1. 
2. Help
3. Log In

BIOLOGY 03048, ANATOMY: WEEKS 2 AND 3: HEAD AND NECK; MORE TISSUE TYPES 9/7/99

W. Crone (303 FTZ, 629-7439, cronewil@hvcc.edu, http://www.hvcc.edu/academ/faculty/crone/index.html)

Texts: Moore and Dalley, Ch. 7, pp. 831-842, 847-875, 899-993; Ch. 8; Ch. 9 (for additional CN information--won't be testing CN lesions formally until the final); Cormack, Chs. 4 (pp. 77-82, 100-111), 5 (p. 127), 10

Possible web sites: http://www.bcm.tmc.edu/oto/studs/anat.html: ENT-relevant anatomy with simplified diagrams

http://visembryo.com/ (pictoral atlas of development)

SOME ISSUES IN DEVELOPMENT OF THE HEAD AND NECK:

In brain development, a neural groove develops neural folds which reach over and form a hollow neural tube. Anencephaly: failure of neural folds to fuse anteriorly.

During development, soft spots or fontanelles allow for molding of the head during passage through the birth canal. The location of these fontanelles help to define major connections or sutures between them.

In contrast to the typical body segment run by spinal nerves seen last week, the head and neck region is dependent on pharyngeal arches with associated pouches innervated by cranial nerves. Arches 1 and 2 form face structures, 3 face and neck structures, and 4 and 6 neck structures (arch # 5 at best transitory!).

This pattern helps to explain patterns such as Di eorge syndrome, with malformations of arches 3 and 4, and subsequent thymus and parathyroid problems.

NB: tongue has multiple embryologic contributions, which explains why so many CN involved with it!

FIRST GO AROUND ON CRANIAL NERVES:

Oh, Oh, Oh, To Touch And Feel Very Green Vegetables, AH!

Head autonomics: unlike in the thorax/abdomen, the parasympathetic ganglia in the head are not small and directly on the target organ. Instead, there are a few specific ganglia (ciliary, pterygopalantine, submandibular, otic) receiving preganglionic fibers from different cranial nerves. The superior cervical ganglion of the sympathetic chain is the site from which postganglionic sympathetic neurons travel to head. Interruption of head sympathetics: Horner syndrome, with ptosis (drooping lid), constricted pupil (miosis), and decreased sweating on the affected side.

FACE AND ORAL CAVITY:

Muscles of facial expression: these muscles are superficially located on the scalp, face, and neck. Generally, they originate from skull bones or flat tendons and insert into the hypodermis of the skin. They are all innervated by the facial nerve (CN VII). Hence, with facial trauma branches of the facial nerve may be easily damaged, and patients with strokes or Bell's palsy, the affected facial muscles do not function, so that the affected portion of the patient's face appears to sag. A common cause of Bell's palsy is inflammation of the facial nerve near the stylomastoid foramen. With Bell's palsy, concern over:

Muscles of mastication: In contrast to the facial muscles, the temporalis and masseter muscles are elevators of the mandible, and are innervated by the trigeminal nerve (CN V). CN V is sensory to the face: tic douloureux or trigeminal neuralgia especially in the maxillary division.¹

Temporomandibular joint (TMJ): a synovial joint in which mandibular heads can dislocate anteriorly. Pain radiates to the ears and temporal regions because of branches of CN V.

The upper 1/3 of the nose is supported by the nasal bones and the rest by cartilage. Paranasal sinuses are air-filled cavities in the bone of the skull, of which the frontal and maxillary sinuses are the most accessible. The lips (labia) that surround the mouth are covered externally by skin and internally by mucous membranes. There are three sets of salivary glands, two of which can be examined clinically: the parotid glands, which when enlarged are certainly palpable and perhaps sometimes visible (e.g., in mumps) superficial to and behind the mandible; and the submandibular glands, deep to the mandible (there are also sublingual glands).

Within the oral cavity, the dorsum of the tongue is covered by papillae, and its intrinsic muscles are innervated by CN XII, the hypoglossal nerve. Also, 32 adult teeth: medial to lateral they are: incisor, canine (cuspid), premolar (bicuspid), and 1st, 2nd, and 3rd molars (6, 12-year molars, and wisdom teeth), with sensory enervation by branches of CN V.

