Transcript PowerPoint Presentation - Nervous System

Nervous System
Electrical Conduction & Impulse to
Control Body Function
Brain
• Contains about 100 billion neurons – these
are your brain cells
• These neurons each have connections to
thousands of neighboring neurons
• Average adult brain has between 100 –
500 trillion synapses
• A child’s brain has about 1 quadrillion
synapses!
Neurons
• Brain Processes
Electrical Impulses
• Neurons Transfer
Electrical Impulses from
Brain to All Portions of the
Body
• Brain is the Control Panel
– Neurons are the Wires
to External Devices
(although both portions
composed of neurons)
Components of Neurons
• The dendrite receives
signals from other
cells
• The axon relays
signals from the
neuron to the next cell
• The spaces between
neurons where
signals are
transferred from cell
to cell are called
synapses
Neurons
• A neuron which carries signals from tissue
to brain is a sensory neuron or afferent
neuron.
• A neuron which carries signals from the
brain to tissue is a motor neuron or
efferent neuron.
Neuron Communication
• Nerve cells convert
electrical signal
(action potential) to a
chemical signal
(neurotransmitter
(NT) molecules).
• Dozens of
neurotransmitters
have been identified,
with different
functions.
Neuron Communication
• NTs are released by
one nerve cell and
bind to receptors on
the post-synaptic
membrane of the next
nerve cell.
• The chemical signal is
then converted back
into an electrical
signal.
Nerve Activation
Electrical Conductivity
• Myelin – insulation
• Motion of electrical impulse along a
neuron is called an action potential
• Difference in charge accumulation
between inside and outside of cell
• The action potential is a self-propagating
event that begins at a dendrite and travels
down the axon to the end of the neuron.
Ion Separation in Cells
• Ion pumps in cell membrane
• For every two negatively charged
potassium ions pumped into cell, three
positively charged sodium ions are
pumped out
• Action potential of 70 mV across cell
membrane (positive outside and negative
inside)
Neuron Signals
1.
2.
3.
4.
5.
6.
7.
Neuron receives impulse
Sodium gates open on cell
Positively charged Na+ ions
flood into cell
Negative charge inside cell
and active cell pumping pull
in the positive charge
As action potential
decreases, more sodium
channels open up allowing
in more positive charge –
positive feedback.
Action potential changes
from -70 mV to +40 mV.
At +40 mV sodium channels
close – negative feedback
Neuron Signals
• Na channels in the cell membrane are
voltage dependent. As Na ions flow
through one channel, the altered voltage
causes the adjacent Na channel to open.
This series of events continues, thus
propagating an action potential along the
cell membrane.
• This propagation can occur at 100 m/s
(over 200 miles/hour)!
Spinal Cord
• A bundle of nerves
which connect the
brain to the body
• Each portion of the
spinal cord innervates
a different part of the
body
Spinal Cord Function
• Cervical – diaphragm
& arms/hands
• Thoracic – chest
muscles & abdominal
muscles
• Lumbar – Legs
• Sacral – Bowel &
Bladder
Nerve Injury & SCI
• Myelin damage – nerves intact but signals
impaired. Multiple sclerosis, GuillanBarre, leukodystrophy.
• Physical break or compression in spinal
cord. Level of injury indicates level of
function.
• Nerve cells in the central nervous system
(brain and spinal cord) do not grow back if
damaged – unlike some other types of
cells (e.g. skin).
Myelin Disorder