5.1 Neuronal Communication Flashcards
1
Q
where is a stimulus detected?
A
by a neurone
»»>This information is processed and a response is initiated
-animals react with electrical and chemical responses
2
Q
how does neuronal communication differ from hormonal communication
A
-much quicker and more targetted than hormonal
can be voluntary and involuntary and impulses are transferred at a synapse
3
Q
how does the nervous system transfer electrical signals locally between neurones
A
at a synapse
4
Q
why is cell signalling vital
A
to coordinate cellular activities which then ultimately affect whole organism
5
Q
what type of signal is released
A
electrical
6
Q
how does the electrical signal travel
A
transmission by neurones
7
Q
how long does the signal take in relation to hormonal responses
A
very fast!
8
Q
how long does the electrical signal last relative to hormonal
A
short lived
9
Q
where is the electrical signal going
A
to localised cells connected to neurone
10
Q
what is the cell body made up of
A
-contain DNA located in a nucleus and plentiful rough endoplasmic reticulum and mitochondria
this is so proteins can be modified and neurotramitters can be formed eg acetylcholine
11
Q
what do dendrons do
________________
what do they look like?
where do they recieve impulses?
A
- protrusions which form branches to other cells and divide into dendrites (smaller branches)
- they are INPUT synapses RECIEVING signals from axons of neighbouring neurones
12
Q
what are Axons?
how big?
A
long projections carrying signals AWAY from cell body
»>can be very long eg toes to spine
-they are 1um in diameter
13
Q
how fast does a neurone travel
A
100m/s
14
Q
where is myelin sheath found and why is it important
A
found inside schwann cells (a type of glial cell)
>many layers (around neurone) of cell membrane of schwann cell which are rich in lipid myelin
it insulates so that impulses travel faster and go to where they need to
15
Q
what are the nodes of ranvier
A
- they have no myelin sheath
- every 1-33mm on axon and 2-3um wide
- they are channels that generate elecrical signals
16
Q
what is a synapse
A
- axon terminal meets/adjacent to recieving dendrite on post synaptic neurone
- synaptic knob
- transmission changes from electrical signal to a chemical signal via neurotransmitter
17
Q
what are schwann cells
A
- they support neurones and make myelin
- they surround the axon
- protect and provide electrical insulation
18
Q
describe the structure of a schwann cell
A
- nucleus
- nerve fibre in the middle
- lipoprotein membrane forming myelin sheath
- fold of schwann cell around fibre
19
Q
what is saltatory conduction
how does myelin sheath help
A
- wave of depolarisation jumping from one node to the next node of ranvier
- myelin sheath improves insulation via sulatatory conduction
20
Q
what is a myelin sheath made up of
A
a phospholipid bilayer
21
Q
how does axon diameter effect speed of conduction
A
Larger diameter axons have a higher conduction velocity, which means they are able to send signals faster.
»»»This is because there is less resistance facing the ion flow.
The larger the diameter of the axon, the less likely the incoming ions will run into something that could bounce them back!
22
Q
what factors in the internal environment must be detected
A
- blood glucose
- cell pH
- temp
- water potential
23
Q
what factors in the external environment must be detected
A
- temp
- humidity
- new or sudden sound
- light intensity
24
Q
what are plant responses based on?
how does this differ with animal responses
A
- plants have chemical communication systems including plant hormones but have no nervous system
- animals have electrical responses by neurones and chemical by hormones
25
why is coordination needed
organisms muct be coordinated so functions of different specialised cells can operate effectively
>>>>few body systems can work in isolation
for example red blood cells need coordination as they have no nucleus so can't replicate but have vital role in transporting oxygen. They need constant supply of r.b.cells from haematopietic stem cells
muscle cells dependent on rb cells
26
example of coordination needed in plants
-flowering must coordinate w/ seasons and pollinators must coordinate w/ plants.