SCALP:

The scalp covers the cranium. 5 layers of S. C. A. L. P. (the first three are fused into the scalp proper):¹

1. skin: a variable hairline is genetically determined.
2. connective tissue: fat in here helps to cushion blows, and decreases with age. In addition to fat, tough connective tissue in this layer ensures that superficial skin lacerations bleed because the connective tissue does not gap and so keeps vessels open.
3. aponeurosis epicranialis (galea aponeurotica): membraneous sheet covering the braincase; the tendon of the bellies of the occipitalis/frontalis muscles. This support ensures that superficial scalp lacerations do not gape wide open, but if there is coronal laceration (and therefore being tugged by the muscles), deep lacerations gape greatly.
4. loose areolar tissue: allows for scalp movement, but can also be a site for spread of infection.
5. pericranium: periosteum of skull, little regenerative power, so need head plates.

NECK:

The U-shaped hyoid bone is the site of attachment for several neck and tongue muscles. The neck is famous for triangles that highlight specific structures found in each. The sternocleidomastoid muscle divides the neck into anterior and posterior cervical triangles.

The sternocleidomastoid muscle is innervated by CN XI, the accessory nerve. It turns the head to the opposite side (hence a great muscle to test for malingerers who complain of hemiparalysis). If both sternocleidomastoids are contracted, the neck is flexed. Torticollis (wryneck), often the result of a difficult breech delivery, is the fibrosing of a sternocleidomastoid into a nonfunctional cord. As a result, the head is tilted and the chin elevated.¹

The scalene muscles are neck flexors. The sternocleidomastoid and the scalene muscles may be noticeable when someone is struggling with respiration as accessory muscles of inspiration.

The thyroid gland is found just below the larynx, consisting of two lobes laterally connected by an anterior isthmus. It is a large endocrine gland that receives a healthy blood flow from various vessels, e.g., superior thyroid arteries. Four parathyroid glands are embedded in the posterior, lateral aspects of the thyroid. The parathyroids secrete parathyroid hormone (PTH) to promote a rise in blood calcium levels. They may be difficult to isolate during thyroidectomy and so subsequent risk of hypocalcemic tetany.

The common carotid arteries course up the lateral sides of the trachea to where they bifurcate into internal and external carotid arteries below the angle of the mandible. Near the bifurcation is the carotid sinus, which contains baroreceptors for blood pressure, and the carotid body, or a receptor that responds to blood chemistries (both innervated by CN IX and some CN X).

The pharynx is the funnel-shaped connector from the oral and nasal cavities to the base of the skull. Within the pharynx are the tonsils or lymphoid organs, especially the palatine tonsils along the posterior lateral wall of the oropharynx. The laryngopharynx extends from the level of the hyoid bone to the esophagus and larynx. Here, food is directed posteriorly to the esophagus, while air is directed anteriorly to the larynx.

The larynx is a triangular box, with 3 unpaired cartilages:

tracheotomy: usually done at the level of 2nd-4th tracheal rings above the jugular notch. The infrahyoid muscles and the isthmus of the thyroid are positioned out of the way to make an opening in the trachea.¹

The laryngeal muscles are the means of closing the glottis in swallowing and speech. The extrinsic muscles move the larynx, e.g., elevate during swallowing, and the intrinsic muscles affect the length, position, and tension of the vocal cords. If the cords are taut, then the pitch is higher. Less tension, lower pitch. Males have thicker cords and thus lower voices than females. Of course, other parts of the head and neck assist in making speech. Vowel sounds are made by constriction of the pharyngeal walls. The sinuses act as resonating chambers.

The lips and tongue also help to form words. Laryngitis is the inflammation of the mucosal epithelium of the larynx (voice box) and vocal cords, which causes a hoarseness or loss of voice.

Cancer of the head and neck is something that all health professionals should be aware of:

THE EAR: The external ear consists of the auricle and ear canal. Tugging on the auricle can help to determine an otitis externa (e.g., Pseudomonas in the external canal). The middle ear is laterally bounded by the tympanic membrane (eardrum). The middle ear is a (normally) air-filled cavity across which sound is transmitted by the ossicles. It is connected by the auditory (eustachian) tube to nasopharynx. On the oval, slightly funnel-like eardrum, aspects of the malleus divide the eardrum into a pars flaccida (superior) vs. pars tensa. One incises for a tympanostomy tube posterioinferiorly away from landmarks, in case tube placement is needed for otitis media refractory to antibiotics.¹ The inner ear, within the petrous part of the temporal bone, performs the functions of sound perception (cochlea) and balance maintenance (vestibule, semicircular canals). Disruption of both functions in Meniere disease.

