Muscle - QA
Which of the following is correctly paired?
a) smooth muscle: striated
b) cardiac muscle: voluntary control
c) cardiac muscle: nonstriated
d) skeletal muscle: voluntary control
*skeletal muscle [is striated and under voluntary control], cardiac muscle [is striated and under involuntary control], smooth muscle [is not striated, and it is under involuntary control]
Which of the following surrounds the individual muscle cell?
Muscle tissue has all of the following properties except ___.
PARTS OF A MUSCLE DIAGRAM
The cross bridge cycle is a series of molecular events that occur after excitation of the sarcolemma. What is a cross bridge?
*What a cross bridge connects to
A myosin head bound to actin.
*as soon as the activated myosin head forms a cross bridge with actin, the power stroke begins
What structure is the functional unit of contraction in a skeletal muscle fiber?
*a sarcomere is a regular arrangement of thin and thick myofilaments that extends from one Z disc to the next (a myofibril consists of a series of sarcomeres)
Calcium ions couple excitation of a skeletal muscle fiber to contraction of the fiber. Where are calcium ions stored within the fiber?
Calcium ions are stored in the sarcoplasmic reticulum
*the sarcoplasmic reticulum is very elaborate in skeletal muscle fibers, allowing for significant storage of calcium ions
*sarcoplasmic reticulum is the specific name given to the smooth endoplasmic reticulum in muscle fibers
After a power stroke, the myosin head must detach from actin before another power stroke can occur. What causes cross bridge detachment?
ATP binds to the myosin head.
*the binding of ATP to the myosin head weakens the bond between myosin and actin, forcing the myosin head to detach (ATP also provides the energy for the next power stroke)
How does the myosin head obtain the energy required for activation?
The energy comes from the hydrolysis of ATP.
*myosin is a large, complex protein with a binding site for actin (it also contains an ATPase) and the energy released during the hydrolysis of ATP activates the myosin head
What specific event triggers the uncovering of the myosin binding site on actin?
a) calcium ions bind to tropomyosin and change its shape
b) sodium ions bind to troponin and change its shape
c) calcium ions bind to troponin and change its shape
d) calcium release channels open in the sarcoplasmic reticulum, and calcium levels rise in the sarcoplasm.
*the shape change caused by the binding of calcium to troponin shifts tropomyosin away from the myosin binding sites on actin
When does cross bridge cycling end?
Cross bridge cycling ends when sufficient calcium has been actively transported back into the sarcoplasmic reticulum to allow calcium to unbind from troponin.
*the sarcoplasmic reticulum contains Ca2+-ATPases that actively transport Ca2+into the SR [without Ca2+, troponin returns to its resting shape, and tropomyosin glides over and covers the myosin binding sites on actin]
Thick myofilaments are made of ___.
*thick myofilaments are made of myosin and thin myofilaments are made of actin.
The distance between Z-discs ___ during muscle contraction.
*during contraction, the distance between Z disks decreases as the thin filaments slide centrally (in fact, during contraction, a muscle cell exhibits an overall shortening)
The first step toward generating a skeletal muscle contraction is:
a) a rise in intracellular Ca2+ levels
b) depolarization of the cellular membrane
c) binding of the myosin heads to actin
d) stimulation of the muscle by a nerve ending
*the first step toward generating a skeletal muscle contraction is nervous stimulation of the muscle to generate an action potential
The response of a motor unit to a single action potential of its motor neuron is called a:
a) multiple motor unit summation
b) muscle twitch
c) wave summation
d) graded muscle response
*muscle twitches [are single jerking contractions although skeletal muscles normally respond to stimulation in a controlled and smooth manner], graded muscle responses are the variations needed in skeletal muscle contraction in order to have controlled movement], wave summation [describes how a muscle response changes with respect to changes in stimulus frequency], multiple motor unit summation [describes how a muscle response changes with respect to changes in stimulus strength]
When muscles are contracting under oxygen deficient conditions, they will form ___ to ensure they maintain a supply of ATP
*under anaerobic (oxygen deficient) conditions, most of the pyruvic acid produced in glycolysis will be converted to lactic acid to ensure that the muscle cell maintains a quickly replenishing supply of ATP
Slow oxidative muscle fibers are best suited for...
... endurance activities.
*slow oxidative muscle fibers [are best suited for endurance activities], fast oxidative fibers [are best suited for sprinting], fast glycolytic fibers [are best suited for short-term powerful or intense movements]
The calcium calmodulin system of contraction regulation is found in...
... smooth muscle only.
*the calcium calmodulin system of contraction regulation is found in smooth muscle (skeletal muscle and cardiac muscle utilize a calcium troponin regulation mechanism)
Which of the following is true?
a) skeletal muscle lacks the coarse connective tissue sheaths that are found in smooth muscle
b) skeletal muscle fibers tend to be shorter than smooth muscle fibers
c) skeletal muscle cells have one nucleus, but smooth muscle cells are multinucleated
d) skeletal muscle fibers contain sarcomeres; smooth muscle fibers do not.
*skeletal muscle fibers are longer than smooth muscle cells and they have coarse connective tissue sheaths, skeletal muscle fibers are multinucleated and appear striated because of their sarcomeres which are absent in smooth muscle fibers.
What is excitation-contraction coupling?
Events leading to the sliding of myofilaments.
*excitation-contraction coupling is the sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments (contraction)
The type of muscle found in the walls of most hollow organs is...
... single-unit smooth muscle.
*smooth muscle is generally classified as being either single-unit smooth muscle or multiunit smooth muscle
*single-unit smooth muscle [is found in the walls of most hollow organs], multiunit smooth muscle [is found in large airways to the lungs, in large arteries, connected to hair follicles, and in the eye]
Which energy production process provides the majority of the energy for muscle activity?
*aerobic respiration [occurs in the mitochondria, requires oxygen, and involves a sequence of chemical reactions in which bonds of fuel molecules are broken and the energy released is used to make ATP], aerobic respiration [provides a high yield of ATP for hours of activity] (whereas the other energy production process provide no more than a few minutes of energy for activity)
Most skeletal muscles contain:
a) muscle fibers of the same type
b) a predominance of fast oxidative fibers
c) a predominance of slow oxidative fibers
d) a mixture of fiber types
*requires different forms of fibers to perform in different energy requiring situations
a) produces the end plate potential
b) stores oxygen in muscle cells
c) breaks down glycogen
d) is a protein involved in the direct phosphorylation of ADP