Neural muscular system Topic 3A: Characteristics and functions of different muscle fibre types for a variety of sporting activities Term Muscle fibre Slow twitch (type I) Fast oxidative glycolytic (type IIa). Identify The main characteristics of the fibre type and type of athlete suited to this fibre type There are three main types of skeletal muscle fibre that can be identified in the human body. Slow oxidative (type 1) also known as slow twitch Fast oxidative glycolytic (type IIa) Fast glycolytic (IIb) Red in colour High myoglobin and mitochondrial content More capillaries per fibre Energy from aerobic pathways High resistance to fatigue Slower energy release Contact slowly Produce less overall force Smaller in size Suited to long lasting activities such as distance running or cross country skiers. Red in colour Fast conduction speed High amounts of force produced Larger in size and a larger motor neurone More resistant to fatigue than type 2b Medium levels of myoglobin content, mitochondrial and capillary density. High anaerobic capacity Explain the characteristics Our skeletal muscles contain a mixture of all three types of fibre but not in equal proportions. Our mix of muscle fibres is mainly genetically determined. The relative proportion of each fibre type varies in the same muscles of different people. For example, an elite endurance athlete will have a greater proportion of slow twitch muscle fibres in their leg muscles, whilst an elite sprinter will have a greater proportion of fast twitch muscle fibres in their leg muscles. This can explain why particular people are most suited to particular sports. Someone with a high % of fast twitch muscle fibres in the leg muscles would be better suited to sprinting for example. Our postural muscles tend to have a greater proportion of slow twitch muscle fibres as they are involved in maintaining body position over a long period of time. Endurance training increases the aerobic capacity of ST fibres. High intensity anaerobic training causes increases in the size and length of FT fibres. A lack of training causes atrophy Slow twitch muscle fibres are red in colour due to the presence of high levels of myoglobin, mitochondria and therefore oxygen. Oxygen combines to myoglobin in the muscle which stores and transports oxygen to the mitochondria where energy production occurs. Due to high levels of myoglobin, mitochondria and capillary density, slow twitch muscle fibres are able to exchange and store more oxygen making them suitable for aerobic activity. Slow twitch muscle fibres have a high aerobic capacity and are more resistant to fatigue, this is linked to the greater number of blood capillaries for the delivery of oxygen per fibre and the ability to remove by-products such as carbon dioxide. Slow twitch muscle fibres are smaller in size, have less fibres per motor unit and contract slowly, this means they produce less force in comparison to fast twitch muscle fibres. Slow twitch muscle fibres contain approximately 10-180 fibres per motor neurone. Slow twitch muscle fibres are suited to aerobic activities lasting long periods of time such as distance running or cycling. Fast oxidative glycolytic fibres (FOG) have approximately 300-800 fibres per neurone and have a larger neurone size and fibres are larger in size, this allows them to generate more force compared to slow twitch muscle fibres. FOG fibres are red in colour as they contain a moderate levels of myoglobin and mitochondrial and are therefore more resistant to fatigue compared to fast glycolytic fibres but less when compared to slow twitch muscle fibres. They manufacture and split ATP at a fast rate by utilising both aerobic and anaerobic metabolism and so produce fast, strong muscle contractions.
