Nerve and Muscle Flashcards
1
Q
Neurons:
A
Make up 10% of the nervous system. They are larger than glia
2
Q
glial cells function
A
- Glia cells make myelin: Oligodendrocytes in the CNS and Shwann cells in the PNS. They are also involved in forming the blood brain barrier
3
Q
myelin
A
Fatty substance that wraps around the axon of the neuron to speed up transmission of nerve impulses along the axon
4
Q
afferent neurons
A
- Afferent neurons take information from the periphery to the CNS (spinal cord). They are excitatory. They can be attatched to sensory receptors like touch receptors.
◦ Enter the dorsal part of the spinal cord
5
Q
efferent neurons
A
- Efferent nuerons take information from the CNS (spinal cord) to the periphery. They are excitatory
◦ Enter the ventral part of the spinal cord. They leave through the ventral root
6
Q
Interneurons
A
Interneurons: They are entirely within the CNS. They carry information inebtween efferent and afferent neurons. It can be excitatory or inhibitory (however never both)
7
Q
mixed peripheral nerve
A
- Mixed peripheral nerve: contains both efferent and afferent nerves. Information is coming towards the spinal cord (afferent) or away from the spinal cord (efferent). This is how information reaches the spinal cord
8
Q
white matter
A
- White matter contains myelin. This is fatty white matter that wraps around the axon. (White=fat)
9
Q
grey matter
A
- Grey matter contains cell bodies and parts of the neuron that don’t have myelin.
10
Q
Dedrites
A
- Dendrites: extend from the cell body and receive input from cells
11
Q
Cell body
A
Cell body: Where the nucleus is situated. (proteins and genes)
The impulse only goes away from the cell body towards the axon terminal or the synaptic terminal
12
Q
axon hillock
A
initial segment of the axon where action potentials are initiated
13
Q
axon length
A
very short in the spinal cord and very long going to the muscle
14
Q
bipolar cell
A
15
Q
pseudo unipolar cell
A
16
Q
multipolar cells
A
17
Q
phospholipid layer
A
Bilayer
Impermeable to ions
18
Q
Protein pumps
A
they’re specific to a given ion, and they allow ions to move either down their electrochemical gradient, or In the case of the sodium potassium pump, they use energy in the form of hydrolysis of ATP to move ions in a given direction, regardless of the electrochemical gradient.
19
Q
Sodium potassium pump
A
20
Q
ion channels
A
Open/closed at rest to allow the free flow of ions in or out of the cell. They depend on the electrochemical gradient
No energy is used
21
Q
leak channels
A
Ion channels that are always open are called passive or leak channels. They are selective to specific ions to go down the concentration gradient into or out of the cell to achieve equilibrium
22
Q
ligand channel
A
ligand-gated ion channels are closed at rest and they need a ligand to bind to a receptor in order to open the channel.
22
Q
Resting membrane potential
A
-70
measure of the electrical potential difference between the inside of the cell and the outside of the cell.
23
Q
Sodium potassiun pump
A
When ATP is hydrolyzed there is a conformational change in the pump.
3 sodium move out of the cell, 2 potassium enter the cell
When phosphate is removed from its binding site, there will be another conformational change and the pump will return to its normal conformation
Electrogenic: moves charge across the membrane
creates gradients
24
potassium leak channels
There is more potassium inside of the cell. Therefore the chemical gradient will force potassium out of the cell
The inside of the cell is negative and potassium is positive, so the electrical gradient will force potassium into the cell
The equilibrium potential for potassium is -90, meaning it will leave the cell to make the cell at this potential
25
equilibrium potential
The electrical and chemical force will be equal and opposite to each other at an equilibrium potential
26
sodium leak channels
more sodium outside of the cell. Therefore chemically it will be driven in the cell (chemical gradient)
The equilibrium potential for sodium is +60. This means that more sodium will want to enter the cell (electrical gradient)
27
relation of leak channels to equilibrium
the more leak channels you have for a given ion, the closer resting membrane potential is to the equilibrium potential for that ion (the more permanent the ion, the greater its ability to force the membrane potential to its own equilibrium potential)
Therefore there is more potassium channels
28
chloride
more outside of the cell then in
equilibrium potential for chloride is at the resting membrane potential
29
Action Potentials
1. physical or chemical stimuli disrupts the steady state by causing voltage gated ion selective channels (sodium to open). The activation gate for the sodium channels is going to move. This allows sodium moves down its electochemical gradient and enter through the voltage gated channel. These gates are closed until threshold is reached. Sodium will make the cell positive
2. Membrane potential is going to reach that of sodium (+60)
3. After a fixed amount of time, the activation gate for sodium is going to move, and the inactivation gate will block off the channel. This will prevent sodium from entering
4. The voltage gated potassium channel is going to have its activation gate move, allowing potassium to leave the cell and make it negative.
