline and Choline is recycled into ACh
what are three things synapses allow
one-way transmission of impulses
Divergence: One neurone can connect to several other neurones at a synapse, allowing nerve signals to be sent in several directions from a single presynaptic neurone
Amplification of nerve signals by summation as
a single impulse that arrives at a synaptic knob may be insufficient to generate an action potential in the post-synaptic neurone
- effect of multiple impulses can be added together to overcome this known as summation
how can summation be achieved
Several presynaptic neurones converging to meet a single postsynaptic neurone
Many action potentials arriving at a postsynaptic knob in quick succession
what are receptors
specialised cells that can generate an electrical impulse in a sensory neurone when stimulated by a particular stimulus
where does light focus in the eye
what muscle controls how much light enters the eye
region of the retina called the fovea
muscles of the iris
what focuses the light
the lens, the shape of which is controlled by ciliary muscles attached to the lens by suspensory ligaments
where are rod cells located
what are rod cells sensitive to
colour of images by rod cells
outer retina
sensitive to light intensity so can detect presence and brightness of light
black and white images
where are cone cells located
what are cone cells sensitive to
colour of images by cone cells
grouped together in the fovea
Sensitive to different wavelengths of visible light and so detect colour
how are action potentials generated in photoreceptor transmitted to the brain
via the optic nerve
The optic nerve leaves the back of the eye from a region known as the blind spot
what do photo receptors in the eye generate when stimulated by bright enough light or by light of a particular wavelength
action potentials
what pigments do rod cells contain and explain what happens when light hits the pigment
light-sensitive pigment called rhodopsin
When light hits rhodopsin it breaks apart into constituent parts retinal and opsin
The breaking apart of rhodopsin is known as bleaching
what does bleaching of light sensitive pigments cause
a chemical change in the photoreceptor that results in the generation of a nerve impulse
Nerve impulses travel along a bipolar neurone to the optic nerve, which carries information to the brain
how are rod cells different to other nerve cells
rather than initiating an action potential when they are depolarised,
rod cells initiate action potentials in neighbouring bipolar neurones when they are hyperpolarised
in the dark what occurs inside rod cells
Sodium ions are actively pumped out of rod cells, generating a concentration gradient
Sodium ions diffuse back down this concentration gradient into the rod cell via sodium channels
there is little difference in charge between the outside and inside of the rod cell, and the cell is said to be depolarised
In reality the inside of the rod cell is slightly negative in comparison to the outside
The depolarised rod cell releases neurotransmitters which diffuse across a synapse to a bipolar neurone
Rather than initiating an action potential in the bipolar neurone this neurotransmitter inhibits the generation of an action potential, preventing a nerve impulse from being sent to the optic nerve
This neurotransmitter is said to be an inhibitory neurotransmitter
what happens inside rod cells in the light
Light bleaches rhodopsin, causing it to break apart into retinal and opsin
The bleaching of rhodopsin causes the sodium ion channels in the cell surface membrane of the rod cell to close, preventing sodium ions from diffusing back into the rod cell
The lack of positively charged ions entering the rod cell causes its interior to become more negative until it reaches a hyperpolarised state
The hyperpolarised rod cell stops releasing an inhibitory neurotransmitter, so the generation of an action potential in the neighbouring bipolar neurone is no longer inhibited
An action potential is generated in the bipolar neurone attached to the rod cell and an impulse is sent to the optic nerve
how can plants respond to stimuli
altering their growth (tropism)
where are growth factors produced
in the growing parts of a plant before moving from the growing regions to other tissues where they regulate cell growth in response to a directional stimulus
example of growth factor and what it does
auxin is a growth factor that stimulates cell elongation in plant shoots and inhibits growth in cells in plant roots
what is the role of these plant hormones
gibberellin
cytokines
absicisic acid (ABA)
and ethene
Stem elongation / Flowering / Seed germination
Cell growth and division
Leaf loss / Seed dormancy
Fruit ripening / Flowering
what is IAA (Indoleacetic acid)
a type of auxin
brings about plant responses such as phototropism by altering the transcription of genes inside plant cells
Altering the expression of genes that code for proteins involved with cell growth can affect the growth of a plant
what is IAA produced by
cells in the growing parts of a plant before it is redistributed to other plant tissues
what is redistribution of IAA affected by
environmental stimuli such as light and gravity, leading to an uneven distribution of IAA in different parts of the plant
This brings about uneven plant growth
where does transport of IAA over long distances occur
in the phloem
what happens if concentration of IAA isnt uniform across stem
then uneven cell growth can occur
where does IAA move when light shines on a stem
IAA is transported from the illuminated side of a shoot to the shaded side
An IAA gradient is established, with more on the shaded side and less on the illuminated side
The higher concentration of auxin on the shaded side of the shoot causes a faster rate of cell elongation, and the shoot bends towards the source of light
what is the response called in shoots/roots
shoots phototropism
roots geotropism
how does IAA concentration affect cell elongation
higher concentrations result in a lower rate of cell elongation
as IAA is transported towards the lower side of plant roots
The resulting high concentration of auxin at the lower side of the root inhibits cell elongation
As a result, the lower side grows at a slower rate than the upper side of the root, causing the root to bend downwards
what is the flowering in plants controlled by
stimulus of night length
When the nights reach a certain length, genes that control flowering may be switched on or off, leading to the activation or inhibition of flowering
Genes that are switched on are expressed, leading to production of the polypeptides for which they code, while genes that are switched off are not expressed, so the polypeptides for which they code are not produced
what is Pr
inactive form of phytochrome, it absorbs light from the red part of the spectrum
what is phytochrome
photosensitive leaf pigments which are used by the plant to detect periods of light and darkness.
