Physiology mod 6

a bundle of adjacent muscle cells t tubules sarcomere muscle fiber sarcolemma fascicle

fascicle

Which fibers generate more force? fast-twitch fibers slow-twitch fibers

fast-twitch fibers

A contraction that generates enough force to move a load is known as ________, whereas one that generates force that equals the load is known as ________. isotropic, isometric isometric, eccentric isotonic, isometric isometric, isotonic isotonic, eccentric

isotonic, isometric isotonic contractions move loads, isometric contractions create force without movement.

The function of the titin protein is to stabilize the position of the myosin filaments. pull Z lines together during contraction. interact with actin during contraction. release calcium during contraction. cover the myosin binding site on the actin molecule.

stabilize the position of the myosin filaments. need explanation

1. List six differences between skeletal and smooth muscle.

1. Under a light microscope skeletal muscle appears striated and smooth muscle appears smooth. 2. This difference in appearance is due to the fact that skeletal muscle has sarcomeres and smooth muscle does not. 3. Skeletal muscle is made up of very large, cylindrical, multinucleate fibers with many mitochondria. Smooth muscle cells are smaller, fewer mitochondria and have only one nucleus per cell. 4. Skeletal muscle contracts quickly and smooth muscle contracts slowly. 5. Skeletal muscle contains t-tubules throughout the fibers to send action potentials quickly. Smooth muscle does not have t-tubules throughout the muscle fibers. 6. Skeletal muscles are controlled by somatic motor neurons and smooth muscles are controlled by autonomic neurons.

The T-tubular membrane contains _____ receptors that are _____ and therefore respond to action potentials. This receptor is mechanically linked to ______ receptors in the adjacent sarcoplasmic reticulum.

DHP, voltage sensitive, RyR T tubule membrane contains voltage sensing dihydropoyridine (DHP) receptors. The DHP are mechanically linked to Ca2+ channels in the adjacent SR. These SR channels are known as ryanodine receptors (RyR). When depolarization reaches DHP receptor the receptor changes confirmation which opens RyR release channels in the SR. Ca2+ then flows into the cytosol where it initiates contraction. skeletal muscle

Compared to skeletal muscle, contraction of smooth muscle cells is a slower response to a stimulus. sustained without fatigue. controlled by the somatic nervous system. a slower response to a stimulus and sustained without fatigue. a slower response to a stimulus, sustained without fatigue, and controlled by the somatic nervous system.

a slower response to a stimulus and sustained without fatigue. smooth muscle contract and relax more much more slowly than skeletal or cardiac muscle. Smooth muscle also uses less energy to generate and maintain a given amount of force. Have the ability to slow down their myosin ATPase so that cross bridges cycle slowly as they maintain their force. Smooth muscle can sustain contractions or extended period of time without fatiguing. Allows organs such as the bladder to maintain tension despite a continued load. Smooth is controlled by autonomic division.

Smooth muscle is controlled by: somatic autonomic

autonomic

Asynchronous activation of motor units is important because it functions to

prevent fatigue nervous system modulates firing rates of motor neurons so that different motor units take turns maintaining muscle tension.

The heavy chain of myosin contains 2 important regions: the first acts as ____ to convert energy into movement whereas the second binds to _____ .

ATPase, actin

Identify the FALSE statement. Adipose tissue is controlled by autonomic efferents. All reflexes require input from the brain. Some reflexes are genetically determined. Muscle spindles are stretch receptors. Proprioceptors detect limb position and movement.

All reflexes require input from the brain. autonomic efferents responsible for control of the bodily functions not consciously directed, such as breathing, the heartbeat, and digestive processes. (adipose is in that category) Reflex can be integrated by the spinal cord only without input from the brain. reflexes that are genetically determined are innate (we are born with them). knee jerk or patellar tendon reflex is innate. muscle spindles are stretch receptors that send information to the spinal cord and brain about muscle length and changes in muscle length. Every skeletal muscle in the body has muscle spindles. All skeletal muscle reflexes have sensory receptors (proprioceptors) located in skeletal muscles that monitor position of limbs in space. All skeletal reflexes also have somatic motor neuron that carries output signal.

1. Based on what you have learned about muscle fatigue in this module, propose a mechanism by which some people (Kenyan or otherwise) might be genetically predisposed to be better distance runners than others.

