Survival+ Response + Nervous Coordination Flashcards
Why do organisms need to respond to changes in their environment
Avoid harmful environments, competition, predators
Keep in a favourable environment (correct temperature/humidity)
Grow towards/away from a stimuli
Dispersing to find new mates
Kinesis
Movement is random
Rate in change of movement
Taxes and the 2 types
Movement is directional towards or away from a stimulus
Positive taxis- towards a stimulus
Negative taxis- away from a stimulus
Earthworms moving away from light
What behaviour is this
List advantages of this
More chance of survival in soil
Les likely to dehydrate
More likely to find food and avoid predators
Positive tropism
Growth towards a stimulus
Negative tropism
Growth away from a stimulus
E.g plants grow away from light
Roots grow into soil
More likely to absorb water and mineral ions
What does the nervous system involve
Fast or slow?
Detection of stimuli by receptors
Transmission of nerve impulses/electrical by neurones
Response by effectors
Rapid response
What does the endocrine system involve
Fast or slow?
Communication by hormones
Slower and longer lasting response
CNS
Brain+ spinal chord
Peripheral nervous system
Nerves that originate from brain/spinal chord
Different types of neurones
Sensory
Relay
Motor
Whats the potential difference at resting potential
Whys it negative?
-70mV
More positive ions outside the cell than inside so inside slightly negative compared to the outside
How resting potential established
📈 conc of potassium ions inside cell
📈conc of sodium ions outside cell
Sodium potassium pump
Pumps 3 sodium ions outside the cell
Pumps 2 potassium ions inside the cell
Requiring energy released from ATP
Active transport of sodium ions outside of neurone
Different permeabillity to K+ and Na+
Membrane more permeable to K+
Voltage gated channel proteins in Resting neurone
Sodium ion voltage gates channel proteins r closed
So sodium ions cannot facilitatedly diffuse back in
Some potassium ion channel proteins are open as
Membrane more permeable to potassium ions so diffuse
Membrane potential in depolarisation
-70mV to 40mV
Depolarisation
Stimulus causes the membrane to be more permeable to Na*
Membrane reaches threshold then all Na+ voltage gated channel proteins open
Higher conc of Na+ ions outside cell than inside
So Na+ ions facilitatedly diffuse in
Higher conc of Na+ ions inside cell reverses resting potential
K+ ion voltage gates channel protein remains closed
+40mV
Repolarisation
Na+ voltage gates channel proteins close and K+ voltage gated channel proteins open
Higher conc of K+ inside cell than outside
So K+ diffuse out cell down conc gradient
Hyperpolarisation
K+ channel protein remain open for longer
Causes potential difference to go to -90mV
Sodium potassium pump restores resting potential back to -70mV
All or nothing response
Action potential only occur when membrane reaches threshold so all Na+ channel protein open
Minimum intensity of stimulus is threshold
Sub threshold= no action potential
Above threshold= action potential given
Refractory period
Limits number of impulses per second
When maximum frequency reached no further increase in info
Time taken to restore resting potential
Impulse transmission along the axon
Nerve impulse is the movement of an action potential along neurone
Action potential act as stimulus to adjacent polarised areas of the membrane and this causes the action potential to be passed along
Synaptic transmission
Electrical impulses
Cannot jump the gap between neurones
Impulses transmitted between neurones across a synapse using neurotransmitters
Synaptic transmission
Unidirectional
Impulses are unidirectional from
Presynaptic neurone to post synaptic neurone
Neurotransmitters are only found in the presynaptic neurone and neurotransmitter receptor proteins are only found in the post synaptic membrane
How the synapse works
Action potential arrives at the synaptic knob in the presynaptic neurone and this causes Ca2+ voltage gated channel proteins to open
Ca2+ facilitatedly diffuse into synaptic knob as there is a higher conc in the synaptic cleft
Ca2+ activate enzymes which cause synaptic vesicles to move towards presynaptic membrane
Vesicle fuses with the presynaptic membrane releasing acetylcholine via exocytosis- requires ATP
Acetylcholine diffuses down a conc gradient across the cleft and binds to acetylcholine receptors in the post synaptic membrane as they are complementary
When it binds it causes Na+ channel proteins to open causing Na+ to diffuse in
If membrane reaches threshold then membrane becomes depolarised and action potential occurs (sub-threshold=no action potential)
In cholinergic synpase acetylcholinesterase hydrolyses acetylcholine into choline and ethanoic acid
Which diffuses across the synaptic cleft into preysnaptic neurone
Mitochondria releases Atp to resynthesises acetylcholine to be stored in vesicles in presynaptic neurone
Points to remember for synpase
Synapse wil delay impulse slightly
(Refactory period)
Synapses prevent impulse going in wrong direction
Neuromuscular junction
Synapse between a motor neurone and a muscle cell
