BIOH111 o Cell Module o Tissue Module o Integumentary system o Skeletal system o Muscle system o Nervous system o Endocrine system Endeavour College of Natural Health endeavour.edu.au 1
TEXTBOOK AND REQUIRED/RECOMMENDED READINGS o Principles of anatomy and physiology. Tortora et al; 14 th edition: Chapter 10 Endeavour College of Natural Health endeavour.edu.au 2
BIOH111 MUSCLE SYSTEM MODULE o Session 11 (Lectures 17 and 18) Muscle physiology: Building of muscle organ cells, tissue, organ and muscle contraction process and regulation o Session 12 (Lectures 19 and 20) - Skeletal muscle metabolism o Session 13 (Lectures 21 and 22) Major muscle groups Endeavour College of Natural Health endeavour.edu.au 3
BIOH111 Lectures 17 and 18 Muscle physiology: Building of muscle organ and muscle contraction process and regulation Department of Bioscience endeavour.edu.au
PREPARATION FOR THIS SESSION o Review: plasma membrane and endoplasmic reticulum structure and function difference between channels and receptors think about this: can they be both in one protein? regulated exocytosis tissue types Endeavour College of Natural Health endeavour.edu.au 5
Lecture 17: Muscle cells and tissue OBJECTIVES Name and describe muscle cells and their function in building and function of skeletal muscle tissue Describe structure of connective tissue, nervous tissue and blood supply within the structure and function of skeletal muscle tissue Regulation of muscle contraction Describe process of muscle contraction at the neuromuscular junction Lecture 18: Muscle contraction process Describe the sliding filament theory of muscle contraction from both an anatomical and physiological viewpoint Discuss the contraction mechanism and the structures required for this occur Endeavour College of Natural Health endeavour.edu.au 6
FUNCTIONS OF MUSCULAR SYSTEM 1. Producing body movements - occurs at the cellular level where chemical energy is changed into mechanical energy 2. Stabilizing body positions skeletal muscle contractions stabilize joints and maintain body positions (e.g. siting/standing) 3. Regulating organ volumes - bands of smooth muscle called sphincters 4. Movement of substances within the body - blood, lymph, urine, air, food and fluids, sperm 5. Producing heat - involuntary contractions of skeletal muscle (shivering) Endeavour College of Natural Health endeavour.edu.au 7
PROPERTIES OF MUSCLE TISSUE 1. Excitability respond to chemicals released from nerve cells 2. Conductivity ability to propagate electrical signals over membrane 3. Contractility ability to shorten and generate force 4. Extensibility ability to be stretched without damaging the tissue 5. Elasticity ability to return to original shape after being stretched Endeavour College of Natural Health endeavour.edu.au 8
MUSCLE TISSUE Consists of elongated cells called musle fibres or myocytes that are modified for contraction using ATP as energy. Muscle tissue provides motion, maintenance of posture and heat. o Classified into 3 types based on function and location: 1. Skeletal muscle tissue striated, voluntary control 2. Cardiac muscle tissue - striated, involuntary control 3. Smooth (visceral) muscle tissue non-striated, involuntary control Endeavour College of Natural Health endeavour.edu.au 9
Skeletal Cardiac Smooth Multi-nucleated cells Motion, posture, heat protection and production Attached to bones by tendons Branched, mononucleated cells Contraction Heart Mononucleated cells Motion Walls of hollow internal structures (e.g. blood vessels, airways) Endeavour College of Natural Health endeavour.edu.au 10
SKELETAL MUSCLE TISSUE o Skeletal muscle is made up of several tissues: muscle cells (fibers), adipose tissue, connective tissue and nervous tissue o 1 skeletal muscle = 1 organ Building a muscle: cells tissue organ Endeavour College of Natural Health endeavour.edu.au 11
cells tissue organ MUSCLE FIBER OR MYOFIBER o Long, cylindrical & multinucleated o Sarcolemma: muscle cell membrane; form T tubules o Sarcoplasm: muscle cell cytoplasm; filled with sarcoplasmic reticulum, mitochondria and myofibrils; contains large amount of glycogen for energy production and myoglobin for oxygen storage Endeavour College of Natural Health endeavour.edu.au 12
TRANSVERSE (T) TUBULES Structure: invaginations of the sarcolemma into the center of the cell; filled with extracellular fluid Function: to carry and quickly spread the muscle action potential to all parts of the muscle fiber. Endeavour College of Natural Health endeavour.edu.au 13
SARCOPLASMIC RETICULUM o Sarcoplasmic reticulum: AND MITOCHONDRIA Structure: system of tubular sacs similar to smooth ER in nonmuscle cells Function: storage of Ca+2 in relaxed muscle (release triggers contraction) o Mitochondria: Structure: same structure as in non-muscle cells; lie in rows throughout the myofibre Function: provides ATP needed for contraction Endeavour College of Natural Health endeavour.edu.au 14
