Overview of the Nervous System Flashcards
1
Q
Current (I)
A
- Electrical charge flowing through the neuronal membrane per unit time (units: amperes or A)
- Water analogy: how much water (charge) is flowing through the pipe per second
2
Q
Potential/Voltage (E or V)
A
- The relative “pressure” on a charge across the membrane (units: volts or V)
- Water analogy: how much pressure is being exerted on the water throughout the pipe?
3
Q
Conductance (g)
A
- The ease with which charge flows across the membrane (units: siemens or S)
- Water anology: how wide is the pipe?
4
Q
What influences conductance (g)?
A
- The number of open ion channels for a given ion
- E.g. during the rising phase of an action potential, there are many sodium channels open –> gNA is high at this point
5
Q
Is the intracellular surface of a cell more negative or positive than its extracellular surface?
A
- The intracellular surface is more negative than the extracellular surface. This is the resting membrane potential of the cell
6
Q
Resting membrane potential
A
- A steady-state potential of the cell (when there are no changes occuring)
- The potential across the membrane tends to remain at the resting membrane potential
7
Q
What charge do many macromolecules in cells have?
A
Many macromolecules in cells (e.g. nucleic acids, proteins, etc.) have a negative charge
8
Q
“leak” ion channels
A
- Open (no gating mechanisms)
- Allow for the free flow of ions
- K+ has the most leak channels, then Cl-, then Na+
- Thus K+ plays the biggest role in creating the resting membrane potential
9
Q
Sodium-Potassium ATPase
A
- Uses ATP to counteract the effects of the leak ion channels
- Pumps Na+ and K+ against their electrochemical gradients
- Pumps 3 Na+ ions out for every 2 K+ in
- Helps maintain the resting membrane potential
10
Q
What is the approximate resting membrane potential in mV?
A
-65mV
11
Q
Can neurons excite or inhibit other neurons?
A
Neurons can both excite or inhibit other neurons
12
Q
Depolarization
A
- Making the membrane potential more positive
- Excitation signals depolarize the cell
13
Q
Hyperpolarization
A
- Making the membrane potential more negative
- Inhibitory signals hyperpolarize the cell
14
Q
Repolarization
A
- Return towards resting membrane potential after depolarization or hyperpolarization
15
Q
Threshold potential
A
- Membrane potential at which it is possible for an action potential to occur
- Generally occurs around -55 mV (about 10mV more positive than the resting membrane potential)
16
Q
General phases of the Action Potential
A
- Threshold potential met: action potential becomes inevitable (all-or-nothing principle of action potentials)
- Rising/depolarization phase: rapid depolarization of the membrane
- Falling/repolarization phase: slower repolarization of the membrane back towards resting membrane potential (RMP)
- Undershoot phase: After hyperpolarization membrane potential dips under RMP
17
Q
Voltage-gated ion channels
A
- Become permeable and impermeable within specific membrane potential ranges. Important examples:
- Voltage-gated Na+ channels
- Voltage-gated K+ channels
18
Q
Biophysic stages of the action potential
A
- Voltage-gated Na+ channels open –> Depolarization
- Voltage-gated K+ channels open –> Hyperpolarization
- Voltage-gated Na+ channels close –> K+ channels close slower
- Overshoot phase –> then repolarization
19
Q
Where are action potentials typically initiated?
What do they propagate down?
A
Axon Hillock
Axon
20
Q
Saltatory Conduction
A
- Action potential jumping from node to node (nodes of Ranvier) for faster signaling
- Nodes of Ranvier have much higher voltage-gated Na+ channel density
21
Q
How does myelination conserve energy?
A
- Sodium Potasium ATPase only has to work at nodes of Ranvier
- Fewer axonal ion channels and ATPases needed
22
Q
General result of demyelinating disorders
A
- Action potential velocity reduced
- Greater amount of action potentials fail
- Sensory/motor and sometimes autonomic/cognitive symptoms
23
Q
What is a common demyelinating disorder of the CNS?
A
Multiple Sclerosis
24
Q
What is a common demyelinating disorder of the PNS?
