Muscular System Muscle Contractions

Neuromuscular Interactions: Neuromuscular Junction: The site where the motor neuron and muscle fiber meet is the neuromuscular junction The muscle fiber membrane (sarcolemma) forms a _______ ____ _______ in which the sarcolemma is tightly folded and where nuclei and mitochondria are abundant. Motor End Plate

Acetylcholine – neurotransmitter released from the _____ of the neuron. Acetylcholinesterase – What is it’s function? Where is it found? Motor Unit: A _______ neuron and the muscle _____ it controls make up a motor unit; when stimulated to do so, the muscle fibers of the motor unit contract all at once. Axon Breaks down acetylcholine; stops muscle contraction Motor End Plate Motor Fiber

Skeletal Muscle Contraction: Muscle Contraction involves several components that result in the shortening of sarcomeres, and the pulling of the muscle against it’s attachment.

http://www.sumanasinc.com/webcontent/animati ons/content/muscle.html http://highered.mheducation.com/sites/00724958 55/student_view0/chapter10/animation__sarcome re_contraction.html http://wps.prenhall.com/wps/media/objects/2688 /2752944/Web_Tutorials/25_A01.swf

Myosin The protein _______ consists of two twisted strands with globular cross- bridges projected outward along the strands. _______ is a globular protein with myosin binding sites. What two proteins are associated with it? Cross Bridge Actin Tropomyosin Troponin

4 1 2 7 6 3 5

According to the sliding filament theory of muscle contraction, if allowed to, myosin cross bridge attaches to the binding site on the actin filament and bends, pulling on the actin filament; it then releases and attaches to the next binding site on the actin, pulling again. What prevents this from happening continuously? Energy from the conversion of ATP to ADP is provided to the cross-bridges from the enzyme ATPase, causing them to be in a cocked position. Aceytlycholinesterase

Stimulus for Contraction The motor neuron must release the neurotransmitter ____________________ from its synaptic _________________ into the _____________ cleft in order to initiate a muscle contraction. Aceytlycholine Vesicles Synaptic

Daily Warm Up C G F H I B J E D A ___ Sarcoplasmic Reticulum a. Enzyme that breaks down acetylcholine ___ Sarcolemma b. Part of the myosin filament that attaches to actin ___ T Tubule c. Net like structure that surrounds each myofibril and stores Calcium ions (Ca2+) ___Troponin d. Neurotransmitter that triggers a muscle contraction ___Tropomyosin e. Cytoplasm of a muscle fiber ___ Cross Bridge f. Tubes are found around the myofibril and signal the sarcoplasmic reticulum to release calcium ___ Calcium Ion g. Cell membrane of a muscle fiber ___Sarcoplasm h. Protein found on actin that interacts with calcium ions ___Acetylcholine i. Ribbon like protein on Actin that covers up binding sites ___Acetylcholinesterase j. Ion that causes troponin and tropomyosin to shift and expose the myosin binding sites G F H I B J E D A

Stimulus for Contraction Protein receptors in the motor end plate detect the neurotransmitters, and a muscle impulse spreads over the surface of the sarcolemma and into the __________ tubules, where it reaches the ___________ reticulum Transverse Sarcoplasmic

Stimulus for Contraction Upon receipt of the muscle impulse, the sarcoplasmic reticulum releases its stored ___________ to the sarcoplasm of the muscle fiber. The high concentration of calcium in the sarcoplasm interacts with the ________ and ___________ molecules, which move aside, exposing the myosin binding sites on the actin filaments. https://www.youtube.com/watch?v=gJ309LfHQ3M Calcium (Ca 2+) Troponin Tropomyosin

Stimulus for Contraction Myosin ______________ now bind and pull on the _____ filaments, causing the sarcomere to shorten. After the nervous impulse has been received, the enzyme __________________ rapidly decomposes the acetylecholine. Then, calcium is returned to the sarcoplasmic reticulum, and the linkages between myosin and actin are broken. Cross bridges Actin Acetylcholinesterase

Contraction cycle Start with a cocked myosin head (ADP and P are attached) Myosin head binds to the actin when troponin and tropomyosin move to expose the binding sites Myosin head goes through the powerstroke and moves the actin filament (ADP and P detach) Myosin head is stuck until ATP releases it from the actin filament (ATP attaches; Myosin head releases) Myosin head goes back into cocked position) (ATP breaks down into ADP and P. ADP and P is still attached to the myosin head)

Muscle contractions begin at the neuromuscular junction. The axon of a motor neuron is attached to the motor end plate of a muscle fiber’s sarcolemma. To create a muscle contraction, acetylcholine is released from the motor neuron axon. Acetylcholine will trigger a muscle impulse. The muscle impulse will travel across the sarcolemma and through the muscle fiber via the T tubules. The muscle impulse travelling through the T tubules will cause the sarcoplasmic reticulum to release Calcium Ions into the sarcoplasm. The calcium ions released will attach to troponin and cause the ribbon like tropomyosin to shift. This exposes the myosin binding sites necessary for muscle contraction.

