nervous controll Flashcards
1
Q
what is the function of nerve cells
A
transmit signals around the body
2
Q
what are the adaptations of a nerve cell
A
- large amount of RER - make proteins and neurotransmitters
- dendrite to connect with other nerve cells
- axon long to carry electrical impulses quickly
Schwan cells made of fat and insulate axon. can also carry out phagocytosis and help nerve regeneration. Make up myelin sheath. Gaps called nodes of ranveir - lots of mitochondria for AT
3
Q
what 2 states can a nerve be found in
A
- resting potential
- action potential
4
Q
which is an active process resting/action potential?
A
resting potential state
5
Q
explain how cell achieves resting potential
A
- sodium ions pumped out of cell
- same time potassium ions pumped in (for every 3 sodium ions, only 2 pumped in )
- mroe sodium outside, chemical gradient
- small number of ions move through membrane by facilitated diffusion through specific channel proteins. There are more channel proteins specific to K+ then Na+ ions
- net result of these ions movements is that mroe positive ions outside the neurone then inside - leading to resting potential fo -70mV (polarised)
6
Q
how does the cell achieve action potential
A
- stimulus received by cell - membrane depolarised - action potential
- energy from stimulus causes voltage gated channel open allowing sodium diffuse in
- sodium diffuses in, mroe channels open -> more sodium ions
- once cells reached +40mV, gate closes and pot ions gates open
- Pot ions diffuse out of cell - repolarise
- cell then re-polarises as before, during refractory period no mroe action pot can be produced
7
Q
how is an action potential passed on in an unmyelinated axon
A
when action potential starts; like chain reaction in an unmyelinated axon
- at rest. More Na+ outside cell. More K+ inside. Axon polarised. Overall -ve
- stimulus cuases Na+ rush in to axon and membrane depolarised
- localised circuit continues along axon. Areas behind closing Na gates and openeing Pot gates
- action potential moves along axon, areas behind become poalrised
- Na+ actively pumped out to bring cell back to restiating state/pot
8
Q
how is the action potential passed on in a myelin sheath
A
- instead action pot moving at steady pace, moves in localised cirucits instead
- along axon gaps (nodes of ranvier) action pot only occur at these points as myelin sheath - insulator
- action potential jumps from node to node - quciker
9
Q
what method is the transmittion of action potential myelin sheath known as
A
saltatory conduction
10
Q
what affects the speed of an action potential
A
- myelin sheath (x3 faster)
- diameter of axon (greater dimater - faster - less leakage
- temperature - greater temp - faster ROD (resp controlled enzymes, higher temp faster AT)
11
Q
why is it important to have a refractory period after an action potential?
A
- ensures impulses is uni-directional
- makes action potentials discrete - compeltely seprate from each other
- limits number of action potentials
- strength of stimulus can therefore be determined by freuqnecy of nerve impulses, not the size of impulse as this does not change
12
Q
where is a synpase found
A
between end of neurone and effector
13
Q
what happens during the pre synaptic period?
A
- voltage gated calcium channels open
- causes influx of Ca2+ into cell
- increase in Ca2+ causes vesicles containing the neurotransmitter to fuse with pre-synaptic membrane causing the contents to be released by exocytosis
- neurotransmitter then floods the synaptic cleft and diffuses across
14
Q
what happens in the post synaptic membrane
A
- when ach released in synaptic cleft binds to specific regiosn on the channel
- binding causes a conformational chnage and wihtin a few ms, the channel opens allowing Na+ to pass into the post synaptic cell
- the influx of Na+ causes the cell to become depoalrised and initates an action ptoential
- this type of neurotransmitter said to be excitatory
- some neurotransmitters (GABA) allow Cl- to move into cell instead, opposite effect said to be inhibatory
15
Q
what is found in abundance on the post-synaptic memebrane
A
transmitter-gated ion chanel
16
Q
what does an inhibitory transmitter do
A
make action ptoentials less likely as they make membrane more negative
stimulu needs to be even bigger to exceed threshold
17
Q
what does acetlycholine do
A
found at neuromusuclar junctions mainky used in voluntary nervous system
18
Q
what is a synpase that uses Ach called
A
cholinergic synpase
19
Q
how are neurotrasmitter removed from synatic cleft to allow another round of synaptic transmittion?
