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- "A" Bands, the darker of the microscopically observable, alternating dark and light striations across myofibrils. Represent those areas where thick myofilaments are located
- polarize visible light
- The darker areas at the ends of each A band are caused by the overlap of the thinner I myofilaments and the thick A myofilaments
the potential motion(s) associated with the muscle contraction. When a muscle contracts this motion may or may not occur (depending on opposing forces)
a muscle that has an opposing action to another muscle. When given body motion occurs, the opposite can be effected by antagonists, gravity, or elastic recoil
the outer connective tissue proper encasement of a skeletal muscle. at the ends of a muscle belly, epimysium condenses with the ensheathments formed by perimysium (around muscle fascicles) and endomysium (around individual muscle cells) to form the tendons of the muscle.
a small bundle of muscle, nerve, or tendon fibers.
a muscle whose action is antagonistic to one or more actions of a multi-actioned muscle. they are contracted to "limit" or "select" certain actions of multi-actioned muscles by negating (neutralizing) one or more of their unwanted actions
- "I" bands - the lighter of the microscopically observable, alternating dark and light striations across a myofibril. occur btwn the A bands in the loci where the central parts of thin myofilaments are not overlapped by thick myofilaments
- Do Not polarize light
the nerve supply of a muscle or another body structure.
insertion of a skeletal muscle
"termination" - the site of attachment of the more moveable end of a skeletal muscle. in the limbs, insertion is typically at the distal site of attachment
body movement; is effected by contraction of skeletal muscles, but gravity and elastic recoil also play a role
a motor neuron plus the group of skeletal muscle cells that are innervated by it. Skeletal muscles contain many motor units which vary in size from small to large
a muscle cell (myocyte, muscle fiber) contraction of an individual muscle fiber is "all or none"
- a contractile organelle found in the cytoplasm of a muscle cell. The strength of contraction of a given muscle cell is related to the number of myofibrils that it contains
- is an elongated cylinder that contains the rod-like contractile structures called myofilaments
a proteinaceous contractile element found within a myofibril. Two major myofilaments are recognized: thick myofilaments composted primarily of myosin, and thin myofilaments composed mainly of actin (along with signif amounts of troponin and tropomyosin)
origin of a muscle
the site of attachment of the less moveable end of a skeletal muscle. In the limbs, the origin is always the proximal site of attachment
a band of connective tissue that courses transversely across one of more tendons to hold (bind) them in a certain location. Retinacula, ligaments, and tendons are similar structurally and they vary mainly in locus and function
a muscle that has the same action as another muscle. To effect a given motion, several synergists typically contract simultaneously
a fluid filled structure, similar to a synovial joint capsule, located btwn a bony prominence and the tendon or belly of a muscle. Functionally, a synovial bursa reduces friction degradation as the muscle moves reciprocally over the prominence
synovial tendon sheath
a synovial "bursa" that completely envelopes a tendon. same function as a bursa
a fibrous connective tissue structure found at each end of a skeletal muscle belly. It is the non-contractile part of a muscle with attaches the belly to other structures (bone, cartilage, or another muscle)
the largest body system and forms nearly half the body weight. skeletal muscle develops from middle embryonic germ layer (mesoderm)
involves the maintenance of body position in spite of gravitational or other extrinsic forces
functions of skeletal muscles
locomotion, posturing, respiration, digestion, orfice opening and closure, abdominal press, vocalization, eye movements, venous return and heat production
getting food and drink into the oral cavity
locations of orfice closure
exhibited by external anal sphincter muscle, and skeletal muscles surrounding the mouth and each eye
tissues present in any skeletal muscle
skeletal muscle tissue, connective muscle tissue, smooth muscle tissue, epithelium, nervous tissue, and blood
broad, sheet-like tendons
all three muscle ensheathments (epimysium, perimysium, endomysium) serve as...
avenues of penetration for nerves and vessels. Are continuous with each other and merge near the ends of the belly to form the tendons and aponeuroses by with bellies are attached.
accessory structure w/ skeletal muscles; is the irregular collagenous connective t..p. that bonds the skin to the underlying musculature, binds muscles into groups, and serves as an avenue of penetration for vessels and nerves.
accessory structure with skeletal muscles; also called hypodermis,subcutaneous tissue. it is the fascia which is directly under the skin. fibers are usually loosely packed
accessory structure w/ skeletal muscles; fascia which surrounds groups of muscles, has densely packed, irregular fibers and is continuous with the epimysium of each muscle
accessory structure; bands of dense regular collagenous connective tissue that bind tendons into groups and hold them in certain locations
- accessory structure; are synovial fluid-filled sacs that are structurally similar to joint capsules (they have fibrous outer layer and a synovial membrane lining)
- Occur btwn tendons and adjacent bony prominences where they cushion (protect) the tendons and reduce sliding friction.