Uses acetylcholine which binds to nicotinic cholinergic receptors
Differences between neuromuscular junction and cholinergic synpase
Neuromuscular junctions have more folds so larger SA so MORE acetylcholinesterase enzymes hydrolyse acetylcholine at faster rate
More receptors on post synaptic membrane
Action potential always triggers a response in the muscle cell
( not the case for a synapse between two neurones)
Summation
Whys it required
Two types
The build of neurotransmitters within the synapse
Sometimes the arrival of an impulse does not lead to sufficient release of enough neurotransmitters to depolarise the post synaptic membrane and generate action potential
Spatial
Temporal
Fatigue
If the rate of transmitter release is higher than the rate at which it is being reformed- fatigue
The pre synaptic neurone cannot release enough neurotransmitters to generate an action potential in post synaptic neurone
Excitatory neurotransmitters
They cause action potentials in post synaptic neurone by making the resting potential less negative so less Na+ required to reach threshold
Inhibitory neurotransmitters
Cause the resting potential to be more negative hyperpolarised
Post synaptic membrane less likely to reach threshold and generate action potential
The effects of drugs on synapses
2 ways
They can either
Stimulate nervous system by creating more action potentials- excitatory effect
They can create fewer action potential
Drugs may inhibit release of neurotransmitter or bind and block the receptors on post synaptic membrane
Why are nerve impulses able to transmit an electrical impulse
Because there is a difference in electrical potential across the membrane
Describe how inhibition if acetylcholineesterase affects action of synpase
Acetylcholine not broken down
Na+ continue to enter
Depolarisation continues. action potential
Myelination affects rate of conduction of nerve impulse
How
Depolarisation only occurs at nodes of ranvier
Fewer nodes
Binding of GABA causes Chloride ions to enter the post synaptic neurone
Explain how this inhibits transmission of nerve impulses
Neurone becomes more negative
More Na+ required to reach threshold
Depolarisation
Potential across the membrane is reversed when an action potential is produced
How
Na+ channel proteins open
Allowing Na+ to diffuse in
Leads to depolarisation
Other than temperature, give 2 other factors that affect speed of impusle
Myelination
Axon diameter
What happens when calcium ion channel proteins close
Leas diffusion of calcium ions into the synaptic knob of presynaptic neurone
Synaptic vesicles dont fuse w the presynaptic neurone
So dont release neurotransmitter
So neurotransmitter doesn’t diffuse across the synapse and bind to receptor on post synaptic membrane
No action potential
No depolarisation as sodium ion channels dont open
Damage to the myelin sheath of neurones can lead to problems controlling contracting muscles
Why
Action potentials travel slower
So muscles contract slower
Na+ + K+ can only cross through the axon membrane through proteins
Why
Cannot pass through phospholipid bilayer
Because not lipid soluble
After exercise some atp is used to re-establish resting potential
How
Sodium potassim pump
Sodium out potassium in
Student did not carry our repeats but was able to carry our statistical test
Why
Collected paired data
Resting potential -70mv to 0mV
After adding respiratory inhibitor
Why
Respiratory inhibitor so no ATP produced
No active transport of ions
No ner movement of sodium and potassium ions
Explain why the speed of transmission of impulses is faster along a myelinated axon than along a non-myelinated axon
Myelinated axon provides electrical insulation and saltatory conduction
Depolarisation only occurs at the nodes of ranvier
However in non-myelinated axon depolarisation occurs along whole length of axon
Features of axons that conduct impulses faster and why
Myelinated
Shows saltatory conduction
Large diameter so larger SA of channel proteins
Less resistance of flow of ions
Synapses ensure that nerve impulses only travel in one direction
How
Neurotransmitters only stored in presynaptic neurone
Neurotransmitter receptor proteins only found in post synaptic neurone
Simple reflex arc
Only involves 3 neurones
IAA in the shoots
Promotes cell elongation
IAA synthesises in the shoot tips and diffuses into the growing regions
Light causes movement of IAA from the light side to shaded side
Higher conc of IAA on the shaded side
Causes directional growth as there is greater cell elongation on shaded side
Shaded side grows faster and causes shoot to bend towards the light
IAA in the roots
Inhibits cell elongation
IAA synthesised in the root tips ans then diffuses into the growing regions
Light causes movement of IAA from light side to shaded side and towards gravity
Higher conc of IAA on the shaded side
Cell elongation inhibited on shaded side
Results in directional growth away from light and towards gravity
Binding of GANA causes chloride ions to enter post synaptic neurones
Explain how this inhibits transmission of nerve impulses
Neurone becomes more negatibe
More Na+ required to reach threshold
For ACTION POTENTIAL/DEPOLARISATION
