Cerebral Duramater

 The dura mater is the outermost, thickest and toughest membrane covering the brain 

There are two layers of dura:

a. An outer or endosteal layer which serves as an internal periosteum or endosteum or endocranium for the skull bones.

b. An inner or meningeal layer which surrounds the brain. The meningeal layer is continuous with the spinal dura mater.

The two layers are fused to each other at all places, except where the cranial venous sinuses are enclosed between them.

Endosteal Layer or Endocranium:

1. The endocranium is continuous:

a. With the periosteum lining the outside of the skull or pericranium through the sutures and foramina.

b. With the periosteal lining of the orbit through the superior orbital fissure.

2. It provides sheaths for the cranial nerves, the sheaths fuse with the epineurium outside the skull. 

Over the optic nerve, the dura forms a sheath which becomes continuous with the sclera.

3. Its outer surface is adherent to the inner surface of the cranial bones by a number of fine fibrous and

vascular processes. 

The adhesion is most marked at the sutures, on the base of the skull and around the foramen magnum.

Meningeal Layer

At places, the meningeal layer of dura mater is folded on itself to form partitions which divide the cranial cavity into compartments which lodge different parts of the brain.

 The folds are:  

1. Falx cerebri, 

2. Tentorium cerebelli, 

3. Falx cerebelli, 

4. Diphragma sellae.

Falx cerebri

The falx cerebri is a large sickle-shaped fold of dura mater occupying the median longitudinal fissure

between the two cerebral hemispheres. 

It has two ends:

1. The anterior end is narrow, and is attached to the crista galli.

2. The posterior end is broad, and is attached along the median plane to the upper surface of the tentorium

cerebelli.

The falx cerebri has two margins:

1. The upper margin is convex and is attached to the lips of the sagittal sulcus.

2. The lower margin is concave and free.

The falx cerebri has right and left surfaces each of which is related to the medial surface of the corresponding cerebral hemisphere.

Three important venous sinuses are present in relation to this fold. 

1. The superior sagittal sinus lies along the upper margin; 

2. The inferior sagittal sinus along the lower margin

3. The straight sinus along the line of attachment of the falx to the tentorium cerebelli

Tentorium cerebelli

The tentorium cerebelli is a tent-shaped fold of dura mater, forming the roof of the posterior cranial fossa. 

It separates the cerebellum from the occipital lobes of the cerebrum, 

broadly divides the cranial cavity into supratentorial and infratentorial compartments. 

The infratentorial compartment, in other words, is the posterior cranial fossa containing the hindbrain and the lower part of the midbrain.

The tentorium cerebelli has 

a free margin and 

an attached margin  

The anterior free margin is U-shaped and free. 

The ends of the 'U' are attached anteriorly to the anterior clinoid processes. 

This margin bounds the tentorial notch which is occupied by the midbrain and the anterior part of the superior vermis.

The outer or attached margin is convex. 

Posterolaterally, it is attached to the lips of the transverse sulci on the occipital bone, and on the posteroinferior angle of the parietal bone.

Anterolaterally, it is attached to the superior border of the petrous temporal bone and to the posterior clinoid processes. 

Along the attached margin, there are the transverse and superior petrosal venous sinuses.

The trigeminal or Meckel's cave is a recess of dura mater present in relation to the attached margin of the

tentorium. 

It is formed by evagination of the inferior layer of the tentorium over the trigeminal impression on the petrous temporal bone. 

It contains the trigeminal ganglion.

The free and attached margins of the tentorium cerebelli cross each other near the apex of the petrous

temporal bone. 

Anterior to the point of crossing, there is a triangular area which forms the posterior part of the roof of the cavernous sinus, and is pierced by the third and fourth cranial nerves.

The tentorium cerebelli has two surfaces. 

The superior surface is convex and slopes to either side from the median plane. 

The falx cerebri is attached to this surface, in the midline; 

the straight sinus lies along the line of this attachment. 

The superior surface is related to the occipital lobes of the cerebrum. 

The inferior surface is concave and fits the convex superior surface of the cerebellum. 

The falx cerebelli is attached to its posterior part

Falx cerebelli

The falx cerebelli is a small sickle-shaped fold of dura mater projecting forwards into the posterior cerebellar notch.

