The Muscular System EQS 110

Transcription

1 The Muscular System EQS 110

2 Table of Contents Click on the different sections of the table of contents to jump through this document Function of Muscles... 3 Types of Muscle Tissues... 3 Smooth Muscle... 3 Cardiac Muscle... 3 Skeletal Muscle... 4 Deep & Superficial... 4 Muscle Movement... 5 Muscle Fiber Types... 5 Slow Twitch... 5 Fast Twitch... 5 Flexors & Extensors... 6 Sphincters... 6 Cutaneous... 6 Management of Muscles Tying Up... 7 What is Tying Up?... 7 Types of Tying Up... 7 Signs of Tying Up... 8 Causes... 8 Treatment of Tying Up... 8 Management of Tying Up... 9 Dietary Management... 9 Exercise Management... 9 Effect on Performance... 9 Self-Knowledge Checks Answers Glossary... 12

3 Function of Muscles The muscular system of the horse forms the largest tissue mass in the body and is responsible for controlling every aspect of movement, both internal and external. In addition to movement, muscles also function to: Produce heat Maintain posture Types of Muscle Tissues The horse s muscular system can be broken down into three types of tissue: Smooth Cardiac Skeletal We will look at each of these muscle types individually, placing the largest focus on the last category, skeletal muscle. Smooth Muscle Smooth muscle is an involuntary muscle which functions automatically. It surrounds all internal tissues and organs and responds to stimuli from the nervous system. Smooth muscle can be found in areas of the body that do not require conscious control, such as the urinary tract and digestive system. Cardiac Muscle Cardiac muscle is also an involuntary muscle but its function is to coordinate the propulsion of blood in and out of the heart. With the heart beating around 100,000 times a day throughout a horse s lifetime, this muscle is fatigue resistant. For a racehorse, proper development of cardiac muscle through training is crucial for performance!

4 Skeletal Muscle Skeletal muscle is a voluntary muscle responsible for external movement as well as: Maintaining posture Controlling range of movement Protecting from trauma Thermoregulation A horse has over 700 different skeletal muscles! Muscles are able to produce movement via tendons, a type of connective tissue that attaches muscles to bones. Muscles are then signaled to contract via nerve impulses. Relaxation occurs when the nerve impulses cease. Due to their immense role in creating movement, we will take a closer look at the categorization and functions of skeletal muscle. Deep & Superficial Skeletal muscles can be categorized based on their depth of placement in the body. For purposes of this course, you will not be required to know the names of each individual deep and superficial muscle. Deep Muscles Deep muscles are for posture and stability. They attach directly to the bone and are located close to the joints. Superficial Muscles Superficial muscles are located between the deep muscles and the skin. Although they vary in size and shape, they are generally known as movement muscles and are greatly responsible for a horse s athletic performance. As movement muscles, superficial muscles can become tense and sore no different than a human athlete. This, in turn, can affect performance as well as mental attitude. Since these muscles are the outermost layer, they can be easily felt for tension, heat, and swelling and be readily influenced by complementary therapies, such as massage, magnetic therapy, and stretching.

5 Muscle Movement Muscle is made up of thousands of fascicles, which are bundles of fibers running parallel to each other this is what gives muscle its striated appearance. Skeletal muscle, which is the muscle category primarily responsible for movement, can consist of two muscle fiber types. The type and proportion of muscle fibers a horse has can determine what activity he/she may excel at. Slow Twitch Slow twitch, also called Type I, are muscle fibers that contract slowly for long periods of time in the presence of oxygen; they use aerobic metabolism to produce the energy needed for muscle contraction. Since these are slow-burning muscle fibers, they do not create toxic end products of muscle contraction, such as lactate, which can cause a horse to cramp. This makes them ideal for non-strenuous work. Fast Twitch Fast twitch, also called Type II, are powerful and fast contracting muscle fibers that produce quick energy without the presence of oxygen; they use anaerobic metabolism to produce the energy needed for muscle contraction. While these muscle fibers produce speed, they also tire quickly and create a by-product during muscular contraction known as lactic acid. Lactic acid can result in cramping if allowed to build up in the body. Every horse has a mix of fast and slow twitch muscle fibers. The proportions are determined by breed and genetics. Horses with a higher proportion of slow twitch fibers have more stamina, tire less easily, and make good endurance or leisure horses. Those with a higher proportion of fast twitch fibers have less stamina but more explosive energy. Arabians are a breed of horse that show higher proportions of slow twitch muscle fibers while Quarter Horses and Thoroughbreds show higher levels of fast twitch muscle fibers. Appropriate training can have an immense impact on performance and bring each type of horse to its peak level of fitness. For example, a Thoroughbred must have stamina as well as speed adapting the muscular system to exercise can improve the muscle s ability to store oxygen and increase its aerobic and anaerobic capacity. While training and conditioning can have a significant impact on the muscular system, it cannot entirely rewrite what type of muscle fibers the horse was given; this is why we don t see certain breeds racing competitively!

