NERVOUS SYSTEM (LECTURE 14) Flashcards
How many functions does the nervous system have?
3
Name the 3 functions of the nervous system.
Sensory input, integration, motor output.
Sensory input is the response to…
external and internal stimuli, made possible by sensory neurons.
Describe integration.
It is the interpretation of sensory input - decides the appropriate response.
Describe motor output.
It is the conduction of signals from the central nervous system to the effector cells, made possible by motor neurons.
Neurons are cells specialized for…
transmitting electrical and chemical signals.
Neurons are comprised of what 2 structural components?
The cell body and fiber-like extensions.
What are the 2 classes of fiber-like extensions found on neurons?
Dendrites and axons.
Describe dendrites.
These convey signals towards the cell body - they are short and numerous.
Describe axons.
These conduct impulse away from the cell as long, single processes. Some are insulated by a myelin sheath and they all end in an axon terminal.
What do axon terminals do?
They relay signals to other cells by releasing neurotransmitters.
Neurons communicate via…
synapses.
Neurotransmitters are released from a ____ neuron and act on a ____ neuron.
Neurotransmitters are released from a pre-synaptic neuron and act on a post-synaptic neuron.
Nerve signals/impulses are changes in…
voltage across the plasma membrane.
Nerve signals/impulses (changes in voltage) are caused by…
the movement of ions across the membrane.
What (positively charged) ions move across a neuron’s membrane to cause changes in voltage?
Na+ and K+.
What is the membrane potential of a resting neuron?
About -70 mV.
Is the inside or outside of a resting neuron more negative?
The inside is more negative than the outside.
What determines membrane potential?
The ion distribution across the membrane.
What negatively charged molecules (anions) can cause a change in membrane potential? (5)
Negatively charged proteins, amino acids, sulfate and phosphate, Cl-.
Charged molecules can cross a neuron membrane using what 2 ways?
Either through passive ion channels or gated ion channels.
What are passive ion channels important for? When do they close?
These are important for maintaining -70mV membrane potential. They are open all the time.
Describe gated ion channels.
These require a stimulus to open.
Give an example of a stimulus that can open a gated ion channel.
A change in voltage.
What does the Na+/K+ ATPase pump do?
These maintain concentration gradients of Na+ and K+ across the membrane (High [Na+] outside and high [K+] inside).
For every 1 ATP used, how many Na+ / K+ are pumped into / out of the neuron?
3 Na+ pumped out. 2 K+ pumped in.
There are many passive ____ ____ channels that are always ____.
There are many passive K+ channels that are always open.
What does K+ do with the help of the many passive K+ channels?
K+ diffuses down its concentration gradient out of the cell (gradient created by the Na+/K+ ATPase pump).
Stimuli can cause changes in ____ ____.
Stimuli can cause changes in membrane potential.
Stimuli opens ____ ____ ____, changing the ____ ____ across the membrane.
Stimuli opens gated ion channels, changing the charge distribution across the membrane.
Hyperpolarization is occurring when…
the inside of the neuron becomes more negative due to gated K+ channels opening, allowing K+ to diffuse out of the cell.
Depolarization is occurring when…
the inside of the neuron becomes more positive due to Na+ channels opening, allowing Na+ into the cell.
When is an action potential generated?
When a depolarizing stimulus is strong enough to pass the threshold potential.
What does an action potential do if it is generated?
Action potential moves along the entire length of the axon and stimulates the release of neurotransmitters from the axon terminal.
Name the steps to generate (propagate) an action potential. (5)
(1) Resting state. (2) Threshold. (3) Depolarization. (4) Repolarization. (5) Undershoot.
Describe the resting state. (2)
No gated channels are open; -70mV resting potential.
Describe threshold - what occurs at threshold?
Stimuli causes gated Na+ channels to open ; Na+ flows in causing depolarization.
Describe depolarization.
If depolarization reaches threshold, an action potential will begin. At threshold, voltage-gated Na+ channels open causing a large depolarization.
Describe repolarization.
Na+ channels close AND K+ channels open - K+ moves out of the cell.
Describe undershoot.
K+ channels are slow to close allowing more K+ to leave. Membrane potential is more negative than resting potential.
Why is the neuron’s membrane insensitive to stimuli during repolarization and undershoot?
Na+ channels are closed and thus membrane is insensitive to stimuli.
An action potential is a ____ ____ event.
An action potential is a localized electrical event.
Describe the propagation (path) of the action potential.
If stimulation is strong enough to reach threshold, an action potential will be initiated and move along the length of the axon to the axon terminal.
How does the action potential propagate along the axon?
Depolarization in one part of the axon causes depolarization in the region right next to it by opening voltage gated Na+ channels.
Why can an action potential only move in one direction?
Since during repolarization and undershoot (processes directly following depolarization), a membrane cannot be depolarized - so action potential can only move in one direction.
What is a synapse?
It is a space between presynaptic (transmitting) cell and a postsynaptic (receiving) cell.
What occurs at chemical synapses?
Neurotransmitters are released from the axon terminal of a presynaptic cell and act on a postsynaptic cell.
Describe what happens at a synapse in 4 steps.
(1) Action potential arrives at the axon terminal. (2) Ca2+ stimulates the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane. (3) Neurotransmitters bind to ligand-gated ion channels on the postsynaptic membrane. (4) Neurotransmitters are quickly degraded or taken back up by the presynaptic cell.
How does the arrival of the action potential at the axon terminal result in the introduction of Ca2+?
Depolarization of the presynaptic membrane causes voltage-gated Ca2+ channels to open and Ca2+ to move into the axon terminal.
How does the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane lead to the release of neurotransmitters in to the synapse?
Neurotransmitters are released into the synaptic cleft via exocytosis.
A postsynaptic neuron will form ____ (____ to ____) with many ____ ____.
A postsynaptic neuron will form synapses (hundreds to thousands) with many presynaptic neurons.
What is excitatory postsynaptic potential (EPSP)?
Where Na+ and K+ channels are involved in depolarization.
What is inhibitory postsynaptic potential (IPSP)?
When K+ and Cl- channels are involved in hyperpolarization.
