Lecture 9 Outline of Last Lecture I. Joints- Synovial Joints continueda. Articular disc b. Ligaments c. Nerves d. Blood vesselsII. The Temporomandibular JointIII. Musclesa. Development of muscles Outline of Current LectureI. Introduction to Muscle HistologyII. Smooth MuscleIII. Skeletal MuscleIV. Cardiac MuscleCurrent LectureI. Introductiona. Key specialization of muscle cells- contract forcefullyb. Muscles lie along bones which they contract or stabilizec. Muscles also occupy walls of hollow organsi. Squeezes things through themd. Most muscle cells – called fibers because longi. 2 special properties1. Both conductive and contractilea. Conductivity: property of the muscle cell’s plasmalemma: a wave of electrical impulse moves of the membrane. It is the impulse passing over the membrane that signals to contract b. Contractility: the muscle fibers can shorten, producing a pulling forcee. Muscle tissue contains many muscle cellsf. 3 types of muscle tissue:i. Smooth muscle (mostly in the walls of hollow organs)ii. Skeletal muscle (in the muscles that attach to bones)iii. Cardiac muscle (in the wall of the heart)g. Shared properties: i. Shortening and contraction always occur on the long axis of the cellii. All contain contractile elements : myofilaments 1. Actin2. Myosin (longer and more abundant in muscle cells)3. Generate contractile force by sliding along one anotheriii. the cytoplasm of any muscle cell: sarcoplasm1. plasma membrane: sarcolemma BIOL_315 1nd EditionII. Smooth Musclea. Fibersi. Long, spindle-shaped cellsii. Elongated oval nucleusiii. Cytoplasm appear smooth except at high magnification iv. The myofilaments fill all the cytoplasm except for small area around the nucleusb. Grouping of fibersi. Smooth muscles grouped into bundles call fascicles or in sheetsii. Sheet arrangement is much more commoniii. Note: when cut in cross-section, smooth muscle has an unusual appearance showing circular sections, resembling cobblestoneiv. Adjacent sheets of smooth muscle are separated from each other by connective tissue1. Which contains nerves and vesselsc. Locations of smooth musclei. In the walls of hollow organs1. Digestive tube, bladder, and uterusii. In walls of arteries and veinsiii. Functions1. Either squeeze things through the hollow organs2. Change the diameter of vessels to adjust how much fluid can flow throughd. Contraction of smooth musclei. Involuntary ii. Nerve fibers that stimulate smooth muscle are signaled by the brainiii. These nerves belong to the autonomic nervous systemiv. Slow, but can remain contracted for a long time without tiringIII. Skeletal musclea. Fibersi. Very large, cylindrical ii. Can extend the entire length of the muscle, but most are only a few centimeters longiii. Multi-nucleated cells1. Because arise from fusion of many muscle-forming cells in the embryo2. Arranged around the periphery of the muscle fiber, just inside of the plasma membraneiv. Striations 1. Myofibrilsa. Long, unbranched cylinders that occur in numbers and fill most of the cytoplasm of the muscle fiberb. Separated by thin streaks of cytoplasm containing rows of abundant mitochondria, which provide energy for muscular contractionc. long row of repeating segments call sarcomeres (muscle piece) is the basic unit of contraction in skeletal muscle i. boundaries of sacromeres are called Z lines ii. attached to the Z lines or Z discs are thin (actin) filaments 1. consist of actin2. contain other proteins as welliii. overlapping the inner ends of the thin filaments, is a cylindrical bundle of thick (myosin) filaments 1. studded with little knob-like projections called myosin headsv. sliding filament hypothesis – explains the mechanism of muscular contraction1. when the myosin heads of the thick filaments bind to the thin filaments at both ends of the sarcomere2. then the heads pivot and pull the thin filaments closer together3. myosin heads let go, bind, and pull again, repeating many times during a single contraction4. makes the sarcomere shorten during contractionb. the sarcoplasmic reticulumi. elaborate smooth endoplasmic reticulum within skeletal muscle fiber ii. plays key role in initiating muscular contraction iii. consists of tubules that occupy the regions of cytoplasm between the myofibrils ,these tubules form elongated cylindrical baskets around individual myofibrils 1. most tubules run parallel to the length of the myofibrils and such tubules are called longitudinal sarcotubules**see textbook for a good visual**iv. function: to store calcium ions1. signaled to release by impulses passing over the sarcolemma 2. then diffuse into nearby sarcomeres and trigger the binding of thick and thin filaments to start contraction3. after completed the calcium ions are taken up again by the sarcoplasmic reticulum c. grouping of skeletal muscle fibersi. grouped into bundles called fascicles 1. easily visible to the naked eye2. many bound together by connective tissue to form a while skeletal muscleii. there are 3 classes or layers of connective tissue in a skeletal muscle of the body1. epimysium: layer of dense connective tissue surround the whole skeletal muscle2. perimysium: connective tissue runs around each fascicle, as well as between the fascicles in the skeletal muscle3. endomysium: delicate connective tissue is within the fascicles, between the individual fibers iii. these tissues are continuous with the tendons at the ends of the muscle 1. contracting muscle fibers full on these 3 tissues, which transmit the pulling force to the tendon and boneiv. the nerve and blood vessels run in these 3 d. contractioni. controlled voluntarily ii. contract more rapidly iii. tire more easily and cannot sustain repeated contraction as readilyiv. can shorten down to 2/3 or ½ its resting length1. smooth muscle can shorten much more than thise. pharyngeal arch musculaturei. forms in the wall of the pharynx ii. arises around part of the gut but it is skeletal muscleiii. develops from head of mesodermiv. must have voluntary control over the acts of swallowing and chewing** see textbook for a summary of the organization of skeletal muscle**IV. Cardiac Musclea. Muscle of the heart wallb. Contracts to pump bloodc. Share some features with smooth muscle and skeletal muscled. Similarities with smooth musclei. The cardiac muscle cell is a single cellii. Single nucleus located in the center of the celliii. Contract slowly and do not tire easily 1. Due to an abundance of mitochondria in