Histological Features of Skeletal Muscle

Histological Features of penurious MuscleObjectivesThe aim of this report is to describe the basic histological features of a point slight vigour and the differences between type I and type II skeletal muscularity fibres. I will also describe the move neuron building block and explain Hennemans size principle of recruiting motor unit of measurements.ObservationsThe basic features of skeletal muscleGeneral Structure The important function of skeletal muscle is to provide support, carry posture and provide movement. Skeletal muscles comprise of densely packed groups of elongated cells which argon known as muscle fibres, which are held together by stringy connective tissue. Many capillaries penetrate this tissue to enable muscles to be supplied with oxygen and glucose needed for muscle contraction. Skeletal muscle is comprised of bundles of long striated fibres the striated appearance is caused by the perennial structure of the fibres inside the muscle cell (Page, 2001). Indiv idual muscle cells are called myocytes and muscles are made up of bundles of individual muscle cells. These bundles are called fascicles. Each muscle cell is surrounded by a connective tissue cover called the endomysium, and each bundle is surrounded by a connective tissue screening called the perimysium. Fascicles form muscle which is surrounded by a connective tissue called the epimysium.Skeletal muscles are made up of three types of fibres. Type I (red/ dimmed fibres), type IIa (red/ fast fibres) and type IIb (white/ fast fibres). Type I fibres are slow-contracting muscle fibres and they have a very dense capillary tube network, because these fibres have a high capacity for ATP production and a low myosin ATPase activity compared to type II fibres the main pathway for ATP production is aerobic cellular respiration. Type IIa fibres have a high myosin ATPase activity than type I fibres, a high capacity for ATP production and a dense capillary network because of this the main pa thway for ATP production is aerobic cellular respiration. Type IIa also has high levels of intracellular myoglobin. Type IIb fibres have a higher myosin ATPase activity than type I fibres but a lower capacity for ATP production and a lighter capillary network this means that the main pathway for ATP production is anaerobic glycosis, which is fast but not sustainable for as long as aerobic respiration which means muscle fatigue happens sooner. There is no intracellular myoglobin unlike type I and IIa, which means that it is white in colour (Types of skeletal muscle Fibres, 2016).The structure of the sarcomereThe germ plasm membrane of the skeletal muscle fibre is the sarcolemma and contains cylindrical structures called myofibrils. The myofibrils practically fill the cells and push the nuclei to the edges of the cell. Each myofibril have light and dark bands and are aline with each another(prenominal) so that the light and dark bands are next to each other this gives the cells the ir striated appearance. The light bands are called I bandsand the dark bands are called A bands. In the middle of the I bands there is a line which is called the Z line and in the middle of the A bands there is a light govern called the H zone. In the middle of the H zone there is another line called the M line. The sarcomere consists of several individual protein elements and some of these proteins are thread-like proteins called myofilaments.There are two main types of myofilaments. The thick myofilaments which are made up of proteins molecules called myosin. The myosin molecules are shaped like golf game clubs with long shafts. Myosin forms the thick myofilaments by forming bundles in which the heads of the golf clubs stick out at either end of the filament and the shafts form a bare zone in the middle of the filaments. The heads of the thick myofilaments form attachments with the other type of myofilaments, the thin actin myofilaments and these attachments are called cross brid ges.The heads are the areas on the thick myofilaments that use the energy in the ATP molecule to power the muscle contraction. The foster type are the thin myofilaments, which are made of the protein actin. They have binding sites to which the heads of the thick myofilaments attach (Hwang, 2015).The triadA triad is a structure that is organize from a T-tubule with a sarcoplasmic reticulum known as the terminal cisternae on either side. Each skeletal muscle fibre has many thousands of triads, visible in muscle fibres that have been sectioned longitudinally (Al-Qusairi Laporte, 2011).Table 1 Comparison of the different types of skeletal muscle fibres(Bushell, 2013)The structure of a motor unitA motor unit is made from a motor neuron and the skeletal muscle fibres innervated by that motor neurons axonal terminals (Purves, et al., 2001). A group of motor units is called a motor pool and the twist of fibres in each unit can differ within muscles. This impacts precision and attract g eneration. Differential initiation of single or multiple motor units with a motor pool can therefore control precision and legions of movement.Hennemans size principle of motor unit recruitmentHennemans size principle states that motor units are recruited from smallest to largest and as more force is needed, motor units are recruited in a certain order per the extent of their force output. This means that the smaller units are recruited first which means that it reduces the amount of fatigue an organism experiences by only using fatigue resistant muscle fibres, unless a higher force is needed and then fatigable fibres are used. This means that slow twitch, low-force, and fatigue resistance muscle fibres are activated before fast twitch, high-force, less fatigue resistant muscle fibres (Bawa, Jones, Stein, 2014).The motor unit and the Hennemans size principle of motor unit recruitment The structure of the motor unitA motor unit is constructed from a motor neuron and skeletal muscl e fibres, they innervated by the axonal terminals (Purves, et al., 2001). The motor neuron and its muscle unit are inseparable in function, this is because the action potetial in the neurons activates the fibres of the muscle unit (Karpati, 2010). A group of motor unit are gathered in columnar, spinal nuclei and this is called motor neuron pools. The number of fibres in each unit can differ from another and this then affects the force generation and the precision of the movement (Present, 1997).The Hennemans size principle of recruiting motor unitThe Hennemans size principle expresses that motor units that are recruited from the smallest to the largest, this is because if more force is needed, then are recruited in a certain order due to the extent of their force output. Therefore, this means that the smallest motor units are employed first and this reduces the amount of fatigue that an organism experiences, by only using fatigue resistant muscle fibres, unless a higher force is nee ded, then fatigable fibres are used (Bawa, Jones, Stein, 2014).ReferencesAl-Qusairi, L., Laporte, J. (2011). T-tubule biogenesis and triad formation in skeletal muscle and implication in human diseases. Skeletal Muscle, 1(1). doi10.1186/2044-5040-1-26Bawa, P., Jones, K., Stein, R. (2014). Assessment of size ordered recruitment. 8. Retrieved from https//www.ncbi.nlm.nih.gov/pmc/articles/PMC4112781/Bushell, D. (2013). Muscle-specific hypertrophy Chest, Triceps and shoulders. Retrieved from TheGymLifestyle http//blog.thegymlifestyle.com/muscle-specific-hypertrophy-chest-triceps-shoulders/Hwang, P. (2015). Targeting the sarcomere to correct muscle function. Nature Reviews Drug Discovery, 14(5). doi10.1038/nrd4554Page, M. (2001). Human body An illustrated guide to every articulation of the human body and how it works. (A. Baggaley, Ed.) London Dorling Kindersley Publishers.Purves, D., Augustine, G., Fitzpatrick, D., Katz, L., LaMantia, A.-S., McNamara, J., Williams, M. (2001). The M otor Unit. Sinauer Associates. Retrieved from https//www.ncbi.nlm.nih.gov/books/NBK10874/Types of skeletal muscle Fibres. (2016). Retrieved from Ivy Roses http//www.ivyroses.com/HumanBody/Muscles/types-of-skeletal-muscle-fibers.php