BIOL14108- WEEK 9 - Lecture notes 9 PDF

Preview

Summary

BIOL14108: Human Biology
WEEK 9: Muscular System...

Description

November 29, 2017

BIOL 14108- WEEK 9 MUSCULAR SYSTEM 8.1 INTRODUCTION TO THE MUSCULAR SYSTEM  All movements require muscles  Muscles are organs that use chemical energy from nutrients to contract and move attached structures  Muscles also provide muscle tone, propel body fluids and food, generate the heartbeat, and generate body heat  The 3 types of muscle tissue in the body are skeletal, smooth, and cardiac muscle 8.2 STRUCTURE OF A SKELETAL MUSCLE  Each muscle is an organ, composed of skeletal muscle tissue, nervous tissue, blood, and other connective tissues  Connective tissue coverings over muscles: o Layers of dense connective tissue, called fascia, surround and separate each muscle o This connective tissue extends beyond the ends of the muscle, and gives rise to tendons that are fused to the periosteum of bones o Sometimes muscles are connected to each other by broad sheets of connective tissue called aponeuroses o Fascial blends with the epimysium, the layer of connective tissue around each skeletal muscle o The perimysium extends inward from the epimysium; it surrounds bundles of skeletal muscle fibers, called fascicles, within each muscle o Each muscle cell (fiber) is covered by a connective tissue layer called endomysium Skeletal muscle and its connective tissues

Skeletal Muscle Fibers  Each muscle fiber is a single, long cyndrical muscle cell  Fibers respond to stimulation by contracting  The cell membrane of a muscle fiber is the sarcolemma  The cytoplasm of a muscle cell is the sarcoplasm; it contains many mitochondria and nuclei  The sarcoplasm contains parallel myofibrils, which are active in muscle contraction: o Thick filaments in myofibrils consist of the protein myosin o Thin filaments in myofibrils are mainly composed of the protein actin, but also contain troponin and tropomyosin o The organization of these filaments produce bands called striations The Sarcomeres of Myofibrils  Myofibrils are made up of many units called sacromeres, joined end- to end

November 29, 2017

     

A sarcomere extends from one z line to the next Striations consist of an alternating pattern of light and dark bands I bands (light bands) are made up of actin filaments, which are anchored to the Z lines A bands (dark bands) are made up of overlapping thick and thin filaments In the center of the A band is the H zone, which consists of myosin filaments only The M line, in the center of the H zone, consists of proteins that hold the myosin filaments in place

Structure of a Skeletal Muscle Fiber

The Structure of a sarcomere

The sarcoplasm of a skeletal muscle fiber  Beneath the sarcolemma of a muscle fiber lies a network of membranous channels, called the sarcoplasmic reticulum (SR), which is the endoplasmic reticulum of a musclecell  The SR is associated with transverse (T) tubules, invaginations of thesarcolemma  EachTtubuleliesbetween2cisternaeofthesarcoplasmicreticulum;Ttubulesareopentotheoutsideofthe musclefiber  The sarcoplasmic reticulum and transverse tubules activate the muscle contraction mechanism when the fiber is stimulated The SR and T Tubules of the sarcoplasm

Neuromuscular Junction

November 29, 2017

         

The site where the motor neuron and muscle fiber meet is the neuromuscularjunction Skeletal muscle fibers contract only when stimulated by a motorneuron Each skeletal muscle fiber (cell) is functionally (not physically) connected to the axon of a motor neuron, creating asynapse Theneuroncommunicateswiththemusclefiberbywayofchemicalscalledneurotransmitters,whichare released at the synapse Neuromuscular junction: a synapse between a motor neuron and a muscle fiber that it regulates The cytoplasm of the distal end of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters The muscle fiber membrane in this area contains a specialized region called the motor end plate, in which the sarcolemma is tightly folded The motor end plate contains specific receptors for the neurotransmitter When an electrical impulse reaches the end of the axon of a motor neuron, synaptic vesicles release neurotransmitter into the synaptic cleft, the gap between the membranes of the neuron and muscle fiber The neurotransmitters diffuse across the cleft, bind to the motor end plate, and stimulate the muscle fiber to contract

