Muscle Physiology 2023-1.ppsx

Muscle Chapter 8 Objectives  Describe & compare the 3 types of muscle; know locations in the body for each  Describe the microscopic anatomy of each type & learn proper terminology  Describe the role of the nervous system in the contraction of muscles  Describe the process of a contraction ...

Muscle Chapter 8 Objectives  Describe & compare the 3 types of muscle; know locations in the body for each  Describe the microscopic anatomy of each type & learn proper terminology  Describe the role of the nervous system in the contraction of muscles  Describe the process of a contraction  Understand the phases of a contraction  Understand how cardiac muscle contracts  Understand how smooth muscle contracts Muscle Types  Three types of muscles Skeletal – voluntary striated Cardiac – one place in body, involuntary Smooth – visceral, involuntary See Table 8.1, pg 216  Terminology  myo - refers to muscle (ex: Myocyte)  sarco - refers to muscle cells Microscopic Anatomy of Skeletal Muscles  Cell membrane = sarcolemma  Transverse (T) tubules  Numerous nuclei  Cytoplasm = sarcoplasm  Sarcoplasmic reticulum (SR)  Myofibrils  Actin (thin); I Band  Myosin (thick); A Band  Sarcomere = contracting unit of skeletal muscle = series of protein filaments (area from one Z line to the next Z line) Skeletal Muscle Actions  Work in groups to produce desired movement (prime mover or agonist) w/ others stabilizing joints (fixator) & providing smooth control over movements  Synergist - contracts at same time as prime mover & assists its movement  Antagonist – directly opposes action of prime mover; w/ partial contractions can smooth out movements or prime mover Neuromuscular Junction  Skeletal muscle is under conscious voluntary control & must receive nerve impulses to contract & produce the desired action  Neuromuscular junction = site where ends of motor nerve fibers “connect” w/ muscle fibers  Synaptic space  Synaptic vesicles w/ acetylcholine  Acetylcholinesterase in synaptic space (See FIG. 8.8, pg 222) Motor Unit  One nerve fiber & all the muscle fibers it innervates  The number of muscle fibers per nerve fiber determines the size of the resulting movement  Delicate muscles have fewer muscle fibers per motor unit than large muscles making larger movements Muscle Contraction Nervous Control of Muscle Contraction  Individual muscle fibers contract completely when stimulated by their nerve(s) = (all - or - nothing principal) but whole muscles do not so …  To produce movements that vary in range & strength, the numbers of muscle fibers stimulated for a particular movement is carefully controlled Twitch Contraction  = a single muscle fiber contraction Latent Phase – time between the nerve stimulus & beginning of contraction Contracting Phase Relaxation Phase  Entire contraction cycle lasts ~ 0.1sec  Nerve impulses are timed so that twitches of muscle fibers occur at slightly different times resulting in smooth, sustained muscle contractions Initiation of Muscle Contraction Acetylcholine binds to receptors on sarcolemmal surface -> impulse travels through transverse tubules to interior of cell -> to sarcoplasmic reticulum -> release of stored calcium ions (Ca++) into the sarcoplasm -> diffuse into myofilaments -> shorten (contraction) powered by ATP Muscle Relaxation  Sarcoplasmic reticulum pumps calcium ions back in, pulling it out of the myofibrils -> muscle fiber returns to original length (relaxes)  Energy needed to pump calcium back into SR Mechanics of Contraction  When relaxed, the actin and myosin filaments in a muscle fiber overlap a little  When stimulated to contract by a nerve impulse, cross bridges on myosin filaments move back and forth pulling the actin filaments on both sides toward the center myosin filament  Sliding of filaments over each other causes shortening of the sarcomeres  Combined shortening of the end to end sarcomeres in a muscle fiber -> contraction Chemistry of Contraction  ATP produced by mitochondria powers the sliding of actin & myosin filaments  ADP is formed & must be converted back to ATP -> phosphate group added to ADP by splitting of creatine phosphate (CP)  Source used to produce ATP & CP = catabolism of nutrients -> glucose & O2  Glucose stored as glycogen; oxygen in myoglobin Chemistry of Contraction  With adequate oxygen -> process = aerobic metabolism & maximum energy is extracted from each glucose molecule  When need for oxygen exceeds supply, muscle fibers shift to anaerobic metabolism to produce energy -> lactic acid builds up as byproduct of incomplete glucose breakdown Heat Production  Muscle activity generates heat  Mechanisms to eliminate excess heat panting or sweating  Spasmodic muscle contractions that increase heat production shivering Microscopic Anatomy of Cardiac Muscle  Striated, involuntary muscle  Only one central nucleus per cell  Long, branched fibers form networks of cells  Firm end-to-end attachments between cells = intercalated disks Transmit impulses from cell to cell to allow large groups of cardiomyocytes to contract in a coordinated manner Cardiac Muscle Contraction  Contracts without external stimulation  Groups of cardiac muscle cells adopt the contraction rate of the most rapid cell in the group  Cells contract in a rapid, wavelike fashion  Allows blood to be effectively “squeezed” out of the chambers  Internal impulse conduction system (“Mini internal nervous system”) Innervation of the Heart  Not needed to initiate contractions, but modifies heart’s contractile activity  Autonomic (involuntary) portion of NS  sympathetic – faster  parasympathetic - slower Smooth Muscle  Nonstriated, involuntary muscle  Found in two main forms Visceral - large sheets of cells in walls of hollow organs Multiunit - small discrete groups of cells; iris & ciliary body, blood vessels, bronchioles Microscopic Anatomy of Smooth Muscle  Small, spindle shaped (tapered ends)  Single, central nucleus  Smooth homogeneous appearance; dense bodies - attached to actin and myosin filaments at both ends (pg 225)  When the contractile units contract they cause the cell to “ball up” (not arranged into parallel sarcomeres so individual cells can shorten to greater degree than striated muscle cells Visceral Smooth Muscle  In walls of many soft internal organs  Contracts w/out external stimulation  No fine movements possible; contracts in large, rhythmic waves  It reacts to stretching by contracting more strongly (except in the uterus) Nerve Supply  Not necessary to initiate contractions but serves to modify them  Autonomic NS Sympathetic - slower Parasympathetic - faster Multiunit Smooth Muscle  Made up of individual smooth muscle cells or small groups of cells  Used for small delicate movements  Require specific impulses from the autonomic nerves to contract  Actions are specific and carefully controlled Review  Describe the three types of muscle in terms of function & location  Describe the microscopic anatomy of each type of muscle noting their differences; Review terminology  Understand the role of the nervous system in contraction of the different muscle types  Review the process of a contraction  Understand the phases of a contraction  Understand how cardiac muscle contracts  Understand how smooth muscle contracts