Muscles acting on the Temporomandibular Joint

• Movements of the temporomandibular joint are chiefly from the action of the muscles of mastication.
• The temporalis, masseter, and medial pterygoid muscles produce biting movements.
• The lateral pterygoid muscles protrude the mandible with the help from the medial pterygoid muscles and retruded largely by the posterior fibres of the temporalis muscle.
• Gravity is sufficient to depress the mandible, but if there is resistance, the lateral pterygoid, suprahyoid and infrahyoid, mylohyoid and anterior digastric muscles are activated.

LYMPHOID SYSTEM

Consists of cells, tissues and organs

Protects the body against damage by foreign substances

Immuno competent cells in the lymphoid system distinguish between the bodies own molecules and foreign molecules.

The response is immunity.

lymphoid tissues have a: - reticular framework (collagen III) consisting of:  reticular cells , (indistinguishable from fibroblasts) , lymphocytes, macrophages,  antigen presenting cells, plasma cells

Each organ has special features:

Capsulated – spleen, lymph nodes, thymus

Unencapsulated – tonsils,  Peyers patches. lymphoid nodules in: - alimentary canal

- Nodules in: respiratory tract,  urinary tract, reproductive tracts

2 Types of immunity:

- Cellular: Macrophages - destroy foreign cells

- Humeral – immunoglobulins and antibodies (glycoproteins) interact with foreign substances

- cellular and humeral immune system require accessory cells like: macrophages, antigen presenting cells

Thymus

Lymphocytes develop from mesenchym. The lymphocytes then invade an epithelial premordium .The epithelial cells are pushed apart by lymphocytes. Epithelial cells remain connected through desmosomes to form the epithelial reticular cells.  Septae from the capsule divide the thymus up into incomplete lobules (0,5-2 mm ). Each lobule has a cortex which is packed with lymphocytes. In the middle of the lobule is the lighter staining medulla. The cortex and medulla are continuous. Hassall's corpuscles, consisting of flat epithelial cells, lie in the medulla .The corpuscles increase in size and number through life

Thymus cells:

- Cortex and medulla have the same cells – only their proportions differ

- The predominant cell is the T lymphocytes and precursors

- There are also epithelial reticular cells with large oval nuclei. The cells are joined by desmosomes.

- A few mesenchymal reticular cells are also present.

- There are many macrophages.

Cortex:

- Only capillaries (no other vessels)

- small lymphocytes predominate

- here they do not form nodules

- epithelial cells surround groups of lymphocytes and blood vessels

- around the capillary is a space

- forms blood thymus barrier

- Layers of the blood thymus barrier:

- capillary wall endothelium

basal lamina

little CT with macrophages

- epithelial reticular cells - basal lamina

- cytoplasm of epithelial reticular cells

Medulla:

- Stains light because of many epithelial reticular cells

- 5% of thymic lymphocytes found in medulla

- mature lymphocytes - smaller than that of cortex

- leave through venules to populate organs such as the spleen and lymph nodes

- In the medulla the covering of capillaries by epithelial reticular cells is incomplete - no barrier

- Hassall's corpuscles

- 30 - 150µm .

- consists of layers of epithelial reticular cells

- the central part of the corpuscle may only be cell remnants

- unknown function

Lymph nodes

- Encapsulated

- found throughout the body

- form filters in the lymph tracts

- lymph penetrate through afferent lymph vessels on the convex surface

- exit through efferent lymph vessels of the hilum

- capsule send trabeculae into the node to divide it up into incomplete compartments

- reticular tissue provide the super structure

- under the capsule is a cortex – the cortex is absent at the hilum

- At the centre of the node and at the hilum is a medulla

- The cortex has a subcapsular sinus and peritrabecular sinuses

The sinuses:-

- Incompletely lined by reticular cells

- Have numerous macrophages

- fibres cross the sinuses

- they slow the flow of lymph down -

- so that the macrophages can get a chance to perform their function.

Primary and secondary lymphoid nodules

- Some lymphocytes in the cortex form spherical aggregations 0,2-1 mm Ø called primary nodules (or follicles)

- They contain mainly B lymphocytes but some T- lymphocytes are also present

- A germinal centre may develop in the middle of the nodule when an antigen is present. The nodule then becomes a secondary nodule, which is:

- light staining in the centre because:

- many B lymphocytes increase in size to become plasmablasts

- plasmablasts undergo mitosis to become plasmacytes

- plasmacytes migrate to the follicular periphery and then to the medullary cords where they mature

into plasma cells that secrete antibodies into the efferent lymph.