what is Pfr
active form of phytochrome, it absorbs light from the far red part of the spectrum
What happens:
when Pr absorbs red light
when Pfr absorbs far red light
toPfr , In the absence of red light
it is converted into PFR
it is converted back to Pr
gradually converts back into PR
what happens to Pfr during the day
During the day levels of PFR rise
Sunlight contains more wavelengths at 660 nm than 730 so the conversion from PR to PFR occurs more rapidly in the daytime than the conversion from PFR to PR
what happens to Pr during the night
During the night levels of PR rise
Red light wavelengths are not available in the darkness and PFR converts slowly back to PR
what happens in long day plants and why
high levels of the active form of phytochrome activate flowering
Days are long so PR is converted to PFR at a greater rate than PFR is converted to PR
The active form of phytochrome, PFR, is present at high levels
High levels of PFR activate flowering
PFR activates expression of genes that stimulate flowering
The active gene is transcribed and translated
The resulting protein causes flowers to be produced rather than stems and leaves
how does low serotonin levels in an individual affect the transmission of impulses in the brain
serotonin is a neurotransmitter / there will be less neurotransmitter (1)
(less serotonin) results in fewer
depolarisations of post synaptic membranes (1)
threshold not achieved / less chance of action potential being produced
how does nicotine cause an action potential in the post synaptic neurone that released noradrenaline
nicotine similar in shape to acetylcholine
increases permeability of membrane to sodium ions / changes shape of (receptors / channel proteins } (1)
nicotine causes the depolarisation of the post-synaptic membrane (1)
depolarisation reaches threshold level (1)
process that occur at synapse that leads to habituation
(repeated stimulus) decreases {sensitivity / permeability} of pre-synaptic membrane / calcium channels not opening
(1)
so {fewer / no} Ca?+ ions move into pre-synaptic neurone
(1)
so {fewer / no} vesicles {move towards / fuse with} (pre-synaptic) membrane
(1)
so {less / no} neurotransmitter {released / can diffuse across gap}
(1)
{action potential / depolarisation} less likely to occur in post-synaptic neurone
role of sodium ions in the functioning of mammalian rod cell
sodium ions are pumped out of the rod calls.
in the light they do not move back into the rod cell
in the dark sodium ions move back into rod cells
in light when the sodium ions dont move back into rod cell they are hyperpolarised and in the dark they are depolarised when sodium ions move back in
explain how IAA affects growth
it diffuses from the tip of the …
taken up by cells in the zone of elongation
causing cells to elongate
leads to lowering in pH of cell wall
causes the … to grow towards the light
explain effect of light intensity on current produced by rod cell
increasing light intensity decreases the current (1)
- because (rhodopsin is broken down / opsin is released} (1)
- therefore, more opsin binds to the channel proteins in the outer segment (1)
- sodium-gated voltage channels close (1)
- (reducing / stopping) the influx of sodium ions / making membrane impermeable to sodium ions (1)
Explain what happens at the synapse to cause a decrease in saliva production
when the child was shown a cheeseburger on more than six occasions.
reduced permeability of presynaptic membrane to calcium ions / fewer calcium ions enter the pre-synaptic neurone (1)
(so fewer) vesicles { move towards / fuse with } the presynaptic membrane (1)
(therefore) less neurotransmitter binds to receptors on the post-synaptic membrane (1)
action potential may not occur in the post-synaptic neurone / membrane may not be depolarised (1)
role of dendrites
{ form synapses / connections } with other neurones (1)
{ integrate / receive } impulses from other neurones (1)
involved in summation
{ propagate a signal / initiate an action potential } to the {cell body / axon?
compare contrast structure of sensory and motor neurones
Similarities
* both have a cell body containing a nucleus (1)
* both have an axon (1)
- both have dendrites at one end of neurone and terminal branches at the other end (1)
Difference - location of cell body (1)
describe the interaction of the muscles in the eye that led to the dilation of the pupils
- antagonistic (interaction) of muscles (1)
- in the iris (1)
radial muscles contract and circular muscles
relax (1)
explain why the neurone gets hyperpolarised
potassium ions (continue) leaving the {axon / cytoplasm} (1)
* (therefore) preventing another depolarisation occurring / it is the refractory period (1)
* allowing time for the neurone to reset (1)
* so that nerve impulses travel in one direction only (1)
describe the process that occur at a synapse that lead to habituation
(repeated stimulus) decreases {sensitivity / permeability} of pre-synaptic membrane / calcium channels not opening
(1)
so {fewer / no} Ca?+ ions move into pre-synaptic neurone (1)
so {fewer / no} vesicles {move towards / fuse with} (pre-synaptic) membrane
(1)
so {less / no} neurotransmitter {released / can diffuse across gap}
(1)
{action potential / depolarisation} less likely to occur in post-synaptic neurone
