Introduction Part 1 Flashcards
Where are motor neurons located?
In the CNS, controls the contraction of a muscle or the secretion of a gland
Where are most interneurons located?
Within the CNS and connect neurons to each other, all sensory neurons are connected by interneurons
What is a major substrate of brain plasticity?
Dendrites, and the small membranous protrusions which dictate dendritic spine density
The thicker the axon the ____ the action
faster, usually thicker because of the myelin sheath
What are the supporting cells of the CNS?
Glial cells, which provide nutrients for the neurons
What do astrocytes do?
Digest debris and participate in phagocytosis, the most numerous glia in the brain
What do oligodendrocytes do?
Help produce myelin sheath
What do microglia do?
Smallest immune cells of the CNS, help destroy pathogens and migrate to the site of infection and injury
What are ependymal cells?
Line brain ventricles and produce the CSF - protection of the brain & means of removing metabolic waste
What are mylenating glia?
Includes oligodendrocytes and shwann cels
(T/F) Schwann cells insultate the PNS
T, and Oligo cells insulate the CNS
What is the BBB lined by?
Astrocytes, and helps keep tight junctions and substances require active transport. Area postrema is less conservative
What is MS?
An attack on the oligodendrocytes in the CNS, breaks down the myelin and makes communication thry these circuits less reliable
Dicsuss the role of inhibition in a reflex arc
The excitatory synapses can be overriden by inhibitory synapses if our brain wants to. An interneuron will inhibit the motor neuron preventing a muscular contraction
Which cell type has the smallest (most negative) RMP?
Skeletal muscle (-95 mV)
What are three ways of measuring electrical potentials of axons?
1) Electrode (apply electrical stimulation or record electrical stimulation)
2) Microelectrode (record activity of individual neurons)
3) Membrane potential ( the electrical charge across a cell membrane)
What are the three main players necessary for maintaining RP?
- The neuronal membrane
- Fluid
- Ion channels (proteins) in the neuronal membrane q
What are the two key factors at play when it comes to RMP?
- Diffusional force
- Electrostatic force
What is electrostatic force determined by?
- Electric potential (voltage) - reflects the difference in charge between anode and cathode
- Electrical conductance - refers to the relative ability or inability (resistance)of an electrical charge to migrate
Which force initially rules?
-Diffusion, and then electrical potential difference across the membrane
How is an equilibrium achieved?
When the electrical force of the ion is equal in the diffusion force of the ion (for example, K+)
(T/F) there is a higher water concentration inside the cell
F, more outside as there is a higher concentration of salt outside the cell, more K+ inside the cell
-Adding more sodium on the outside helps achieve greater osmotic balance
What causes Na+ to “leak” inside the cell?
Due to the concentration gradient (more Na+ outside vs inside), however is offset by the electrical force (As the +Na ions enter, space inside is less negative and therefore Na+ is less pulled inside)
What causes K+ to leak outside the cell?
Due to the concentration gradient, however K+ leaving the cell makes it more polarized, therefore there is a stronger electrical pull to bring the K+ back into the cell
What is RMP more skewed towards? Why?
k+, as the membrane is much more permeable to K+, there are 40x more channles
(T/F) the membrane is maintained at it’s equilibrium potentail
False, as membranes are always leaky, K+ is leaking out, and Na+ is leaking in
What is the solution for the leaks?
The sodium potassium pump, energy drives 3 K+ into the cell and 2 Na+ out of the cell
How do astrocytes regulate potassium?
Will take up K+ when extracellular levels are high, this is important because if more K+ is outside the cell then the cell is more negative, and therefore will be harder to depolarize
What is an action potential caused by?
A brief increase in membrane permeability to Na+, then a brief increase in permeability of membrane to K+
(T/F) the AP is of fixed size and duration
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What are the two laws for the principles of generation of an AP?
1) All or none law
2) rate law
What is the all or none law?
The AP will be generated entirely across the length of the axon, or not at all
What is the rate law?
The magnitude, or size of each AP is constant, but what changes is how often it fired and the frequencies when we consider a weak stimulus compared to a strong stimulus
In an AP, what is the current?
Net movement of K+ across a membrane
In an AP, what is the potassium channel number proportional to?
Electrical conductance (i.e. more or less resistance)
What is the flow and driving force of an AP?
The membrane potassium current
(T/F) K+ will not leave the cell until Na+ channel cloes
F, starts to leave prior to the apex of the AP, and right after the Na+ channles have opened up and before the Na+ channels become refractory
What causes the slight period of hyperpolaization
Extra K+ will diffuse out of the cell, still permeable to K+
-Not the voltage gated channels, but the K+ channels are open, therefore as we know that K+ is greater on the inside, more diffusion will push K+ out than needed
What are the 4 properties of Na+ channels?
- These channels are closed at normal RMP, and will only open when less negative
- When depolarized, the individual channles will open qucikly
- They will be inactivated (stay open) for 1 ms
- They will not open again until they repolarize (becomes negative)
- Must be de-inactivated
What serves to rectify or reset membrane potential?
Potassium conductance
What are the two ways depolarization can occur? What is this known as?
Thru both chemical and electrical signals
-Collectively known as generator potentials
When are voltage gates K+ channles closed?
