Lec. 26: The Nervous System 2 Flashcards
Refractory Period
A result of a temporary inactivation of the Na+ channels due to inactivation loops (a second action potential cannot be initiated)
How can action potentials travel long distances along an axon?
They can regenerate itself along the axon. An electrical current depolarizes the neighboring region of axon membrane.
Why do action potentials travel in 1 direction?
Inactivated Na+ channels behind zone of depolarization. They only travel down axon towards synaptic terminal
Why do some axon’s action potentials travel faster than others ?
- the larger an axons diameter=the faster the speed of an action potential
- axons insulated by myelin sheath which increases speed of action potential
- Action potentials are formed at Nodes of Ranvier, which are gaps in myelin sheath where Na+ channels are found
Na+ jumps from node to node is called satatory conduction
What is a chemical synapse
A chemical neurotransmitter carries information across the gap junction called a synaptic cleft
How does a signal go from a presynaptic cell to a postsynaptic cell?
What is a postsynaptic potential and when is it made?
- Arrival of action potential at synaptic terminal depolarizes membrane, allowing voltage gated Ca2+ channels to diffuse in terminal
- Triggers vesicles to fuse with membrane and release of a neurotransmitter
- Diffuses across snyaptic celft, binds to ligand gated ion channels in post synaptic membrane which opens channels
A change in membrane potential of the post synaptic cell when the neurotransmitter binds and opens ion channels
Temporal summation
If two excitary postsynaptic potentials are produced in rapid succession, temporal summation occurs
-a single EPSP is usually too small to trigger an action potential
Spatial summation
EPSP’s produces simmultaneously by different syanpses on the same postsnyaptic neuron add together
After a ligand gated ion channel opens, what happens to the neurotransmitter?
- diffuse out of synaptic cleft
- may be taken up by surrounding cells
- degraded by enzymes (located in postsynaptic membrane)
The surrounding cells can be glial cells like astrocytes
What is the result of blocking an inactivating enzyme in the postsynaptic cell?
Nerve agents, such as sarin, block neurotransmitter degrading enzymes called acetylcholinesterase. The neurotransmitters will remain in synaptic cleft and activate the ligand gated ion channels and stimulate action potentials which paralyzes body.
What are the 5 major classes of neurotransmitters
What are the 3 important ones?
(important)
1. acetylcholine
2. biogenic amines
3. amino acids
(Not important)
4. neuropeptides
5. Gases
Acetylcholine
What toxins disrupt acetylcholine neurotransmission
- common neurotransmitter involved in muscle stimulation, memory formation, and learning
- ## Vertebrae have 2 major classes of receptors: ligand gated, metabtropic *such a G coupled protein recepeptors *
Nerve gas (sarin), botulism toxin (food poisoning)
Botulism toxin used for botox (beauty enhancer)
Difference between cholinergic neurons and dopaminergic neurons
cholinergic: Use acetylcholine neurotransmitters in the brain
Dopaminergic: Use dopamine neurotransmitters in the brain
Biogenic amines
- Neurotransmitters derived from amino acids
- Examples include serotonin, dopamine, epinephrine and nonepineripirine
- Affect sleep, mood, attention, learning, memory
What are some functions of seratonin and dopamine (mentioned in the lecture)?
LSD and mescaline, Parkinsons, Prozac
LSD and mescaline produce hallucinatory effects by binding receptors for serotonin and dopamine
Parkinsons associated with the lack of dopamine
Depression drugs such as Prozac block reuptake of serotonin