Suited to activities such as a 1500 m running. FOG fibres are predominantly used for short high intensity events such as a 400 m swim or 1500m run. Fast glycolytic (type IIb). White in colour Fast contractile speed Produce high amounts of force Large in size and large motor neuron size Low oxidative capacity Fatigue quickly Low myoglobin content, mitochondria density and capillary density. Produce energy anaerobically High anaerobic capacity Suited to activities such as a sprinter or weightlifter Fast glycolytic fibres (FG) are white in colour due to a low presence of myoglobin and few mitochondria. FG fibres contain approximately 300-800 fibres per motor neurone. FG fibres are larger in size and have a larger and thicker motor neurone and therefore able to produce high amounts of force. They produce ATP rapidly by anaerobic metabolism and break it down very quickly. This results in short, fast bursts of power and a rapid contractile speed. Due to the low presence of myoglobin and mitochondria, they fatigue quickly and have a low aerobic capacity. FG fibres are suited to high intensity activities of short duration such as sprinter or weightlifting. Muscle fibre type comparison table Comparison variable Type 1 Slow oxidative Type 2a Fast oxidative glycolytic Type 2b Fast glycolytic Fibres per neurone 10-180 300-800 300-800 Contraction speed Slow Fast Very fast Force production Low High Very High Diameter of muscle fibre Small Medium Large Aerobic capacity High Medium Low Resistance to fatigue High Medium Low Capillary density High Medium Low Mitochondrial density High High Low Main metabolic pathway for ATP Aerobic Aerobic and anaerobic Anaerobic
Topic 3B: Nervous system Cardiovascular system progress chart Sympathetic Nervous system responsible for fight or flight and preparing us before and during exercise. Parasympathetic Nervous system responsible for rest and digest, slowing down bodily functions. Sympathetic stimulation increases during exercise. Parasympathetic stimulation decreases during exercise and increases after exercise. The sympathetic nervous system could be considered the pedals. The sympathetic nervous system is responsible for fight or flight. During exercise the sympathetic nervous system is stimulated resulting in the release of adrenaline and noradrenaline. These hormones increase breathing rate, heart rate and promote the redistribution of blood. The parasympathetic nervous system could be considered the brakes. The parasympathetic nervous system is responsible for slowing things down. During exercise parasympathetic nervous stimulation decreases and post exercise it increases resulting in the release of acetylcholine. The autonomic nervous system (ANS) regulates the function of our internal organs and controls our skeletal muscles. The ANS is involuntary, which means things take place without us noticing. The sympathetic and parasympathetic nervous systems are both branches of the ANS. The movement of our muscles is controlled by the ANS via nerves (motor neurones). The neuromuscular system is where the nervous system and the muscles work together to create movement. The neuromuscular system makes up part of the ANS. Changes in the neuromuscular system takes place before, during and after exercise to meet the changing demands of different intensities. A motor unit consists of a motor neurone and the muscle fibres it stimulates. When a motor neurone is stimulated via the nervous system, this results in the muscle fibres within that motor unit being stimulated, as long as a minimum threshold is met, causing muscles to contract. Topic 3C: Role of proprioceptors in PNF What is PNF Proprioceptive Neuromuscular Facilitation (PNF) is a advanced form of flexibility training that involves both the stretching and contraction of the muscle group being targeted. PNF stretching was originally developed as a form of rehabilitation and is excellent for targeting specific muscle groups as well as increasing flexibility and assisting muscular strength development. During PNF stretching an isometric stretch is completed just before a passive stretch to achieve autogenic inhibition. Muscle spindles located within muscle cells, protect the muscles from injury, they sense how fast/far a muscle is being stretched and when activated initiate the stretch reflex, causing the muscles to contract and prevent overstretching. The Golgi tendon organ (GTO) senses how much tension is being placed on a tendon. When the GTO is activated it relaxes the muscles. Autogenic inhibition is reflex relaxation that occurs in the same muscle where the GTO is stimulated. Stretch > muscle spindles detect stretch >stretch reflex prevents overstretching >Hold isometric contraction> golgi tendon organs senses tension > send signals to brain > CNS relaxes antagonistautogenic inhibition > allows greater range of movement Proprioceptors Sensory organs in the muscles, tendons and joints that inform the body of the extent of movement that has taken place. Muscle spindles and golgi tendon organs are types of
