nerves Flashcards
what is the peripheral nervous system composed of
spinal nerves, cranial nerves and their roots and branches
what is the central nervous system composed of
the brain and spinal cord
give the general reflex arc
stimulus–> sensory neurone–>relay neurone–>motor neurone–>effector (muscle/gland)
whats the difference between endocrine and nervous responses
endocrine responses are slower but last longer, it involves hormones being released into the bloodstream (affecting target organs)
why is the white matter white
contains myelinated neurones, lipids
why is the grey matter grey
contains many nuclei, cell bodies and non-myelinated neurons
what is the middle of the spinal cord called
central canal
what is the swelling called before the white matter, that contains a cell body (and what’s it called on the lower side)
dorsal root ganglion, ventral root
what does the dorsal root ganglion hold
cell bodies of the sensory neurones
give an example of a nerve net
hydra
give some characteristics of hydra
- sensory receptors respond to a limited range of stimuli
- number of effectors is small
- contains one type of nerve cell
- signal travels in many directions
- unmyelinated
what is the degree of response in hydra dependent on
the strength of the stimulus and how many receptors are stimulated
name parts of the motor neurone starting from the cell body
cell body, dendrites, myelin sheath, axon, nodes of Ranvier, synaptic end bulb (axon terminals)
what is resting potential
-70mV
how is potential difference represented
oscilloscope
describe resting potential
- sodium potassium pump using ATP actively transporting 3 Na+ out of the neurone and 2 K+ into the neurone.
- potassium ion channels are leaky and K+ ions pass out of the axoplasm by facilitated diffusion
- sodium ion channels are closed so sodium ions remain outside
what makes the neurone -70mV
- large plasma proteins and organic phosphates in the cytoplasm (negative)
- ion movement (3 Na+ out and 2K+ in)
what happens after a stimulus is applied to the axon
the permeability of the membrane to sodium ions increases = sodium ions open
what’s the result of the sodium ion channels being opened by a stimulus
sodium ions diffuse into the axon through the channels (reducing the potential difference)
what value is threshold
-55mV
what happens to the sodium ion channels once passed threshold
all sodium ion channels open = full action potential is generated = sodium ions RAPIDLY diffuse into the cell
what happens if the threshold (-55mV) is not reached
the sodium ion channels close and resting potential restores quickly
value for depolarisation
+40mV
describe what happens in depolarisation
sodium ions rapidly diffuse into the cell, which changes the potential difference from -70mV to +40mV
describe the all or nothing law
the action potential is either generated if the threshold level is reached or not if it isn’t
how are different strengths of stimuli differentiated
number of action potentials per second (not by size)
what’s it called when you return to resting potential from the action potential (depolarisation)
repolarisation
what occurs in repolarisation
potassium ions leave the axoplasm by facilitated diffusion (travel down concentration gradient and potential difference falls quickly)
what is the overshoot after repolarisation called
hyperpolarisation
what occurs in the refractory period
hyperpolarisation (potential difference lower than resting potential) – keeps the transmission from travelling in one direction
why does the refractory period make the transmission travel in one direction
during an action potential & repolarisation, further action potentials are not possible = keeps the transmission along the axon moving in one direction as the part of the membrane immediately behind an action potential is still repolarising and cannot be stimulated to respond
what type of conduction can occur in myelinated neurones
saltatory conduction
explain saltatory conduction
due to the Schwann cells, the action potentials are only generated at the nodes of Ranvier, so the action potential ‘jumps’ from one node to the next
give 2 advantages of myelinated vs unmyelinated
- faster conduction (100m/s vs 1m/s)
- sodium potassium pump only operates at the nodes, so less ATP is used in myelinated neurons
give 3 factors that affect transmission rates in axons
- diameter of the axon (wider=less resistance therefore faster)
- higher temperatures
- myelination
what is the synapse
where 2 neurons meet/ motor neurone meets an effector
name the parts of the synapse (generally)
synaptic knob, mitochondria for ATP, presynaptic neurone, vesicles containing transmitters, post synaptic neuron, synaptic cleft
describe the first step in synapse (acetylcholine)
when a wave of depolarisation reaches the axon terminal, calcium ion channels in the membrane of the synaptic knob
describe the second step in synapse (acetylcholine)
the calcium ions stimulate the vesicles containing neurotransmitter to move to the presynaptic membrane and fuse with it
describe the third step in synapse (acetylcholine)
neurotransmitter is released into the synaptic cleft by exocytosis (requires ATP)
what does the neurotransmitter do after it diffuses across the synaptic cleft
binds to ligand gated receptors on the post synaptic membrane = sodium ion channels open on the post-synaptic membrane so sodium ions diffuse into the cell = depolarisation
what do the enzymes do in the synaptic cleft
it breaks down the neurotransmitter and take the products back to the synaptic knob (to be resynthesised and packaged into vesicles)
what prevents the simultaneous transmission of impulses (3 things)
- enzymes (transport of products
back to synaptic knob) - active transport of calcium ions out of the synaptic knob (prevents vesicles releasing neurotransmitter simultaneously)
- reabsorbing the neurotransmitter back into the synaptic knob
give 4 ways in which antagonists may work
- preventing calcium ion channels opening
- preventing exocytosis
- blocking receptors
- causing hyperpolarisation of post-synaptic membranes (so it’s harder to reach threshold)
give 3 way in which agonists may work
- inhibiting the enzymes (like acetylcholinesterase) that break down neurotransmitter
- causing more exocytosis; preventing uptake of neurotransmitter from the cleft
- mimicking the effect of neurotransmitter by linking to the receptors
what’s the enzyme called in the example of synapses (acetylcholine)
acetylcholinesterase
