this chapter covered the basics of muscle contraction, the neuromuscular junction, and the prioprioceptors involved in reflex loops. a review of the skeletal muscle structural hierarchy: skeletal muscle is surrounded by epimysium connective tissue and contains bundles of fascicles, which are surrounded by perimysium and contain muscle fibers, which are surrounded by endomysium and contain myofibrils, which are surrounded by sarcoplasmic reticulum and are composed of the basic contractile unit of muscles, the sarcomeres, which are made up of thin and thick filaments.
the neuromuscular junction is the site at which the motor neuron synapses with the muscle, at the motor plate. muscle contraction occurs when an action potential propagates down to the end of the axon, which causes release of acetylcholine, which migrates to the motor plate and binds to receptor channels, causing a membrane potential which propagates down the t tubules of the myofibrils, causing release of calcium from the terminal cisternae of the sarcoplasmic reticulum, which initiates the contraction of the myofilaments. relaxation occurs which calcium is sequested back into the sarcoplasmic reticulum and acetylcholine esterase breaks down the acetylcholine that was released into the NMJ.
muscle contraction can be classified in several different manners depending on frequency, intensity, and relaxation between contractions. a twitch is a single contraction and a full relaxation. within a twitch there are three stages: the latent, contraction, and relaxation phase. "treppe" is repeated contractions of increasing intensity with a return to full relaxation in between. "wave summation" is similar to treppe but without the full relaxation in between. "tetanus" is a higher frequency, maximal intensity contraction with barely any or no relaxation in between contractions.
there are several different types of axons which provide motor and sensory innervation to muscles. A-alpha, thickest and fastest conducting, seen in motor efferents and muscle spindle receptor afferents. A-beta, seen in touch and pressure mechanoreceptor afferents. A-gamma, seen in muscle spindle efferents. A-delta, seen in skin temperature and pain afferents. B fibers, seen in sympathetic preganglionics, and C fibers (unmyelinated), seen in sympathetic postganglionics.
there are three main types of proprioceptors: muscle spindles receptors, golgi tendon organs, and joint kinesthetic organs. muscle spindles are located within the muscle belly (called "extrafusal fibers") and are composed of intrafusal fibers, either "bags" or "chains", which are wrapped with a sensory nerve ending. nuclear bag fibers have contractile ends that are attached to the extrafusal fibers, nuclei in the center of the fiber, and detect fast changes in muscles length-- whereas nuclear chain fibers are attached to the nuclear bag fibers themselves and detect slow, steady chains. primary "Ia" sensory endings are wrapped around the center of spindle receptors and respond to change in muscle length; secondary "flower spray" sensory endings are slower conducting and respond to the overall length of the fiber.
spindle receptors are involved in both rapid adjustments to maintain balance as well as slower adjustments to maintain posture. the reflex they are involved in is called the "quick stretch reflex"-- extrafusal muscle causes stretching of the muscle spindle, which activates the primary or secondary nerve, which activates an interneuron which activates the motor innervation of the muscle itself-- in essence providing a balancing / feedback system for quickly contracting muscles. spindle receptors also mediate the reciprocal inhibition reflex pathway, which inhibit the antagonist muscles.
golgi tendon organ receptors are embedded within the tendon of the muscles and are involved in a complementary reflex loop- at the extremes of contraction, when tension is high in the tendon of the muscle, golgi tendon organs stimulate 1b sensory nerves, which activate the inhibitory interneurons for the muscle, causing it to relax (while simultaneously activating the antagonist muscles).
the third type of proprioceptor is the joint kinesthetic receptor, which are located within joints and detect joint movement, tension, and angle. pacinian corpuscles are located within connective tissue and sense rapid pressure changes, stretch, and acceleration of the joint motion. ruffini corpuscles are located in synovial capsules and ligaments and sense deep/rapid sustained pressure, lateral stretch, and joint angle changes. free nerve endings are found throughout and sense both rapid and sustained pressure.
questions
what are these functional units surrounded by and what do they contain?
1. skeletal muscle
2. muscle fascicle
3. muscle fiber
4. myofibril
5. sarcomere
NMJ...
6. what is a neuromuscular junction?
7. what are "motor points" and where are they generally?
