بسم الله الرحمن الرحيم

1. بسم الله الرحمن الرحيم ﴿و ما أوتيتم من العلم إلا قليلا﴾ صدق الله العظيم الاسراء اية 58

2. Nerve and Muscle By Dr. Abdel Aziz M. Hussein Lecturer of Medical Physiology Member of American Society of Physiology

3. Nerve and muscle , Abdelaziz Hussein

4. Nerve and muscle , Abdelaziz Hussein

5. Organization of Human Body • The human body is made up of different systems e.g. digestive system, whose functions are coordinated and integrated together. • Each system consists of many organs that made up of many tissues of complementary functions. • Each tissue consists of millions of similar cells. • The cell is the basic unit of structure and function in the body Nerve and muscle , Abdelaziz Hussein

6. Nerve and muscle , Abdelaziz Hussein

7. Nerve and muscle , Abdelaziz Hussein

8. Nervous System • Nervous system is divided into; • i) Central NS→consists of the brain and the spinal cord. • ii) Peripheral NS→ consists of; • 12 pairs of cranial nerves arising from the brain. • 31 pairs of spinal nerves arising from the spinal cord. Nerve and muscle , Abdelaziz Hussein

9. Nerve and muscle , Abdelaziz Hussein

10. Functions of NS Nerve and muscle , Abdelaziz Hussein

11. Functions of NS • 1-Sensory functions: • It receives the sensory stimuli coming from skin, viscera and special sense organs (eye, nose, and ear). • 2-Motor functions: • It controls the activity of skeletal ms, smooth ms and cardiac ms. • 3-Higher mental functions: • As learning and memory. Nerve and muscle , Abdelaziz Hussein

12. Types of cells in NS • NS is composed of 2 types of cells: Nerve and muscle , Abdelaziz Hussein

13. Types of cells in NS Nerve and muscle , Abdelaziz Hussein

14. Neuron (Nerve Cell) • 1) Def., • Itis the structural and functional unit of the nervous system. • 2) No. • One trillion neurons • 3) Classification of neurons: • a) Histological classification: • Neurons are either multipolar, bipolar and unipolar neurons Nerve and muscle , Abdelaziz Hussein

15. Neuron (Nerve Cell) • b) Functional (physiological) classification: • i) Sensory (afferent) neurons: • They conduct impulses from receptors to the CNS. • ii) Motor (efferent) neurons: • They conduct impulses from the CNS to the effector organs. • iii) Interneurons: • They are small neurons. • They serve the integrative functions of the NS. • They are about 99% of all neurons. Nerve and muscle , Abdelaziz Hussein

16. Structure of Neuron • 4) Structure of neuron: • It is formed of cell body and cell processes Nerve and muscle , Abdelaziz Hussein

17. Cell Body or Soma • The cell body is the enlarged part of the neuron, which contains the nucleus. • It controls the metabolic processes and provides nutrition for the whole neuron. • It contains; mtiochondria, microtubules and microfilaments etc Nerve and muscle , Abdelaziz Hussein

18. Cell Processes • There are 2 cell processes; Nerve and muscle , Abdelaziz Hussein

19. Cell Processes • There are 2 cell processes; Nerve and muscle , Abdelaziz Hussein

20. Axonal Sheaths • There are two sheaths that cover the axons: Nerve and muscle , Abdelaziz Hussein

21. Axonal Transport • Transport of materials in the axons can be done by 2 mechansims; Nerve and muscle , Abdelaziz Hussein

22. Nerve Fibers • The nerve (or nerve trunk) is composed of a larger number of nerve fibers. • Each nerve fiber is an axon covered by a myelin sheath and a Schwann sheath. Nerve and muscle , Abdelaziz Hussein

23. Properties of nerve fibers • The nerve fibers have 2 properties, • Excitability is the ability of the nerve fibers to respond to stimuli, and convert these stimuli into nerve impulses • Conductivity is the ability of the nerve fibers to conduct nerve impulses from one site to another Nerve and muscle , Abdelaziz Hussein

24. Stimulus • 1) Def. • It is a change in the surrounding environment (either external or internal environment) • 2) Types of stimuli: • a) Electrical stimuli: • b) Chemical stimuli • c) Physical stimuli Nerve and muscle , Abdelaziz Hussein

25. Factors that determine the effectiveness of the stimulus • a) Strength of the stimulus Nerve and muscle , Abdelaziz Hussein

26. Factors that determine the effectiveness of the stimulus • b) Duration • -The stimulus to be effective must act for a certain length of time known as the excitation time. Within limit, the stronger the stimulus, the shorter is excitation time Nerve and muscle , Abdelaziz Hussein

27. Strength and Duration curve (Excitability curve) Nerve and muscle , Abdelaziz Hussein

28. Factors that determine the effectiveness of the stimulus • c) Rate of rise of intensity Nerve and muscle , Abdelaziz Hussein