>>>in temperate climates like UK, light sensitive chemicals enable plants to coordinate the development of their buds w/ lengthening days that signal approach of spring/summer
27
why must organisms maintain homeostasis
to maintain a constant internal environment for metabolic processes to take place
>>>vital in organs to maintain homeostasis
28
what does cell signalling rely on
nervous+hormonal systems coordinate activities of organisms which rely on cell signally through release of chemicals which effect target cells
>>> neurotransmitters at neurones and synapses can stranfer electrical signal across distance using hormones eg) ADH to kidney cells
29
why must plants respond to their ext. environement
they dont have a nervous system
30
why are neurones not myelinated at CNS
(relay neurone)
| takes up too much space but does slow process
31
which neurones are unmylinated
relay
32
how do you usually identify a sensory neurone
cell body in middle
- has a dendron which is attached to receptor cells on skin
- one dendron one axon
33
how do you usually identify a motor neurone
- long axon which is connected to muscle cells
- dendrites but no dendron
- nissil granule nucleus
- nerve ending forms motor endplate in muscle
34
what is the order of neurones
sensory, relay, motor
silly rabbit moo :)
35
what do sensory neurones do
transmit electrical impulse from sensory receptor cell to relay neurone
36
how do you identify a relay neurone
- lots of short dendrites which carry impulse from sen. neurone to cell body
- lots of short axons to carry impulse from cell body to motor neurone
37
which neurones have a resting potential of -70mV
sensory and motor
38
which neurone transmits impulse from CNS
motor
39
which neurones connect to other neurones via synapse
sensory and motor
40
which neurones connect to effectors
motor
41
what are receptors and where are they usually found
detect a stimulus
- eyes (rods and cones have pigment which is bleached white) and skin (pacinian coruscles)
- found at either periphery ends of sensory neurones or separate specialised cells adjacent to sensory neurons
42
what do receptors do with energy
transduce it
they convert a stimulus eg light energy, to a generator potential
magnitude of this is determined by stimulus intensity
43
what is an action potential
an impulse
44
what is a generator potential
it creates a voltage
a bigger generator potential means bigger action potential
45
what is a resting potential
when neurone is at 'rest'
| positive charge outside membrane relative to inside
46
what is an action potential
- an electrical impulse when the charges are reversed
| - all or nothing principal (must be above threshold potential)
47
what is a generator potential
-produced when a receptor turns a stimulus into an impulse eg) light into electrical impulse
>>>magnitude of potential graded according to intensity of stimulus
mechanical deformation of cell membrane generates impulse in some as more ions go in (mechanoreceptors)
48
example of chemoreceptor
carotid
you can also get mechanoreceptors eg pacinian corpuscle, thermoreceptors and photoreceptors such as rods and cones
49
where are pacinian corpuscles found
most abundant in skin and mucus membranes
50
what is the structure of a pacinian corpuscle
- concentric lamellae of connective tissue (with viscous gel between)
- non mylinated at terminal of sensory fibre but mylin sheath on sensory nerve fibre
51
what do pacinian corpuscle detect
pressure
52
which ions cause an influx of a generator potential at a pacinian corpuscle
sodium ions
53
how do pacinian corpuscles result in an impulse
- pressure change in skin causes mechanical deformation of membrane
- this causes sodium ion channels to open and sodium ions to flow through channel
- generator potential varies depending on strength of stimulus and length of stimulus
- impulse created sent to sensory neurone
54
what does increasing intensity of stimulus have on
a) generator potential
b) action potential
a-increases intensity of stimulus
b-no difference in intensity/ all or nothing principle
55
why does deformation of plasma membrane cause membrane to become more permeable to Na+
causes sodium ion channels to open forming gaps in phospholipid bilayer
56
what are gated channels dependent on
particular membrane affecting agents to either open or close the gate. these can be ion specific
-ions need channels as cant diffuse through phospholipid bilayer
57
what do voltage gated channels do when on axon of neurones
- used for generation and propagation of action potentials
- they only open if certain potential difference reached. but voltage changes to potential across membrane can alter these gates.
58
where are mechanically gated ion channels found
- on dendrites of sensory neurones and sensory receptor cells
- the opening/close of them is dependent on mechanical deformation of cell membranes from pressures or vibrations eg) pacinian corpuscle.