8. what is the neurotransmitter that is released from axons at the NMJ?
9. what is involved in the relaxation of a muscle in the NMJ?
10. describe the process of contraction starting from release of neurotransmitter from the axon at the NMJ.
11. describe the process of muscle relaxation.
contraction types...
12. what is a "motor unit"?
13. what are examples of small and large motor units?
14. what is a muscle "twitch"?
15. what is a "treppe"?
16. what is a "wave summation"?
17. what is "tetanus"?
18. what is the difference between incomplete and complete tetanus?
19. what are the three phases to the muscle twitch?
axonal classifications...
20. what are three types of neurons?
21. describe the A-alpha classification of nerve fiber.
22. ...A-beta.
23. ...A-gamma.
24. ...A-delta.
25. ...B fibers.
26. ...C fibers.
27. what are the 5 components to a spinal cord reflex arc?
spindles...
28. what are the three types of proprioceptors?
29. where are muscle spindle receptors located? what do they measure?
30. what are intrafusal and extrafusal fibers?
31. what are the two types of intrafusal fibers and what is the difference between them?
32. what are the two types of sensory neurons from muscle spindle receptors and what is the difference between them?
33. what are the two types of responses to stretch that muscle spindle receptors are involved in?
34. describe the role of gamma motor neurons in maintaining balance.
golgi tendon organs...
35. what are golgi tendon organs?
36. what do golgi tendon organs detect?
37. describe how a golgi tendon organ can protect a muscle from damage.
38. describe the two types of stretch responses that a golgi tendon organ can be involved in.
joint kinesthetic receptors...
39. what are the three types of joint kinesthetic receptors?
40. what do joint kinesthetic receptors sense?
41. describe the different locations and functions of the different types of joint kinesthetic receptors.
proprioceptors affect on reflex muscle tone...
42. what are the three types of reflexes that proprioceptors mediate?
43. describe the quick stretch reflex.
44. describe the reciprocal inhibition reflex.
answers
1. surrounded by epimysium, contains muscle fascicles.
2. surrounded by perimysium, contains muscle fibers.
3. surrounded by endomysium, contains myofibrils.
4. surrounded by sarcoplasmic reticulum, consists of sarcomeres.
5. contains thick and thin filaments.
6. where a motor nerve synapses with a muscle fiber.
7. the actual point at which the nerve synapses- generally in the center of the muscle belly.
8. AcH.
9. breakdown of AcH by AcHesterase.
10. acetylcholine released from axon into NMJ, which bind to receptors on motor end plate and creates action potential, which propogates through the t tubules, causing calcium to be released from sarcoplasmic reticulum, which initiates the contraction of the myofilaments by binding to troponin and exposing binding sites on tropomyosin.
11. calcium is sequestered into the sarcoplasmic reticulum, acetylcholine broken down by esterase in the NMJ.
12. a nerve and all the muscle fibers it innervates.
13. extraocular muscles (20 fibers) vs. gastrocnemius (1,000 fibers)
14. a single brief stimulus that produces a short contraction and relaxation.
15. repeated stimuli in which the intensity of the contraction increases but returns back to full relaxation in between.
16. repeated stimuli which increase in intensity and do not return to full relaxation.
17. higher frequency stimuli which maintains nearly maximum intensity of contraction.
18. incomplete has partial relaxation.
19. latent, contraction, relaxation.
20. sensory, motor, interneuron.
21. fastest conducting (100ms), largest diameter, seen in motor efferents and muscle spindle afferents.
22. (50ms), touch and pressure mechanoreceptor axons.
23. (20ms), muscle spindle efferents.
24. (15ms), skin temperature and pain.
25. slower myelinated fibers seen in sympathetic preganglionics.
26. unmyelinated fibers seen in sympathetic postganglionics.
27. sensory receptor, sensory neuron, interneuron, motor neuron, effector organ.
28. muscle spindle receptors, golgi tendon organs, joint kinesthetic receptors.
29. located in between muscle fibers, measure length of muscle and speed of contraction.
30. the muscle spindle receptors have intrafusal fibers which are embedded within the extrafusal muscle fibers of a muscle.
