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13/10/2016 Anatomy 12 Muscles of the back Nour Erekat Salam Mustafa 1|Page Quick revision of the previous lecture: o What is the forward nodding movement of the head called? Flexion. o What results in this movement? Which joint? The atlanto occipital joint. o What is the anterior atlanto-occipital membrane? It is the membrane that connects the anterior arch of the atlas to the anterior margin of foramen magnum. o What does ligamentum nuchae (nuchal membrane) connect? It is the greatly thickened supraspinous and infraspinous ligament in the cervical region that connects the spine of the 7th cervical vertebra to the external occipital protuberance of the skull. Do not be confused between the spine of the scapula and that of the vertebrae. Whenever it is mentioned as spine alone, it is referred to the scapula. Whenever we refer to the vertebral spine, we will mention it. o What connects laminae of the vertebrae? It is the ligamentum flavum which is similar to posterior atlanto occipital membrane. Posterior atlanto occipital membrane which connects the posterior arches of atlas to the posterior margin of foramen magnum is similar to ligamentum flavum which connects the laminae of adjacent vertebrae. o How many articular fossae are in each individual vertebra? 4, 2 superior fossae and 2 inferior ones. o How many foramina are in each vertebra? 3 in the cervical vertebrae (2 transverse that are unique for cervical vertebrae and 1 vertebral foramen which is present in each vertebra in the vertebral column), and 1 in the other vertebrae. 2|Page o What movement does the atlanto-axial joint allow? Rotation of the atlas and thus of the head around the odontoid process of the axis. Axis is called as such because it provides its odontoid process as an axis for rotation of the atlas and the skull articulating with the atlas, around that process. o What part does the mandibular fossa belong to? The temporal bone. Why is the fossa present in the temporal bone called the mandibular fossa? This is because it articulates with a part of the mandible. Particularly, it articulates with the head of the condylar process of the mandible forming the tempomandibular joint called TMJ. 3|Page Objectives: Describe the superficial muscles of the back including the attachments. Describe the components of the deep muscles of the back including the attachments. Describe the movements produced by each of the back muscles. Describe the innervation of each muscle of the back. MUSCLES OF THE BACK The muscles of the back are divided into 2 groups. This is done so according to their location and association (i.e where is it located and to what is it associated) These are the Superficial, Intermediate, and Deep groups. o Superficial Group These are connected with the shoulder girdle (clavicle and scapula). These include the Trapezius, Latissimus dorsi (the one on the opposite side?), Levator scapulae, Rhomboid minor, and Rhomboid major. The last 3 muscles are all attached to the medial border of scapula. Rhomboid muscles can either be called rhomboid or rhomboidus. 4|Page 5|Page 1. Trapezius: The trapezius muscle arises from the occipital bone, ligamentum nuchae, spinous process of the 7th cervical vertebra, and spinous process of all thoracic vertebrae (all 12 thoracic vertebrae). However, it inserts into 3 different sites and hence is divided into 3 parts; the upper, middle and lower parts. The upper part inserts into the lateral third of the clavicle, whereas the middle and lower parts insert into acromnion and spine of the scapula. Now, you can easily anticipate the movement each part causes. Upper fibers elevate the scapula, whereas lower fibers do the opposite. They depress the scapula. Middle fibers pull the scapula medially. This muscle is innervated by the spinal part of accessory nerve. Now have a look at the image next page. This is the posterior triangle of the neck (the dashed triangle). You can see that the spinal accessory nerve has already innervated the sternocleidomastoid muscle. It then continues backwards through this triangle into the deep surface of the trapezius to innervate it. The landmark for the spinal accessory nerve in the posterior triangle is Levator scapulae. The nerve crosses backwards through the triangle, anterior to the levator scapulae. 6|Page 2. Latissimus dorsi: It arises from the ileac crest, lumbar fascia, spinous process of the lower 6 thoracic vertebrae, the 3rd and 4th ribs and finally the inferior angle of the scapula. It inserts into the floor of bicipital groove of humerus (intertubercular sulcus). This muscle adducts, extends and medially rotates the arm. It acts as an antagonist to the pectoralis major muscle. This muscle is innervated by thoracodorsal nerve which arises from the posterior cord of brachial plexus and its fibers are derived from the 6th, 7th, and 8th cervical nerves. In these 2 pictures you can see the thoracodorsal nerve innervating latissimus dorsi. 