Topics Covered. General muscle structure non-muscle components, macro-structure, contractile elements, membrane components.

Transcription

1 1 Topics Covered General muscle structure non-muscle components, macro-structure, contractile elements, membrane components. Contractile function Contractile and regulatory proteins, force production. Neuromuscular junction structure, function, individual components. Basis of myofiber type Myofiber identification and analysis techniques.

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6 6 Krogh s Constant August Krogh Nobel Laureate in Physiology or Medicine, Based on a cylindrical model of diffusion of gases from a central capillary. Capillary dilation (response to exercise) decreases diffusion distance (for O 2, CO 2, energy sources, other metabolites) Changes in capillary density and tortuosity associated with muscle remodeling (i.e. hypertrophy, atrophy, neural damage, etc.) The Muscle Spindle Muscle spindles are specialized skeletal myofibers that have a sensory function. Numbers of specialized intra-fusal myofibers are surrounded by a capsule of connective tissue, the complete structure being known as the muscle spindle. The intrafusal fibers are innervated by efferent γ (gamma) motor nerve fibers. Afferent sensory nerve fibers (mechanosensory nerve ending, the most prominent of these are called "annulospiral endings") surround the intra-fusal myofibers.

7 7 The Muscle Spindle If the muscle is stretched, the intra-fusal myofibers in the muscle spindle are also stretched, sensory afferent nerves are stimulated, and a change in contractile state of the muscle is perceived by the CNS. Different types of intra-fusal myofibers and nerve endings allow the perception of position, velocity and acceleration of a particular muscle contraction. The Muscle Spindle The contraction of the intrafusal myofibers, after stimulation by the efferent γ nerve fibers, may counteract or magnify the changes imposed on the muscle spindle by the surrounding muscle. Hence the intra-fusal myofibers and the efferent nerves are responsible for setting the sensitivity for the sensory nerve ending or annulospiral endings in the muscle spindle. For a much more detailed discussion of Motor Spindle structure and function go to the following link.

8 8 Thin Filament Components Force Production in Skeletal Muscle actin_myosin.mov

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11 1 Acetyl Cholinesterase Staining of the NMJ in Skeletal Muscle Stereoscopic image of NMJ in skeletal muscle immunofluorescently stained with a neuronal protein (green) and α bungarotoxin (red). α bungarotoxin binds the ACh receptor of the motor end plate. Triad

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14 14 Metachromatic ATPase Stain (Toluidine Blue) (B&W) Metachromatic ATPase stain in human muscle crosssection. Note high incidence of Type IIc myofibers in this area. Indication of de-innervation/ re-innervation injury in adults. Loss of innervation of myofiber, reverts to Type II, incomplete re-innervation by slow twitch neuron results in intermediate Type IIc myofiber type. Type IIbx (-ve) Type IIa Type I (+ve ve) Myosin Heavy Chain Isoform Separation by Gel Electrophoresis (muscle contractile proteins are extracted from muscle tissue using a negatively charged detergent (sodium dodecyl sulphate - SDS). Proteins are then separated in a specialized glycerol-polyacrylamide gel, negatively charged proteins migrating through the gel from the cathode (-) to the anode ( +) end of the gel. The gel acts as a molecular weight sieve, the smaller the protein the faster it can move through the gel matrix.)

15 15 Type I MHC Antibody Staining of Skeletal Muscle Western blot of a MHC gel stained with different anti-mhc antibodies (Western blot named after Dr. Western. Developed to allow protein detection by antibodies after gel electrophoreis. Proteins separated on gel to purity, electrically transferred to a membrane in a renaturing buffer, the membranbe then stained with antibody. This technique is used to determine if an antibody is specific for a single type or isoform of protein.)