During gentle exercise the body uses fatty acids as an energy source, however, once our mitochondrial oxidative enzymes reach their maximum capacity the body begins to use the glycogen stores in the muscles for energy. If a person is born with a form of mitochondrial oxidative enzyme that works better or longer at using the fatty acids then that person will use less of their glycogen reserves in their muscles and be able to run longer. Additionally, if a person is born with a larger quantity of glycogen stored within their muscles then they will have more reserve to be able to continue running longer.

1. Why is mitochondrial oxidative enzyme content considered to be a measure of lipid utilization, and why might it specifically be helpful for an endurance athlete to have high levels of these enzymes?

During gentle exercise the body uses the most readily available fuel source to produce ATP, glucose. Glucose, however, is a limited precious molecule in the body so the body begins to use fatty acids as an alternative fuel source when the exercise persists. The quicker the body begins to use fatty acids the less glucose/glycogen the body will waste. The mitochondria is the organelle within the cell responsible for the production of ATP. The mitochondria oxidative enzymes catalyze fatty acids oxidation in order to produce ATP. Once these enzymes reach their maximum capacity, however, the body then begins to use glucose as a fuel source again. If there are more mitochondria oxidative enzymes to catalyze the fatty acid oxidation then it may be assumed that the body will use fatty acids sooner and longer and not waste their glycogen reserves and be a better endurance runner.

Describe Golgi tendon organs and muscle spindles.

Golgi tendon organ (GTO) is a type of receptor found at the junction of tendons and muscle fibers. respond to muscle tension during isometric phase of contraction . don't respond as much to muscle stretch. when muscle contraction is initiated the golgi tendon organ causes a relaxation reflex as a protective measure. Muscle spindles are stretch receptors that send information to the spinal cord and brain about muscle length and cause contraction reflex.

Smooth muscle

Governs involuntary muscles - gut movement - blood vesicles Does not have sarcomeres - does not have mega cell with many nuclci. regular size cell with one nucleus. more actin and less myosin than skeletal muscle. myosin in smooth muscle has more heads. It has an extensive cytoskeleton. Made up of Intermediate filaments and dense bodies. Lacks troponin. caveolae instead of t tubules send action potentials through the cell. no sarcomeres. Actin filaments attach to cytoskeletal elements called dense bodies

Describe the muscle condition called tetanus. Is this a normal or a pathological event? If it is normal, what is the function? If it is pathological, what is the cause? The bacterium Clostridium tetani causes a disease called tetanus or lockjaw; you may have been vaccinated against tetanus, especially if you ever had hospital treatment for a skin wound. Speculate on whether or not the name of this disease is related to the muscle condition and why the disease can be fatal.

If action potentials stimulate muscle fibers repeatedly at short intervals or high frequency then there is less relaxation between contractions. If this continues then there will eventually be no relaxation and is in a state of maximum contraction known as tetanus. It is a normal event Tetanus is a state of maintained contraction that occurs as a result of increased frequency of stimulation by the nerve that does not allow enough time between twitches for the muscle to relax. Tetanus is a normal event, which allows a muscle to develop its maximal force. The bacterial disease results in maintained contraction that is similar in charter to the tetanus that can result from high frequency muscle stimulation. The disease is fatal if respiratory muscles are unable to relax because then breathing would stop.

1. What is the difference between isometric and isotonic exercise?

Isotonic exercise is a muscle contraction that creates force and moves a load, such as a bicep curl. During an isotonic muscle contraction, the muscle contracts and causes it to shorten so that it can create enough force to move the load. The muscle does not shorten significantly, but there are elastic cytoskeletal proteins within the muscle fibers that work together collectively to provide the power. Isometric exercise is a muscle contraction that creates force but does not move a load, such as holding weights out in front of you. During an isometric muscle contraction, the muscle contracts but does not shorten because it does not need to create force the move the load.

Movement of Skeletal muscle contraction

Myosin and actin slide past each other to contract the muscle. Myosin is an ATPase which means it hydrolyzes ATP to ADP and an inorganic phosphate. ATP hydrolysis energy is trapped by myosin and stored as potential energy. troponin controls positioning of tropomyosin. tropomyosin wraps around actin filaments and covers myosin binding sites in resting state. Myosin is blocked from completing power stroke. Myosin is weakly bound to actin because tropomyosin blocking myosin from binding site on actin. When calcium is present, it will bind to troponin and will cause troponin to interact with tropomyosin. This action moves tropomyosin and unblocks the binding site for myosin on actin. Myosin binds strongly to actin and completes power stroke. Actin filament moves. Myosin heads step along actin filaments. In rigor state, myosin is bound to actin and not bound to ATP or ADP. Then ATP binds and myosin detaches. ATP is hydrolyzes for myosin head to rotate and reattach to actin. When tropomyosin moves off binding site, myosin has power stroke. Actin filament moves. myosin releases ADP at the end of the power stroke. Myosin tightly binds actin again.

