Lecture 3 Flashcards
myelinated fiber
enclosed in a sheath made of nonneural cells (glial cells)
The ____________ has breaks (Ranvier nodes) where action potentials are generated
myelin sheath
Slow nerve conduction speed
0.5 m/s
Sprinter Speed
10.0 m/s
Speed Limit
30 m/s
Fast nerve conduction speed
100 m/s
Sound in air speed
330.0 m/s
Light or electromagnetic field
300,000,000 m/s
Conduction of an Action Potential
- Membrane depolarization to the threshold
- Generation of an action potential
- Local currents spread passively
- They depolarize adjacent areas of the membrane
- A new action potential is generated
Myelin increase what in local currents?
Myelin increases the effective distance of local currents
What is the velocity of conduction in myelinated fibers?
6*d (m)
velocity in m/s
Orthodomic Conduction
from soma to terminal branches
Anti-orthodomic conduction
from the end of the axon to the soma
Soma
body of the cell; the site of input signals
Dendrites
shot branches originating from the soma; sites of inputs
Axon
a long branch; transmits output signals
Axon Hillock
the site where the axon exits the soma; typically, the site of generation of action potentials
terminal branches
a “brush” at the end of the axon
myelin
a fatlike substance covering the axon; it increases the speed of conduction of action potentials
ranvier nodes
breaks in the myelin sheath; places where action potentials are generated
Nerve (peripheral) or neural tract (central)
many axons running together
How many ion channels are there under the myelin sheath in a neuron?
there are virtually no ion channels under the myelin sheath.
How many ion channels are there in the Ranvier nodes in neurons?
There are many ion channels in the Ranvier nodes.
the importance of ______ for the generation of APs has gained prominence lately (steady depolarization) in neurons.
dendrites
What is a PIC?
a depolarizing inward current that activates as long as the membrane potential is depolarized
PIC’s allow for an increase _________________.
in the number of action potentials that are generated.
Recent studies have reported that PIC’s are strong in ____________ during everyday tasks.
human alpha motorneurons
PIC’s are likely strong enough to play a major role in defininf the patterns of ________________________.
recruitment and derecruitment of motor units
PIC’s are very sensitive to ___________ inhibition, meaning they can be controlled?
postsynaptic
What effect does the all or none law have on action potential generation?
Each action potential transmits 1 bit of information
How can a neuron encode significant amounts of information?
By generating sequences of action potentials
- by changing the frequency of firing
- neurons take into account the timing and number of action potentials
What does a synapse consist of?
A synapse consists of a presynaptic membrane, a synaptic cleft, and a postsynaptic membrane.
What happens with an action potential in a presynaptic fiber?
An action potential in a presynaptic fiber makes synaptic vesicles move to the membrane, fuse with it, and release molecules of neurotransmitters into the cleft.
What changes the potential of the postsynaptic membrane?
The neurotransmitters act at the postsynaptic membrane and change its potential.
Obligatory synapse
AP on the presynaptic membrane always gives rise to an AP on the post synaptic membrane
Nonobligatory Synapse
A single AP on the presynaptic membrane is typically unable to induce an AP on the postsynaptic membrane?
A presynaptic action potential can induce either a depolarization or a hyperpolarization of the postsynaptic membrane. These eggects are called __________.
EPSP and IPSP
Synaptic Transmission
- A presynaptic action potential arrives
- The presynaptic membrane lets vesicles with molecules of neurotransmitters pass though
- The vesicles release the neurotransmitters into the synaptic cleft
- The molecules diffuse across the cleft to the postsynaptic membrane and act at special sites (receptors).
- The postsynaptic membrane is either depolarized or hyperpolarized.
How long does the synaptic transmission process take?
0.5 ms
Gap junction channels in electrical synapses
Gap junction channels provide a low resistance pathway for the electrical current to flow between cells
Current flow in Electrical synapses
current flows from the presynaptic cell into the postsynaptic cell, depositing a positive charge
Depolarization in electrical synapses
If depolarization exceeds threshold, the postsynaptic cell will generate an action potential
Synaptic delay in Electrical Synapses
Very little synaptic delay
What kind of current can electrical synapses transmit?
can transmit both depolarizing and hyperpolarizing currents
Where are electrical synapses located?
between glial cells and schwann cells in the brain
What are electrical synapses likely to be involved in?
brain signaling and myelin formation
temporal summation
occurs when several action potentials arrive at a presynaptic membrane at intervals that do not allow individual EPSPs to disappear. Their effects can sum up and induce an action potental
spatial summation
spatial summation occurs when several action potentials arrive simultaneously synapses on the same presynaptic membrane so that their individual EPSPs sum up and can induce an action potential.
temporal and spatial summation can occur for both _____.
EPSPs and IPSPs.
increases the amount of inhibition.
The phenomenon of ________ does not allow an action potential to “backfire.” If an action potential comes to point 2 from point 1, it cannot go back. It can only travel forward to point 3.
inactivation of sodium channels