The voltage gated sodium and potassium have the same thresholds for avtivation. Sodium channels are much faster, which causes them to open before potassium channels
30
stretch receptor sodium channels
At rest, the pores in the stretch receptor at the efferent neuron are too small for sodium to enter
When the muscle is tapped, the muscle is stretched, also stretching the receptor. This allows sodium to enter ion channels that it coulnd't fit through before. Sodium can enter the afferent fibre and depolarize the afferent fibre
31
What is happening for the channel to reach threshold
By tapping the patellar tendon, the receptor is stretched, allowing sodium to enter the cell and make it more positive. When the cell reaches -55, this is when the voltage gated sodium channels open
32
repolarizaton
The voltage-cated potassium channels open and you get a relatively fast repolarization of the membrane potential.
33
hyperpolarization
During the after-hyperpolarization phase, we have sodium leak channels, we have potassium leak channels, we have the sodium-potassium pump active.
We also have some of those voltage-gated potassium channels which remain open. They haven't closed yet. So because we have that extra permeability to potassium, we're a little bit closer to the potassium equilibrium potential.
As they start to close, the cell gets close to its resting membrane potential
34
refractory period
an action potential cannot be generated
35
absolute refractory period
impossible to generate an action potential
the voltage-gating sodium channels are open, so they are unable to open again. Therefore you cannot generate another action potential in this neuron. The inactivation gate is blocking the channel
36
relative refractory period
harder to generate another action potential: stronger stimulus is needed. The inactivation gate has moved.
The potassium channels are open. Potassium is leaving making the cell more negative. This makes it harder to make the cell positive enough
37
electronic conduction
deplorization of neighbouring tissue along an axon
As the action potential is generated in one region of the axon, it triggers the opening of voltage-gated sodium channels in the adjacent region, allowing them to reach threshold
This sequential opening of sodium channels and depolarization allows the action potential to propagate along the axon in one direction, from the initial site of stimulation toward the spinal cord
slow process
38
how does an action potential travel in one direction only across the axon
This is due to the refractory period. The sodum channels are already open (the inactivation gate is blockign them). this prevents the potential from going backwards
39
saltatory conduction
When an action potential is initiated at the initial segment of the axon hillock it depolarizes the membrane.
In myelinated axons, the action potential, can travel through the myelin without losing current
At the nodes, where the membrane is exposed, the action potential is regenerated. The myelin-covered segments of the axon do not require continuous regeneration of the action potential.
40
myelin
Insulator: prevents the current from leaking out of the membrane
41
nodes of ranvier
Nodes of ranvier are in between the myelinated segments (myelin is discontinous)
The voltage-gated sodium channels are at the nodes of ronge and that is where the action potential is going to need to be regenerated.
42
schwann cells myelinated
A single schwann cell is required to generate a single myelinated segment (PNS)
43
oligodendrocytes myelination
A single oligodendrocyte ensheaths multiple segments. More efficient (CNS)
44
what is happening in a myelinated axon
in a myelinated axon both sultatory conduction and electronic conduction are occurring.
45
what determines speed
Speed is determined by how thick the nerve fibre (not myelin) is and how much myelin there is
46
where would the fastest nerve fibres be
-skeletal muscle for a stretch reflex
- proprioceptors for body position
47
second fastest fibres
mechanoreceptors: touch and pressure
48
slowest fibres
Sharp pain that happens immediately is from groups 3, but the dull throbbing pain after is from the slower group 4 receptors
49
what is the function of electrical synapses
It's thought to play a fairly large role in synchronizing large groups of neurons to fire simultaneously.
50
Electrical synapses
Allow for molecules to pass between synaptic terminals in either direction (bidirectional)
Electrical: coordinates large amounts of neurons at the same time; difficult to change
51
connexons
electrical synapses: The connexons on one cell's membrane interact with those on the neighboring cell, creating a continuous channel that connects the cytoplasm of the two cells.
