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Announcements Mid term room assignments posted to webpage A – HoS361 (Pavilion) Hoang – LischkaS309 Lishingham - NguiS143 Nguyen – SeguinS128 Sek – Zia.

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Presentation on theme: "Announcements Mid term room assignments posted to webpage A – HoS361 (Pavilion) Hoang – LischkaS309 Lishingham - NguiS143 Nguyen – SeguinS128 Sek – Zia."— Presentation transcript:

1 Announcements Mid term room assignments posted to webpage A – HoS361 (Pavilion) Hoang – LischkaS309 Lishingham - NguiS143 Nguyen – SeguinS128 Sek – Zia H305 ( correction) Lecture 02S319 Lecture 01

2 Office hours: today 2-4pm, Wed TA Office hours: Wed 12-1 Tutorial Thurs – extra office hours only Answers to practice questions will be posted later today Bring a calculator to the midterm test –Scientific OK ; Not programmable Midterm schedule conflicts –Wednesday 5pm deadline – bring your ROSI timetable Material on midterm – end of today’s lecture

3 Last Lecture –Synaptic integration Spatial & Temporal Summation Today –Synaptic Plasticity

4 Soma and dendrites Synaptic inputs Axon Hillock Passive current flow Above threshold? Yes No Action Potential Passive Current Decays to zero Summation Synaptic Plasticity

5 Changes in the strength of synaptic transmission associated with activity or experience Basis for behaviour such as learning and memory

6 1.Heterosynaptic Modulation 2.Long-term Potentiation 3.Homosynaptic Modulation 1.Facilitation 2.Post-tetanic Potentiation Types of synaptic plasticity

7 Heterosynaptic facilitation Aplysia californica (sea slug)

8 Tap the tail and the gill is withdrawn weakly Tap the head and then the tail the gill is withdrawn strongly Aplysia (sea slug) gill withdrawal reflex

9 Heterosynaptic facilitation Aplysia (sea slug) gill withdrawal reflex Gill Muscle Motor neuron Sensory neuron tail Head interneuron Sensory neuron serotonin

10 Heterosynaptic facilitation 1.Serotonin released from interneuron 2.  cAMP in sensory nerve terminal 3.Closes potassium channels 4.Delays repolarization of action potentials 5.Allows more Ca++ to enter the nerve terminal 6.More transmitter release

11 Tail Sensory Neuron Action potential After Serotonin Motor Neuron Synaptic potential Broader AP allows more Ca++ in

12 Long-term Potentiation Mammalian hippocampus, and other brain regions Hippocampus is a structure that is important for learning, especially spatial learning

13 Long-term Potentiation Long-lasting increase (hours to days) in synaptic strength following short high frequency stimulation EPSP Amplitude Time 100% 200% 100 Hz 2 hours

14 Long-term potentiation Depends on two types of glutamate receptors 1.AMPA permeable to Na+, K+ Function under all conditions 2.NMDA Permeable to Na+, K+, and Ca++ BUT normally blocked by Mg++ Only operate under high frequency stimulation

15 Na+ NMDA AMPA Mg++ Normal Stimulation

16 Ca++ Na+ Depolarization Ca++ NMDA AMPA Ca++ Ca++ activates second messenger Mg++ Strong Stimulation

17 NMDA receptor Key Points 1.Normally blocked by Mg++ 2.Strong depolarization removes Mg++ and allows Ca++ to enter postsynaptically 3.Ca++ activates second messenger pathways that strengthen synaptic transmission Probably activates more AMPA receptors

18 Homosynaptic Modulation Facilitation Use-dependent increase in synaptic transmission eg. two stimuli are applied to a motor nerve in rapid succession, the second response is bigger than the first Not the same as temporal summation

19 Synaptic potentials Stimuli close together 1 2 Facilitation Amplitude of 2 is greater than amplitude of 1 Stimuli farther apart – amplitudes are the same

20 Why get facilitation? If two stimuli are close together there is an accumulation of Ca++ inside the presynaptic nerve terminal –Called residual calcium If the two stimuli are far apart the Ca++ from first stimulus dissipates before second stimulus Lasts for seconds

21 Ca++ Na+ Depolarization

22 Ca++ Na+ Depolarization Ca++

23 Post-tetanic potentiation Tetanic stimulation  high frequency (50 – 100 times per second) Lasts for minutes

24 EPSP Amplitude Test stimuli 1 / 30 sec 50 Hz for 1 min Potentiation 10 minutes 0 Time Normal Ca++ saline depression

25 Initial test stimuliestablish baseline During tetanus High release  depletion of vesicles Accumulation of internal Ca++ Post-tetanus Replenishment of Vesicles by recycling Greater release due to high internal Ca++ Post-tetanic potentiation

26 Summary Synaptic plasticity is a use-dependent change in synaptic strength Heterosynaptic plasticity – one synapse modulates another –Aplysia gill withdrawal reflex Homosynaptic plasticity includes: facilitation and potentiation –Both depend on calcium


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