Chapter 8 Review

1. Chapter 8 Review The Muscular System

2. The Muscles Each muscle is an organ, comprised of skeletal __________ tissue, several ____________ tissue coverings, ____________ tissue to cause it to contract, and _______________ to nourish it.

3. Connective Tissue Coverings Layers of dense connective tissue, called ____________, surround and separate each muscle. This connective tissue extends beyond the ends of muscle and gives rise to cord like ___________ that are fused to the periosteum of bones. Sometimes muscles are connected to each other by broad sheets of connective tissue called _____________. Under the outer layer another layer of connective tissue around each whole muscle is called the _____________. The _______________ surrounds individual bundles of fibers called ___________ within each muscle. Each muscle cell (fiber) is covered by a connective tissue layer called ___________________.

4. Skeletal Muscle Fibers Structure The muscle fiber membrane is called the ____________ which contains the cytoplasm called ______________. Within the sarcoplasm are many perpendicular myofibrils composed of smaller filaments called ______________. These myofilaments are actually two types of filaments, a thicker filament composed of the protein __________ and a thinner mostly made of the protein ____________. The dark stripes are called ____ bands and the light bands are called ____ bands. A ____________ is defined as a unit extending from one _____ line to the next (center of the light band). T tubules = transverse tubules. Where are they located? __________________ Are they open or close to the outside? What other tubular structure are they associated with? What ion does this other tubular structure contain?

5. Neuromuscular Interaction Neuromuscular junction: The site where the motor neuron and muscle fiber meet The muscle fiber membrane forms a _________________ in which the sarcolemma is tightly folded and where nuclei and mitochondria are abundant. Acetylcholine � neurotransmitter released from the __________________ of the neuron. Acetycholinesterase � what is its function? Where is it found? Motor Unit: A _________ neuron and the muscle __________ it controls make up a motor unit; when stimulated to do so, the muscle fibers of the motor unit contract all at once.

6. Skeletal Muscle Contraction Muscle contraction involves several components that result in the shortening of sarcomeres, and the pulling of the muscle against its attachments. The protein _________ consists of two twisted strands with globular cross-bridges projected outward along the strands. _________ is a globular protein with myosin binding sites. What two proteins are associated with it?

7. What is the sarcoplasmic reticulum? A series of channels inside the muscle cell that stores calcium ions.

8. Skeletal Muscle Contraction According to the sliding filament theory of muscle contraction, if allowed to, the myosin crossbridge attaches to the binding site of the actin filament and bends, pulling on the actin filament; it then releases and attaches to the next binding site on the actin, pulling again. What is preventing this from happening continuously? Energy from the conversion of ATP to ADP is provided to the cross-bridges from the enzyme ATPase, causing them to be in a �cocked� position.

9. Creatine phosphate stores energy that is used to convert ADP to ATP during muscle contraction

10. Stimulus for Contraction The motor neuron must release the neurotransmitter acetylcholine from its synaptic vesicles into the synaptic cleft in order to initiate a muscle contraction. Protein receptors in the motor end plate detect the neurotransmitters, and a muscle impulse spreads over the surface of the sarcolemma and into the T tubules where it reaches the sarcoplasmic reticulum.

11. When a nerve impulse reaches the end of a motor neuron, Acetylcholine is released!

12. Stimulus for Contraction Upon receipt of the muscle impulse, the sarcoplasmic reticulum releases its stored calcium ions to the sarcoplasm of the muscle fiber. The high concentration of calcium in the sarcoplasm interacts with the troponin and tropomyosin molecules, which move aside, exposing the myosin binding sites on the actin filaments. Myosin heads now bind and pull on the actin filaments, causing the sarcomeres to shorten. After the nervous impulse has been received, the enzyme acetylcholinesterase rapidly decomposes the acetylcholine. Then, calcium is returned to the sarcoplasmic reticulum, and the linkages between myosin and actin are broken.

13. Energy Sources for Contraction The pigment myoglobin stores oxygen in muscle tissue. What happens to the respiration rate during exercise? It increases.

14. Oxygen Debt Oxygen deficiency may develop during strenuous exercise, and lactic acid accumulates as an end product of anaerobic respiration. This acid diffuses out of muscle cells and is carried in the bloodstream to the liver. When a muscle loses its ability to contract during strenuous exercise, it is referred to as fatigue. This usually arises from the accumulation of lactic acid in the muscle causing a lowered pH. A muscle cramp occurs due to lack of ATP required to return calcium ions back to the sarcoplasmic reticulum so muscle fibers can relax. Know what causes a muscle strain.

15. Muscle fatigue can be caused by all of the following except� Lowering of pH due to lactic acid build-up Interruption of blood supply Formation of a cramp Lack of acetylcholine

16. Muscle Responses A muscle fiber remains unresponsive to stimulation unless the stimulus is of certain strength, called the threshold stimulus. When a muscle fiber contracts, it contracts to its full extent, it cannot contract partially. This is called the all-or-none response. Muscle twitch: A single, short contraction involving only a few motor units is referred to as a twitch. Is this considered a very useful contraction? No.

17. The strength of a muscle in response to different levels of stimulation is determined by the� Number of motor units receiving a threshold stimulus

18. Muscle Responses A muscle fiber receiving a series of stimuli of increasing frequency reaches a point when it is unable to relax completely and the force of individual twitches combine by the process of summation. If the sustained contraction lacks any relaxation, it is called a tetanic contraction (result of summation & recruitment together!) NOT ALL MOTOR UNITS HAVE BEEN RECRUITED! An increase in the number of activated motor units within a muscle at higher intensities of stimulation is called recruitment. How is this done? By activating more motor units. Muscle tone is achieved by a continuous state of sustained contraction of motor units within a muscle. Why would this be useful? Useful in maintaining posture.

19. Smooth Muscles Describe smooth muscle cells. They are elongated with tapered ends Are they voluntary or involuntary? Involuntary In multi unit smooth muscle, such as in the blood vessels and iris of the eye, fibers occur separately rather than as sheets. Visceral smooth muscle occurs in sheets and is found in the walls of hollow organs; these fibers can stimulate one another and display rhythmically, and are thus responsible for peristalsis in hollow organs and tubes.

20. Smooth Muscles Smooth muscle contraction: How is it like skeletal muscle? Similar myosin binding to actin mechanism. How many neurotransmitters are there that act on smooth muscle? Two: Acetylcholine and norepinephrine How is it unlike skeletal muscle? Lacks striations (do not have an organized arrangement of myosin and actin filaments), have relatively underdeveloped sarcoplasmic reticulum

21. Cardiac Muscles Describe cardiac muscle cells. Rectangular shaped cells with single nucleus in each How is it like skeletal muscle contraction? Involves similar myosin binding to actin process. What are the three ways it differs from skeletal muscle contraction? Involuntary, contracts for longer periods, intercalated disks spread impulses of muscle (very quickly!).

22. Muscle Terminology Origin and Insertion: The immovable end of a muscle is the origin, while the moveable end is the insertion. What does contraction do? Pulls the insertion towards the origin, causing movement Prime mover - the one doing most of the work Synergist � helper muscles (assist) Antagonist � opposing muscles (perform opposite movements of those of the prime mover)

23. Need to Know: Muscles Buccinator � compresses the cheeks inward Muscles of Mastication - Temporalis � Insertion: Coronoid process of mandible Deltoid � abducts upper arm and can flex and extend humerus Psoas Major � flex the thigh Iliacus � flex the thigh Sternocleidomastoid � Insertion: mastoid process of the temporal bone Rectus Femoris - Fibularis Longus � produces plantar flexion Rectus abdominis � primary flexor of vertebral column