Nerves Flashcards
1
Q
What are the subdivisions of the nervous system
A
- CNS: Brain, Spinal cord
- PNS: Autonomic (symoathetic/parasympathetic/enteric), Somatic
See diagram
2
Q
Lable parts of brain (name them)
See sheet for diagram
A
- Meninges
- Gyrus vs. sulcus
- Cerebellum
- Cerebrum- frontal lobe, temporal lobe, parietal lobe, occipital lobe
- Diencephalon- thalamus, hypothalamus
- Brainstem- midbrain, pons, medulla oblongata
3
Q
Number of pairs of spinal nerves
A
31
4
Q
give the arrangement of spinal nerves
A
- 8 cervical (although 7 vertebrea)= neck, shoulders and arms
- 12 thoracic= chest and abdomen
- 5 lumbar= hips and legs
- 5 sacral= genitalia and gastrointestinal tract
- 1 coccygeal
5
Q
Lable the spinal chord cross section
A
See diagram
6
Q
Nerve afferent
A
Sensory info (go in)
7
Q
Nerve efferent
A
Motor (go out)
8
Q
What is grey matter/what makes it grey
A
cell bodies
9
Q
Why is white matter white
A
myelin - white fibres
10
Q
Anatomy of a neuron
A
- dendrites- receive information
- cell body (soma)- contains the nucleus
- initial segment (axon hillock)- triggers action potential
- axon- sends action potential
- axon (presynaptic) terminals- releases neurotransmitter
see picture
11
Q
Types of neuron
A
Afferent (sensory) neurons PNS —> Interneurons CNS —> efferent (motor) neurons PNS
12
Q
Moorphology of neurons
A
- afferent (sensory) neurons= bipolar, pseudounipolar
- interneurons= multipolar, anaxonic
- efferent (motor) neurons= multipolar
13
Q
what are glia
A
Cells that support neurons (non-neuronal cellsof the brain/nervous system)
14
Q
Types of glia cells in CNS
A
astrocytes, oligodendrocytes, microglia, ependymal cells
15
Q
What do astrocytes do
A
- Maintain external environment for the neurons
- Surround blood vessels and form blood brain barrier
16
Q
What do oligodendrocytes do
A
Form myelin sheaths in the CNS
17
Q
what do microglia do?
A
macrophages of the CNS, hoover up infection
18
Q
What do ependymal cells do?
A
produce the cerebrospinal fluid
19
Q
Tyopes of glial cells in PNS
A
Schwann cells and satellite cells
20
Q
What do Schwann cells do?
A
form myelin sheath in PNS
21
Q
What do satellite cells do?
A
support neuron cell bodies
22
Q
What does a neuron look like?
A
see picture
23
Q
How do neurons send electrical signal
A
Action potentials= transmit signals over long distances
Graded potentials= decide when an action potential should be fired
Resting membrane potentials= keeps cell ready to respond
24
Q
What is the resting membrane potential
A
- Inside potential of cell relative to outside
- Outside taken as 0mV and inside relative to this (usually -70mV in neurons)
- Aka potential difference
- Inside is negative
25
How do we create a resting membrane potential
1. Phospholipid bilayer impermeable to water and ions
2. Assume equal concentrations of NaCl and KCl inside and outside the cell
3. Everything is balanced inside and outside the cell - **No membrane potential**
Then...
4. Na/K pump uses ATP to pump K into and Na out of the cell
5. charges still balanced (ish) - **still no membrane potential**
Then...
6. Add "leaky K" channel
7. Some K leaks out cell down its conc gradient
8. Builds up electrical gradient
9. Equilibrium is reached when electrical gradient is equal and opposite to conc gradient
10. Have resting membrane potential
26
Explain the movement of K+ in terms of conc and electrical gradient
* Conc gradient - K+ beign pulled out
* Electrical grad - K+ being pulled in
27
How is resting membrane potential determined
By size of initial conc gradient:
* Small conc grad = small resting membrane potential
* Large resting membrane potential = need lots of K+ to leak out to reach equilibrium
28
What is the equilibrium potential
The equilibrium potential is the membrane potential at which the electrical gradient is exactly equal and opposite to the concentration gradient
29
Nernst equation
equation predicts the equilibrium potential for a single ion species
| see picture
30
What is the nernst equation usually at 37 degrees
for K+, approx -90 mV, for most neurons it is closer to -70 mV due to other "leaky" channels, especially Na+ and Cl-
31
What does the Goldman-Hodgkin-Katz (GHK) equation do
Predict the equilibrium potential generated by several ions
| see picture
32
why is the Na/K+ ATPase not completely responsible for generating the resting membrane potential?
