Physiology of Excitable tissue L 6 Changes in

Physiology of Excitable tissue L 6 Changes in Muscle during contraction Prof. Fakhir Al-Ani fakeralani 2000@yahoo. com

Fatigue On slow repetitive stimuli there will be Gradual in amplitude & gradual in duration of SMT, end with failure of relaxation. All the phases are prolonged / Failure of relaxation

Fatigue Site of Fatigue: 1. Firstly at the NMJ. 2. Then in the muscle. 3. Then in the nerve. Psychological Fatigue How to prove the site of Fatigue

Causes of fatigue: 1. Neurotransmitter: Ach. 2. Energy of muscle or nerve. 3. Metabolites & waste products (lactic acid, CO 2) 4. Failure of repolarization due to loss of energy.

Failure of repolarization: In resting condition: There is R. M. P. in all the excitable tissues On stimulation: There will depolarization as a result of influx of Na+. Followed by repolarization (Regaining the R. M. P. ) by the effect of Na-K pump, which needs energy in the form of (ATP). During fatigue due to in ATP So Na-K pump will be in efficient in repolarization.

4. Thermal Changes: 1. Resting heat. 2. Initial heat. a. Activation heat. b. Shortening heat. 3. Relaxation heat. 4. Recovery heat.

Resting heat: Any living tissue uses energy to maintain life by chemical reaction. Chemical reactions are associated with heat production This amount of heat is important to keep the body temperature constant To get normal enzyme & metabolic function Resting heat: Heat liberated from energy utilization to maintain normal R. M. P. by Na-K pump & other cell biological activities.

Initial heat: Heat produced when muscle start excitation & contracts Initial heat is then divided into 2 types: 1. Activation heat: During isometric contraction i. e. 2. Shortening heat: During isotonic contraction. Shortening heat depends on degree of shortening in m. Activation heat depends on degree of tension in m.

Relaxation & recovery heat: Relaxation heat: Passive relaxation Active relaxation heat produced is zero. heat is released. Recovery heat: After completing relaxation, there will be production of another amount of heat due to Rearrangement of disturbance that occurred in the muscle during contraction.

Thermal changes: Recovery heat Relaxation heat Shortening heat Activation heat Initial heat Resting heat

Smooth muscles

Function of the smooth muscle Smooth muscle in general are responsible for production for 1. Pr. in some organs like B. Pr. 2. Move the content of some organs like bladder.

Smooth muscle: 1. Small mono-nucleated cells. 2. Plain (non-striated) muscles. 3. Form a sheath around the viscera. 4. Involuntary. 5. Myogenic. 6. Nerve regulated. 7. Supplied by autonomic nerve fibers. 8. Slow contracting muscle fibers. 9. Usually present deep in the body.

Types of smooth muscles 1. Multiunit 2. Unitary

1. Unitary smooth muscle: Stimulation of one m. fiber will spread to a large region or even the whole organ (all the muscle fibers will act as a single unite) e. g. Smooth muscle of the bladder. There is : 1. Electrical connection. 2. Mechanical connection

1. Unitary smooth muscle

Smooth muscle cell & Gap Junction Na K Ca Channel Gap Junction

2. Multi unit smooth muscle: - More specialized - Formed of individual units - No interconnecting bridge in between cells. - Regulated more by there nerve supply. - Present mainly in the arterioles of blood vessels & some of the structure like iris, sphincters.

Other Properties of smooth muscle: 1. Unstable tone 2. The nerve supply is autonomic 3. Response to stimulation either contraction or relaxation 4. Rhythmicity 5. Electrical property of smooth muscle 6. Stimulation: 7. Mechanism of contraction.

1. Tone: - Partial state of muscle contraction. - Unstable all the time, not like the tone of the skeletal muscle. - It can be changed from one moment to another according to: - Thermal changes. - Pressure in the lumen. - Chemical stimuli.

2. The nerve supply In smooth muscles: The nerve supply is autonomic nerve fibers (sympathetic or parasympathetic). - Sympathetic: -Inhibitory in most tissues - Parasympathetic: Excitatory in most tissues In skeletal muscles: The nerve supply is somatic nerves

3. Response to stimulation Response of the smooth is either excitatory or inhibitory not like that of the skeletal muscle which is always excitatory This is depending on: 1. Types of their nerve supply: (Sympathetic or Parasympathetic) 2. Types of the receptors: Adrenergic: - α 1, α 2, β 1, β 2, β 3 Cholinergic: - (Mch 1, Mch 2, 3, 4, 5)

4. Rhythmisity: Nearly all smooth muscle fibers have some sort of rhythmisity. Rhythmisity: A state of synchronized contraction & relaxation This sequence of events occur spontaneously. i. e. myogenic property. Vary in its shape, rate & amplitude according to: - Different tissues - In the same tissue at different time by effect of: Nerve, Content, chemical, e. t. c.

5. Electrical property of SM - Smooth muscle has unstable RMP - It is ranging around – 70 to – 50 m. V R. M. P. is unstable due to: 1. High permeability of cell membrane in comparison with that of skeletal muscle. 2. Small size of the muscle fibers. So it shows slow sine waves of fluctuation in basal line Basal electrical rhythm

Electrical property of SM On the top of sine waves there may be spikes some of these spikes may reach the firing level that will excite the muscle fiber i. e. overshoot the zero potential (causing an AP) Smooth muscle action potential has long duration of about 50 msec.

Electrical property of SM Pacemaker Potential Effect of stimulation: -

6. Stimulation: Smooth muscle is highly sensitive to: 1. Chemical. 2. Mechanical stimuli. Less to temperature & electrical stimuli (nerve supply). So during studies, chemical & mechanical stimulation are used rather than electrical stimuli of its nerve supply Mechanical stimuli e. g. is by distension of blood vessels or the intestine as we increase its content.

7. Structure: Smooth muscle fiber has actin & myosin but they are not arranged as in skeletal muscle (No striation). No troponin or tropomyosin Instead they contain Calmodulin can react with Ca+2 on excitation activation of Myosin light chain kinas enzyme stimulates phosorylation of the myosin, binding & sliding of actin in between myosin.

Smooth muscle contraction

Excitation Contraction coupling 1. 3. Source of Ca+2 : 2. 5. 4. 1. Extra-cellular. 2. Stored in external surface of membrane (Cavea-olae). 3. Stored Ca in the internal surface of membrane. (bounded to protein). 4. From mitochondria. 5. Under developed endoplasmic reticulum.

Plasticity Tension It is a property of the smooth muscle. Plasticity means: On stretching of smooth m. Sudden in tone followed by in tone. But it stays higher than the original tone This continue till we reach maximum tension. Stretching of the smooth muscle