31. nuclear bag fibers and nuclear chain fibers. bag fibers have nuclei in the center, contractile elements attached to extrafusal fibers (which receive motor efferents from A-gamma neurons), detect fast changes in muscle length. chain fibers have nuclei spread throughout, contractile elements attached to the bag fibers, and detect slow and steady changes in muscle length.
32. primary (Ia) sensory neurons are wrapped around the center of muscle spindle receptors, are faster conducting, and respond to change in muscle length. secondary "flower spray" sensory endings are smaller diameter and slower conducting and respond to the overall length of fiber.
33. monosynaptic spinal reflexes (rapid adjustments to prevent falls) and cerebellum controlled stretch response (to regulate muscle tone.
34. firing of gamma motor neurons causes shortening of the contractile elements within the spindle fibers, increasing their sensitivity to stretch; useful when trying to maintain balance because quick and precise feedback is needed.
35. free nerve endings located at junction between tendon and muscle.
36. force of muscle contraction / tension exerted at the tendon.
37. it can detect excess force applied to a muscle, which fires the 1b sensory fiber, which activates the inhibitory interneuron, which has an inhibitory effect on the motor neuron that innervates the muscle, causing it to relax and reduce tension.
38. dynamic response, an involuntary relaxation due to a sudden increase in muscle tension, and static response; an ongoing relaxation in response to a gradual increase in muscle tension.
39. pacinian corpuscles, ruffini corpuscles, free nerve endings.
40. movement, tension, acceleration, strain, postural changes in joint.
41. pacinian corpuscles are located within connective tissue and sense rapid pressure changes, stretch, acceleration/deceleration. ruffini corpuscles are located in synovial capsules and ligaments and sense deep rapid/sustained pressure, lateral stretch, and joint angle changes. free nerve endings are ubiquitous and sense rapid and sustained pressure.
42. quick stretch reflex, reciprocal inhibition, autogenic inhibition.
43. mediated by muscle spindle receptors, produces a quick contraction of muscle fiber in response to stretching.
44. also mediated by muscle spindle receptors, producing an inhibition in the antagonist muscles in response to stretching.
Showing posts with label skeletal muscle. Show all posts
Showing posts with label skeletal muscle. Show all posts
Saturday, May 9, 2009
Saturday, April 25, 2009
biomechanics: skeletal muscle
week 2 in biomechanics covered the basics of skeletal muscle from a biomechanics perspective. skeletal muscle is the main muscle type in the body and is responsible for voluntary, gross movements, and makes up 40-50% of body weight. some muscle basics: tension produced by muscle is proportional to the amount of cross sectional muscle fibers. the strength of a muscle is defined as the tension produced from a single maximal effort, while the power produced by a muscle is the tension produced over time. muscle contractions can either be isotonic or isometric, the former being constant force with movement and the latter being varying force with no movement. within isotonic contractions, there are concentric contractions, in which the muscle gets shorter, and eccentric contractions, in which the muscle gets longer. the "line of pull" of a muscle is the primary direction in which the muscle pulls the bone.
each muscle is made of muscle fibers that are arranged in different ways according to the specific function of the muscle. parallel muscles such as the sartorius are designed for a greater range of motion / muscle shortening. fusiform muscles are similar to parallel except with a larger muscle belly, in a spindle shape, such as the biceps brachii. pennate muscles have muscle fibers oriented obliquely to the muscle tendon so as to increase the muscle's cross sectional diameter and increase strength- such as the deltoid muscles. convergent muscles such as the pectoralis major have a broad origin and a pointed origin, and varied lines of pull. circular muscles such as the sphincters and orbicularis oris have concentric muscle fibers that close over a hole when contracted.
agonists are defined as the prime muscle that produces a given movement. antagonists are the muscle that directly opposes the agonist movement- such as the biceps and triceps brachii. stabilizers are muscles that stabilize the action of the agonist-- such as the way that the rhomboids and pectoralis minor stabilize the deltoid by immobilizing its point of origin, the scapula. synergists are muscles that aid the movement of the agonist muscle.
muscles can be analyzed in terms of the type of "lever" that are schematically similar to. there are two important types of levers which produce complementary functions. a mechanical advantage lever is one in which the effort (the force applied) is far from the fulcrum (the point of rotation), which is close to the load (the object being moved). this type of lever (note that a car jack fits this description) lifts a large load a small distance for a small effort over a long distance. the other type of lever is a speed lever, in which the effort is close to the fulcrum, which is far away from the load. this type of lever allows for high speeds at the cost of high effort/tension. levers in the body can also be classified in the "class system"- first class levers have the fulcrum between the load and the effort, as in the posterior cervical muscles. second class levers are mechanical advantage levers that have the fulcrum between the effort and load and closer to the load, as in the gastrocnemius. third class levers are speed levers in which the effort is closer to the load than the fulcrum, as in the biceps.
questions
muscle introduction...
