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H.Gaub / SS 2007BPZ§4.11 Biophysics of excitable cells.

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Presentation on theme: "H.Gaub / SS 2007BPZ§4.11 Biophysics of excitable cells."— Presentation transcript:

1 H.Gaub / SS 2007BPZ§4.11 Biophysics of excitable cells

2 H.Gaub / SS 2007BPZ§4.12 Axons are specialized for the conduction of an electrical impulse called an action potential

3 H.Gaub / SS 2007BPZ§4.13 Specialized regions of neurons carry out different functions

4 H.Gaub / SS 2007BPZ§4.14 Experimental techniques are conceptually simple

5 H.Gaub / SS 2007BPZ§4.15

6 H.Gaub / SS 2007BPZ§4.16 Cell-Semiconductor-Hybrids: Neuron on the Chip More: Fromherz MPI Martinsried

7 H.Gaub / SS 2007BPZ§4.17 Cell-Semiconductor-Hybrids: Neuron on the Chip

8 H.Gaub / SS 2007BPZ§4.18 Synapses are specialized sites where neurons communicate with other cells

9 H.Gaub / SS 2007BPZ§4.19 Multiple exitatory and inhibitory synaptic contacts allow complex neuronal interconnects

10 H.Gaub / SS 2007BPZ§4.110 Neurons are organized into circuits The knee-jerk reflex arc in the human.

11 H.Gaub / SS 2007BPZ§4.111 A schematic of the vertebrate nervous system

12 H.Gaub / SS 2007BPZ§4.112 Membrane depolarizations spread passively only short distances

13 H.Gaub / SS 2007BPZ§4.113 The electrical activity of neurons results from the opening and closing of specific ion-channels proteins in the neuron plasma membrane

14 H.Gaub / SS 2007BPZ§4.114 Voltage-gated cation channels generate action potentials

15 H.Gaub / SS 2007BPZ§4.115 The structure and function of the voltage-gated Na + channel

16 H.Gaub / SS 2007BPZ§4.116 Action potentials are propagated unidirectionally without diminution Movements of only a few Na + and K + ions generate the action potential

17 H.Gaub / SS 2007BPZ§4.117 Myelination increases the velocity of impulse conduction

18 H.Gaub / SS 2007BPZ§4.118 Formation and structure of a myelin sheath in the peripheral nervous system

19 H.Gaub / SS 2007BPZ§4.119 Each region of myelin formed by an individual glial cell is separated from the next region by an unmyelinated area called the node of Ranvier

20 H.Gaub / SS 2007BPZ§4.120 Action potentials travel rapidly from one node to the next

21 H.Gaub / SS 2007BPZ§4.121 Patch clamps permit measurement of ion movements through single channels

22 H.Gaub / SS 2007BPZ§4.122 Different patch clamping configurations

23 H.Gaub / SS 2007BPZ§4.123 Current flux through individual voltage-gated channels determined by patch clamping of muscle cells

24 H.Gaub / SS 2007BPZ§4.124 The oocyte expression assay can be used to determine if a protein is an ion channel

25 H.Gaub / SS 2007BPZ§4.125 Voltage-gated K + channels have four subunits each containing six transmembrane helices

26 H.Gaub / SS 2007BPZ§4.126 All five subunits in the nicotinic acetylcholine receptor contribute to the ion channel

27 H.Gaub / SS 2007BPZ§4.127 P segments form the ion-selectivity filter

28 H.Gaub / SS 2007BPZ§4.128 All pore-forming ion channels are similar in structure

29 H.Gaub / SS 2007BPZ§4.129 Acetylcholine and other transmitters can activate multiple receptors Acetylcholine is released by motor neurons at neuromuscular junctions

30 H.Gaub / SS 2007BPZ§4.130 Neurotransmitters are small molecules that transmit impulses at chemical synapses

31 H.Gaub / SS 2007BPZ§4.131 Influx of Ca 2+ triggers release of neurotransmitters Synaptic vesicles can be filled, exocytosed, and recycled within a minute

