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#03: CELLS, SYNAPSES & CIRCUITS behavior analysis in a natural environment in the laboratory cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior relating nerve cells to behavior #03: CELLS, SYNAPSES & CIRCUITS behavior analysis in a natural environment in the laboratory cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior relating nerve cells to behavior #03: CELLS, SYNAPSES & CIRCUITS behavior analysis in a natural environment in the laboratory cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior relating nerve cells to behavior CELLS, SYNAPSES & CIRCUITS nervous systems have amazing complexity # of cells... e.g. human brain has 1012 neurons 1 neuron can perform many cellular functions # of synapses... 1 neuron can talk to > 104 others assessing function in behavior difficult CELLS, SYNAPSES & CIRCUITS nervous systems have amazing complexity # of cells... e.g. human brain has 1012 neurons 1 neuron can perform many cellular functions # of synapses... 1 neuron can talk to > 104 others assessing function in behavior difficult however... all neurons are ~ similar in many aspects can chose appropriate model organism to study in general, we can understand the “units”... but there are usually an overwhelming # of them CELLS, SYNAPSES & CIRCUITS nervous system structure (bottom up approach) ... NEURON SYNAPSE RESTRICTED NEURAL CIRCUIT (NEURAL ASSEMBLY) STRUCTURES NEURAL NETWORK (CIRCUIT) BEHAVIOR CELLS, SYNAPSES & CIRCUITS nervous system structure... NEURON SYNAPSE RESTRICTED NEURAL CIRCUIT (NEURAL ASSEMBLY) STRUCTURES NEURAL NETWORK (CIRCUIT) BEHAVIOR CELLS, SYNAPSES & CIRCUITS nervous system structure... NEURON SYNAPSE RESTRICTED NEURAL CIRCUIT (NEURAL ASSEMBLY) STRUCTURES NEURAL NETWORK (CIRCUIT) BEHAVIOR CELLS, SYNAPSES & CIRCUITS nervous system structure... NEURON SYNAPSE RESTRICTED NEURAL CIRCUIT (NEURAL ASSEMBLY) STRUCTURES NEURAL NETWORK (CIRCUIT) BEHAVIOR CELLS, SYNAPSES & CIRCUITS nervous system structure... NEURON SYNAPSE RESTRICTED NEURAL CIRCUIT (NEURAL ASSEMBLY) STRUCTURES NEURAL NETWORK (CIRCUIT) BEHAVIOR CELLS, SYNAPSES & CIRCUITS nervous system network (circuit) structure... NEURONAL ARCHITECTURE OF BEHAVIOR nervous system network (circuit) structure... SENSORY INPUT CENTRAL PROCESSING MOTOR OUTPUT BEHAVIOR #03: CELLS, SYNAPSES & CIRCUITS behavior analysis in a natural environment in the laboratory cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior relating nerve cells to behavior #03: CELLS, SYNAPSES & CIRCUITS general neuron anatomy – 4 main bits cell body or soma axon terminals dendrites BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma axon terminals dendrites BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma axon terminal dendrites BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma axon terminals dendrites BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma axon terminals dendrites BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma... nucleus axon... project distances to other cells terminals... output (typically) dendrites... input (typically) BASIC PROPERTIES OF NERVE CELLS general neuron anatomy – 4 main bits cell body or soma... nucleus axon... project distances to other cells terminals... output (typically) dendrites... input (typically) “typical” vertebrate neuron BASIC PROPERTIES OF NERVE CELLS vertebrate neurons... often bi- or multipolar cell body or soma axon terminals dendrites BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... BASIC PROPERTIES OF NERVE CELLS invertebrate neurons... tend to be monopolar cell body or soma axon terminals dendrites... typically develop off of the axon, not cell body often terminals & dendrites difficult to distinguish... input & output functions not always clear BASIC PROPERTIES OF NERVE CELLS neurons conduct electrical current current = rate of movement of charge = I (pA) voltage = charge difference between 