Satellite cells are immature myoblasts and are below the external lamina. SiO2+CheatSiC+CO(balanced?) from one myocyte to the next? Autonomic nerves function only to speed up and slow down heartbeat. (b) \beta-particle emission? Smooth muscle contracts under certain stimuli as ATP is freed . A myofibril is made up of many myofilaments. What is a sarcomere, and what are the major proteins found in the sarcomere? Skeletal muscle is attached to bone by a tendon at the myotendinous junction. . c. volatile In a relaxed cell, myosin is in a high energy state (cocked) but is unable to bind actin due to tropomyosin covering the myosin binding site. There are no sarcomeres. The function of SR in skeletal muscle is The SR regualtes intracellular levels of calcium in skeletal muscle which in turn regulates contraction/relaxation of muscles. This allows for coordinated contraction of many cells at once. Vous pouvez choisir l'offre qui vous convient. The depolarzation of the motor end plate on a muscle cell. Muscles are held in place and covered by: endomysium fascia tendons sarcomeres 3. Lab 9 Report Muscle Physiology Lab Report-Complete the Labster Skeletal muscle simulation and answer the questions below 1) What is the importance of Myosin ATPase? myosin heads bind to actin, initiating the sliding filament mechanism. Leiomyosarcoma most often begins in the abdomen or uterus. Smooth muscle contracts under certain stimuli as ATP is freed . Let knowledge be the cure. Sem categoria. Muscle tissue is classified into three types according to structure and function: skeletal, cardiac, and smooth ( Table 4.2 ). Intercalated discs join adjacent cardiac myocytes (*double check*) and adhering junctions occur on transverse sfc; attachment points for actin filaments of last sarcomere of myofibrils, desmosomes are on transverse sfc, and gap junctions are on the longitudinal surface. Continue your investigation by examining the muscle tissues at the cellular level to see how the individual muscle cells of each muscle tissue compare and contrast from one another. Which is largest and which is smallest? I absolutely have to say that I think the costume for my character in the play looks ridiculous! Skeletal muscle a discrete organ made up of several kinds of tissues; muscle fibers predominate, blood vessels nerve fibers and connective tissue also present Epimysium an overcoat of dense regular connective tissue that surrounds the entire muscle Fascicles bundles of muscle fibers Perimysium The sarcomere is the basic contractile unit of muscle fiber, and it is composed of two protein filaments: actin and myosin. You can now upload the .zip file into your LMS by the following these instructions: Discover one of 200+ learning simulations available today, Describe the major roles of muscle tissue. Skeletal a neurotransmitter ___ is released from the neuron and binds to the muscle cell, causing it to ___. All myofibers in the unit contract at once. Unlike a fossil skeleton, however, your skeleton is a structure of living tissue that grows, repairs, and renews itself. skeletal muscles allow us to show our emotions via ___ and ___. Smooth muscle cells have different diameters when cut in cross section because of their spindle-shape. Smooth Muscle Definition Smooth muscle is a type of muscle tissue which is used by various systems to apply pressure to vessels and organs. contains highly adaptive smooth muscle layer that stretches to accomodate the growing fetus during pregnancy. An example is eye movements. Elevate your nursing program with UbiSim, a VR solution dedicated to clinical excellence. The cells are long and slender so they are sometimes called muscle fibers, and these are usually arranged in bundles or layers that are surrounded by connective tissue. ___ binds to a protein known as ___, to initiate muscle contraction. Get started for free! 7 Seater Cars For Sale Basildon; What Channel Is Shark Tank On Xfinity; Talladega County Pistol Permit Online; Real Estate Asset Management Blackstone; Vans Men's Ward Sneaker; Escribe definiciones de la siguiente palabra. The functional unit of a muscle is the: neuron reticulum Z line sarcomere 4. Blog Home Uncategorized muscle tissue: an overview labster quizlet. Ach from motor neuron is released at the NMJ , binds to LGICs on motor end plate; removed by acetylcholinesterase. Sarcomeres contract but myofilaments do not. cardiac muscle tissue uses aerobic respiration almost exclusively to avoid fatigue Multi-unit smooth muscles are like skeletal muscles and allows more fine-tuned control and example is in walls of large arteries and the large airway of the lung. Whole skeletal muscle is made up of many fibers(cells) held together with _______________________________ tissue. With access to our simulations, you will have hundreds of hours of engaging, high-quality learning content available to you. Some of these muscles