________ is the backup energy molecule that can be rapidly converted to ATP in active skeletal muscle. Protein Glucose Fatty acid Phosphocreatine

Phosphocreatine

Briefly compare and contrast the structure and behavior of cardiac, smooth, and skeletal muscles.

Skeletal muscle is involved in voluntary muscle control which is part of the somatic motor neural control. These muscles are made up of muscle cells which have many mitochondria, multiple nuclei and are large, long, cylindrical cells. Skeletal muscle is made up of larger units called sarcomeres which are multiple different proteins weaved together. Sarcomeres are what allows skeletal muscles to contract by sliding past one another. Smooth muscle and cardiac is the muscle that is involved in involuntary movements that are very important for homeostasis. These two muscle types of both part of the autonomic nervous system. Both cardiac and smooth muscle cell are not as large as the skeletal muscle, do not contain as many mitochondria as skeletal muscle cells and only have one nuclei per cell. Cardiac muscle, however, contains sarcomeres but smooth muscle does not. All three muscle types have sarcoplasmic reticulum which is a modified endoplasmic reticulum and function to store calcium. In all three muscle types calcium is used to control their muscle contraction. Skeletal muscle fibers all act independently of one another, cardiac fibers are all linked to each other through gap junctions and smooth muscle fibers can act independently or communicate through gap junctions.

______ reflexes involve skeletal muscles.

Somatic

Write down the steps in patellar tendon (knee jerk reflex).

The first step in this reflex is a stimulus, which in this case is a hammer tapping the tendon below the kneecap. This tap causes the muscle that runs up the front of the thigh, the quadriceps muscle, to stretch. This stretching will activate the muscle spindles and fire an action potential. This action potential will travel through a sensory neuron into the central nervous system and activate efferent path 1 and efferent path 2. In efferent path 1, the sensory neuron will synapse onto motor neurons that cause contraction of the quadriceps. Contraction of these muscles causes the leg to swing forward. In efferent path 2, the sensory neuron branches in the spinal cord and synapses onto inhibitory interneurons. These inhibitory interneurons suppress the motor neurons that control the hamstring allowing the hamstring to relax when the quad is activated. The hamstring relaxation is necessary to allow the leg to swing forward without resistance.

1. On the basis of what you learned about muscle fiber type in this module, propose a mechanism by which some people might be genetically predisposed to be better distance runners than others.

There are different types of skeletal muscle fibers and some are more resistant to fatigue than others. There are three types of muscle fiber types, slow-twitch fibers (type I), fast-twitch oxidative-glycolytic fibers (type 2A), and fast-twitch glycolytic fibers (type 2X). Type 2 fibers can split ATP more quickly which causes them to contract faster. Type 2X muscle fibers also produce more acid from ATP hydrolysis and the presence of acid fatigues muscles quicker. In contrast, type I muscle type relies on oxidative phosphorylation in order to produce ATP. Therefore, type I contains more mitochondria than type 2 because mitochondria are the site of oxidative phosphorylation. Type I also have more blood vessels to bring in oxygen to the cells and contains more myoglobin, an oxygen binding pigment, to bring more oxygen to the cells. The combination of these traits allows type 1 muscle fibers to obtain and use oxygen better than Type 2 fibers. This characteristic prevents type 1 fibers from fatiguing as quickly as type 2 fibers. Therefore, if a person were born with more type I muscle fibers than the average person they will probably not fatigue as quickly and be able to run longer.

During heavy exercise, the ATP requirements of active muscle are likely to be met by metabolism of protein fatty acids. carbohydrates nucleotides

carbohydrates muscles can obtain energy from fatty acids when oxygen is present. During light exercise skeletal muscles burn fatty acids along with glucose. This process, however, is relatively slow and cannot produce ATP quickly enough during strenuous exercise. During strenuous exercise muscle fibers rely on glucose.

