Muscles of the Pharynx

• This consists of three constrictor muscles and three muscles that descend from the styloid process, the cartilaginous part of the auditory tube and the soft palate.

External Muscles of the Pharynx 

• The paired superior, middle, and inferior constrictor muscles form the external circular part of the muscular layer of the wall.
• These muscles overlap each other and are arranged so that the superior one is innermost and the inferior one is outermost.

• These muscles contract involuntarily in a way that results in contraction taking place sequentially from the superior to inferior end of the pharynx.
• This action propels food into the oesophagus.

• All three constrictors of the pharynx are supplied by the pharyngeal plexus of nerves, which lies on the lateral wall of the pharynx, mainly on the middle constrictor of the pharynx.
• This plexus is formed by pharyngeal branches of the glossopharyngeal (CN IX) and vagus (CN X) nerves.

The Superior Constrictor Muscle

• Origin: pterygoid hamulus, pterygomandibular raphe, posterior end of the mylohyoid line of the mandible, and side of tongue.
• Insertion: median raphe of pharynx and pharyngeal tubercle.
• Innervation: though the pharyngeal plexus of nerves.

• The pterygomandibular raphe is the fibrous line of junction between the buccinator and superior constrictor muscles.

The Middle Constrictor Muscle

• Origin: stylohyoid ligament and greater and lesser horns of hyoid bone.
• Insertion: median raphe of pharynx.
• Innervation: through the pharyngeal plexus of nerves.

The Inferior Constrictor Muscle

• Origin: oblique line of thyroid cartilage and side of cricoid cartilage.
• Insertion: median raphe of pharynx.
• Innervation: through the pharyngeal plexus of nerves.

• The fibres arising from the cricoid cartilage are believed to act as a sphincter, preventing air from entering the oesophagus. 

Gaps in the Pharyngeal Musculature

• The overlapping arrangement of the three constrictor muscles leaves 4 deficiencies or gaps in the pharyngeal musculature.
• Various structures enter and leave the pharynx through these gaps.

• Superior to the superior constrictor muscle, the levator veli palatini muscle, the auditory tube, and the ascending palatine artery pass through a gap between the superior constrictor muscle and the skull.
• Superior to the superior border of the superior constrictor, the pharyngobasilar fascia blends with the buccopharyngeal fascia to form, with the mucous membrane, the thin wall of the pharyngeal recess.

• Between the superior and middle constrictor muscles, the gateway to the mouth, though which pass the stylopharyngeus muscle, the glossopharyngeal nerve (CN IX), and the stylohyoid ligament.

• Between the middle and inferior constrictor muscles, the internal laryngeal nerve and the superior laryngeal artery and vein pass to the larynx.

• Inferior to the inferior constrictor muscles, the recurrent laryngeal nerve and inferior laryngeal artery pass superiorly into the larynx.

Smooth Muscle

Light microscopic Structure:

cells - long - spindle shaped,  nucleus lies in the widest widest part of the fiber,  when the fiber contract the nucleus become folded, 30 - 200 µm long,between fibres lie endomycium

Electron microscopic structure:

 Mitochondria, ribosomes, golgi, rough EPR, myofilaments are present but no sarcomeres and no Z lines,thin filaments - actin and tropomyosin (7nm), thick filaments - myosin (17nmØ)

- intermediate filaments (10 nm)

- actin and myosin overlap more than in skeletal muscle and can therefore contract more

 A rudimentary sacroplasmic reticulum is present in the form of invaginations on the surface called caveolae , So there are no T-tubules,  Cells communicate through gap junctions.

Dense bodies

Filaments are attached to dense bodies which take the place of the Z line in skeletal muscle

There are two types of dense bodies - cytoplasmic and membrane

contains a percentage actinin (like the Z line)

dense bodies transmit contractile force to adjacent fibres

Arrangement:

Fibres can be single or in groups, normally arranged in sheaths,  In the GIT are 2 or 3 layers

Nerve supply:

2 types:

Where it is arranged in layers a few fibres are innervated together

impulse spread through the gap junctions between fibres (slow contraction)

In the iris and the vas deferens each fiber is individually supplied (quick contraction)

Skull bones

• 26 bones: 22 bones + hyoid (small bone in neck for swallowing) + 3 auditory ossicles (middle ear: incus, malleus, stapes)
• 21 bones: tightly connected; mandible is freely mobile at temperomandibular joint (synovial)
• connective-tissue interface b/w bones = suture
• bones – mandible = cranium
• cranium
  • neurocranium: covers brain anteriorly, laterally and posteriorly
  • brain supported by bones of basicranium
    • also contributes to interorbital region; b/w eyes and superior to nasal passages
  • viscerocranium/splanchnocranium: bones of face
• sutures
  • coronal: separates frontal from parietals
  • sagittal: separates two parietal bones
  • lambdoidal: separates parietal form occipital
  • squamosal: b/w temporal and parietal; overlapping sutures
  • At birth: 2 frontal bones which eventually fuse; metopic suture disappears