8.3 SKELETAL MUSCLE CONTRACTION  Muscle contraction involves several events, that result in the shortening of sarcomeres, and the pulling of the muscle against its attachments  The pulling force is exerted by the binding of myosin molecules to actin molecules  The shortening of a muscle fiber results from an increase in the overlap between actin and myosin filaments, as they slide past each other  Shortening of muscle fibers results in shortening of the entire muscle, which then pulls on the attached body part to cause movement Role of Mysoin and Actin  Myosin consists of two twisted strands, with globular heads projected outward along the strands  A group of myosin molecules forms a thick filament  Actin is a globular protein arranged in twisted filaments (a double helix), containing myosin binding sites  Troponin and tropomyosin are 2 proteins associated with the surface of the actin molecules; together, these 3 proteins form the thin filaments o Thin and Thick Filaments

November 29, 2017



According to the sliding filament model of muscle contraction, during muscle contraction, a myosin head attaches to a binding site on the actin filament, forming a cross- bridge o The sliding filament model



This binding causes the head to bend, pulling on the actin filament, and moving it toward the center of the sarcomere The head them releases, and attaches to the next binding site on the actin, pulling this site toward the center As this occurs again and again, the filaments increase their overlap, and the sarcomere shortens from both ends When many sarcomeres shorten at the same time, the muscle fiber shortens Energy from the conversion of ATP to ADP is provided to the cross- bridges by the enzyme ATPase; ATP breakdown causes the heads to return to the “cocked” position, ready to bind to another actin binding site

   

Sarcomere shortening in muscle contraction

November 29, 2017

Stimulus for Contraction  Acetylcholine is the neurotransmitter for skeletal muscle fiber contraction at the neuromuscular junctions o Acetylcholine is produced in the motor neuron, and stored in the synaptic vesicles at the distal end of the neuron o Acetylcholine is released into the synaptic cleft in response to an impulse in the motor neuron; it then stimulates the muscle fiber  Upon receipt of the muscle impulse, the sarcoplasmic reticulum releases its stored calcium to the cytosol of the muscle fiber  The high concentration of calcium in the sarcoplasm interacts with the troponin and tropomyosin molecules, which move aside, exposing the myosin binding sites on the actin filaments  Cross- bridges now form, and pull on the actin filaments, using the energy of ATP; this causes the sarcomere to shorten  The contraction continues as long as the nerve impulse continues  After the nerve impulse stops, these events lead to relaxation of the muscle: o The enzyme acetylcholinesterase, in the motor end plate, rapidly decomposes the acetylcholine o Calcium is returned to the sarcoplasmic reticulum, using ATP as an energy source o ATP now binds to the myosin heads, and the linkages between myosin and actin are broken  The actin returns to its original position and the muscle relaxes Major events of muscle contraction and relaxation

November 29, 2017

Energy Sources for Contraction  Energy for muscle fiber contraction comes from molecules of ATP; this chemical is in limited supply, and so must be regenerated  The initial source of energy for muscle contraction is ATP that is stored in the muscle  Creatine phosphate is present to initially regenerate ATP from ADP and phosphate, as it also contains high energy bonds  Whenever the supply of ATP is sufficient, the enzyme creatine phosphokinase promotes the synthesis of creatine phosphate  As ATP decomposes, the energy from creatine phosphate can be transferred to ADP molecules, converting them back to ATP  Creatine phosphate is rapidly used up too, and as its supply declines, the cell must rely on cellular respiration to generate ATP Creatine phosphate regenerates ATP

Oxygen Supply and Cellular respiration  Glycolysis is the first phase of cellular respiration; it is anaerobic and occurs in the cytoplasm o Glycolysis is an incomplete breakdown of glucose, and yields 2ATP per molecule of glucose  Aerobic respiration is a complete breakdown of glucose; it is aerobic (requires oxygen) and occurs in the mitochondria o Aerobic respiration yields 28ATP per molecule of glucose  Hemoglobin in red blood cells carries oxygen to muscle tissue  The pigment myoglobin stores oxygen in muscle tissue for aerobic respiration; this increases oxygen availability

