4%20-%20Muscle%20Structure%20and%20Physiology%20I

4%20-%20Muscle%20Structure%20and%20Physiology%20I - HKIN...

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Unformatted text preview: HKIN 190 Anatomy & Physiology I Muscle Structure and Physiology I Learning Objectives 1.  To know the different types of muscle tissues in the body.   Within this, to understand how they differ. 2.  To understand the properties and functions of muscle in the body. 3.  To understand common terms associated with skeletal muscle. 4.  To understand the anatomy of skeletal muscle.   Within this, to understand:   The gross anatomy of skeletal muscle, including its connective tissue components   The microscopic anatomy of skeletal muscle. 5.  To understand the how muscle contracts.   Within this, to understand:   The arrangement of actin and myosin within the sarcomere.   The sliding filament theory.   Excitation-Contraction coupling Tissue types in the body – CMEN Blood Smooth Muscle Skeletal Bone Connective Tissue Cardiac Cartilage Connective Tissue Proper Squamous Cuboidal Epithelial Columnar Pseudostratified Transitional Nervous Tissue types in the body – CMEN Blood Smooth Muscle Skeletal Bone Connective Tissue Cardiac Cartilage Connective Tissue Proper Squamous …and it’s connective tissue associations Cuboidal Epithelial Columnar Pseudostratified Transitional Nervous Learning Objective 1 To know the different types of muscle tissues in the body.   Within this, to understand how they differ. Types of muscle in the body Smooth Cardiac Skeletal Types of muscle in the body Smooth Cardiac Skeletal Muscle types differ according to: Smooth Cardiac Skeletal Location walls of hollow organs (eg: stomach, bladder, blood vessels, resp passages) Heart Voluntary muscles Type of control ANS (involuntary) (ANS) involuntary SNS (voluntary) *also reflex (voluntary vs involuntary) Appearance of cells Spindle-shaped, uni- Long, striated, uninucleated nucleated Long, striated, multinucleated Function  Movement  Movement Note: Consider asthma meds of substances/fluids/ gases through body (eg: blood, food, urine, O2/CO2) Pump heart & posture  Thermoregulation via shivering  Some fuel storage (creatine phosphate) Learning Objective 2 To understand the properties and functions of muscle in the body. Tissue types in the body – CMEN Blood Smooth Muscle Skeletal Bone Connective Tissue Cardiac Cartilage Connective Tissue Proper Squamous Cuboidal Epithelial Columnar Pseudostratified Transitional Nervous Properties of Muscle Tissue   Electrical excitability* - ability to conduct electrical impulses along tissue   Contractility - ability for muscle to shorten and thicken (contract), generating force to produce movement (occurs in response to electrical impulse)   Extensibility* - ability to be extended (stretched) without damaging the tissue   Elasticity* - the ability to return to original shape after contraction or extension * => not entirely unique to muscle tissue Functions of Muscle Tissue? Tissue types in the body – CMEN Blood Smooth Muscle Skeletal Bone Connective Tissue Cardiac Cartilage Connective Tissue Proper Squamous Cuboidal Epithelial Columnar Pseudostratified Transitional Nervous Functions of Muscle Tissue Smooth Cardiac Skeletal Location walls of hollow organs (eg: stomach, bladder, blood vessels, resp passages) Heart Voluntary muscles Type of control ANS (involuntary) (ANS) involuntary SNS (voluntary) *also reflex (voluntary vs involuntary) Appearance of cells Spindle-shaped, uni- Long, striated, uninucleated nucleated Long, striated, multinucleated Function  Movement  Movement of substances/fluids/ gases through body (eg: blood, food, urine, O2/CO2) Pump heart & posture  Thermoregulation via shivering  Some fuel storage (creatine phosphate) Learning Objective 3 To understand common terms associated with skeletal muscle. Common terms associated with skeletal muscle   The two muscle attachments across a joint are referred to as either the:     Origin – attachment to the immovable bone and Insertion – attachment to the movable bone or the:     Proximal attachment – attachment closest to centre of body and Distal attachment – attachment furthest from centre of body Common terms associated with skeletal muscle   Agonist (prime movers) – provide the major force for producing a specific movement   Antagonists – oppose or reverse the movement of the agonist   Synergist (helpers) - add force to the agonist’s movement   Example for elbow extension:   Agonist – prime mover   Antagonist – opposite action   Synergist – “helper” to prime mover Triceps Biceps Anconeus Examples of questions using the terms on the previous slide:               What is the agonist for elbow flexion? What is the origin of this muscle? What is the proximal attachment of this muscle? What is the insertion of this muscle? What is the distal attachment of this muscle? What is the antagonist of this muscle for elbow flexion? Name 2 synergists for this muscle in flexing the forearm. Learning Objective 4a To understand the gross anatomy of skeletal muscle.   