Structure and Function of Body Systems Flashcards
What is the difference between the axial skeleton and appendicular skeleton?
The axial skeleton consists of the skull, vertebral column, ribs and sternum. The appendicular skeleton consists of the shoulder girdle, arm and hand bones, pelvic girdle, and the leg, ankle and foot bones.
What is the difference between fibrous joints, cartilaginous joints, and synovial joints?
Fibrous joints are connected by dense connective tissue, usually collagen, and allow for very little movement. Cartilaginous joints are connected by fibrocartilage or hyaline and allow some movement.
Synovial joints join bones with a fibrous joint capsule that contains synovial fluid and are the most moveable joints.
How does the structure of the sarcoplasmic reticulum allow the discharge of an action potential to reach all depths of the muscle fiber nearly simultaneously?
The sarcoplasmic reticulum is a system of tubules that runs parallel to and surrounds each myofibril, terminating in vesicles near the Z-line. Transverse tubules run perpendicular to the sarcoplasmic reticulum between the vesicles, allowing calcium to be released throughout the muscle.
What is the structure of a myofibril? What are the A-band, I-band, H-zone, M-line and Z-line?
Myofibrils are primarily composed of myosin and actin filaments. The H-zone is at the center of the sarcomere where only myosin filaments are present and contains the M-line (or bridge), where adjacent myosin filaments are anchored to one another. The Z-line is formed by actin filaments only and is at each end of the sarcomere. The darker A-band corresponds to the alignment of the myosin filaments, while the lighter I-band contains only actin filaments.
What is the sliding-filament theory of muscular contraction?
The sliding-filament theory of muscular contraction is that the actin filaments at each end of the sarcomere slide inward on myosin filaments, pulling the Z-lines toward the center of the sarcomere and thus shortening the muscle fiber.
What are the five steps of muscle contraction (with regard to myosin/actin binding)?
- Initiation of ATP splitting by myosin ATPase caused myosin head to be in an “energized state” which allows it to move into a position to bond with actin.
- The release of phosphate from the ATP splitting process then causes the myosin head to change shape and shift.
- This pulls the actin filament in toward the center of the sarcomere and is referred to as the ‘power stroke’; ADP is then released.
- Once the power stroke has occurred, the myosin head detaches from the actin, but only after another ATP binds to the myosin head because the binding process facilitates detachment.
- The myosin head is now ready to bind to another actin, and the cycle continues as long as ATP and ATPase are present and calcium is bound to the troponin.
What are the characteristics of Type I muscle fibers?
Type I muscle fibers are less powerful but more fatigue-resistant. They have low ATPase activity, but have more connection to capillaries to help them sustain aerobic activity. They develop force and relax slowly, and have a long twitch time.
What are the characteristics of Type IIa muscle fibers?
Type IIa muscle fibers are more suited to powerful, anaerobic activity, but have more capacity for aerobic metabolism and more capillary support than Type IIx fibers. They develop force and relax rapidly, and have a short twitch time.
What are the characteristics of Type IIx muscle fibers?
Type IIx muscle fibers are the most powerful fibers and have the highest activation threshold. The thick fibers have high levels of ATP and ATPase, but receive little blood supply. The fibers are most suited for contribution to anaerobic activity. They develop force and relax rapidly, and have a short twitch time.
What are the two ways to vary or gradate muscular force?
One is to vary the frequency at which the motor unit is activated. If the forces of the twitches begin to overlap or summate, the resultant force produced is much greater.
The other way is recruitment - stimulating more motor units.
What is the function and structure of the muscle spindle?
The muscle spindle relays information about changes in muscle length and velocity to the spinal cord, in addition to outputting to motor neurons of the same muscle and interneurons of antagonistic muscles.
The specialized intrafusal fibers of the muscle spindle run parallel to extrafusal fibers of the muscle. The spindle is composed of 5-14 muscle fibers, which include dynamic nuclear bag fibers, static nuclear bag fibers, and nuclear chain fibers. Primary Ia sensory fibers spiral around all intrafusal muscle fibers and end near the middle of each fiber. Secondary II sensory fibers end adjacent to the central regions of the static bag and chain fibers. There are also up to a dozen gamma motor neurons and one or two beta motor neurons (collectively fusimotor neurons) that activate the muscle fibers within the spindle.
What is the difference between dynamic nuclear bag fibers (bag1), static nuclear bag fibers (bag2), and nuclear chain fibers?
All of the fibers have equatorial regions containing nuclei, but nuclear chain fibers have only single strand of 20-50 nuclei, while the bag fibers have clusters of 50-100 nuclei than can be 5-6 abreast. Feedback from the dynamic bag fibers provides information about the rate of change in length of muscle fibers (sensory receptor transduces rapid stretch, but adapts to sustained stretch), while the static bag and chain fibers provide information about only change in length.
How does input from fusimotor neurons affect the muscle spindle?
Stimulation of the gamma-motor neurons does not cause movement of the joint to which the extrafusal muscles are attached; it only places tension on the central portion of the intrafusal fibers. Therefore, although they are not part of the stretch reflex per se, they set the sensitivity of the muscle to stretch by regulating the tension of the intrafusal fibres; that is, they keep the muscle spindle taut. γ-Motor neurones receive little peripheral afferent input; most of their input is from supraspinal descending pathways such as the reticulospinal and vestibulospinal pathways.
Appreciating the relationship between the extrafusal and intrafusal fibres is important in understanding motor function. As the extrafusal fibres of the muscle contract, the stretch on the muscle spindles is reduced, and sensory information from the muscle spindles would stop unless the muscle spindles themselves also shortened. During intentional activity, at the same time as the α-motor neurones fire to produce shortening of the extrafusal fibres, the γ-motor neurones are stimulated to shorten the intrafusal fibres. This α–γ co-activation ensures that the muscle spindle is shortened at the same rate as the muscle and the sensitivity of the muscle spindles is maintained despite the shortening of the muscle.
What is the function of the Golgi tendon organ?
Golgi tendon organs are proprioceptors in tendons that activate when the musculotendinous unit is stretched. The afferent signal activates inhibitory interneurons in the spinal cord, which synapse with and inhibit a motor neuron for the same muscle. The effect is minimal at low forces, but reflexive inhibition causes the muscle to relax when an extremely heavy load is placed on the muscle.
What is the difference between afferent and efferent pathways, and how does that change between the CNS and PNS?
Within the central nervous system, afferent pathways lead toward the brain, while efferent pathways exit the brain. Within the peripheral nervous system, afferent pathways provide sensory information, while efferent pathways are the axons of motor neurons.