- Some are continuous with joint capsules and other have no connection to them
- accessory structure; bursae that completely surround tendons and form closed, fluid-filled encapsulations.
- Many tendons near the wrists and ankles are encased in tendon sheaths
accessory aspects of sesamoid bones
- serve as bearing surfaces and protect tendons from frictional degeneration.
- Are found in the tendons of muscles in three locations:
- quadriceps femoris muscles, flexor pollicis brevis muscles, flexor hallucis brevis muscles
sliding filament mechanism
- muscle contraction involving the sliding together (interdigitation) of linear filaments composed of the contractile proteins actin and myosin.
- Essentially identical in all three types of muscle tissue
differentiate the usage of the term "fibers" in myofibers vs. nerve fibers & collagenous, elastic, and reticular fibers
- in myofibers, it means muscle cells.
- in nerve fibers, it refers to nerve cell processescollagenous, elastic, and reticular fibers, it refers to extra-cellular proteinaceous strands
cell membrane of a myocyte, formerly sarcolemma
actin, troponin, and tropomyosin
the thinner proteinaceous filaments of myofilaments
the thicker proteinaceous filament of myofilaments
arrangement and color of myofilaments
the filaments are arranged in partially overlapping alternating "stacks" throughout the length of each myofibril. The alternating impart the striated appearnace because the thick myosin filaments stain darker than thinner actin filaments
Why don't smooth muscle cells appear striated?
because the myofibrils in their cytoplasm are less neatly arranged, consequently, the stacks of thick and thin filaments in adjacent myofibrils are staggered
the lighter central region of each A band which consists of thick filaments ONLY (no overlapping from I band)
- At the very center of the H band, a darker transverse line.
- Caused by cross-linking proteins that bind the thick filaments together and keep them in proper alignment
- located at the center of each I band
- formed by crosslinking proteins that bin the thin myofilaments together
- from Z-line to Z-line to considered a myomere
the basic unit of skeletal muscle microstructure from Z line to Z line
When contraction occurs:
- nervous impulse causes electrochemical changes in actin and myosin, making them electrostatically attractive to each other, causing them to slide together (interdigitate)
- occurs throughout the length of each myofibril and results in shortening of muscle cell
- A band DOES NOT shorten
- I Band, H band, and distances btwn Z lines and M lines grow narrower
differences in the strength of a contraction of a whole muscle result from...
different numbers of muscle cells contracting
when a muscle contracts, 3 possibilities exist
- no movement - occurs if contraction produces insufficient force to overcome the resistance
- the movement described by it's stated action
- the opposite movement from it's stated action - occurs if the resistance is larger than the applied force
any muscle that is contracting
what controls skeletal muscles
CNS... under direct voluntary control. Skeletal muscles must be stimulated by nervous impulses.
where are smaller motor units found
In those muscles capable of very precise movements (eye muscles)
where are larger motor units found
In muscles which lack precise control
how many named skeletal muscles in the body?
how many and what are the subgroups of skeletal muscles
- 7 subgroups
- muscles of the head, neck, back, thorax, abdomen, superior limb and inferior limb
how many and what are the groups of the muscles of the head
- 6 groups
- muscles of the face, eye, ear, and tongue, muscles of mastication and those associated with the palate and gullet
how many and what are the groups of the muscles of the neck
- 6 groups
- suprahyoid muscles
- Infrahyoid muscles
- suboccipital muscles
- pharyngeal muscles
- laryngeal muscles
- and other muscles
differentiate the pelvic and urogenital diaphragms
- the urogenital diaphragm is at the anterior floor of the pelvic cavity
- the pelvic diaphragm is at the posterior floor of the pelvic cavity
- those muscles of the anterior trunk which are positioned anterior to the transverse processes of the vertebrae.
- Include the muscles of the thorax and those of the abdomen
the muscles of the posterior trunk which are positioned behind the transverse processes of the vertebrae
how many and what are the subdivisions of the muscles in the superior limb?