1. describe the role of skeletal muscle in the body.
2. how many skeletal muscles are there in the body and how much of the body weight do they take up?
3. a muscle's cross sectional diameter...
muscle types...
4. what are the different types of fiber arrangements in muscle and what are examples of each?
5. describe the arrangement and function of parallel muscles. what is an example of this type of muscle?
6. describe the arrangement and function of fusiform muscles. what is an example of this type of muscle?
7. describe the arrangement and function of pennate muscles. what is an example of this type of muscle?
8. describe the arrangement and function of convergent muscles. what is an example of this type of muscle?
9. describe the arrangement and function of circular muscles. what is an example of this type of muscle?
muscle contraction...
10. define muscle strength, power, and torque.
11. muscle contractions are either...
12. what is an isometric contraction?
13. what is an isotonic contraction?
14. what is the difference between a concentric and eccentric isotonic contraction?
15. what is the "line of pull" of a muscle?
16. what is an example of a muscle which has different actions because of a shifting line of pull?
17. how is line of pull related to proper muscle function?
18. what is the "angle of pull" of a muscle?
19. what are the two components to the angle of pull and what do they do?
muscle function terminology...
20. range of motion of a muscle depends on...
21. tension produced in a muscle depends on...
22. what is muscle irritability?
23. what is contractility?
24. what is extensibility?
25. what is elasticity?
muscle roles...
26. what are agonists?
27. what are antagonists? what is an example of an agonist/antagonist pair?
28. what are synergist muscles?
29. what are stabilizers? what is an example?
levers...
30. what is a fulcrum?
31. describe a mechanical advantage / power lever.
32. describe a speed lever.
33. what is a first class lever? what is an example in the body?
34. what is a second class lever? what is an example in the body?
35. what is a third class lever? what is an example in the body?
36. most levers in the body are...
answers
1. skeletal muscle is always attached to bone and is responsible for the movement of the body and all of its joints, as well as aiding in fluid and blood movement throughout the body, and providing protection and postural support.
2. over 600, 40-50% of body weight.
3. ...affects the muscle's ability to exert a force.
4. parallel, fusiform, pennate, convergent, circular.
5. muscle fibers are oriented parallel to muscle direction. designed for greater range of motion. example is sartorius.
6. similar to parallel muscles but with more of a spindle shape- larger cross sectional diameter in the middle. example is biceps brachii.
7. high cross sectional area muscle due to fibers being arranged perpendicularly to tendon. examples are extensor digitorum, rectus femoris, deltoid.
8. a muscle with a broad origin and a pointed insertion. the direction of pull can be varied. example is the pectoralis major.
9. fibers are arranged concentrically so as to form a sphincter. examples are orbicularis oris or sphincter muscles.
10. muscle strength= amount of tension a muscle can produce for a single maximal effort. muscle power= the amount of tension or contraction over a given period of time. muscle torque= muscle force causing rotation around an axis.
11. isometric or isotonic.
12. a muscle contraction in which the length of the muscle or the angle of the joint stays the same regardless of the tension.
13. a muscle contraction in which the tension in the muscle is relatively constant, producing motion in the joint or shortening / lengthening of the muscle.
14. concentric contraction is an isotonic contraction in which the muscle is being shortened, and in eccentric the muscle is being elongated.
15. the direction in which the muscle pulls when contracted.
16. when the humerus is abducted sufficiently such that the line of pull for the pectoralis major is above the glenohumeral joint, the pectoralis major can become an abductor of the humerus in addition to its primary flexion role.
17. each muscle has an optimal line of pull. an altered line of pull can cause hypertonicity and inefficiency, ultimately leading to weakness, trigger points, imbalance, etc.
