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Muscular System (body
movement terminology structure (Circumduction is…
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external oblique, torso, rotates torso
latissimus dorsi spinous processes of thoracic T6-T12, thoracolumbar fascia, iliac crest and inferior 3 or 4 ribs, pulls the forelimb dorsally and caudally
trapezius down the midline, from the external occipital protuberance, the nuchal ligament, the medial part of the superior nuchal line, and the spinous processes of the vertebrae C7-T12 retraction and elevation of scapula.
serratus anterior, fleshy slips from the outer surface of upper 8 or 9 ribs, protract and stabilize scapula, assists in upward rotation
pectoralis major anterior surface of the medial half of the clavicle. Clavicular head: flexes the humerus. Sternocostal head: extends the humerus. As a whole, adducts and medially rotates the humerus. It also draws the scapula anteriorly and inferiorly.
deltoid clavicle, acromion, spine of the scapula Axillary nerve shoulder abduction, flexion and extension
teres major- posterior aspect of the inferior angle of the scapula,Internal rotation of the humerus
infraspinatus infraspinous fossa of the scapula Lateral rotation of arm & Adduction of arm and stabilizes humerus
biceps brachii short head: coracoid process of the scapula.
long head: supraglenoid tubercle, flexes elbow and supinates forearm
brachialis anterior surface of the humerus, particularly the distal half of this bone, flexion at elbow joint
flexor carpi ulnaris medial epicondyle of the humerus (common flexor tendon), flexion and adduction of wrist
sartorius superior to the anterior superior iliac spine, flexion, lateral rotation and abduction of thigh; flexion and medial rotation of leg
vastus lateralis Greater trochanter, Intertrochanteric line, and Linea aspera of the femur, Extends and stabilizes knee
The sliding filament theory is the explanation for how muscles contract to produce force. The actin and myosin filaments within the sarcomeres of muscle fibres bind to create cross-bridges and slide past one another, creating a contraction. The sliding filament theory explains how these cross-bridges are formed and the subsequent contraction of muscle.
- Muscle activation: The motor nerve stimulates an action potential (impulse) to pass down a neuron to the neuromuscular junction. This stimulates the sarcoplasmic reticulum to release calcium into the muscle cell.
- Muscle contraction: Calcium floods into the muscle cell binding with troponin allowing actin and myosin to bind. The actin and myosin cross bridges bind and contract using ATP as energy (ATP is an energy compound that all cells use to fuel their activity – this is discussed in greater detail in the energy system folder here at ptdirect).
- Recharging: ATP is re-synthesised (re-manufactured) allowing actin and myosin to maintain their strong binding state
- Relaxation: Relaxation occurs when stimulation of the nerve stops. Calcium is then pumped back into the sarcoplasmic reticulum breaking the link between actin and myosin. Actin and myosin return to their unbound state causing the muscle to relax. Alternatively relaxation (failure) will also occur when ATP is no longer available.