- 6 subgroups
- Include muscles of the (1) shoulder and scapula (2) anterior brachium (3) posterior brachium (4) anterior antebrachium (5) posterior antebrachium (6) manus
how many and what are the subdivisions of the muscles in the inferior limb
- 9 subgroups
- Include muscles of the (1) anterior muscles of the hip; (2) posterior muscles of the hip; (3) medial muscles of the hip; (4) anterior muscles of the thigh; (5) medial muscles of the thigh; (6) posterior muscles of the thigh; (7) anterolateral muscles of the crus; (8) posterior muscles of the crus; (9) intrinsic muscles of the pes
Name 3 divisions of mesoderm on each side of the notochord, state which one gives rise to myoblasts
- Immediately adjacent to the notochord is called paraxial mesoderm *RISES MYOBLASTS
- Furthest from the notochord is called that lateral plate mesoderm
- Paraxial and Lateral plate are connected by intermediate mesoderm (mesomere)
- a muscle condition related to defective transmission of the nervous impulses btwn the neurons and the skeletal muscle cells.
- chronic, progressive disease that usually bigins in the face and cervical region
- involves muscle atrophy. is progressive
- several types, most common one is sex-linked affecting males. affected boys usually die before maturity
painful involuntary contractions that are believed to be related to alterations of the normal levels of certain electrolytes
what causes muscle "burn" during strenuous and repetitive muscle contraction?
Due to the accumulation of lactic acid - an end product of glucose metabolism under low oxygen conditions
- physical exercise that can be sustained for a considerable time (10 mins)
- implication is that oxygen intake is keeping up with the rate the muscles are using it
- exercise that is more vigorous and cannot be sustained (heavy weight lifting, running up stairs)
- implication is that the oxygen intake is not keeping up with the oxygen needs of the contracting muscles
TQ: Does a muscle have to cross more than one joint to have more than one action?
- In theory, every joint a muscle spans can be acted on; BUT in some cases the positions of attachment are such the force produced at the joint is minimal or negligible.
- However, the # of actions can exceed the number of joints crossed if more than one action can be produced at a given joint.
TQ: Why can weight-lifters life more weight or do more repetitions after "warming up" with lighter weights and fewer repetitions?
The warm up increases the blood flow to the exercised muscles with, in turn, facilitates removal of lactic acid during the subsequent, more vigorous exercise
TQ: What are the advantages of midline abdominal incisions for surgical invasion of the abdomen vs. paramedian or paracostal approaches?
- Midline abdominal incisions pass through the linea alba and avoid the bellies of the abdominal muscles altogether.
- Sutures in the linea alba have more holding power and form a more secure abdominal closure
- The other surgical approaches to the abdomen DO have advantages in certain procedures and they ARE used
TQ: Most skeletal muscles in the limbs are involved in third class lever systems. Since third class levers always lose mechanical advantage, of what benefit is this design?
- Although third class levers lose mechanical advantage, they gain total distance moved (or speed of movement) at the insertion vs. the origin.
- Thus, contraction of the biceps brachii muscle may cause significant motion at the elbow joint even though the muscle belly itself may shorten only a few centimeters
TQ: The carpal flexor retinaculum is a band of connective tissue that stabilizes the tendons of the anterior antebrachial muscles which continue distally into the manus. Tendons of which anterior antebrachial muscles are held in place by this retinaculum?
- All of them except the three antebrachial rotators
- Those whose tendons are held in place by the retinaculum are the flexor carpi radialis and ulnaris muscles, superficial and deep digital flexor muscles, palmaris longus muscle, and flexor pollicis longus muscle
TQ: Muscle A is said to be a fixator muscle in regard to a certain action of muscle B. What does this imply about muscle A? About muscle B?
- Muscle A must be antagonistic to one (or more) actions of muscle B (But A is not antagonistic to the specific action of B under discussion)
- Muscle B must be a multi-actioned muscle
TQ7: To which three groups of muscles of the superior limb do the eight "pollicis" muscles belong?
- One of them is anterior antebrachial muscle
- Three are posterior antebrachial muscles
- four are intrinsic muscles of the hand (three in the thenar group and one in the intermediate group)
TQ8: What is wrong with the following description of muscle action: Extend the brachium
Extension and flexion are terms applied to joints. Rigid body parts like the brachium, antebrachium, and thigh cannot be extended or flexed
TQ8: What is wrong with the following description of muscle action: Abduct the shoulder
Abduction/adduction are terms describing the movement of body parts in frontal (coronal) planes. The shoulder is not abducted - the superior limb is abducted at the shoulder joint
TQ8: what is wrong with the following description of muscle action: flex the biceps brachii muscle
- Muscles are contracted.