* Exchanges 3 Na+ for 2 K+ meaning it is Electrogenic (makes the inside of the cell slightly negative)
* Only contributes about 5 mV Na+/K+ pump is needed to set up the ion gradients
* Without leaky K+ channels, only a small membrane potential would be generated
33
What is resting membrane potential dominated by
The permeability of the resting membrane to K+
34
briefly summarise leaky K+ channels
K+ continually leaks out the **cell down its conc gradient (against electric grad)**, which was established by Na/K pumps. Why resting membrane potential close to K+ equilibrium potential - only close due to other leaky channels
35
Blood-brain barrier
Capillaries in brain which prevent polar substances from crossing through/between endothelial cells. Protects brain from changes in plasma ion conc
36
What does the resting membrane potential produce
Evoked potentials (graded or action)
37
2 types of potential
1. graded
2. action
38
Graded potential
any change in electric potential of a neuron that is not propagated along the cell (as is an action potential) but **declines** with distance from the source
39
What do graded potentials decide?
| Jotted down, might not be "true"
Whether a cell is depolarised past a threshold to fire an action potential - **decide when action potential is fired**
40
examples of graded potentials
* Generator potentials- at sensory receptors
* Postsynaptic potentials- at synapses
* End plate potentials- at neuromuscular junction
* Pacemaker potentials- in pacemaker tissues (heart)
41
How do graded potentials respond to small and large stimuli
* Small stimulus opens a few channels and evokes a small response (small depolarisation)
* Strong stimulus opens many channels and evokes a large response (large depolarisation)
42
What does this mean graded potentials can also signal (what other bit of info can they share)
Stimulus intensity in their amplitude
43
What is a key propety of graded potentials
| think how they change
They are **decremental**
44
Why are graded potentials decremental?
Become **smaller as they travel along the membrane**, therefore only useful over very** short distances**, this is why graded potentials are also called local potentials
45
What 2 things can graded potentials be
Depolarising or hyperpolarising
46
explain depolarising and hyperpolarising of graded potentials
Neurotransmitters can open channels that depolarise the cell, or different channels that hyperpolarise the cell. Since firing an action potential depends on reaching a firing threshold. Graded potentials at synapses can therefore **excite or inhibit** a cell
47
What does depolarising a cells do/mean
| graded potentials
Less negative value - **Exitory postsynaptic potential** (EPSP)
48
What does hyperpolarising a cell do
| graded potentials
Away form threshold (less likely to fire action potiential) - **Inhibitory postsynaptic potential** (IPSP)
49
What can multiple graded potentials do together?
Summate
50
how can graded potentials summate?
* A single neuron has lots of synapses, evoking their own postsynaptic potential - 1 neuron can have hundreds of neurons attached on dendrites
* If two occur at the same time, they can **add** to together
* This is important for synaptic integration
51
Ionic bases of graded potentials
| summary
* We already know that at rest there are lots of leaky K+ channels - continually allow K+ into cell down conc grad (generates resting membrane potential)
* That explains why the RMP is close to the K+ equilibrium potential of -90 mV
* The opening of other ion channels generates other ion gradients
* We can predict what would happen in each case
52
What can happen with ion channels in relation to graded potential
Can open/close them to hyperpolarise or depolarise the cell
53
Ionotripic receptor
ligand gated ion channels (ion channel + receptor) - through which ions pass in response to a neurotransmitter
54
Metabotropic recepor
metabotropic receptors require G proteins and second messengers to indirectly modulate ionic activity in neurons
55
what are the properties of graded potentials?
graded, decremental, depolarising or hyperpolarising, can summate
56
What causes a fast IPSP (hyperpolarising)
ionotropic receptor (Cl- into cell)
57
What causes a slow IPSP
metabotropic receptor (K+ out)
58
Non-specific monovalent cation channel
For aqueous pathway for single positively charged ions to flow down their electrochemical gradient into/out of a cell
59
What causes fast EPSP
ionotropic receptor (for Na/K...)
60
What causes a slow EPSP
metabotropic receptor (stops movenet of K+ out of cell - closes)
61
What does the G-protein act as with metabotropic receptors
Doorman: to find and close "leaky" K channels (Na/K pump still going so cell depolarises
62
How are EPSPs generated?
EPSPs generated by opening (non-specific monovalent) Na+/K+ channels or closing leaky K+ channels
63
how are IPSPs generated?
