GENERAL MUSCLE CHARATERISTICS Flashcards
What is the energy that powers actin and myosin in muscle contraction?
ATP
What is the initial source of energy used to replenish ATP?
Creatine Phosphate
- includes a high-energy phosphate bond
How is creatine phosphate synthesized?
- when sufficient amounts of ATP are present, creatine phosphate is formed by an enzyme in the mitochondria called “creatine phosphokase”
- creatine phosphate stores excess energy in its high-energy bonds
What does creatine phosphate do once ATP is decomposed to ADP?
- creatine phosphate cannot directly supply energy, so it transfers one of its phosphate bonds to ADP to convert it back to ATP
What happens when creatine phosphate can no longer supply sufficient energy to ATP?
- muscle starts to use glycolysis to replenish energy
What are the sources of oxygen required for the aerobic reactions in cellular respiration?
- oxygen is delivered to the muscle fibers thru blood flow, where it is carried by hemoglobin in the red blood cells
- oxygen can also be stored in the muscle fibers temporarily when bound to myoglobin
What are the different types of contractions?
- isotonic: muscle contracts and changes length; equal force
- isometric: muscle contracts but does not change length; change in force
What is concentric/eccentric isotonic contraction?
- concentric: shortening contraction
- eccentric: lengthening contraction
what are the 3 different types of muscle fibers?
- slow-twitch fibers (type II)
- Fast-twitch glycolytic fibers (type IIb)
- fast-twitch fatigue resistant fibers (type IIa)
What are the general characteristics of slow-twitch fibers? (type II)
- always oxidative
- resistant to fatigue
- red fibers
- abundant myoglobin
- good blood supply
- many mitochondria
- slow ATPase activity; slow to contract
What are the general characteristics of fast-twitch glycolytic fibers (type IIb)
- anaerobic respiration (glycolysis)
- white fibers (less myoglobin)
- poorer blood supply
- fewer mitochondria than slow-twitch
- more SR than fast-twitch
- susceptible to fatigue
- fast ATPase activity; contracts rapidly
What are the general characteristics of fast-twitch resistant fibers? (type IIa)
- intermediate twitch fibers
- intermediate oxidative capacity
- intermediate amount of myoglobin
- pink fibers
- resistant to fatigue
- rapid ATPase activity
What type of contraction happens when someone pushes against a wall but the muscles do not lengthen/shorten
- isometric contraction
What type of contraction happens when someone flexes their bicep?
- isotonic
What are the primary characteristics of fast-twitch fibers?
- primarily glycolytic (prone to fatigue)
- or primarily oxidative (fatigue resistant)
What are the primary characteristics of slow-twitch fibers?
- are oxidative and always resistant to fatigue
Where are white fibers (fast-twitch) found?
- certain hand muscles, muscles in the eye
- contract rapidly and are more susceptible to fatigue
What is a threshold stimulus?
- is the degree of stimulus that elicits an action potential in a single muscle fiber or single neuron
What is the difference between fast-twitch fibers and slow twitch?
- fast twitch: contract more rapidly due to the presence of more extensive SR and faster ATPase activity, and are more dependent on glycolysis and therefore are prone to fatigue
- Slow twitch: slower to react but have many mitochondria and myoglobin and are therefore more able to produce ATP aerobically and are therefore more resistant to fatigue
What are the general characteristics of smooth muscle?
- shorter
- single, centrally located nucleus
- elongated with tapering ends
- myofilaments randomly organized
- lack striations
- lack transverse tubulse
- SR not well developed
What are the general characteristics of multiunit smooth muscle?
- muscle cells are well organized
- function as separate units
- found in irises of the eyes and large blood vessels
- typically are stimulated by neurons or certain hormones
What are the general characteristics of visceral smooth muscle?
- composed of sheets of spindle-shaped cells held in close contact by gap junctions
- the thick portion of each cell lies next to the adjacent cells
- respond as a single unit
- if one cell is stimulated, it might excite other adjacent cells
- some displays a rhythmicity, which causes spontaneous repeated
contractions - found in hollow organs such as the bladder, uterus, and digestive tract
What is peristalsis?
- rhythmic waves of muscular contraction in certain tubular organs
What is vascular smooth muscle?
- form of visceral smooth muscle
- found in the walls of many smaller blood vessels and plays a role in controlling blood flow and blood pressure
What are the general characteristics of smooth muscle contraction?
- doesn’t include troponin, and uses calmodulin instead
- calmodulin binds to calcium ions released when the cell is stimulated, activating contraction
- calcium needed for contraction diffuses into the cell from the extracellular fluid
What special characteristics of visceral smooth muscle make peristalsis possible?
- visceral smooth muscle is characterized by repetitive contractions, or rhythmicity, that transmits impulses from cell to cell via gap junctions
- this enables peristalsis which is a wave of muscle contractions that moves the contents of tubular organs in a specific direction
How is cardiac muscle similar to skeletal muscle?
- both are striated
- highly developed transverse tubules and SR
- many mitochondria
- their mechanisms of contraction are very similar
How does cardiac muscle differ from skeletal muscle?
- have less developed cisternae in their SR, so they store less calcium than skeletal muscle cells
- contain larger transverse tubules; they bring in most of calcium through the extracellular fluid
- only have one nucleus
- connected by gap junctions in intercalated discs, and function as a unit
How does cardiac muscle differ from skeletal muscle?
- have less developed cisternae in their SR, so they store less calcium than skeletal muscle cells
- contain larger transverse tubules; they bring in most of calcium through the extracellular fluid
- only have one nucleus
- connected by gap junctions in intercalated discs, and function as a unit
What is the function of intercalated discs in cardiac muscle?
- connects the ends of adjacent cardiac muscle
- contain desmosomes that connect adjacent cells together, and gap junctions that provide passageways for ions
- provide a mechanism for conducting the force of the contraction between the cells that make it possible the heart to contract as one unit
What is the function of intercalated discs in cardiac muscle?
- connects the ends of adjacent cardiac muscle
- contain desmosomes that connect adjacent cells together, and gap junctions that provide passageways for ions
- provide a mechanism for conducting the force of the contraction between the cells that make it possible the heart to contract as one unit
What characteristics of cardiac muscle causes the heart to contract as a unit?
- the transmission of impulses from cell to cell thru the gap junctions of the intercalated discs help the heart contract as a unit
What two NT triggers smooth muscle?
- ACh and norepinephrine (NE)
What are the general characteristics of cardiac muscle?
- located only in the heart
- striated muscle cells
- muscle fibers joined together by intercalated discs
- fibers branch, contain a single nucleus
- network of fibers contracts as a unit
- self-exciting and rhythmic
- longer refractory period than skeletal muscles
- no sustained or titanic contractions
What are the general characteristics of cardiac muscle?
- located only in the heart
- striated muscle cells
- muscle fibers joined together by intercalated discs
- fibers branch, contain a single nucleus
- network of fibers contracts as a unit
- self-exciting and rhythmic
- longer refractory period than skeletal muscles
- no sustained or titanic contractions
What are the special characteristics of skeletal muscles?
- striations: present
- multiple nuclei
- transverse tubule system is well developed
- contracts and relaxes relatively rapidly
What are the special characteristics of smooth muscle?
- striations: absent
- single nucleus
- lacks transverse tubules
- contracts and relaxes relatively slowly; some types are self-exciting and rhythmic
What are the special characteristics of cardiac muscle?
- striations: present
- single nucleus
- transverse tubules are well developed, intercalated discs connect cells
- contracts as a unit, self-exciting, remains refractory until contraction ends