proprioceptors. Muscle spindles Very sensitive proprioceptors that lie between skeletal muscle fibres. Provide information to the CNS about how fast and how far a muscle is being stretched. Also known as stretch receptors, they provide information to the CNS about how fast and how far a muscle is being stretched. The CNS then sends an impulse back to the muscle signalling it to contract, which triggers the stretch reflex. This reflex action causes the muscle to contract to prevent over stretching reducing the risk of injury. Golgi tendon organ These are found between the muscle fibre and tendon. Detect levels of tension in the muscle They detect levels of tension in the muscle. When the muscle is contracted in PNF they sense the increase in muscle tension and send signals to the brain which allows the antagonist muscle to relax and lengthen. This is known as autogenic inhibition Topic 3D: The recruitment of muscle fibres Motor units A motor unit comprises of a motor neuron and all of the muscle fibers that it stimulates. All or none law A minimum amount of stimulation (threshold) is required to activate the muscle fibres. During exercise more motor units in the muscles are recruited. Slow twitch muscle fibres will be recruited during activities such as jogging whereas fast twitch motor units will be recruited for activities such as sprinting or power lifting. More powerful contractions require the recruitment of more motor units, less powerful contractions will result in the recruitment of less motor units. Slow twitch motor units have a smaller motor neurone and each unit activates approximately 10-180 muscle fibres. Fast twitch motor units have a larger and thicker motor neurone and activates approximately 300-800 fibres resulting in a more forceful and quicker contractile time. Muscle fibres are grouped together into motor units. A motor unit consists of a motor neurone and the muscle fibres it stimulates. Within a muscle there are many motor units.only one type of muscle fibre can be found in one particular motor unit. Muscle fibres work with the nervous system so that muscular contractions can occur. One motor neurone cannot stimulate a whole muscle, it is only capable of stimulating the muscle fibres within its unit. The motor neurone transmits the nerve impulse from the CNS to the muscle fibre. Each motor neurone has branches that end in the neuromuscular junction on the muscle fibre. The point where the motor neurone meets the muscle is known as the motor end plate. Muscle fibres work with the nervous system so that a contraction can occur. In powerful actions such as jumping as high as you can, more motor units are recruited resulting in a more powerful contraction. In small movements such as blinking, less motor units will be recruited. In order for muscle fibres to contract, a minimum amount of stimulation is required. If a nerve impulse meets or exceeds the minimum threshold then all the muscle fibres within a motor unit will contract. However, if the minimum threshold is not met then none of the muscle fibres within a motor unit will contact, hence the name all or none law!
Spatial summation The strength of a muscle contraction depends largely on the number of units recruited and the size of the units involved. To create a greater force of contraction the brain recruits more and larger motor units. Increased likelihood of spatial summation Occurs when nerve impulses are received at the same time at different places within the muscle, which add up to fire up more neurones. The strength of a contraction can change by altering the number and size of the muscles motor units which are stimulated. If you recruit additional or bigger motor units within a muscle, the muscle will contract with more force. Wave summation Refers to the frequency of stimuli and frequency of impulse. When rapid firing of stimuli occurs this increases the strength of contraction. Increased likelihood of wave summation An increase in the frequency of stimuli and impulses result in an increased strength of contraction. If a stimulus quickly follows the previous stimulus, thus not allowing sufficient time for fibers to relax, this results in a greater force being generated. Wave summation is when there is a repeated nerve impulse with insufficient time for the muscle to relax, resulting in a more forceful contraction. Tetanic A tetanic contraction is when a sustained muscle contraction is caused by a series of fast repeating stimuli. Increased likelihood of tetanic summation A tetanic contraction occurs when a muscle's motor unit is stimulated by multiple impulses at a high frequency. Each stimulus causes a twitch. If stimuli are delivered at high frequency, the twitches will overlap, resulting in a tetanic contraction. A tetanic contraction can be either unfused (incomplete) or fused (complete). An unfused tetanus is when the muscle fibers do not completely relax before the next stimulus because they are being stimulated at a fast rate, Fused tetanus is when there is no relaxation of the muscle fibers between stimuli and it occurs during a high rate of stimulation. A fused tetanic contraction is the strongest single-unit twitch in contraction. When tetanized, the contracting tension in the muscle remains constant in a steady state.