1 Muscular System Chapter 8

2 Homework Read Chapter 8 pages –Do Part A Q1-24 page 203 –Do Part B Q1-23 pages –Do Part C page 204 –Parts A-C Due NLT 4/8/11 (Friday) Chapter 8 Packet Due: 4/11/11 (Monday) –Exercises #18-22

3 I. Muscle Types A. Skeletal Muscle

4 B. Smooth Muscle

5 C. Cardiac Muscle

6 II. Skeletal Muscle A. Skeletal muscle is composed of muscle tissue, nervous tissue, blood, and connective tissues B. Fascia: layers of connective tissue that cover the muscle –May connect via tendons to the periosteum of bone –OR may connect to coverings of neighboring muscles via aponeuroses

7 C. Epimysium closely surrounds the muscle (connective tissue) D. Perimysium seperates muscle tissue into small compartments (connective tissue) –Fascicles: bundles of muscle fibers in the perimysium C. Endomysium: covers each individual muscle fiber (connective tissue) D. Figure 8.1: pg 172 text (next slide)

8 Skeletal Muscle Fig 8.1

9 E. Skeletal Muscle Fibers –A single cell that contracts in response to stimulation and then relaxes when the stimulation ends Sarcolemma – muscle cell membrane Sarcoplasm – muscle cell cytoplasm –Contains many mitochondria and nuclei –Myofibrils in sarcolemma: contain 2 main proteins, creating striations (note: there are other proteins) 1. myosin: thick 2. actin: thin –Within sarcoplasm: sarcoplasmic reticulum (like ER) and transverse tubules activate muscle contraction when stimulated Fluid filled channels that connect to the outside of the fiber

10 F. Motor neurons: nerve cells that connect to the muscle cells G. neuromuscular junction: connection between the motor neuron and the muscle fiber H. Neurotransmitters: chemicals released from the neuron to induce a response in the muscle fiber I. Motor unit: one neuron connects to many muscle fibers simultaneously enabling unified contraction of all fibers

11 III. Muscle Contraction A. Actin and myosin slide past each other causing a contraction B. Structure: –1. actin is composed of a double helix –2. myosin contains extensions called cross bridges C. Sliding filament model –Cross bridges pull on actin contracting the muscle –The cross bridge then releases and binds with a section further down

12 D. ATPase: enzyme that releases energy for the myosin to latch to actin and pull E. Acetylecholine: neurotransmitter that stimulates skeletal muscle tissue F. Muscle relaxation: occurs due to decomposition of acetylcholine via catalysts known as cholinesterases –Cholinesterase inhibitors can be found in some insecticides, Serin & VX neurotoxin gases, some snake toxins –Causes the action of acetlyecholine to keep muscles contracting –Tetanus toxin is not a cholinesterase inhibitor

13 G. Energy requirement– mostly from ATP (adenosine triphosphate) –Creatine phosphate: enzyme catalyzing rxn of ADP (adenosine diphosphate) to ATP –O 2 is necessary for the production of ATP -muscle cells can store some O 2 (in myoglobin) making it unnecessary for a continuous supply of oxygen during contraction but this reserve is not endless

14 H. muscle fatigue: a muscle that has lost the ability to contract due to overuse, loss of blood supply, lack of acetyocholine, or most likely from the build up lactic acid from anaerobic respiration –Cramp: sustained involuntary contraction –Rigor mortis – condition in which muscle fibers contract ~72h post-mortem; caused by increase in sarcolemma to Ca ++ permeability causing decrease in ATP in muscle fibers; cells contract and remain so until the cells begin to decompose

15 I. Muscles are a major source of heat production –Excess heat removed via blood supply J. Recruitment: increase in motor units being activated –This causes the entire muscle to contract with maximal tension –Twitches – small motor units easily stimulated; often low stimulus cause muscle contraction of small muscle groups –Muscle tone – term applied to small sustained muscle contractions when muscle is at rest; responsible for maintaining posture

16 IV. Smooth Muscle A. lack striations because of less developed sarcoplasmic reticulum B. Slower to contract/relax (than skeletal); able to maintain more forceful contraction with same amt of ATP; able to change length w/o changing tautness (so as the stomach & intestines fill, strength is not lost) C. Two types: –1. Multiunit smooth muscle: muscle fibers are separate; found in blood vessel walls and iris of the eye –2. Visceral smooth muscle: sheets of spindle- shaped cells; found in walls of hollow organs Stimulation of one muscle stimulates the adjacent muscles to cause rhythmic contractions thru the entire organ; peristalsis is term applied to this rhythmic muscle movement of digestive tract

17 V. Cardiac Muscle A. Found only in the heart B. Striated cells form 3-D networks C. When one portion of the muscle is stimulated the impulse carries across to other fibers; intercalated discs aid in the transmission of impulses D. Self-exciting & rhythmic; necessary to carry out the primary function of heart – to beat. E. Pacemaker - the sinoatrial (SA) node or sinus node; a small mass of specialized cells in the top of the heart's right atrium (upper chamber); makes the electrical impulses that cause the heart to beat.

18 VI. Muscle Movement A. Origin: immovable end of the muscle B. Insertion: movable end of the muscle –When muscle contracts, its insertion is pulled toward its origin C. Prime mover: the muscle that provides most of the movement –Called the agonist D. Synergists: the muscles that contract and assist the prime mover E. Antagonist: resist a prime mover’s actions and causes movement in the opposite direction