Nervous System III

Question 0

I. AP Refractory Period

definition

Answer 0

prevents back-firing

Question 1

Nervous Systems III

parts

Answer 1

I. AP Refractory Period
II. Saltatory Conduction
III. Generator Potentials (GPs)
IV. Chemical Synapses
V. Model Example: Vertebrate Neuromuscular Junction (NMJ)
VI. Postsynaptic Potentials (PSPs)
VII. Summation of PSPs

Question 2

I. AP Refractory Period

parts

Answer 2

A. Absolute Refractory Period (about 1 ms)

B. Relative Refractory Period (2-3 ms)

Question 3

Absolute Refractory Period

Answer 3

about 1ms

VGNaC’s remain inactive about1 ms

Question 4

Relative Refractory Period

Answer 4

about 2-3 ms

still have VGRC’s open (producing the “undershoot”)

Question 5

II. Saltatory Conduction

parts

Answer 5

A. Big axons wrapped in MYELIN

B. AP moves by “jumping” from node to node

Question 6

Big axons wrapped in myelin

Answer 6

• “insulates”

- open “nodes”along axon allow local ion flux

Question 7

AP moves by “jumping” from node to node

Answer 7

(this is faster for AP conduction along the axon, jumping from node to node

Figure 37.13 Schwann Cells and the myelin sheath
Figure 37.14 Saltatory Conduction

Question 8

III. Generator Potentials (GPs)

Answer 8

• in sensory neurons
• transduces physical stimulus (ex. touch) into electrical signal.

ex)
-crayfish stretch receptor neuron- diagram (lots of diagrams)
- stretch muscle (increase length) cause depolarization of Vm in neuron = GP
Figure: Sensory Transduction in the crayfish stretch receptor

Question 9

IV. Chemical Synapses

parts

Answer 9

A. Structure

B. Synaptic Transmission

Question 10

A. Structure

parts

Answer 10

1. Presynaptic nerve terminal

2. Postsynaptic neuron

Question 11

1. Presynaptic nerve terminal

Answer 11

- synaptic vesicles (SVs)
contain neurotransmitter (NT)

Question 12

2. Postsynaptic neuron

Answer 12

localized high concentration of NT receptors (membrane proteins)
“ligand-gated ion channel”

Question 13

B. Synaptic Transmission

Answer 13

1. AP invades presynaptic terminal
   - induce “EXOCYTOSIS” of S.V. & release NT
2. NT diffuses fast across synaptic cleft
3. NT binds to NT receptors of postsynaptic cell
   - opens internal channels
4. Ions flow through receptors –>

Question 14

IV. (Model Example): Vertebrate Neuromuscular Junction (NMJ)

definition

Answer 14

Motor neuron (spinal cord)
--> axon to skeletal muscle

[Motor neuron (in spinal cord) sends axon out to muscle fiber and makes a synapse on it (NMJ)]

Question 15

IV. (Model Example): Vertebrate Neuromuscular Junction (NMJ)

parts

Answer 15

A. Neuromuscular Junction (NMJ) Chemistry

B. Role of Ca++

Question 16

IV. (Model Example): Vertebrate Neuromuscular Junction (NMJ)

A. Neuromuscular Junction (NMJ) Chemistry

Answer 16

1. NT= acetyl choline (ACh)

2. Postsynaptic NT R’s

Question 17

1. NT= acetyl choline (ACh)

Answer 17

a) made in nerve terminal:
choline + acetylCo-A => ACh + Co-A

b) pack into SVs

Question 18

2. Postsynaptic NT R’s

Answer 18

a) Nicotinic AChR, (NAChRs)
b) Ion Channels permeable to cations (K+, Na+)
ACh + nAChR(closed) = ACh-nAChR(open)

Question 19

IV. Vertebrate Neuromuscular Junction (NMJ)

B. Role of Ca++

Answer 19

1. AP arrives in presynaptic nerve terminal, (DEPOLARIZING the Vm)
2. ⬆️Vm => open VGCaCs in membrane
   => allow Ca+ influx
3. Ca+ influx => ⬆️ [Ca] in –> induce exocytosis of “docked” SVs
4. NT release
5. SV recycled & refilled

Figure: 37.15 A Chemical Synapse
Figure 37.10 Depolarization Can Induce an AP

Question 20

IV. Postsynaptic Potentials (PSPs)

Parts

Answer 20

A. Ionic Basis
B. Excitatory Postsynaptic Potentials (EPSPs)
C. Inhibitory Postsynaptic Potentials (PSPSs)

Question 21

IV. Postsynaptic Potentials (PSPs)

A. Ionic Basis

Answer 21

e.g. NT opens Rs permeable to Na+; this allows Na+ influx

diagram/graphs

Question 22

IV. Postsynaptic Potentials (PSPs)

B. Excitatory PSPs

Answer 22

1. NT can drive Vm to threshold for AP
2. Examples: ACh & glutamate
3. Stimulate presynaptic nerves
   - diagram

Question 23

IV. Postsynaptic Potentials (PSPs)

C. Inhibitory PSPs

Answer 23

1. diagram
2. E(Na) = +60
   E(K) = -90
   E(Ca) = +50
   E(Cl) = -60
3. Visual NT’s for IPSPs
   a) ⬆️ Cl- flow –> Cl- in
   => more negative Vm
   b) usually GABA (gamma - amino- butyric acid) & glycine

Question 24

VII. Summation of PSPs

parts

Answer 24

A. PSP properties
B. Spatial summation
C. Temporal Summation
D. Integration

Question 25

VII. Summation of PSPs

A. PSP properties

Answer 25

1. Local “graded” responses

2. PSPs not equal to APs

Question 26

1. Local “graded” responses

Answer 26

amplitude proportional to number of ions flowing

–> proportional to R’s opened. (therefore PSPs can be ADDITIVE.)

Question 27

2. PSPS are not equal to APs

Answer 27

a) not all-or-none
b) not actively propagated
i. e. not regenerative

Question 28

VII. Summation of PSPs

B. Spatial summation

Answer 28

1. Multiple synapses / neuron ( > 10^3 / neuron in CNS)
2. EPSPs arrives simultaneous can add
   (simultaneous EPSPs at multiple synapses can spatially summate to
   reach AP threshold)

Diagram

Question 29

VII. Summation of PSPs

C. Temporal Summation

Answer 29

Fire 1 synapse repeatedly & rapidly

Diagram

Question 30

VII. Summation of PSPs

D. Integration

Answer 30

diagram

EPSPs & IPSPs co-occurring: IPSPs can prevent EPSPs from driving Vm to threshold