Neuronal communication Flashcards
blurt: three neurone structures (53 cards)
1
Q
sensory neurone
A
transmits nerve impulses from a receptor to a relay neurone
2
Q
relay neurone
A
intermediates found entirely in the CNS that connect sensory and motor neurones
3
Q
motor neurones
A
transmits nerve impulses from relay neurones to an effector (muscle or gland)
4
Q
why is transmission of action potentials along the axon slower in the absence of saltatory conduction?
A
depolarisation must occur across the whole length of the axon rather than just sections between Shwann cells
5
Q
what features are found in all types of neurones?
A
- axon (long fibre)
- cell body with a nucleus + organelles
- axon terminal (end of an axon)
- nerve endings at the axon terminal
6
Q
what is a myelin sheath made up of?
A
- Schwan cells
- nodes of Ranvier (gaps)
7
Q
axon terminal
A
end of an axon that connects to other neurones, muscles or glands
8
Q
structure of motor neurones
A
- cell body at one end
- dendrites from the cell body
- long axon
9
Q
structure of relay neurones
A
- cell body at one end
- many dendrites
- shorter but highly branched axon
10
Q
structure of sensory neurones
A
- dendron from receptor cell
- cell body in the middle
- axon
11
Q
adaptations of neurone cell bodies
A
- many mitochondria
- many rough ER
to produce many neurotransmitters
12
Q
receptor cell
A
cell that responds to a stimulus
13
Q
five types of sensory receptors (and what is stimulus so they convert into electrical energy/transduce?)
A
- photoreceptors (light)
- chemoreceptors (chemicals)
- mechanoreceptors (kinetic in muscles)
- baroreceptors (kinetic in blood vessels)
- osmoreceptors (water potential)
14
Q
structure of Pacinian corpuscles (from inside out)
A
- end of sensory neurone
- connective tissue layers
- gel in between layers (containing Na+)
- blood capillary
- capsule
15
Q
steps in converting mechanical pressure into a nervous impulse (Pacinian corpuscles)
A
- neurone of the Pacinian corpuscle has resting potential
- pressure applied
- corpuscle changes shape
- neurone membrane stretches
- stretch-mediated Na+ channels present in the neurone membrane widen
- Na+ diffuse down an electric chemical gradient into the neurone
- membrane becomes depolarised
- initiates a generator potential
- generator potential creates an action potential that passes along the sensory neurone
16
Q
resting potential vs action potential
A
- electrical charges on either side of the cell plasma membrane are reversed
- during the resting potential, the inside of the cell is more negative than the outside
- during the action potential, the inside of the cell is more positive than the outside
17
Q
what three processes establish and maintain the resting potential?
A
- active transport of Na+ and K+ via a Na+/K+ pump
- passive diffusion of Na+ and K+ through permanently open ion channels
- diffusion through voltage-gated Na+ and K+ channels (which open and close in response to changes in local charges)
18
Q
how many of each ion does the Na+/K+ pump actively transport and where?
A
- three Na+ out of neurone
- two K+ into neurone
19
Q
differential membrane permeability (at resting potential)
A
- more K+ than Na+ channels open
- more K+ can diffuse back down their concentration gradient out of the axon at a faster rate than Na+
- increases positive charge on the outside of the neurone, increases potential difference
20
Q
why is the movement of an action potential along a neurone an example of positive feedback?
A
diffusion of Na+ stimulates the opening of more Na+ channels so more Na+ diffuse
21
Q
depolarisation steps
A
- if threshold potential is reached then an action potential is stimulated
- stimulus triggers some voltage-gated Na+ channels to open
- membrane becomes more permeable to Na+
- Na+ diffuse into the axon down their electrochemical gradient
- inside of the axon becomes less negative
22
Q
what happens when the potential difference reaches approximately +40mV
A
- voltage-gated Na+ channels close
- voltage-gated K+ channels open
23
Q
repolarisation steps
A
- voltage-gated K+ channels are open
- membrane is more permeable to K+
- K+ ions diffuse out of axon down their electric chemical gradient
- inside off the axon becomes more negative
24
Q
hyperpolarisation steps
A
- voltage-gated K+ channels are slow to close
- potential difference becomes more negative than the resting potential
- voltage-gated K+ channels close
(Na+/K+ pump and passive diffusion through ion channels restores the resting potential)
25
why is repolarisation an example of negative feedback?
as potential difference reaches a certain point (+40mV), voltage-gated Na+ channels close to decrease and reverse the potential difference
26
four factors that affect the propagation of action potentials
- myelin sheath
- diameter of axon
- temperature
- refractory period
27
how does the myelin sheath affect the propagation of action potentials and why?