7. Once the myosin binding sites are exposed, myosin cross bridges will attach to the actin and perform a power stroke which will move the actin filaments closer together. 8. The myosin cross bridge is stuck to the actin filament until an ATP molecule attaches. 9. Breaking ATP into ADP and P will cock the myosin head. Preparing it for another Power Stroke 10. In order to stop a muscle contraction, acetylcholinesterase will break down the acetylcholine.

Reading Review Read from your textbook pages 172 – 178. On a separate piece of paper, answer the check your recall questions in complete sentences. 175 (1-4) 178 (1-4)

Muscle Contraction Paragraph Using the following vocabulary words, write a paragraph explaining how muscles contract. Neuromuscular Junction, Motor End Plate, Synaptic bulb, synaptic cleft, synaptic vesicles, Acetylcholine, Sarcolemma, Sarcoplasm, Myofibril, T Tubule, Sarcoplasmic Reticulum, Calcium Ions, Actin Filaments, Myosin Filaments, Cross Bridges, Troponin, Tropomyosin, Power stroke, ATP, ADP/P, Acetylcholinesterase.

Review Video https://www.youtube.com/watch?v=4201SrN0WlY

Daily Warm Up List the steps of muscle contraction from 1 to 6. 1 being first and 6 being last. 1. ___ Myosin cross bridges attach to the binding sites, go through a power stroke and move the actin filaments closer together. 2. ___ Calcium ions attach to the troponin causing the tropomyosin to move and expose the myosin cross bridge binding sites 3. ___ Acetylcholine is released from the axon of the motor neuron into the synaptic cleft of the sarcolemma triggering a muscle impulse. 4. ___ When the muscle contraction is over, Acetylcholinesterase breaks down acetylcholine. 5. ___ The muscle impulse travels across the sarcolemma and down through the T tubules stimulating the sarcoplasmic reticulum to release Calcium Ions (Ca2+) into the sarcoplasm. 6. ___ Attachment of ATP to the myosin cross bridge releases them from the binding sites. The breakage of the ATP cocks the myosin cross bridge preparing it for its next powerstroke. 4 3 1 6 2 5

Respiration increases Energy Sources for Contraction ATP: Energy for contraction comes from molecules of ATP. This chemical is in limited supply and so must often be regenerated. Creatine Phosphate: As ATP decomposes, the energy from creatine phosphate can be transferred to ADP molecules, converting them back to ATP. Cellular Respiration: The early phase of cellular respiration yields few molecules of ATP, so muscle has a high requirement for oxygen, which enables the complete breakdown of glucose in the mitochondria. The pigment ______________ stores oxygen in muscle tissue. What happens to respiration during exercise? Cross bridges Respiration increases

https://www.youtube.com/watch?v=BR3dDO1Sz0E

Oxygen Debt: Oxygen deficiency may develop during strenuous exercise, and ___________ acid accumulates as an ened product of anaerobic respiration. This acid diffuses out of muscle cells and is carried in the bloodstream to the liver. Oxygen debt refers to the amount of oxygen that liver cells require to convert the accumulated lactic acid into glucose, plus the amount that muscle cells need to resynthesize ATP and creatine phosphate to their original concentrations. Repaying oxygen debt may take several hours. Lactic

When a muscle loses its ability to contract during strenuous exercise, it is referred to as ________ _________. This usually arises from the accumulation of lactic acid in the muscle causing a lowered ____ A muscle ________ occurs due to a lack of ATP required to return calcium ions back to the sarcoplasmic reticulum so muscle fibers can relax. Muscle fatigue pH cramp

HEAT: Why does muscle contraction cause so much heat? Muscles make up a large proportion of the body and therefore give off a lot of heat

Muscle Responses: A muscle fiber remains unresponsive to stimulation unless the stimulus is of a certain strength, called the _________________ ______________. When a muscle fiber contracts, it contracts to its full extent, it cannot contract partially. This is called the ___ __ ______ response. Muscle Twitch: A single short contraction involving only a few motor units is referred to as a twitch. Is this considered a very useful contraction? Threshold Stimulus All or none No

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 ____________. If the sustained contraction lacks any relaxation, it is called a _______________ contraction. An increase in the number of activated motor units within a muscle at higher intensities of stimulation is called _______________. How is this done? summation tetanus recruitment Increases the stimulus

A series of twitches Summation Tetanic contraction

tone Muscle _______ is achieved by a continuous state of sustained contraction of motor units within a muscle. Why would this be useful? Maintain Posture

Reading assignment Use 184 – 187 to complete your notes Read: 8.5, 8.6, and 8.7