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The Muscular System and Homeostasis

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Daley Schneider

on 17 June 2013

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Transcript of The Muscular System and Homeostasis

Atrophy: reduction in the size, tone and power of a muscle.
Hypertrophy: exercise-induced increase in muscle mass due to an increase in size, not number, of individual skeletal muscle fibres
The Muscular System and Homeostasis
by Daley Schneider
Creatine phospate: builds up when muscles are resting. It is not directly apart of contraction, but regenerates ATP through rebuilding ADP, while filaments are sliding. Fastest way to make ATP available.
Fermentation: Also forms ATP quickly. Lactate is formed through the deconstruction of glucose. Lactate accumulation in muscle fibre can make sarcoplasm more acidic and eventually, cease enzyme function. Glucose and ADP react, creating lactate and ATP.
Aerobic Cellular respiration: Taking place in the mitochondria, it provides most of the ATP for muscles. Glycogen and fat stored in muscle cells, are used to obtain glucose and fatty acids to produce ATP. Myoglobin (oxygen carrying red-brown cell) temporarily stores oxygen, making it available for the mitochondria for cellular respiration. Carbon dioxide, heat and water are byproducts of reaction.
Muscles, Health, and Homeostasis
Muscle fatigue rarely occurs, thanks to the constant relaxing and contraction of the muscle pairs. Even when appearing at rest, some muscles are still contracting, "low level" activity resulting in what is called tone. This is important for maintaining posture. If all muscles were to relax completely all over the body, we would collapse like a broken table.
Muscle twitch
A muscular contraction that only lasts a second, muscle twitch occurs after reaching a certain threshold hold of stimulus before consecutively contracting and releasing. It is used to classify muscle fibres by the speed at which they contract
There are two main types of muscle twitch, along with a third only found in human muscles, each with corresponding fibres.

Slow twitch (fibre)
Fast twitch (fibre)
Intermediate* twitch (fibre)
Slow twitch fibre
A muscle fibre that produces most of its energy aerobically; contracts slowly, but can maintain a steady, prolonged production of ATP when oxygen is available
Also called
Type I fibre
Fast twitch fibres
Acquiring Energy (ATP)
The muscular system, a collection of tissues that are highly specialized to convert chemical energy into kinetic energy - Movement
Contraction Mechanism
Contraction involves 2 types of myofilaments: actin and myosin. The actin portion consists of 2 strands of protein molecules wound together, while the myosin, while the same format, is 10 times longer and is different in shape, a long rod with a double "head" end region.
Myofilaments contract thanks to the release of calcium ions, which then leads to the sliding filament model*, the actin and myosin myofilaments sliding past each other, the "head" of the myosin attaching to the actin and 'flexing' to advance actin filament aided by ATP.
The calcium ions responsible for this contraction, bind to troponin*, which causes the tropomyosin* threads winded around the actin to shift position, revealing the area where the myosin "head" can bind to.
The usage of ATP is for detachment of myosin from actin. This allows for more links to binding sites farther along the actin.
There are Three types of Muscle cells
Smooth Muscle
Aiding in the digestion of food thanks to contractions, smooth muscle (SM) can be found in blood vessels, and many hollow organs, contracting involuntary (without conscious control). Long and tapered, the cells of SM are arranged in parallel lines, forming sheets and contain only one nucleus.
While slower to contract than Skeletal muscle, it can sustain prolonged contractions and can endure stress with little fatigue.
Cardiac muscle
Fun Facts:
In walls of certain blood vessels, the contraction of smooth muscle helps regulate blood pressure and blood flow
In eyes, smooth muscle is what decides the size of the eye's opening to light.
It is non-striated, just as it's name says, no linear markings or ridges on it.
Unique to the heart, cardiac muscle (CM) cells are tubular and striated, unlike smooth muscle, and contain only one nucleus, like smooth muscle.
Forming the walls of the heart, CM cells branch, and create netlike structures.
Alike smooth muscle again, contraction of CM is involuntary.
Skeletal Muscle
Known as the "meat flesh" of animal bodies, skeletal muscle (SKM) is responsible for most day to day movement, thanks to over 600 SKM with multiple functions*. Contraction of SKM cells is voluntary, controlled by the nervous system, unlike other muscles, and the cells are incredibly long and contain many nuclei to coordinated the needed energy and materials for them. Like CM, SKM are striated and tubular in shape.
*Functions of Skeletal Muscles
SKM supports the body, its contractions opposing the force of gravity, enabling us to stand and remain upright
SKM makes the bones move, contraction accounting for arm, leg and eye movement, and breathing.
SKM helps maintain constant body temperature through ATP breakdown from contraction, releasing heat to distribute to the body
SKM helps protect internal organs and stabilize joints, padding the bones protecting organs and containing tendons to hold bones together at
the joints
To contract or not to...
That is the question
A muscles work occurs during contraction. When they contract, they shorten, allowing them to only pull and not push.
With relaxation the passive state of the muscle, a force must always be available to stretch the muscle after it finishes contracting and relaxes. Due to that muscles in charge of movement are always presented in pairs.
For each action of the muscle, the second does the opposite, allowing for more force and a "fulcrum" for movement around joints.
In the previous image, skeletal muscle was organized into levels. The first was a tendon (heavy band of tissue that can grow up to 20 cm long) attaching the ends of the muscle to the bond.
Next are bundles of muscle fibre, that cluster to create muscles. Connective tissue wraps around individual fibres, bundles of fibres, and the muscle itself.
Between these muscle fibre bundles, blood vessels, supplying nutrients and oxygen and removing cellular waste, and nerves, triggering and controlling muscle contractions, run between them.
Placement/Composition of Muscles
The volume of muscle fibre is mostly from
, which are made up of even smaller
. These tiny units contain protein structures that make muscles contract. The rest of the muscle fibre is made up of mitochodria (300 per fibre) and organelles found in most cells