- lymphocytes that don’t differentiate into plasma cells remain small lymphocytes and are called memory

cells – which migrate to different parts of the body

- memory cells are capable of mounting a rapid humoral response on subsequent contact with the same antigen.

- In the nodules there are also follicular dendritic cells which are:

- non phagocytic

- with cytoplasmic extensions

- trap antigens on their surface

- present it to B and T lymphocytes which then respond

Paracortical Zone

- Between adjacent nodules and between the nodules and the medulla are loosely arranged lymphocytes which form the paracortical area or deep cortical area.

- The main cell type in this area is the T lymphocyte.

- They enter the lymph node with the blood and migrate into the paracortical zone.

- T lymphocytes are stimulated when presented with an antigen by the follicular dendritic cells.

- They transform into large lymphobasts which undergo mitosis to produce activated T lymphocytes.

- These activated T lymphocytes must go to the area of antigen stimulation to perform its function.

- When this happens the paracortex expand greatly.

- Later they join the efferent lymph to leave the lymph node.

- These lymphocytes disappear when the thymus is removed - especially if done at birth

The medulla

- Consists of medulla with branching cords separated by medullary sinusses.

- Througout the medulla are trabeculae.

- The cords contain numerous B lymphocytes and plasma cells.

- A few macrophages and T lymphocytes may also be present.

- Receive and circulate lymph from the cortical sinuses.

- Medullary sinuses communicate with efferent lymph vessels.

Spleen

- Largest lymphatic organ

- Many phagocytic cells

- Filters blood

- Form activated lymphocytes which go into the blood

- Form antibodies

General structures:

- Dense CT capsule with a few smooth muscle fibres encapsulate the spleen

- The capsule is thickened at the hilum.

- Trabeculae from the hilum carry blood vessels and nerves in and out of the spleen.

- The capsule divide the spleen into incomplete compartments.

- The spleen has no lymph vessels because it is a blood filter and not a lymph filter like the lymph nodes.

Splenic pulp

- The lymph nodules are called the white pulp

- The white pulp lies in dark red tissue called red pulp

- Red pulp is composed of splenic cords (Billroth cords) which lie between sinusoids

- Reticular tissue forms the superstructure for the spleen and contains:

- reticular cells

- macrophages

Blood circulation

- The splenic artery divide as it enters the hilum

- The arteries in the trabeculae are called trabecular arteries

- The trabecular arteries give of braches into the white pulp (central arteries).

- The artery may not lie in center but is still called a central artery.

- The central arteries give off branches to the white pulp which go through the white pulp to end in the marginal sinuses on the perimeter of the white pulp.

- The central artery continues into the red pulp (called the pulp artery) where it branches into straight arteries called penicilli.

- The penicilli continue as arterial capillaries some of which are sheated by macrophages.

- The blood from the arterial capillaries flow into the red pulp sinuses that lie between the red pulp cords.

- The way the blood gets from the capillaries into the sinuses is uncertain. It can either:

- Flow directly into the sinuses - closed theory

- Or flow through the spaces between the red pulp cord cells and then enter the sinusoid - open theory.

- Presently the open theory is popular.

- From the sinusoids the blood flow into the: - Red pulp veins

- which join the trabecular veins

- to form form the splenic vein

(Trabecular veins form channels without a wall lined by endothelium in the trabeculae.)

White pulp:

- Forms a lymph tissue sheath around the central artery

- The lymphocytes around the central artery is called the periarterial lymphatic sheath (PALS).

- Which contains mainly T lymphocytes

- So the PALS is chracterized by a central artery.

- True nodules may also be present as an extension of the PALS.

- They displace the central artery so that it lies eccentric.

- Nodules normally have a germinal center and consists mainly of B lymphocytes

- Between the red and white pulp there is a marginal zone consisting of:

- Many sinuses and of  loose lymphoid tissue.

- There are few lymphocytes

- many macrophages

- lots of blood antigens which

- play a major role in immunologic activity.

Red Pulp:

- In the fresh state this tissue has a red colour because of the many erythrocytes.

- Red pulp consists of splenic sinusses separated by splenic cords (cords of Billroth).

- Between reticular cells are macrophages, lymphocytes, granulocytes and plasma cells.

- Many of the macrophages are in the process of phagocytosing damaged erythrocytes.

- The splenic sinusoids are special sinusoidal vessels in the following ways:

- It has a dilated large irregular lumen

- Spaces between unusually shaped endothelial cells permit exchange between sinusoids and adjacent tissues. (The endothelial cells are very long arranged parallel to the direction of the vessel)

- The basal lamina of the sinusoid is not continuous but form rings.