The base of the sickle is attached to the posterior part of the inferior surface of the tentorium cerebelli in the median plane. 

The apex of the sickle is frequently divided into two parts which are lost on the sides of the foramen magnum.

The posterior margin is convex and is attached to the internal occipital crest. 

It encloses the occipital sinus.

The anterior margin is concave and free.

Diaphragma sellae

The diaphragma sellae is a small circular, horizontal fold of dura mater forming the roof of the hypophyseal fossa.

Anteriorly, it is attached to the tuberculum sellae.

Posteriorly, it is attached to the dorsum sellae. 

On each side, it is continuous with the dura mater of the middle cranial fossa.

The diaphragma has a central aperture through which the stalk of the hypophysis cerebri passes.

Blood Supply

The outer layer is richly vascular. 

The inner meningeal layer is more fibrous and requires little blood supply.

1. The vault or supratentorial space is supplied by the middle meningeal artery.

2. The anterior cranial fossa and the dural lining is supplied by meningeal branches of the anterior ethmoidal, posterior ethmoidal and ophthalmic arteries.

3. The middle cranial fossa is supplied by the middle meningeal, accessory meningeal, and internal carotid arteries; and by meningeal branches of the ascending pharyngeal artery.

4. The posterior cranial fossa is supplied by meningeal branches of the vertebral, occipital and ascending pharyngeal arteries.

Nerve Supply

1. The dura of the vault has only a few sensory nerves which are derived mostly from the ophthalmic division of the trigeminal nerve.

2. The dura of the floor has a rich nerve supply and is quite sensitive to pain.

a. The anterior cranial fossa is supplied mostly by the anterior ethmoidal nerve and partly by the maxillary nerve.

b. The middle cranial fossa is supplied by the maxillary nerve in its anterior half, and by branches of the mandibular nerve and from the trigeminal ganglion in its posterior half.

c. The posterior cranial fossa is supplied chiefly by recurrent branches from first, second and third cervical spinal nerves and partly by meningeal branches of the ninth and tenth cranial nerves.

Clinical Anatomy

Pain sensitive intracranial structures are:

a. The large cranial venous sinuses and their tributaries from the surface of the brain.

b. Dural arteries.

c. The dural floor of the anterior and posterior cranial fossae.

d. Arteries at the base of the brain.

Headache may be caused by:

a. Dilatation of intracranial arteries.

b. Dilatation of extracranial arteries.

c. Traction or distension of intracranial pain sensitive structures.

d. Infection and inflammation of intracranial and extracranial structures supplied by the sensory cranial and cervical nerves.

Extradural and subdural haemorrhages are both common. 

An extradural haemorrhage can be distinguished from a subdural haemorrhage because of the following differences.

a. The extradural haemorrhage is arterial due to injury to middle meningeal artery, whereas subdural haemorrhage is venous in nature.

b. Symptoms of cerebral compression are late in extradural haemorrhage.

c. In an extradural haemorrhage, paralysis first appears in the face and then spreads to the lower parts of the body.

In a subdural haemorrhage, the progress is haphazard.

d. In an extradural haemorrhage, there is no blood in the CSF; while it is a common feature of subdural haemorrhage

Watch lectures on YouTube:

Dural Folds | Falx cerebri | Tentorium cerebelli | Falx cerebelli | Diaphragma sella | Attachments |

Muscles of the Back of Neck

The muscles of the entire back can be grouped into the following four layers from superficial to the deeper plane.

1. Trapezius and latissimus dorsi

2. Levator scapulae, rhomboids (two), serratus posterior superior, Splenius

3. a. Erector spinae or sacrospinalis

   b. semispinalis

4. Multifidus, rotatores, interspinales, intertransversii and suboccipital muscles

Splenius muscles are two in number. 

These are splenius cervicis and splenius capitis. 

These cover the deeper muscles like a bandage 

Origin: From lower half of ligamentum nuchae and spines of upper 5 thoracic vertebrae. 

These curve in a half spiral fashion and separate into splenius cervicis and splenius capitis.

Splenius cervicis gets inserted into the posterior tubercles of transverse processes of C1-C4 vertebrae.