MYOFIBRILS & SARCOMERE o Myofibrils: separated by sarcoplasmic reticulum within a sarcolemma; contain the functional units of muscle sarcomere o Sarcomere contains myofilaments (thick & thin filaments) - contractile proteins of muscle Endeavour College of Natural Health endeavour.edu.au 15
cells tissue organ CONNECTIVE TISSUE o Superficial fascia : loose connective tissue & fat underlying the skin o Deep fascia : dense irregular connective tissue around muscle o Connective tissue components of the muscle include epimysium = surrounds the whole muscle perimysium = surrounds bundles (fascicles) of 10-100 muscle cells endomysium = separates individual muscle cells Tendons and aponeurosis Endeavour College of Natural Health endeavour.edu.au 16
CONNECTIVE TISSUE o Tendons and aponeuroses are extensions of connective tissue beyond muscle cells that attach muscle to bone or other muscle. tendon - cord of dense connective tissue that attaches a muscle to the periosteum of a bone aponeurosis - tendon that extends as a broad, flat layer and connects muscle to whatever it is moving Endeavour College of Natural Health endeavour.edu.au 17
cells tissue organ NERVE AND BLOOD SUPPLY o Each skeletal muscle is supplied by a nerve, artery and two veins. o Each motor neuron supplies multiple muscle cells (neuromuscular junction) motor unit o Each muscle cell is supplied by one motor neuron terminal branch and with one or two capillaries (found in the endomysium between individual cells) Endeavour College of Natural Health endeavour.edu.au 18
cells tissue organ MOTOR UNIT o Motor unit = 1 somatic motor neuron + all the skeletal muscle cells (fibers) it stimulates (10 cells to 2,000 cells) muscle fibers normally scattered throughout belly of muscle one nerve cell supplies on average 150 muscle cells that all contract in unison. Motor nerve fibre Anterior horn cell o Total strength of a contraction depends on how many motor units are activated & how large the motor units are Endeavour College of Natural Health endeavour.edu.au 19
REVISION Next.. Endeavour College of Natural Health endeavour.edu.au 20
NEUROMUSCULAR JUNCTION (NMJ) NMJ is a region between the end of axon and the surface of a muscle fiber that is separated by synaptic cleft or gap. Components of NMJ: 1. Synaptic end or bulb - swellings of axon terminals 2. Synaptic vesicles contained within the synaptic bulbs; filled with acetylcholine (ACh) 3. ACh receptors at the sarcolemma of the motor fiber (motor end plate); ~30 million/synaptic bulb Endeavour College of Natural Health endeavour.edu.au 22
MUSCLE CONTRACTION - REGULATION 1. Nerve impulse (action potential) release of ACh from synaptic vesicles (exocytosis) is calcium-dependent Is Na+ inside a cell a good 2. ACh binds to receptors Na + thing? If not, how does the cell influx; K+ efflux fix that? 3. Inside of muscle cell more positive muscle action potential travels over the cell and down the T tubules 4. Ca +2 released from the SR muscle cell contraction (details next lecture) 5. Acetyl cholinesterase breaks down the ACh muscle action potential stops and muscle relaxes Endeavour College of Natural Health endeavour.edu.au 23
Lecture 17: Muscle cells and tissue OBJECTIVES Name and describe muscle cells and their function in building and function of skeletal muscle tissue Describe structure of connective tissue, nervous tissue and blood supply within the structure and function of skeletal muscle tissue Regulation of muscle contraction Describe process of muscle contraction at the neuromuscular junction Lecture 18: Muscle contraction process Describe the sliding filament theory of muscle contraction from both an anatomical and physiological viewpoint Discuss the contraction mechanism and the structures required for this occur Endeavour College of Natural Health endeavour.edu.au 26
SARCOMERE STRUCTURE o Sarcomere: basic functional unit of myofibril; contains: Z disc marks boundary of each sarcomere I band wide light band; contains only thin filaments; Z disc passes through the middle of the I band A band wide dark band in the middle of the sarcomere; contains M line and H zone M line holds thick filaments together in the middle of the sarcomere H zone only thick filaments; extends on either side of M line Endeavour College of Natural Health endeavour.edu.au 27
SARCOMERE STRUCTURE Endeavour College of Natural Health endeavour.edu.au 28
THE PROTEINS OF MUSCLE o Sarcomere contains 3 groups of functionally distinct proteins: 1. contractile proteins: myosin and actin 2. regulatory proteins: turn contraction on & off; troponin and tropomyosin 3. structural proteins: provide proper alignment, elasticity and extensibility, link myofibres to sarcolemma and ECM ; titin, myomesin, nebulin and dystrophin Endeavour College of Natural Health endeavour.edu.au 29