Rhythmic reflexive motor activities, such as breathing or walking, are controlled by networks of neurons in the central nervous system called _____________________________.

central pattern generators

Most of the time, the parallel thick and thin filaments of the myofibrils are connected by ________ that span the space between myosin and actin molecules. tropomyosin molecules crossbridges nebulin molecules sarcomeres calcium ions

cross bridges muscle fibers (cells) are made up of many myofibrils (bundle of sarcomeres). sarcomeres are one repeat in the pattern found in myofibrils. The sarcomere is made up of thick and thin filaments. The thick filaments are made up of myosin which is a motor protein. and the thin filaments are made up of actin (protein). The thick and thin filaments parallel each other and are connected by cross bridges.

Motor units that control skeletal muscles involved with fine motor movements (eye muscles or the hands) have ________ muscle fibers compared to motor units that control more gross movements (gastrocnemius muscle of the lower leg). more fewer the same number of

fewer One somatic motor neuron is associated with muscle fibers (1 or many) The finer the movement the less muscle fibers you have associated with the single neuron, allows for more specific control. never have muscle fiber controlled by more than one neuron. o motor neurons are associated with fewer muscle fibers. All muscle fibers in a single motor unit are the same type - will not have fast and slow twitch in the same motor unit

The brief period of time between the beginning of the action potential in the muscle and the beginning of contraction is referred to as the refractory period. latent period. relaxation phase. depolarization period. repolarization period.

latent period ACh is released from somatic motor neuron (not autonomic motor neuron) and initiates action potential in muscle fiber. Action potential triggers calcium to be released from the sarcoplasmic reticulum in muscle fiber. Calcium combines with troponin, then tropomyosin moves to the "on"position and contraction occurs. There is a short delay between the muscle action potential and the beginning of muscle tension and this time represents the time required for calcium to be released from the sarcoplasmic reticulum and for the calcium to then bind to troponin.

Which of the following is a characteristic of slow-twitch oxidative skeletal muscle fibers? long contraction duration only few mitochondria only high capillary density only long contraction duration and high capillary density long contraction duration, few mitochondria, and high capillary density

long contraction duration and high capillary density Slow-twitch oxidative have long contraction duration, large number of mitochondria and a high capillary density. Fast twitch oxidative is intermediate of all those things and fast-twitch glycolytic has short contraction duration, low number of mitochondria and low capillary density.

In a ____ reflex, a sensory neuron synapses directly on a motor neuron.

monosynaptic only one synapse

a single muscle cell t tubules sarcomere muscle fiber sarcolemma fascicle

muscle fiber

The effector in a reflex is the control center. afferent neuron. efferent neuron. sensory receptor. muscle or gland.

muscle or gland effector is the cell or tissue that carries out the appropriate response to bring the variable back within normal limits. In a reflex, the final step is in the muscle or gland. what is effected in the end (effector)

Which protein is activated by the Ca2+-calmodulin complex to phosphorylate the myosin light chain protein? tropomyosin myosin heavy chain myosin light chain kinase myosin light chain phosphatase

myosin light chain kinase in smooth muscle contraction: cytosolic Ca2+ released from SR and enters extracellular fluid. Ca binds to calmodulin in cytosol. Ca binding to calmodulin. Ca2+- Calmodulin complex activates myosin light chain kinase (MLCK). enzyme phosphorylates myosin light protein chains (myosin light chain is at the base of myosin head). Increases Myosin ATPase activity which leads to actin binding and increase tension in muscle. dephosphorylation of myosin light chain by enzyme myosin light chain phosphatase (MLCP) decreases myosin ATPase activity

The function of transverse tubules in skeletal muscles is to store Ca2+ ions inside the muscle fiber. rapidly conduct action potentials to the interior of the muscle fiber. ensure a supply of glycogen throughout the muscle sarcoplasm. conduct ATP molecules out of the mitochondria throughout the sarcoplasm.

rapidly conduct action potentials to the interior of the muscle fiber. T tubule are tubes that go throughout muscle fibers. allow action potentials to spread over surface of skeletal muscle very rapidly

For antagonistic muscle groups to move a limb, flexor contraction occurs coincident with contraction of the extensor. relaxation of the extensor. no changes in the extensor. contraction of the tendon.

relaxation of the extensor. Stretch reflexes and reciprocal inhibition control movement around a joint. When you contract one muscle you want to relax opposing muscle to prevent damaging it. Therefore when you flex a muscle you are contracting, you want to relax the muscle you are extending.