6 Flexors & Extensors Flexors and extensors are a group of muscles that lay on the limbs to either decrease or increase the angle. Flexor muscles lay on the back of the limb to decrease the angle (axes of the limb are brought closer together) think about when you flex your arm, you are bringing the axes of your bone closer together. Extensor muscles do the opposite; they lay on the front of the limb to increase the angle (axes of the limb are brought farther apart). Flexing Extending Sphincters A sphincter is a ringlike muscle that contracts (closes) a passage or opening. Commonly found in the digestive tract, the strength of the lower esophageal sphincter is one reason why a horse cannot vomit! Cutaneous Cutaneous muscles allow for movement of the skin. Horses use this muscle to twitch and remove irritants like flies.

7 Management of Muscles Tying Up Taken in part from What is Tying up in Horses by Tania Cubitt, PhD, January 17 th, 2004 Muscle disorders are a frequent cause of poor performance in horses, and for a racehorse, can be performance-limiting or even career ending. Tying up, also referred to as Exertional Rhabdomyolysis, Azoturia, or Monday Morning Sickness, is the most common muscle disorder seen in the athletic horse. Understanding this disorder is vital if you wish to be involved in the care and training of horses, no matter the discipline. What is Tying Up? The scientific name for Tying up is rhabdomyolysis, which simply translated means muscle (myo) breakdown (lysis). The causes of Tying up vary but the result is the same, muscle cramping. In this condition, there is a massive contraction of the muscle groups along the back and rump of the horse. The muscles contract and do not relax. The horse will appear to be almost nailed to the floor in the hindquarters and unwilling to move. The horse will appear to be significant pain and show signs of distress, including increased heart rate and sweating. If you place your hands along the muscles on either side of the spine on a horse that has tied up, they feel rock hard. While cases will range in severity, horses that are showing signs of tying up require immediate medical attention from a veterinarian. Types of Tying Up Horses experiencing tying up can be placed in one of two broad categories: 1. Sporadic (acute) exertional rhabdomyolysis this classification applies to horses which, on rare occasion, experiencing an episode of generalized tying up. This will generally involve muscle stiffness and cramps 2. Chronic exertional rhabdomyolysis when a horse experiences repeated episodes of ER, with the first episode usually occurring at a young age. This type is much more problematic for an athletic horse and can result in irreversible muscle damage