18. the angle which is formed between the bone of insertion and the line of pull.
19. the verticle component (perpendicular to the bone of insertion) causes rotational movement at the join and the horizontal component causes a stabilizing force.
20. length of muscle fibers
21. total number of muscle fibers
22. muscle excitability- how sensitive or responsive the muscle is to chemical, electrical, mechanical stimuli.
23. ability of the muscle to develop tension when stimulated.
24. ability of the muscle to be stretched beyond its normal resting length.
25. ability of muscle to return to original length after stretching.
26. the prime muscle that provides the major force for a given movement.
27. muscle that produces a motion opposite to that produced by the agonist. example is biceps and triceps brachii.
28. a muscle which assists the agonist muscle.
29. muscles that support and improve the efficiency of the agonist. rhomboids and pec minor are stabilizers of the scapula when the deltoids are abducting the arm.
30. the fixed point of leverage, as in the joints of the body.
31. load is close to the fulcrum and the effort is far from the fulcrum. small effort over long distance can move a large load over small distance. (car jack)
32. load is far from the fulcrum and the effort is close to the fulcrum. large effort and fast movement.
33. a lever in which the fulcrum lies between the effort and the load, as in the posterior cervical muscles.
34. a lever in which the load lies between the fulcrum and the effort, as in the gastrocnemius. mechanical advantage levers.
35. a lever in which the effort lies between the fulcrum and the load, as in the biceps.
36. third class-- speed levers.
each muscle is made of muscle fibers that are arranged in different ways according to the specific function of the muscle. parallel muscles such as the sartorius are designed for a greater range of motion / muscle shortening. fusiform muscles are similar to parallel except with a larger muscle belly, in a spindle shape, such as the biceps brachii. pennate muscles have muscle fibers oriented obliquely to the muscle tendon so as to increase the muscle's cross sectional diameter and increase strength- such as the deltoid muscles. convergent muscles such as the pectoralis major have a broad origin and a pointed origin, and varied lines of pull. circular muscles such as the sphincters and orbicularis oris have concentric muscle fibers that close over a hole when contracted.
agonists are defined as the prime muscle that produces a given movement. antagonists are the muscle that directly opposes the agonist movement- such as the biceps and triceps brachii. stabilizers are muscles that stabilize the action of the agonist-- such as the way that the rhomboids and pectoralis minor stabilize the deltoid by immobilizing its point of origin, the scapula. synergists are muscles that aid the movement of the agonist muscle.
muscles can be analyzed in terms of the type of "lever" that are schematically similar to. there are two important types of levers which produce complementary functions. a mechanical advantage lever is one in which the effort (the force applied) is far from the fulcrum (the point of rotation), which is close to the load (the object being moved). this type of lever (note that a car jack fits this description) lifts a large load a small distance for a small effort over a long distance. the other type of lever is a speed lever, in which the effort is close to the fulcrum, which is far away from the load. this type of lever allows for high speeds at the cost of high effort/tension. levers in the body can also be classified in the "class system"- first class levers have the fulcrum between the load and the effort, as in the posterior cervical muscles. second class levers are mechanical advantage levers that have the fulcrum between the effort and load and closer to the load, as in the gastrocnemius. third class levers are speed levers in which the effort is closer to the load than the fulcrum, as in the biceps.
questions
muscle introduction...
1. describe the role of skeletal muscle in the body.
2. how many skeletal muscles are there in the body and how much of the body weight do they take up?
3. a muscle's cross sectional diameter...
muscle types...
4. what are the different types of fiber arrangements in muscle and what are examples of each?
5. describe the arrangement and function of parallel muscles. what is an example of this type of muscle?
6. describe the arrangement and function of fusiform muscles. what is an example of this type of muscle?
7. describe the arrangement and function of pennate muscles. what is an example of this type of muscle?
8. describe the arrangement and function of convergent muscles. what is an example of this type of muscle?
9. describe the arrangement and function of circular muscles. what is an example of this type of muscle?
muscle contraction...
10. define muscle strength, power, and torque.
11. muscle contractions are either...
12. what is an isometric contraction?
13. what is an isotonic contraction?
14. what is the difference between a concentric and eccentric isotonic contraction?
