Basics
Name & describe the 2 types of nervous systems
Peripheral Nervous System: "division of nervous system that lies outside the CNS; primary role is to connect CNS to organs, limbs, & skin"
-contains nerves
What is equilibrium potential in a neuron?
Equilibrium potential: "voltage at which electrical + chemical gradient are equal & opposite"
-EP of K+ is -70 mV
What is the refractory period? Why are they so important?
Refractory period: "recently closed Na+ channels CANNOT be opened again immediately"
-important b/c makes signal UNIDIRECTIONAL: cannot travel upstream
What type of signal do neurotransmitters have? Name 3 neurotransmitters
chemical signals
ex: acetylcholine, norepinephrine, dopamine, serotonin, glutamate, GABA, endorphins
1) chemoreceptors
2) mechanoreceptors
3) photoreceptors
1) chemoreceptors: molecule binds to protein receptor; causes ion channel to open
-ex: taste, smell
2) mechanoreceptors: pressure stimulus causes electrical signal response
-ex: touch, hearing
3) photoreceptors: light stimulus interacts w/ receptor, signals ion channel to close
-ex: vision
What is the generic pathway of an electrical signal in the nervous system? Describe the steps!
sensory receptor/neuron --> interneuron --> motor neuron --> muscle [response, aka effector cell]
Sensory receptor/neuron: "converts sensory info --> electrical signal"
**1st 3 steps are generated by the MOVEMENT OF IONS across plasma membranes of nerve cells**
Why does the RMP have an inside negative value? [3 big reasons]
1) Na+/K+-ATPase pump: pumps out 3 Na+ for every 2 K+ it lets into cell
2) K+ Leaky Channels: @ rest, membrane is most permeable to K+ ions [other ion channels are closed]
3) organic anions CANNOT cross plasma membrane
What is an action potential? What must you reach to trigger an AP?
AP: "temporary change in membrane potential"
-entire sequence is VERY fast [milliseconds]
***has ALL OR NONE response*****
-must reach threshold potential for AP to occur
Describe what acetylcholine does
1) AP arrives
2) Ach is released
3) Ach binds to receptor on membrane
4) causes Ca+2 to be released in muscle cell
5) muscle cell contracts!
What type of feedback is membrane depolarization via opening of Na+ channels?
positive feedback :)
What are reflexes?
Reflexes: "automatic responses; sensory info bypasses the brain to cause response"
What is the axon hillock? What does it do?
Axon hillock:
-area of neuron where synaptic stimuli are summed
-if threshold level of membrane depolarization is achieved, an AP will be generated
Differentiate between...
1) no summation
2) temporal summation
3) spatial summation
4) cancellation
1) no summation: summations do NOT reach threshold potential --> no AP
2) temporal summation: EPSPs [from same neurotransmitter] sum to reach threshold --> AP occurs
3) spatial summation: EPSPs [from multiple presynaptic neurons] sum to reach threshold --> AP occurs
4) cancellation: more IPSPs than EPSPs --> threshold not reached --> NO AP
How is information transferred at the postsynaptic neuron?
1) neurotransmitter (aka ligand) diffuses across synaptic cleft --> postsynaptic membrane
2) neurotransmitter binds to receptors on postsynaptic membrane --> changes mem. potential in postsynaptic men.
3) neurotransmitter reabsorbed into PREsynpatic terminal + stored until next AP arrives
What is myelin? What produces myelin? What is saltatory propagation?
Myelin: "a fatty sheath [insulation] around the axon"
-myelin is produced by SCHWANN CELLS
Saltatory propagation: "action potentials jump down axons to increase conduction velocity"
-APs "jump" from node [of ranvier] to node, which increases the speed of conduction ****speed of AP itself does NOT change****
Describe the anatomy of a typical neuron (or draw it)
1) stimuli are received by DENDRITES on cell body
2) incoming stimuli are summed & action potential is generated @ AXON HILLOCK
3) output to dendrites of another neuron/effector cell @ AXONS [typically release neurotransmitters/signal into synapse]
What are neurotransmitters? Describe the two different types.
Neurotransmitters: "bind to ligand gated ion channels to produce a signal"
1) inhibitory (cause membrane hyper polarization)
2) excitatory (cause membrane depolarization)
What occurs at synapses?
At the synapse, electrical signal --> chemical signal
-when depolarization of membrane from AP arrives at axon terminal, voltage-gated Ca+2 channels OPEN --> Ca+2 enter cell
-increased intracellular [Ca+2] triggers exocytosis of synaptic vesicles --> neurotransmitter released into synaptic cleft
What is resting membrane potential? Describe inside/outside environment of neurons
RMP definition: "voltage across a plasma membrane generated by charge separation"
Outside: high Na+, low K+
Inside: low Na+, high K+, &&& negatively charged proteins
Explain EPSPs and IPSPs
EPSP: neurotransmitter dining leads to OPENING of ligand-gated Na+ channels --> Na+ flows INTO cell --> membrane DEPOLARIZATION occurs
IPSP: neurotransmitter binding leads to OPENING of ligand-gated K+ channels --> K+ flows OUT of cell --> membrane HYPERPOLARIZATION occurs
~OR~
neurotransmitter binding leads to OPENING of ligand-gated Cl- channels --> Cl- flows INTO cell --> membrane HYPERPOLARIZATION
Describe the 3 main steps of an AP
1) depolarization: occurs once threshold potential is reached @ axon hillock
-voltage-gated Na+ channels open, Na+ ions flow INTO cell
-positive feedback: Na+ channels opening trigger more Na+ channels to open --> more AP generated
2) repolarization:
-Na+ channels close
-voltage-gated K+ channels open [w/ delay] --> K+ ions flow OUT
3) hyperpolarization:
-overshoot (under membrane potential)
-K+ channels open/close until equilibrium is reached