IPSPs generated by opening Cl- channels or opening K+ channels
64
What is EPSP
an **excitatory postsynaptic potential**, a local depolarization of the cell membrane of the neuron. Summation of EPSPs can lead to the generation of an action potential.
65
What is an IPSP
inhibitory post synaptic potential,
hyperpolarization of cell membrane of neuron
66
What is the principle inhibitory neurotransmitter in the CNS?
GABA
67
Would GABA hyperpolarise or depolarise neurons
As an** inhibitory neurotransmitter**, GABA usually causes hyperpolarization of the postsynaptic neuron to generate an inhibitory postsynaptic potential (IPSP) while
68
Glutamate - neurotranmitter action
glutamate causes depolarization of the postsynaptic neuron to generate an excitatory postsynaptic potential (EPSP)
69
What are GABA and glutamate
GABA - princible inhibitory neurotransmitter in CNS
Glutamate - principle exitory neurotransmitter in CNS
70
Can GABA/Glutamate act on more than one type of recepor (gating an ion channel)
Yes
71
Is depolarising EPSP or IPSP
EPSP
72
Is hyperpolarising EPSP or IPSP
IPSP
73
What does each neuron have hundreds of
exitory and inhibitory synapses
74
What does each exitory/inhibitory synapse evoke
Fast or slow EPSP's and fast or slow IPSP but each is only a few mV high
75
What does adding together all the tiny EPSP/IPSPs do
Either push cell to threshold and fire an action potential or keeps cell away from threshold and tells it to shutup
76
Synaptic integration definition
The summation of the synaptic inputs to decide in the initial segement will reach threshold and fire action potential
77
What happens for synapses that are distant from the initial segment (axon hillock) in terms on firing activity/
Have **less** of an influence on the firing activity of the cell than those that are closer.
78
When are action potentials used
over long distances
79
Steps in firing of an action potential
1. Depolarisation
2. Repolarisation
3. Undershool (more -ve) and then hyperpolarise
80
Give the steps of firing an action potential in more detail
1. Leaky K+ channels maintain membrane potential
2. Voltage-gated Na+ channels open, leading to a **influx** of Na+ into the cell
3. Rapid depolariseation of cell occurs
4. Voltage-gated K+ channels open (letting K+ out) and Na+ ones close, allowing for a slow repolarisation of the cell
5. K+ channels open when reach -55mV
6. K+ channels close and cell returns to resting membrane potential
| + ball and chain blocking channels where appropriate
81
How does the ball and chain function in action potentials
Closes voltage-gated Na/K channels, preventing the entry/exit of ions into the cell
82
What are the 2 periods in the firing of an action potential - describe both
* Absolute refractory period - Is the period of time during which a second action potential ABSOLUTELY cannot be initiated, no matter how large the applied stimulus is
* Relative refractory period - Is the interval immediately following the Absolute Refractory Period during which initiation of a second action potential is INHIBITED, but not impossible.
83
Properties of action potentials
1. Have a threshold
2. All-or-none (always same amplitude)
3. Self-propagating - keeps going
4. Have refractory period - ball/chain inactivation gate
5. Travel slowly
84
What can action potentials only encode
Stimulus intensity in firing frequency, not amplitude
85
What are all action potentials mediated by
Voltage-gated channels (as opposed to ligand-gated channels that generate postsynaptic potentials)
86
What will a stronger stimulus show in an action potential
More action potentials fire
87
Explain the movement of action potentials down the axon
1. Cell -ve at rest
2. Na+ channels open, allowing influx of Na+ into cells at that point on the membrane---> depolarisation
3. Now, neighbouring Na+ channels open, depolarising this part of the membrane
4. Initial Na+ channels blocked by ball and chain, close off, stopping influx of Na+ - clamps channels closed and stops signals going the **wrong way down the neuron**
5. Process continues and signal moves **all the way along the neuron**
88
What mediates the depolarising, repolarising and hyperopolarising phase
* Depolarising - Voltage-gated Na+ channels
* Repolarising - Voltage-gated K+ channels
* Hyperpolarising - Voltage-gated K+ channels
89
Benefit but also drawback of action potentials
Self-propagating = grate but **slow**
90
How can we spped up conduction velocity of action potentials
| 2 ways
1. Larger diameter axons
2. Myelination
91
Explain how large (diameter) axons increase conduction velocity
* Current flows more easily along large axon where **axial resistance** is lower
* Allows the Na+ channels to be more spaced out along the membrane
92
Explain how myelination increases conduction velocity
* Schwann cells in PNS and oligodendrocytes in CNS
* Wrap layers of myelin arounf axons
* **Inc membrane resistance** - less current leaks out of membrane
* **Dec membrane capacitance** -less current wasted charging up membrane
* Action potential spreads passively from nod to node and still reach threshold
* Known as **saltatory conduction**
93
Essentially, what does myelination do?
