psyc 101 ch2 book
Nervous system
- a communication network that conveys messages throughout your body, using electrical and chemical processes
The influx of the positive sodium ions is at the axon hillock raises the internal cell votage of the first segment of the axon from the resting voltage of
-70mV to the -55mV relative to the outside
In the human brain glia cells outnumber neurons by approximately
50 to 1
in the resting state, the voltage inside the cell is about
70 millivolts compared to the voltage on the outside
Nodes of Ranvier
The gap between myelin segments
All or none
a neuron either fires or does not fire; action potentials are always the same strength
the solutions on either side of the membrane wall come into equilibrium with
a slightly more negative charge inside
Because the proportion of sodium and potassium ions inside and outside the cell is not the same as before,
a sodium/potassium pump within the cell membrane brings them back to their original values.
If the total charge of the electrically charged solutions is different
a voltage will be generated between the outside and the inside of the cell
Because myelin is such a good insulator, it does not
allow the exchange of ion fluid between the inside and the outside of the cell membrane
The speed of action potential in an unmyelinated axon is
approximately 157 to 268 mph
process repeats through each segment of the axon, like
arrow of dominoes tumbling down
The message to fire begins
at the dendrites
Due not only to the force of diffusion but also to the force of
attraction that occurs between oppositely charged ions
Terminal buds
axon buds, synaptic knobs terminal buttons
The nervous system contains the
brain, spinal cord, other nerve fibers, and includes some 100 billion (1011) nerve cells
Electrostatic pressure
causes similarly charged ions to spread apart and oppositely charged ions to move toward each other
A typical neuron has three basic parts
cell body, dendrites, and an axon
The potassium gates open and the positive potassium ions now repelled by the much more positively charged
cell interior flow out of the cell as the similarly charged ions repel each other, and returns to resting potential
Glial cell
cells that support, nourish and protect neurons, produce myelin that convers axon
A single instructs the
channels in the membrane to open up
Neurotransmitters
chemical messengers that neurons use to communicate at the synapse
The axon is not entirely enclosed, however it is
covered in segments of myelin
electrical potential
created by the differences in charge between the outside and the inside of the neuron
A neuron conveys the strength of a stimulus by firing more often and
delivering its message to more neurons (difference between loud and quiet sounds)
The channels or gates open freeing the positive sodium ions to move into the cell through
dendrites to the cell body finally reaching the beginning of the axon
Voltage
determined by the electrical characteristics of particles called ions
The difference in the charges inside and outside of the neuron
determines its polarity
Two processes direct the flow of positive and negative ions into or out of the cell
diffusion and electrostatic pressure
Neuroscience extends far beyond the borders of medicine and into disciplines as
diverse as engineering, computer science, and psychology
When we hear a loud bang (2)
each individual neuron fires more often than it would for a quiet sound
Light sensitive cells in the back of your eyes relay signals, using
electricity and chemicals, to various brain regions that transform the black marks on a page into words to remember
A neuron is surrounded by and contains
electronically charged solutions
Inside the cell are negatively charged protein ions which do not
exist outside the cel
The damaged myelination caused by multiple sclerosis can lead to many symptoms including
fatigue, trouble with vision, and cognitive disabilities
Myelin sheath
fatty substance that insulates the axon and speeds the transmission of neural messages
Each action potential takes about 1 millisecond to complete, and a typical neuron can
fire several hundred times per second
Microglia
glial cell that can multiply and secrete substances to defend the brain from infection and inflammation
Schwann cell
glial cell that makes the myelin that envelops axons
Astrocytes
glial cell that restores the barrier between the brain and blood
Inside the neuron the concentration of potassium ions is
greater than that outside the membrane
The voltage inside the section of the axon rises rapidly
increasing from -55mV to +30mV after which the sodium gates immediately close
For an excitatory signal to occur, there has to be more excitatory then
inhibitory signals, and the difference between the two has to meet the threshold potential of -55 mV
The firing of a neuron is facilitated by the myelin sheath which
insulates and protects the tiny spikes in electricity happening inside the axon
The concentration of sodium ions inside the cell is much less than
its concentration on the outside of the cell
Glial cells hold neurons together and
maintain the structure of the nervous system
although the positive sodium ions are being pulled toward the inside of the cell, they cannot
move into the cell until the neuron is stimulated by a neighboring cell.
