Head, Neck & Neuroanatomy

The infratemporal fossa contains two of the four principle muscles of mastication, medial and lateral pterygoid. The tendon of a third muscle, temporalis, is also found in this region. The remaining muscle, masseter, lies on the lateral surface of the ramus, but is considered here with the muscles of mastication. The masticatory muscles are most immediately concerned with movements to the mandible at the temporomandibular joints.

A neuroepithelial receptor is a neuron with a soma situated near a sensory surface and an axon, which conveys sensory signals into the CNS to synapse on second order neurons. This is an evolutionarily primitive arrangement and the only example in man is the sensory neuron of the olfactory epithelium.

Branches of inferior alveolar nerve:
Mylohyoid branch: supplies mylohyoid muscle and anterior belly of digastrics branches supplying lower teeth and gums
Mental nerve: supplies skin of chin along with the skin and mucous membrane of the lower lip

The sublingual gland is the smallest of the main salivary glands. Each gland is narrow, flat, shaped like an almond and weighs 4 g. The sublingual gland lies on mylohyoid and is covered by the mucosa of the floor of the mouth, which is raised as a sublingual fold.

Digastric muscle has two bellies and lies below the mandible, extending from the mastoid process to the chin. The posterior belly, which is longer than the anterior, is attached in the mastoid notch of the temporal bone and passes downwards and forwards.
The anterior belly is attached to the digastric fossa on the base of the mandible near the midline and it slopes downwards and backwards. The two bellies meet in an intermediate tendon, which runs in a fibrous sling attached to the greater cornu of the hyoid bone and is sometimes lined by a synovial sheath. The tendon perforates the stylohyoid.

The floor of the temporal fossa is formed by the frontal and parietal bones, the greater wing of the sphenoid and the squamous part of the temporal bones. All four bones meet on each side at an H-shaped junction of sutures termed as the pterion.

Afferent nerve fibres carrying taste information are the peripheral processes of neuronal cell bodies in the geniculate ganglion of the facial nerve.

Superior constrictor is inserted into the median raphe, being also prolonged by means of an aponeurosis to the pharyngeal spine on the basilar part of the occipital bone.Sternothyroid arises from the posterior surface of the manubrium sterni inferior to the origin of sternohyoid and from the posterior edge of the cartilage of the first rib. It is attached above to the ablique line on the thyroid cartilage, where it delineates the upward extent of the thyroid gland. 

The cervical plexus is formed by the ventral rami of the upper four cervical nerves and supplies some neck muscles and the diaphragm and areas of skin on the head, neck and chest.

Areas 44 and 45 constitute the motor speech area (broca’s area).
Broca’s area is premotor area labelled ‘word formation’ lying immediately anterior to primary motor cortex and immediately above the sylvian fissure.

The inferior orbital fissure connects the orbit with the pterygopalatine and infratemporal fossae. It transmits the infraorbital and zygomatic branches of the maxillary nerve and accompanying vessels, orbital rami from the pterygopalatine ganglion and a connection between the inferior ophthalmic vein and pterygoid venous plexus.

Cubital tunnel syndrome, which involves pain or abnormal sensations in the elbow area, is seen in musicians especially guitarists. The reason of the pain is nerve compression.

A thin, fibrous palatine aponeurois supports the muscles and strengthens the soft palate. It is attached to the posterior and the inferior surface of the hard palate behind the palatine crest.

The tingling sensation felt in the nose just before sneezing is carried by nasociliary nerve which is a branch of trigeminal nerve.
 

Middle meningeal artery

1. Branch of 1^st part of maxillary artery
2. Lies lateral to sphenomandibular ligament and medical to lateral pterygoid in the infratemporal fossa
3. Passes between two roots of auriculotemporal nerve near its origin

Afferent fibres of cornea pass through trigeminal nerve while efferent come by facial nerve.

1. The afferent component of corneal reflex is mediated through the ophthalmic branch of the trigeminal nerve (V nerve).
2. The efferent component is mediated through the facial nerve (VII nerve).

The mylohyoid nerve branches from the inferior alveolar nerve (a branch of the mandibular nerve, the third part of the trigeminal nerve) just before it enters the mandibular foramen.
It descends in a groove on the deep surface of the ramus of the mandible, and reaching the under surface of the mylohyoid muscle, it supplies both the mylohyoid and the anterior belly of the digastrics muscle.

The glossopharyngeal nerve is distributed to the postsulcal part of the tongue (posterior one third) and the circumvallate papillae.

The gonial is very high in children: 130^o in fetus and 140^o at birth, and it progressively decreases in the growth period.

The palatoglossal arch (glossopalatine arch, anterior pillar of fauces) on either side runs downwards, sidewards and forwards to the side of the base of the tongue and is formed by the projection of the glossopalatinus with its covering mucous membrane.

It contains efferent preganglionic parasympathetic (secretomotor) fibres which enter the submandibular ganglion, from which postganglionic fibres are relayed to submandibular and sublingual glands.