A
- simple diffusion
- others use proteins in synaptic cleft to trnamsport the neurotransmitetr back into pre-syaptic neurone where it is either broekn down or re-packaged redy for use again
20
Q
what enzyme makes Ach inactive
A
Acetlycholinesterase
21
Q
what is summation
A
sometimes action ptoential is quite weak and does not cuase enough neruotransmitter to be released to intiate an action potential in the post synaptic neurone or effector
22
Q
what 2 types of summation are there
A
- spatial
- temporal
23
Q
descirbe spatial summation
A
2 or mroe neurones terminate at the same synapse
on their own do not release enough neurotranmitter to intiate action potential
but together release enouhgh
24
Q
what is temporal summation
A
action potential occurs at high frequency causing neurotransmitter to build up in the synaptic cleft
allows the quanitity to build above the threshikd causing an action potential in post synaptic neurone
25
what are corpuscles
receptor respond to mechanical pressure
| mainly in the skin
26
how do pancian corpuscles work
when pressure applied
sodium channel streched and open
allowing sodium ions diffuse causing a generator potential
size of generator potential proportional to size of stimulus
if the generator potential is higher that the threshold value action potential started
27
how do drugs effect synaptic transmission
some have similar shape transmitter bind to protein receptor on post synaptic membrane causing sodium channels open - action pot
some similar shape to transmitter and block protein receptors on post synaptic preventing transmitter
28
HOW DO RODS WORK
light hits rod cell, breaks down rhodopsin found on lamellea
chemical bleeachedas it is broken down into retinal and opsin.
This breakdown results in a series of events which results in an action potential. As the light intensity is very low for this to occur, it may not necessarily result in an action potential in the next cell (called a bipolar cell).
The chemical is then reformed to its unbleached form, which requires many mitochondria.
Rhodopsin can be broken down at very low light intensity, and as many converge onto one sensory neurone, it doesn’t take much to generate an action potential.
However, as a consequence, it is often difficult to distinguish between 2 light sources which reduces the visual acuity.
This means images appear blurred when only the rods are used.
29
who do cones work
Come in three types- blue, green and red
• They contain a different pigment (iodopsin) which can only be broken down in a high light intensity
• As each cone cell usually only attaches to one bipolar cell, it gives a much greater visual acuity.
• Each cone only responds to a specific light wavelength
• Cones cannot be used in low light intensities as it would not be enough to break down the Iodopsin chemical.
• Cones give a greater visual acuity, so they are found in high concentrations in the fovea.
30
why are rods able to see in low light
many rod cells (up to 45) are connected to a single bipolar cell.
Dim light only breaks down small amounts of rhodopsin in each cell. Individually this would not be enough to initiate an action potential.
• However the combined amount of pigment being broken down in numerous rod cells will be enough to produce a generator potential that exceeds the threshold value, causing an action potential.
This is spatial summation.
31
why do cones have little light sensitivity
Cone cells are each connected to a single bipolar cell and therefore have little sensitivity
32
what is visual acuity
Visual acuity is the ability of the eye to resolve two stimuli separately.
It is the property of cone cells which are each connected to a single bipolar cell.
This means that each cone cell generates separate action potentials.
• To be resolved the light from the objects must land on two cones separated by at least one unstimulated cone.
• Rod cells have poor visual acuity because many rod cells converge on a single bipolar cell.
This means that light from two objects may strike two rod cells separated by unstimulated rod cells but only a single action potential would be sent to the brain and only one object would be seen.
33
How does nervous control of the heart work
.Cardiac muscle is myogenic is contraction is initiated from within the muscle itself , rather than by nervous intervention
As wave of electricity from SAN hits the AVN it causes another wave of the electricity to spread down special fibres called the bundle of his which runs between the ventricles.
The wave is conducted down the Bundle of His to the base of the septum where it branches into smaller fibres called purykne fibres.
34
what does the sympathetic system do
speeds things up
35
what does the parasympathetic system do
speeds things down
36
what pathway from the brain to the heart does nervous control come from
The cardioacceleratory centre tells the SAN to send out electrical waves more frequently, which would speed up the heart. Using the sympathetic nervous system more to send impulses to SAN.
The cardioinhibitory centre tells the SAN to send out electrical waves less frequently. Using the parasympathetic nervous system more.
37
what does the pH receptors do in blood
pH - Chemoreceptors
- Found in wall of carotid artery and detect changes in pH
- When the pH falls, chemoreceptors increase the frequency of messages to the medulla oblongata
- Sympathetic nerves tell the heart rate to increase
- Increase of blood flow causes the pH to return to normal
- Chemoreceptors decrease the frequency of messages and the heart rate returns to normal
38
what does the blood pressure receptors do
Blood pressure - Pressure receptors
Also in the wall of the arteries are pressure receptors which detect changes in blood pressure
- when BP is too high, send messages to medulla oblongata which sends messages to SAN via parasympathetic nervous system to heart slow down
- opposite happens when BP is too low this time using sympathetic nervous systems