Splenius capitis forms the floor of the posterior triangle and gets inserted into the mastoid process beneath the sternocleidomastoid muscle

It is supplied by dorsal rami of C1-C6 nerves.

Suboccipital Muscles

1. Rectus Capitis Posterior Major 

Origin - Spine of axis

Insertion - Lateral part of the area below the inferior nuchal line

Nerve Supply - Suboccipital nerve or dorsal ramus Cl

Action

1. Mainly postural

2. Acting alone it turns the chin to the same side

3. Acting together the two muscles extend the head

Rectus capitis posterior minor

Origin - Posterior tubercle of atlas

Insertion - Medial part of the area below the inferior nuchal line

Nerve Supply - Suboccipital nerve or dorsal ramus Cl

Actions

1. Mainly postural

2. Extends the head

Obliquus capitis superior( superior oblique)

 Origin: Transverse process of atlas

Insertion: Lateral area between the nuchal lines

Nerve Supply: Suboccipital nerve or dorsal ramus Cl

Actions:

1. Mainly postural

2. Extends the head

3. Flexes the head laterally

Obliquus capitis inferior (inferior oblique)

Orgin: Spine of axis

Insertion: Transverse process of atlas

Nerve Supply: Suboccipital nerve or dorsal ramus Cl

Actions:

1. Mainly postural

2. Turns chin to the same side

Suboccipital Triangle

Boundaries

Superomedially

Rectus capitis posterior major muscle supplemented by the rectus capitis posterior minor.

Superolaterally

Superior oblique capitis muscle.

lnferiorly

Inferior oblique capitis muscle.

Roof - 

1. Skin

2. Superficial Fascia with greater & third occipital Nerve

3. Trapezius & Sternocleidomastoid

4. Splenius capitis

5. Semispinalis capitis & Longissimus capitis

Floor

1. Posterior arch of atlas.

2. Posterior atlanto-occipital membrane.

Contents

1 Third part of vertebral artery.

2 Dorsal ramus of nerve C1 - suboccipital nerve.

3 Suboccipital plexus of veins.

Applied Anatomy:

1. Neck rigidity, seen in cases with meningitis, is due to spasm of the extensor muscles. This is caused by irritation of the nerve roots during their passage through the subarachnoid space which is infected. 

Passive flexion of neck and straight leg raising test cause pain as the nerves are stretched

2. Cisternal puncture is done when lumbar puncture fails. 

The patient either sits up or lies down in the left lateral position. 

A needle is introduced in the midline above the spine of axis in forward and upward direction parallel to an imaginary line extending from external acoustic meatus to nasion.

It passes through the posterior atlanto-occipital membrane between the posterior arch of atlas and the posterior margin of foramen magnum. The needle enters the cerebellomedullary cistern and small amount of CSF is withdrawn.

3. Neurosurgeons approach the posterior cranial fossa through this region.

Watch the lectures on YouTube:

Suboccipital Region | Boundaries | Suboccipital muscles

The Suboccipital Triangle | Boundaries | Contents

Features of the Contents & Structures in the roof of Suboccipital Triangle | Cisternal Puncture

Atlanto-axial Joint

 Types & Articular Surfaces

• These joints comprise:
• 1 A pair of lateral atlanto-axial joints between the inferior facets of the atlas and the superior facets of the axis. 
• These are plane joints.
• 2 A median atlanto-axial joint between the dens (odontoid process) and the anterior arch and between dens and transverse ligament of the atlas. 
• It is a pivot joint. 
• The joint has two separate synovial cavities, anterior and posterior.

Ligaments

The lateral atlantoaxial joints are supported by:

a. A capsular ligament all around.

b. The lateral part of the anterior longitudinal ligament.

c. The ligamentum flavum.

The median atlantoaxial joint is strengthened by the following:

a. The anterior smaller part of the joint between the anterior arch of the atlas and the dens is surrounded by a loose capsular ligament.

b. The posterior larger part of the joint between the dens and transverse ligament (often called a bursa) is often continuous with one of the atlantooccipital joints. 

Its main support is the transverse ligament which forms a part of the cruciform ligament of the atlas.

The transverse ligament is attached on each side to the medial surface of the lateral mass of the atlas.