2 points = V aka potential difference conductance = ease of current flow = g resistance = restriction of current flow = R () = 1/g Ohm’s law: V=IR or I=gV BASIC PROPERTIES OF NERVE CELLS electrical current carried by ions (charged atoms) 4 important ones cations (+ve charge): Na+ K+ Ca2+ anions (–ve charge): Cl– BASIC PROPERTIES OF NERVE CELLS ions flow in or out of neurons through channels channels = protein complexes ~ membrane “pores” passive or leak channels: always open active or gated channels: require signals to open... voltage-gated: open with specific change in V ligand-gated: open with specific chemical signal BASIC PROPERTIES OF NERVE CELLS neurons conduct electrical current current = rate of movement of charge = I (pA) single channel flow in 1 – 20 pA range (10–13 A) corresponds to 0.6 – 1.2 x 107 ions/s voltage = charge difference between 2 points = V aka potential difference conductance = ease of current flow = g resistance = restriction of current flow = R () = 1/g BASIC PROPERTIES OF NERVE CELLS increased conductance in neurons from... channels opening in membrane current flow in or out of neuron voltage driving flow = equilibrium potential of a neuron ... the voltage difference on either side of membrane ... 1 of the forces driving ions to equal concentration = e.g. ... Na+ flow # open Na+ Na+ equilibrium into cell channels potential BASIC PROPERTIES OF NERVE CELLS resting potential... V difference across membrane of resting neuron glass microelectrode & reference electrode circuit both outside cell no difference microelectrode into neuron it is –ve ~ outside (net) p.16 fig.1.6 BASIC PROPERTIES OF NERVE CELLS what determines resting potential... e.g., K+ ion concentration gradient due to: channel specificity, only certain ions can pass electrical gradient vs chemical gradient... equilibrium rules apply to all other ions typical cells, p.16 fig.1.6 K+ equilibrium potential (EK) = –80 mV BASIC PROPERTIES OF NERVE CELLS Ei = of all equilibrium potentials resting potential typical equilibrium potentials for important ions: EK –80 mV ENa +60 mV ECa +155 mV ECl –65 mV (~ resting potential, distribution) Ei calculated with Nernst equation... we will not bother (but feel free to look it up if you are curious) BASIC PROPERTIES OF NERVE CELLS changes in net intracellular charge neuron functions stimulus neuron net charge... +ve ~ resting potential: membrane depolarized –ve ~ resting potential: membrane hyperpolarized inject +ve current into cell low small depolarization... higher action potential action potential = spike triggered at threshold all-or-none, features characteristic of a neuron p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS changes in net intracellular charge neuron functions stimulus neuron net charge... membrane ~ resting potential: p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS changes in net intracellular charge neuron functions stimulus neuron net charge... membrane ~ resting potential: +ve depolarized p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS changes in net intracellular charge neuron functions stimulus neuron net charge... membrane ~ resting potential: +ve depolarized –ve hyperpolarized p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS action potential has wave form & phases rising overshoot falling undershoot (afterhyperpolarization) p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS action potential ~ with ionic movement rising phase reflects: Na+ inward, V-gated channels open ENa +ve, high conc. outside membrane potential ENa (+ve) repolarization & falling phase reflects: Na+ channels closing Na+ inactivation K+ outward, delayed V-gated K+ channels open EK –ve, high conc. inside p.18 fig.1.7 BASIC PROPERTIES OF NERVE CELLS action potential ~ with ionic movement undershoot reflects: continued K+ conductance membrane potential EK (–ve) return to resting potential reflects: V gated K+ channels closing p.18 fig.1.7 (V insufficient to gate) spike for only ~ 1 or 2 ms travel fast down axon to terminals ... 