Test 1 Study Guide Part 3 Flashcards
Cable properties:
- Limit to diffusion distance:
- Reason for limit:
- Limit to diffusion distance:
The ions can only diffuse 1 - 2 mm - Reason for limit:
High internal resistance (things in the way), external resistance (loss of charge to outside), high capacitance (charge must overcome stored charges by membrane)
Why do multiple action potentials not deplete K+ or Na+ levels?
They happen over a very small localized reason on the surface of the nerve.
The Na+/K+ pumps run constantly, even through action potentials.
What causes the spread of an action potential?
Cable properties. (which are in turn kept going because they stimulate new action potentials, which have new cable properties)
Action potentials in an unmyelinated nerve:
- Continuous wave of action potentials down the length of the axon
- No loss of amplitude (or change in it) will result, so it is conducted without decrement
Why do action potentials take longer in unmyelinated axons?
His reason: action potentials are slow relative to cable properties, so the fewer action potentials you can have the faster the conduction
Other reasons:
Myelin will decrease capacitance (less charge to overcome)
Myelin will decrease external resistance (less charge lost through efflux)
Myelinated axons are often larger, which results in less internal resistance.
The nodes and myelinated action potentials:
- Conc. of Channels at nodes:
- name of conduction:
- Conc. of Channels at nodes:
Much higher at nodes (but still present elsewhere) - name of conduction:
Saltatory conduction (leaping conduction)
Conduction rates:
- Myelinated axon:
- Unmyelinated:
- Reason aside from myelin:
- Myelinated axon: 100 m/s - Unmyelinated: 1 m/s - Reason aside from myelin: Myelinated axons are also usually larger (less internal resistance)
Ca2+ roll in action potentials:
- Disorders which are caused by hypocalcemia:
- Reasons these disorders are caused:
- Disorders which are caused by hypocalcemia:
Hypocalcemic tetany, and (neurological disorders in children) - Reasons these disorders are caused:
Lower interstitial Ca2+ results in less Ca2+ outside of the cell, This results in the outside being less positive, which depolarizes the membrane, making activation of Na+ channels in nerves easier.
Synapses:
- cells synapses occur between in CNS:
- cells synapses occur between in PNS:
- Define effector cell:
- cells synapses occur between in CNS:
Neurons and other neurons - cells synapses occur between in PNS:
neuron to neuron, neuron to effector cells - Define effector cell:
The cell which will respond to the stimuli (muscle cell or glandular cell)
Alternative name for neuron to muscle synapses:
Myoneural or neuromuscular junctions
What experiment did Otto Loewi perform to discover the chemical nature of some synapses?
He had two hearts, one still connected to the vagus nerve, suspended in baths with a pump which could circulate fluid between the baths.
With the pump off only the one connected to the vagus nerve slowed.
With the pump on both hearts slowed, indicating something diffusible, in our case acetylcholine.
He called it vagusstoff
What is necessary for electrical coupling of cells?
How is this accomplished?
Cells must be roughly equal in size and joined by a contact area of low electrical resistance. Gap junctions (cells spaced 2 nanometers apart)
What is the structure of a gap junction?
Six proteins called connexins for a hemichannel (hemi = half, channel = channel)
Two hemichannels form a gap junction when docked together.
Where are gap junctions localized?
Cardiac muscles, most smooth muscles
Gap junctions allow for quick dispersal of a signal unmodified between many cells. Examples:
In cardiac cells this allows the heart to beat in unison.
In smooth muscle cells, like those of the uterus, this allows contractions to occur to in unison.
The brain, where it is uncertain what they do.
Neuroglial cells where it is believed they allow exchange of Ca2+ and other ions.
Are gap junctions adaptable systems?
Yes. The amount of gap junctions between cells can be changed to alter the conductivity.
They can also interact functionally with chemical synapses.
What keeps post-synaptic and pre-synaptic extensions together?
CAMs (cell adhesion molecules)
These act like velcro to hold the synapses right where they need to be.
Why do synapses act as one way gates?
There are only receptors for the neurotransmitter on side (post-synaptic). there is also, in theory, only production of neurotransmitter on one side.
What is a terminal bouton?
How large is the synaptic cleft?
It is what idiots call the presynaptic endings (the end of axons).
Only 10 nms!
What triggers the release of neurotransmitter into the synaptic cleft?
You know its the sweet release of Ca2+ into the pre-synaptic cell. Let me explain. The action potential depolarizes the cell, opening voltage gated Ca2+ channels, which enables a flood of Ca2+ in, which leads to release of neurotransmitter by fusing of synaptic vesicles remarkably quickly.
What is the name of the protein complex which holds vesicles near the membrane walls?
SNARE complex