Types of Tissue Part 3: Muscle Tissue

Types of Tissue Part 3: Muscle Tissue

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hey it's professor Dave let's talk about muscles when you hear the word muscle what comes to mind you might think about the muscles in your legs that help you to run fast or maybe bodybuilders working on their biceps in the gym these muscles belong to a particular type of muscle called skeletal muscle but we actually have three different types of muscles in our bodies and the other two
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are not as obvious in addition to skeletal muscle humans also have cardiac muscle and smooth muscle so let's discuss all three of these types right now first what these different types of muscle have in common is that they are all vital for movement muscle tissue is predominantly comprised of muscle cells and these are highly specialized for a process called contraction which is what
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allows for mobility the three types of muscles are quite different in their functions but there are some similarities in their structure so let's go through them one at a time let's start with skeletal muscle as it's the most abundant these are the muscles that cover our skeleton and give our body its shape the exact number of skeletal muscles in the body is not precisely known but it's thought to be over 650 these attached to bones either
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directly or via connective tissue called tendons and they are responsible for a variety of functions skeletal muscles produce voluntary movements which are the ones that are under our control this includes simple movements like extending limbs or more coordinated movements like running or swimming and they achieve this by pulling on the bones of the skeleton our skeletal muscles also maintain our posture when you're sitting
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down it might feel as though you're totally relaxed but in actuality many of these muscles are constantly working by making small adjustments to maintain your sighs body position skeletal muscle even forms sphincters in the digestive and urinary tracts to allow for the control of actions such as swallowing and urination beyond these functions they help us maintain optimal body temperature by releasing heat as a
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byproduct of muscle contraction so what makes up skeletal muscle we will see that skeletal muscle is different from the cardiac and smooth muscles that will be examined later in that skeletal muscle cells are multinucleated this means they have multiple nuclei cells called myoblasts which have one nucleus each fused together to form a long cylindrical multinucleated cell called a muscle fiber with its nuclei located
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at the periphery and this is surrounded by a sheath of connective tissue called the endemism inside each muscle fiber are many myofibrils and these contain myofilaments which are themselves organized into units called sarcomeres these are the contractile machinery which actively shorten and are therefore responsible for skeletal muscle contraction it is also these sarcomeres that give skeletal muscle a striated or
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striped appearance and they are the smallest functional unit in the muscle the myofilaments within are of two types thinner actin filaments and thicker myosin filaments and the sliding of these filaments past one another is what produces contraction which we will discuss in more detail later so that's what a muscle fiber is made up of now zooming out from there each muscle fiber is arranged into a bundle of muscle
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cells called a fascicle which is surrounded by a layer of fibrous connective tissue called the Paramecium and multiple muscle fascicles will in turn group together to form an even larger structure which is surrounded by a layer of dense irregular connective tissue called the epimysium this group of fascicles along with blood vessels nerves and all the tissue comprise an entire skeletal muscle and these will span joints and
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attach to bones in at least two places attachments can be direct where the epimysium of the muscle is fused to the periosteum of a bone or perichondrium of a cartilage or it can be indirect where the muscles connective tissue extends beyond the muscle as a rope like tendon or a sheet like aponeurosis which anchors to a skeletal element or other muscles for a skeletal muscle to be able
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to contract it needs to be activated or innervated by neurons in the central nervous system and in particular the somatic nervous system which essentially means the voluntary nervous system we will learn about the nervous system a little bit later for now we can just understand that skeletal muscle is the only muscle type under voluntary control which means these are the muscles that move when we decide to move them now
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let's move on to cardiac muscle cardiac means relating to the heart so as one might guess cardiac muscle is only found in the heart and cardiac muscle cells are called cardiomyocytes there is just one role for cardiac muscle and that is to contract in order to push blood out of the heart to the rest of the body which will supply two shoes around the body with vital oxygen and nutrients cardiac muscle is similar to skeletal
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muscle in the sense that they also have a striated appearance which is due to being comprised of myofibrils and sarcomeres for contractility however cardiac muscle is different from skeletal muscle in other ways cardiac muscle cells are short branched cells which is a structure that allows them to communicate with other cells and they typically have one or maybe two centrally located nuclei in between each cardiomyocyte there is an
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intercalated disk which contains gap junctions these gap junctions allow the electrical stimulus that is required for contraction to rapidly spread across the cardiac tissue by allowing ions to move from one cell to the next this means that the cardiomyocytes can contract in a coordinated fashion allowing the heart to work as an efficient pump another difference from skeletal muscle is that we do not
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voluntarily contract the muscles in our heart meaning that we don't consciously think about our heartbeat it just happens automatically this means that our cardiac muscle is innervated by the autonomic nervous system which regulates the speed at which electrical stimuli are generated by specialized cardiac muscle cells called pacemaker cells more on the autonomic nervous system later lastly let's take a look at
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the third type of muscle tissue known as smooth muscle smooth muscle is found in most of our organs and it contracts to regulate many of our bodily functions as we go about our daily business smooth muscle in blood vessel walls will contract or relax to regulate blood pressure and the distribution of blood to our different organs it is present in our Airways to allow more or less air to pass through it contracts in the walls
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of our digestive tract to push material along the smooth muscle in our bladder contracts to expel urine out of the body and has numerous functions in the reproductive system including contraction of the walls of the uterus to push a baby out of its mother during childbirth smooth muscle is typically organized into two layers first a longitudinal layer where a muscle fibers run parallel to the long axis of the organ such that contraction will dilate and shortened
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organ then there is a circular layer where muscle fibers run around the circumference of the organ such that contraction will constrict and lengthen the organ when these layers alternate contraction it can push material through the organ a process called peristalsis similarly to cardiac muscle smooth muscle is innervated by the autonomic nervous system so it contracts and Laxus automatically smooth muscle cells
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also have a single centrally located nucleus but they have a different shape than cardiomyocytes the cells are short but spindle shaped which is referred to as fusiform interestingly smooth muscle differs from skeletal muscle and cardiac muscle because it is not striated due to the lack of myofibrils and sarcomeres there myofilaments are scattered throughout the cytoplasm of the muscle
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cells instead so with that we now know a bit about the three different types of muscle tissue those being skeletal muscle cardiac muscle and smooth muscle we can clearly see how these three types are quite different in terms of functionality but remarkably they are all extremely similar in structure now that we have a decent grasp on the structure of a muscle let's talk about muscle contraction on the molecular level so that we can better understand
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this incredible process thanks for watching guys subscribe to my channel for more tutorials support me on patreon so I can keep making content and as always feel free to email me professor Dave explains at gmail.com [Music]

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