help to express your emotions through gesticulation and facial expressions, while the heart beats more than 3.3 billion times over 80 years! regulates the size of the pupils to adjust how much light enters the eye. Study the science that underlies the understanding and treatment of human diseases, acquire skills in areas of biology and chemistry that are relevant to healthcare. After his graduation from the Normal School, Washington went on to establish a school at Tuskeegee, Alabama the flowering of this school would be his lifes work and one of his greatest achievements. Pick up the cellular 3D models and examine the nuclei, myofibrils, mitochondria and more to understand how the intracellular components enable each muscle cell to perform the functions characteristic for that muscle tissue. Why do skeletal muscle cells appear striated? Muscle Tissue. Finally, immerse yourself in the process of the sliding filament theory by interacting with the contractile proteins of a sarcomere. From what embryonic tissue(s) does muscle tissue develop? Math is a subject that can be . Finally, build the deadly organism by building 4 cells representative of each basic type of animal tissue: neural, epithelial, muscle and connective tissue. If Labster is integrated with your school's LMS, then you don't have an account with Course Manager. Atrial myofibers secrete a hormone (atrial natriuretic factor) from granules to cause loss of Na+ and H20 from kidney to reduce blood pressure. Some of these muscles help to express your emotions through gesticulation and facial expressions, while the heart beats more than 3.3 billion times over 80 years! laboratory introduction to anatomy physiology crash course . May 20, 2021; tapioca starch whole30; barient 32 self tailing winch parts . composed of a big smooth muscle (detrusor muscle) which relaxes to store urine, and contracts to expel it from the body. Terms in this set (4) Smooth Involuntary; longitudinally and circularly arranged layers. no tropomyosin on thin filaments so the myosin binding site is always exposed. Finally, build the deadly organism by building 4 cells representative of each basic type of animal tissue: neural, epithelial, muscle and connective tissue. Overview of Muscle Tissues The three types of skeletal muscle tiss Muscles that move bones are called_____ All other muscle tissue is called _____ Muscle is the tissue in animals that allows for active movement of the body or materials within the body. filaments containing actin and myosin (enable muscles to contract), has very large cylindrical cells (muscle fibers); striated; many nuclei found along the edge of the cell, repeated banding pattern found inside the cell, attached to bones by tendons; skeletal muscles, striated; cells are small and branched; one nucleus; cells are joined by intercalated disks, seen in cardiac muscle, help connect branched fibers of muscle tissue; helps signalize cell to cell, non striated; one central nucleus; cells packed together to form sheets; small and tapered on both ends, nuclei randomly distributed throughout in smooth muscle, dense regular nuclei are aligned parallel, involuntary body activities: churning of stomach and constriction of arteries, TBL 4: Frameworks for Health Promotion, Disea, Human Anatomy and Physiology Laboratory Manual, Elaine N. Marieb, Lori A. Smith, Susan J. Mitchell. This app got your back. Labster answers muscle tissue quizlet Study with Quizlet and memorize flashcards containing terms like The muscle you can see on the microscope screen was dyed for Myosin ATPase and a darker Solve Now. How do single unit and multi-unit smooth muscles differ with respect to innervation and location? Our virtual laboratory simulations are aimed atuniversity, college and high school level, within fields such as biology, biochemistry, genetics, biotechnology, chemistry, physics and more. L'inscription est 100% en ligne, simple et rapide. Find the emissivity of the top surface and the net rates of heat transfer between the top and the bottom surfaces, and between the bottom and side surfaces. Remember that you can access the theory pages in your LabPad at any moment while playing the simulation. Internal movement: Smooth and skeletal muscle tissue is responsible for "hidden movement", including breathing, digestion, circulation of blood, urination and defecation. it can divide by hyperplasia (ex. Ce virement est obligatoire pour ouvrir votre compte et profiter de votre prime. Muscle is one of the most abundant tissues in animals and humans. coach house furniture stockists near me. Skeletal muscle fibers can be quite large for human cells, with diameters up to 100 m and lengths up to 30 cm (11.8 in) in the Sartorius of the upper leg.During early development, embryonic myoblasts, each with its own nucleus, fuse with up to hundreds of other . Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle ().All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from polarized An article in the science section of the newspaper describes the efforts of a group of scientists to develop a new nuclear reactor based on the fission of iron (Fe)(\mathrm{Fe})(Fe). I am thankful to the authority of This app for making this application. Labster answers muscle tissue quizlet - Best of all, Labster answers muscle tissue quizlet is free to use, so there's no sense not to give it a try! The sarcolemma sends closed ended tubules into the sarcoplasm (T-tubules) that associate with terminal cisternae of sarcoplasmic reticulum (smooth ER, a site of Ca2+ storage) forming triads of A-I borders. The A band is the region in teh center of the sarcomere where thick and thin filaments overlap. Neurotransmitters are substances which neurons use to communicate . labster muscle tissue overview quizlet. Skeletal muscle tissue - control, location, cardiac muscle tissue - control, location, smooth muscle tissue, skeletal muscle tissue. Sphincters of both skeletal (voluntary) and smooth (involuntary) muscle tissue control our body openings and passage of food and liquids. Muscle is one of the most abundant tissues in animals and humans. Smooth muscle is found in the wall of the arteries that supply blood to the skin. Labster integrates with all major LMS (Learning Management Systems) so that educators can use their gradebooks to track students performance data and students can keep a record of their work. It is composed of cells with the ability to contract and therefore provide a particular movement to different parts of the body. Because skeletal muscle cells are long and cylindrical, they are commonly referred to as muscle fibers. Cells and Tissues What are the four basic types of tissue in histology? What are some unique features of cardiac muscle with respect to the signal for contraction, metabolism, regenerative ability, and endocrine function? they run the entire length of the cell. large amounts of smooth muscle tissue lie in longitudnal and circular sheets around the organs of the _____? Will you be able to figure out the molecular mechanisms that underlie muscle contraction? Skeletal Banded Appearance; dense connective tissue packaging; voluntary. Train staff and clients quickly, inexpensively, and with better outcomes-in a way that increases efficiency in the workplace. the cells are capable of mitotic division for repair, unlike skeltal and cardiac myofibers. Differentiate smooth, cardiac and skeletal muscle based on their microstructure Describe and identify the general organization and structural components of a skeletal muscle. - May convert fast glycolytic fibers into fast oxidative fibers, exercise that forces muscles to contract against increased resistance; also called strength training, fibers parallel to long axis of organ; contraction dilates and shortens, fibers in circumference of organ; contraction --> constricts lumen, elongates organ, numerous bulbous swellings in the nerve fibers, indentations in sarcolemma; may act like T tubules, tethered to the sarcolemma, act as anchoring points for thin filaments and therefore correspond to Z discs of skeletal muscle, allows a hollow organ to fill or expand slowly to accomodate a greater volume without promoting contractions that would expel their contents, unitary smooth muscle; arranged in opposing sheets, innervated by variscosities, contract as a unit, respond to various chemical stimuli, in the large airways to lungs and in large arteries, arrector pili, internal eye muscles; fibers are structurally independent, richly supplied with nerve endings, responds to neural stimulation with graded contractions that involve recruitment, stem cells that fuse to form each muscle fiber, David N. Shier, Jackie L. Butler, Ricki Lewis, Human Anatomy and Physiology Laboratory Manual, Elaine N. Marieb, Lori A. Smith, Susan J. Mitchell, Anatomy and Physiology: The Unity of Form and Function. What actually gets shorter in the muscle cell? The alignment of sarcomeres within the myofibril and then alighnment of myofibrils within the cell, cause the entire cell to appear striated. In rest, contractions of skeletal muscles produce up to 30% of the body heat. develop a visual knowledge of body structure at the cellular tissue organ system levels understand the SiO2+CheatSiC+CO(balanced?). Four years ago, Valero issued $5 million worth of debenture bonds having a bond interest rate of 10% per year, payable semiannually. Ca2+ is required to dislodge tropomyosin. Myofilaments are smallest and myofiber is largest. Smooth muscle is in walls of hollow organs, spindle-shaped cells, nonstriated, uninucleate, and involuntary. Its also possible to use Labster without an LMS. Smooth muscle is composed of sheets or strands of smooth muscle cells. Download Free Pearson Anatomy Physiology Lab Manual Answer Key Free Download