MCAT Biology Problem Drill 18: The Muscular System

Transcription

1 MCAT Biology Problem Drill 18: The Muscular System Question No. 1 of 10 Question 1. Which statement about muscles is correct? Question #01 A. Muscles have an origin that is usually attached to a movable bone, thick portion called the belly and they are attached to stationary bones by a tendon such as the Achilles tendon. B. Muscles have an origin that is usually attached to a stationary bone, thick portion called the belly and they are attached to stationary bones by a tendon such as the Achilles tendon. C. Muscles provide structural support, are involved in thermoregulation but they have no effect on organ function. D. Cardiac muscle provides the heart pumping action and support and rigidity throughout the body. Muscles have an origin that is usually attached to a stationary bone, thick portion called the belly and they are attached to stationary bones by a tendon such as the Achilles tendon. B. Correct! Muscles have an origin that is usually attached to a stationary bone, thick portion called the belly and they are attached to stationary bones by a tendon such as the Achilles tendon. Muscles provide organ function through contraction. Skeletal muscle provides support and rigidity throughout the body. Muscles have an origin, usually attached to a stationary bone. The thick portion of the muscle between the insertion and origin is called the muscle belly or gaster. Muscles are attached to movable bones by a tendon, such as the Achilles tendon. Muscles are arranged in groups throughout the body. Each group moves/supports the bones and organs in that region, i.e.- muscles of the lower extremity move and support the leg. The muscular system is made of muscles, the central nervous system and the peripheral nerves that control them. The muscular provides structural rigidity and support, and is primarily responsible for heat generated in the body. It is involved in regulating systemic blood pressure by vasoconstriction of smooth muscle in blood vessels. Skeletal muscle provides human motion, cardiac muscle pumps the heart and smooth muscle provides organ function through muscular contraction.

2 Question No. 2 of 10 Question 2. The effect of muscles on the peripheral circulation is? Question #02 A. Smooth muscle in the walls of precapillary arterioles modulates peripheral resistance, such as decreasing systemic blood pressure by contracting. B. Smooth muscle in the walls of precapillary arterioles modulates peripheral resistance, such as increasing systemic blood pressure by contracting. C. The pressure in veins is high, and this aids the contraction of nearby muscles. D. The movement of blood through the venous system occurs because of the heart pumping action, the muscles of the legs do not aid in this process. Smooth muscle in the walls of precapillary arterioles modulates peripheral resistance, such as increasing systemic blood pressure by contracting. B. Correct! Smooth muscle in the walls of precapillary arterioles modulates peripheral resistance, such as increasing systemic blood pressure by contracting. The pressure in veins is low and the contraction of nearby muscles aid in the movement of blood through the venous system. The contraction of nearby muscles near veins, aids in the movement of blood through the venous system. Smooth muscle in the walls of precapillary arterioles contract and cause the peripheral vascular resistance to be increased, thereby increasing systemic blood pressure. The pressure in veins is low and the contractions of nearby muscles aid in the movement of blood through the venous system.

3 Question No. 3 of 10 Question 3. Which of the following statements about the role of muscles in thermoregulation is correct? Question #03 A. Muscle contraction accounts for most of the heat generated and required by the human body. B. Muscle contraction accounts for approximately 25% of the heat generated and required by the human body, the rest comes from the external environment. C. The chemical reactions occurring in muscles during contraction absorb heat and therefore act to lower body temperature. D. If the normal body temperature drops by at least 8-10 C, this can result in shivering. Shivering is an involuntary, rapid contraction of the muscles, which generates more heat quickly to counter the drop in body temperature. A. Correct! Muscle contraction accounts for most of the heat generated and required by the human body. Muscle contraction accounts for most of the heat generated and required by the human body. The chemical reactions occurring in muscles during contraction generate heat. If the normal body temperature drops by even 1-2 C, this can result in shivering. Muscle contraction accounts for most of the heat generated and required in the human body. The chemical reactions occurring in muscle during contraction generate heat. Specifically, glucose is converted to ATP which powers the movement of actin against myosin to create muscle contraction. If the normal body temperature drops even 1-2 C, this can result in shivering. Shivering is an involuntary, rapid contraction of the muscles, which will generate more heat quickly to counter the drop in body temperature.

