4. NERVOUS SYSTEM
It consist of two cells
NEURONS NEUROGLIA
. Larger than neuralgia .Smaller than neurons
. Mainly has ability to .They support nourish &
respond to a stimulus & protect the neurons &
convert into an action maintain homeostasis
potential. in the interstitial fluids.
6. A Typical Neuron Overview
• Dentrites
• Cell Body
• Axon
• Terminal
7. TYPES OF NEURONS
Multipolar Bipolar Unipolar
Severaldendrites one main dendrites &
One axon. dendrite & axon fuse &
eg: Brain, spinalcord one axon divide into
eg: Retina of eye branches
9. ELECTRICAL SIGNALS OF NEURONS
ACTION POTENTIAL GRADED POTENTIAL
Electrical signal that >Used for short distance
Travels along the surface communication.
Of the membrane of
Neurons.
Communicates over
short & long distances
With in body.
12. DESCRIPTION
1. Leakage channels : These randomly alternate b/w open &
closed positions.Has more K ion leakage channels than Na ion.
2. Voltage gated : This opens in response to change in
membrane potential .Participate in generation & conduction of
action potential.
3. Ligand gated : open & closes in response to specific
chemical stimulus eg hormones, neurotransmitters (ACH) by
binding to a portion of channel protein or indirectly via
membrane protein ( G protein).
4. Mechanically gated : By mechanical stimulation
(vibration).
17. Principles of Chemical Synaptic Transmission
• Basic Steps
– Neurotransmitter synthesis
– Load neurotransmitter into synaptic vesicles
– Vesicles fuse to presynaptic terminal
– Neurotransmitter spills into synaptic cleft
– Binds to postsynaptic receptors
– Biochemical/Electrical response elicited in
postsynaptic cell
– Removal of neurotransmitter from synaptic cleft
18. Synaptic Transmission: Four Easy Steps
I. Synthesis and Storage of Neurotransmitters
II. Neurotransmitter Release
III. Neurotransmitter Postsynaptic Receptors
IV. Inactivation of Neurotransmitters
19. Step 1. The neurotransmitter is manufactured by the
neuron and stored in vesicles at the axon terminal
20. Step 2. When the action potential reaches the axon
terminal, it causes the vesicles to release the
neurotransmitter molecules into the synaptic cleft
21. Step 3. The neurotransmitter diffuses across the cleft and binds to receptors
on the post-synaptic cell.
Step 4. The activated receptors cause changes in the activity of the post-
synaptic neuron.
22. Step 5. The neurotransmitter molecules are released from
the receptors and diffuse back into the synaptic cleft
23. Step 6. The Neurotransmitter is re-absorbed by the post
synaptic neuron. This process is known as Reuptake.
24. Myelinated Axons
The axon is a single
long, thin extension
that sends impulses
to another neuron.
They vary in length
and are surrounded
by a many-layered
lipid and protein
covering called the
myelin sheath,
produced by the
schwann cells.
25. Myelination
• Most mammalian axons are myelinated.
• The myelin sheath is provided by
oligodendrocytes and Schwann cells.
• Myelin is insulating, preventing passage of
ions over the membrane.
26. Resting Potential
In a resting neuron (one that
is not conducting an
impulse), there is a
difference in
electrical charges on the
outside and inside of the
plasma membrane. The
outside has a positive charge
and the inside has a negative
charge.
27. Trigger Zone: Cell Integration and
Initiation of AP
• Excitatory signal: depolarizes, reduces
threshold
• Inhibitory signal: hyperpolarizes, increases
threshold
28. Action Potential
When the cell membranes are
stimulated, there is a change
in the permeability of the
membrane to sodium ions
(Na+).
The membrane becomes more
permeable to Na+ and K+,
therefore sodium ions diffuse
into the cell down a
concentration gradient. The
entry of Na+ disturbs the
resting potential and causes
the inside of the cell to
become more positive
relative to the outside.
29. Course of the Action Potential
• The action potential begins with a partial depolarization (e.g. from firing
of another neuron ) [A].
• When the excitation threshold is reached there is a sudden large
depolarization [B].
• This is followed rapidly by repolarization [C] and a brief hyperpolarization
[D].
• There is a refractory period immediately after the action potential where
no depolarization can occur [E]
Membrane
potential
(mV)
[A]
[B] [C]
[D] excitation threshold
Time (msec)
-70
+40
0
0 1 2 3
32. Refractory Period
There are two types of refractory
period:
Absolute Refractory Period – Na+
channels are inactivated and no
matter what stimulus is applied
they will not re-open to allow Na+
in & depolarise the membrane to
the threshold of an action
potential.
• Relative Refractory Period - Some
of the Na+ channels have re-
opened but the threshold is higher
than normal making it more
difficult for the activated Na+
channels to raise the membrane
potential to the threshold of
excitation.
33. Saltatory Conduction
• Myelinated regions of axon are electrically
insulated.
• Electrical charge moves along the axon rather
than across the membrane.
• Action potentials occur only at unmyelinated
regions: nodes of Ranvier.
Myelin
sheath
Node of Ranvier
