Neurons: Cellular and Network Properties. 8. About this Chapter. Organization of the nervous system Electrical signals in neurons Cell-to-cell communication in the nervous system Integration of neural information transfer. Nervous System Subdivisions. Organization of the Nervous System.
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Dendrites receive incoming signals; axons carry outgoing information
Glial cells maintain an environment suitable for proper neuron function
Figure 8-5 (1 of 2)
Subthreshold and suprathreshold graded potentials in a neuron
If a graded potential does not go beyond the treshold at the trigger zone an action potential will not be generated
Depolarizing grading potential are excitatory
Hyperpolarizing graded potentials are inhibitory
Graded potential= short distance, lose strength as they travel, can initate an action potential
Na+ channels have two gates: activation and inactivation gates
Terminology associated with changes in membrane potential (chpt 5 figure)
Animation: Nervous I: The Membrane Potential
Cell is more positive outside than inside
Figure 8-9 (1 of 9)
As ions move across the membrane the potential increases
Figure 8-9 (2 of 9)
Graded potentials have brought the membrane potential up to threshold
Figure 8-9 (3 of 9)
Beyond threshold potential the sodium gated channels allow the ion to move in, making the inside of the cell more positive
Figure 8-9 (4 of 9)
Na+ continues to move into the cell until it reaches electrical equilibrium. At that point Na+ movement stops
Figure 8-9 (5 of 9)
K+ moves out of the cell along its gradient and the inside of the cell becomes more and more negative
Figure 8-9 (6 of 9)
Hyperpolarization (undershoot) occurs when the potential drops below resting; caused by the continuing movement of K+ out of the cell
Figure 8-9 (7 of 9)
Leaked Na+ & K+ in cell increases potential toward resting voltage
Figure 8-9 (8 of 9)
Returns to its original state where the outside is more positive than the inside and the membrane potential is -70mv
Figure 8-9 (9 of 9)
Action potentials will not fire during an absolute refractory period
Each region of the axon experiences a different phase of the action potential
Saltatory conduction- signal seems to “jump” from node to node moving swiftly- compensates for smaller diameter.
Demyelination slows down signal conduction because the current leaks. Sometimes conduction does not reach the next node and dies out.
Since all action potentials are identical, the strength of a stimulus is indicated by the defrequency of action potentials. Neurotransmitter amounts released are directly propertional to frequency as long as a sufficient supply is available
Resting membrane potential is the electrical gradient between ECF and ICF
Inside of the cell is more negative than the outside
Electrical gradient create the ability to do work just like concentration gradients
Resting membrane potential is the electrical gradient between ECF and ICF. Resting membrane potential is due mostly to potassium- it is the equilibrium potential of K+
A relative scale shifts the charge to a -2
Can be calculated using the Nernst Equation
Concentration gradient is opposed by membrane potential
Slow synaptic potentials
and long-term effects
fast synaptic potential
gated ion channel
proteins or regulates
synthesis of new
Ion channels open
Ion channels close
Fast and slow responses in postsynaptic cells involve ion channels and G-protein receptor
Chemical synapses use neurotransmitters; electrical synapses pass electrical signals.
Chemical synapses are most common. Electrical synapses are found in the CNS and other cells that use electrical signals (heart)
An action potential depolarizes
the axon terminal.
The depolarization opens voltage-
gated Ca2+ channels and Ca2+
enters the cell.
Calcium entry triggers exocytosis
of synaptic vesicle contents.
Neurotransmitter diffuses across
the synaptic cleft and binds with
receptors on the postsynaptic cell.
Neurotransmitter binding initiates
a response in the postsynaptic
Synthesis and recycling of acetylcholine at a synapse
Long-term potentiation- mechanism used in learning and memory using Glutaminergic Receptors.
If the cell body is not damaged the neuron will most likely survive. Axon healing is similar to growth cone of a developing axon.