3: Action Potential Conduction & Synaptic Transmission

Question 1

What 3 Things Make the AP Move Slowly?

Answer 1

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

Question 2

What is the Invertebrate Solution?

Answer 2

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

Question 3

What is the Vertebrate Solution?

Answer 3

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

Question 4

How and Where do Oligodendrocytes Myelinate?

Answer 4

• In the CNS
• Wraps membrane around axon
• Adds fatty lipid memb around the axon
• Can myelinate several axons at a time

Question 5

How and Where do Schwann Cells Myelinate?

Answer 5

• In the PNS
• Wrap themselves around an axon
• Squeeze out most of the cytoplasm & press down to create multiple wraps
• -Insulate axons

Question 6

What is the Best Theory Behind Multiple Sclerosis?

Answer 6

• 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

Question 7

What is Guillain-Barre Syndrome?

Answer 7

• 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

Question 8

How was Neurotransmission Proven?

Answer 8

• 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

Question 9

What are the Processes of the Active Synapse?

Answer 9

• 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

Question 10

What is the Function of a Ca Pump?

Answer 10

• Restored the conc grad of Ca after neurT release

- Expels 2 Ca & takes in 2 H to establish conc grad

Question 11

What is the Function of an Ion Exchanger?

Answer 11

• 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

Question 12

How does the Glutamate Receptor Channel Function?

Answer 12

• 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

Question 13

How does the GABA Receptor Channel Function?

Answer 13

• Binding site for GABA only
• When GABA binds, opens ion chan that’s selectively permeable to Cl
• Cl flows in and causes hyperpolarization = EPSP

Question 14

What does the Driving Force Equation Tell Us?

Answer 14

• 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