-they provide organism with sensory input of their surroundings
59
what are ligand gated channels and where found?
| what modifies these channels
- found at cell bodies and dendrites
- hormones and neurotransmitters modify these channels for normal cell maintainance (neurotransmitter binds and channel opens)
60
what is the axoplasm
axon cytoplasm
61
what is the function of the axons phospholipid bilayer of plasma membrane
prevents Na+ and K+ ions diffusing across it
62
which intrinsic proteins are involved in axon plasma membrane
- gated ion channel for Na+ and K+ to move through them at some points but not others
- other channels to allow simple facilitated diffusion of ions across them
- some actively transport K+ into the axon and Na+ out of axon through sodium-potassium pump which requires ATP
63
neurones send messages______ which causes an electrical impulse
what else causes an electrical impulse
electrochemically
the movement of ions across axon membrane can create an impulse
64
what is an impulse in terms of potential difference
momentary reversal in electrical potential difference in the membrane causes DEPOLARISATION
-reversal travels from one end of neurone to other in fraction of second.
65
what is the neurone doing between impulses
'at rest' but still uses energy so not strictly true!
66
how is a wave of depolarisation created
when a nerve impulse called an action potential moves along length of axon
depolarisation caused when channels open causing a change in the membrane potential
67
what kind of channels occupy the length of an axon
voltage gated channels which open in response to a change in membrane potential
depolarisation at one point in axon triggers the openng of ion channelsin the next segment of the axon so depolarisation is spread along length of axon as undirectional wave
68
what is a electrochemical gradient
concentration gradient of ions
69
a nerve at rest is _____
| what is the resting potential
polarised
-70mV (the minus means polarised)
70
why must neurones be repolarised
so another depolarisation can take place and more action potentials can be created
71
explain how the resting potential is established and how it is maintained in sensory neurone
- active transport of sodium ions being pumped out of the cell and potassium ions being pumped in through sodium potassium channels which require ATP
- ions gradually concentrate on either side with 2 K+ions diffusing in and 3 Na+ diffusing out
- this gives the membrane a net positive potential relative to the inside with a net negative potential
- some K+ diffuse and leak freely back out of cell
- membrane less permeable to Na+ as few Na+channels open
- voltage gated channels closed
72
what is the action potential in mV
+40mV
73
describe the charges of inside cell during resting potential
net negative inside cell relative to outside cell
Positive outside
74
are voltage gated channels involved during resting potential
no as there is no impulse
75
the membrane is ___ permeable to sodium
less
| there are fewer sodium ion channels as we dont want as much sodium to get back in keeping net negative inside
76
more Na+ on the _____ and more K+ on the _____ of the membrane during resting potential
outside
| inside
77
what does the uneven distribution of ions during resting potential causes
Explain how resting potential reached through 4 points
1) fascilitated diffusion of K+ ions out via leaky channels
2)Na+ diffuse in via channels
>>>>but most Na+ channels closed as membrane more permeable to K+ flowing out than Na+ ions going in
3) more positive ions outside axon in tissue fluid than inside in cytosplasm
4) as inside more negative the membrane is polarised and resting potential created
78
what is the action potential voltage
+40mV
79
what does the energy of a stimulus do to voltage gated channels (depolarisation)
causes sodium ion volatge gated channels to openand the permeability of Na+ increases
80
true or false? during the action potential, sodium ions diffuse in through the axon membrane down an electrochemical gradient into the cytosplasm
what does this cause
true
causes axon cytoplasm to become less negative
81
what does the change in potential difference after an inpulse cause
what kind of feedback is this
causes further sodium ion voltage gated channels to open so more Na+ ions move in
positive feedback system
82
when does the moving in of sodium ions after an impulse continue until?
how long does this last
continues until the P.D reaches +40mV by depolarisation and reaches an action potential
>>> which lasts 2ms
83
what happens when action potential (40mV) reached
Think channels!
how has the charge inside changed at the end of this
voltage gated sodium ion channels close and the potassium ion channels open
this causes K+ ions to exit the cell down their electrochemical gradient into the tissue fluid which reduces the positive charge inside
84
large numbers of K+ ions diffuse out after action potential reached which causes ______
hyperpolarisation
this is where the axon is more negative inside than in resting state (remember how the graph goes below resting potential!)
