1. بسم الله الرحمن الرحيم
NEURON

2. OBJECTIVES By the end of this lecture you should be able to
Describe the functional structure of neuron – Cell body, Dendrites, Axon.
List the types of Nerve Conduction
List the factors that affecting nerve conduction
Illustrate the functional importance of is myelin sheath & Node of Ranvier
Discreminate between Contiguous Conduction and Saltatory Conduction

3. NEURON Neuron (nerve cell) consists of Three Basic Parts :
1– Cell Body
2– Dendrites
3– Axon

4. Neuron Cell body Dendrites Houses the nucleus and organelles
Project from cell body and increase surface area available for receiving signals from other nerve cells
Signal toward the cell body
Dendrite and cell body serve as the neurons input zone.

5. Neuron Axon Nerve fiber
Single, elongated tubular extension that conducts action potentials away from the cell body
Conducting zone of the neuron

6. Axon
Axon hillock
First portion of the axon plus the region of the cell body from which the axon leaves
Neuron’s trigger zone(where Action Potential are generated).
Axon terminals
Release chemical messengers that simultaneously influence other cells with which they come into close association
Output zone of the neuron

7. Neuron

8. NEURON (cont) REMEMBER Dendrites & cell body – Input zone ( Receive)
Axon -- Conducting zone
Axon Terminals – Output zone
Action Potential are initiated at Axon Hillock (trigger zone)

9. Action Potentials are propagated from the Axon Hillock to the Axon terminal
In cell body Graded Potentials (Local potentials) are produced in response to incoming signals.
Action potentials are Initiated at the Axon Hillock, and conducted throughout a nerve fiber

10. Conduction of Action Potentials
Two types of propagation
Contiguous conduction
Conduction in unmyelinated fibers
Action potential spreads along every portion of the membrane
Saltatory conduction
Rapid conduction in myelinated fibers
Impulse jumps over sections of the fiber covered with insulating myelin

11. Contiguous Conduction

12. Myelinated Fibers

13. Saltatory Conduction

14. Saltatory Conduction: Action Potential Propagation in a Myelinated Axon

15. Saltatory Conduction
Propagates action potential faster than contiguous conduction because action potential does not have to be regenerated at myelinated section
Myelinated fibers conduct impulses about 50 times faster than unmyelinated fibers of comparable size
Myelin
Primarily composed of lipids
Formed by oligodendrocytes in CNS
Formed by Schwann cells in PNS

16. CONDUCTION IN NERVE FIBERS
Conduction depends on Two factors:
1) Diameter of the nerve fiber
2) Axon (Nerve fiber) is Myelinated or Unmyelinated

17. CODUCTION IN NERVE FIBERS (cont)
Diameter of Nerve fiber
Nerve fiber with small diameter – conducts slowly
Nerve fiber with large diameter – conducts fast

18. CONDUCTION IN NERVE FIBER (cont)
Myelinated Nerve Fibers
Myelinated nerve fibers conduct FAST then Unmyelinated nerve fibers.
Why?
Myelinated nerve fibers have saltatory conduction.

20. CONDUCTION IN NERVE FIBER (cont)
SUMMARY
Small diameter fiber conduct SLOW
Large diameter fiber conduct FAST
Myelinated nerve fiber conduct VERY FAST.

21. Regeneration of Nerve Fibers
Regeneration of nerve fibers depends on its location
Schwann cells in PNS guide the regeneration of cut axons
Fibers in CNS myelinated by oligodendrocytes do not have regenerative ability
Oligodendrocytes inhibit regeneration of cut central axons

22. References Human physiology by Lauralee Sherwood, seventh edition
Text book physiology by Guyton &Hall,11th edition
Text book of physiology by Linda .s contanzo,third edition