Year 13 - Survival and response, nervous coordination Flashcards
(15 cards)
How does movement of IAA impact plant growth in the shoots and roots?
Shoot:
- Shoot tip produces IAA
- IAA moves by diffusion away from light
- More elongation of cells where there is a higher concentration of IAA
- Shoot grows towards light (positive phototropism)
Root:
- Root tip produces IAA
- IAA moves by diffusion to lower side of root
- Inhibition of elongation of cells where there is a higher concentration of IAA
- Results in more elongation of cells in lower conc of IAA so roots grow downwards (away from light)
Name the different types of stimuli a receptor may respond to.
Light, pressure, touch, temperature, chemical, noise, smell
Why do nerve impulses only travel in one direction?
- NT only made in and released from pre-synaptic neuron
- Complementary NT receptors are only on post-synaptic membrane
- NT packaged into vesicles that are in the pre-synaptic neuron
Describe saltatory conduction and compare myelinated vs non-myelinated.
- Schwaan cells produce myelin that acts as an electrical insulator, causing saltatory conduction
- Hydrophilic Na+ and K+ ions can’t diffuse over this part of the membrane
- Depolarisation only occurs at nodes of ranvier so impulse jumps node to node
- Non-myelinated neurons transfer nerve impulse by depolarising next section of the membrane, occuring along the whole length of the neuron
- Therefore, nerve impulse is faster in myelinated neurons.
Describe resting potential.
- Higher concentration of K+ inside and higher concentration of Na+ outside membrane
- Both K+ and Na+ voltage gated channels shut
- Axon membrane more permeable to K+ so some diffuse out
- Na+/K+ pump actively transports 3 Na+ out and 2 K+ in
- So resting potential is maintained at -70mv across axon membrane
Describe depolarisation
- Threshold potential (-55mv) reached so maximal response due to the all or nothing principle
- Na+ voltage gated channels open increasing axon permeability to Na+
- Na+ enter by facilitated diffusion
- More Na+ channels open so positive feedback as potential becomes more positive
- Leading to depolarisation
- Membrane potential changes so it is positive (+40mv)
Describe a reflex arc and state their advantages
A three neuron (sensory neuron, interneuron, motor neuron) that provide a pathway along which action potentials are transmitted from a receptor to an effector without involving ‘conscious’ regions of the brain.
- Rapid and automatic adjustments to the environment
- Protect against damage to body tissues
- Do not have to be learnt
- Enable homeostatic control
Describe 3 factors that speed up the transmission of a nerve impulse.
Myelinated axon so saltatory conduction.
larger diameter so less resistance to flow of ions.
Higher temperature so faster diffusion of ions through channel proteins
Describe repolarisation
Na+ (voltage gated) channels close at +40mv.
K+ (voltage gated) channels open increasing axon membrane permeability to K+.
K+ leave by moving from a high concentration to low concentration by facilitated diffusion .
leading to repolarisation.
Describe the refractory period
K+ (voltage gated) channels open so membrane potential becomes more negative than resting potential.
Na+ (voltage gated) channels closed.
Is in refractory period so further away from threshold
requires greater stimulation to cause depolarisation
Important in producing discrete impulses and limiting frequency of impulse transmission
Describe events at a synapse that allow for transmission of nerve impulse
Depolarisation of presynaptic membrane at presynaptic knob causes Ca2+ channels to open
Influx of Ca2+ by facilitated diffusion into synaptic knob.
Cause synaptic vesicles to move to and fuse with presynaptic membrane
Releasing (named) neurotransmitter that diffuses across synaptic cleft.
Binds to complementary receptors on post synaptic membrane.
Opens Na+ channels on post synaptic membrane so Na+ enters by facilitated diffusion
Causing depolarisation of postsynaptic membrane
Action potential produced
Importance of removing/recycling/breaking down neurotransmitters in synaptic cleft
If not removed, NT’s continue to bind to the receptors, keeping Na+ channels open so Na+ diffuse in causing depolarisation of the post-synaptic membrane.
Why do nerve impulses only travel in one direction?
Neurotransmitter only made in and released from pre-synaptic neuron
Neurotransmitters are packaged into vesicles that are in pre-synaptic neuron (do not write in membrane)
Complementary neurotransmitter receptors are only on post-synaptic membrane
Describe how an inhibitory synapse works
Inhibitory neurotransmitter (GABA) binds to it’s post-synaptic receptor
Opens Cl- channels and Cl- enters by facilitated diffusion.
Opens K+ channels so K+ leave by facilitated diffusion. (not often required)
Inside of post-synaptic neuron becomes more negative so is hyperpolarised.
Needs increased stimulation to open more Na+ channels
So More Na+ required to enter to reach threshold for depolarisation so action potential is less likely
Suggest why a named drug can be used to treat a disorder caused by too much NT
Has similar shape/(tertiary structure if protein) as named NT
Complementary to binding site on receptor on post-synaptic membrane.
Binding of named drug to receptor does not lead to Na+ channels opening
It blocks receptor so named NT can’t bind to receptor and open Na+ channels.
So threshold is not reached -> no depolarisation of post-synaptic membrane -> no Action potential in post-synaptic neuron.
