Theme B: B3 Organisms - B3.3 Muscle and Motility Flashcards
& an example
motile
organisms that have adaptations allowing movement within their habitat are called motile.
e.g. Brown-throated three-toed sloth:
* a motile but very slow moving animal
* the several species of sloth are all native to Central or South America
* sloths are arboreal (tree dwelling) and herbivorous
* their digestive process of slow and it takes about a month for them to process an ingested leaf
* once a week the sloth descends to the ground to defaecate, being the equivalent of about a third of its body mass
* They have three long toes on each foot that, in combination with their bone structure and musculature, are adapted to hanging from branches and moving using a pulling motion. These adaptations make movement on the ground almost impossible for a sloth.
& an example
sessile
sessile organisms cannot move from place to place, but are still able to alter thei rbody form in response to environmental stimuli.
e.g. Venus flytrap.:
* a carnivorous plant native to the subtropical wetland found in North and South Carolina in the United States.
* this species lives in soils that are deficient in minerals, especially nitrogen
* the plant’s trap is a pair of leaves with short but strudy trigger hairs. the Venus flytrap waits for an insect to crawl or fly inside its paired leaves and trigger the hairs
* within about a second of the hairs being triggered, the leaves close around the prey animal to prevent it from escaping
* the internal portion of these leaves then secretes hydrolytic enzymes to digest the trapped insect after approx. one week
composition of muscle tissue
muscle tissue is made up of highly modified cells for contraction, and thus their cellular structure is not as apparant as in other types of cells.
Each muscle is composed of muscle fibres because of their elongated shape. Muscle fibres are multinucleate because each fibre actually represents several cells that have merged together.
composition of muscle fibres
Each muscle fibre is composed of many protein filaments called myofibrils that run parallel to each other. Sequentially placed along each myofibril are contracting units called sarcomeres.
Sarcomeres are repeating sections inside each myofibril
& its role in muscle contraction
composition of sarcomeres
All sarcomeres are attached to each other end to end. When one sarcomere contracts, all the sarcomeres in that same muscle contract. The resulting action makes the muscle fibre and entire muscle shorter.
The key to understanding the contraction of a muscle is to understand how an individual sarcomere contracts. The striations (bands) of SKELETAL and cardiac muscle are the result of alternating fibres of two proteins called myosin and actin.
you can identify one sarcomere by locating the ‘Z lines’ in a relaxed sarcomere. Each Z line is shared by two sarcomeres, one to the right of the Z line and one to the left. It is these connections that allow muscle fibres to contract as a unit and shorten the entire muscle.
the dark areas of sarcomeres are a reuslt of the presence of both actin and myosin in those areas; the lights are a result of the presence of either actin or myosin but not both.)
study diagram. only striated muscle body tissues skeletal + cardiac
sliding filament theory
When sarcomeres contract, the actin and myosin fibres do not shorten. Instead the actin filaments slide over the myosin fibres. This results in each sarcomere shortening. This model of muscle contraction is often called the sliding filament theory:
1. the myosin heads are actviated by splitting ATP. when ATP is hydrolysed it prepares the myosin head by changing its position.
2. Myosin heads are attracted to and attatch to exposed binding sites of actin to form cross-bridges. Inorganic phosphate is released.
3. as myosin forms corss-bridges, ADP is released and the myosin bends due to the loss of energy. The bending is towards the center of the sarcomere and the actin is moved inwards.
4. myosin binds to ATP and this allows detachment of the myosin heads formt he actin attachment sites.
* the contraction cycle continues if ATP is available and the Ca2+ levels in the sarcoplasm are high.
origin and insertion
tendons
connective tissues that muscles use to attatch to two bones, one at each end of the muscle. Tendons attach muscles to bones at two main points: the ORIGIN and the INSERTION.
Origin: This is the point where the tendon is attached to the stationary (immovable) bone. In most cases, this bone remains in place when the muscle contracts.