This allows direct communication and passage of ions, metabolites, and signaling molecules between the cells. (physical coupling)
open state: allow the free flow of molecules
closed state
can occur anywhere, axons, cell bodies, dendrites
52
chemical synapses
Between presynatpic and postsynaptic terminal of the dendrite
larger gap than electrical synapse
The release of a neurotransmitter (ligand) moves across the gap between the presynaptic cell and the postsynaptic cell, and it will bind to a receptor for that ligand on the postsynaptic cell.
inhibition is only possible with chemical synapses
53
Directly gated chemical synapses
stretch reflex
synaptic vesicles contain neurotransmittes. They fuse with the presynaptic membrane and release their contents into the synaptic gap.
The neurotransmitter will bind to the iontropic receptor on the postsynaptic cell. Attatched to the receptor is an ion channel. When the neurotransmitter binds, this opens the ion channel
Effects are fast and short lasting. Once the neurotransmitter is released from the receptor, the ion channel closes and depolarization stops
54
excitatory neurotransmitter
glutamate. this causes sodium channels to open and sodium to enter the cell.
55
inhibitory neurotransmitter
glutamate and glycine
open channel permebale to potassium or chloride. Equilibrium potential for potassium is -70, so potassium will leave the cell
chloride will hyperpolarize the cell
56
indirectly gated chemical channel
No iontropic receptor. Metatropic receptor
slow events, but long lasting like protein synthesis or memories
Activates second messenger system. G proteins are activated which activates adenyl cyclase.
This convertws ATP to cAMP (second messenger). This activates protein kinases which phosphorylate a channel and cause it to open or close. Depolarization or hyperpolarization can occur
57
synaptic transmission
1. action potential arrives in presynaptic terminal
2. presynaptic terminal depolarizes
3. voltage gated calcium channels open
4. calcium causes the presynaptic vessels to fuse with the presynaptic membrane
5. Transmitter released by exocytosis and diffuse across the synaptic clef. They bidn ot and open ligand gated ion channels
6. Ions flow acrossed the membrane to depolarize or hyperpolarize the cell
7. transmitter removed and recyled or degraded. Ion channel closes. PSP ends
58
temporal summation
Multiple post synaptic potentials overlap in time
If a presynaptic neuron repeatedly releases neurotransmitters over a short period, the effects of the EPSPs or IPSPs can accumulate, potentially reaching the threshold for an action potential.
59
spatial summation
Spatial summation involves the addition of PSPs from different synapses on different regions of the postsynaptic neuron. These occur at the same time. The effects of the EPSPs or IPSPs can accumulate, potentially reaching the threshold for an action potential.
60
EPSP and IPSP amplitude
small amplitude that as they travel decreases in amplitude. The location where the IPSP or EPSP is generated effects the postsynaptic potential. EPSP and IPSP can have an action potential generated at the axon hillock. Because the signal does not have to travel, the amplitude will be higher
61
amplitude in PSP and AP
PSP: much smaller. Amplitude is graded. It can be depolarizing or hyperpolarizing
AP: Much larger. They are all or nothing which means that its the exact same amplitude.
61
PSP and AP duration
AP: msec; faster
PSP: msec-sec; slower
61
Synaptic Integration
The process of summing together all the inputs into a pattern of action potential outputs in the postsynaptic cell
61
Synaptic integration increases the complexity of behaviour
given the exact same stimulus in different situations, the response of the central nervous system is going to vary.
Whether or not your expecting something. This can cause inhibitory or excitaotry input from the cortex to the spinal cord
62
PSP and AP location
AP: generated at action hillock and travel down to the synaptic terminals
PSP: Dendrites and soma of postynaptic cell
62
PSP and AP conduction
AP: active/long: Regenerated at every point along the axon as they travel
PSP: Passive (Short distances)
62
Function of a PSP and AP
Neurotransmitters will cause the PSP to either be inhibited or excitatory in relation to threshold. If the summation of impulses is enough to depolarize the membrane to threshold an AP will be released.
If the summation of impulses is enough to depolarize the membrane, an action potential will be conducted ot hte therminal where it can cause another PSP in the postsynaptic neuron
63
Stretch reflex