Allows action potentials to "jump" from one node to the next
94
What are some consequences of demyeination
* multiple sclerosis in CNS and Guillain-Barre syndrome in PNS
* both demyelinating diseases that attack the myelin sheath
* Dec membrane resistance and inc membrane capacitance
* ** Conduction fails** - depolarisation fails to spread
95
How can nerve fibres differ?
| nerve fibre types
Axons different:
* small and large unmyelinated and myelinated axons
all conduct at different velocities, genertes a compound action potential
96
Give nerve fibre types going from fastest to slowest
* Large myelinated (Aa) - proprioception, motor neurons
* Large myelinated (AB) - Touch, pressure
* Small myelinated (Ay) - motor neurons of muscle spindles
* Smallest myelinated (A#) - touch, cold, "fast" pain
* Unmyelinated (C) - warmth, "slow" pain
97
What do extracellular recording from a nerve (bundle of axons) generate
A **compound** action potential - looks nothing like an action potential
98
Compare action potential to compound action potential
Action potential:
* Intracellular recording
* microelectrode through membrane
* relative to outside the cell
Compound action potential:
* extracellular recording
* electrodes outside axons
* relative to earth
* each action potential very small but add up to large waves
99
thus, differennces in axon anatomy will lead to differences in ...
Conduction velocity
100
What correlates with an axons function
Anatomy and conduction velocity
101
Nodes of Ranvier
specialized regions in the axonal membrane that are not insulated by myelin
102
Briefly summarise the neuromuscular junction and why we have it
Synapse between motor neuron and skeletal muscle
First step in triggering muscle contraction is to evoke an action potential in the skeletal muscle membrane (the sarcolemma)
103
Describe the anatomy of the nmj moving across the junction
1. Preynaptic terminal filled with vesicles containing acetylcholine (ACh)
2. Synaptic cleft
3. Postsynaptic end plate of the **skeletal** muscle fibre
Fold in end plate - allows greater uptake
104
What does depolarisation of a motor neuron do
Depolarises skeletal muscle (nmj) ---> action potenital being evoked leading to **contraction** of muscle
105
Give steps of firing of the nmj
| 12 steps
1. Action potential in motor neuron - mediated by voltage-gated Na channels (depolarises)
2. Opens voltage-gated Ca2+ channels in presynaptic terminal - Ca2+ pulled in by conc and elec gradient
3. Fusion of vesicles (Ca2+ dependent exocytosis)
4. ACh diffuses across synaptic cleft
5. ACh binds to ACh (nicotinic) receptors - ionotropic (non-specific cation channels)
6. opens ligand-gated Na+/K+ channles ---> pull into cell
7. Evokes end plate potential (graded potential), very large
8. (Always) depolarises membrane to a threshold
9. Opens voltage-gated Na+ channels
10. Evokes action potential
11. Action potential propagated along muscle cell membrane leading to **muscle contracts**
12. Acetylcholine (ACh) cleared up by acetylcholinesterase
106
Describe acetylcholine (ACh) receptors
Contain integral ion channel - ligand gated (non-specific monovalent cation channel) - muscarinic or nicotinic
107
What are some key characteristics of the nmj
* Ligand gated Na/K (2 diff channels) channels evoke the end plate potential
* Very large graded potential which is always bid enough to reach threshold
* Thus, no synaptic integration - **nmj acts like a switch**
* Post-junctional folds inc number of voltage-gated Na+ channels close to where it is evoked
108
What is the end plate potential (with nmj)
very large
109
What do post-junctional folds allow for
The end plate potential has a short distance to travel to the voltege-gated Na+ channels
110
how is the sequence of events similar/different in CNS synapses to that in NMJ
Same, however CNS synapses have added complexities
111
CNS synapses compared to NMJ in terms of **neurotransmitters**
NMJ: acetylcholine
CNS: **many** inc *amines* (adrenaline/noradrenaline/dopamine, serotonin (5HT), histamine), *amino acids* (glutamate, GABA, glycine), *peptides* (endorphins, cholecystokimim. substance P), *purines* (ATP, adenosine), *gases* (nitric oxide)
112
How can postsynaptic potentials be in the CNS
exitory, inhibitory, fast or slow
(e.g. slow IPSP or fast EPSP)
this range allows for **complex synaptic integration**
113
How may postsynaptic potentials are there in the NMJ
1
114
How can CNS synapses be arranged (3)
1. Axo-dendritic - typically exitory
2. Axo-somatic - typically inhibitory
3. Axo-axonal - can be both but usually inhibitory (work by regulating how much neurotransmitter is released)
115
How is CNS synapse anatomy different to that of NMJ