THE EYE: The eyelids have an internal coating of conjunctiva continuous with the conjunctiva covering the (white) sclera, with the epithelium not containing blood vessels over the cornea overlying the iris and the pupil. Lacrimal glands are found within the superolateral orbit, and tears are drained by a medial lacrimal sac. Muscles within the iris control pupil size, and ciliary muscles within the ciliary body control thickness of the lens for accomodation.

The anterior chamber in front of the lens and iris is filled by aqueous humor produced by the ciliary body. The aqueous humor, in a nutrient role, circulates and drains out to exiting via the canal of Schlemm. If this drainage is blocked, pressure builds up and glaucoma results.

The visual pathway is long and involved. Briefly, relected light must pass through the cornea, aqueous humor, lens, vitreous humor, and be focused on retina. Images are upside down and switched from left to right. An oval blind spot (15% from line of gaze) is from the location of the optic disc from the optic nerve, CN II.

HISTOLOGY; COMPLETION OF OVERVIEW

CONNECTIVE TISSUE: MAJOR CHARACTERISTICS

Overall, support/medium of exchange/protection/repair/fat storage

cells vs. matrix

1. cells: fibroblasts (elongated cells with oval nuclei) and others
2. extracellular matrix: a) ground substance and b) fibers (collagen, reticular, elastic)

LOOSE (AREOLAR) CONNECTIVE TISSUE

Collagen, few fibers, many cells, well vascularized, flexible, not resistant to stress, widespread in location.

DENSE IRREGULAR CONNECTIVE TISSUE

Large bundles of thick collagen fibers in multiple directions, seen in dermis, joint capsules

DENSE REGULAR CONNECTIVE TISSUE

Large bundles of thick collagen fibers in parallel with fibroblasts, in tendons and ligaments.

ADIPOSE TISSUE

Unilocular adipose cells; appear"empty" because of slide preparation

ELASTIC TISSUE

Elastic fibers appear wavy, e.g., in dermis, large blood vessels

RETICULAR CONNECTIVE TISSUE

Branched, netlike fibers that cover liver sinusoids, stroma of bone marrow, lymphatic organs

HYALINE CARTILAGE

cartilage: a firm, avascular extracellular matrix, with chondrocytes in lacunae. Large chondrocytes in the middle, with smaller ones on the periphery. Hyaline (Gr."glass"), found at the articular ends of long bones, larger respiratory passages. Other cartilage issues to be dealt with in week 11 lecture.

COMPACT BONE

Calcified extracellular matrix with hydroxyapatite (calcium and phosphate). Osteocytes in lacunae, connected by canaliculi, and in overall patterns of lamellae ringing Haversian canals. Other bone issues in week 11 lecture.

MUSCLE TISSUE: MAJOR CHARACTERISTICS

Designed for contractility; striations are a reflection of the overlapping patterns of the actin and myosin fibers within sarcomeres.

SKELETAL MUSCLE

Extremely long fibers with striations, with peripheral nuclei.

CARDIAC MUSCLE

Nuclei in middle, branching fibers, intercalated discs, to enhance conduction.

SMOOTH MUSCLE

Single, centrally located, fusiform nuclei uniform in size and distribution (no sarcomeres).

NERVOUS TISSUE: MAJOR CHARACTERISTICS

Cell bodies, dendrites, axons; myelin sheath around axons; supportive neuroglial cells

PERIPHERAL NERVE

Note the"bullseyes" of the axons with their surrounding myelin sheaths.

MOTOR NEURONS IN CROSS SECTION OF SPINAL CORD

In anterior horns of spinal cord, with large cell bodies"pointy" with dendrites.

|main page| |background| |03028: Physiology| |03048: Anatomy|

|03050: Invertebrate Zoology| |03051: Vertebrate Zoology| |03074: Economic Botany|

Please send comments and questions to: cronewil@hvcc.edu

HVCC home page

Copyright 1999 by Wilson Crone

External and unofficial links are not endorsed by Hudson Valley Community College

This page updated on September 15, 1999