85
what does hyperpolarisation cause
voltage gated potassium ion channels to close and so the resting potential is re-established by pump and fascillitated diffusion
86
what does the refractory period mean
can't recieve an action potential
- it isolates the impulse so each impulse is individual
- keeps current in one direction
87
at rest the axon membrane is ______
polarised
88
why do we need to repolarise the membrane behind area with action potential
(this is the role of K+ voltage gated channels) so it can happen again/ another action potential can be reached (isolates impulse) it resets back to resting potential by repolarising!! :)
89
which axons are usually non myelinated in human body
autonomic nervous system (saves space but conducts impulse more slowly)
90
what is a feature of dendrons and their branches dendrites which makes them specialised for their function
they give the nerve cell a large SA to link with other neurones via synapses
91
how does axons branched end aid their function
what is at the end of these branches and what happens here
increases SA for making synapses
synaptic knob >>> cell vesicles which make and release neurotransmitters are
92
why are there many mitochondria in the neurone
>>provide energy for acetylchloline synthesis
| >>and for maintaining sodium and potassium ion pumps needed for impulse transmission
93
what does the axoplasm contain and how is it adapted for its function
- streams between cell body and axon in both directions
| - it has microtubules and microfilaments made of the protein actin running through along axon in axoplasm
94
what is the function of the microtubules and microfilaments in the axoplasm
>>>help direct the streaming of the axoplasm from cell body to axon to help carry out transport in cell
>>> also act as cytoskeleton to maintain the cells shape
95
what are the Nissil Granules in the neurone
organelles conatining mitochondria, free ribosomes and rough endoplasmic reticulum which help with protein synthesis of the enzymes involved in impulse transmission
>>> they also help with the synthesis of trophic factors which regulate growth and differentiation of nervous tissue
96
describe the motor neurones is the autonomic nervous system
non-myelinated and slow conducting.
| >>>they supply smooth muscle in organs, cardiac muscle in heart and glands (no control over)
97
describe the motor neurones in the voluntary nervous system
myelinated and fast conducting
| >>> supply skeletal muscles
98
What is MS and how is it caused
- cause unknown
- where the nerve axon breaks down and in some cases the whole axon is destroyed
- thought to be an autoimmune disease where own T cells attack healthy nerve cells
- could be genetic
- could be due to persistent attempts to kill pathogen which damages myelin
99
What are the symptoms of MS
- blindness cause by lesions of optic nerve
- muscle weakness and loss of limb control and paralysis
- speech impairment
- abnormal nerve sensations
- dizziness
100
How is MS diagnosed
- made based on development of lesions to the myelin over both space and time
- often the fluid contains many antibodies and myelin base proteins
- detected inflammation using a CAT scan or thermal imaging/PET scan
101
What are the major obstacles to overcome when creating an MS vaccine
- T-cells of every patient are very different so producing a one size fits all vaccine will be difficult
- extracting and purifying individual patients cells is cells is time consuming and expensive
102
What is the all or nothing principal
Action potential only occurs if threshold potential reached allowing a sudden flood of sodium ions to enter cell
-if depolarisation not great enough to reach threshold potential than action potential not reached/produced
103
Stronger stimulus means...
More frequency of impulses carrying information
-action potentials are always the same size
-
104
What do receptors do to energy
Transduce the external energy of the stimulus into the code of the nerve impulse
>>>leads to formation of a receptor potential 😌 whose magnitude is determined by stimulus intensity
105
Which 2 things can sensory receptors be?