Pdf laboratory manual for anatomy physiology pearson the anatomy of a virtual a p lab . The major proteins found in a sarcomere are F-actin and myosin (. It occurs with tropomyosin in the thin filaments of muscle tissue. . Follow the pathway that allows a nerve signal initiated in the brain to induce an actual muscle contraction in a skeletal muscle. The fixed point around which a lever pivots, fulcrum is between the out force and in force(OFI), in-force is between the out-force and the fulcrum(FIO), Skeletal Muscle: Learn about the muscles we u, Chapter 1: Introduction to the Human Body, Chapter 2: The Origin of Life, Basic Chemistr, Lecture 30: Drugs for the treatment of asthma, Lecture 29: Sex hormones and Gonadotrophins II, Lecture 28: Sex Hormones and Gonadotropins, Anatomy and Physiology: An Integrative Approach, Michael McKinley, Theresa Bidle, Valerie O'Loughlin, Human Anatomy and Physiology Laboratory Manual, Fetal Pig Version, Essentials Of Human Anatomy And Physiology, Hole's Essentials of Human Anatomy and Physiology, David N. Shier, Jackie L. Butler, Ricki Lewis. The tissue is highly cellular and is well supplied with blood vessels. Levers serve to ____________ muscle contraction. There are three major types of muscle tissues in the human body: skeletal, smooth, and cardiac muscle tissues. Engage students in science through interactive learning scenarios. d. mutable. Is smooth muscle voluntary or involuntary? Une fois vos informations traites et valides (la plupart du temps en quelques jours), la banque vous demandera de raliser un virement bancaire de du montant demand vers votre nouveau compte afin de l'activer. Skeletal Muscle Tissue To solve a math equation, you need to find the value of the variable that makes the equation true. Amazing if you don't want to wait for your teacher every time you get stuck. Study with Quizlet and memorize flashcards containing terms like types of muscle tissue, all muscle tissues consists of.., skeletal muscle consists of Learn step-by-step Learning a new skill can be daunting, but breaking the process down into small, manageable steps can make it much less overwhelming. muscle tissue an overview labster quizlet. All our simulations run on laptop and desktop computers, and you can play our simulations without having to install any browser plugins. If you're struggling with your math homework, our Math Homework Helper is here to help. Muscular thermoregulation-In rest, contractions of skeletal muscles produce up to 30% of the body heart. What is the relationship between the sarcolemma, T-tubules, and the sarcoplasmic reticulum (SR)? The A band does not change its length, but the I bands and H bands shorten which brings the Z bands closer together. There are three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle. Explore relevant bioscience simulations for nursing students. Apply cell theory Students will be introduced to each principle of cell theory and apply it to understand how the cellular organization of animal cells in the forest compares to algae . jogging, swimming, biking leads to increased: Skeletal muscle is attached to bones, has cylindrical cells, is striated, multinucleate, and voluntary control. muscle tissue an overview labster quizlet. Getting all the right answers, best app for math. a. constant What connective tissue layers are found in cardiac muscle? Mostly anaerobic metabolism is used. The H zone is a region in teh center of the A band composed of thick filaments only with the M line in the middle (visible only with TEM). Leiomyosarcoma is a rare type of cancer that begins in smooth muscle tissue. Myofibrils are composed of individual: sarcomeres striations myofilaments fascicles 2. Which of the following is NOT a function of muscle? Labster virtual labs also include quiz questions that accompany each lab. Follow the pathway that allows a nerve signal initiated in the brain to induce an actual muscle contraction in a skeletal muscle. What is the relationship between skeletal myofibers and capillaries? About this Simulation Regeneration sounds like a superpower, but some reptiles and amphibians are perfectly able to regrow entire parts of their bodies. Pick up the cellular 3D models and examine the nuclei, myofibrils, mitochondria and more to understand how the intracellular components enable each muscle cell to perform the functions characteristic for that muscle tissue. Two muscles involved in thermoregulation by generating heat and adjusting the distribution of blood flow? a section through the heart to observe its interior b examining the surface of a bone c viewing muscle tissue . Uses aerobic metabolism of fatty acids (decreased glycogen content) and is in postural muscles of neck and back. Smooth muscle tissue is found in many areas of the body, such as the digestive system, urinary system, blood vessels and uterus. You can take pictures of your