Definition: Composite muscles are those, whose functions are regarded the same in terms of skeletal structure and muscle arrangement condition, as a single muscle model, e.g. vastus intermedius, lateralis and medialis working with rectus femoris on the knee joint for its extension.

Synovial joints are called diarthroses with few exceptions (the temporomandibular joint and those involving the clavicles, which have intervening fibrocartilaginous discs). They occur between the ends or other defined surfaces of endochondral bones.

Efferent nerves: III, IV, XI, XII
Afferent nerves: I, II, VIII
Mixed: V, VII, IX, X

The marginal mandibular branches, of which there are usually two, run forwards towards the angle of the mandible under platysma, at first, superficial to the upper part of the digastrics triangle, then turning up and forwards across the body of the mandible to pass under depressor anguli oris.

Branches of the auriculotemporal and masseteric nerves and postganglionic sympathetic nerves supply the tissues associated with the capsular ligament and the looser posterior bilaminar extension of the disc.

When a jaw muscle contracts in the absence of a restraint, the mandible is pulled in the direction of the shortening muscle.
The lateral pterygoids are each capable of exerting about 160 N force, a total of 320 N, and yet less than 5% of this is used to protrude or open the jaw.

Brachycephaly: Early fusion of coronal suture

The anterior belly of digastric is supplied by the mylohyoid branch of the inferior alveolar nerve and the posterior belly is supplied by the facial nerve. The different innervation of the two parts reflects their separate derivation from the mesenchyme of the first and second branchial arches.

At the epiphyseal growth plate (physes) new bone growth occurs by the process of enchondral ossification, i.e. ossification of proliferating cartilage. This process sequentially involves proliferation and hypertrophy of chondrocytes, their calcification and vascular invasion. Replacement of red bone marrow with the white marrow is not seen.

Clear segmentation equivalent to the somites of the trunk is seen only in the paraxial mesoderm of the occipital region, which gives rise to the occipital part of the skull and the extrinsic musculature of the tongue.

The basal lamina is a layer of extracellular matrix on which epithelium sits and is secreted by the epithelial cells. It is often confused with the basement membrane, and sometimes used inconsistently in the literature.

The facial nerve supplies the second arch.

Lesions of the sympathetic supply result in the drooping of the upper eyelid (ptosis), as seen in Horner’s syndrome.

Causes of epiphora include occular irritation and inflammation (including trichiasis and entropion) or an obstructed tear outflow tract, which is divided according to its anatomical location (i.e. ectropion, punctual, canalicular or nasolacrimal duct obstruction). The latter is often due to ageing (a spontaneous process), infection (i.e. dacryocystitis), rhinitis and in neonates or infants, failure of the nasolacrimal duct to open.

Anesthesia dolorosa is one of the most dreaded complications of neurosurgery and is considered to be nonreversible. It occurs when the trigeminal nerve is damaged by surgery or physical trauma in such a way that the feeling sensation in part of the face is reduced or eliminated entirely while the sense of pain remains.

Cartilaginous joints are themselves classified into synchondroses (primary cartilaginous joints) and symphyses (secondary cartilaginous joints).
When fully formed, each group shares common features and also has distinctive structural and functional features. The terms primary and secondary are only useful in the instances of certain symphyses which, developmentally, are preceded by synchondroses within which further differentiation occurs.

Motor supply: All the intrinsic muscles, except the palatoglossus are supplied by the hypoglossal nerve. The palatoglossus is supplied by the cranial part of accessory nerve through the pharyngeal plexus.

A gomphosis is a peg-and-socket joint and is restricted to the fixation of teeth in their alveolar sockets in the mandible and maxillae. The collagen of the periodontium connects dental cement with alveolar bone. The fibrous connection between a tooth and its socket is a periodontal ligament. In modern, more anatomical, joint classification, the gomphosis is simply considered a fibrous joint because the tissue linking the structures is ligamentous.

Following a similar course on both sides, the common carotid artery ascends, diverging laterally from behind the sternoclavicular joint to the level of the upper border of the thyroid cartilage of the larynx (C3-C4 junction), where it divides into external and internal carotid arteries. This bifurcation can sometimes be at a higher level.

The fibrous membrane, forming the cranial vault before ossification, is unossified at the angles of the parietal bones, leaving six fonticuli (fontanelles), two medians (anterior and posterior) and two lateral pairs (sphenoidal and mastoid). The anterior fontanelle is the largest. The anterior fontanelle is triangular in shape.

The parotid duct crosses masseter and turns medially at its anterior border at almost a right angle to traverse the buccal fat pad and buccinator opposite the crown of the upper third molar tooth.

The middle constrictor is a fan-shaped sheet attached anteriorly to the lesser cornu of the hyoid and the lower part of the stylopyiod ligament (the chondropharyngeal part of the muscle) and to the whole of the upper part of the greater cornu of the hyoid (the ceratopharyngeal part).