Nervous system (neuron & ion channels)

1. NERVOUS SYSTEM

3. Introduction
-Nervous system controls all the activities of the
body.
-It is quicker than the other control system in the
body namely endocrine system.
-Primarily, the nervous system is divided into
two parts.
-Central nervous system
-Peripheral nervous system

4. CNS
• CNS includes Brain & Spinal Cord.
• It is formed by neurons and the supporting cells
called neuroglial cells.
• The structures of brain and spinal cord are arranged
in two layers.
-Gray matter is formed by nerve cell bodies
-White matter is formed by nerve fibers.

7. Central Nervous System (CNS)
• brain
• spinal cord
Peripheral Nervous System (PNS)
-PNS is formed by neurons and their processes
present in all regions of the body. It consists of
• cranial nerves (12 pr)
• spinal nerves (31 pr)

8. CNS PNS

9. sensory receptor
sensory input
integration
motor input
effector

11. Neuroglia (glia) are cells that support and protect neurons. The following four neuroglia
are found in the CNS:
•Astrocytes have numerous processes that give the cell a star-shaped appearance.
Astrocytes maintain the ion balance around neurons and control the exchange of
materials between blood vessels and neurons. They are part of the BBB
•Oligodendrocytes have fewer processes than astrocytes. They wrap these cytoplasmic
processes around neurons to create an insulating barrier called a myelin sheath.
•Microglia are phagocytic macrophages that provide a protective function by engulfing
microorganisms and cellular debris.
•Ependymal cells line the fluid-filled cavities of the brain and spinal cord. Many are
ciliated. They make CSF
Read more: http://www.cliffsnotes.com/WileyCDA/CliffsReviewTopic/Neuroglia.topicArticleId-
22032,articleId-21933.html#ixzz0YK3TiUTl

12. NEURON
• Neuron is defined as the structural and functional unit of the
nervous system.
• It is like any other cell in the body having nucleus and all the
organelles in cytoplasm.
• Neuron is different from other cell by two ways:
1. Neuron has branches or process called axon & dendrites.
2.Neuron does not have centrosome so it does not undergo
division.

13. cell body
dendrite
axon
Myelin
sheath

14. Structure of Neuron
• Neuron is made up of three parts:
-Nerve cell body
-Dendrites
- Axon
Nerve cell body
-Nucleus
- Nissl granules
-Neurofibrils
- Mitochondria
-Golgi Apparatus
Dendrites
Axon

16. Schwann Cells
Axon
Nodes of Ranvier

17. bipolar
eye, ear, & olfactory
unipolar multipolar
most abundant type in CNSDorsal root
ganglion cells

18. Protein channels
Tube shaped channels extend in the cell membrane from
extracellular to the intracellular ends.
Properties
Selective permeability
Gating mechanism
Selective permeability
Permit only one type of ion to pass through it.
Due to characteristics of channel itself such as diameter, shape &
nature of charge on it.
E.g. Sodium channels
Potassium channels

19. Gating mechanism
Equipped with gate like extensions .
Controlled by 3 principal pathways
• Voltage gated channel
Responds when there is change in the electrical potentials.
E.g . Ca channels in NMJ.
• Ligand gated channels (chemical gating)
Extracellular ligands- are first messenger
E.g . Acetylcholine .
Intracellular ligands are second messenger
E.g . Ca+, cAMP, G protein.
• Mechanically gated channels
Opening of channel by mechanical stretch.
E.g. pressure receptors, receptor cell of organ of corti

20. sodium-potassium pump
• The sodium-potassium pump is a protein complex that
continually pumps three sodium ions out of the cells while
drawing two potassium ions into the cell.
– helps to maintain the electrical gradient.
• The electrical gradient and the concentration gradient
work to pull sodium ions into the cell.
• The electrical gradient tends to pull potassium ions into
the cells.

21. Fig. 2-15, p. 41
Figure 2.15: The sodium and potassium gradients for a resting membrane.
Sodium ions are more concentrated outside the neuron; potassium ions are more
concentrated inside. Protein and chloride ions (not shown) bear negative charges inside
the cell. At rest, very few sodium ions cross the membrane except by the sodium-
potassium pump. Potassium tends to flow into the cell because of an electrical gradient
but tends to flow out because of the concentration gradient.

22. Carrier protein consists of 2 subunits-
a) α subunit
b) β subunit
α subunit – concerned with Na and K transport whereas function of
β subunit is unknown.
α subunit has 6 sites-
I. 3 receptor sites for binding Na ions.
II. 2 receptor sites for K ions.
III. 1 receptor site for binding of enzyme ATPase.
Na+-k+ pump

23. Mechanism of Na+–K+ pump
• Enzymes ATPase
• 3 Na and 2 K bind to the
respective receptor site of carrier
protein.
• Activates enzyme ATPase.
• Breakdown of ATP in to ADP –
relaese of one high energy
phosphate.
• Conformational change in the
carrier protein – extruding Na
into ECF and K into cytoplasm.

24. Na+– k+ pump
K+ is released and Na+ sites
are ready to bind Na+ again;
the cycle repeats.
Binding of cytoplasmic Na+ to the pump protein
stimulates phosphorylation by ATP.
Phosphorylation causes the
protein to change its shape.
The shape change expels Na+ to the
outside, and extracellular K+ binds.
K+ binding triggers release of the
phosphate group.
Loss of phosphate restores the
original conformation of the pump
protein.
Extracellular
fluid
Cytoplasm
1
2
3
4
5
Concentration gradients of K+
and Na+

25. • Functions of Na+– K+ pump
- Controlling cell volume
- Electrogenic activity
• Regulation of Na+ – K+ pump
Increased by – cAMP, DAG, Thyroid hormone,
Aldosterone, Insulin.
inhibited by – Low temp. , Lack of O2, dopamine and
digitalis.
Ca++ Pump
Calcium pump helps in maintaining extremely low conc.
Of
Ca in ICF.
E.g. 1) cell membrane- extrudes Ca out of cell.

26. K+- H+ PUMP
• Operates through K+-H+ ATPase activity.
• Present at 2 places in human body-
1) Parietal cells of gastric gland – H+ Is actively
transported into lumen of gastric gland and K+ in to the
cell.
2) Renal tubules – located at DCT and collecting ducts.
Excretes large amount of H+ in to the tubules to control
blood pH.

27. Resting Membrane Potential(RMP)
• It is electrical potential difference (voltage) across the
cell membrane (between inside and outside of cell)
under resting condition.
• It is also called membrane potential/ transmembrane potential/
transmembrane potential difference or transmembrane potential
gradient.
• RMP is measured by cathode ray oscilloscope.
• There is negativity inside and positivity outside the membrane.

28. Fig. 2-13, p. 40
Figure 2.13: Methods for recording activity of a neuron.
(a) Diagram of the apparatus and a sample recording. (b) A microelectrode and stained
neurons magnified hundreds of times by a light microscope.

29. Action potential
• Action potential is created in excitable cell membrane .
• It is electrochemical fluctuation in excitable cell
membrane which spreads over membrane and act as
signaling mechanism in our body.
CHANGES are:
Electrical changes
Chemical changes