Tonsils

- Tonsils are incompletely encapsulated lymphoid tissues

- There are - Palatine tonsils

- pharyngeal tonsils

- lingual tonsils

Palatine Tonsil

- Contains dense lymphoid tissue.

- Covered by stratified squamous non-keratinized epithelium

- with an underlying CT capsule

- Crypts that enter the tissue end blind.

Lingual Tonsil

- Lie on the posterior 1/3 of the tongue.

- Crypts link up with underlying glands that flush them.

- Epithelial covering is the same as that of the palatine tonsil.

The Lateral Wall of the Orbit

• This wall is thick, particularly its posterior part, which separates the orbit from the middle cranial fossa.
• The lateral wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid bone.

• Anteriorly, the lateral wall lies between the orbit and the temporal fossa.

• The lateral wall is partially separated from the roof by the superior orbital fissure.

Muscles of the Soft Palate

The Levator Veli Palatini (Levator Palati)

• Superior attachment: cartilage of the auditory tube and petrous part of temporal bone.
• Inferior attachment: palatine aponeurosis.
• Innervation: pharyngeal branch of vagus via pharyngeal plexus.

• This cylindrical muscle runs inferoanteriorly, spreading out in the soft palate, where it attaches to the superior surface of the palatine aponeurosis.

• It elevates the soft palate, drawing it superiorly and posteriorly.
• It also opens the auditory tube to equalise air pressure in the middle ear and pharynx.

The Tensor Veli Palatini (Tensor Palati)

• Superior attachment: scaphoid fossa of medial pterygoid plate, spine of sphenoid bone, and cartilage of auditory tube.
• Inferior attachment: palatine aponeurosis.
• Innervation: medial pterygoid nerve (a branch of the mandibular nerve).

• This thin, triangular muscle passes inferiorly, and hooks around the hamulus of the medial pterygoid plate.
• It then inserts into the palatine aponeurosis.

• This muscle tenses the soft palate by using the hamulus as a pulley.
• It also pulls the membranous portion of the auditory tube open to equalise air pressure of the middle ear and pharynx.

The Palatoglossus Muscle

• Superior attachment: palatine aponeurosis.
• Inferior attachment: side of tongue.
• Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.

• This muscle, covered by mucous membrane, forms the palatoglossal arch.

• The palatoglossus elevates the posterior part of the tongue and draws the soft palate inferiorly onto the tongue.

• Superior attachment: hard palatThe Palatopharyngeus Musclee and palatine aponeurosis.
• Inferior attachment: lateral wall of pharynx.
• Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.

• This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
• It passes posteroinferiorly in this arch.

• This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.

The Musculus Uvulae

• Superior attachment: posterior nasal spine and palatine aponeurosis.
• Inferior attachment: mucosa of uvula.
• Innervation: cranial part of accessory through the pharyngeal branch of vagus, via the pharyngeal plexus.

• It passes posteriorly on each side of the median plane and inserts into the mucosa of the uvula.
• When the muscle contracts, it shortens the uvula and pulls it superiorly.

The Orbital Vessels

• The orbital contents are supplied chiefly by the ophthalmic artery.
• The infraorbital artery, the continuation of the maxillary, also contributes blood to this region.
• Venous drainage is through the superior orbital fissure to enter the cavernous sinus.

The Ophthalmic Artery

• This artery arises from the internal carotid artery as it emerges from the cavernous sinus.
• It passes through the optic foramen within the dural sheath of the optic nerve and runs anteriorly, close to the superomedial wall of the orbit.

The Central Artery of the Retina

• This is the one of the smallest but most important branches of the ophthalmic artery.
• It arises inferior to the optic nerve until it approaches the eyeball.
• It then pierces the optic nerve and runs within it to emerge through the optic disc.
• The central artery of the retina spreads over the internal surface of the retina and supplies it.

The Ophthalmic Veins

The Superior Ophthalmic Vein

• The superior ophthalmic vein anastomoses with the facial vein.
• It has no valves and blood can flow in either direction.
• It crosses superior to the optic nerve, passes through the superior orbital fissure and ends in the cavernous sinus.

The Inferior Ophthalmic Vein

• This begins as a plexus on the floor of the orbit.
• It communicates with the inferior orbital fissure with the pterygoid plexus, crosses inferior to the optic nerve, and ends in either the superior ophthalmic vein or the cavernous sinus.

Muscles Around the Nose

The Nasalis Muscle

• This muscle consists of a transverse (compressor naris) and alar (dilator naris) parts.
• It is supplied by the buccal branch of the facial nerve.