CNS: 3 arrangements
NMJ: 1
116
How can are synapses connected in the CNS and how does this differ to the NMJ
* Divergence - influences cells further down
* Convergence
NMJ: Only have divergence (1 motor neuron synaps onto multiple muscle fibres)
117
Do NMJ have feedback inhibition
No
118
Explain feedback inhibition in relation to CNS synapses
* When action potential fired, collateral (branch) activates an inhibitory interneuron
* Inhibitory neurotransmitter released
* Initial neuron hyperpolarises
* it is prevented from repeated firing
Net effect: initial neuron inhibited from repeated firing of action potential
119
Give an overview of the complexity of pathways in the CNS
Monosynaptic reflex: stereotyped: detect stimuli and fire action potential, limited scope for synaptic integration or for the behaviour of motor neuron to be influenced bu convergent pathways (simple)
Polysynaptic reflex: multiple sites of peotential synaptic integration so multiple neurons where behaviour will be influenced by convergent pathways. Much more complex decisions made and less likely to be stereotyped (same every time)
120
Explain inhibitory reflex pathways in the CNS
Inhibitory interneuron releases inhibitory neurotransmitter (e.g. GABA) and stops efferent (motor) neuron intitiating a response
121
What is synaptic plasticity
* Ability of synapses to change their strength.
* can be activity-dependent
* Many diff types of synaptic plasticity:
Long-term potentiation (LTP involved in learning and memory)
Long-term depression
122
Overall, what makes CNS synapses more complicated than the nmj?
* Range of neurotransmitters
* Range of postsynaptic potentials
* Arrangement of synapses
* Arrangement of wiring
123
Synaptic pathway
hormones are produced in the neuron, secreted, and travel along the axon to the synapse where they are released and taken up by a nearby neuron with the appropriate receptors to exert an effect, enter via afferent (sensory) neuron and leave via afferent (motor) neuron
124
how do we classify nerve fibre types
divided into three types on the basis of the **relationship between their diameter and conduction velocity**: group A, group B and group C nerve fibres.
125
What is a synapse in basic terms
Jucntion between neurons and a way of communicating between neurons
126
Common exitory neurotransitter
Glutamate
127
Common inhibitory neurotransitter
GABA
128
What can we call the process of 1 neuron releasing a neurotransmitter at its synapse which evokes a reponse in the next neuron
signal transduction
129
Where are interneurons found
The CNS only
130
function of acetylcholinesterase
to terminate neuronal transmission and signaling between synapses to prevent ACh dispersal and activation of nearby receptors. - breaksdown ACh
131
Function of graded potential (postsynaptic, generator potential, end-plate potential)
to determine when/weather a cell will fire its action potential
132
Where does Acetylcholinesterase remove ACh from
Acetylcholinesterase does not directly remove ACh from the receptors. Instead it continuously removes ACh from the synaptic cleft so there is less chance of ACh activating the receptors.
133
Synaptic integration in the CNS
In the CNS the EPSP evoked at a single synapse is likely to be in the order of 1-5mV. It is therefore not going to let the cell reach threshold. Instead, summation of EPSPs from many synapses is required. This is the concept of synaptic integration.
| Also IPSP's so add/subtract
134
When does the equilibrium potential for an ion occurs
when the concentration gradient for the ion is matched by an equal and opposite electrical gradient
135
Multiple sclerosis
demyelinating disease which impairs the ability of the action potential to be conducted from one node of Ranvier to the next
136
Can action potentials summate?
No (graded postsynaptic potentials can)
137
What effect would inc extracellular [K+] have on the resting membrane potential
Will decrease the K+ concentration gradient. This will sustain a smaller electrical potential at equilibrium and therefore depolarise the resting membrane potential.
138
effect of poisining Na/K pumps
The electrogenic nature of the Na+/K+ pump (pumping 3 Na+ ions for every 2 K+ ions) makes only a small contribution (about 5mV) to the resting membrane potential. Setting up the K+ concentration gradient is far more important. Poisoning the pump will therefore only cause a **small immediate decrease in membrane potential**. The remainder of it **decays slowly** as the K+ concentration gradient gradually runs down.
139
What could we say is at the NMJ (in terms or 1 motor neurone innervatign multiple muscle fibres)
Divergence