November 29, 2017

Overview of Cellular Respiration of Glucose

Oxygen Debt  During rest or moderate activity, there is enough oxygen available to support aerobic respiration  Oxygen deficiency may develop during 1-2 minutes of strenuous exercise  In this case, pyruvic acid forms, and then reacts to form lactic acid, which accumulates as an end product of anaerobic respiration in the form of lactate o Lactate diffuses out of muscle cells and is carried in the blood stream to the liver o Using ATP, liver cells convert lactate back into glucose  During strenuous exercise, oxygen is used to produce ATP for muscle contraction, rather than for converting back to glucose  As lactate builds up, an oxygen debt develops; this must be repaid  Oxygen debt refers to the amount of oxygen that liver cells require to convert the accumulated lactate back into glucose, plus the amount that muscle cells need to resynthesize ATP and creatine phosphate to their original concentrations  Oxygen debt is also called excess post- exercise oxygen consumption  Repaying the oxygen debt may take several hours  Physical training helps to increase a muscles capacity to improve energy production Muscle Metabolism

Heat Production and Muscle Fatigue  Less than half of energy released in reactions of cellular respiration is used to form ATP; the rest becomes heat  This heat is carried by the blood to other tissues, and helps maintain body temperature  When a muscle loses its ability to contract during strenuous exercise, it is referred to as fatigue  Muscle fatigue may arise from electrolyte imbalances and decreased ATP levels  The role of lactic acid in muscle fatigue is now not clear  A muscle cramp, a sustained, painful, involuntary contraction, is thought to occur due to changes in the extracellular fluid around the muscle fibers, leading to uncontrolled muscle fiber stimulation by its motor neurons

November 29, 2017

8.4 MUSCULAR RESPONSES  One method of studying muscle function is to remove a single fiber and connect it to a device that records its responses to electrical stimulation  Isolated muscle fibers in a lab can be exposed to stimuli of various strengths; fibers will be unresponsive until the threshold stimulus is reached  Threshold stimulus: the minimum strength of stimulus required to generate an impulse through the muscle, release calcium ions, activate cross- bridges, and contract the muscle  In the body, one motor neuron impulse relases sufficient acetylcholine (Ach) in the neuromuscular junction to bring a muscle fiber to its threshold Recording of a Muscular Contraction  The response of a single muscle fiber to a single impulse is referred to as a twitch; a twitch consists of a cycle of contraction and relaxation  A myogram is the recording of an electrically- stimulated muscle contraction  The latent period is a brief delay between the stimulation and beginning of the contraction  The latent period is followed by a period of contraction and a period of relaxation  When a muscle fiber contracts, it contracts to its full extent, with each twitch generating the same force; this is called the all-or none response  Muscle fibers vary in the speed of contraction, but muscles usually consists of a combination of both types: o Fatigue- resistant slow twitch fibers o Fatigable fast twitch fibers Myogram of a single Muscle Twitch

Summation  A muscle fiber receiving a series of stimuli of increasing frequency reaches a point when it is unable to relax completely, and the force of individual twitches combine by the process of summation  Summation allows for a greater force of contraction than a single twitch can generate  When exposed to higher frequency of stimulation, relaxation time becomes very short; this is called partial tetany  If the frequency of stimulation is very high, and the sustained contraction lacks any relaxation, it is called a complete tetanic contraction  Partial tetany occurs in the body, but complete tetany can only be accomplished in a lab Myograms of twitches, summation and tetany

November 29, 2017

Recruitment of Motor Units  A motor neuron and the muscle fibers it controls make up a motor unit; when stimulated, the muscle fibers of the motor unit contract all at once  An increase in the number of activated motor units within a muscle at higher intensities of stimulation is called recruitment  Recruitment will cause an increase in the strength of a contraction  A muscle achieves maximum tension when all of its motor units have been recruited Sustained contractions  Summation and recruitment together can produce a sustained contraction of increasing strength  Sustained contraction of muscles allow for performance of daily activities  Muscle tone is achieved by a continuous state of sustained contraction of a few motor units at a time within a muscle  Muscle tone is important for maintenance of posture 8.5 SMOOTH MUSCLE Smooth muscle cells  Smooth muscle cells are elongated with tapered ends, lack striations (look “smooth”), and have a relatively undeveloped sarcoplasmic reticulum  Contain thick and thin filaments, but they are arranged more randomly Types of smooth muscle  In multiunit smooth muscle, such as in the blood vessels and iris of the eye, fibers occur separately rather than as sheets; stimulated by neurons and some hormones  Visceral smooth muscle occurs in sheets, and is found in the walls of hollow organs; these fibers can stimulate one another and display rhythmicity; these features accomplish peristalsis (Ex. Like when u make ur bed)in tubular organs Smooth Muscle Contraction * if you contract muscles slowly its better * more efficient with less energy source