In the median plane, its fibres are prolonged upwards to the basiocciput and downwards to the body of the axis, thus forming the crucifurm ligament of the atlas vertebra. 

The transverse ligament embraces the narrow neck of the dens, and prevents its dislocation.

Movements

• Movements at all three joints are rotatory and take place around a vertical axis. 
• The dens forms a pivot around which the atlas rotates (carrying the skull with it). 
• The movement is limited by the alar ligaments 
• The rotatory movements are brought about by the obliqus capitis inferior, the rectus capitis posterior major and the splenius capitis of one side, acting with the sternocleidomastoid of the opposite side

Clinical Anatomy

Death in execution by hanging is due to dislocation of the dens following rupture of the transverse ligament of the dens, which then crushes the spinal cord and medulla. 

However, hanging can also cause fracture through the axis, or separation of the axis from the third 

cervical vertebra

Watch the lectures on YouTube:

Atlanto - Axial Joints | Median & Lateral Joints | Articular surfaces Ligaments| Movements| Muscles

Atlanto-occipital Joint

 Type & Articular surface

• These are synovial joints of the ellipsoid variety.
• Above: The occipital condyles, which are convex
• Below: The superior articular facets of the atlas vertebra.
• These are concave. 
• The articular surfaces are elongated, and are directed forwards and medially.

Ligaments

• I. The fibrous capsule surrounds the joint. 
• It is thick posterolaterally and thin anteromedially.
• 2. The anterior atlanto-occipital membrane extends from the anterior margin of the foramen magnum above, below to the upper border of the anterior arch of the atlas. 
• Laterally, it is continuous with the anterior part of the capsular ligament, 
• anteriorly it is strengthened by the cord-like anterior longitudinal ligament.
• 3. The posterior atlanto-occipital membrane extends from the posterior margin of the foramen magnum above, to the upper border of the posterior arch of the atlas below. 
• Inferolaterally, it has a free margin which arches over the vertebral artery and the first cervical nerve. 
• Laterally, it is continuous with the posterior part of the capsular ligament.

Blood Supply & Nerve Supply

The joint is supplied by the vertebral artery and by the first cervical nerve.

Movements 

• they permit movements around two axes.
• Flexion and extension (nodding) occur around a transverse axis. 
• Slight lateral flexion is permitted around an anteroposterior axis
• I. Flexion is brought about by the longus capitis and the rectus capitis anterior.
• 2. Extension is done by the rectus capitis posterior major and minor, the obliquus capitis superior, the semispinalis capitis, the splenius capitis, and the upper part of the trapezius.
• 3. Lateral bending is produced by the rectus capitis, the semispinalis capitis, the splenius capitis, the sternocleidomastoid, and the trapezius

Watch the lectures on YouTube:

Atlanto Occipital Joint | Type | Articular Surfaces | Ligaments | Movements | Muscles

Oesophagus (Cervical Part)

• The oesophagus is a muscular food passage lying between the trachea and the vertebral column.
• Normally, its anterior and posterior walls are in contact.
• The oesophagus expands during the passage of food by pressing into the posterior muscular part of the trachea.
• The oesophagus is a downward continuation of the pharynx
• begins at the lower border of the cricoid cartilage, opposite the lower border of the body of vertebra C6. 
• It passes downwards behind the trachea, traverses the superior and posterior mediastina of the thorax, and 
• ends by opening into the cardiac end of the stomach in the abdomen. 
• It is about 25 cm long.

The cervical part of the oesophagus is related:

a. Anteriorly, to the trachea and to the right and left recurrent laryrngeal nerves.

b. Posteriorly, to the longus colli muscle and the vertebral column.

c. On each side, to the corresponding lobe of the thyroid gland; and on the left side, to the thoracic duct.

The cervical part of the oesophagus is supplied by the inferior thyroid arteries. 

Its veins drain into the left brachiocephalic vein. 

Its lymphatics pass to the deep cervical lymph nodes. 

The oesophagus is narrowest at its junction with the pharynx, the junction being the narrowest part of 

the gastrointestinal tract, except for the vermiform appendix.

