3.8 nervous system Flashcards
label spinal cord
label neurone
resting potential
words to remember
-sodium potassium pump
-70mV (more positive outside than inside) 3Na out/ 2K in
-Diffusion/closed channel
-K+ diffuse x20 faster
-more positive inside than outside
action potential
words to remember
-70mV to +40mV
-depolarisation
-stimulus
-Na sodium channels open
-Na flood in to the axon
40 mV peak
words to remember
-more positive out than in
- maximum Na in the axon
-sodium gates close
repolarisation
words to remember
- K gates open
-K+ flood out the axon - less positive in the axon, more positive out the axon
-return to rp - sodium potassium pump
hyperpolarisation
words to remember
- below -70mV
- delay in closing gates
- return to rp
- NA/K pump
what does the nervous system do
allows us to respond to changes in the environment
what is a stimulus
any detectable change in the internal or external environment of the organism
what do specialised receptor cells do
act as transducers as they detect energy in one form and convert it to electrical energy
what do the electrical energy that travels along neurones travel as
a nerve impulse
role of nerve impulse
initiate a response in an effector which is always a muscle/gland
what is the nervous system composed of
nerve cells or neurones
what is the CNS composed of
the brain and spinal cord
what does the CNS do
processes information provided by a stimulus and co-ordinates a response
what is the PNS made up of
neurones
2 parts of the PNS
the somatic nervous system
autonomic nervous system
somatic nervous system:
is made up of pairs of nerves, branching from the brain and spinal cord, these neurones carry impulses from receptor cell to the CNS and then from the CNS to the effectors
autonomic nervous system
provides unconscious control of the internal organs
e.g. breathing and heartbeat
what are neurones
highly specialised cells which carry nerve impulses in one direction
3 neurones
sensory neurone
relay neurone
motor neurones
sensory neurone
also afferent neurone
carries messages/ nerve impulses from receptors to the brain or spinal cord
relay neurone
also interneurone
found in the CNS (brain and spinal cord)
relays messages from sensory neurone to the motor neurone
draw and label motor neurone
motor neurone
also efferent neurone
relays messages from the brian or spinal cord (CNS) to the muscles and organs (effectors)
what does a dendrite do
carries impulses towards the cell body
what’s an axon
long fibre that carries impulses away from the cell body
what’s the node of ranvier
a region of exposed cell membrane which can be depolarised
and they speed up transmission
what are synapses
the produce neurotransmitters
what’s the name for all the schwann cells wrapped around the axon
myelin sheath
what are Schwann cells
they produce the fatty myelin sheath which provides electrical insulation
how do Schwann cells act as an insulator
the plasma membrane becomes extended, lipids prevents movement of NA+ and K+ ions into and out of the nerve fibre so acts as an insulator
what is the cell body
it contains the nucleus, most organelles, nerve fibres extending from its dentrites
Nissl’s granules
what are Nissl’s granules
groups of ribosomes and rough ER for protein synthesis and mitochondria
what organisms have nerve nets
invertebrates such as jellyfish and hydra
compare a nerve net with a mammalian nervous system
-nerve net has shorter neurones which branch in all directions (vertebrates have longer neurones which branch in one direction - axon)
- impulse travels slower and in all directions but in vertebrates the impulse travel quicker and in one direction
- nerve nets only have one type of neurone, in mammals there are three
hydra nervous system
simple nervous system, have a network of neurones called ganglia but no brain, neurones have no myelin sheath,
hydra have no recognisable CNS and fewer types of receptor cells so can only respond to a limited number of stimuli. they can’t detect the direction of a stimulus but will initiate a greater response if the intensity of the stimulus is higher
parts of the spinal cord that i need to know
meninges
sensory neurone
relay neurone
motor neurone
grey matter
dorsal root ganglion
dorsal root
ventral root
white matter
central canal
where is the spinal cord
from the base of the brain to the lumbar region
what’s the spinal cord protected by
vertebrae
central canal:
contains a fluid with nutrients, same fluid as in the brain
grey matter:
contains cell bodies (more dense) and synapses
containing mainly relay neurones
white matter:
contains axons (less dense)
surrounded by myelin
what makes white matter white
the myelin
which way does the dorsal root go
into the CNS
which way does the ventral root go
away from the CNS
dorsal root:
holds the sensory neurone
has a swelling called the dorsal root ganglion
ventral root:
holds the motor neurone
dorsal root ganglion
