nervous system Flashcards
what are the 3 functions of nervous system?
1) sensory input
2)integration
3)motor output
what is sensory input?
- Response to external and internal stimuli
- Sensory neurons
what is integration?
- Interpretation of sensory input
- Decides appropriate response
what is motor output?
- Conduction of signals from the CNS to the effector cells
- Motor neurons
what are neurons?
- Cells specialized for transmitting electrical and chemical signals
what are the 2 components to a neuron?
-cell body
-fiber-like extensions
what are the two fiber like extensions in a neuron?
- Dendrites
o Convey signals towards the cell body
o Short and numerous - Axons
o Conduct impulse away from the cell body
o Long single processes
o Some are insulated by a myelin sheath
o Ends in axon terminal
what do axons do?
Relay signals to other cells by releasing neurotransmitters
how do neurons communicate?
Neurons communicate via synapses
- Neurotransmitters are released from a pre-synaptic neuron and act on a post-synaptic neuron
what are nerve impulses?
Nerve impulses are changes in voltage across the plasma membrane
o Caused by the movement of ions across the membrane (Na+, K+)
what is the membrane potential of a resting neuron?
A resting neuron has a membrane potential of about -70 mV
* Inside is more negative than outside!
what determines the potential of a neuron?
ion distribution across membrane
what are the ions that determine the potential across the membrane of a neuron?
-negatively charged molecules (anions): proteins, amino-acids, sulfate and phosphate, Cl-
-positively charged molecules (cations): K+ and Na+
how do charged molecules cross the membrane?
-passive ion channel (open all the time)
-gated ion channel (require a stimulus to open)
what are the 2 types of gated ion channels?
-voltage-gated channels
-ligand-gated channels
what does the Na+/K+ ATPase pump do?
- Maintains concentration gradients of Na+ and K+ across the membrane
- High Na+ outside and high K+ inside o 3 Na+ pumped out
o 2 K+ pumped in
o 1 ATP used
true or false, neurons have many passive K+ channels?
true.
* Always open; K+ diffuses down its concentration gradient (created by the Na+/K+ pump) out of the cell
how can a stimuli cause changes in membrane potential?
-stimuli opens gated ion channels, changing the charge distribution across the membrane
what is hyperpolarization?
- Inside becomes more (-)
- K+ channels open
- K+ diffuses out of the cell
what is depolarization?
- Inside becomes more (+)
- Na+ channels open
- Na+ diffuses into the cell
what are the 2 types of changes in membrane potential?
hyper polarization and depolarization
what is an action potential?
nerve impulse
what happens if a depolarization stimulus is strong enough to pass the threshold potential?
an action potential is generated
what does an action potential do?
moves along the entire length of the axon and stimulates the release of neurotransmitters from the axon terminal!
what are the steps to generate an action-potential?
(1) Resting state
* No gated channels are open; -70mV resting potential (2) Threshold
* Stimuli causes gated Na+ channels to open; Na+ flows in causing depolarization
(3) Depolarization
* If depolarization reaches threshold an action potential will begin
* At threshold, voltage-gated Na+ channels open causing a large influx of Na+ and a large
depolarization
(4) Repolarization
* Na+ channels close and K+ channels open * K+ moves out of the cell
(5) Undershoot
* K+ channels are slow to close allowing more K+ to leave
* Membrane potential is more negative than resting potential
what is the refractory period?
neuron is insensitive to stimuli. Constitutes of repolarization and undershoot
where does the action potential go?
moves along the length of the axon to the axon terminal
true or false, an action potential is a localized electrical event
true (happens in one part of axon)
why can an action potential only move in one direction?
-Depolarization in one part of the axon causes depolarization in region right next to it by opening voltage gated Na+ channels
-During repolarization and undershoot (refractory period) a membrane cannot be depolarized so action potential can only move in one direction!
what is a synapse?
- Synapse is a space between a presynaptic (transmitting) cell and a postsynaptic (receiving) cell
what is a presynaptic cell?
transmitting cell
what is a post synaptic cell?
receiving cell
what happens at chemical synapses?
neurotransmitters are released from the axon terminal of a presynaptic cell and act on a postsynaptic cell
what are the steps that happen at a synapse?
(1) Action potential arrives at the axon terminal
* Depolarization of the presynaptic membrane causes voltage-gated Ca2+ channels to open and Ca2+ to move into the axon terminal
(2) Ca2+ stimulates the fusion of synaptic vesicles containing neurotransmitters with the presynaptic membrane
* Neurotransmitters are released into the synaptic cleft via exocytosis
(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 many synapses will postsynaptic neurons form?
Postsynaptic neuron will form synapses with many (hundreds to thousands) presynaptic neurons
what are the 2 types of potentials formed on the post synaptic neuron?
-Excitatory postsynaptic potential (EPSP)
-Inhibitory postsynaptic potential (IPSP):
what is an Inhibitory postsynaptic potential (IPSP):
- Involve K+ and Cl- channels
- Causes hyperpolarization
what is an excitatory postsynaptic potential (EPSP)
- Involve Na+/K+ channels
- Causes depolarization
how can we determine whether or not an action potential will be generated in the post synaptic neuron?
Sum of EPSPs and IPSPs determine whether an action potential will be generated
what are the summation rules for the post synaptic potentials?
(a) Subthreshold / no Summation
* By the time a single EPSP arrives at the postsynaptic neuron, it may not be large enough to trigger a response
(b) Temporal Summation
* If 2 EPSPs (or IPSPs) from the same presynaptic neuron arrive in rapid succession, the effect is additive
(c) Spatial Summation
* If 2 EPSPs (or IPSPs) from different presynaptic neurons arrive in rapid succession, the effect is also additive
(d) Spatial Summation of EPSP and IPSP
* An IPSP can counter the effect of an EPSP