Watch the lectures on YouTube:

Oesophagus | Extent | Parts | Relations Of Cervical Part | Oesophagoscope

Trachea (Cervical Part)

• The trachea is a noncollapsible, wide tube forming the beginning of the lower respiratory passages. 
• It is kept patent because of the presence of C-shaped cartilaginous ‘rings' in its wall. 
• The cartilages are deficient posteriorly, this part of the wall being made up of muscle (trachealis) and fibrous tissue. 
• The soft posterior wall allows expansion of the oesophagus during passage of food.

DIMENSIONS

• The trachea is about 10 to 15 cm long. 
• Its upper half lies in the neck and its lower half in the superior mediastinum. 
• The external diameter measures 2 cm in the male and 1.5 cm in the female.
• The lumen is smaller in the living than in cadavers. 
• It is about 3 mm at l year of age, and corresponds to the age in years during childhood, with a maximum of 12 mm at puberty.

CERVICAL PART OF TRACHEA

1. The trachea begins at the lower border of the cricoid cartilage opposite the lower border of vertebra C6.

It runs downwards and slightly backwards in front of the oesophagus, follows the curvature of the spine,

and enters the thorax in the median plane.

2. In the neck, the trachea is comparatively superficial and has the following relations.

Anterior

1. Isthmus of the thyroid gland covering the second and third tracheal rings.

2. Inferior thyroid veins below the isthmus.

3. Pretracheal fascia enclosing the thyroid and the inferior thyroid veins.

4. Sternohyoid and sternothyroid muscles.

5. Investing layer of the deep cervical fascia and the suprasternal space.

6. The skin and superficial fascia.

7. In children, the left brachiocephalic vein extends into the neck and, then, lies in front of the trachea.

Posterior

1. Oesophagus

2. Longus colli

3. Recurrent laryrngeal nerve in the tracheo-oesophageal groove.

On Each Side

1 The corresponding lobe of the thyroid glands.

2 The common carotid artery within the carotid sheath

• The trachea is supplied by branches from the inferior thyroid arteries. 
• Its veins drain into the left brachiocephalic vein. 
• Lymphatics drain into the pretracheal and paratracheal nodes.
• Parasympathetic nerves (from the vagus through the recurrent laryngeal nerve) are sensory and secretomotor to the mucous membrane, and motor to the trachealis muscle. 
• Sympathetic nerves (from the cervical ganglion) are vasomotor.

Clinical Anatomy

• The trachea may be compressed by pathological enlargements of the thyroid, the thymus, lymph nodes and the aortic arch. This causes dyspnoea, irritative cough, and often a husky voice.
• Tracheostomy is an emergency operation done in cases of laryngeal obstruction (foreign body, diphtheria, carcinoma, etc.). 
• It is commonly done in the retrothyroid region after retracting the isthmus of the thyroid gland.

Watch lectures on YouTube:

Trachea | Extent | Dimensions | Structure | Relations | Clinical Anatomy

Cervical Plexus

FORMATION

• The cervical plexus is formed by the ventral rami of the upper four cervical nerves. 
• The rami emerge between the anterior and posterior tubercles of the cervical transverse processes, grooving the costotransverse bars. 

• The four roots are connected with one another to form three loops

Position and Relations of the Plexus

The plexus is related:

1. Posteriorly, to the muscles which arise from the posterior tubercles of the transverse processes, i.e.the levator scapulae and the scalenus medius.

2. Anteriorly, to the prevertebral fascia, the internal jugular vein and the sternocleidomastoid.

Branches

Superficial or cutaneous branches

1. Lesser occipital (C2)

2. Great auricular (C2, C3)

3. Transverse (anterior) cutaneous nerve of the neck(c2, c3)

4. Supraclavicular (C3, C4)

Deep Branches

1. Grey rami pass from the superior cervical ganglion to the roots of C1-C4 nerves.

2. A branch from C1 joins the hypoglossal nerve and carries fibres for supply of the thyrohyoid and geniohyoid muscles (directly) and the superior belly of the omohyoid through the ansa cervicalis.

3. A branch from C2 to the sternocleidomastoid and branches from C3 and C4 to the trapezius communicate with the accessory nerve

Muscular Branches

Muscles supplied solely by cervical plexus:

1. Rectus capitis anterior from C1.

2. Rectus capitis lateralis from C1, C2.

3. Longus capitis from C1- C3.

4. Lower root of ansa cervicalis (descendens cervicalis) from C2, C3 (to sternohyoid, sternothyroid and inferior belly of omohyoid.