A
Guillain-Barre syndrome
25
Chemical Synapses
* Presynaptic neuron secretes neurotransmitters into synaptic cleft which bind to postsynaptic neuron
* Can amplify signal (one neuron can synapse on many neurons)
* Are highly plastic (modifiable)
26
Electrical Synapses
* Direct exchange of ions/molecules at physical junctions between two neurons
* Rapid precise communication
* Useful for large-scale synchronization of neurons
* Can be bidrectional
27
Neurotransmitters
Molecules synthesized within neurons that mediate signaling at chemical synapses
28
What are the three main classes of neurotransmitters?
* Amino Acids
* Monoamines
* Neuropeptides
29
What are three important amino acid neuro transmitters?
* Glutamate (Glu) --\> excitatory
* y-amino butyric acid (GABA) --\> inhibitory
* Glycine (Gly) --\> inhibitory
30
What are some of the main monoamine neurotransmitters?
* Serotonin (5-HT)
* Epinephrine (Epi)
* Norepinephrine (NE)
* Dopamine (DA)
Note: DA, NE, and Epi are also catecholamines
31
What classes of neurotransmitters are small-molecule NTs?
* Amino Acid NTs
* Monoamine NTs
32
Small-molecule neurotransmitters synthesis
* Synthetic enzymes are synthesized on the soma and transported down axon via microtubules
* NT precursors transported into axon terminal
* NTs synthesized by synthetic enzymes and packaged in synaptic vesicles
33
Neuropeptide neurotransmitter synthesis
* NT precursors and synthetic enzymes are synthesized in the soma and packaged into synaptic vesicles
* These synaptic vesicles are then transported down the axon via microtubules
* Synthetic enzymes cleave precursors into NTs prior to release
34
Chemical Synapse (Synthesis, Release, and Binding)
* NTs synthesized at presynaptic axon terminal and stored in synaptic vesicles
* Action potential (AP) reaches axon terminal to activate voltage-gated Ca2+ channels --\> influx of Ca2+
* Increased [Ca2+] --\> promotes vesicle exocytosis via interactions between _synaptotagmin_ and _SNARE_ complexes
35
What determines the neurotransmitter's effect(s)?
The NT receptor determiens the NT's effect(s)
Note: Multiple receptors are associated with most NTs
36
Ionotropic Receptors
* Have two domains:
* Extracellular: ligand-binding site
* Transmembrane: ion channel
* Can gate specific/nonspecific cation (NA+, K+, CA2+) or anion (Cl-) channels that induce postsynaptic potentials
* Rapid and transient with specific responses in membrane potential
37
Metabotropic Receptors
* Most are G protein-coupled receptors
* Slow and sustained with many potential responses
* Different types:
* Indirect gating of ion channels
* Activation of 2nd-messenger pathways which can:
* Gating of ion channels
* Induce other changes postsynaptic membrane
* Regulate gene transcription
38
Excitatory Postsynaptic Potentials (EPSPs)
_Depolarize_ the neuron and make it _more_ likely for an AP to occur
39
Inhibitory Postsynaptic Potentials (IPSPs)
_Hyperpolarize_ the neuron and make it _less_ likely for an AP to occur (with some exceptions)
40
Postsynaptic Potentials (PSPs)
* Are **graded potentials**: their amplitudes (sizes in mV) scale with the sizes of the input(s) that generate them (the number of NT-receptor binding events)
* _PSPs can sum together_!
41
Temporal Summation
* Type of graded potential (PSPs)
* Rapid PSPs from the same source within a short period of time accumulate
42
Spatial Summation
* Type of graded potential (PSPs)
* PSPs from different sources arrive in close succession to sum at the same location
43
What stops the continued generation of PSPs after presynaptic action potential due to continued neurotransmitter-receptor binding events?
* Neurotransmitters are removed from the synaptic cleft through two mechanisms:
* **Reuptake**: presynaptic neuron reuptakes NTs via transporters
* **Catabolsim**: Enzymes degrade NTs
44
What do reuptake inhibitors do?
What are some common examples?
* Cause NT binding to occur over a greater period of time
* Common examples:
* SSRI
* Psychostimulants (Cocaine)
* Anticonvulsants