29. Nature of Excitability • Excitability is a, bioelectric phenomenon in which the nerve fibers respond to stimuli by rapid changes in their resting membrane potential and conduct action potentials along the nerve fibers to their terminals Nerve and muscle , Abdelaziz Hussein

30. Resting membrane potential (RMP) • 1-Def. • It is the potential difference between the outside and inside of nerve fiber during rest. • 2-Value: • It is about 70 mV (in nerve fiber) and 90 (in skeletal ms) • It is -70 mV because the inner surface of the cell membrane is -vely charged relative to the interstitial fluid. Nerve and muscle , Abdelaziz Hussein

31. Resting membrane potential (RMP) • 3-Measurement of the resting membrane potential • By two microelectrodes with very fine tips less than 1 um connected with a special voltmeter. • One electrode is introduced inside the nerve fiber and the other electrode is placed on its outer surface. Nerve and muscle , Abdelaziz Hussein

32. Resting membrane potential (RMP) • 3-Measurement of the resting membrane potential Nerve and muscle , Abdelaziz Hussein

33. 4-Causes of the resting membrane potential Nerve and muscle , Abdelaziz Hussein

34. Causes of RMP • A) Distribution of ions inside and outside the nerve fiber Nerve and muscle , Abdelaziz Hussein

35. Causes of RMP • B) Selective permeability of the cell membrane • The cell membrane is made up of double layers of lipids, with specialized proteins penetrating the double layers. • These proteins form channels which regulate the movements of ions across the membrane. • Certain ions (Na, K, Cl and Ca) can cross the membrane only through these protein pores channels Nerve and muscle , Abdelaziz Hussein

36. AS Biology, Cell membranes and Transport

37. Causes of RMP • B) Selective permeability of the cell membrane • These channels are 3 types • Passive ion channels • Chemically activated ion channels • Voltage activated ion channels Nerve and muscle , Abdelaziz Hussein

38. Causes of RMP • B) Selective permeability of the cell membrane • Diffusion of ions through the cell membrane • a) K diffusion: (the main cause of RMP ( • b) Na diffusion • c) Cl diffusion Nerve and muscle , Abdelaziz Hussein

39. Causes of RMP • Diffusion of ions through cell membrane Nerve and muscle , Abdelaziz Hussein

40. Causes of RMP • C) Sodium and potassium pump: (Na- K Pump): • i) Structure: • The pump is formed of a large protein molecule (act as a carrier) in the cell membrane, which has: • ATPase property (ability to split ATP). • Na binding site→ at the inner surface • K binding site→ at the outer surface of the cell membrane. Nerve and muscle , Abdelaziz Hussein

41. Causes of RMP • C) Sodium and potassium pump: (Na- K Pump): • ii) Operation: Nerve and muscle , Abdelaziz Hussein

42. Causes of RMP • C) Sodium and potassium pump: (Na- K Pump): • iii) Function of Na-K pump: • It helps to maintain a high concentration of Na ion outside and a high concentration of K ion inside the nerve cells • Any condition decreases the metabolic activity of the cell e.g. by cooling →inhibits Na-K pump →Na+ ions will accumulate inside the cell and neutralize the -ve charges of protein ions and K ions that held on the outer surface escape away, and RMP becomes progressively lost. Nerve and muscle , Abdelaziz Hussein

43. THANKS

44. Action Potential • A) Def. • It is the electrical changes, which occur in the RMP as a result of stimulation of N.F. by an effective stimulus • B) Initiation or phases of action potential • i) Depolarization • ii) Repolarization • iii) Redistribution of ions inside and outside Nerve and muscle , Abdelaziz Hussein

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46. i) Depolarization • The stimulus ↑esthe permeability of the cell membrane (several hundred folds) to Na ions, which diffuse inside causing gradual change in the membrane potential from the resting potential(-70m.v) to the threshold potential or the firing level (-55m.v). • At -55m.v, mgates of the voltage activated sodium channels open and Na ions flow into the cell (Na influx). • As a result of sudden Na influx, the membrane potential quickly reaches zero potential and then overshoots to about +35 mv, so there is a momentary reversal in polarity Nerve and muscle , Abdelaziz Hussein

47. i) Depolarization Nerve and muscle , Abdelaziz Hussein

48. ii) Repolarization • At the threshold potential (-55 mv), the voltage sensitive K channels also open, but begin to act after a slight delay time. • Repolarization results from closure of h gates of voltage gated Na channels and opening of the n gates of voltage gated K channels, allowing K ions to diffuse out of the cell (K efflux or outflux). • Diffusion of K ions outside returns the inside of the membrane to its original -ve potential l(-70m.v) i.e. restore the RMP i.e. repolarization Nerve and muscle , Abdelaziz Hussein

49. ii) Repolarization Nerve and muscle , Abdelaziz Hussein

50. iii) Redistribution of ions inside and outside • After depolarization and repolarization, the ionic composition inside and outside the cell membrane is slightly disturbed. • Redistribution of Na and K ions to the normal resting condition is established by the Na-K pump which actively transports Na out and K into the cell Nerve and muscle , Abdelaziz Hussein