Cranial Cavities: 5 major cavities

            Endocranial, left and right orbits, nasal cavities, oral cavity, middle ear cavities

Endocranial cavity

• contains brain, meninges, cerebrospinal fluid, brain’s vascular supply and most proximal portion of cranial nerves
• enclosed by neurocranium and basicranium
• basicranium: foramina for neurovascular bundles
• foramen magnum: spinal cord exit
• floor of endocranial cavity divide into fossae
  • anterior: frontal lobes of brain
  • middle: pair temporal lobes
  • posterior: cerebellum and brainstem

Mylohyoid Muscle

• Origin: Mylohyoid line of the mandible.
• Insertion: Median raphe and body of the hyoid bone.
• Nerve Supply: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
• Arterial Supply: Sublingual branch of the lingual artery and submental branch of the facial artery.
• Action: Elevates the hyoid bone, base of the tongue, and floor of the mouth; depresses the mandible.

ENDOCRINE

Endocrine glands have no ducts

They secrete into the blood from where the secretion (hormone) reaches a target cell

The following is a list of endocrine glands:

• Hypophysis
• Thyroid
• Parathyroid
• Adrenals
• Islets of Langerhans
• Pineal
• Gonads

Hypophysis: Develops from oral ectoderm and nerve tissue,  The oral part forms an upgrowth with an invagination (Rathke's pouch) The nervous part grows from the floor of the diencephalon - staying intact .The oral part separates from the mouth

Ectoderm – adenohypophysis - pars tuberalis

- pars distalis

- pars intermedia .

Diencephalon – neurohypophysis   - pars nervosa .

- infundibulum

- median eminence

Rathke's pouch remains as Rathke's cysts

Pars Distalis: Forms 75% of the gland, The cells form cords,  with fenestrated capillaries in-between

2 Cell types:

Chromophobes :  50% of the cells, do not stain  lie in groups, they are resting chromophils

granules have been used

Chromophils: Stain

They can be subdivided according to their reaction with different stains

Acidophils (40%) :Cells have acidophilic granules in their cytoplasm. The cells are secretory.

They have a well developed EPR and Golgi apparatus.They have secretory granules.

subdivided into:

- Somatotropin cells: secrete somatotropin (growth hormone)

- Mammotropic cells:  secrete prolactin

Basophils (10%) :  These cells have basophilic granules in their cytoplasm and can be subdivided into:

Thyrotropin cells:  secrete thyroid - stimulating hormone (TSH)

Corticotrophin cells:  secrete adrenocorticotropic (ACTH)

Gonadotropic cells:  secrete two hormones:  Follicle stimulating hormone (FSH):

Stimulate follicle development and spermatogenesis

Luteinizing hormone (LH): Stimulate the formation of the corpus luteum and Leydig cells

Pars Tuberalis:  Cells lie around the infundibulum . It is continuous with the pars distalis

Cells are cuboidal with no granules. Their function is unknown

Pars Intermedia:  Poorly developed in the human. Follicles lined by cuboidal cells and filled with colloid are found Known as Rathke's cysts .There are also a few big basophilic cells

Their function is unknown

Pars Nervosa: Contains: - myelinated axons  pituicytes,  blood vessels

Axons:

The cell bodies of the axons lie in the supra-optic and paraventricular nuclei of the hypothalamus .From the cell bodies the axons go through the infundibulum forming the  hypothalamohypophyseal tract to end in the pars nervosa

 The axons have dilated blind endings filled with hormones (Herring bodies) coming from the cell bodies.

Two hormones are secreted:

Oxytoxin: - Cause contraction of the uterus

    - Cause contraction of the myoepithelial cells of the milkgland

    - The hormone is secreted by the paraventricular nuclei

Vasopressin :- Cause reabsorption of H2O in the kidney (also known as antidiuretic hormone ADH)  The hormone is secreted by the supraoptic nuclei.  A hypophyseal portal system exists

A primary capillary plexus of fenestrated capillaries form around the median eminence. Inhibitory hormones are secreted into these capillaries

The capillaries rejoin to form the portal veins that traverse the pituitary stalk

The portal veins break up into a secondary capillary plexus which lies close to the cells of the adenohypophysis

This portal system regulates the functions of the anterior pituitary function.

