ANATOMY & PHYSIOLOGY OF NERVE, MUSCLE AND NMJ

ANATOMY & PHYSIOLOGY OF NERVE, MUSCLE AND NMJ

1. Anatomy & Physiology of muscle, nerve and neuromuscular junction - Nithin nair ( Mpt - 1)

2. LEARNING OBJECTIVES After this session, the students will be able to:

3. ANATOMY & PHYSIOLOGY OF MUSCLES Classification of Muscles

4. ANATOMY & PHYSIOLOGY OF MUSCLES Skeletal muscle is made up of many long thin cells called muscle cells or muscle fibers. Each muscle fiber consists of many contractile units called myofibrils . Each myofibril is 1-2µm in diameter and lies parallel to one another. Fibrils are divisible into filaments made up of contractile proteins : myosin, actin, tropomyosin and troponin. Cytoplasm in the muscle fibers called sarcoplasm contains numerous mitochondria ( sarcosomes ), smooth surface endoplasmic reticulum (sarcoplasmic reticulum) and rich in glycogen.

5. ANATOMY & PHYSIOLOGY OF MUSCLES

6. ANATOMY & PHYSIOLOGY OF MUSCLES SARCOMERES are the smallest functional unit of skeletal muscle and are composed of two protein filaments ; actin and myosin.  Actin is a thin filament and myosin is a thick filament, as shown on the following diagram, and it is the interaction between these two filaments that causes a muscle to contract and shorten.

7. ANATOMY & PHYSIOLOGY OF MUSCLES TYPE I FIBER Slow-twitch fiber Slow-oxidative fibers Highly resistant to fatigue Red in colour TYPE IIA FIBERS Intermediate fibers Fast oxidative glycolytic Resistant to fatigue Red in colour TYPE IIB FIBER Fast fibers Fast glycolytic fibers Easily gets fatigued White in colour

8. PHYSIOLOGY OF MUSCLE CONTRACTION SEQUENCE OF EVENTS DURING MUSCULAR CONTRACTION Stimulation of muscle fiber by impulse Generation of action potential in muscle Spreading of action potential through sarcolemma and ‘T’ tubules Arrival of action potential at cisternae of ‘L’ tubules Release of calcium ions from cisternae to sarcoplasm Binding of calcium ions to troponin C and change in position of troponin C Exposure of active site of F actin Binding of myosin head with F actin and power stroke in myosin head Sliding of actin filaments over myosin filaments Muscular contraction.

9. PHYSIOLOGY OF MUSCLE CONTRACTION

10. Properties of Skeletal muscles EXCITABILITY Response of an tissue to stimulation CONTRACTILITY Internal events of the muscle which are manifested by change in length or tension of the muscle fibers. They are of 2 types A. ISOMETRIC CONTRACTION B. ISOTONIC CONTRACTION MUSCLE TONE Continuous and partial contraction of the muscles with certain degrees of tension

11. ANATOMY & PHYSIOLOGY OF NMJ It is the junction between the terminal branch of the nerve fiber and muscle fiber .

12. ANATOMY & PHYSIOLOGY OF NMJ SEQUENCE OF EVENTS DURING NEUROMUSCULAR TRANSMISSION Action potential Opening of voltage gated calcium channels Entry of calcium ions from extracellular fluid Opening of vesicles and release of Ach Passage of Ach Binding of Ach with receptor and formation of Ach – Receptor complex Opening of ligand gated sodium channels Entry of sodium ions from extracellular fluid Development of endplate potential Generation of action potential Excitation contraction coupling Muscular contraction Axon terminal Post synaptic membrane Synaptic cleft Motor nerve fiber Muscle fiber

13. ANATOMY & PHYSIOLOGY OF NERVE Enclosed cable like bundle of peripheral axons. These are collection of nerve fibres . Basic structure of Neuron: Axon Dentrite Myelin sheath Nodes of Ranvier Internodes Neurilemma

14. ANATOMY & PHYSIOLOGY OF NERVE CLASSIFICATION OF NERVE FIBERS: Depending upon structure : Myelinated, Non-myelinated Depending upon distribution : Somatic, Visceral or Autonomic Depending upon origin : Cranial, Spinal Depending upon function : Sensory, Motor Depending upon secretion (Neurotransmitter): Adrenergic, Cholinergic Depending on diameter and conduction of impulse : Type A, Type B, Type C

15. Properties of nerve fibers

16. References Essentials of Medical Physiology – K Sembulingam (5 th ed.) Handbook of General Anatomy – BD Chaurasia (4 th ed.)