Functional Anatomy of Skeletal Muscles | PES Year 12 PDF

PES Year 12 Functional Anatomy Structure of skeletal muscle Are attached to the skeleton by tendons They link two bones 2 different types of skeletal muscle Slow twitch (red) used for duration events Fast twitch (white) used for speed and power events Diagram of muscle fibers and muscles Des...

PES Year 12 Functional Anatomy Structure of skeletal muscle Are attached to the skeleton by tendons They link two bones 2 different types of skeletal muscle Slow twitch (red) used for duration events Fast twitch (white) used for speed and power events Diagram of muscle fibers and muscles Description automatically generated with medium confidence  Muscle belly is suraounded by an epimysium Muscele bellyis made up of bundles of muscle fascicles Each fascicle has individual muscle fibres, sourounded by an endomysium Each fibre is arranged into myofibrals , running parralel to eachotherand the length of the muscle fibre Myofibrils contain a chain of sarcomeres, which are composed of actin and myosin filiments responsible for creating movement When a muscle contracts it pulls on one of two bones it is connected to Movement is created when a muscle changes length The length of a muscle is changed when the myofibril changes length Myofibrils are made up of many sarcomeres joined end to end Sarcomere are the unit between the two z-lines and is the the functional unit of a muscle fibre Actin Thin protean filament attatched to z-line Cross bridges on the myosin attatch to the actin when stimulated by the release of calcium Myosin The thick protean filament contains cross bridges. the myosin cross bridge s attatch to the actin when stimulated by calcium z-line found at either end of the sarcomere, they come closer in concentric contractions and expand during eccentric contractions cross bridges tiny progections from myosin filiments that attatch temporarily to actin filiments, pulling the actin forward H-zone The space between the actin filaments, which get longer or shorter as the sarcomere changes length I-band The light band that contain thin actin filament In a relaxed muscle, the thin filaments do not completely overlap the thick myosin filaments A-band Contains both thick and thin filiments and is the center of the sarcomere that spans the h-zone Sliding Filement Theory A theory used to explain the mechanisum of muscle contraction based on the interaction of actin and myosin filaments to generate movement 1. A neuromechanical stimulation releases calcium from the sarcoplasmic reticulum into the sarcomere 2. This causes the actin filiments to reveal a binding site for the myosin head to connect (due to calcium binding to troponin to reveal a binding site for the myosin head to connect) 3. Myosin head brings the actin filiments, creating a cross bridge 4. Breakdown of ATP releases energy to stimulate the myosin cross bridges to pull the actin filiments towards the midline of the sarcomere 5. This results in the shortening of the sarcomere as the actin and myosin filiments slide over eachother, causing the z-lines to come closer together and the h-zone to shorten 6. Shortening each sarcomere shortens the myofibril, resulting in the shortening of the muscle fibres and movement occurs 7. Cross bridges attatch and reattatch at different times to create movement and maintain tension 8. The prosses keeps repeating if the neural impulse is present or the muscle relaxes if the neural impulse ends When drawing the sliding filliment theory draw two sarcomere One at rest (long) One when contracted (short) Contraction is initiated by the release of calcium into the muscle -------------------------------------------------------------------- ----------------------- ------------------------ Eccentric contraction Concentric contraction Distance between z-lines increases decreases Size of h-zone increases decreases I-band increases decreases A-band Stays the same Stays the same Sarcomere length increases decreases Myofibril length increases decreases Muscle fibre length increases decreases Muscle length increases decreases Nervous control of the muscular system Before the the muscle contracts to produce movement, the muscle fibres must be stimulated by a nerve or electrical impulses sent from the brain. Brain send a message in the form of an action potential to the spinal cord Spinal cord spinal cord is responsible for the transmission of the message between the brain and the muscle, and muscle to the brain Motor neuron receive the message / action potential form the spinal cord and delivers it to the targeted muscle and where movement occurs Sensory neurons sends messages back to the brain via the spinal cord Brain analyses the information delivered by the spinal cord to determine the next action then the process repeats 3 key functions of the nervous system Through sense organs and sensory nerves, it receives information about changes in the body and the environment, it sends this information to the brain The brain determines a suitable response The brain sends commands to muscles to carry out the selected response Nervous system is split up into two parts, the central and peripheral nervous system  Central nervous system Brain and spinal cord are the main parts of the CNS Spinal cord is used for delivering messages from the brain to the body, and from the body to the brain The brain analyses messages received from the sensory neurons It determines the most suitable response, then sends a message to the targeted muscle via the spinal cord and peripheral nerves to contract, creating movement Peripheral nervous system The remainder of the nervous system, it includes sensory neurons and motor neurons, which transmit messages to and from the CNS The PNS is made up of the sensory division and the motor division Sensory is made of sensory neurons Motor is made of motor neurons Information received by the environment by the eyes, ears, taste and smell goes strait to the brain bypassing the spinal cord Motor