Muscular System Ch10

Coordination among muscles

- Movements are the result of several muscles acting in a group. - Skeletal muscles are arranged in opposing (antagonistic) pairs at joints. - Muscles are studied in groups called agonists (prime movers) and antagonists. Action (specific body movement a muscle contraction causes) of muscle (agonist or prime mover) is opposed by antagonist (biceps, which is prime mover, bends elbow; triceps, which is antagonist, extends it). These roles can change based on movements. Muscles also tend to function in groups to accomplish specific movements. Muscles of group are called synergists (ex.: deltoid, biceps and pectoralis major all help flex shoulder); The synergist in a movement is the muscle(s) that stabilizes a joint around which movement is occurring, which in turn helps the agonist function effectively; ex. Flexing fingers & radiocarpal joints; - in a group of synergists, muscle that contributes most to the movement is called prime mover. The fixator in a movement is the muscle(s) that stabilizes the origin of the agonist and the joint that the origin spans (moves over) in order to help the agonist function most effectively (= more efficient); - fixator holds one bone in place relative to the body while a more distal bone is moved; ex.: when moving humerus, muscles of scapula act as fixators to hold scapula in place. Better definition: Two muscles are called synergists if their contraction leads to a movement into the same direction about the axis of a joint. Take the elbow: Two of its parts (the humero-ulnar and humero-radial articulations) form a common joint moving about a single axis allowing flexion and extension (supination and pronation are produced by the third part of the elbow joint, the proximal radioulnar articulation). Two well-known muscles , the biceps and the brachioradialis muscles, are synergistic for the flexion-extension movement, as the contraction of both leads to flexion. Fixator muscles, on the other hand, are all the muscles that serve to fix a joint in a given position during the movement of other joints

arrangement of fascicles

1) Circular: fascicles arranged in a circle around an opening and act as constrictors to close the opening. Ex: those that surround eye called orbicularis oculi, and muscles that surround mouth called orbicularis oris. 2) Triangular (aka convergent): fascicles joint at one common tendon from a wide area; large range of motion; ex.: pectoralis muscles in chest. 3) Parallel: can shorten to a large degree cuz fascicles are in direct line with tendon; ex: hyoid muscles in neck and sartorius in leg; fascicles parallel to one another and to long axis. 4) Unipennate: fascicles on one side of tendon that runs through the entire length of muscle; ex.: extensor digitorum longus. 5) Multipennate: fascicles are arranged at many places around the central tendon; they are spread out at angles to many smaller tendons; ex.: deltoid. 6) Bipennate: fascicles are on both sides of the tendon; ex.: rectus femoris. 7) Fusiform: spindle-like, twisted; fascicles lie parallel to long axis, they run the length of entire muscle and terminate at tendons; muscles have wider belly than the ends; stronger than other parallel arrangements; ex.: biceps brachii.

Muscle Attachment

1. Muscles cross at least one joint & usually attached to articulating bones that form the joint. 2. Origin (fixed end) - attachment of the muscle's tendon to the stationary bone; usually most stationary, proximal end of muscle; some muscles have more than one origin. 3. Insertion (mobile end) - attachment of the muscle's other tendon to the movable bone; usually distal end of muscle attached to the bone being pulled toward the other bone of the joint.

Functional of Muscular System

1. Stabilizing body position and bones 2. Producing movements 3. Regulating organ volume 4. Moving substances within the body 5. Producing heat But most serve to generate movement

Lever System

3 basic parts of a leverage: Fulcrum - moving joint (hinge); Load - what is moving; Effort - muscle that is contracting. Classes of levers (classification based on location of fulcrum, load, and effort): 1) First-class lever: fulcrum is between load and effort; ex.: head, where atlantooccipital joint in the necl is fulcrum, posterior neck muscles provide effort (aka pull) depressing back of the head, and face (which is elevated) is the load (aka weight). This lever is limited on how much weight can be lifted and how high it can be lifted. 2) Second-class lever: load (weight) is in the middle between fulcrum and effort (pull); ex.: gastrocnemius contracting to lift heel with ball of foot as the fulcrum; or when doing pushups - toes are fulcrum, body is load, and arms are effort. 3) Third-class lever: effort in middle; this type does not allow as great a weight to be lifted, but it can be lifted a greater distance (but similar to 1st class); ex.: bicep contraction is effort, while elbow joint is fulcrum, and the forearm is load.

node of ranvier

Nodes of Ranvier are microscopic gaps found within myelinated axons. Their function is to speed up propagation of action potentials along the axon via saltatory conduction. The Nodes of Ranvier are the gaps between the myelin insulation of Schwann cells which insulate the axon of neuron.Oct 20, 2018