- The term flex should be reserved for joints
TQ9: Identify this muscle
most of the tendons visible subcutaneously on the back of the metacarpus
Digital extensor muscle
TQ9: identify this muscle
the one bruised by a law enforcement officer who discovers that the door he is trying to break down with his shoulder is solid oak
TQ9: Identify this muscle
the one whose tendon bulges forward on the front of the ankle when the tarsal joint is forcefully flexed
Anterior tibial muscle
TQ9: Identify this muscle
The one responsible for the rippled appearance of the anterior abdomen in a thin, well exercised individual
Rectus abdominus muscle
TQ9: Identify this muscle
The ones accentuated by wearing high-heeled shoes
- Gastrocnemius and soleus muscles
- (collectively called triceps surae m.)
TQ10: Where does the superficial digital flexor (SDF) muscle go deep and the deep digital flexor (DDF) muscle become superficial?
- The trade superficial/deep positions near the metacarpophalangeal joints.
- The four tendons of the SDF form loops (holes) which the 4 tendons of the DDF pass
- Those of the SDF (now deep) attach to middle phalanges 2,3,4,5.
- Those of DDF (now superficial) attach to distal phalanges 2,3,4,5
TQ11: Bo and Jo (meat cutters) severed their second (Bo) and third (Jo) digits through the proximal interphalangeal joints. What muscles did they injure
- Bo severed tendons of the superficial and deep digital flexors, the tendon of the digital extensor m., and the tendon of the extensor indicis m.
- Jo severed other tendons of these same muscles except for the extensor indicis muscle
TQ12: What is wrong with the statement "skeletal muscles are composed of skeletal muscle tissue?"
- It ignores the fact that many other tissues are found in skeletal muscles.
- These include conn t.p., smooth muscle tissue, blood and epithelium (in vessels) and nervous tissue
TQ13: What is the difference btwn a tendon and an aponeurosis?
- Aponeuroses are broad, flat tendons.
- Thus, all aponeuroses are tendons but not all tendons are aponeuroses
TQ13: What is the difference btwn a tendon and a ligament?
Tendons are subparts of muscles, whereas ligaments (of the skeletal system) are bands of conn. tissue that stabilize the skeletal components around joints
TQ13: What is the difference btwn a ligament and a retinaculum?
Retinacula group tendons together and hold them in certain places
TQ14: What are the possible consequences of a muscle contracting with a force greater than the body's structure can withstand?
- (1) The muscle belly can rupture
- (2) One of it's tendons can rupture
- (3) A tendon can be pulled loose (avulsed) from it's attachment. May be involved tearing away a small bone fragment while leaving most of the bone intact
- (4) A bone can be fractured
TQ15: Why do men generally have bigger and stronger muscles than women?
Testosterone (which women produce but in lesser quantities) promotes skeletal muscle development and strength
TQ16: Some extremely fit individuals have a negative specific gravity (their bodies sink instead of float in water) Why?
- Fat floats in water, but skeletal muscle tissue sinks.
- Due primarily to the iron containing myoblobin (an oxygen binding muscle pigment similar to hemoglobulin in red corpuscles)
- Very fit individuals have a low fat content in their bodies
TQ17: The contraction of a muscle cells is "all or none" but a named muscle can contract with varying force. Explain.
The strength of contraction depends on how many skeletal muscle cells within a named muscle contract
TQ18: Name two muscles that have inherently antagonistic actions (actions that are antagonistic to themselves)
- The deltoideus muscle (can both extend and flex the shoulder joint)
- The brachioradialis muscle (can both pronate and supinate the manus/antibrachium)
TQ19: The connective tissue band joining the patella to the tibial tuberosity has two acceptable names. What are they?
- Patellar ligament or tendon of insertion of the quadriceps femoris muscle.
- Should not call this muscle the patellar tendon or the quadriceps femoris ligament
TQ20: What do bursae, tendon sheaths and sesamoid bones have in common?
All share functional purpose of protecting tendons from frictional degradation
TQ21: Why do various sources cite different totals for the number of bones in the skeleton?
- Some authors do not count the sesamoid bones. These sources list 206 bones.
- When totaling bones, the ox sacrum is counted as only one bone, even though 5 sacral vertebrae fuse.
- Similar logic is used when counting the 4 fused coccygeal vertebrae (they form one bone)
- In like manner, each os coxae is counted as 1 one despite 3 different bones fuse to form it