L20 Signal Transmission Flashcards
How is the myelin sheath created?
By neuroglial cells
What are the two types of axons?
1) Unmyelinated
2) Myelinated
How does unmyelinated axons influence propagation?
- Depolarization and repolarization occurs across entire length patch by patch
- Continuous propagation
- Very slow ~1meter/sec in shorter axons
How does myelinated axons influence propagation?
- Myelin prevents ion leakage
- Membrane proteins responsible for adjusting membrane potential are found at the Nodes of Ranvier
- Signals travel much faster since depolarization jumps from node to node
What is saltatory propagation?
- Very quickly
- Jumping conduction
- 18-140 meters per second
- In all axons (sensory and motor neurons)
What types of myelinated axons do we have?
- Type A
- Type B
- Type C
Which type of axons are myelinated?
Typa A axons ( most myelinated conduct signals very fast)
Type B axons ( less myelinated then A)
Which type of axons are unmyelinated?
Type C axons
Conduct singlas more slowly
What are the roles of the fastest axons?
Conduct position and balance signals
What are the roles of the slower axons?
Conduct temperature and pain signals instructions to autonomic effectors
What is neuronal communication?
- Nerves talk to each other and to effectors accros synapses
- Sensory neurons and interneurons pass their signals onto other neurons
- motor neurons synapse onto somatic and autonomic effectors
What happens at a synapse?
and electrical signal is converted into a chemical signal via neurotransmitter release
What are neurotransmitters?
Chemicals stored in synaptic vesicles and released by a neuron at a synapse into a synaptic cleft
What are the types of neurotransmitters?
Acetycholine (Ach)
norepinephrine/noradrenaline (NE)
Other, less common neurotransmitters include: dopamine, GABA, serotonin, nitric oxide (gas), and carbon monoxide (gas)
The cholinergic synapse releases which neurotransmitter?
Acetycholine (Ach)
The adrenergic synapse release which neurotransmitter?
Broken down by acetycholine esterase
norepinephrine/noradrenaline (NE)
These are broken down by monoamine oxidase
What are the components of a synapse?
- Presynaptic membrane
- Synaptic cleft
- Postsynaptic membrane
What is the first step of a electrical signal converting into a chemical signal (consider it a cholinergic synapse)
1) Arrival of an action potential at axon terminal
Second step of a electrical signal converting into a chemical signal?
- Presynaptic membrane is depolarized , causing voltage gated calcium channels to open
- Ca2+ moves down its conc. gradient into the cell
- Triggers exocytosis of synaptic vesicles full of neuro transmitter
Step 3 of a electrical signal converting into a chemical signal?
- Neurotransmitter diffuses across the synaptic cleft
- Binds to chemically- gated Na+ channels on postsynaptic membrane (causes postsynaptic membrane to depolarize)
- If this graded potential is strong enough to reach threshhold, an action potential is propagated
Step 4 of a electrical signal converting into a chemical signal?
- Neurotransmitter resorbed into presynaptic cell
- Broken down by acetylcholine esterase (enzyme)
- When neurotransmiter is removed, ready to respond to another event.
What are the two types of effect neurotransmitters can cause?
Excitatory effect (depolarize)
Inhibitory effects (hyperpolarize)
Which channels and neurotransmitters are correlated to excitatory effects (depolarize)
-Chemically gated Na+ channels
- Ach, NE, and dopamine
Which channels and neurotransmitters are correlated to inhibitory effects (hyperpolarize)
- Open chemically gated K+ channels
- GABA, serotonin, and dopamine
What can change synaptic activity?
External compunds
What happens with medication and drugs that cross the blood-brain barrier?
Affects the nervous system commonly work at the level of the synapse
What do selective serotonin reuptake inhibitoes do? (SSRIs)
- prevent serotonin from being resorbed
- Helps relieve symptons of depression
What does cocaine do?
- Inhibits removal of dopamine from excitatory synapses
- Leads to a feeling of euphoria and alertness
What does MDMA do?
- Increases the release of serotonin, NE, and dopamine from presynaptic neurons and prevents their reuptale
- Leads to symptoms of euphoria, alertness, and increased empathy
What are neuromodulators?
- Small peptides
- Released from a neuron into a synaptic cleft
- Alters responsiveness of a presynaptic or postsynaptic cell
How do neurdomodulators alter neuronal responsiveness?
- Changes how many synaptic vesicles are released by presynaptic
- How postsynaptic cells respond to the neurotransmitter
Give examples for neuromodulators and how they work
Endorphins
Ex: endogenous opioids, opium, moprhine, and heroic act as pain relievers by inhibiting the release of neurotransmitters in pain circuits.
The activity of a neuron depends on the balance between?
the sum of excitatory and inhibitory signals
(Postsynaptic cell may have synapses with axon termini of multiple presynaptic cells)
What are the postsynaptic potentials?
- Excitatory postsynaptic potentials (EPSP)
- Inhibitory postsynaptic potentials (IPSP)
What is EPSP
A graded potential that depolarize the postsynaptic cell
What is IPSP
Graded potential that hyperpolarize the postsynaptic cell causing it to become refractory
What can the combination of EPSP and IPSP do?
Prevent a cell from reaching threshold
What does EPSPs do ?
open chemically gated Na+ channels, causing depolarization towards -55mV
What do IPSPs do?
Open chemically gated K+ channels, causing hyperpolarization towards -90mV, thus requiring a greater stimulus to reach threshold
How does a cell reach threshold?
- A single strong EPSP can depolarize to threshhold
- Several small additive EPSPs
What is temporal summation?
- combination of many small graded potentials, following each other very quickly at a single synapse (causes enough Na+ to reach threshhold)
- IPSPS can also act like this but lead to hyperpolarization
What is Spatial summation?
- Combination of many small graded potentials arriving simultaneously at different synapses on the same neuron
- IPSPs can also act like this but they lead to hyperpolarization