4 Question No. 4 of 10 Question 4. Skeletal muscles? Question #04 A. Are striated, attached to bone they are generally under involuntary control. B. Are made up of 2 fiber types: (a) red (slow-twitch) and (b) those with sarcomeres. C. Are striated, attached to bone they are generally under voluntary control. D. White (fast-twitch) fibers have more mitochondria and are associated with endurance. Skeletal muscles are striated and attached to bone they are generally under voluntary control. Are made up of 2 fiber types: (a) red (slow-twitch) and (b) white (fast-twitch). C. Correct! Skeletal muscles are striated and attached to bone they are generally under voluntary control. White (fast-twitch) fibers have fewer mitochondria and are explosive. Skeletal muscle is striated, and attached to bones. Skeletal muscle facilitates movement by applying forces to bones and joints through its contraction. They are generally under voluntary control. Skeletal muscle has striations due to many sarcomeres (basic unit of contraction). Individual muscle myofibrils make up a muscle fiber. There are 2 types of muscle fibers: (a) red (slow-twitch) have more mitochondria and are associated with endurance (b) white (fast-twitch) have fewer mitochondria and are explosive.

5 Question No. 5 of 10 Question 5. Which of the following statements about sarcomeres is correct? Question #05 A. Sarcomeres are the basic unit of muscle, made up of actin and myosin. B. Sliding filament model: the muscle generates its own signal to contract and then an action potential spreads over the muscle fiber. C. During muscular contraction ATP is formed. D. During muscular contraction zinc is released and binds to tropomyosin, which unblocks actin-binding sites. A. Correct! Sarcomeres are the basic unit of muscle, made up of actin and myosin. Sliding filament model: after the signal to contract comes from the central nervous system, an action potential spreads over the muscle fiber. During muscular contraction ATP is hydrolyzed. During muscular contraction calcium is released and binds to tropomyosin, which unblocks actin-binding sites. Sarcomeres are the basic unit of muscle, made up of actin and myosin. Skeletal muscles contract according the sliding filament model. Sliding filament model: after the signal to contract comes from the central nervous system, an action potential spreads over the muscle fiber. Calcium is released and binds to tropomyosin; which unblocks actin binding sites. Myosin (bound with ATP) binds to actin hydrolyzes ATP and the released energy delivers a power stroke. This hydrolysis also causes the myosin head to turn and ratchet the Z lines closer together.

6 Question No. 6 of 10 Question 6. Cardiac muscle? Question #06 A. Cardiac muscle is a voluntary striated muscle found exclusively in the heart. B. Stimulates its own contraction with the required electrical impulse from the central nervous system (CNS).C. Special pacemaker cells in the sinoatrial node contract in response to the contraction rate of the adjacent skeletal muscle. D. Cardiac muscle is an involuntary striated muscle found exclusively in the heart. Cardiac muscle is an involuntary striated muscle found exclusively in the heart. Stimulates its own contraction without the required electrical impulse from the central nervous system (CNS). Special pacemaker cells in the sinoatrial node spontaneously contract and send electrical impulses throughout the heart. D. Correct! Cardiac muscle is an involuntary striated muscle found exclusively in the heart. Cardiac muscle is an involuntary striated muscle found exclusively in the heart. Cardiac muscle has unique properties: (a) Stimulates its own contraction without the required electrical impulse from the central nervous system (CNS). (b) Special pacemaker cells in the sinoatrial node (located in the right atrium), spontaneously contract and send electrical impulses throughout the heart. (c) Normally the resting heart rate is between bpm, determined by the pacemaker cells. The CNS doesn t directly create the impulse to contract, but modulates it through the autonomic nervous system.

7 Question No. 7 of 10 Question 7. Which of the following statements about smooth muscle is correct? Question #07 A. Smooth muscle is a voluntary non-striated muscle found in the walls of hollow organs such as the bladder and in blood vessels. B. Smooth muscle can only be stimulated directly from the central nervous system. C. Smooth muscle does not require ATP for contraction instead it contracts passively. D. Smooth muscle is spindle-shaped and contains actin and myosin, although they are not arranged in a sarcomere. Smooth muscle is an involuntary non-striated muscle found in the walls of hollow organs such as the bladder and in blood vessels. Smooth muscle can be directly stimulated by the CNS or can react to hormones secreted locally, such as vasodilators and vasoconstrictors. Smooth muscle hydrolyzes ATP and contracts by myosin and actin fibers sliding over each other. D. Correct! Smooth muscle is spindle-shaped and contains actin and myosin, although they are not arranged in a sarcomere. Smooth muscle is an involuntary non-striated muscle found in the walls of hollow organs such as the bladder, and in blood vessels. Smooth muscle can be directly stimulated by the CNS or can react to hormones secreted locally, such as vasodilators and vasoconstrictors. Smooth muscle is spindle shaped and contains actin and myosin, although there are not arranged in a sarcomere. Smooth muscle hydrolyzes ATP and contracts by myosin and actin fibers sliding over each other. Smooth muscle fibers are arranged in sheets within the walls of organs.