- either peripheral ends of sensory neurons
| - or, separate specialised cells adjacent to sensory neurons
106
What are exteroceptors
Respond to stimuli from external environment
107
What are enteroceptors
Respond to stimuli from the internal environment
108
What Are proprioceptors
Respond to tension within tendons and muscles
109
What do baroreceptors detect
Blood pressure
110
What is the function of a generator potential
- trigger an action potential in a sensory neurons
111
What do sensory receptors monitor?
Changes in either the external or internal environment
112
What kind of receptors are pacinian corpuscles and when are they found
Mechanoreceptors found in skin and certain mucus membranes
113
What do pacinian corpuscles respond to
Pressure or any kind of mechanical deformation of the receptor
114
What does the pacinian corpuscle consist of
Single sensory nerve fibre
Terminal region which is enclosed in multilayered connective tissue capsule
Myelinated nerve fibre -but terminal region is not myelinated and is within the central core of the pacinian corpuscle
-Concentric lammellae of connective tissue with viscous gel between
115
are voltage gated channels found in the nerve terminal of pacinian corpuscle (which is sensitive to mechanical compression)
where are the voltage gated sodium ion channels found in pacinian corpuscle
No- no voltage gated sodium ion channels found here
there are V-G Na+ channels present at NODES OF RANVIER in myelinated region of corpuscles nerve fibre
116
how are most generator potentials created
when stimulus triggers opening of sodium ion channels which results in depolarisation of receptor cell membrane
117
when does a stimulus actually cause the closing of the sodium ion channels unlike usual?
effect of light on photoreceptor cells of retina where stimulus triggers a closing of Na+ channels
>>>>and generator potential develops as receptor cells become MORE NEGATIVE
118
how can we record a typical action potential
HARDer so maybe just read
with a microelectrode penetrating a myelinated region of sensory neurone fibre, action pot. recorded on cathode ray oscilloscope in response to an adequate stimulus
If G.Pot. reaches thresh. Pot. it has sufficant strength to open Na+ V-gated channels at first node of sensory fibre
119
when pressure applied to pacinian corpuscle it causes _____ of the ____ ____ capsule and also ____ of the surface membrane of the non-myelinated portion of sensory neurone
_____-_____ sodium ion channels in surface membrane of pacinian corpuscle open and ___ diffuse into the neuron
deformation
connective tissue
stretch-mediated
sodium ions/ Na+
120
if there is no compression of pacinian corpuscle there is no....
no deformation of nerve ending
no generator potential
no action potential
unlike if there was
pretty self explanatory
121
which channels are open during repolarisation and which is closed
whats happening to the membrane potential
sodium ion channels closed
potassium channels open
the membrane potential is decreasing
122
when a neurone is at resting potentail....
describe the conc. of sodium and potassium ions
permeability of cell-surface membrane to Na+ ions
level of activity of Na+ K+ pump
low conc. sodium ions
high conc. of potassium ions
low permeability
active
123
why is the refractory period important
```
-resulted from HYPERPOLARISATION
it ensures that when there is a second stimulus there will be another action potential and ensures:
-action potentials are discrete
-action potentials dont overlap
-action potentials are unidirectional
```
124
which v-gated ion channels are closed during refractory period
Na+ channels inactivated during this time and additional depolarising stimuli don't lead to new action potentials
125
describe the propagation of nerve impulses as localised circuits
1))Overall net positive outside mem. and membrane is polarised w/ more Na+ outside
2)stimulus causes influx of ions, charge reversal on membrane, action pot reached DEPOLARISATION
3)localised circuit est. by influx of Na+ causes depolarisation and behind this Na+ channels close and K+ open and leave down EC grad.
4) action pot. propogate along axon in 1 direction
movement of K+ out means membrane behind action pot. is repolarised
5) after repolarisation axon mem. returns to resting pot. for another stimulus
126
how does myelination affect conductions rates
speeds up rate of conduction as it insulates axons and helps assemble nodal molecular organisation
127
how does axon diameter affect conductions rate
bigger axon diameter faster the impulse as less resistance to flow in cytoplasm and it gives a larger surface area too
128
how does temperature effect conductions rate
higher temps conduct faster nerve impulse
due to ions diffusing faster at high temps.