Pineal

Surrounded by pia which sends septae into the gland Cells are mainly pinealocytes and astroglial cells

Pinealocytes:Irregular shaped cells. with processes ending in flattened dilatations

Have a well developed smooth surfaced endoplasmic reticulum, Also a rough EPR not well developed, Lots of microtubules

Astroglial Cells: Elongated nucleus, Cells have long processes, They perform a supporting function

Hormones:

Melatonin - secreted during the night .suppress the onset of puberty

Serotonin - secreted during the day

In humans the pineal form concretions of calcified material called brain sand

Brain sand vary in size and number with age and is visible on X-rays

Mast cells are also found in the pineal and cause the high histamine contend of the gland

THYROID

Has a CT capsule that sends septae into the gland to divide it up into incomplete lobes and lobules. In the lobules are follicles, Follicles vary in size,  They are surrounded by surrounded by reticular CT and capillaries

Cells of the Follicle:

Follicular Cells :  Single layer of cuboidal cells,  lie around the colloid, Follicular cells can become columnar when very active, Nucleus  central, EPR has wide cisternae ,Golgi present

• microvilli on the free surface

Parafollicular Cells:  Also known as C-cells, Form part of the epithelium or form clusters between the follicles

- They never come into contact with the colloid

- Larger and stain less intensely than the follicular cells, Form 2% of the cells, Secrete calcitonin

Hormones: Thyroxine and thyriodothyronine - stimulate the metabolic rate, Calcitonin - lower the blood calcium

Parathyroid:

Has a CT capsule which send septae into the gland to divide it up into incomplete lobules, The CT contains fat which increase with age - may eventually be 50% of the gland, Glandular cells are arranged in cords

Glandular Cells:

Chief Cells:  Small cells so their nuclei lie close together, Rich in glycogen, Biggest omponent

Secrete parathyroid hormone - essential for life

Oxyphil Cells:Develop at puberty, Bigger than the chief cells, Nuclei are smaller, Acidophilic

Hormones:

Parathyroid hormone - regulate calcium and phosphate ions in the blood

ADRENAL

- Thick CT capsule that do not send septae into the gland

Cortex:

Has 3 layers

Zona glomerulosa: 15% of the cortex, Directly under the capsule, Cells are columnar or pyramidal,  Arranged in small groups or clusters, Wide fenestrated capillaries surround the clusters, Cells have an extensive smooth EPR

Zona Fasciculata: 78% of the cortex, Cells are arranged in cords ,1 to 2 cells wide perpendicular to the surface, Sinusoids lie between the cords, Cells are polyhedral with a central nucleus which is bigger than that of the zona glomerulosa, Lots of lipid in the cytoplasm cause the cells to stain lightly,  Cells have a well developed smooth and rough EPR

The mitochondria in the cells are round with tubular or vesicular cristae

Zona Reticularis:  7% of the cortex, Cells form a network of cords with wide capillaries in-between The mitochondria in the cells are more ofte6n elongated than that in the zona fasciculate  Degenerating cells with pyknotic nuclei are found.  Cells contain numerous large lipofuscin granules. Cells of the cortex do not store their secretions but form and secrete on demand.

Hormones:

3 Groups:

Glucocorticoids (e.g. cortisol) - have an affection on carbohydrate metabolism

Mineralocorticoid (e.g. aldosterone) - control water and electrolyte balans

Androgens (e.g. dehyroepiandrosterone) - not very important

Medulla:

- Cells are big and oval and lie in groups and cords around bloodvessels

- Oxidising agents stain the granules in these cells brown - cells are therefore called chromaffin cells

- Granules contain adrenaline or non-adrernalin

- A few parasympathetic ganglion cells are also present

Hormones:

- Adrenaline - increase oxygen uptake

- increase blood pressure

- Noradrenaline - maintain blood pressure

Blood Supply:

- Blood vessel enter from the capsule to form the wide capillaries

- They flow into venules that form a central vein

- Between the endothelium of the capillaries and the glandular cells there is a subendothelial

- space.

- The glandular cells have microvilli protruding into this space.

ISLES OF LANGERHANS

Endocrine part of pancreas.  The isles are round clusters in the exocrine tissue

- 100 - 200 µm

Islands consists of slightly stained polygonal or rounded cells,  The cells are separated by fenestrated capillaries

- Autonomic nerve fibres innervate the blood vessels and the island cells

- 4 different cell types have been described

A cells : 20% of the cells,  Bigger than B cells, Lie at the periphery, Have secretory granules ,Contain glucagon

B cells :  80%,  Lie in the centre of the island,  The cells are small with granules which are crystals,  Granules are formed by insulin

D cells :  Not numerous, Membrane bound granules, Store somatostatin (inhibit somatotropin)

F cells :  Have membrane bound granules,  Store pancreatic polypeptide, The hormone inhibits pancreatic exocrine secretion

The Muscles of Facial Expression

• These lie in the subcutaneous tissue and are attached to the skin of the face.
• They enable us to move our skin and change our facial expression. They produce their effects by pulling on the skin but do not move the facial skeleton.
• These muscles surround the facial orifices and act as sphincters and dilators.
• All facial muscles receive their innervation from the branches of the facial nerve (CN VII)-temporal, zygomatic, buccal, marginal mandibular, cervical.