7|Page 3. Levator scapulae, 4.Rhomboid minor, 5.Rhomboid major: These 3 muscles insert onto the medial border of the scapula but at different parts of it of course. However, they have different origins. They are all innervated by the dorsal scapular nerve which arises from the brachial plexus. Levator scapulae: It originates from the transverse process of the upper 4 cervical vertebrae. As the name indicates, its function is to elevate the scapula upwards. In addition to being innervated by dorsal scapular nerve like the other 2 muscles, it is also innervated by branches from the anterior ramus of spinal nerve C5*. Spinal nerve C5 is a nerve that originates from the spinal column from above the cervical vertebra 5. This nerve then contributes to dorsal scapular nerve. So, dorsal scapular is actually part of spinal nerve c5. 8|Page Rhomboid minor: It originates from the inferior part of ligamentum nuchae and the spinous process of 7th cervical vertebra and 1st thoracic vertebra. Since it is inserted into the medial border of scapula, it pulls the border of the scapula upwards and medially. Rhomboid major: It arises from spinous processes of 2nd thoracic vertebra until 5th thoracic vertebra. It has the same action as rhomboid minor, it pulls the border of scapula upward and medially. *The doctor specifically said spinal nerve C5 and then said that snell mentions C3 and C4 instead. But you need to know it as C5 I guess. Levator scapulae, rhomboid minor and major being innervated by dorsal scapular nerve. 9|Page Everything that has been said so far is summarized in this table. You need to know every single detail. But everything has been mentioned so this shouldn’t be a problem to you (supposedly though :3). o Intermediate Group: These are involved in the movement of the thoracic cage. 10 | P a g e And now we move on to the last group of muscles: o Deep Group: These are also referred to as postvertebral muscles. This is because they are located right behind the vertebral column. They are divided into 3 groups according to their location and orientation of their fibers. First, the Superficial vertically running muscles. Next, the Intermediate oblique running muscles. Last, the Deepest muscles. They are innervated by dorsal or the posterior rami of the spinal nerves. Each individual muscle causes one or several vertebrae to be extended or rotated on the vertebra below. 1. Superficial Vertically Running Muscles: These are the long muscles. They are the longest out of all the deep muscles. They are the most superficial of this group of course and their fibers run in a straight line vertically. They run from the sacrum to the rib angles, the transverse processes, and the upper vertical spines. These muscles are Iliocostalis, Erector spinae longissimus, and Spinalis. Clarification Erector spinae is the 3 muscles together; Iliocostalis, Longissimus, and Spinalis. Each of these muscles is a group of 3. For example, there are 3 muscles that make up the Iliocostalis group. The same thing applies to the 2 other groups. Check the picture next page. 11 | P a g e 12 | P a g e 2. Intermediate Oblique Running Muscles: These muscles are deeper than the previous group we just talked about, but more superficial in comparison to the Deepest group (like that’s a surprise). The deepest group is the shortest of all. They are intermediate in length and run obliquely from the transverse processes to the spines of the vertebrae. These muscles are Semispinalis, Transversospinalis multifidus, and Rotatores. 3. Deepest Muscles: These are the shortest, the deepest and run between the spines and between the transverse processes of adjacent vertebrae. The ones that run between the spines are called Interspinales, whereas the ones the run between transverse processes are called Intertransversarii. 13 | P a g e 4. Splenius: One last deep muscle that is detached from all the other muscles is the Splenius. The splenius has 2 parts that originate from the same location but differ in their insertion. They both originate from the lower part of the ligamentum nuchae and the upper four thoracic spines. Splenius capitis: It inserts into the scalp. More specifically, into the superior nuchal of the occipital bone and the mastoid process of the temporal bone. Splenius cervicis: It inserts onto the transverse processes of the upper 4 cervical vertebrae. Edited by: Sajda Drine 14 | P a g e