holds the cell body of the sensory neurone
meninges
is the protective layer on the outside of the spinal cord
what is potential difference
difference in charge between 2 points
what is the refractory period
the whole time where the neurone cannot be re-stimulated because the channels are recovering
how to describe a reflex=][#’
fast automatic and protective
other reflexes
examples
blinking to protect the eye
contraction of the iris to reduce the amount of light hitting the retina
need to be able to draw the neuroness onto an outline of the spinal cord
reflex arc
example of one
stimulus (camel)
receptor (eyes)
sensory neurone
relay neurone (didn’t think about it)
motor neurone
effector (muscles in leg)
response (running away)
difference in reflex arc when voluntary and involuntary
when voluntary= no relay neurone
when involuntary= relay neurone as it is a shortcut
explain how a withdrawl reflex would work
stimulus may be heat from a fire, receptor cells in skin act as a transducer, nerve impulse travels around S neurone to the spinal cord (via dorsal root)
impulse passes to R neurone and then to M neurone. the nerve impulse exits the spinal cord along the M neurone (via ventral root) to the muscle (effector) when the impulse reaches the muscle it contracts to pull arm away from heat
what is happening at resting potential in aneurone
the potential difference between in side and outside the axon is a minus value (-70mV in humans) this is because it is more positive outside the axon than inside (the membrane is polarised)
how is the axon more positive outside than inside (At resting potential
- ions are actively transported against their electrochemical gradient by sodium-potassium pumps, ATP is used
3 NA+ ions removed from the axon for every 2 K+ ions taken up - most of the channels allow ions to leak through by diffusion. K+ ions diffuse back out of the axon 20 times faster than NA+ ions
- higher concentration of negative ions inside the axon than outside
explain the generation of an action potential
changes from -70mV to +40mV, this polarity change is called an action potential, the membrane of the axon is depolarised
why does an action potential happen
due to a sudden increase in permeability of the membrane to NA+ because the NA+ volted gated channels open allowen a sudden influx of NA+ which depolarises the membrane
how does the generation of an action potential happen
a stimulus causes slight depolarisation which causes sodium channels to open suddenly because they open when as a response to a change in charge. Na+ flood in by diffusion
number of positive ions inside increases so axon is further depolarised
what is needed to maintain a resting potential and what is it produced by
ATP produced by lots of mitochondria that are present in the axon
explain the 40mV peak
here the potential difference across the membrane becomes positive (more+in acxon)
+40mV meant theres the maximum number of Na+ ions that can enter the axon
the sodium gates start to close
explain repolarisation
after Na+ gates begin to close K+ gates open (due to depolarisation of axon membranes)
K+ flood out of the axon
inside of axon becomes less positive
returns to original resting potential
what helps axon return to original resting potential
sodium potassium pump will be working to help this happen, trying to get to -70
2K out 3 NA in
explain hyperpolarisation
where it’s more negative than the original resting potential (below -70 mV)
why does hyperpolarisation happen
there’s a slight delay in closing all the K+ gates, will return to resting potential due to Na+/K+ pump working normally after the K+ gates close
why is hyperpolarisation useful
it ensures the action potential only flows in one direction as the region behind has not recovered
why does the axon need to return to -70
for the neurone to be stimulated again
what is the threshold potential
-50mV
if depolarisation doesn’t reach -50mV then no action potential is created
what is the law of all or nothing
if the intensity of a stimulus is below -50mV no action potential will be generated
why is having a threshold potential important
each action potential is separate, no overlapping of potentials
this ensures that potentials only go in one direction
what does the size of the stimulus mean
it doesn’t affect the speed of the action potential but affects the frequency of the action potential (more per second)
what are the factors affecting the speed of transmission
temperature
diameter of axon
myelination
how does temperature affect the speed of transmission
increase kinetic energy, speeds up transport of ions so speeds up nerve transmission
how does the diameter of the axon affect the speed of transmission
greater the diameter the lower the resistance to the movement of ions so speed of nerve transmission will be higher
how does myelination affect the speed of transmission
