basic properties of nerve cells
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Transcript basic properties of nerve cells
#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