Muscles supplied by cervical plexus along with the brachial plexus or the spinal accessory nerve:

a. Sternocleidomastoid from C2 along with accessory nerve.

b. Trapezius from C3, C4 along with accessory nerve.

c. Levator scapulae from C3, C4 with C5 (dorsal scapular nerve).

d. Phrenic nerve from C3, C4, C5.

e. Longus colli from C3-C8.

f. Scalenus medius from C3-C8.

g. Scalenus anterior from C4-C6.

h. Scalenus posterior from C6-C8.

Watch lectures on YouTube:

Cervical Plexus | Formation, Branches, Communicating Branches | Ansa Cervicalis|

Cervical Pleura

• The cervical pleura covers the apex of the lung. 
• It rises into the root of the neck, about 5 cm above the first costal cartilage and 2.5 cm above the medial one-third of the clavicle. 
• The pleural dome is strengthened on its outer surface by the suprapleural membrane 
• so that the root of the neck is not puffed up and down during respiration

Relations

Anterior

1. Subclavian artery and its branches

2 Scalenus anterior.

Posterior

Neck of the first rib with the following structures in front of it.

1. Sympathetic trunk 

2. First posterior intercostal vein

3. Superior intercostal artery

4. The first thoracic nerve.

Lateral

i. Scalenus medius

ii. Lower trunk of the brachial plexus.

Medial

1. Vertebral bodies

2. Oesophagus

3. Trachea

4. Left recurrent laryngeal nerve

5. Thoracic duct (on left side)

6. Large arteries and veins of the neck.

Scalene Muscles

• There are usually three scalene muscles, the scalenus anterior, the scalenus medius and the scalenus posterior. 
• The scalenus medius is the largest, and the scalenus posterior the smallest, of three. 
• These muscles extend from the transverse processes of cervical vertebrae to the first two ribs. 
• They can, therefore, either elevate these ribs or bend the cervical part of the vertebral column laterally

Scalenus anterior

Origin 

Anterior tubercles of transverse processesof cervical vertebrae 3, 4, 5 and 6

Insertion

Scalene tubercle and adjoining ridge on the superior surface of the first rib (between subclavian artery and 

vein)

Nerve Supply

Ventral rami of nerves C4-C6

Action

a. Anterolateral flexion of cervical spine

b. Rotates cervical spine to opposite side

c. Elevates the first rib during inspiration

d. Stabilises the neck along with other muscles

Relations of scalenus anterior. 

The scalenus anterior is a key muscle of the lower part of the neck because of its intimate relations to many important structures in this region. It is a useful surgical landmark.

Anterior:

a. Phrenic nerve covered by prevertebral fascia.

b. Lateral part of carotid sheath containing the internal jugular vein.

c. Sternocleidomastoid.

d. Clavicle.

Posterior:

a. Brachial plexus.

b. Subclavian artery.

c. Scalenus medius.

d. Cervical pleura covered by the suprapleural membrane

The medial border of the muscle is related:

a. In its lower part to an inverted ‘V'-shaped interval, formed by the diverging borders of the scalenus anterior and the longus colli. 

This interval contains many important structures as follows:

i. Vertebral vessels running vertically from the base to the apex of this space.

ii. Inferior thyroid artery arching medially at the level of the 6th cervical transverse process.

iii. Sympathetic trunk.

iv. The first part of the subclavian artery traverses the lower part of the gap.

v. On the left side, the thoracic duct arches laterally at the level of the seventh cervical transverse process

vi. The carotid sheath covers all the structures mentioned above.

vii. The sternocleidomastoid covers the carotid sheath.

b. In its upper part, the scalenus anterior is separated from the longus capitis by the ascending cervical artery.

