Lecture 8 – June 16, 2011MuscleThere are three types of muscle:SmoothCardiacSkeletal – voluntary and striatedFor a tissue to be a muscle tissue it has to demonstrate these five things:Excitability – ability to respond to a stimulusContractility – ability to shorten and lengthenExtensibility – pulled outElasticity – snap backConductivity – can respond to a stimulus and sent it along itselfThe purpose of muscle is for movement with conjunction with bone. It is important for us to have posture and maintain body temperature with heat production.Calf muscle (a.k.a. gastrocnemius muscle)Muscle – many cells and many motor units. For a muscle to be effective and useful, it must be attached to something immovable.Origin – attached to a bone that is less movable and more to the center axis (closer to mainline of the body).Insertion – attached to a bone that is more movable and further from the center axis.Belly – widest portion of a muscleFascia – connective tissue below the skin, over the surface of the muscle, and intertwining within muscle. Responsible for anchoring of muscle cells to tissue.Cross Section of MuscleEpimysium is the outside lining of the WHOLE big muscle, composed of connective tissue; whole muscle is not homogenous, it is subdivided into numerous groupings called fasciles; each fascicle has individual skeletal muscle cells; these fascicles are lined by connective tissue called endomysium. In between all the fascicles is connective tissue called perimysium.To get a muscle to shorten you must supply a stimulus.Fibroblasts are in connective tissue.Lecture 9 – June 17, 2011The motor unit is a neuron and all the cells to which it is associated.Most motor units will have 5-200 or more skeletal muscle cells. The fewer cells attached to a neuron, the finer control you have. Each one has a cell associated with it. Axon ends have knobs filled with a neurotransmitter, acetylcholine (ACH). Each motor unit is independent of the ones around it. When you are moving your muscles, you aren’t moving all of them usually, just a few at a time.Depending upon what you need to do determines how many motor units you will use at any one time. When you apple a certain amount of energy to a skeletal muscle cell, and nothing happens, that is called a sub threshold stimulus. When you gradually increase the amount of energy, and things begin to happen, you would say that this amount of energy is called the threshold for this motor unit. Each motor unit has its own threshold. If the amount of voltage is less than .5V, nothing will really happen at all. If you do have a .5V, you’ve met the threshold, and something will happen. Each motor unit has its own level of threshold.The space between the axon knob and the skeletal muscle cell is called the neuromuscular junction. If we want a muscle cell to shorten, we will have to send a message across this neuromuscular junction (synaptic space).The perimysium, epimysium, and endomysium have two jobs: 1 Anchors the whole muscle and 2. It’s a place where neurons can live (it anchors, secures, and holds the neurons so that when you need to shorten the muscle, they can zap it).Neurons have to be nestled and protected.You also need to provide connective tissue cells with nutrents – in the form of the blood. You have to have blood vessels coming in and out. Capillaries are the only place where things go into and out of the cardiovascular system. Coming out of the blood will be oxygen, glucose, growth hormone, insulin – they all provide cells with what they need and are picking up carbon dioxide and break down products and leaving the cell with it. This connective tissue houses capillaries and delicate blood vessels.If you ant to have a lot of control over your fasciles and individual cells, you have got to have connective tissue.Each cell tends to be elongated, cylindrical, with blunt ends. It is noted for more than one nucleus (multi nucleated). The nuclei are usually located right under the cell membrane. The cell membrane is called the sarcolemma. It has cytoplasm called sarcoplasm. The basic unit of structure and function is going to be the sarcomere. There are cross striations and it’s going to be the unique relationship of the thick and thin myofilaments. It will be multinucleated and the cells are close to the membrane. These adult cells aren’t going through mitosis like fetal ones are, so they cannot easily repair themselves.Holes that go all the way though, to the other side of the cell, are called t-tubules (transverse tubules). The t-tubule is lined by cell membrane (sarcolemma). The t-tubules contain extracellular fluid because they are OUTSIDE the cell! You have numerous t-tubules extending along each muscle cell. Smooth muscle WOULD NOT have t-tubules. Cardiac muscle would have wider t-tubules than the skeletal muscle.The endoplasmic reticulum of pivotal cells will be called sarcoplasmic reticulum. It does exist scattered about but there are special places where they are stacked. The place where they are stacked (3D) is all around each t-tubule. Each stack is called a cisternae (like pancakes). In the cisternae will be a special storage of enzymes, raw materials, minerals, calcium ions.Example: T-tubules are the pole in the fire station. The spiral staircase around the pole is the sarcoplasmic reticulum.Sarcoplasmic reticulum (cisternae) and t-tubules make up a triad.The sarcomere in the cell gives the skeletal muscle its striated appearance.The skeletal muscle has a lot of mitochondria, but even more in cardiac muscle.You will have a lot of myoglobin, which is a protein in the cell that has the ability to hold oxygen, which is great to have if you are a competitive athlete. Glycogen is the storage form of carbohydrates for us, plants it is starch. The more glycogen you have, the greater opportunity you have to have more energy.If you encourage a neuron to send a message (a series of action potentials), when they get to the end of the neuron the axon knobs will encourage Acetylcholine to ooze out and ACH finds its special receptor in the skeletal muscle cell. It is going to set up a wave of depolarization. The action potentials will now move along inside the skeletal muscle cell and the action potentials get into the “belly” of the skeletal muscle cell. When the action potentials gets there, each action potential is an electrical event and this causes the calcium (that is stored in the cisternae) to slip