Insertion: This is where the tendon attaches to the movable bone, the one that moves when the muscle contracts.
antagonistic muscle pairs
a muscle can only exert a force when it contratcs, so once a bone has been moved the opposite movement requires a different muscle. two muscles that accomplish opposite movements are said to be antagonistic to each other.
e.g. biceps and triceps are an antagonistic pair. the contraction of the bicep muscles resuts in the relaxation of the tricep, casuing the forearm to curl upwards. the contraction of the triceps results in the relaxation of the bicep, causing the forearm to extend.
titin fibres
muscle also use a force to help with relaxation, as a reuslt of the spring-like action of a protein called titin (titin is the lagrest known proetin in the human body). titin is an immense protein that has multiple folds that allow it to acts as a spring.
when sarcomeres shorten during a contratcion, the two sides of each sarcomere move towards the center. this creates a spring-like tension in titin that is released when the muscle relaxes. this allows each sarcomere of the muscle to undergo a contraction once again. the titin also holds myosin fibres in place in the sarcomere and prevents muscle fibres overstretching.
what controls skeletal muscle contractions?
Skeletal muscle contractions are under the control of the nervous system. Every movement made requires many electrical impulses originating in your brain and terminating at synapses called neuromuscular junctions. These junctions are a type of synapse where a chemical message is sent into the muscle tissue to stimulate a contraction. Neurons that carry these “messages” are called motor neurons.
hint: motor units
what does the intensity of a muscle contraction depend on?
Each muscle is able to contract with varying intensity, depending on how many of the total muscle fibres within the muscle receive a nervous system impulse to contract.
Each single motor neuron has a set number of muscle fibres that it controls and is called a motor unit. If a low intensity contraction is needed, a relatively low number of motor units is activated by the brain. If your brain predicts a high intensity contraction will be needed, more motor units receive impulses. The ratio of motor neurons to muscle fibres varies from about 1:10 to 1:200.
vertebrate animals
They have an internal skeleton (endoskeleton) made of bones. Muscles are attached to the bones at variouspoints to allow the movements characteristic of that animal. relative differences in bone length and muscle attachments result in different movements such as the hopping of a kangaroo compared to the walking of a human.
anthropods
Arthropods, such as insects, have an exoskeleton made of a substance called chitin. Because the skeleton is on the outside of the animal’s body the muscle attachment points are on the inside of the hollow skeleton.
in terms of vertebrate animals
the role of bones as levers
Many individual bones and segments of skeletons act as levers, to maximize efficiency for a variety of movements. A lever is a rod (a bone) able to rotate about a fixed point known as a fulcrum (a joint).
Levers lower the force necessary to accomplish work, for example the work to move an arm, leg, or perhaps fingers. The lever action of bones and joints allows muscles to exert a lower force to accomplish any one movement.
e.g. head is able to move up and down in a nodding movement because the attachment point of the cranium to the vertebrate acts as a fulcrum: * One set of muscles contracts to bring the head down from the fulcrum point and another set brings it back up. This is another example of how muscles work as antagonistic pairs.
how do anthropods take advantage of leverage?
Arthropods, with their exoskeletons, often take full advantage of leverage. Arthropods not only have jointed legs but also jointed body parts. It is as if they are medieval knights in body armour made of chitin. The muscles that attach to the inside of this “armour” are in antagonistic pairs, just as in animals with endoskeletons. Arthropods are capable of an amazing range of motion by maximizing leverage.
Examples
* Fleas have been measured jumping 200 times their body length using the muscles and leverage provided from their jointed “toes”.
* A mantis shrimp can throw out its front appendage to stun a prey at a speed of about 80 km h-‘ (50 miles h-‘).
synovial joints
Synovial joints occur in the body where two bones need to move against each other, and are notable for the wide range of motions that they allow. Common examples include the joints at your elbow, knee, shoulder and hips.
& use hip as example
ball-and-socket synovial joint
example using the hip:
* The head of a femur forms a ball that fits into a rounded socket in the pelvis bone, thus it is called a ball-and-socket joint.
* Cartilage covers both bones to avoid bone on bone contact.
