Lec 2 RMP PDF - Resting Membrane Potential Lecture Notes

Excitable tissues and RMP Prof. Dr. Shereen Samir  Questions The main cation of ICF is: a) Na b) K c) HCO3 d) CL e) Ca  True or false The total body fluids constitute about 40% ICF nearly equal 14 – 15 L Interstitial fluid is the fl...

Excitable tissues and RMP Prof. Dr. Shereen Samir  Questions The main cation of ICF is: a) Na b) K c) HCO3 d) CL e) Ca  True or false The total body fluids constitute about 40% ICF nearly equal 14 – 15 L Interstitial fluid is the fluid inside the cell and nearly equal 10 L Lecture Objectives At the end of this lecture you will be able to: 1. Define the resting membrane potentials 2. Explain the causes of the resting membrane potential 3. Explain the mechanisms of development of RMP in neurons Only nerves, muscles and some glands have plasma membranes capable of responding to stimuli i.e. excitable tissues During rest, the inner surface of the nerve fiber is negatively charged compared with outer surface which is positively charged Measurement of the resting membrane potential: DURING REST Resting Membrane Potential: Definition : It is the potential difference between the outer and inner surfaces of the cell membrane during rest. So , the cell membrane during rest is polarized  Values: The membrane potential is measured in millivolts ( mV). In nerve fibers ,70 m.v. and expressed as: - 70 m m.v. because the inner surface is negative in relation to the outer surface. In skeletal muscle fibers resting membrane potential is — 90 mV.  Causes of RMP 1. Distribution of Ions 2. Selective permeability 3. Na-K pump 9 unequal distribution of ions on both sides of the membrane  2) Selective permeability of the cell membrane: Cell membrane is formed of lipid bilayer with proteins channels penetrating them. Diffusion of ions thorough leak channels is the cause of RMP The cell membrane is 100 times more permeable for K+ than for Na+ ions. The cell membrane is impermeable to proteins, due to large molecular weight. The cell membrane is a semipermeable membrane: It is more permeable to k+ ions It is less permeable to Na+ ions. It is impermeable to the intracellular proteins.  K+ K+ K+ K+ ECF + + + + ++ + + + + + + + + + + + + + + + + + + + + ------------------------------------ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ K+ Pr- Pr- Pr- Pr- Pr- ICF 13 3) Sodium and potassium pump: (Na+ - k+ pump) Definition: Large protein molecule located in the cell membrane. Composition:  Has ATP binding site (ability to split ATP)  Has 3 binding sites for Na+ (inner surface of membrane)  Has 2 binding sites for K+ (outer surface of membrane) Mechanism of Na* - K+ pump: When all sites on Na+- k+ pump are occupied, the carrier molecule undergoes transformation which results in splitting of ATP, release of 3 Na+ to outside and release of 2 K+ to inside the cell. 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) Phases of action potential a) Depolarization b) Repolarization c) Redistribution of ions 16 17 Skeletal ms Innervation 1 Outcome i) The axon terminal (presynaptic) : contains; a) Vesicles→ contains Acetylcholine. b) Mitochondria→ provides the ATP. iii) Motor end plate (MEP) (Postsynaptic): a) Junctional folds →↑ the surface area of MEP. b) Cholinergic receptors→ the receptors for Ach., also it acts as an ion channel. Normally, when Ach is attached to the binding sites, Na and K ions can pass through these chemically activated channels. c) Cholinesterase enzyme→ hydrolyzes Ach to choline and acetic acid. 19  Sarcomere Def : - It is the distance between 2 adjacent Z lines or discs. - It is the functional units of the ms Structure :It is composed of filaments (contractile proteins) 1. Thick filaments : myosin 2. Thin filaments: Actin 1) Def.,  It is the process by which an action potential initiates the ms contraction 2) Steps:  4 steps Nerve and Muscle, Abdelaziz M.Hussein 21 1) Propagation of the AP and release of Ca+2 ions 2) Binding of the cross-bridges between myosin and actin 3) Cross bridge cycling: Binding, Bending, detachment, return to original site 4) Relaxation: need ATP 22  Questions The resting membrane potential in nerve fibers is a) – 70 mV b) – 90 mV c) – 10 mV d) – 120 mV e) – 30 mV  References 1. Costanzo, Linda S. "BRS Physiology (Board Review Series)." (2018). 2. Ganong, William F. "Review of medical physiology." (2020). THANK YOU