3: Action Potential Conduction & Synaptic Transmission Flashcards
What 3 Things Make the AP Move Slowly?
Leaky Axon: Low Membrane Resistance (Rm)
-Lots of leaky channels let ions out
Stick Axon: High Membrane Capacitance (Cm)
- Electrostatic force cause intra &extracellular cells to become attracted to eachother
- -Thinner memb = + capacitance
- -Smaller distance = + force
This Axon: High Axoplasmic Resistance (Ra)
- 1-10 microns in diam
- Hard to move ions down b/c axon is resistant
What is the Invertebrate Solution?
Ie. Sea Slug & Squid
- Developed wide axons (up to 1mm in diam!!)
- Conducts AP faster b/c it solved the thin (Ra) problem
- -Easier for ions to fuse down the axon
- Less sophisticated however, can’t fit as many axons in
What is the Vertebrate Solution?
Evolved Myelin
- Fat that wraps around the axon
- Covered lots of leaky channels - reducing leak
- Greater distance b/w intra/ extracellular ions = weaker attraction
- Saltitory Conduction
- -Jumps b/w sheaths
- -Regenerats @ next node
- -A lot more time efficient
How and Where do Oligodendrocytes Myelinate?
- In the CNS
- Wraps membrane around axon
- Adds fatty lipid memb around the axon
- Can myelinate several axons at a time
How and Where do Schwann Cells Myelinate?
- In the PNS
- Wrap themselves around an axon
- Squeeze out most of the cytoplasm & press down to create multiple wraps
- -Insulate axons
What is the Best Theory Behind Multiple Sclerosis?
- Damaged myelin around axons in the CNS
- Difficulty conducting APs
- -Attack diff parts of the nervous system
- Most likely autoimmune
- -Person is exposed to a virus & produce antibodies to kill it
- -Antibodies attack protein in virus
- -Protein is similar to one in myelin, so antibodies attack myelin
- -Immune system attacks myelin
- Gets worse over time
- -Depends on the person
What is Guillain-Barre Syndrome?
- Similar to MS but in the PNS
- Autoimmune, rare & antibodies attack PNS
- Rapid onset & recovery after weeks or years
- Symptoms = parasthesia, paralysis, loss of sensation
How was Neurotransmission Proven?
- Two hearts placed in separate chambers, connected by a tube
- Stimulated heart 1 w vagus nerve & this had an inhib effect on the other heart
- -Proven chemical release & transmission to communicate b/w neurons etc
What are the Processes of the Active Synapse?
- Strong Ca gradient
- -10X more Ca on outside than inside
- charge from Na/ Ap repels +ve gate & it opens
- Ca flows in and catalyzes membrane function
- Vesicles move down & dock- SNARE complexes form to pull membranes together
- Entering Ca binds to synaptotagmin
- -Ca-bound synaptotagmin catalyzes membran fusion
- NeuroTs from vesicle diffuse out in a process of exocytosis
What is the Function of a Ca Pump?
- Restored the conc grad of Ca after neurT release
- Expels 2 Ca & takes in 2 H to establish conc grad
What is the Function of an Ion Exchanger?
- Use force from one ion coming in to push out another ion
- Doesn’t use ATP –> no hyrolysis
- -Na/ Ca exchanged = indirectly gets energy from Na/ K pump
How does the Glutamate Receptor Channel Function?
- Is a receptor for neuroT & ion channel
- NeuroT binds (at either of two binding sites) & channel opens
- Channel is permeable to Na or K equally
- -K wants to leave the cell, but not as much as Na wants to come in
- -Both can flow easily though this pore, however the NET EFFECT is that much more Na will enter than K will leave
- Glutamatergic & causes EPSP
- -Depol –> + flux of voltage
How does the GABA Receptor Channel Function?
- Binding site for GABA only
- When GABA binds, opens ion chan that’s selectively permeable to Cl
- Cl flows in and causes hyperpolarization = EPSP
What does the Driving Force Equation Tell Us?
- Whether partic ion is flowing in or out of the cell
- Think about it in terms of a positive ion
Positive = Outward Current
- Losing positive charge
- OR gaining negative charge
Negative = Inward Current
- Gaining positive charge
- Losing negative charge
Ix = Gx(Vm-Ex)
Gx = memb conduct Vm = memb potential Ex = equilib potential