15. what is the "line of pull" of a muscle?
16. what is an example of a muscle which has different actions because of a shifting line of pull?
17. how is line of pull related to proper muscle function?
18. what is the "angle of pull" of a muscle?
19. what are the two components to the angle of pull and what do they do?
muscle function terminology...
20. range of motion of a muscle depends on...
21. tension produced in a muscle depends on...
22. what is muscle irritability?
23. what is contractility?
24. what is extensibility?
25. what is elasticity?
muscle roles...
26. what are agonists?
27. what are antagonists? what is an example of an agonist/antagonist pair?
28. what are synergist muscles?
29. what are stabilizers? what is an example?
levers...
30. what is a fulcrum?
31. describe a mechanical advantage / power lever.
32. describe a speed lever.
33. what is a first class lever? what is an example in the body?
34. what is a second class lever? what is an example in the body?
35. what is a third class lever? what is an example in the body?
36. most levers in the body are...
answers
1. skeletal muscle is always attached to bone and is responsible for the movement of the body and all of its joints, as well as aiding in fluid and blood movement throughout the body, and providing protection and postural support.
2. over 600, 40-50% of body weight.
3. ...affects the muscle's ability to exert a force.
4. parallel, fusiform, pennate, convergent, circular.
5. muscle fibers are oriented parallel to muscle direction. designed for greater range of motion. example is sartorius.
6. similar to parallel muscles but with more of a spindle shape- larger cross sectional diameter in the middle. example is biceps brachii.
7. high cross sectional area muscle due to fibers being arranged perpendicularly to tendon. examples are extensor digitorum, rectus femoris, deltoid.
8. a muscle with a broad origin and a pointed insertion. the direction of pull can be varied. example is the pectoralis major.
9. fibers are arranged concentrically so as to form a sphincter. examples are orbicularis oris or sphincter muscles.
10. muscle strength= amount of tension a muscle can produce for a single maximal effort. muscle power= the amount of tension or contraction over a given period of time. muscle torque= muscle force causing rotation around an axis.
11. isometric or isotonic.
12. a muscle contraction in which the length of the muscle or the angle of the joint stays the same regardless of the tension.
13. a muscle contraction in which the tension in the muscle is relatively constant, producing motion in the joint or shortening / lengthening of the muscle.
14. concentric contraction is an isotonic contraction in which the muscle is being shortened, and in eccentric the muscle is being elongated.
15. the direction in which the muscle pulls when contracted.
16. when the humerus is abducted sufficiently such that the line of pull for the pectoralis major is above the glenohumeral joint, the pectoralis major can become an abductor of the humerus in addition to its primary flexion role.
17. each muscle has an optimal line of pull. an altered line of pull can cause hypertonicity and inefficiency, ultimately leading to weakness, trigger points, imbalance, etc.
18. the angle which is formed between the bone of insertion and the line of pull.
19. the verticle component (perpendicular to the bone of insertion) causes rotational movement at the join and the horizontal component causes a stabilizing force.
20. length of muscle fibers
21. total number of muscle fibers
22. muscle excitability- how sensitive or responsive the muscle is to chemical, electrical, mechanical stimuli.
23. ability of the muscle to develop tension when stimulated.
24. ability of the muscle to be stretched beyond its normal resting length.
25. ability of muscle to return to original length after stretching.
26. the prime muscle that provides the major force for a given movement.
27. muscle that produces a motion opposite to that produced by the agonist. example is biceps and triceps brachii.
28. a muscle which assists the agonist muscle.
29. muscles that support and improve the efficiency of the agonist. rhomboids and pec minor are stabilizers of the scapula when the deltoids are abducting the arm.
30. the fixed point of leverage, as in the joints of the body.
31. load is close to the fulcrum and the effort is far from the fulcrum. small effort over long distance can move a large load over small distance. (car jack)
32. load is far from the fulcrum and the effort is close to the fulcrum. large effort and fast movement.
33. a lever in which the fulcrum lies between the effort and the load, as in the posterior cervical muscles.
34. a lever in which the load lies between the fulcrum and the effort, as in the gastrocnemius. mechanical advantage levers.
35. a lever in which the effort lies between the fulcrum and the load, as in the biceps.
36. third class-- speed levers.
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