myofibrils: one of hundreds of thousands of cynlindrical subunits that make up a skeletal muscle cell (fibre).
myofilament: one of many microscopic, string-like structures, composed of of actin ( one of two chief protein component of muscle) and myosin (second chief protein component of muscle), that make up myofibrils; responsible for muscle contraction
Oxygen Deficiency
Fermentation requires oxygen to supply its energy needs, as so can create an oxygen deficit. Athletes don't have this happen to them, as they have built up their mitochondria levels, so fermentation is not required for ATP production. The reason as to why a deficit occurs is because lactate, a result of fermentation, requires oxygen to complete its metabolism as it accumulates. An example of oxygen deficiency is when a person breathes heavily after exercising. Because lactate is produced less in trained personnel, blood pH remains steady and oxygen deficit is lessened.
Muscle Complications
Caused by reduced stimulation, from damage to the nervous system or paralyzing injuries, it can be initially reversed, but dead/dying muscle will not be replaced and in extreme cases, loss of muscle function is permanent.
Outlines the importance of physical therapy for any injury resulting in loss of mobility.
Exercise and Contraction
Exercise also stimulates enzyme activation and production along with mitochondria. Because of this, athletes can withstand more muscle exertion before fermentation occurs.
Athletes also receive more blood ( additional blood vessels) and store more glycogen.
* This is just a placeholder name for this type of muscle contraction. Another name more commonly used is Intermediate form.
Are you feeling
Compared to fast twitch fibres, slow twitch fibres are small and more resistant to fatigue.
Containing lots of mitochondria and myoglobin (resulting in dark colour), they are surrounded by capillary beds, drawing more blood + oxygen than fast twitch ones.
Also including an abundant reserve of glycogen + fat, the mitochondria can consistently produce ATP for a prolonged amount of time when oxygen is available.
Important for: biking, jogging, swimming, and long distance running.
A muscle fibre that produces most of its energy anaerobically; adapted for the rapid generation of power, but dependance on anaerobically produced energy results in vulnerability to accumulation of lactate, causing rapid fatigue. Also called
Type II fibre.
Rich in glycogen, fast twitch fibres have little to no myoglobin (leading to a light colour in the fast twitch fibres) and few mitochondria and blood vessels when compared to slow twitch fibres.
Important for: sprinting, weight lifting, and swinging around a hockey stick or tennis racket.
Intermediate form (twitch)
Found in human muscles
Adapted for rapid generation of power.
High oxidative capacity, thus more resistant to fatigue.
Fast Twitch Aspect
Slow Twitch Aspect
Endurance training increases the proportion of these fibres in muscle
the process which the body is able to maintain a
state of stable physiological balance or basically maintain equilibrium.
Without homeostasis in our bodies, we wouldn't be able to survive!
The muscular system interacts with all the other systems of the human body in ways that promote and maintain homeostasis.
Heat/cold reaction:
If to hot/cold, one has the ability to move to a cooler/hotter area. At a physiological level, when cold smooth muscle in the blood vessels supplying skin constrict, reducing the amount of blood near the body's surface. Thus the body's core conserves heat. If cold enough, involuntary skeletal muscle contractions will occur, or shivering, an action initiated by temperature sensitive cells located in the hypothalamus (brain).
How it happens:
Stimulus-A change occurs in the internal or external environment that disturbs homeostasis. (Heat, cold, noise, pressure, lack of oxygen are external stimulus. Internal stimulus includes changes in blood pressure, pH balance, and salt concentration, high or low blood sugar.) Receptor-A has a sensor that monitors the environment and responds to the stimulus by sending information to the control center. The flow of the information occurs along the afferent pathway.
Control Centre-determines a set point and is where a variable is to be maintained. A set point is the level or range. Information travels from the control center to the effector along efferent pathway.
Effector-provides means for the control centers response to the stimulus. The results of the response feedback are influenced the stimulus.
Feedback-it can either be positive or negative. Negative feedback depresses the stimulus so that the whole control mechanism is shut off. Most of the body’s homeostatic mechanisms are negative feedback systems.
Negative feedback returns the body from being outside the steady state (too high, too low) back to the steady state. Positive feedback enhances the stimulus so that the reaction continues at an even faster rate. Feedback is positive as change occurs in the same direction as original stimulus and causes variable to deviate further from original range and usually controls infrequent.
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