LECTURE 8

• "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.

"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)

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

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

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

chewing food

swallowing

exhibited by external anal sphincter muscle, and skeletal muscles surrounding the mouth and each eye

skeletal muscle tissue, connective muscle tissue, smooth muscle tissue, epithelium, nervous tissue, and blood

broad, sheet-like tendons

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

• 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

• 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

• in myofibers, it means muscle cells.
• in nerve fibers, it refers to nerve cell processes
• collagenous, elastic, and reticular fibers, it refers to extra-cellular proteinaceous strands

cell membrane of a myocyte, formerly sarcolemma

the thinner proteinaceous filaments of myofilaments

the thicker proteinaceous filament 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

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

• 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

different numbers of muscle cells contracting

• 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

CNS... under direct voluntary control. Skeletal muscles must be stimulated by nervous impulses.

In those muscles capable of very precise movements (eye muscles)

In muscles which lack precise control

230

• 7 subgroups
• muscles of the head, neck, back, thorax, abdomen, superior limb and inferior limb

• 6 groups
• muscles of the face, eye, ear, and tongue, muscles of mastication and those associated with the palate and gullet

• 6 groups
• suprahyoid muscles
• Infrahyoid muscles
• suboccipital muscles
• pharyngeal muscles
• laryngeal muscles
• and other muscles

• 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

• 6 subgroups
• Include muscles of the (1) shoulder and scapula (2) anterior brachium (3) posterior brachium (4) anterior antebrachium (5) posterior antebrachium (6) manus

• 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

• 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

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

• 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.

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

• 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

• 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

• 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

• 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

• 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)

Extension and flexion are terms applied to joints.  Rigid body parts like the brachium, antebrachium, and thigh cannot be extended or flexed

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

• Muscles are contracted.
• The term flex should be reserved for joints

Digital extensor muscle

Deltoideus muscle

Anterior tibial muscle

Rectus abdominus muscle

• Gastrocnemius and soleus muscles
• (collectively called triceps surae m.)

• 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

• 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

• 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

• Aponeuroses are broad, flat tendons.
• Thus, all aponeuroses are tendons but not all tendons are aponeuroses

Tendons are subparts of muscles, whereas ligaments (of the skeletal system) are bands of conn. tissue that stabilize the skeletal components around joints

Retinacula group tendons together and hold them in certain places

• (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

Testosterone (which women produce but in lesser quantities) promotes skeletal muscle development and strength

• 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

The strength of contraction depends on how many skeletal muscle cells within a named muscle contract

• The deltoideus muscle (can both extend and flex the shoulder joint)
• The brachioradialis muscle (can both pronate and supinate the manus/antibrachium)

• Patellar ligament or tendon of insertion of the quadriceps femoris muscle.
• Should not call this muscle the patellar tendon or the quadriceps femoris ligament

All share functional purpose of protecting tendons from frictional degradation

• 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