Muscles PDF

Muscles ILOs: At the end of the lecture, the student should be able to Differentiate between different types of muscle fibers. Classify skeletal muscles. Explain types of the muscle action. Discuss the nerve supply of skeletal muscles. The muscles form about ½ o...

Muscles ILOs: At the end of the lecture, the student should be able to Differentiate between different types of muscle fibers. Classify skeletal muscles. Explain types of the muscle action. Discuss the nerve supply of skeletal muscles. The muscles form about ½ of body weight and they have contractile ability. They are classified into three types: 1- Smooth muscles: Plane and spindle in shape. Supplied by autonomic fibers i.e. involuntary. Sites:Wall of blood vessels and viscera. 2- Cardiac muscle fibers: Striated but branched. Found in the heart. Supplied by autonomic fibers i.e. involuntary 3- Skeletal muscles Striated, not branched, voluntary. Have bony attachments; an origin and insertion. Supplied by at least one somatic nerve and receive blood supply from surrounding blood vessels. 32  1- Smooth muscles 2- Cardiac Muscles 3- Skeletal muscles Types of striated muscles 1- Pale fibers: Rapid contraction and rapid fatigue. Located in prime mover muscles which start the movement. 33 2- Red fibers (high myoglobin content): Slow contraction but sustained. Located in antigravity muscles where continuous contraction is needed to maintain the posture of the body. Examples: The gastrocnemius muscle is rich in pale fibers which is needed for rabid performance of movement. The soleus muscle is rich in red fibers where maintenance of the movement is required (maintenance of posture). Muscle Attachments: The muscle is attached at its both ends where in contraction, one of the ends is fixed (the origin, usually the proximal end) and the other end is approximated to it (the insertion, usually the distal end). Origin Insertion 34 Types of Muscle Attachments 1. Attachment to bone: It is the commonest type. A muscle may be attached to bone either directly by fleshy fibres or by a tendon. 2. Attachment to a fibrous raphe: It is a band or septum of fibrous tissue through which 2 muscles fuse together e.g. mylohyoid muscle. 3. Attachment to deep fascia e.g. tensor fascia lata 4. Attachment to aponeurosis, which is a flat expanded tendon e.g. external oblique muscle. 5. Attachment to skin: A muscle is inserted into the dermis of the skin and by its contraction it could move the skin, e.g. facial muscles. 6. Attachment to an intermediate tendon: A muscle may have 2 fleshy bellies and an intermediate tendon in between; the bellies are inserted into this tendon; e.g. digastric muscle. 7. Attachment to cartilage: As in the muscles of the larynx e.g. cricothyroid muscle. Deep fascia Aponeurosis Iliotibial tract 35 Form 36  Form of the Skeletal Muscles The form of the skeletal muscles are divided according to the direction of the muscle fibers in relation to the line of pull into: a) Parallel fibers ( parallel to the line of pull): 1. Strap like: Sartorius 2. Quadrate: Quadratus femoris 3. Fusiform: Palmaris longus 4. Tendinous intersection: Rectus abdominus 37 b) Oblique fibers (oblique to the line of pull): 1- Pennate fibers (feather like): Unipennate: Fibers attached to one side of the tendon: flexor pollicis longus Bipennate: Fibers at 2 sides of tendon: rectus femoris Multipennate: Series of bipennate: deltoid. Circumpennate: The fibers attached all around the tendon: tibialis anterior muscle. 38 2- Oblique non pennate: Triangular as temporalis Spiral as latissimus dorsi. Cruciate as masseter Circular as Orbicularis oculi Triangular Circular Muscle Action It is a range of contraction which produces a definite movement. Factors affecting the action: 1- Length of the muscle fibers. 2- Number of fibers 3- Direction of the muscle fibers 39