Schwann cells wrap around the axon and secrete a fatty myelin sheath. only the Nodes of Ranvier become depolarised. the action potential can jump from node to node and speeds up transmission. the greater the distance between the nodes means a greater rate of transmission
what is saltatory conduction
where Na+ ions jump from node to node
only happens in long neurones, not relay neurones as they’re too short
what is a synapse
a junction between two neurones or between a neurone and an effector e.g. a muscle
able to draw and label a synapse
a chemical synapse
cholinergic synapse
neurotransmitter we need to know for cholinergic synapse
Acetylcholine
how are neurotransmitters released
released from pre-synaptic membrane by exocytosis
how is exocytosis able to happen
receptor proteins on post synaptic membranes are complementary to part of the neurotransmitters
roles/ function of synapses
allow the interconnection of many nerve pathways
act as jinctions
prevents over stimulation
determine the direction of nerve impulse transmission
ensure one way transmission
how do synapses prevent over stimulation
by filtering out low level stimulation (depolarisation must reach -50mV at the post synaptic membrane )
explain synaose transmission
when an action potential reaches the synaptic membrane (synaptic knob) Ca+ channel open, Ca+ enter the synaptic knob. synaptic vessels (containing neurotransmitters) migrate towards the presynaptic membrane and fuse with it, acetylcholine released by exocytosis. the neurotransmitter diffuses across the synaptic cleft and binds to receptor proteins on the post synaptic membrane, opening Na+ channels and Na+ will flood into the post-synaptic neuron. if enough Na+ enters the post synaptic neuron an action potential will be generated
what is aceytlcholine
a neurotransmitter
why can acetylcholine not be left in the cleft
it would continue to initiate new impulses in the post-synaptic membrane
how is acetylcholine prevented from being left in the cleft
direct uptake of the neurotransmitter into the post-synaptic neuron so there is none left in the cleft
2. active transport of calcium ions out of the pre-synaptic knob so no more acetylcholine is released into the cleft
3. acetylcholinestrase enzyme hydrolyses the acetylcholine into ethanoic acid and choline
what is the synaptic knob
swelling at the end of the pre-synaptic neuron
special features of the synaptic knob
- many mitochondria- active process needing ATP is involved
2.a large amount of smooth ER
3.vesicles of a chemical called acetylcholine (diffuses across the membrane - voltage-gated calcium ion channels in the membrane
explain how acetylcholine (ACh) is recycled
1.ACh broken down by acetylcholinesterase after it has bound with postsynaptic membrane. broken down into ethanoic acid and choline.
2.this is reabsorbed back into the presynaptic vesicle
Ca2+ ions are actively transported out of synaptic knobs
what affect can drugs have on synaptic transmission
either amplify or inhibit them
how is the pre-synaptic neuron affected by drugs that amplify synaptic transmission
- acceleration neurotransmitter production in the synaptic knob (cocaine)
- opening calcium channels in the pre-synaptic membrane
-accelerating the release of neurotransmitters from the synaptic knob by exocytosis
-blocking the removal or recycling of neurotransmitter substance from the synaptic cleft back into the synaptic knob (cocaine)
how is the pre-synaptic neuron affected by drugs that inhibit synaptic transmission
inhibiting neurotransmitter production in the synaptic knob
closing calcium channels in the pre-synaptic membrane
inhibiting the release of neurotransmitter from the synaptic know by exocytosis
how is the post-synaptic neuron affected by drugs that amplify synaptic transmission
making the post-synaptic receptors more sensitive to the neurotransmitter
opening the sodium channels on the post synaptic membrane
inhibiting cholinesterase activity in the synaptic cleft
mimicking the neurotransmitter substance (Cannabis)
how is the post-synaptic neuron affected by drugs that inhibit synaptic transmission
making the post-synaptic recptors less sensitive to the neurotransmitter
closing sodium channels on the post-synaptic membrane
increasing cholinesterase activity in the synaptic cleft
masking the effect of the neurotransmitter substance
blocking receptors on the post-synaptic membrane
what chemicals have an affect on synapses
nicotine
botulinum toxin
organophosphorus insecticides
nerve gas
cocaine
what affect does organophosphates have on transmission
they inhibit the action of acetylcholinesterase
ACh continually stimulates post-synaptic membrane
what is organophosphorus
in flea sprays and cat collars
it;s dangerous in large amounts
affect of cocaine
psychoactive drug
affects CNS by targetting different neurotransmitters or their receptors
it accelerates the production of neurotransmitters
