Neurobiology 3 Flashcards
Where is the action potential located
only generated in the axon
What property of action potentials details its ‘entirety’ nature
All or none
What is required for action potential to fire
Threshold stimulus
What is constant about the action potential
Amplitude
What can an action potential not fire
Refractory period
What ensures unidirectional transmission of the action potential along an axon
The inability for an action potential to fire during the refractory period
Is the action potential propagated with or without decrement
Without decrement
What are the name of the two types of refractory periods
- Absolute refractory period
2. Relative refractory period
What is the absolute refractory period
When the axon is incapable of generating a new action potential
What is relative refractory period
This is when only very strong stimuli can generate a new action potential
What stages does the absolute refractory period consist of
Action potential up and down (but not the undershot stage)
What stages does the relative refractory period consist of
The undershoot stage when the membrane potential is lower than the resting potential
What is electrotonic conduction
This is the process of a local depolarization spreading the action potential passively through the axon
What ensures the directional propagation of the action potential
The inactivation gates of the voltage-gated Na+ channels
How can you tell how strong a stimulus is
By measuring the action potential frequency
What are two strategies that are utilized by neurons to maximize action potential conduction
- Large diameter axons
2. Myelin Sheaths
Properties of having a large diameter axon:
Very low intracellular resistance to current flow (so current flows far and fast)
How do myelin sheaths promote action potential speed
By insulating the able/axon to favor speed of conductance
What is saltatory conduction
When a nerve impulse (the action potential) skips down the axon due to Schwann cells. This results in faster propagatioin
What are Nodes of Ranvier
Parts of the axon where myelin is absent, but Na+ and K+ channels are present. Slow
What are internode regions
Regions of the axon where there is myelination. No Na+ and K+ channels are present
What is Multiple Sclerosis (MS)
An autoimmune disorder where the immune system attacks myelin-forming cells
What is a consequence of Multiple Sclerosis (MS)
The neurons have slower propagation of the electrical signal and this decreases muscular control and results in paralysis
Where do neurons transmit their signals
At electrical or chemical synapses
What is bidirectional signaling (electrical synapse)
When there are gap junctions between the presynapse neuron and the postsynaptic neuron/dendrite
What is unidirectional signaling (chemical synapse)
When an electrical signal stimulates neurotransmitter release from the presynaptic neuron to bind to a receptor in the postsynaptic neuron, generating a new electric signal in the postsynaptic neuron
Stages of the chemical synapse
- Action potential arrives at axon terminal
- Voltage-gated Ca 2+ channels open
- Ca 2+ enters the presynaptic terminal
- Ca 2+ signals vesicles
- Vesicles move to the membrane
- Vesicles secrete neurotransmitters by exocytosis
- Neurotransmitters diffuses and binds to postsynaptic terminal receptors
- Binding activates signal transduction pathway
Neurotransmitter receptors can be classified as these two types
Ionotropic & metabotropic
What is an ionotropic neurotransmitter receptor
A receptor that allows ions to flow into and out of the neuron
What is a metabotropic neurotransmitter receptor`
Ligand-based channel that works with a neurotransmitter to elicit a change in the signal transduction pathway
What is neurotransmitter action determined by
- Rate of release
- Mode of action - excitatory vs. inhibitory
- Rate of degredation - Neurotransmitter uptake and/or rapid degredation
When is acetylcholine stimulatory
When it binds to ionotropic acetylcholine receptors, such as in the muscle
When is acetylcholine inhibitory
When it binds to GPCRs->inhibits adenyl cyclase and maintain open K+ channels->hyperpolarization
What happens to acetylcholine in the synaptic cleft
- Acetylcholine binds to postsynaptic receptors (cholinergic ion channels)
- Acetylcholine-esterase (AChE) degrades Ach in the synaptic cleft to choline and acetate
What are the components of degraded ACetylcholine (Ach)
Choline & Acetate
What happens to Choline once it is degraded from Ach
Taken up by the presynaptic neuron to re-synthesize Ach
What happens to Acetate once it is degraded from Ach
Diffuses out of the synaptic cleft and into the blood stream
What is an example of an Acetylholine-esterase blocker
Nerve Gas (“Sarin”)
How do AchE blockers work
Cause a buildup of Ach in the synaptic cleft at the neuromuscular junction
What is a consequence of AchE blockers
Causes sustained activation of the muscle, leading to desensitization, muscle paralysis, and death
What are two excitatory amino acid neurotransmitters
Glutamate & Aspartate
How do amino acid neurotransmitters work
Via ionotropic and metabotropic neurotransmitter receptors
What are two inhibitory amino acid neurotransmitter
Glycine & Gamma Amino Butyric Acid (GABA)
What are two types of GABA receptors
- GABA-A: Ionotropic Cl- channel
2. GABA-B: Metabotropic GPCR
What happens when GABA binds to GABA-A
GABA-A then causes an influx of Cl- ions, resulting in a hyperpolarization
What types of drugs inhibit epileptic and other types of seizures
Drugs that increase GABA receptor activation
What are biogenic amine neurotransmitters
Neurotransmitters with tyrosine derivatives, called Catecholamines or with tryptophan derivatives
Examples of biogenic amines
Dopamine and Norepinephrine
Precursor of norepinephrine
Dopamine
Where is dopamine found
In the midbrain
What is associated with dopamine deficiency
Parkinson’s Disease
What is associated with excessive dopamine
Schizophrenia
Name 1 biogenic amine neurotransmitter with a tryptophan derivative
Serotonin
What does serotonin do
Affects sleep, mood, attention, and learning
Why does milk help you fall asleep
Because it has tryptophan in it
What is similar in structure and function with serotonin
LSD - a hallucinogenic drug
Biogenic amines are also called
Monoamines
How do monoamines act at the cellular level
Through GPCRs, activating second messenger systems
What happens after monoamines/biogenic amines activate their receptor
They are rapidly inactivated in the synaptic cleft or taken up by the presynaptic neuron for recycling
How does the presynaptic neuron recycle monoamines/biogenic amines
It metabolizes them with monoamine oxidase (MAO) both in the presynaptic neuron or in the synaptic cleft
What types of drugs are used as anti-depressants
Selective serotonin reuptake inhibitors (SSRI)
What are Parkinson’s Disease patients usually treated with
Monoamine oxidase (MAO) inhibitors
How are neuropeptide neurotransmitter synthesized
Gene transcription/translation
How do neuropeptides act at the cellular level
Through GPCRs
What are three examples neuropeptides
- Alpha melanoctye stimulating hormone (alpha-MSH)
- Met-enkephalin
- Gonadotropic-releasing hormone (GnRH)
What does (alpha-MSH) do
Acts within the hypothalamic feeding control circuit to suppress appetite
What does Met-enkephalin do
It is an endorphin and analgesic
Define analgesic
Inhibits perception of pain
What is GnRh responsible for
Stimulating LH & FSH, and promoting sexual behavior
What is a neuromodulator
Some mechanism that modulates the presynaptic neuron to elicit a response
