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[[Image:Anatomy_and_physiology_of_animals_Regions_of_a_vertebral_column.jpg|thumb|right|250px|Divisions of the spinal cord- Copyright Ruth Lawson Otago Polytechnic ]]

[[Image:Anatomy_and_physiology_of_animals_Regions_of_a_vertebral_column.jpg|thumb|right|250px|Divisions of the spinal cord- Copyright Ruth Lawson Otago Polytechnic ]]

The trunk consists of three segments; the thorax, the abdomen, and the pelvis, each of which is bounded by body wall and contains a cavity. The thoracic cavity lies cranial to the diaphragm, whereas the abdominal cavity lies caudal. The pelvic cavity is defined by the borders of the bony pelvis and communicates with the abdominal cavity. Dorsally, the roof of all three cavities is formed by the spinal column and associated muscles. Vertebrae develop segmentally from '''somitic sclerotomes''', whereas muscles develop from '''somitic myotomes'''. Within each myotome is a single nerve leaving the central neural tube. Motor innervation in the adult is therefore segmental. The ventral and lateral body walls are initially formed by '''somatopleure''' (ectoderm and lateral plate mesoderm), but is later invaded by somitic cells migrating ventrally. These differentiate to form ribs and sternum and associated muscles.

 

The trunk consists of three segments; the thorax, the abdomen, and the pelvis, each of which is bounded by body wall and contains a cavity. The thoracic cavity lies cranial to the diaphragm, whereas the abdominal cavity lies caudal. The pelvic cavity is defined by the borders of the bony pelvis and communicates with the abdominal cavity. Dorsally, the roof of all three cavities is formed by the spinal column and associated muscles. Vertebrae develop segmentally from '''somitic sclerotomes''', whereas muscles develop from '''somitic myotomes'''. Within each myotome is a single nerve leaving the central neural tube. Motor innervation in the adult is therefore segmental. The ventral and lateral body walls are initally formed by '''somatopleure''' (ectoderm and lateral plate mesoderm), but is later invaded by somitic cells migrating ventrally. These differentiate to form ribs and sternum and associated muscles.

==Divisions and Landmarks==

==Divisions and Landmarks==

===Cervical Vertebrae===

===Cervical Vertebrae===

The first two cervical vertebrae are known as the '''atlas''' and the '''axis''' respectively, and are modified to allow movement of the head. The atlas has no conventional body, instead it is composed of two lateral masses joined by dorsal and ventral arches. The atlas and axis are fused in embryonic life. The '''wing of the atlas''' is the transverse process of this vertebra and allows the spinal column to articulate with the skull, by providing a resting place for the occipital condyles. The axis is the longest vertebra. The '''nuchal ligament''' connects the spinous process of the axis to the spinous process of the first thoracic vertebra (T1). The last (C7) cervical vertebra has a taller spinous process than those proceeding it, and articulates with the first pair of ribs.

The first two cervical vertebrae are known as the '''atlas''' and the '''axis''' respectively, and are modified to allow movement of the head. The atlas has no conventional body, instead it is composed of two lateral masses joined by dorsal and ventral arches. The atlas and axis are fused in embryonic life. The '''wing of the atlas''' is the transverse process of this vertebra and allows the spinal column to articulate with the skull, by providing a resting place for the occipital condyles. The axis is the longest vertebra. The '''nuchal ligament''' connects the spinous process of the axis to the spinous process of the first thoracic vertebra (T1). The last (C7) cervical vertebra has a taller spinous process than those preceding it, and articulates with the first pair of ribs.

===Thoracic Vertebrae===

===Thoracic Vertebrae===

Thoracic vertebrae articulate with the ribs. They are distingushed by short bodies with flattened extremities, costal facets, short transverse processes, and prominent spinous processes. They reach a maximum height, a few vertebrae behind the cervicothoracic junction (constituting the '''withers''' of the horse) and then decline. The orientation of spinous processes shifts from caudo- to craniodorsal.