The axon is not covered with
myelin and the nodes of Ranvier
Because the protein ions cant get out, the inside of the neuron is
negatively charged when the neuron is not active
The signal to release neurotransmitters is the voltage change from the action potential which results in vesicles that contain
neurotransmitters attaching to the membrane on the terminal bud allowing neuro transmitters into the synaptic gap
The exchange of ion fluid can only happen at the
nodes of ranvier where the is no myelin
Some will send inhibitory Signal, instructing the neuron
not to fire
There is no such thing as a
partial action potential, or a strong or weak action potential
The membrane is impermeable to
positive sodium ions and negative protein ions
The firing of the first segment of the axon produces excess
positive sodium ions on the inside of the cell, and these positive sodium ions diffuse to the next segment with in the axon
Produces a spike in the value of the voltage within the cell as the charge inside the cell becomes more
positive than the outside of the cell
The majority of neurotransmitters drift across the synaptic gap and come into contact with
receptor sites of the receiving neurons dendrites
Action potentials strength
remains the same no matter what occurs
The solutions inside and outside this segment of the Axon
return to equilibrium
Not all neighboring neurons
send an excitatory signal
Axon
skinny tube-like structure of a neuron that extends from the cell body, and which sends messages to other neurons
Vesicles
small fluid filled sacks
Nerve cells are interlinked through
some 100 quadrillion (1015) connections
A neuron is encased in a membrane that is selectively permeable, allowing only
some of the ions to pass in and out of its channels
The brain is processing nonvisual sensory input such as
sound and smells, working with other nerve cells in your body to make sure your heart lungs, and glands and organs keep releasing hormones properly
Threshold potential
stimulus threshold
Astrocytes have been found to
support communication between neurons as well
The concentrations inside and outside of the cell of a positively charged ions and negatively charged ions determine
the activity in most neurons
Axon hillock
the beginning of the axon
Glial cells come to the rescue if
the brain is injured
Biological physiology
the branch of psychology that focuses on how the brain and other biological systems influence human behavior
An action potential moves down the axon eventually reaching
the branches of the terminal buds
Neurons
the building blocks of the nervous system that transmit electrical and chemical signals in the body
Chemical messages from surrounding neurons are sent to
the cell body
The sodium ions on the outside are attracted to
the cell wall
The positive sodium ions cannot leave the cell because
the channels in the dendrites closed immediately after they entered
Polarity
the degree to which it is positive or negative overall
resting potential
the electrical potential of a cell "at rest" the state of a cell when it is not activated
Negative protein ions move toward the membrane from
the inside
The brain may be regarded as
the last frontier of medicine
If enough sending neuron signal the receiving neuron to pass along
the message, their combined signal become excitatory and the neuron will fire
Diffusion
the natural tendency of the ions to spread out or disperse
When we hear a loud bang (1)
the number of sensory neurons being fired is greater than the number that would have been fired for a quiet sound
Positive sodium ions move toward the membrane from
the outside
Pumping the excess positive sodium ions back outside the cell and
the positive potassium ions back in
The change in voltage causes the sodium gates to open and
the positive sodium ions flood into the cell
Every time a segment of the axon buyers the positive sodium ions flood in from The outside of the cell, while
the prior segment returns to its resting potential, all along the length of the axon to its end
Cell body
the region of the neuron that includes a nucleus containing DNA, protein-producing mechanisms, and other structures that nourish the cells
Action potential
the spike in electrical energy that passes through the axon of a neuron the purpose of which is to convey information
Neuroscience
the study of the brain and nervous system
If enough positively charged ions enter the cell the potential of the neuron increases and reaches
the threshold, or trigger points, and the cell fires
Positive sodium ions and negative protein move closer to
their side of the membrane wall
Neurons are activated in response to sensations, thoughts, and other neurons, and this forms
then basis for all that we think
Protein ions are attracted to the excess positive charge outside and move toward the membrane, but
they are too big to go through
Unmyelinated axon
those damaged from multiple sclerosis or other disease, have slower transmission speeds because the signal must make its way down the entire length of the axon
Brain houses
thoughts emotions, personality and orchestrates behavior
The voltage of the second segment of the Axon to reach that
threshold potential, opening it's sodium gates and causing a Spike of voltage there
Synapse
tiny gap between a terminal bud and one axon and a neighboring dendrite of the next neuron, junction between neurons where communication occurs
Dendrites
tiny, branchlike fibers extending from the cell body that receive messages from other neurons and send information in the direction of the cell body
The action potential appears to jump from node to node, as opposed to
traversing the entire axon in one continuous movement speeding the transmission of the signal
