Lecture 3 Flashcards by Amber Finley

myelinated fiber

enclosed in a sheath made of nonneural cells (glial cells)

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The ____________ has breaks (Ranvier nodes) where action potentials are generated

myelin sheath

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Slow nerve conduction speed

0.5 m/s

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Sprinter Speed

10.0 m/s

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Speed Limit

30 m/s

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Fast nerve conduction speed

100 m/s

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Sound in air speed

330.0 m/s

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Light or electromagnetic field

300,000,000 m/s

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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

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Myelin increase what in local currents?

Myelin increases the effective distance of local currents

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What is the velocity of conduction in myelinated fibers?

6*d (m)

velocity in m/s

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Orthodomic Conduction

from soma to terminal branches

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Anti-orthodomic conduction

from the end of the axon to the soma

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Soma

body of the cell; the site of input signals

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Dendrites

shot branches originating from the soma; sites of inputs

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Axon

a long branch; transmits output signals

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Axon Hillock

the site where the axon exits the soma; typically, the site of generation of action potentials

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terminal branches

a “brush” at the end of the axon

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myelin

a fatlike substance covering the axon; it increases the speed of conduction of action potentials

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ranvier nodes

breaks in the myelin sheath; places where action potentials are generated

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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

1. A presynaptic action potential arrives 2. The presynaptic membrane lets vesicles with molecules of neurotransmitters pass though 3. The vesicles release the neurotransmitters into the synaptic cleft 4. The molecules diffuse across the cleft to the postsynaptic membrane and act at special sites (receptors). 5. 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