>>>generally occurs up to 40 degrees as too high dentaures proteins such as Na+/K+ pump
129
why does a squid need a giant axon
connects to water jet propultion system which allows it to rapidly escape predators. thickness of neurone transmits faster as larger number of electrons flow through at any one time so dont need myelin
>>>survival benefits!
130
how efficient is saltatory conduction
more energy efficent
saltatory conduction makes more efficient as repolarisation needs ATP in Na+ pump so reduces the amount of repolarisation needed
131
where does depolarisation occur
myelinated axons >>>depolarisation can only occur at node of ranvier
here Na+ pass through protein channels in membrane
132
where do longer localised circuits arise
how is saltatory conduction involved
why is it faster than wave of depolarisation across whole membrane
between 2 adjacent nodes where action pot. jumps from one node of ranvier to another through saltatory coduction
much faster as everytime channels open and ions move it takes time so reducing number of places where this happens speeds action potential transmission
133
what is a synapse
junction between neurones and involved in the chemical transmission in form of neurotransmitters and consists of pre and post synaptic neurone
134
how big is a synaptic cleft and what is it
20-30nm wide gap
| separates the neurones
135
where does the impulse arrive at a synapse
where recieves neurotransitter
presynaptic neurone (sensory)
postsynaptic neurone
136
what is the synaptic knob
what does it have many of
swollen end of presynaptic knob
has many:
mitochondria and RER
137
what do the synaptic vesicles contain
contain the neurotransmitter
138
where do the vesicles diffusing over synapse bind
to receptors on the post synaptic membrane
| specific protein molecule receptors
139
why are mitochondria abundant at synapse
active transport as pumps need energy and moving vesicles through cytoplasm needs energy as well as making molecules (anabolism) requires energy
140
why are there lots of ribosomes at presynaptic neurone
packaging vesicles at Golgi and also synthesis of proteins
141
when will the ligand gated protein channel open on post-synaptic membrane
wont open unless acetylcholine binds and changes tertiary structure
142
what is the role of synapses
- ensure unidirectional flow as receptors are only present on post synaptic membrane
- allow an impulse from one neurone to transmit to a number of neurones at multiple synapses (single stimulus creates multiple simultaneous responses
- allow a number of neurones to syanpse with a single postsynaptic neurone so stimuli from different receptor cells produce a single result
143
what is a choligenic synapse
Each cholinergic synapse is a miniature transducer that converts a presynaptic electrical signal into a chemical signal (acetylcholine), which diffuses across the synaptic cleft, where it triggers another electrical signal on the postsynaptic side by interacting with acetylcholine receptors.
144
why do calcium ions enter neurones from the tissue fluid
what process do they use to move in
because inside is less positive than outside due to depolarisation
move in by diffusion in presynaptic knob
145
what is found w/in synaptic vesicle
what effect do calcium ions have on synaptic vesicles
neurotransmitters such as acetylcholine
fuse w/ presynaptic membrane
>>> Ca2+ triggers synaptic vesicle exocytosis, thereby releasing the neurotransmitters contained in the vesicles and initiating synaptic transmission
146
how are vesicles moved w/in cell
which structures are involved in this
which other organelles are required to support this movement
exocytosis
mitochondria and cytoskeleton
mitochondria for ATP, plasma membrane, Golgi Ap. and RER
147
what is exocytosis
fusion of vesicles w/ cell surface membrane
148
what are the receptors on post synaptic mem. made of
what allows them to span the membrane
how do they achieve this specificity
glycoproteins
intrinsic proteins
specific 3D shape/ tert. struct
149
what does the binding of neurotransmitters to postsynaptic neurone do
causes conformational change to 3D shape and tert struct
150
why are enzymes found in post synaptic cleft
to break down neurotransmitters and prevent impulse carrying on
151
where are cholinergic neurones found and what gives them this name
where motor neurone and muscle cells meet
>>>>they use neurotransmitter acetylcholine
152
how is unidirectional transmission of impulses achieved
- only receptors of post synaptic membrane
- acetylcholine is broken down at post. syn. membrane
- only presynaptic membrane contains acetylcholine
- only presynap has Ca2+ channels which help with exocytosis
153
what can't occur if a toxin was to bind to the receptors on the post syn. mem. eg) atropine
due to competitive inhibition action potential can't be reached as acytlcholine can't bind to post syn mem. so....
sodium ions can't enter and depolarisation doesn't occur and threshold not reached
atropine used as antedote to nerve gas and prevents constant stimulation to nerve cells!