THICK FILAMENTS o Thick filaments are composed of myosin each molecule resembles two golf clubs twisted together myosin heads (cross bridges) extend toward the thin filaments o Held in place by the M line proteins. Endeavour College of Natural Health endeavour.edu.au 30
THIN FILAMENTS o Thin filaments are made of actin, troponin, & tropomyosin o The myosin-binding site on each actin molecule is covered by tropomyosin in relaxed muscle o The thin filaments are held in place by Z lines. Endeavour College of Natural Health endeavour.edu.au 31
STRUCTURAL PROTEINS: TITIN o Titan anchors thick filament to the M line and the Z disc and maintains position of thick filament in the middle of the sarcomere o The portion of the molecule between the Z disc and the end of the thick filament can stretch to 4 times its resting length and spring back unharmed. o Function: role in recovery of the muscle after contracting or stretching Endeavour College of Natural Health endeavour.edu.au 32
STRUCTURAL PROTEINS: MYOMESIN AND NEBULIN o Myomesin: structural protein of the M line; function: connects to titin and adjacent thick filaments o Nebulin, inelastic protein; function: assists in the alignment of the thin filaments Endeavour College of Natural Health endeavour.edu.au 33
STRUCTURAL PROTEINS: DYSTROPHIN o Dystrophin links thin filaments to sarcolemma and transmits the tension generated to the tendon. Endeavour College of Natural Health endeavour.edu.au 34
SLIDING FILAMENT THEORY o Sarcomere shortens during contraction: Z discs move toward each other and thin filaments slide inward Contraction cycle o Overall action: sarcomeres shorten muscle fiber shortens muscle shortens Endeavour College of Natural Health endeavour.edu.au 35
CONTRACTION CYCLE https://www.youtube.com/watch?v=ct8abzn_a8a Endeavour College of Natural Health endeavour.edu.au 36
RELAXATION CYCLE Contraction cycle has several break points: 1. Degradation of ACh: Acetylcholinesterase (AChE) breaks down ACh within the synaptic cleft muscle action potential ceases and Ca +2 release channels close 2. Sequestration of Ca +2 : Ca +2 active transport pumps pump Ca +2 ion back into storage (SR); calciumbinding protein (calsequestrin) helps hold Ca +2 in SR End result: Tropomyosin-Troponin complex covers myosin-binding site on the actin Endeavour College of Natural Health endeavour.edu.au 37
MUSCLE CONTRACTION OVERVIEW Basic steps: 1. Release of ACh in response to AP 2. Initiation of muscle AP results in release of Ca+2 from SR 3. Ca+2 interacts with troponin on thin filament. If thick filament is activated the sarcomere contraction is initiated sliding theory 4. Ca is sequestered back into SR and sarcomere relaxes tropomyosin and titin Endeavour College of Natural Health endeavour.edu.au 38
2 molecules are critical for contraction: Ca +2 and ATP. We know where Ca +2 comes from, but where does the ATP used in contraction cycle come from? Next session!! Endeavour College of Natural Health endeavour.edu.au 39
WHY IS IT HARDER TO LIFT SOMETHING WITH AN EXTENDED ARM? o Length-Tension relationship o Optimal overlap at the 100% o Cell too stretched myosin heads are not close to actin so no binding can occur little force is produced o Cell is too short: myosin heads overlap with actin, thick filaments crumpled by Z discs so little binding can occur little force is produced Graph of Force of contraction (Tension) vs Length of sarcomere Endeavour College of Natural Health endeavour.edu.au 41
WHY STRETCHING AFTER SITTING FEELS GOOD? o Muscle tone constant, slightly contracted state of all muscles, which does not produce active movement resistance to stretch in resting muscle normal muscle tone is provided by titin and weak myosin-actin bonds (when myosin head is bound to ADP) Stretching leads to breaking those weak interactions and overstretching is prevented by titin Endeavour College of Natural Health endeavour.edu.au 42
Recap of Session 11 Muscle tissue is classified into 3 types: skeletal, smooth and cardiac (we only cover skeletal in BIOH111) Skeletal muscle cells (myofibers) contain a specialised component called myofibril which contain a unit responsible for muscle contraction sarcomere Sarcomere contraction is regulated by nervous system at the NMJ and the outcome of the regulation is release of calcium from SER Sarcomere is composed of 3 functional groups of protein: regulatory, structural and contractile. All work together to enable sarcomere, myofibril and myofiber to contract Endeavour College of Natural Health endeavour.edu.au 43
PREPARATION FOR NEXT SESSION o Complete any missing concepts and linking words from Session 11 o Review: mitochondria structure and function contraction cycle Endeavour College of Natural Health endeavour.edu.au 44