Chapter 12 – Transport across cell membranes
Ion channels and nerve cell signaling
Task of nerve cell/neuron; receive, integrate and transmit a signal
Neuron consist of
Cell body with nucleus
Axon; long, away from the cell body. Divides at the end into many branches
each of which ends in a nerve terminal.
Dendrite; short, toward the cell body
Neurons solve the long-distance communication by an active signaling mechanism.
The traveling wave of electrical excitation action potential
The action potential
Depolarization; Na+ channels opens, Na+ enters the cell. So, shift from negative
value to positive value.
Repolarization; Na+ channels close, K+ opens. K+ go out of the cell. So, shift from
positive to negative.
Hyperpolarization; additional K+ go out of the cell. So, more negative
Na+ channels go from;
Open inactivated closed.
The Na+ channel remain in inactivated state until the membrane potential has
returned to its initial negative value
Synapse
Action potential reached the nerve terminals, the signal must be relayed to target
cells.
Synapses transmitted the signal.
The electrical signal is converted into a chemical signal known as neurotransmitter.
Neurotransmitters are stored in the nerve terminals within membrane enclosed
synaptic vesicles.
The depolarization opens Ca2+ channels, which are in the plasma membrane of the
presynaptic nerve terminal. The increase in Ca2+ in the cytosol triggers the
membrane fusion that releases the neurotransmitter.
Neurotransmitter receptors
Neurotransmitters bind to neurotransmitter receptors that causes a change in the
membrane potential of the target cell which if large enough triggers the action
potential.
Neurotransmitters in the synaptic cleft are destroyed by enzymes.
Neurotransmitter receptor types
1. Slow responses
2. Rapid responses – transmitter-gated ion channels; function is to convert the
chemical signal carried by neurotransmitter back into an electrical signal. The
Ion channels and nerve cell signaling
Task of nerve cell/neuron; receive, integrate and transmit a signal
Neuron consist of
Cell body with nucleus
Axon; long, away from the cell body. Divides at the end into many branches
each of which ends in a nerve terminal.
Dendrite; short, toward the cell body
Neurons solve the long-distance communication by an active signaling mechanism.
The traveling wave of electrical excitation action potential
The action potential
Depolarization; Na+ channels opens, Na+ enters the cell. So, shift from negative
value to positive value.
Repolarization; Na+ channels close, K+ opens. K+ go out of the cell. So, shift from
positive to negative.
Hyperpolarization; additional K+ go out of the cell. So, more negative
Na+ channels go from;
Open inactivated closed.
The Na+ channel remain in inactivated state until the membrane potential has
returned to its initial negative value
Synapse
Action potential reached the nerve terminals, the signal must be relayed to target
cells.
Synapses transmitted the signal.
The electrical signal is converted into a chemical signal known as neurotransmitter.
Neurotransmitters are stored in the nerve terminals within membrane enclosed
synaptic vesicles.
The depolarization opens Ca2+ channels, which are in the plasma membrane of the
presynaptic nerve terminal. The increase in Ca2+ in the cytosol triggers the
membrane fusion that releases the neurotransmitter.
Neurotransmitter receptors
Neurotransmitters bind to neurotransmitter receptors that causes a change in the
membrane potential of the target cell which if large enough triggers the action
potential.
Neurotransmitters in the synaptic cleft are destroyed by enzymes.
Neurotransmitter receptor types
1. Slow responses
2. Rapid responses – transmitter-gated ion channels; function is to convert the
chemical signal carried by neurotransmitter back into an electrical signal. The