* The entire joint is encased by a membrane that contains a lubricant known as synovial fluid.
* The hip joint is encircled by tough, fibrous ligaments that hold the bones in place but also allow a range of motion.
* There are numerous muscles that control the movements of the hip joint, each with tendons that connect the bones.
the function of different pelvis structures
- Pelvis and femur: Bones forming the ball-and-socket joint of the hip
- Cartilage: A smooth protective connective tissue that lines both the pelvis and femur within the hip joint
- Synovial fluid: Lubricating fluid within the hip joint that reduces friction
- Ligaments: Tough connective tissue that holds the bones of the hip joint in place
- Tendons: Connective tissue that connects each of the muscles of the hip joint to its appropriate bones
- Muscles: Muscle tissues that contract and relax to enable movement of the femur within the socket of the pelvis
goniometer
Physical therapists often use an inexpensive device known as a goniometer to measure the range of motion of a joint. Range of motion is the distance and direction that a joint can move, and is usually measured in degrees. The measurements can be used to document improvements in joint movement after an injury or surgery. Some joints such as the hip are capable of movement in a number of dimensions.
origin and insertion points
intercostal muscles
The intercostal muscles lie between each pair of ribs and use the ribs as their origin and insertion points.
* Each set works collectively to change the shape of the entire ribcage. If looking at the ribcage from the outside, the first intercostal muscles that you would see would be the external intercostal muscles. The origin and insertion points on each pair of ribs lie at an angle.
* Beneath this set would be the internal intercostal muscles, also using the ribs as their origin and insertion points, but they lie at an angle almost opposite that of the external set.
* Both sets of muscles use the attachment of the ribs to the vertebrae as the fulcrum point.
intercostal muscles as an examples of antagonistic muscle action
When the external intercostal muscles contract, the rib cage is pulled upwards and out.
If you recall, when you felt your ribcage, this movement occurs when you breath in (an inspiration). The antagonistic internal intercostal muscles move the ribcage down and inwards. This is typical of a breath out (an expiration).
The movement of the ribcage and different orientations of the muscle fibres permit a stretching of the muscle layer that is not being contracted. In other words, when the external intercostal muscles contract the expansion of the ribcage results in stretching of the internal intercostal muscles. This stretches the titin fibres in each sarcomere of this muscle layer, creating potential energy that will be used for the next contraction of the internal intercostal muscles. The contraction of the internal intercostal muscles stores potential energy by stretching the titin in the external intercostal muscles.
reasons / need for animal locomotion
- Foraging for food (Honey bees): Flying from flower to flower to collect nectar and pollen
- Escape danger (Flying fish): Escaping predators by swimming fast and extending their very long pectoral fins to glide over the water
- Searching for mate (Loggerhead sea turtle): Both males and females swim back to the beach where they were hatched to mate and lay eggs
- Migration (Arctic tern): Migrating from their Arctic breeding grounds to the Antarctic region and back each year, to take advantage of available food
- Dispersal (Hoary bat): North American populations have established permanent colonies on the Hawaiian Islands
how are marine animals anatomically related to land animals?
Marine mammals such as dolphins, whales and seals are all descended from ancestral species that once lived on land. Their internal anatomy is adapted to a marine environment but still has many similarities with their land ancestors.
adaptations of dolphins that allow them to be sucessful inhabitants of ocean waters
- streamlined body, allowing the animal to move through the viscous water with relative ease and at great speeds
- lost almost all body hair, to reduce drag through the water
- tail adapted to form a fluke, which allows an up-and-down motion for propulsion
- lost their rear legs, because movement is provided by the fluke
- front limbs adapted to become flippers primarily used for steering
- airway called a “blowhole” located on the dorsal (top) surface of the head, to exchange air at periodic intervals with a minimum of the body leaving the water
- can seal the blowhole tightly between breaths so that water does not enter the airway
- can stay underwater for several minutes without breathing, so they can make deep dives
- retained mammalian characteristics, such as being endothermic, producing milk for their young, having an advanced two-sided circulatory system, and long-term parental care of their young.
