The Muscular System

• composed of skeletal muscles only
• study of is called myology

voluntary striated muscle that is usually attached to one or more bones

• exhibits microscopic pattern of alternating light and dark bands
• result from overlapping arrangement of contractile proteins within each cell
• about 100um in diameter and 3 cm long

• aka myofibers
• typical skeletal mscles that have extraordinary length

• Also Striated
• involuntary
• short stumpy cells

• aka myocytes
• short stumpy cells like logs with notched ends
• commonly only about 80um long by 15 um wide

• involuntary
• lacks striations, hence name
• contains same contractile proteins but not arranged in regularly overlapping way
• thick in middle and tapered at ends
• avg about 200um long by 5um wide

• Movement
• Stability
• Control of body openings and passages
• Heat production
• Glycemic control

• Excitability (responsiveness)
• Conductivity
• Contractility
• Extensibility
• Elasticity

• thin sleeve of loose connective tissue that surrounds each muscle fiber
• creates room for blood capillaries and nerve fibers to reach e/ muscle fiber
• provides extracellular chem environ for muscle fiber and assoc. nerve ending
• excitation based on xchange of calcium, sodium and ptassium ions tween tissue fluid and nerve and muscle fibers

• thicker connective tissue sheat that wraps muscle fibers 2gether in bundles called fascicles
• fascicles- visible to naked eye as parallel strands

• fibrous sheath that surrounds entire muscle
• outer surface grades into fascia and inner surface issues projections tween fascicles to form perimysium

• sheet of connective tissue
• separates neighboring muscles of muscle groups from each oterh and from subcutaneous tissue
• muscles grouped in compartments sep from e/ o/ by fascia

• thick in middle tapered at end
• ex- biceps brachii and gastrocnemius
• relatively strong

• fairly uniform width and parallel fascicles
• some are elongated straps (rectus abdominis)
• some squarish and are called quadrilateral msucles (masseter of jaw)
• can span long dist and shorten more than o/ muscle types
• produce less force

• Fan-shaped
• ex-pectoralis major
• relatively strong cause of large number of fibers in wider part of muscle

• feather shaped
• fascicles insert obliquely on tendon
• Three types;
• _{unipennate, fascicles approach tendon from one side}
• bipennate, fascicles approach tendon from both sides
• multipennate, shpaed like bunch of feathers with quills converging on single point

generate more force than others cuze they fit more muscle fibers into given length of muscle

• form rings around certain body openings
• contract, constrict opening and tend to prevent passage of material thru itex- eyelids

• ends conspicuously short of bony destination
• gap bridged by fibrous band or tendon

• broad sheet of tendon
• refers to tendons assciated with certain ab, lumbar, hand and foot muscles

So little separation between muscle and bone that to the naked eye, red muscular tissue seems to emerge directly from bone

site of attachment at relatively stationary end

attachment site at more mobile end

middle, usually thicker region

• muscle opposing primary mover
• maintains sum tension on joint and limits speed or range of prime mover

muslce that produces most of force during particular joint action

effect produced by muscle to produce or prevent movement

muscle that aids prime mover

act on opposite sides of a joint

muscle that prevents a bone from moving

• entirely contained within particular region
• both origin and sertion there

actws upon designated region but its origin is elsewhere

any elongated, rigid object that rotates around a fix point

fixed point rotated around by lever

occurs when an effort overcomes a resistance (load)

part of lever from the flucrum to point of effort

part from the fulcrum to the point of resistance

• ratio of its output force to its input force
• equal to length of the effort
• L_E= effort arm, L_R= resistance arm
• MA=L_E/L_R

• one with the fulcrum in the middle (EFR)
• like a seesaw
• atlanto-occipital joint of neck, muslces of back of neck pull down on occipital bone of skull and oppose tendency of head to tip forward

• one in which resistance in middle (FRE)
• Wheelbarrow
• mandible, digastric muscle pulls down on chin to open mouth, fulcrum is temporomandibular join-effort is digastric muscle and resistance is tension of muscles like temporalis muscle

• effort applied between fulcrum and resistance
• paddling cannoe
• effort applied to middle of shaft and resistance produced by water against blade, relatively stationary grip at upper end of paddle
• most musculoskeletal levers are 3rd class

plasma membrane of muscle fiber

• Cytoplasm of muscle fibers
• occupied by long protein bunderls, (myofibrils)
• abundance of glycogen-starchlike carbohydrate that provides energy for cell during periods of heightened excercise
• red pigment myoglobin-stores oxygen till needed for muscular activity

• smooth endoplasmic reticulum
• forms network around each myofibril

dilated end-sacs of sarcoplasmic reticulum

• formed when sarcolemma turns inward at many points
• penetrate thru cell and emerge on other side
• carries 2 electrical signals from cell surface into interior and induces gates in SR membrane to open

• parallel protein microfilaments
• makes up myofibrils
• 3 Kinds; Thick filaments, thin filaments, elastic filaments

• made of several hundred molecules of myosin protein
• bundle of 200-500 myosins

• composed primarily of two intertwined strands of protein
• called fibrous (f) actin- like bead necklace
• also contains protein tropomyosin- has smaller calcium-binding protein called troponin

• made of huge springy protein titin (connectin)
• helps to stabilize thick filament, center it tween thin filaments and prevent overstretching

