Neural Basis of Movement
There are more nerve cells in the human body than there are
stars in the Milky Way
The Nervous System
• Brain
• Spinal Cord
• Nerves
The nervous system uses
sense organs and nerve
endings to detect changes both
inside and outside the body.
• The nervous system issues
• commands to muscles and
• glands to initiate changes based The nervous system
processes the information
• on its information.
received, relates it to past
experiences, and determines
what response is appropriate.
The nervous system issues
commands to muscles and
glands to initiate changes based
Types of Nervous System Cells
• Neurons: are the excitable, impulse-conducting
cells that perform the work of the nervous
system
• Neuroglia: protect the neurons.
euron Structure
Impulse Conduction
• In the body, whenever ions with opposite electrical
charges are separated by a membrane, the potential
exists for them to move toward one another
(depending, of course, on the permeability of the
membrane). This is called membrane potential.
• A membrane that exhibits membrane potential—an
excess of positive ions on one side of the membrane
and an excess of negative ions on the other side—is
said to be polarized.
When a neuron is not conducting an electrical signal, its interior has a negative electrical charge, whereas the charge
on the outside is positive. The outside of the cell is rich with sodium ions (Na), and the inside contains an abundance
of potassium ions (K). The interior of the cell contains other ions as well, particularly large, negatively charged proteins
and nucleic acids. These additional particles give the cell’s interior its overall negative charge. Because of the
membrane’s permeability, a certain amount of sodium and potassium ions leak across the membrane. However, the
sodium-potassium pump constantly works to restore the ions to the appropriate side. (For more information on the
sodium-potassium pump, see Chapter 3, Cells.) This state of being inactive and polarized is called resting potential.
The neuron is resting, but it has the potential to react if a stimulus comes along.
When a stimulus (such as chemicals, heat, or mechanical pressure) comes along, channels on the resting
neuron’s membrane open and the Na from outside the membrane rushes into the cell. The addition of all
these positively charged ions changes the charge of a region of the cell’s interior from negative to positive.
As the membrane becomes more positive, it is said to depolarize.
2
Depolarization
• Stimulus causes Na+ to enter cell
• Region of interior changes from
negative to positive
If the depolarization is strong enough—in other words, if the stimulus goes above what’s known as the
threshold level— adjacent channels also open, allowing even more Na to flood the cell’s interior. This
creates an action potential, meaning that the neuron has become active as it conducts an impulse
along the axon. Another term for action potential is nerve impulse. The action potential continues down
the axon as one segment stimulates the segment next to it.
3
Action potential
• Channels in adjacent areas open
and more Na+ enters the cell
• Nerve impulse continues down the
length of the axon
Meanwhile, the sudden influx of Na+ triggers the opening
of other channels to allow K to flow out of the cell. Soon
after
K begins to exit, the Na channels shut to prevent any more
Na from flowing into the cell. This repolarizes the cell;
however, Na and K are now flip-flopped, with the outside
containing more K and the inside containing more Na.
4
Repolarization
• K+ flows out of cell
• Electrical balance restored: interior
has negative charge and exterior
has positive charge
Although the membrane is polarized, the neuron won’t
respond to a new stimulus as long as the Na and K are on
the wrong sides of the membrane. This is known as the
refractory period. The sodium-potassium pump works to
return Na+ to the outside and K+ to the inside. When this
is completed, the nerve is again polarized and in resting
potential until it receives another stimulus.
5
Refractory period
• Membrane is polarized, but Na+
and K+ are on wrong sides of
membrane
• Sodium-potassium pump works
restore ions to rightful sides
https://youtu.be/b2ctEsGEpe0
https://youtu.be/oa6rvUJlg7o
Synapse
https://youtu.be/ecGEcj1tBBI
Electromyography (EMG)
• The study of muscle electrical activity
EMG
• Resting Membrane Potential
• Muscle Fiber Action Potential
• Motor Unit Action Potential: The summed electrical activity of all the
muscle fibers activated within the motor unit.
• EMG: A composite electrical sum of all the active motor units
Application of EMG in Ergonomics
Application of EMG in Ergonomics
• To assess risk factors for musculoskeletal disorders
• Assessment of chairs, posture
• Muscle fatigue in repetitive work
• To assess the effectiveness of exoskeletons
• To design keyboards and mouse to avoid carpel tunnel
syndrome
• To decide the allowable maximum load for manual
workers
Example of two electrode grids applied to the trapezius
muscle to study its activity during typing on a keyboard
with and without arm rest on the desk. Images are
interpolated and show the sEMG RMS distribution in
space
https://youtu.be/uVzLVZa5_Uk?list=TLGGXdePF7w35towNDAx
MjAyMg
https://youtu.be/CAIwOqidzz4?list=TLGGYBASmXbOqswwNDA
xMjAyMg