8 Question No. 8 of 10 Question 8. Which of the following statements about the nervous control of muscle is correct? Question #08 A. Sensory (afferent) information travels to the CNS, providing information about temperature, pressure and pain. B. Peripheral nerves transmit afferent information only. C. Sensory (afferent) information travels from the CNS, providing muscles information about temperature, pressure and pain.d. Motor (efferent) impulses travel from the muscle to the CNS along the peripheral nerves. A. Correct! Sensory (afferent) information travels to the CNS, providing information about temperature, pressure and pain. Peripheral nerves transmit both sensory and motor impulses. Sensory (afferent) information travels to the CNS, providing information about temperature, pressure and pain. Motor (efferent) impulses travel from the CNS along the peripheral nerves, to the target muscles. The CNS (brain and spinal cord), is connected to muscles by peripheral nerves. These nerves transmit both sensory and motor impulses. Sensory (afferent) information travels to the CNS, providing information about temperature, pressure and pain. Motor (efferent) impulses travel from the CNS along the peripheral nerves to the target, i.e. foot; and initiate movement.

9 Question No. 9 of 10 Question 9. Motor neurons. Question #09 A. Originate in the spinal cord and transmit afferent (sensory) impulses to the target muscle. B. Originate in the spinal cord and transmit motor (effector) impulses to the target muscle. C. Are divided into two branches: (a) autonomic and (b) lower motor neurons. D. Lower motor neurons connect the brain to the spinal cord.. Originate in the spinal cord and transmit motor (effector) impulses to the target muscle. B. Correct! Originate in the spinal cord and transmit motor (effector) impulses to the target muscle. Are divided into two branches: (a) upper motor neurons and (b) lower motor neurons. Lower motor neurons connect the spinal cord to the muscles.. The motor neuron and the muscle fibers it innervates is called the motor unit. Groups of motor units work together to contract a muscle. Motor neurons originate in the spinal cord and transmit motor (effector) impulses to the target muscle. Motor neurons are divided into 2 branches: (a) upper motor neurons- connects the brain and spinal cord and (b) lower motor neurons connect the spinal cord to the muscles.

10 Question No. 10 of 10 Question 10.Which if the following statement about the autonomic nervous system is correct? Question #10 A. Parasympathetic nervous system: (a) slows the heart rate, which conserves energy and (b) uses acetylcholine to induce the release of adrenaline. B. The parasympathetic branch of the autonomic nervous system has been called fight or flight because it stimulates the heart and prepares the skeletal muscles for increased work. C. The autonomic nervous system is divided into two components, the parasympathetic branch and the sympathetic branch. D. The sympathetic branch of the autonomic nervous system has been called rest and digest, because it slows down the body and increases digestive activity. Parasympathetic nervous system: (a) slows the heart rate, which conserves energy and (b) Increases intestinal blood flow and activity for digestion and absorption. The sympathetic branch of the autonomic nervous system has been called fight or flight because it stimulates the heart and prepares the skeletal muscles for increased work. C. Correct! The autonomic nervous system is divided into two components, the parasympathetic branch and the sympathetic branch. The parasympathetic branch of the autonomic nervous system has been called rest and digest, because it slows down the body and increases digestive activity. If the alveoli in the lung are compared to an air bubble in water then (a) both are wet and surround a pocket of air and (b) surface tension acts at the air water interface to make the bubble smaller or, in the case of the lung, the alveoli to shrink. The surfactant polar head adsorbs into the liquid/ water covering of the alveoli. The surfactant nonpolar tail faces towards the air inside the alveoli. Surfactant adsorbed into the liquid layer on the alveoli decreases surface tension. This increases lung compliance and makes the lungs easier to inflate, as well as preventing the lungs from collapsing at the end of expiration.