Similarities to skeletal muscle contraction:  Both types involve reaction between actin and myosin  Both types are stimulated by membrane impulses, require an increase in calcium ions in the cells, and use ATP energy Differences from skeletal muscle contraction:

November 29, 2017

    

Both acetylcholine (Ach) and norepinephrine stimulate and inhibit smooth muscle contraction, while only Ach stimulates skeletal muscle Hormones can stimulate or inhibit contraction of smooth muscle, but not skeletal muscle Smooth muscle is slower to contract and relax Smooth muscle maintains a contraction longer with the same amount of ATP Smooth muscle can change length without change in tautness

8.6 CARDIAC MUSCLE  Cardiac muscle is only found in the heart  Cardiac muscle consists of branching, striated cells that interconnect in three- dimensional networks  The mechanism of contraction in cardiac muscle is essentially the same as that for skeletal and smooth muscle, but with some differences: o Sarcoplasmic reticulum is not well- developed; does not store much calcium o Transverse tubules supply extra calcium from extracellular fluid, so cardiac muscle cell twitches last longer o Cardiac muscle is self- exciting and rhythmic, creating a pattern of contraction and relaxation and the whole structure contracts as a unit o Complex membrane junctions, called intercalated discs, join cells and transmit the force of contraction from one cell to the next as well as aid in the rapid transmission of impulses throughout the heart Types of Muscle Tissues

8.7 SKELETAL MUSCLE ACTIONS Body Movement:  Bones and muscles interact as levers for movement  Bending and straightening of the arm (upper limb) at the elbow is a good example of bones and muscles acting as levers  Parts of a lever, using bending of upper limb as example: o Rigid bar or rod: forearm bones o Fulcrum or pivot, on which bar turns: elbow joint o Object moved against resistance: the hand is moved against the resistance of a weight being lifted o Force supplying energy for movement: anterior arm muscles  Bending is accomplished by the biceps brachii muscle pulling on its tendon as it contracts; the tendon is attached to the radius, a bone of the forearm Levers and Movement

November 29, 2017

Origin and Insertion *** know definition( Where muscles originate from, less movable part)  Origin: the less movable end of a skeletal muscle  Insertion: the more movable end of a skeletal muscle  Muscle contraction pulls the insertion toward the origin  Some muscles have more than one insertion or origin  Example: biceps brachii in the arm

o o o o o

Biceps means 2 origins or heads Both heads attach to portions of the scapula (coracoid process and tubercle above glenoid cavity) Insertion is the radial tuberosity of the radius Muscle is located on the anterior surface of humerus Action is flexion of the forearm at the elbow

Movements and Interaction of Skeletal muscles Common changes in the angle between bones at a joint  Flexion: decrease in the angle between bones at a joint o Example” flexion of the arm at the elbow bends at the arm  Extension: increase in the angle between bones at a joint o Example: extension of the arm at the elbow straightens the arm  Skeletal muscles usually function in groups: o The muscle that causes an action, and does the majority of the work is the agonist (prime mover) o Muscles that assist the prime mover are called synergists o Muscles that oppose an action are called antaonists o The relationships between muscles depends on the action; a muscle can be a synergist for one action and an antagonist for another action 8.8 MAJOR SKELETAL MUSCLES Skeletal muscles are named according to any of these: size, shape, location, action, number of attachments,

November 29, 2017

direction of its fibers, or combinations of the above. Examples:  Pectoralis major: named for size and location; large size, located in chest  Deltoid: named for shape; shaped like a triangle  Extensor digitorum: named for action; extends digits (fingers, toes)  Biceps brachii: named for number of attachment and location; has 2 origins/heads, and is found in the arm (brachium)  Sternocleidomastoid: named for attachments; attaches to sternum clavicle, and mastoid process  External oblique: named for location and direction of fibers; located near outside of body, and fibers run at a slant Anterior view of superficial skeletal muscles

Posterior view of superficial skeletal muscles *On test / know how to label

Muscles of Facial Expression

* master and temporalis respinsible for chewing  Muscles of facial expression attach to underlying bones and overlying connective tissue ofskin  They are responsible for the variety of facial expressions possible in the human face, communicating anger, fear, pain, disgust, surprise, happiness  Major muscles include the epicranius, orbicularis oculi, orbicularis oris, buccinator,

November 29, 2017

zygomaticus, and platysma

Muscles of Mastication  Chewing movements are derive...