MUSCLES and MOVEMENT

General Function Movement or locomotion of Muscle Tissue Movement or locomotion Heat production – maintain the body’s homeostasis of temperature Posture – using partial contraction of the “anati-gravity” muscles

Contractility Specific Function of Skeletal Muscle Tissue Excitability or irritability The ability to be stimulated or simply stated “responds to stimulus” from nerve signals Contractility The ability to contract or shorten including contraction without movement isometric contraction is muscle tissue contracting, tension increasing but the there is not enough strength to “move the fixed object”

Extensibility The ability to extend or stretch allowing muscles to return to their resting length after a contraction They may also extend while still exerting force as when lowering a heavy object

Muscle cells are different than other body cells Muscle cells have a long, thin, thread-like shape During tissue development cells fuse together to form a multi-nuclei cell that becomes a muscle cell Adult muscle cells can even have some of the stem cells hanging out to produce more muscle cells after an injury.

Muscle cells have similar parts but different names Sacrolemma – plasma membrane Sarcoplasm – cytoplasm contains many mitochondria and more than one nuclei Sarcoplasmic reticulum (SR) – a type of endoplasmic reticulum however the SR stores and pumps calcium ions

T tubules – transverse tubules that allow electrical impulses traveling along the sarcolemma to move deep into the cell The SR butts up against both sides of the T tubule in a muscle fiber (called a triad) Impulses travel along the T tubule to stimulate the membranes of the SR to pump Ca++ into the channels of the SR causing the contraction to happen

Myofribrils – not found in other cells cytoskeletal filaments that extend lengthwise along the muscle fiber and fill the sarcoplasm. Myofribrils are made up of finer fibers called Myofilaments of which there are two types Thick filaments Thin filaments

Sarcomere – is a contractile unit located between the Z lines. Many sarcomeres line up end to end to form a myofibril Look at page 399 box 11-1 - use overhead for picture The microscopic bands give the muscle the “striated” name

Myofilaments Myofilaments are made of 4 types of proteins myosin make up the thick filaments actin, tropomyosin and troponin make up the thin filaments The myosin heads of the thick filaments are chemically attracted to the actin molecules on the thin filaments. They are called “cross bridges” because they bridge the gap between the think and thin filaments

Muscles are at rest unless they are stimulated by a motor neuron The motor neuron endplate forms a junction called a neuromuscular junction. The narrow gap between the nerve and the fiber is called a synapse or synaptic cleft The nerve releases a neurotransmitter acetylcholine into the gap to begin the electrical impulses in the sarcolemma -excitation-

The impulse is conducted over the muscles fiber’s sarcolemma When it reaches the t-tubule it spread deeper into the fiber where it release Ca++ into the SR The calcium ions combine with troponin molecules in the thin filament causing it to shift to expose the actin molecule

This is called the sliding-filament model 4. The myosin heads are chemically attracted to the actin so they “grab” it and pull, then grab the next actin and pull past it and so on until an 80% contraction is reached This is called the sliding-filament model

Muscle fibers contract to about 80% or their starting length If a muscle is pulling against an immovable object it is still in a state of active contraction and uses energy to maintain the contraction.

Types of Muscle Fibers

Contains type I myosin in the thick filaments Slow twitch Contains “red fibers” Red fibers have a high concentration of myoglobin, a redish pigment used by muscle cells to store oxygen in the muscle cell itself – gives the muscle its red color Contains type I myosin in the thick filaments that reacts or contracts at a slow rate and is able to produce ATP at a rate that keeps pace with the muscle’s energy needs, this type of muscle is found in anti-gravity muscles--because they can contract for a long time and not fatigue—and in the muscles used for endurance activies

Fast Twitch White fibers They contain very little myoglobin Contain type II myosin that contracts more rapidly than slow fibers and has t-tubules that are more efficient at delivering Ca++ to the SR Rapid contraction depletes ATP rapidly even though they tend to contain a higher concentration of glycogen they have fewer mitochondria and rely on anaerobic respiration to regenerate more ATP Fast twitch muscles have great force but cannot sustain activity for very long because of lactic acid production from anaerobic activity Fingers, eyes, muscles used by sprinters

muscles of the leg would be a good example Intermediate fibers Have characteristics in between both fast and slow twitch muscle fibers They are more fatigue resistant than fast fibers yet can generate more force more quickly than slow fibers Example would be: Muscles that are anti-gravity yet are needed for other activities such as jumping muscles of the leg would be a good example

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Motor Unit Consists of the nerve that stimulates the muscles fibers and the muscle fibers it is stimulating Some motor units are only a few muscle fibers Some motor units have thousands of muscle fibers Fine motor movements have smaller motor units that only stimulate a few fibers at time , gross motor movements have large motor units that stimulate many fibers at once

Myography Twitch contraction Threshold stimulus Terms you need to know Graphing muscle contraction Terms you need to know Threshold stimulus The amount of stimulus applied to make a muscle contract Twitch contraction A quick jerk of the muscle

Use the information that you learned about the physiology to explain what is happening on the myograph

Twitch contractions rarely happen the body We can’t make our muscles twitch individually Our nervous system “smooths out” our muscle movements Smooth movements are more useful – sustained movements Prevents injury to muscle groups

The staircase effect is why we warm up before exercise. Calcium diffused through the sarcoplasm of muscles has not had time to relax and pump all of it back into their SR so the muscle can contract with more force. The relaxation phase become shorter and finally disappears – the muscle stays in partial contraction called a contracture After a while the muscle becomes fatigued and won’t respond to even the strongest stimuli

Ever had your muscles shake after over working them? That is what you are feeeling! It is rarely the entire muscle but certain motor units that are fatigued causing the shaking

Tetanus This graphic represents what a sustained contraction looks like. In a normal body tetanus results from two factors working together at the same time Rapid –fire of nerve fibers that permit this wave summation to happen in each fiber Coordinated contractions of different motor units in a muscle organ in an overlapping sequence or “relay team” effect This is called muscle Tone

Tonic contraction or “tone” Muscles organs with less than normal “muscle tone” are called flacid Muscles organs with more than normal muscle tone are called spastic Stretch sensors in muscles and tendons detect the degree of stretch and adjust the strength of the tonic contraction. This mechanism is a negative feedback mechanism located in the spinal cord.

Graded Strength Principle Muscle organs can produce varying degrees of strength Influenced by the individual “type” of fibers Fast twitch, slow twitch or intermediate Number of motor units contracting more units are recruited when more strength is needed

The maximum strength of a muscle is directly related to the initial length of it fibers If a muscle contractions begins from a shortened length its sarcomers are already compressed If the muscle begins a contraction from an overstretched length it cannot develop much tension because the thick and thin myofilaments are too far apart to effectively pull and shorten the sarcomeres.

Now feel the stretch reflex, page 412 Try flexing you biceps: extended, 90 degrees and completely flexed Page 411 bottom of the 2nd column Now feel the stretch reflex, page 412

Concentric Contraction Movement result in shortening of muscle Effects of Exercise on Skeletal Muscles Page 412 Concentric Contraction Movement result in shortening of muscle Eccentric Contraction Movement results in lengthening of muscle

Isometric contraction Muscle stays the same length as tension increases “Tightening to resist a force”