Within this, to understand:   The connective tissue components of skeletal muscle. Gross anatomy of skeletal muscle Each muscle is a composed of muscle tissue, blood vessels, nerve fibers, and connective tissue. What “level of organization” of the body are we looking at? Smooth muscle cell Molecules 2 Cellular level Cells are made up of molecules. Atoms 1 Chemical level Atoms combine to form molecules. 3 Tissue level Tissues consist of similar types of cells. Smooth muscle tissue Heart Cardiovascular system Blood vessels Epithelial tissue Smooth muscle tissue Connective tissue 4 Organ level Organs are made up of different types of tissues. Blood vessel (organ) 6 Organismal level The human organism is made up of many organ systems. 5 Organ system level Organ systems consist of different organs that work together closely. Gross anatomy of skeletal muscle: CT components             Tendon: CT attachment to bone Fascia: CT encasement of several muscles Epimysium: CT covering around a single muscle within the fascia Fascicle: bundle of muscle fibers/cells (~10-100) Perimysium: CT covering around a fascicle Endomysium: fine sheath of CT surrounding each muscle fiber/ cell   Note difference between endomysium and sarcolemma Connective tissue components of skeletal muscle Epimysium Muscle fiber in middle of a fascicle Endomysium (b) Perimysium Blood vessel Connective tissue components of skeletal muscle fascia or aponeurosis? tendon fascia or aponeurosis? Q: Other examples of aponeuroses or fascia in the body? Q: What is the name of the connective tissue covering of bone that the tendon would attach to? Learning Objective 4b To understand the microscopic anatomy of skeletal muscle. Muscle cells/fibres       muscle fascicle muscle fibers/cells   fascicle       Intracellular fluid = sarcoplasm Cell membrane = sarcolemma myofibrils thick & thin filaments (myosin & actin)   sarcomere sarcomere muscle fiber myofibril Terms       plasma membrane = ___________ intracellular fluid/cytoplasm = _________ contractile organelles = ______________ Muscle cells/fibres       skeletal muscle fascicle muscle fibers (cells) myofibrils muscle fibres/cells are made up of 100’s-1000’s of myofibrils   muscle cells/fibres run the length of the muscle   myofibrils run the length of the muscle myofibrils are made up of actin and myosin arranged into sacromeres: this is what “shortens” when a muscle contracts   sarcomeres DO NOT run the length of the muscl fascicle muscle fiber/cell myofibril Myofibrils composed of sarcomeres   Myofibrils:   Contain contractile proteins   Actin (thin filament)   Myosin (thick filament)   Contain structural proteins   Titan and dystrophin   Contain regulatory proteins   Troponin and tropomyosin   Are organized into contractile units called sarcomeres   Sarcomeres include Z line, H zone, A band, I band Myofibrils are composed of 3 types of proteins 1.  Contractile proteins •  generate force •  actin and myosin 2.  Regulatory proteins •  help turn contraction on/off •  troponin and tropomyosin 3.  Structural proteins (about 12 of these) •  keep thick/thin filaments in place (titan) •  give myofibril elasticity and extensibility (titan) •  anchor myofibrils to sarcolemma (dystrophin) Thick filaments (myosin) 2 heads (“crossbridges”): •  binding site for actin •  binding site for myosin ATPase (helps break down ATP) Thin filaments (actin) Actin is shaped like a double-helix and is associated with 2 proteins: •  Tropomyosin (long molecule; at rest, it covers the myosin binding site) •  Troponin (shorter molecule; when Ca++ binds to it, it causes the tropomyosin molecule to move away from the mysoin binding site on actin) Sarcomeres             Z-disc: border between one sarcomere and the next I-band: contains thin filaments (actin) only A-band: contains thick & thin filaments (actin & myosin) H-zone: contains thick filaments only (myosin) M-line: proteins lined up along the centre of the sarcomere During contraction, the sarcomeres shorten Sarcomeres – the A band       A for anisotropic length of thick filaments forms dark stripes in striated muscle Sarcomeres – the I band       I for isotropic only thin filaments forms light stripes in striated muscle Sarcomeres – the H zone     H for heller (german for “brighter”) only thick filaments Sarcomeres – the M line       M for middle middle of H zone row of proteins holding thick filaments in place Sarcomeres – the Z discs/line     connects thin filaments forms boundaries of sarcomere Sarcomeres Learning Objective 5 To understand the how muscle contracts.   Within this, to understand:   The arrangement of actin and myosin within the sarcomere.   The sliding filament theory.   