32 H.Gaub / SS 2007BPZ§4.132 Synaptic-vesicle and plasma-membrane proteins important for vesicle docking and fusion

33 H.Gaub / SS 2007BPZ§4.133 Chemical synapses can be excitatory or inhibitory

34 H.Gaub / SS 2007BPZ§4.134 Ligand-gated receptor ion channels function at fast synapses

35 H.Gaub / SS 2007BPZ§4.135 G protein-coupled receptors function at slow synapses

36 H.Gaub / SS 2007BPZ§4.136 Transmitter-mediated signaling is terminated by several mechanisms Following release of a neurotransmitter or neuropeptide, it must be removed or destroyed to prevent continued stimulation of the post-synaptic cell To end the signaling, the transmitter may –diffuse away from the synaptic cleft –be taken up by the pre-synaptic neuron –be enzymatically degraded Signaling by acetylcholine and neuropeptides is terminated by enzymatic degradation Signaling by most classic neurotransmitters is terminated by uptake

37 H.Gaub / SS 2007BPZ§4.137 Impulses transmitted across chemical synapses can be amplified and computed

38 H.Gaub / SS 2007BPZ§4.138 Opening of acetylcholine-gated cation channels leads to muscle contraction

39 H.Gaub / SS 2007BPZ§4.139 Cardiac muscarinic acetylcholine receptors activate a G protein that opens an ion channel Catecholamine receptors also induce changes in second-messenger levels that affect ion-channel activity

40 H.Gaub / SS 2007BPZ§4.140 A serotonin receptor indirectly modulates K + channel function by activating adenylate cyclase

41 H.Gaub / SS 2007BPZ§4.141 Membrane disks in the outer segments of rod cells contain rhodopsin, a light- sensitive protein

42 H.Gaub / SS 2007BPZ§4.142 Absorption of a photon triggers isomerization of retinal and activation of opsin

43 H.Gaub / SS 2007BPZ§4.143 Cyclic GMP is a key transducing molecule in rod cells

44 H.Gaub / SS 2007BPZ§4.144 A thousand different G protein-coupled receptors detect odors

45 H.Gaub / SS 2007BPZ§4.145 Impulse transmission across electric synapses is nearly instantaneous

46 H.Gaub / SS 2007BPZ§4.146 Comparison of action potential transmission across electric and chemical synapses

47 H.Gaub / SS 2007BPZ§4.147 Learning and memory Learning is the process by which animals modify their behavior as a result of experience or acquisition of information about the environment Memory is the process by which this information is stored and retrieved –Long term memory involves the formation or elimination of certain synapses –Short-term memory involves changes in the release and function of neurotransmitters at specific synapses

48 H.Gaub / SS 2007BPZ§4.148 Study of the gill withdrawal reflex of Aplysia has provided insight into short- term learning processes This simple behavior exhibits the most elementary forms of learning familiar in vertebrates: habituation, sensitization, and classical conditioning

49 H.Gaub / SS 2007BPZ§4.149 Facilitator neurons mediate sensitization of Aplysia withdrawal reflex Individuals were restrained in small aquariums in a manner that the gill was exposed. A tactile stimulus was administered to the siphon and elicited the gill and siphon withdrawal reflex. A photocell was placed under the gill to record amplitude and duration of the response elicited by the stimulus. Habituation was observed when the stimulus was delivered repeatedly to the siphon. Stimulus every 90 seconds resulted in a rapidly declined response. By delivering an electric shock to the tail the response was rapidly restored, dishabituation occurred. Sensitization was observed when a strong stimulus was administered to the tail, this enhanced a completely rested reflex in Aplysia californica.

50 H.Gaub / SS 2007BPZ§4.150 Coincidence detectors participate in classical conditioning and sensitization

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