Structures and functions of cells of the nervous system.
Anatomy of the Nervous system:
We have various types of neurons.When we talked about sensory neurons for instance the
Unipolar sensory neurons and they pick up the touch(In spinal cord),They pick up pain and
they pick up temperature,we have sensory neurons that they pick up olfactory information
so all of the senses have their own distinction neurons,with distinctive structures.
So a lot of them are responsible for getting information from our environment like light
for vision,or sound waves for auditory input and basically transmitting them into neural
We have Motor Neurons so they allow you to interact with our environment ,they have
synapses into our muscles and also onto our glands and we have Interneurons-They are
thinker neurons,they take the input from sensory neurons for instance and they decide
what they are gonna do with motor neurons wether activate it or inhibit it.
These two neurons are a types of Multipolar neurons.
Multipolar NeuronˠLots of extensions out of the cell body,a types of neuron that
possesses a single axon and many dendrites allowing for the integration of a great deal of
information from other neurons.These dendritic branches can also emerge from the nerve
cell body.(Somaˠwhere it has the nucleus,DNA is in it and all other cellular structures
+Protein is made in there-Vesicles are made and they have transporters in them.) And then
we have axons that essentially they can cover various distances and it has terminal buttons
and neural dendrites have synapses into the soma of the post synaptic neuron +Synapses to
other axons to affect the output.
Bipolar NeuronsˠFound in the ear for auditory transmission,so two extensions off of the
cell body: 1-One Dendrites 2-One axon attached to the cell body. Unipolar NeuronˠHave one process from the cell body,an axon,It branches to connect to
receptors and the spinal cord on the brain.
CNSˠBrain+Spinal Cord.3 Meninges.CSF.Skull.Blood Brain Barrier.HIGH PROTECTION.
PNSˠAll the other Neurons within the body.
Throughout our body they are capillaries that supply blood ,capillaries wall essentially have
spaces in between them,and so things in the blood can easily leave these capillaries and
headed to all parts of our body,but BBB is a separation of a circulating blood from the
barrier extracellular fluid in the CNS.
It is selectively permeable.
Area PostremaˠIt has a weak Blood-Brain barrier,it controls vomiting.These region is
there to detect the presence of toxic substances in the blood.
NoteˠBlood brain barrier is also help action potential,where they should be a selective
number of ions inside and outside the cell.you sometimes don’t want to have any extra ions
or changes that may distract action-potential.
What does it mean when we say a neuron is excited or a neuron is inhibited?
Every neuron has membrane potential,it is the differences of charges across the
membrane,so we have ions in both inside and outside the cell,we have some proteins that
they have charges as well,so normally the inside of the cell is more negatively charged than
outside the cellˠMembrane potential.
Noteˠwe can hook up electrodes across the membrane,to measure the electrical charges
greated by an axon.membrane potential is always in voltage.
Action potentialˠ The brief electrical impulse that provides the basis for conduction of
information along the axon.2 m/seconds long. • We can record action-potential with Oscilloscope.
• we can stimulate an action-potential with micro-electrodes and record its activity.Micro-
electrodes is a glass.
• Resting membrane potential is -70mV we can understand the mV amount needed for an
action-potential to happen by understanding threshold of excitation.
Threshold of excitationˠThe value of the membrane potential that must be reached to
produce an action potential-Small @ 70mV.
DepolarizationˠMembrane potential becoming more and more positive .
Re-polarizationˠWhere they all back down to negative.
HyperpolarizationˠWhere it goes pass -70mV and it over shoots. and then it goes back to
resting membrane potential.
Purpose of hyperpolarizationˠIt always happens,It directs action potential ,finding its
direction towards the cell body.
What is exactly happening in the stages of depolarization and re-polarization?
we have different concentration of ions inside and outside the cell.
So outside the cell we have NA+ ,CL-(Sea water)
Inside we have Organic anions and lots of K+.,But due to the concentration of ions the
inside is more negative than outside the cell.
We have two forces that are acting on ions to move across the membrane:
• Diffusionˠhigh concentration to low.Molecules wanna reach the state of
• Electrostatic pressureˠIons that are positively charge are going to repel,and the
ones that are oppositely charge are gonna attract.
So,The action potential which happens when the cell is depolarized to the threshold of
excitation,largely depends on Sodium(Na+)And Potassium(K+),and they pass through these
pores in the cell’s membrane called the “Ion channels”. So the ion channels are really just like the bunch of proteins forming a particular channels
sitting in the membrane and these channels are voltage-gated ion channels.
They will open and close depending what the membrane potential is.
Breaking down what’s happening in action potential:
Threshold of excitation is reached.
(1)Na+ channels open, Na+ begins to enter the cell.
(2)K+Channels open,K+begins to leave the cell
(3)Na+Channels become refractory,no more Na+ enters the cell.(Depolarization)
(4)K+ continues to leave the cell,causes membrane potential to return to resting level.
(5)K+channels close,Na+channels reset.
(6)Extra K+outside diffuses away.(Hyperpolarization)
Conduction of Action-potential:
Sodium-potassium pumpˠA protein found in the membrane of all cells that extrudes
sodium ions from and transports potassium ions into the cell.(2K+in and 3Na+out)
MyelinˠWhat covers axons.
Saltatory conductionˠWe have segments of myelin along our axon and what’s gonna
happen those that are not myelinated are gonna be nodes of ranvier,And action potential
only happens at those segments and areas.
So,the action potential actually jumps that is why its fast.
Decremental ConductionˠImpaired conduction in a portion of a fiber because of the
progressively lessening response of the unexcited portion of the fiber to the action
potential coming toward it;It is manifested by the decreasing speed of
conduction;amplitude of action potential.
• Active inhibitory interneurons that form synapses with the motor neurons What exactly is the myelin?
It is made by glial cells,it is 80% fatty tissues that is why its white.
It is the supporting cells of the central nervous system.
In CNS it is made by oligodendrocytes (soma and several segments and several
axons~50)and in PNS is made by Schwann cells.(Only one cell and one segment)
The three most important myelin cells in CNS are:
3. MicrogliaˠSmallest of the glial cells.
★ ASTROCYTES :
•They are looking like a star.
•It provides support for neurons of the CNS.
•They provides nutrients,by extracting glucose from the blood.
(Glycogenˠglucoseˠlactate)ˠHigh metabolic rate.
•physical supports to neurons(nerve glue)
•they also remove waste through a process called Phagocytosis.
Phagocytosisˠthe process by which the cells engulf and digest other cells or debris
caused by cellular degeneration.
Producing myelin sheath in CNS-50segments each time.1mm long.
They are acting like the white blood cells,they are the smallest of the glial cells.They are
responsible for inflammatory reaction for after the brain is damaged.They are the prime
representative of immune system in the brain. Glial cells in the PNS:
They are in the peripheral nervous system,they form the myelin but at the same time they
do other things as well:
They help the axons growth after the damage.They will guid axons to find their way after
the damage by creating tunnels that helps them find the right target.
Noteˠ In CNS the after the damage,the astroc