Thoracic vertebrae articulate with the ribs. They are distinguished by short bodies with flattened extremities, costal facets, short transverse processes and prominent spinous processes. They reach a maximum height, a few vertebrae behind the cervicothoracic junction (constituting the '''withers''' of the horse) and then decline. The orientation of spinous processes shifts from caudo- to craniodorsal.

===Lumbar Vertebrae===

===Lumbar Vertebrae===

Provides direct connections between vertebral bodies. The bodies of adjacent vertebrae are connected by thick, flexible intervertebral discs, consisting of two parts:

Provides direct connections between vertebral bodies. The bodies of adjacent vertebrae are connected by thick, flexible intervertebral discs, consisting of two parts:

'''Nucleus pulposus''': slightly eccentric, notochord derivative, contained under pressure and prone to escape.

:'''Nucleus pulposus''': slightly eccentric, notochord derivative, contained under pressure and prone to escape.

 

:'''Annulus fibrosus''': encircling bundles of fibrous tissue that pass obliquely from one vertebra to another, with changing orientation.

'''Annulus fibrosis''': encircling bundles of fibrous tissue that pass obliquely from one vertebra to another, with changing orientation.

2. '''Synovial''':  

2. '''Synovial''':  

'''Joints of the atlas'''

'''Joints of the atlas'''

 

#Atlanto-occipital joint - Between the condyles of the skull and corresponding cavities of the atlas. It functions as a ginglymus, movement is restricted to flexion/extension in the sagittal plane (eg nodding).

1. Atlanto-occipital joint - Between the condyles of the skull and corresponding cavities of the atlas. It functions as a ginglymus, movement is restricted to flexion/extension in the sagittal plane (eg nodding).

#Atlantoaxial joint - The ventral arch of atlas and the body of the axis face into a single synovial cavity with limited areas of contact. Movement is rotational about a longitudinal axis (eg. head shaking).

 

2. Atlantoaxial joint - The ventral arch of atlas and the body of the axis face into a single synovial cavity with limited areas of contact. Movement is rotational about a longitudinal axis (eg. head shaking).

==Spinal Cord==

==Spinal Cord==

The details of the spinal cord are found [[Spinal Cord - Anatomy & Physiology|here]].

The details of the spinal cord are found on [[Spinal Cord - Anatomy & Physiology|spinal cord]] page.

==Hypaxial and Epaxial Muscles==

==Hypaxial and Epaxial Muscles==

1. Lateral column

1. Lateral column

 

:''Iliocostalis'' arises from the ilium and transverse processes of the lumbar vertebrae to insert on cranial lumbar vertebrae and ribs, spanning about 4 vertebrae.

''Iliocostalis'' arises from the ilium and transverse processes of the lumbar vertebrae to insert on cranial lumbar vertebrae and ribs, spanning about 4 vertebrae.

2. Middle column

2. Middle column

 

:''Longissimus'' is the strongest, extending from the ilium and sacrum to the head and neck.

''Longissimus'' is the strongest, extending from the ilium and sacrum to the head and neck.

3. Medial column

3. Medial column

 

:''Transversospinalis'' is the most complex, lying between the medial vertebral arches and the spinous processes.

''Transversospinalis'' is the most complex, lying between the medial vertebral arches and the spinous processes.

Innervation comes from the dorsal branches of the spinal nerves. They are rarely of clinical importance.

Innervation comes from the dorsal branches of the spinal nerves. They are rarely of clinical importance.

'''Longus colli'''

'''Longus colli'''

 

:From the cranial thoracic region to the atlas, covering the ventral vertebral bodies

From the cranial thoracic region to the atlas, covering the ventral vertebral bodies.

'''Rectus capitis ventralis'''

'''Rectus capitis ventralis'''

 

:From the atlas to ventral skull

From the atlas to ventral skull.

'''Longus capitis'''

'''Longus capitis'''

 

:From the midcervical vertebrae to the skull

From the midcervical vertebrae to the skull.

'''Scalenus''' muscles

'''Scalenus''' muscles

From the caudal cervica vertebrae to first few ribs, which they stabilize on inspiration.

 

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[[Category:Musculoskeletal System - Anatomy & Physiology]]

[[Category:Musculoskeletal System - Anatomy & Physiology]]

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