Chap-5-Muscle phy.pptx

Chapter 5 Muscle physiology By Zewdu Jima  Types of muscle tissue  generally, muscles may be grouped according to Their location in relation to other body structures Their histological (tissue) structure The way their action is controlled...

Chapter 5 Muscle physiology By Zewdu Jima  Types of muscle tissue  generally, muscles may be grouped according to Their location in relation to other body structures Their histological (tissue) structure The way their action is controlled 2 Muscle comprises Non- striated the body, 3 Striations 4  Skeletal Muscle: skeletal muscle Muscle fiber Myofibrils Myofilaments Thick filaments Thin filaments 5  Fine structure of the skeletal muscle Muscle fiber cell membrane is known as sarcolemma - generates and conducts action potentials much like those of nerve cells. sER is known as sarcoplasmic reticulum - Function: Ca 2+ storage 6  T-tubule= conducts AP from sarcolemma to SR 7  Myofibrils Each muscle fiber contains rod like structures called myofibrils myofibrils are made up of myofilaments (proteins) 8  Myofilaments 2 types of myofilaments (thick & thin) make up myofibrils Myofibrils Thin myofilame nt Thick 9 10  Thick myofilament/myosin filament Composed of the protein myosin (myosin molecules) Myosin molecule has - Head - Tail - hinge (neck) * is flexible 11   The head portion of myosin: - contains an actin-binding site and an ATP-binding site 12  Thin Myofilaments Each thin filament is made up of 3 different types of proteins: actin, tropomyosin, and troponin. - On each actin protein, there is a myosin binding site 13 Regulatory proteins  Tropomyosin molecules- wrap around actin In the relaxation state, lie on top myosin binding site on actin Should be removed for contraction to occur  Troponin - composed of three attached subunits: Troponin T: binds other troponin components to tropomyosin Troponin I: inhibits contraction Troponin C: Binds Ca++ 14 15 Excitation-contraction coupling in Skeletal Muscle fibers We can actually divide the whole process of muscle contraction into 2 steps: – Excitation – Contraction 16  The Neuromuscular Junction  The NS 'communicates' with muscle via neuromuscular (also called myoneural) junctions  Each nerve ending makes the neuromuscular junction, with the muscle fiber near its midpoint/motor end plate. 17  Components Synaptic terminal button synaptic cleft & motor end plate (depression in the sarcolemma at the synaptic cleft) The synaptic end bulb is filled with vesicles that contain the neurotransmitter, acetylcholine. (Ach) The motor end plate is chock full 18  1. Excitation steps  NM junctions work very much like a synapse b/n neurons: 1. When an AP reaches the axon terminal  - it causes voltage gated Ca2+ channels to open Ca2+ rushes into the cell 2. The terminal region is loaded with vesicles containing the transmitter Ach 3. Ca2+ causes some of the vesicles to fuse with the membrane and release their ACh 19 4. ACh diffuses across the synaptic cleft  - binds to the nicotinic (N1(m)) which is ionotropic in the postsynaptic membrane-sarcolemma - acetylcholinesterase enzyme, responsible for the catabolism of released ACh so that its effect on the post-synaptic receptors is not prolonged 5. Finally Na+ influx depolarizes the sarcolemma/the skeletam muscle fiber 20 21 22 6. Then the AP is conducted from the sarcolemma to the SR through T-tubule and causes release of Ca2+ from the SR 23  2. Contraction steps 7. The Ca++ from the SR binds with Tn.C.  Myosin binding sites on the actin filament are uncovered from tropomyosin  the actin is ready for contraction 24 8. At the same time, to make myosin ready, the myosin head binds with ATP - the myosin head immediately cleaves the ATP causes the myosin head to bend and then to attach to actin-----Muscle contraction 9. While the contraction is occurring, a new ATP is attached to myosin head 10. the head of myosin is detached from actin - relaxation occurs 25 26  Smooth Muscle  Involuntary, non-striated muscle tissue  Found in – Cardiovascular system: in blood vessels – Digestive systems: Rings of smooth muscle, called sphincters lining the alimentary canal/digestive tract. – Respiratory system Alters the diameter of the airways – Urinary system Sphincters the urinary bladder – Reproductive system Males – the male reproductive tract. Females – the female reproductive tract – eyes: the ciliary muscle – Skin: pilomotor muscles 27  The Myofilaments are : - thick filaments : Myosin - thin filaments: Actin and tropomyosin  No Troponin  tropomyosin molecules do not cover active sites on actin  depolarization phase of a smooth muscle action potential is due to calcium in 28 Excitation-Contraction Coupling in smooth muscle Calcium induced calcium release Relaxation: by another enzyme called 29 Phosphatase-detaches myosin from actin 30 ………end………. 31