At rest and during the rising phase, only have one gate
What is the refractory period?
The time after the Ap when no other AP can occur
What is an absolute RP?
When Na+ channels are inactivated (must be de-inactivated by more -charge) and no AP is possible
What is a relative RP?
Some, but not all Na+ channels are de-inactivated (or activated)
- K+ channels are open
- AP can occur, but requires a stronger depolarization because inside of cell is still very negative (K+ flowing out still)
What does orthodromic conduction mean?
APs travel in one direction, and goes from soma down the axon terminal
What does antidromic conduction mean?
Backwards propogation of nerve impulse, from axon terminal to soma
What is the typical conduction velocity of an AP?
10m/sec
What are the four factors which influence conduction velocity?** (PAMS)
- Path of positive charge
- Axonal excitability
- Myelin
- Spread of AP across the membrane
Discuss the path of the positive charge
- If the path across a wide axon with few open membrane pores (inside axon), the conduction will be faster
- If the path is a narrow axon with many open pores, it will be slower (across the axonal membrane)
Discuss Axonal excitability
Depends on the axonal diameter (where bigger = faster) and the number of voltage-gated channels
Discuss myelination
- larger axon=faster conduction
- Insulate the axon
- Creates saltatory conduction where there are Na+ channels concentrated at the nodes of ranvier
Discus the spread of AP along a membrane
Speed of the AP depends on how far the depolarization is ahead of the AP spread, and depends on the axon structure –> garden hose analogy: If there are holes in a garden hoe, the larger the diameter the less AP charge is lost
When there are less voltage gates channels on a membrane, what happens?
-require greater depolarization, and more sensitive to anesthetics (channel blockers)
What is synaptic transmission?
The primary means of communication between neurons
What is postsynaptic potentials?
Brief periods of depolarization or hyperpolarizations
Where can a postsynaptic potential be terminate on?
The dendrite or the soma
Most of the synaptic transmission in the nervous system is ___
chemica
Discuss axodendritic arrangement
Axon –> dendrite
Discuss axosomatic arrangement
Axon –> cell body
discuss axoaxonic arangement
Axon –> axon
Discuss dendrodendritic arrangement
Dendrites –> dendrites
How does the arrival of AP trigger NP release?
Depolarization of terminal membrane causes the opening of voltage Ca+ gated channelsWhat (Ca+ pulls outwards, but has an inward driving force as the inside of the cell becomes much more negative)
What are the two types of NP receptor?
1) Transmitter-gated (Amines, AA) Ionotropic –> Allows for fast synaptic transmission
2) GPCR Metobotropic receptors –> slower and more diverse actions, where ANY type of NT can bind. Most autoreceptors are G-protein-coupled.
What is an example of an Ionotropic receptor?
- ACh
- Will bind to alpha subunit, channel opens and Na+ now enters the postsynaptic cell
_____ are less specific than voltage gated ion channels
NT channels - Ach channles are pearmeable to both Na+ and K+
As a rule of thumb, when the membrane is permeable to ___ it is excitatory, and when permeable to ___ it is inhibitory
Na+ (EPSP)
Cl- (IPSP)
both are found in higher concentration outside the cell
How do GPC receptors function?
Thru effector proteins, where the downstream proteins will effectuate the opening of a G-protein-gated ion channel
-Can also synthesize secondary messengers which alter cellular metabolism
Influx of Na+ causes ___
depolarization, EPSP
Efflux of K+ causes ____
Hyperpolarization, IPSP
Influx of CL- causes ____
Hyperpolarization, IPSP
Influx of Ca+ causes ___
Activation of enzymes/contractions of ions
Why must Nts be cleared from the synaptic cleft?
-Because the signals must terminate, and there is a risk for desensitization
How are NTs removed from the synaptic cleft?
- Diffusion
- Re-uptake into the presynaptic axon terminal
- Enzymatic degradation
What is neural intergration?
When potentials summate to have a greater effect within a synaptic neuron, depends on whether summation is EPSP or IPSP
What are the two types of EPSP summation?
- Spatial summation
- Temporal summation
What is spatial summation?
-Adding of EPSPs generated at different synapses in the same dendrite
What is temporal summation?
-Adding EPSPs to generate the SAME synapse in rapid succession
What are autoreceptors?
- Found ont he presynaptic axon terminal, usually controlled by GPCRS
- Are often inhibitory and turn off the release of APs
- Can be though of as a “safety valve”
What can axoaxonic synapses produce?
- Presynaptic inhibition
- Presynaptci facilitation
How do axoaxonic synapses produce presynaptic inhibition?
By reducing the amount of NT released by the terminal button, as in the terminal button it is effectuating its action on
How do axoaxonic synapses produce presynaptic facilitation?
By increasing the amount of NT released by the terminal button
How can IPSPS function?
-Can bind to different transmitter, an allow different ions to pass thru channels, causing hyperpolarization
What are two types of nonsynaptic chemical communication?
1) neuromodulators
2) hormones
How do neuromodulators work?
Chemicals released by neurons which will travel further and be dispersed further than NTs
How do hormones work?
-Secreted by endocrine glands, where there are target cells which contain receptors for particular hormones