The lateral border of the muscle is related to the trunks of the brachial plexus and the subclavian artery which emerges at this border and enter the posterior triangle

Scalenus medius

Origin

a. Posterior tubercles of transverse processes of cervical vertebrae 3, 4, 5, 6,7

b. Transverse process of axis and sometimes also of the atlas vertebra

Insertion

Superior surface of the first rib behind the groove for the subclavian artery

Nerve Supply

Ventral rami of nerves C3-C8

Action

a. Lateral flexion of the cervical spine.

b. Elevation of first rib

c. Stabilises neck along with other muscles

Scalenus posterior

Origin

Posterior tubercles of transverse processes of cervical vertebrae 4,5,6

Insertion

Outer surface of the second rib behind the tubercle for the serratus anterior

Nerve Supply

Ventral rami of nerves C6-C8

Action

Lateral flexion of cervical spine

Elevation of the second rib

Stabilises neck along with other muscles

Sometimes a fourth, rudimentary scalene muscle, the scalenus minimus is present. 

Origin 

from the anterior border of the transverse process of vertebra C7 and

Insertion 

the inner border of the first rib behind the groove for the subclavian artery and into the dome of the cervical pleura. 

The suprapleural membrane is regarded as the expansion this muscle.

Contraction of the scalenus minimus pulls the dome of the cervical pleura

Watch lectures on YouTube:

Paravertebral Muscles - The Scalenus Anterior muscle| Attachments | Nerve supply| Action | Relations

Para-vertebral muscles - Scalenii medius, posterior & minimus muscles | Attachments | Morphology |

Vertebral Artery

• The vertebral artery is one of the two principal arteries which supply the brain. 
• In addition, it also supplies the spinal cord, the meninges, and the surrounding muscles and bones. 
• It arises from the posterosuperior aspect of the first part of the subclavian artery near its commencement. 
• It runs a long course, and ends in the cranial cavity by supplying the brain. 
• The artery is divided into four parts

First Part

• The first part extends from the origin of the artery (from the subclavian artery) to the transverse process of the sixth cervical vertebra.
• This part of the artery runs upwards and backwards in the triangular space between the scalenus anterior and the longus colli muscles called as the scalenovertebral triangle

Relations

Anterior

1. Carotid sheath with common carotid artery

2. Vertebral vein

3. Inferior thyroid artery

4. Thoracic duct on left side.

Posterior

1. Transverse process of 7th cervical vertebra 

2. Stellate ganglion

3. Ventral rami of nerves C7, C8.

Second Part

The second part runs through the foramina transversaria of the upper six cervical vertebrae. 

Its course is vertical up to the axis vertebra. 

It then runs upwards and laterally to reach the foramen transversarium of the atlas vertebra.

Relations

1. The ventral rami of second to sixth cervical nerves lie posterior to the vertebral artery.

2. The artery is accompanied by a venous plexus and a large branch from the stellate ganglion

Third Part

Third part lies in the suboccipital triangle. 

Emerging from the foramen transversarium of the atlas, the artery winds medially around the posterior aspect of the lateral mass of the atlas. 

It runs medially lying on the posterior arch of this bone, and enters the vertebral canal by passing deep to the lower arched margin of the posterior atlanto-occipital membrane.

Relations

Anterior: Lateral mass of atlas.

Posterior : Semispinalis capitis.

Lateral: Rectus capitis lateralis.

Medial: Ventral ramus of the first cervical nerve.

Inferior:

1. Dorsal ramus of the first cervical nerve

2. The posterior arch of the atlas

Fourth Part

1. The fourth part extends from the posterior atlantooccipital membrane to the lower border of the pons.

2. In the vertebral canal, it pierces the dura and the arachnoid, and ascends in front of the roots of the hypoglossal nerve. 

3. As it ascends, it gradually inclines medially to reach the front of the medulla.

4. At the lower border of the pons, it unites with its fellow of the opposite side to form the basilar artery

BRANCHES OF VERTEBRAL ARTERY

First part has no branches.

Cervical Branches

1. Spinal branches from the second part enter the vertebral canal through the intervertebral 

foramina, and supply the spinal cord, the meninges and the vertebrae.

2. Muscular branches arise from the third part and supply the suboccipital muscles.

Cranial Branches

These arise from the fourth part. 

They are:

1. Meningeal branches

2. The posterior spinal

3. The anterior spinal artery

4. The posterior inferior cerebellar artery

5. Medullary arteries

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Vertebral Artery | Origin| Termination| Parts| Course| Relations|Branches| Subclavian Steal Syndrome