- impulse jumps from one node of Ranvier to another
- only small sections of the axon must be depolarised rather than full length
- propagation speeds up
28
how does the diameter of axon affect the propagation of action potentials? (with two reasons)
- greater diameter, faster impulse speed
- thicker axons have an axon membrane with a greatest surface area which increases the rate of diffusion of ions
- thicker axons also process a great volume of cytoplasm which contains ions
- this reduces their electrical resistance so that an action potential can push into the next section faster
29
how does temperature affect the propagation of action potentials and why?
- higher temperature, faster rate of diffusion of ions, higher impulse speed
- too high temperature may denature proteins and stop propagation
30
what is the name given to transmission of nerve impulses through myelinated neurones?
Saltatory conduction
31
two parts of the refractory period and what are they?
- absolute refractory period - no new action potential can be initiated
- relative refractory period - action potential can be initiated if normal threshold has been exceeded
32
when does the absolute refractory period occur?
duration of depolarisation and repolarisation
33
when does the relative refractory period occur?
during hyperpolarisation
34
what causes Na+ to diffuse along the axon to depolarise the other sections?
Na+ or attracted by the negative charge on the inside of the neurone ahead
35
why are action potentials unidirectional?
- after one section of the neurone depolarises the next, the section behind it is repolarised then hyperpolarised
- this is a refractory period so an action potential cannot be initiated
- by the time the resting potential of that section has been restored, the action potential will be further down the neurone
36
three steps in the movement of an action potential along a neurone
- generation (first section depolarises)
- propagation (next section depolarises)
- refractory period (section behind hyperpolarises)
37
what causes the refractory period?
closure of both voltage-gated Na+ and K+ channels
38
what does the length of the refractory period determine?
maximum frequency to which impulses can be transmitted along neurones
39
purpose of the factory period
- insure action potentials in unidirectional
- ensure action potentials do not overlap and instead occur as discrete impulses
40
why is Saltatory conduction more energy efficient?
- Na+/K+ pumps require ATP to restore resting potential after each impulse
- in myelinated neurones, there are less places where pumps are being used
- reduces the amount of ATP required
41
what determines the strength of a stimulus?
frequency of nerve impulses (all or nothing principle)
42
why are synapses unidirectional?
- neurotransmitter containing vesicles only present in the presynaptic cleft
- neurotransmitter receptors only present on the post synaptic membrane
43
two types of summation
- spatial summation
- temporal summation
44
summation
build up of a neurotransmitter in a synapse to sufficient levels to trigger an action potential
45
spatial summation
- number of presynaptic neurones connect to one postsynaptic neurone
- neurotransmitters from all presynaptic neurones build up to a high enough level to initiate and action potential
46
temporal summation
- single presynaptic neurones releases neurotransmitters several times in quick succession
- build up in the synapse until the quantity is sufficient to trigger an action potential in the postsynaptic neurone
47
two types of neurotransmitter
- excitatory
- inhibitory
48
excitatory neurotransmitters
- result in the depolarisation of the postsynaptic neurone
- if threshold potential is reached in the postsynaptic membrane an action potential is initiated
49
example of an excitatory neurotransmitter
acetylcholine
50
inhibitory neurotransmitters
- result in hyperpolarisation of the postsynaptic membrane
- action potential is prevented from being initiated
51
example of inhibitory neurotransmitters
gamma-aminobutyric acid (GABA)
52
why does saltatory conduction require less energy?
- fewer sections of the axon are depolarised
- less energy is needed for the Na+/K+ pumps to restore resting potential
53
absolute vs relative refractory period
absolute refractory period - no stimulus can initiate an action potential
relative refractory period - only a much stronger stimulus can initiate an action potential