Excitation-Contraction coupling The role of Ca++ in crossbridge formation at rest excited The powerstroke Sliding filament mechanism of muscle contraction Muscle contraction occurs when actin and myosin, the major proteins of the thin and thick filaments, respectively, slide past each other in an ATP-driven enzymatic reaction. Next topic: Excitation – Contraction coupling We have discussed muscle anatomy and how muscle contracts, but we still have not discussed what initiates the muscle contraction. The step before the muscle contracts is known as the “excitation – contraction coupling”. This is the bridge between the neural input from the nerve and the passage of its signal to the muscle fibre, causing it to contract. This “bridging” occurs at the neuromuscular junction (NMJ). Excitation – Contraction Coupling The neuromuscular junction Excitation-Contraction Coupling Question What causes the Ca++ to be released into the area of the actin/myosin (inside of the skeletal muscle fibre/cell) so that it can bind with troponin so that powerstroke can occur and the sarcomere can shorten? “Excitation-Contraction” coupling   Nerve impulses (action potentials) are relayed to the muscle fiber via the neuromuscular junction.     Details: As the action potential travels down the synaptic end bulb, it causes Ca++ channels to open here, which results in the release of Ach from synaptic vesicles into the NMJ. The Ach attaches to receptors on the motor end plate of the muscle, stimulating the opening of Na+ channels on the muscle side of the NMJ. An action potential results.   From here, action potentials travel across the muscle fibre membrane (sarcolemma) both along the length of the fibre/cell and deep (through invaginations of the cell membrane known as Ttubules).   As the action potentials reach the T-tubules, they stimulate the release of Ca++ from the nearby sarcoplasmic reticulum into the sarcoplasm (or cell interior). “Excitation-Contraction” coupling   Nerve impulses (action potentials) are relayed to the muscle fiber via the neuromuscular junction.     Details: As the action potential travels down the synaptic end bulb, it causes Ca++ channels to open here, which results in the release of Ach from synaptic vesicles into the NMJ. The Ach attaches to receptors on the motor end plate of the muscle, stimulating the opening of Na+ channels on the muscle side of the NMJ. An action potential results.   From here, action potentials travel across the muscle fibre membrane (sarcolemma) both along the length of the fibre/cell and deep (through invaginations of the cell membrane known as Ttubules).   As the action potentials reach the T-tubules, they stimulate the release of Ca++ from the nearby sarcoplasmic reticulum into the sarcoplasm (or cell interior). “Excitation-Contraction” coupling   Nerve impulses (action potentials) are relayed to the muscle fiber via the neuromuscular junction.   From here, action potentials travel across the muscle fibre membrane both along the length of the fibre/cell and deep (through invaginations of the cell membrane known as T-tubules.   As the action potentials reach the T-tubules, they stimulate the release of Ca++ from the nearby sarcoplasmic reticulum into the sarcoplasm (or cell interior). “Excitation-Contraction” coupling   Nerve impulses (action potentials) are relayed to the muscle fiber via the neuromuscular junction.   From here, action potentials travel across the muscle fibre membrane both along the length of the fibre/cell and deep (through invaginations of the cell membrane known as T-tubules.   As the action potentials reach the T-tubules, they stimulate the release of Ca++ from the nearby sarcoplasmic reticulum (portion known as the “terminal cisternae”) into the sarcoplasm (or cell interior). Nerve impulse 1 Nerve impulse arrives at axon terminal of motor neuron and triggers release of acetylcholine (ACh). 2 ACh diffuses across synaptic cleft, binds to its receptors in the motor end plate, and triggers a muscle action potential (AP). ACh receptor Synaptic vesicle filled with ACh 3 Acetylcholinesterase in synaptic cleft destroys ACh so another muscle action potential does not arise unless more ACh is released from motor neuron. Muscle action potential Transverse tubule 4 Muscle AP travelling along transverse tubule opens Ca2+ release channels in the sarcoplasmic reticulum (SR) membrane, which allows calcium ions to flood into the sarcoplasm. SR Ca2+ 9 Muscle relaxes. 8 Troponin–tropomyosin complex slides back into position where it blocks the myosin binding sites on actin. 5 Ca2+ binds to troponin on the thin filament, exposing the binding sites for myosin. Elevated Ca2+ Ca2+ active transport pumps 7 Ca2+ release channels in SR close and Ca2+ active transport pumps use ATP to restore low level of Ca2+ in sarcoplasm. 6 Contraction: power strokes use ATP; myosin heads bind to actin, swivel, and release; thin filaments are pulled toward center of sarcomere. Importance of ATP in muscle contraction resting muscle crossbridge formation and powerstroke need ATP for crossbridges to detach Consider “rigor mortis” When does contraction stop?   Contraction will continue with presence of:   neural message need all 3 for contraction to continue   ATP   calcium   When neural activity ceases:   Ca++ is removed from the sarcoplasmic reticulum by the Ca++ pump   tropomyosin covers active sites on actin   muscle relaxes (weak binding state) End of physiology lecture Next Class: Anatomy: Upper Limb Muscles ...
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