Problems and it will give you every answer to the problem. Action potential in sarcolemma, then T tubules . What's that? which two contains desmosomes and gap junctions. The tissue in the human body is part which is going all around the human body. What structures or molecules occur in the following regions: I band, A band, H zone, M line? 4. Muscle is one of the four primary tissue types of the body, and the body contains three types of muscle tissue: skeletal muscle, cardiac muscle, and smooth muscle ( [link] ). The individual unit in the kidney increased ca2+ binds troponin, which displaces tropomyosin, thus exposing myosin binding site. They give limited ability for regeneration and possibly growth. james mcbride spouse 6 juin 2022. Silicon carbide, an abrasive, is made by the reaction of silicon dioxide with graphite (solid carbon). The major functions of muscle tissue are movement: body, parts, blood, and food; maintenance of posture (skeletal muscle); joint stability: shoulder/knee (skeletal); heat production-85% (skeletal). What is the structural relationship between thick and thin filaments in a myofibril cut in cross section? characteristics of smooth muscle -found in walls of gastrointestinal tract, blood vessels -nonbranched -no striations -1 nucleus -actin and myosin -no troponin and tropomyosin -not under voluntary control characteristics of skeletal muscle -voluntary -multi nucleated -nonbranched -found in muscles -contains actin, myosin, troponin, tropomyosin contain elastic proteins and provide anchoring for the thick filament. During exercise, the heat production increase up to 40x as much. A myofiber is made up of many myofibrils. Muscle fatigue is due to low ATP and increased lactic acid. The outermost connective tissue sheath surrounding the entire muscle is known as epimysium. Using the control panel to navigate the different models, you will have to collect information about the tissues to solve different scenarios related to the muscular system. Overview of Cardiac, Smooth, and Skeletal Muscle. In this simulation, you will take a closer look at the three distinct muscle tissues we find in the human body and what purpose they serve. and x.s.) What is the role of the nervous system in controlling heart beat? Muscle contraction is initiated by a signal sent by the central nervous system via a motor neuron. Choose your Learning Management System below: Congratulations! Classify each substance as either a reactant or product in the chemical reaction: ethanol, oxygen, water, carbon dioxide. The embyronic origin of skeletal muscle cells is the mesoderm. For short bursts of activty fast intermediate oxidative glycolytic fibers are involves (lla) which use aerobic and anaerobic metabolism and the major muscles of the leg are used. Did you know that you have more than 600 muscles in your body? There is an increased number of myofibrils per cell. What are the initial sources of energy for muscle cell contraction? How is the signal to contract passed the cardiac muscle cell is resistant to fatigue because of the large number of ___, they contain access to oxygenated blood via the ___. Myosin ATPase is going to help hydrolyze, meaning it will break down ATP. I love it, it helps me whenever I'm stuck on a problem and always has a solution, you don't even need to take a picture of the problem just type it in and you're all set. Interact with the anatomical 3D holograms to explore the distribution and main functions of skeletal, smooth, and cardiac muscle tissues. cardiac muscle tissue is only found in the ___? It can be expressed in terms of the carbon fixed by the sun for the entire system. (*could not find answer to third question?). exam 1 flashcards quizlet human anatomy physiology i lab online course university of north dakota p d f . Muscle weakness, loss of mobility or paralysis. How do smooth muscle cells differ from striated cells with respect to the role of T-tubules, tropomyosin, and attachment of thin fibers? Explore the distribution and function of the three different muscle tissues found in the human body. Holds thick filaments in place; helps recoil after stretch; resists excessive stretching, extends from Z discs to thick filament and runs within the thick filament to attach to M line; holds thick filaments in place, Links thin filaments to proteins of sarcolemma, an elaborate smooth endoplasmic reticulum; regulates intracellular levels of ionic calcium; stores calcium and releases it on demand when contracting, dilated end sacs of the sarcoplasmic reticulum, formed by t tubules that run between the paired teminal cisternae of SR; organelles come into closest contact here; encircle each sarcomere, states that during contraction the thin filaments slide past the thick ones so that the actin and myosin filaments overlap to a greater degree, a neural impulse; a brief electrical charge that travels down an axon; a