• myosin and actin
• do work of shortening muscle fiber

• tropomyosin and troponin
• act like switch to determine when fiber can contract and when it cannot

• enormous protein located just under sarcolemma
• links actin filaments to transmembrane proteins in sarcolemma

• dark bands in striated muscle
• consists of thick filaments lying side by side

Light bnads in striated muscle

• thin filaments do not reach
• in middle of A band

thick filaments originate at a dark M line

• bisect I band
• provides anchorage for thin filaments and elastic filaments

• functional contractile unit of muscle fiber
• muscle shortens because its individ sarcomeres shorten and pull z discs closer to each other and dystrophin and the linking proteins pull on the extracellular proteins of muscle

any point where a nerve fiber meets and stimulates another cell

• lead to the skeletal muscles
• axons of cell bodies of somatic motor neurons

• aka motor end plate
• nerve fiber approaches and individ muscle fiber and branches again to establish sever points of cantact within NMJ
• each terminal branch of nerve fiber within NMJ forms synapse with uscle fiber
• sarcolemma of NMJ is irregularly indented
• one nerve fiber stimulates muscle fiber at several points within each NMJ

• end of nerve fiber at each synapse
• doesnt directly touch muslce fiber but is separated from it by a narrow space called synaptic cleft

filled with chemical called acetycholine (ACh) when a when nerve signal arrives at synaptic knob, some of these vesicles release their ACh by exocytosis

respond to ACh by inititating electrical devents that lead to muscle contraction

increase membrane surface area in sarcolemma and allow for more ACh receptors, thus allow more sensitivity of muscle fiber to nervous stimulation

• enzyme that is found in both sarcolemma and basal lamina
• breaks down ACh after the ACh has stimulated muscle cell
• import in turning off muscle contraction

• group of muscle fibers innervated by one nerve fiber
• not clustered together but dispersed throughout muslce
• when stimulated cause weak contraction over wide area, not just localized twitch in small region
• effective muscle contraction usually requires activation of several motor units aqt once
• abg about 200 fibers per motor neuron
• mult motor units in muscle= they can "work in shifts", also mena strength can be controlled

• nerve fiber releases ACh, which excites mucle fiber
• wave of electrical excitation spreads into the sarcoplasm by way of T tubules

• consists of events that link this electrical stimulus to the onset of muscle tension
• Excitation of the T tubules induces the sarcoplasmic reticulum to release calcium ions, and calcium clears way for myosin of thick filaments to bind the actin of the thin filaments

myosin heads reepeatedly attach to the thin filaments and pull on them, cause the thin filaments to slide across the thick filaments and shorten the cell

nerve signaling ceases, myosin once again blocked from binding to actin and muscle tension subsdies

• aka slow-twitch, red or type I fibers
• relatively abundant mitochondria, myoglobin and blood capillaries. felatively deep red color
• do not faituge easily: well adapted to aerobic respiration, way to make ATP that requires oxygen but does not generate lactic acid- majore contributor to muscle fatigue
• exhibit a relatively long twitch or contraction

• aka fast-twitch, white, or type II fibers
• rich in enzymes for anaerobic fermentation, process that is independent of oxygen but produces lactic acid
• respond quickly but fatigue more easily than SO
• poorer in mitochondria, myoglobin and blood capillaries, relatively pale
• well adapted for quick responses but not endurance

• combine fast-twitch responses with aerobic fatigue-resistant metabolism(sub fg fibers)
• relatively rare except in in some endurance-trained athletes

• dark lines in cardiac muscle that exhibits characteristic dark lines where cells meet
• like steplike regions allow cells to communicate with each other

instead of z discs, little masses of protein scattered throughout the sarcoplasm and on inner face of the sarcolemma

occurs in some of the largest arteries and pulmonary air passages, in piloerector muscles of hair follicles and in iris of eyehas a motor unit, but contracts independently of others

• more widespread
• occurs in most blood vessels and in digestive, respiratory, urinary and reproductive trachts- thus also called visceral muscle
• nerve fibers in this type of muscle do not synapse with individ muscle cells but pass thru tissue and exhibit swellings called varicosities at which they release neurotransmitters, thus directly stimulating each other almost as if they were a single cell

maintains blood pressure by keeping blood vessels partially constricted and it prevents such organs as stomach, intestines, urinary bladder and uterus from becoming flaccid when empty

waves of contraction made by smooth muscle that propel contents through an organ (esophagus)

• stem cells that persist throughout life
• some fuse with growing muscle fibers and contribute nuclei to it through childhood
• may regenerate a limited amount of damaged skeletal muscle even in adults

diseases of muscular tissue

• collective term for several hereditary diseases in which skeletal muscles degenerate, lose strength, and are gradually replaced by fat and scar tissue
• the new connective tissue impedes blood circulation which in turn accelerates muscle degeneration creating a fatal spiral of positive feedback

• most prevalent in women from 20-40 years old
• autimmune disease in which antibodies attack neuromuscular junctions and trigger destruction of ACh receptors
• muscle fibers bcome less and less sensitive to ACh
• effects often appear first in facial muscles and include drooping eyelids and doble fision
• often followed by difficulty swallowing, weakness of the limbs, and poor physical endurance
• some die quickly as a result of respiratory failur, while others have normal life span