8 Signs of Tying Up The signs of tying up vary with the severity of the condition and the speed of onset. In mild cases, the horse s gait gradually stiffens and he becomes reluctant to move. The muscles are actually cramping and feel very much to the horse like muscle cramps do to human athletes. The large, heavy muscles of the hind legs are most affected, but the triceps muscles above the elbow of the front legs may also appear stiff and painful. Additional signs include sweating, elevated heart and respiratory rate, and dark red/brown urine due to muscle damage. Most cases of tying up are diagnosed by these clinical signs, but bloodwork can be taken to evaluate the muscle enzyme levels, which can help develop a specific treatment plan. Causes Horses often tie up when exercise exceeds the horse s underlying state of training. We may see this occur with young horses when they first go to the track and do too much too soon or with older horses returning from a rest (also called a layoff) and exercising beyond their current level of fitness. Tying up may also occur due to excitability and stress (traveling, breeding, showing). Tying up may also have a nutritional basis, such as an electrolyte imbalance, abnormal carbohydrate metabolism, or mineral/vitamin deficiencies. Unfortunately, for some horses, the cause of Tying up may be unknown. Working with your veterinarian is going to be key in the treatment and management of horses that tie up. Treatment of Tying Up Horses showing signs of tying up should cease exercise immediately do not force a horse to walk if it cannot as this can increase muscle damage. If it is cool, cover the horse, especially its hindquarters with a cooler or blanket to keep warm. Horses that are able to walk should continue to do so unless otherwise directed. Your veterinarian should be contacted but in the meantime, determine if the horse is dehydrated and provide fluids via small frequent sips of water. In order to relax the muscles and allow the horse to move, your veterinarian may need to administer a non-steroidal anti-inflammatory drug (NSAID) and/or a sedative depending on the severity. Horses that suffer from an episode of Tying up should be rested for 3-5 days with a gradual increase in exercise.

9 Management of Tying Up Diet and exercise are closely linked to Tying up and the most important preventative strategies are based upon diet and exercise management. Exercise Management Dietary Management The most common dietary change made to horses that tie up involves a reduction in grain. High cereal grain diets can overload the normal digestive processes of the small intestine and overflow to the hindgut, which is not meant to digest grain products. Too much grain in the horse s hindgut can increase lactic acid production, fluctuate blood glucose levels, and increase fluid and electrolytes losses due to increased heat production. Checking the diet for balanced levels of minerals and vitamins will also be key. Incorporating the assistance of an equine nutritionist is beneficial for horses suffering from Tying up. An exercise protocol is going to vary horse to horse but several basic principles can help horses that suffer from Tying up: Consistent, structured program Grading the level of exercise with a slow increase in intensity as fitness develops Following hard work with a slow trot or canter to stimulate the delivery of oxygen and removal of lactic acid from the muscles Adequate warming up and cooling down procedures Effect on Performance There is no cure for horses with chronic forms of Tying up. Severe and recurrent episodes can result in irreversible muscle damage and impact the ability for a horse to perform. Even if a horse does not show repeated bouts of this disorder, the appearance of these signs needs to be taken seriously to not only prevent muscle damage but prevent future episodes. Horses that tie up due to excitability and nervousness will need to managed carefully avoiding stress and excitement will be key, but that is difficult for a racehorse. Working closely with your veterinarian, as well as an equine nutritionist if needed, will be vital for your horse s health and success.

10 Self-Knowledge Checks 1. Muscle that is involuntary and surrounds all internal tissues and organs is characterized as: a. Cardiac b. Smooth c. Skeletal 8. The image below is engaging which group of muscles? 2. Muscles are able to produce movement via this structure, which attaches muscles to bones a. Tendon b. Ligament c. Joint d. Fascia 3. Which type of skeletal muscle will be most readily influenced by therapies such as massage and stretching? a. Deep b. Superficial 4. twitch are muscle fibers that contract slowly for long periods of time in the presence of oxygen a. Slow b. Fast 5. Fast twitch muscles use anaerobic metabolism to produce quick energy which statement correctly describes this process? a. Fast twitch muscles produce quick energy without oxygen b. Fast twitch muscles produce quick energy with oxygen a. Extensors b. Sphincters c. Flexors d. Cutaneous 9. When a horse twitches his skin to remove an irritant, like a fly, he is engaging which muscle group? a. Flexors b. Cutaneous c. Sphincters d. Extensors 10. Severe muscle cramping that involves distress, inability to move, and increased heart rate is known as: a. Stocking Up b. Bucked Shins c. Tying Up d. EPM 6. A buildup of lactic acid in the body can result in: a. Heart failure b. Muscle cramping c. Inability to breathe d. Inability to defecate 7. Appropriate training can improve muscle fiber ability a. True b. False