120 m/s #03: CELLS, SYNAPSES & CIRCUITS behavior analysis in a natural environment in the laboratory cells, synapses & circuits basic properties of nerve cells synaptic transmission neuronal architecture & behavior relating nerve cells to behavior SYNAPTIC TRANSMISSION communication between neurons at synapse presynaptic cell terminal + postsynaptic cell dendrites two types of signals & synapses: chemical electrical SYNAPTIC TRANSMISSION chemical synapse transmitter release from presynaptic cell into synaptic cleft between cells bind to receptors on postsynaptic cell opens (or closes) ion channels in postsynaptic cell ions flow across membrane relatively slow signal can be plastic (modified) by experiences SYNAPTIC TRANSMISSION electrical synapse gap junctions between pre- & postsynaptic cells physically continuous current passes between cells relatively fast signal less easily modified what behavior might these be best suited for ? SYNAPTIC TRANSMISSION chemical synapse (A) action potential in presynaptic cell depolarizes presynaptic membrane opens V-gated Ca2+ channels Ca2+ ions flow into cell ... where neurotransmitters are stored in vesicles Ca2+ triggers vesicle docking at release sites p.20, fig.1.8 SYNAPTIC TRANSMISSION chemical synapse vesicles & membrane fuse neurotransmitter released into synaptic cleft ... by exocytosis transmitter diffuses across synaptic cleft p.20, fig.1.8 SYNAPTIC TRANSMISSION chemical synapse ... either docks with receptors on postsynaptic membrane opens V-gated Na+ channels Na+ ions flow into postsynaptic cell depolarizes cell = potential p.20, fig.1.8 difference across membrane depolarizing potential = excitatory postsynaptic potential (EPSP) ... neuron spikes SYNAPTIC TRANSMISSION chemical synapse ... or docks with receptors on postsynaptic membrane opens V-gated K+ channels K+ ions flow out of postsynaptic cell hyperpolarizes cell = potential p.20, fig.1.8 difference across membrane hyperpolarizing potential = inhibitory postsynaptic potential (IPSP) ... neuron silent SYNAPTIC TRANSMISSION chemical synapse (B), two types of signals: EPSP postsynaptic neuron depolarizes... spikes p.20, fig.1.8 SYNAPTIC TRANSMISSION chemical synapse (B), two types of signals: EPSP postsynaptic neuron depolarizes... spikes IPSP postsynaptic neuron hyperpolarizes... silent p.20, fig.1.8 SYNAPTIC TRANSMISSION neurotransmitters, 3 categories: amines ... ~ small & stored in vesicles amino acids peptides ... ~ large & stored in secretory granules secretory granules also release Ca2+- } dependent SYNAPTIC TRANSMISSION neurotransmitters, additional function also serve as 1st messenger signals bind G-proteincoupled receptors 2nd messenger cascades in postsynaptic cell amplify signals gene activity SYNAPTIC TRANSMISSION neuron symbols inhibitory excitatory SYNAPTIC TRANSMISSION neuron symbols inhibitory excitatory SYNAPTIC TRANSMISSION neuron symbols inhibitory excitatory SYNAPTIC TRANSMISSION synaptic plasticity = variability in transmission efficacy homosynaptic = through repeated activity of 1 cell: low rate synaptic depression p.22, fig.1.9 SYNAPTIC TRANSMISSION synaptic plasticity = variability in transmission efficacy homosynaptic = through repeated activity of 1 cell: low rate synaptic depression high rate synaptic facilitation or potentiation p.22, fig.1.9 SYNAPTIC TRANSMISSION synaptic plasticity = variability in transmission efficacy heterosynaptic = through activity of >1 neuron, modulated by neurons extrinsic to the synapse (C): inhibitory signal presynaptic inhibition p.22, fig.1.9 SYNAPTIC TRANSMISSION synaptic plasticity = variability in transmission efficacy heterosynaptic = through activity of >1 neuron, modulated by neurons extrinsic to the synapse (C): inhibitory signal presynaptic inhibition excitatory signal presynaptic facilitation p.22, fig.1.9
