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The Nervous System What did you learn at school today? Neurophysiology!
The Nervous System
What did you learn at school today? Neurophysiology!
The Nervous System…
Connects all other organ systems
together
Protects you using reflexes. (eg.
stove)
Controls heart rate, emotions,
memories, consciousness, and
much more.
The most intricate and
beautifully complex of all the
systems.
Spinal and Cranial Nerves
● Spinal Nerves: Nerves that originate from the spinal
cord
● Cranial Nerves: Nerves that originate from the brain
Organization of the Nervous System
Afferent vs. EfferentAfferent: Neurons that transmit action potentials (an electrical signal) from the
sensory organs to the CNS (brain and spinal cord).
Efferent Neurons: Neurons that transmit action potentials from the CNS to the
effector organs.
The Cellular Level of Neurons (the axon)● Nerves: The body’s
communication system
● Dendrite: Tiny extensions that help neurons communicate with each other
● Soma: The cell body of the neuron
● Axon: The long extension that carries electrical signals (action potentials).
● Axon Terminal: Exactly what we learned about in module 5
The structure of a nerve is
incredibly similar to the
structure of a muscle!
Classification of Neurons (Page 202)● Unipolar: One process that carries action potentials away from its cell body
● Bipolar (interneurons): Two process.
● Multipolar: Many processes
Neuroglia (neural glue) ● The “connective tissue” of the nervous system
● There are about 9 neuroglia for every nerve
● Nerves cannot reproduce, but neuroglia can
● Without these, the function of the nervous system would not be possible
Neuroglia 1. Oligodendrocytes: Binds together and
insulates the CNS neurons
2. Schwann Cells: Insulates PNS neurons
3. Microglia: Fight infection with
phagocytosis
4. Astrocytes: Form the blood-brain barrier
5. Ependymal Cells: Move and secrete
cerebrospinal fluid (more on this later)
Action Potential:
How the nerves
send this “electrical
signal” that tells
just about
everything in our
body what to do
and when to do it.
There’s an app for that… ● Single electrical impulses are responsible for setting everything your
body does into motion.
● There is no such thing as a more “powerful” action potential.
The frequency changes but the intensity does not.
- Seeing a tiger inside a cage vs. being inside the cage with the
tiger
The Action Potential Chart
Sodium (+) and Potassium (+)● Responsible for causing this electrical signal!
● Your neuron is like a battery with a positive and negative charge on each
side of the membrane.
● Both sodium and potassium are positive. The concentration gradient and the
proteins make the inside (-)
● NATURE HATES GRADIENTS: Sodium potassium pump makes the inside
have a negative charge
(1) Resting Potential ● Potential Difference:
Measure of the charge across the cell membrane.
● At rest the cell is “polarized” meaning it is negative with a measure of -70mv of electricity.
● NATURE HATES GRADIENTS. The -70 charge is only possible by the sodium potassium pump.
-70mv
The different channels in the cell membrane
(2) Stimulus “Build up” ● This can happen when something causes some of the smaller sodium channels to
open allowing a small amount sodium to come inside the cell making it “less
negative.”
What causes this “Build Up”?-> Graded Potentials.
(3) Threshold is reached. DROP THE BASS! Action Potential begins. ● Neurons work in
something called an
“all-or-nothing”
phenomenon.
● -55mv is the magic
number.
● Once -55mv is reached, all
the sodium gates open up!
-55 mv
4: DEPOLARIZATION of the membrane
● The sodium channels of the cell open when the threshold is
reached.
● Most of the sodium travels inside the cell and the membrane
potential rises steadily until it goes from -70 to about +30 mv.
● This occurs along the entire axon and is the electrical signal that
your body uses for everything.
(5) Saturation reached. Potassium channels open. ● At +30mv, the sodium channels close and sodium stops coming into the cell
● Now both sodium and potassium are crammed inside of the cell
● Potassium gets uncomfortable with sodium invading its space.
● Potassium channels open and potassium now begins to leave the cell.
(6) REPOLARIZATION
● The potassium leaves the cell rapidly through the potassium
channels and the membrane potential steadily drops again.
● Now potassium is on the outside and sodium is on the inside.
(7 and 8) Hyperpolarization and Potassium Gates Shut
● Because SO much potassium leaves the
inside of the cell, the membrane potential
drops to about -75 or -80mv.
● The potassium gates shut and potassium
stops flooding out of the cell.
(9) Back to normal
Here is a link that illustrates the
entire process….
https://www.youtube.com/watch?v=y
Q-wQsEK21E
● What is wrong now?
● The potassium is on the outside and
the sodium is on the inside.
● The Sodium Potassium Pump
restores everything back to normal
by bringing 3 sodium out of the cell
and 2 potassium into it.
● After a while, everything goes back
to the way it was before.
● This entire process occurs down the entire axon and it is the cornerstone for understanding how the nervous system works!
Absolute and Relative Refractory Periods ● Action Potentials can only fire at a
certain rate.
● Think of a toilet. After one flush you cannot immediately flush it again.
● Repolarization can only happen so fast…
Myelinated Axon vs. Unmyelinated ● Myelin (Schwann Cell): A fatty sheath that covers an acon and speeds up the
action potential drastically.
● Unmyelinated axons are much slower
● When you get a cut, there is a sharp pain followed by a dull ache. The initial pain
is from the myelinated axons and the dull ache later is from the unmyelinated.
● Cattle can stand right after birth because most of their axons are instantly
myelinated. Humans develop it later.
How do nerves communicate with each other?● Similar to neuromuscular junction
● See page 223
Homework● By 12 tonight all of the homework will
be listed
● Watch the lecture for module 8 and
familiarize yourself with the brain by
completing the study guide!
● Next week we have the brain dissection
● Start working on your essay
● Take module 8 quiz (open book,
online)