11 Answers 1. Muscle that is involuntary and surrounds all internal tissues and organs is characterized as: b. Smooth Smooth muscle in an involuntary muscle that functions automatically. It surrounds all internal tissues and organs 2. Muscles are able to produce movement via this structure, which attaches muscles to bones a. Tendon Tendons are a connective tissue that attaches muscles to bones, allowing for movement 3. Which type of skeletal muscle will be most readily influenced by therapies such as massage and stretching? b. Superficial Superficial skeletal muscles are the outermost layer and can easily felt for tension, heat, and swelling. As a result, complementary therapies, such as massage and stretching, can help relax them 4. twitch are muscle fibers that contract slowly for long periods of time in the presence of oxygen a. Slow Slow twitch, also called Type I, are muscle fibers that contract slowly for long periods of time in the presence of oxygen 5. Fast twitch muscles use anaerobic metabolism to produce quick energy which statement correctly describes this process? a. Fast twitch muscles produce quick energy without oxygen Anaerobic metabolism is not dependent on oxygen to break down fuel stores. This means that fast twitch muscles produce quick energy without the presence of oxygen 6. A buildup of lactic acid in the body can result in: b. Muscle Cramping Lactic acid is a by-product of fast twitch muscular contraction. When allowed to build up in the body, it can result in muscle cramping 7. Appropriate training can improve muscle fiber ability a. True Appropriate training and conditioning can help adapt the muscular system to physical demands by improving the ability of the muscle fibers to store oxygen or increasing its aerobic and anaerobic capacity. Training cannot rewrite the genetics and breed of a horse, which is how proportions of muscle fiber is determined 8. The image below is engaging which group of muscles? c. Flexors In the presented image, the axes of the hindlimb are being brought closer together. When the axes of a limb are brought closer together, the flexor muscles are being engaged 9. When a horse twitches his skin to remove an irritant, like a fly, he is engaging which muscle group? b. Cutaneous Cutaneous muscles allow for movement of the skin. Horses use these muscles to twitch and remove irritants like flies 10. Severe muscle cramping that involves distress, inability to move, and increased heart rate is known as: c. Tying Up Tying up is a muscular disorder characterized by severe muscle cramping, distress, inability to move, and increased heart rate

12 Glossary Acute Sudden and severe, quick onset Aerobic Metabolism Is dependent on oxygen to break down fuel stores inhaled oxygen during aerobic exercise is carried to the muscles and liver to metabolize (utilize) carbohydrates and fats for the production of ATP, the energy source for muscle contraction. Exercise is classified as aerobic if the heart rate is less than 150 beats per minute. The waste products of aerobic metabolism are carbon dioxide, water, and heat Anaerobic Metabolism Is not dependent on oxygen to break down fuel stores, provides a rapid means of producing a limited supply of energy during anaerobic exercise. Exercise is classified as anaerobic if the heart rate is greater than 150 beats per minute. In the absence of oxygen, only carbohydrates can be metabolized for ATP production and the waste products of anaerobic metabolism are heat and lactic acid Cardiac Muscle An involuntary muscle tissue that functions to coordinate the propulsion of blood in and out of the heart Chronic Long term Cutaneous A muscle group that allows for the movement of the skin Deep Muscles A classification of skeletal muscle that provides the horse with posture and stability Extensors A muscle group that lays on the front of the limb to allow for extension (increase limb angle) Fast Twitch A type of muscle fiber that creates quick energy via anaerobic metabolism Flexors A muscle group that lays on the back of the limb to allow for flexion (decrease limb angle) Involuntary Do not have conscious control over Lactic Acid A waste product of fast twitch muscle fiber use and anaerobic metabolism, can result in cramping if allowed to build up Layoff A period of rest, may include turnout and/or stall rest Skeletal Muscle A voluntary muscle tissue responsible for the production and control of external movement, maintaining posture, and thermoregulation Slow Twitch A type of muscle fiber that that contracts slowly for long periods via aerobic metabolism Smooth Muscle An involuntary muscle tissue that surrounds all internal tissues and organs Sphincter A muscle group that contracts (closes) a passage or opening

13 Superficial A classification of skeletal muscle found between deep muscles and the skin, generally known as movement muscles Tendon A type of connective tissue that connects muscle to bone Tying Up A muscular disorder that results in severe cramping of the large hindquarter muscles Voluntary Can be consciously controlled