154
what does depolarisation of presynaptic membrane cause
Ca2+ channels to open!
| >>>> so calcium ions diffuse into presynaptic knob and causes vesicles to fuse w/ membrane!!
155
what kind of gated channels are the Na+ ion channels on the post synaptic membrane
ligand gated
156
what does the diffusion of Na+ into post synaptic membrane cause
triggers ACTION POTENTIAL! and impulse is propagated along the post synaptic neurone and the post syna. mem. depolarised
157
what do excitatory neurotransmitters do
trigger depolarisation which increases the liklihood of a response!
eg) Noradrenaline
they do this by opening ligand-gated sodium or calcium ion channels
158
what do inhibitory neurotransmitters do
trigger hyperpolarisation decreasing the liklihood of a response
eg) Gaba
they do this by opening ligand gated potassium or chlorine channels
159
what is dopamine
pleasure neurotransmitter
160
what is noradrenaline
concentration neurotransmitter
161
what is sertonin
a mood neurotransmitter
162
what kind of neurotransmitter is acetylcholine
learning neurotransmitter
163
what are small changes in the membrane potential aka
graded potentials
| a threshold pot must be reached for action pot
164
what is the threshold pot
-55mV
165
what is summation
the combination of graded potentials in the post synaptic neurone
166
the sum of excitatory post synaptic potentials (EPSP) and inhibitory post synaptic potentials (IPSP) determines......
whether nervous pathways will be activated or not
as EPSPs trigger depolarisation and therefore action potential in post syn. mem whereas IPSPs trigger hyperpolarsation in post syn. mem
167
describe what is meant by spatial summation
where EPSPs generated by MULTIPLE presynaptic neurons simultaneously to reach threshold
EPSPs of different synapses aren't strong enough to to individually generate action potential but by reinforcing one another can generate action potential (ADD TOGETHER TO REACH THRESHOLD)
must be noted that EPSPs and IPSPs cancel out
so if A was going up on graph and C went down (hyperpolarise) then no action pot reached
168
describe what is meant by temporal summation
Temporal summation occurs when multiple subthreshold EPSPs from one SINGLE neuron occur close enough in time to combine and trigger an action potential at the axon hillock.
-Can occur with IPSPs
-can occur because post. syn. pot. last longer than action potentials
>>> Postsynaptic potentials last for approximately 4 millliseconds.
169
what is the difference between Spatial and Temporal summation
Temporal summation occurs when a single pre-synaptic neuron fires many times in succession, causing the post-synaptic neuron to reach its threshold and fire.
Spatial summation occurs when excitatory potentials from many different pre-synaptic neurons cause the post-synaptic neuron to reach its threshold and fire.
170
In terms of summation: _______ the stimuli cannot evoke a response but ______ they can
this determines whether or not....
individually
collectively
an action potential can be triggered by combined effects of postsynaptic potentials
171
drugs that stimulate the nervous system are called
agonists
172
drugs that inhibit nervous system are called
antagonists
173
name the ways a drug can affect a synapse
- increase number of impulses
- release neurotransmitters from vesicles w/ or w/out impulses
- block reuptake or block receptors
- produce more/ less neurotransmitters
- prevent vesicles from releasing Neurotransmitters
174
when do drugs switch on synapse
- mimicing a neurotransmitter
- stimulate release of Neurotrans.
- open a neuroceptor protein channel
175
when do drugs switch off a synapse
- block neuroreceptor protein channel
| - inhibit breakdown of enzyme
176
when do drugs stop action potentials
-when they block Na+ or K+ channels
