3- Epaxial Structures.docx

- **Axial Structures: General Info** - **Axial muscles** encompass any muscles of the trunk and neck. - Axial muscles can be epaxial or hypaxial. - The **external jugular vein** (jugular groove or furrow) has a dorsal and ventral boundary. - **Dorsal bou...

- **Axial Structures: General Info** - **Axial muscles** encompass any muscles of the trunk and neck. - Axial muscles can be epaxial or hypaxial. - The **external jugular vein** (jugular groove or furrow) has a dorsal and ventral boundary. - **Dorsal boundary:** Brachiocephalicus (cleidocephalicus muscle- cervical part) muscle - **Ventral boundary:** Sternocephalicus muscle - The **muscles of inspiration** include the: Diaphragm, serratus dorsalis cranialis, scalenus, and rectus thoracis muscles. - Inspiration involves breathing in. - The **muscles of expiration** include the: Serratus dorsalis caudalis, transverse thoracis, abdominal muscles, and iliocostalis (epaxial) muscles. - Expiration involves breathing out. - **Epaxial Muscles: General Info** - Epaxial muscles lie dorsal to the transverse processes of the vertebra, and they act as extensors of the vertebral column (neck, trunk, tail). - Epaxial muscles produce lateral movements when acting on one side, and they stabilize the vertebral column. - Epaxial muscles are innervated by the dorsal branch of spinal nerves. - The 3 systems ("I Love Tacos") of epaxial muscles include: - Iliocostalis system: lumborum, thoracis - Longissimus system: lumborum, thoracis, cervicis, capitis - Transversospinalis system: - Splenius muscle - Semispinalis capitus muscle, which has 2 parts: - Semispinalis capitus biventer cervicis muscle - Semispinalis capitus complexus muscle - **Epaxial Muscles: Iliocostalis System** - The iliocostalis system is the most lateral epaxial muscle system, and it courses between the ilium and the C7 vertebra, meaning that it is NOT present in the neck. - The iliocostalis system consists of the **iliocostalis lumborum muscle**, and the **iliocostalis thoracis muscle**. - The **actions** of the iliocostalis system include: fixation of the vertebral column; lateral movement ("wiggle butt") when 1 side contracts; aids in expiration (breathing out) by pulling ribs caudally. - **Fixation**: If a dog has all 4 paws on the ground, fixation refers to the prevention of the dog from falling/collapsing on the ground, allowing them to keep their body up (while standing in place). - **Epaxial Muscles: Longissimus System** - The longissimus system is located medial to the iliocostalis system of epaxial muscles. - The longissimus system extends from the ilium to the head (mastoid process of the skull). - The longissimus system consists of the **longissimus thoracis et lumborum muscle**, **longissimus cervicis muscle**, and the **longissimus capitis muscle**. - The **action** of the longissimus system is: extension and flexion of the vertebral column. - **Epaxial Muscles: Transversospinalis System** - The transversospinalis system is the most medial epaxial muscle system, and it courses between the sacrum and the head. - Some of the muscles of the transversospinalis system include: - **Splenius muscle** - The splenius muscle is a flat, triangular-shaped muscle that courses from the T2-T3 spinous processes and median raphe of the neck to the temporal bone of the skull. - The **action** of the splenius muscle includes: extending the neck and raising the head; unilaterally draws the head and neck laterally - **Semispinalis capitis muscle**, which has 2 parts: - **Semispinalis capitis biventer cervicis muscle** - The semispinalis capitis biventer cervicis muscle courses from T4-T2 to the caudal aspect of the skull. - **Semispinalis capitis complexus muscle.** - The semispinalis capitis complexus muscle courses from T1-C3 to the caudal aspect of the skull. - The **action** of the semispinalis capitis muscles is to: extend the neck and raise the head; unilaterally draws the head and neck laterally - **Hypaxial Muscles: General Info** - Hypaxial muscles lie ventral to the transverse processes of the vertebra, and they act as flexors of the vertebral column. - Hypaxial muscles include cervical, thoracic and abdominal muscles. - **Neck muscles:** longus capitus, longus coli, and (sternocephalicus, sternothyroideus, sternohyoideus) muscles - **Thoracic wall muscles:** scalenus, serratus ventralis (cervicis and thoracis), serratus dorsalis (cranialis and caudalis), external intercostal, internal intercostal, and rectus thoracis muscles - **Abdominal wall muscles:** external abdominal oblique, internal abdominal oblique, transverse abdominis, and rectus abdominis muscles - Hypaxial muscles also include sublumbar muscles, ventral tail muscles, and muscles of the pelvic outlet. - **Hypaxial Muscles: Neck Muscles** - The **innervation** of the neck hypaxial muscles is from the ventral branches of the cervical spinal nerves. - The **action** of the neck hypaxial muscles include: flexing the atlanto-occipital joint, and drawing the neck downward. - The **longus capitis muscle** is located along the ventral vertebral bodies from C6 to the skull, which is lateral to the longus colli muscle. - The **longus colli muscle** is located along the ventral vertebral bodies from T6 to C1 (atlas), which is medial to the longus capitis muscle. - **Cervical Viscera** - The **ventral boundary** of the cervical visceral space is composed of the following muscles: Sternocephalicus, sternohyoideus, and sternothyroideus muscles. - The **dorsal boundary** of the cervical visceral space is composed of the following muscles: Longus capitus, and longus colli muscles. - The **cervical viscera** is composed of the: trachea, esophagus located dorsal to the trachea towards the left), and the thyroid and parathyroid glands. - The **carotid sheath** encompasses the: common carotid artery, vagosympathetic trunk, and internal jugular vein. - The recurrent laryngeal nerves are also a part of the cervical viscera. - **Major Cervical (region) Nerves** - The **accessory nerve (cranial nerve 11**) is considered to be a cranial nerve rather than a cervical spinal nerve. - The accessory nerve provides [motor] innervation to the following muscles: Cleidocephalicus, Omotransversarius, Sternocephalicus, and Trapezius muscles. - **Second cervical spinal nerve (C2), ventral branch** - **Great auricular nerve** which provides [sensory] innervation from the neck, ear, and caudal part of the head. - **Transverse cervical (colli) nerve** provides [sensory] innervation from the cranioventral part of the neck. - **Third, fourth, fifth cervical spinal nerves (C3-C5), ventral branches** - These nerves provide [motor] innervation to the muscles of the neck, and [sensory] innervation from the skin of the neck. - These nerves penetrate through the Omotransversarius muscle. - The ventral branch of the C5 spinal nerve gives rise to the branch the contributes to the **phrenic nerve**.