large change in membrane potential that spreads rapidly over long distances within a cell, the neurotransmitter that motor neurons use to tell skeletal muscle to contract, opened by neurotransmitters; creates small local changes in the membrane potential, Channels that open or close in response to a change in the membrane potential; underlie all action potentials, point of contact between a motor neuron and a skeletal muscle cell; motor end plate, a gap into which neurotransmitters are released from the axon terminal, small membranous sacs containing neurotransmitter ACh, Sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments. All three muscle tissues have some properties in common; they all exhibit a quality called excitability as their plasma membranes can change their electrical states (from . Perform experiments in virtual lab simulations to achievecore science learningoutcomes. What are the functions of troponin and tropomyosin? Muscle capillaries Number of mitochondria Myoglobin synthesis Skeletal Muscle Fibers. 0-compliant courses. This article was last modified: Feb. 14, 2022, 2:05 p.m. Powered by django-wiki, an open source application under the GPLv3 license. Define the sliding filament theory of skeletal muscle contraction. Train staff and clients quickly, inexpensively, and with better outcomes-in a way that increases efficiency in the workplace. muscle contracts by performing several in vitro experiments and help your friend identify the . noter que vos revenus doivent remplir les conditions de l'offre laquelle vous souscrivez, si ce n'est pas le cas votre compte ne sera pas ouvert. Find and select the simulations that you want to add to your course. What is the function of the SR in skeletal muscle? Differentiate smooth, cardiac and skeletal muscle based on their microstructure. depolarization of sarcolemma causes increased cytoplasmic ca2+ from SR (via GPCR) and extracellular fluid (via voltage-gated channel). defines the boundaries of a muscle sarcomere and provide anchoring for the thin actin filaments. The connective tissue sheath covering each fasciculus is known as perimysium, and the innermost sheath surrounding individual muscle fiber is known as endomysium. (b) Determine I1,I2,IDI_1, I_2, I_{\mathrm{D}}I1,I2,ID, and ISI_{\mathrm{S}}IS Study with Quizlet and memorize flashcards containing terms like 3 types of muscle tissue, skeletal muscle tissue (all info), involuntary muscle tissues and, Study with Quizlet and memorize flashcards containing terms like striations, what are the 2 forms of muscle cells?, what is an alternate name for a skeletal. Skeletal muscle cells appear striated due to regular arrangements of two types of protein filaments in sarcomeres. This can occur through resistance exercises. At the end of this simulation, you will be able to. It has a relatively weak contractile force, but impressive durability. Which of the following changes when an unbalanced force acts on an object? There are two types of bone tissue: compact and spongy.The names imply that the two types differ in density, or how tightly the tissue is packed together. What structure joins adjacent cardiac myocytes, and what types of cell junctions occur in this structure? Structure of Bone Tissue. uses aerobic respiration almost exclusively to avoid fatigue, involved in controlling speech, gesticulation, facial expressions. Please fill out the form below to talk with one of our Lab Experts. Unique features of smooth muscle cells are that it stretches wihtout developing tension which is important for the bladder and the stomach. Each myofiber is in contact with one or more capillaries, which supply nutrients and oxygen and remove wastes. Describe the sliding filament mechanism in smooth muscle cells, pointing out the differences with skeletal muscle contraction, especially with respect to the role of calcium. Slow red oxidative fibers (type 1) have high myoglobin content, have mitochondria and capillaries, contract slowly and are for resistance to fatigue. What are the 2 general mechanisms by which an organ can increase in size, and which mechanism applies to enlarged skeletal muscles? release of Ca2+ from sarcoplasmic reticulum. What is the embryonic origin of skeletal muscle cells? involved in regulating blood glucose levels by absorbing a large portion of it. Dive into the molecular level and see how the myofibrils are arranged in repeating units of sarcomeres. Faites le virement ds qu'il vous est demand et ne l'oubliez surtout pas. Anaerobiosis is myofiber death in five minutes. aerobic and anaerobic metabolism is used, and they are in major muscles of the leg. In the Regeneration Biology simulation, you get to dissect axolotls and observe the cells responsible for the restoration of missing limbs under the microscope. The ___ ___ spreads across the muscle cell plasma membrane and enters into invaginations called ___.