neurons are made of three parts Dendrites, they act as an antenna to detect the impulse from the sensory receptors and deliver it to the cell body Cell body, it contains the nucleus which directs the neurons activities and sends the messages to the axon Axon, transmits the message away from the cell body to the muscle Motor neurons attach to muscles at the motor end plates The neural impulse is transmitted to the muscle, initiating the process of muscle contraction  Motor units The motor neuron and the fibres it activates are called a motor unit A whole muscle contain many different motor units, which allows the muscle to generate different amounts of force Muscle fibres need to be stimulated by nerves or electrical impulses sent via motor neurons or nerves to contract For this to take place 1. A message is sent from the brain in the form of an action potential (electrical impulse) down the spinal cord 2. The action potential is detected by the dendrites of motor neurons, which send the information to the body 3. The cell body directs this information down the axon to the motor end plate 4. The action potential is delivered to the targeted muscle, which is innervated as long as the signal is strong enough Size of motor unit The number of muscle fiberes within each motor unit an vary, some have small ammounts where as some have thousends The smaller a motor unit the more precise the action of the muscle The larger a motor unit requires a larger action potential and results in the creation of a gross motor skill A motor unit requires a action potential ti reach a certain threshold before it will activate If it dosnt reach the requires threshold the muscle will. Not contract If the impulse reaches the required threshold, all the muscle fibres in the motor unit will contract at 100% of its capacity Decreasing weight/ sise will affect how many motor units are required All of none law Motor unit requitement Refers to the increasing number of motor units firing to increase the force being generated. Motor units are requited in order depending on exercise intensity Slow twitch (type 1) have low activation levels, and are requited first for light to moderate activity Higher threshold motor units (type 2a) are requited as exercise intensity increases, the slow twitch fibres are still activated When generating peak force, motor units that generate the greatest forces (type 2b) and have the highest stimulus threshold are requited. Slow twitch and 2a motor units are still being activated due to the size of the stimulus. 15 k run - low sustained force required, low intensity stimulus sent will innervate motor units containing type 1 units, the stimulus is not strong enough to activate type 2 muscle fibres 800m -- a sustained high intensity event where type 1 fibres are not able to provide enough force, the brain sends a higher intensity signal to the muscles and will innervate type 2a fibres, the signal is not intense enough to innervate a large % of type 2b fibres 100m -- maximum force required over a short distance, brain sends an even larger stimulus which innervates motor units containing type 2b fibres to generate maximum force, type 1 and 2a are also activated due to the size of the stimulus Force from a muscle can be increases in two ways Bigger stimulus or more frequent stimuluses Muscle fibre type Type 1 'slow twitch' -- red Purely aerobic and are suited to events which require continuous activity Slow contraction speed, used for endurance exercises, it uses the aerobic system and is fatigue resistant Small diameter, can be stimulated by a small neuron Type 2a 'Fast twitch' -- white Partially aerobic and are suited to events that require both aerobic and anaerobic qualities Intermediate speed of contraction, moderate force of contraction (more than type 1 but less than type 2b), fatigue resistant (less than type 1) Intermediate size diameter, can be stimulated by intermediate sized neurons Type 2b 'Fast Twitch' -- white Purely anaerobic and are suited to events that require explosive movements Large cross-sectional area which allows for greater muscle force and power tp be generated, high force of contraction, rapid speed of contraction used for speed strength and power-based activities Large diameter, needs a large neuron to stimulated it Role of genetics People are given a specific amount of red and white fibres that are genetically determined and cannot change An athlete with more fast twitch fibres will be better at explosive events An athlete with more slow twithc fibreswill be better at endurance events Fibre type Type 1 Type 2a Type 2b ----------------------- ---------------------------- --------------------------------- --------------------------------- Colour red white white Contraction time slow fast Verry fast Force production small high Verry high Fibre diameter small intermediate large Resistance to fatigue high medium low Activity type aerobic Long term anaerobic Short term anaerobic Sise of motor neuron small large Verry large Capillary density high intermediate low Mitochondrial density high intremediate low Oxidative density high moderate low Glycolic capacity low high high Major fuel source Triglycerides and glycogen Creatine phosphate and glycogen Creatine phosphate and glycogen Force velocity -- the relationship between force production and the velocity of the movement The muscle can create a large force with a decrease in the velocity of the concentric contraction More force is generated during the concentric contraction going slowly as it is able to recruit more motor units, giving the sarcomere more time to fully contract A diagram of a graph Description automatically generated Force length -- the amount of muscle force that can be produced at varying muscle lengths The length of a muscle will affect the amount of force it can generate, muscles will generate less force when contracted and lengthend past their optimal lengths The greater amount of cross bridges that can be formed the greater force can be generated