Which class of movement can be considered a combination of the other two? reflex voluntary rhythmic

rhythmic movement can be classified as reflex, voluntary, rhythmic. Reflex are least complex, integrated in spinal cord (knee jerk). Voluntary is most complex, require integration at cerebral cortex and can be initiated at will without external stimuli. rhythmic movements are a combination of reflex and voluntary (walking or running).

the muscle cell membrane t tubules sarcomere muscle fiber sarcolemma fascicle

sarcolemma

basic contractile unit in a skeletal muscle from Z disc to Zdisk t tubules sarcomere muscle fiber sarcolemma fascicle

sarcomere

Three types of muscle fibers

slow twitch oxidative fibers (type 1) fast-twitch oxidative fibers (type 2) fast-twitch glycolytic fibers (type 2) fast twitch split ATP more rapidly. Twitch duration depends on how long it takes for the SR to remove Ca2+ from cytosol. glycolytic fibers (fast-twitch glycolytic) rely on anaerobic glycolysis to produce ATP. Accumulate H+ faster so they fatigue more easily than oxidative fibers. Oxidative fibers (slow and fast oxidative fibers) rely on oxidative phosphorylation for ATP production. have more mito (citric acid cycle). Have more capillaries to bring in oxygen.

Skeletal muscle is controlled by: somatic autonomic

somatic

Explain the events leading up to a skeletal muscle twitch, starting with the arrival of neurotransmitter in the neuromuscular junction.

somatic motor neuron releases ACh at neuromuscular junction. Each binds to receptor on muscle fiber which initiates entry of Na+ and leads to action potential. Action potential in t tubule alters DHP receptor which causes RyR Ca2+ release channels in sarcoplasmic reticulum to open. Ca2+ flows out of SR and into cytosol. Ca2+ then binds to troponin, troponin changes conformation to move tropomyosin from blocking the myosin binding site on actin. Myosin head then binds to actin binding site and myosin heads execute a power stroke using ATP. Actin filaments slide toward the center of the sarcomere (similar to rope being pulled). Sarcoplasmic Ca2+-ATPase pumps Ca2+ back into the SR. The decrease in cytosolic Ca2+ causes Ca2+ to unbind from troponin. Tropomyosin re-covers the binding site and myosin is back in relaxed position.

Muscle spindles are ____ receptors and cause reflex ____ , whereas Golgi tendon organs respond primarily to ____ and cause a ____ reflex.

stretch, contraction, muscle tension, relaxation Golgi tendon organ (GTO) is a type of receptor found at the junction of tendons and muscle fibers. respond to muscle tension during isometric phase of contraction . don't respond as much to muscle stretch. when muscle contraction is initiated the golgi tendon organ causes a relaxation reflex as a protective measure. Muscle spindles are stretch receptors that send information to the spinal cord and brain about muscle length and cause contraction reflex.

inward extensions of the muscle cell membrane t tubules sarcomere muscle fiber sarcolemma fascicle

t tubule

After death, when metabolism stops, in which step of the contractile cycle must skeletal muscles remain? It depends on what part of the contractile cycle they were in at the time of death. the power stoke phase the rigor state a weak binding state

the rigor state need ATP to release from this state so the muscle is contracted in dead people who have run out of ATP.

Calcium, released by the sarcoplasmic reticulum, binds to _____ to move the _____ , which allows actin to form a _____ with myosin.

troponin C, tropomyosin, high-force crossbridge

How does calcium signal muscle contraction to turn on or off?

troponin controls positioning of tropomyosin. tropomyosin wraps around actin filaments and covers myosin binding sites in resting state. Myosin is blocked from completing power stroke. Myosin is weakly bound to actin because tropomyosin blocking myosin from binding site on actin. When calcium is present, it will bind to troponin and will cause troponin to interact with tropomyosin. This action moves tropomyosin and unblocks the binding site for myosin on actin. Myosin binds strongly to actin and completes power stroke. Actin filament moves

Autonomic reflexes are also called ______________ reflexes.

visceral because they often involve the internal organs of the body. urinating and defecating are autonomic spinal reflex. Some are integrated in the brain. all polysynaptic with at least one synapse in the CNS between sensory neuron and preganglionic autonomic neuron. Many have tonic activity.