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  • Explain the process by which electric signals are transmitted along a neuron.
  • Explain the effects myelin sheaths have on signal propagation.
  • Explain what the features of an ECG signal indicate.

Nerve conduction

Electric currents in the vastly complex system of billions of nerves in our body allow us to sense the world, control parts of our body, and think. These are representative of the three major functions of nerves. First, nerves carry messages from our sensory organs and others to the central nervous system, consisting of the brain and spinal cord. Second, nerves carry messages from the central nervous system to muscles and other organs. Third, nerves transmit and process signals within the central nervous system. The sheer number of nerve cells and the incredibly greater number of connections between them makes this system the subtle wonder that it is. Nerve conduction is a general term for electrical signals carried by nerve cells. It is one aspect of bioelectricity    , or electrical effects in and created by biological systems.

Nerve cells, properly called neurons , look different from other cells—they have tendrils, some of them many centimeters long, connecting them with other cells. (See [link] .) Signals arrive at the cell body across synapses or through dendrites , stimulating the neuron to generate its own signal, sent along its long axon to other nerve or muscle cells. Signals may arrive from many other locations and be transmitted to yet others, conditioning the synapses by use, giving the system its complexity and its ability to learn.

The figure describes a neuron. The neuron has a cell body with a nucleus at the center represented by a circle. The cell body is surrounded by many thin, branching projections called dendrites, represented by ribbon-like structures. The ends of some of these dendrites are shown connected to the ends of dendrites from another neuron at junctions called synapses. The cell body of the neuron also has a long projection called an axon, represented as a vertical tube reaching downward and ending with thin projections inside a muscle fiber, represented by a tubular structure. The ends of the axon are called nerve endings. The axon is covered with myelin sheaths, each of which is one millimeter in length. The myelin sheaths are separated by gaps, called nodes of Ranvier, each of length zero point zero zero one millimeter.
A neuron with its dendrites and long axon. Signals in the form of electric currents reach the cell body through dendrites and across synapses, stimulating the neuron to generate its own signal sent down the axon. The number of interconnections can be far greater than shown here.

The method by which these electric currents are generated and transmitted is more complex than the simple movement of free charges in a conductor, but it can be understood with principles already discussed in this text. The most important of these are the Coulomb force and diffusion.

[link] illustrates how a voltage (potential difference) is created across the cell membrane of a neuron in its resting state. This thin membrane separates electrically neutral fluids having differing concentrations of ions, the most important varieties being Na + size 12{"Na" rSup { size 8{+{}} } } {} , K + size 12{"K" rSup { size 8{+{}} } } {} , and Cl - size 12{"Cl" rSup { size 8{ +- {}} } } {} (these are sodium, potassium, and chlorine ions with single plus or minus charges as indicated). As discussed in Molecular Transport Phenomena: Diffusion, Osmosis, and Related Processes , free ions will diffuse from a region of high concentration to one of low concentration. But the cell membrane is semipermeable    , meaning that some ions may cross it while others cannot. In its resting state, the cell membrane is permeable to K + size 12{"K" rSup { size 8{+{}} } } {} and Cl - size 12{"Cl" rSup { size 8{ +- {}} } } {} , and impermeable to Na + size 12{"Na" rSup { size 8{+{}} } } {} . Diffusion of K + size 12{"K" rSup { size 8{+{}} } } {} and Cl - size 12{"Cl" rSup { size 8{ +- {}} } } {} thus creates the layers of positive and negative charge on the outside and inside of the membrane. The Coulomb force prevents the ions from diffusing across in their entirety. Once the charge layer has built up, the repulsion of like charges prevents more from moving across, and the attraction of unlike charges prevents more from leaving either side. The result is two layers of charge right on the membrane, with diffusion being balanced by the Coulomb force. A tiny fraction of the charges move across and the fluids remain neutral (other ions are present), while a separation of charge and a voltage have been created across the membrane.

Questions & Answers

explain how a light wave can be propagated in accordance with the principal of reversibility
Chibuzo Reply
what is the meaning of musical instruments
Chibuzo
the definition of photon
Bright Reply
8kg of a hot liquid initial T is 90°© is missed with another liquid 3kg at 20° calculate e équilibrium T
Balki Reply
8kg of a hot liquid initial T is 90°© is missed with another liquid 3kg at 20° calculate e équilibrium T
Balki
answer plz
Bright
what are the products when acid and base mixed?
Austin
salt and water
Gift
What's this place about?
michael
@Austin your answer should be SALT and WATER
michael
salts and water
Roben
i guess salt and water
Chibuzo
what work done
Dennis Reply
work done is the product of force and distance moved in the direction of force
Gift
Work done = force (F) * distance (D)
abdulsalam
what is resounance
Abdul
y
Tracy
explain the three laws of isaac Newton with the reference
glory Reply
1st law ; a body will continue to stay at a state of rest or continue to move at a uniform motion on a straight line unless an external force is been acted upon
Austine
3rd law; in every action there is an equal or opposite reaction
Austine
2nd law: F=ma
Austine
why am i not having access to the Link in your exemples /figures ?
Augustine Reply
what is circut
hasiya Reply
newtons law of motion
hasiya
First law:In an inertial frame of reference, an object either remains at rest or continues to move at a constant velocity, unless acted upon by a force.
Manan
a circuit is an electric part Wich is linked by a wire
Chibuzo
is the ability to do work
Adjah Reply
Energy
Nwany
u from
Hejreen
any body online hain
Hejreen
ability to do work is energy
Irshad
energy
Chibuzo
what is energy
Mercy Reply
energy is ability of the capacity to doing work
shafiu
what is vector
mosco Reply
A quantity that has both magnitude and direction
Donaldo
can a body with out mass float in space
mosco
Is the quantity that has both magnitude and direction
Amoah
Yes it can float in space,e.g.polyethene has no mass that's why it can float in space
Amoah
that's my suggestion,any other explanation can be given also,thanks
Amoah
A charge of 1.6*10^-6C is placed in a uniform electric field in a density 2*5^10Nc^-1, what is the magnitude of the electric force exerted on the charge?
Omotosho Reply
what's phenomena
Enoch Reply
Phenomena is an observable fact or event.
Love
Prove that 1/d+1/v=1/f
James Reply
What interference
Moyinoluwa Reply
What is a polarized light called?
Moyinoluwa
what is a half life
Mama Reply
the time taken for a radioactive element to decay by half of its original mass
ken
what is radioactive element
mohammed
Half of the total time required by a radioactive nuclear atom to totally disintegrate
Justice
radioactive elements are those with unstable nuclei(ie have protons more than neutrons, or neutrons more than protons
Justice
in other words, the radioactive atom or elements have unequal number of protons to neutrons.
Justice
state the laws of refraction
Fabian
state laws of reflection
Fabian
Why does a bicycle rider bends towards the corner when is turning?
Mac
When do we say that the stone thrown vertically up wards accelerate negatively?
Mac
Give two importance of insulator placed between plates of a capacitor.
Mac
Macho had a shoe with a big sole moving in mudy Road, shanitah had a shoe with a small sole. Give reasons for those two cases.
Mac
what is the matter
Mohammed
Practice Key Terms 4

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Source:  OpenStax, College physics. OpenStax CNX. Jul 27, 2015 Download for free at http://legacy.cnx.org/content/col11406/1.9
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