Cardiac Muscle

Fibres anastomose through cross bridges

Fibres are short, connected end to end at intercalated discs, also striated,  contract automatically

Light microscopic Structure:

Short fibres connected at intercalated disks,  85 - 100 µm long,  15 µm

same bands as in skeletal muscle,  1 or 2 nuclei - oval and central,  in perinuclear area is a sarcoplasmic reticulum, intercalated discs lie at the Z line

Electron microscopic structure:

 Between myofibrils lie the mitochondria,  2,5 µm long mitochondria,  dense cristae

and are as long as the sarcomere, fibres have more glycogen than skeletal muscle fibres

myofilaments, actin and myosin are the same as in skeletal muscle,  the sarcoplasmic reticulum differs in that there is no terminal sisterna. The sarcotubules end in little feet that

sit on the T-tubule

Intercalated Disc:

on Z lines,  fibres interdigitate,

 3 types of junctions in the disc

Transverse Part:

zonula adherens

desmosomes

Lateral Part:

Gap junctions (nexus) - for impulse transfer

Mechanism of Contraction:

slide - ratchet like in skeletal muscle, certain fibres are modified for conduction,  Impulses spread from cell to cell through gap junctions,  Purkinje cells are found in the AV bundle

they have less myofibrils,  lots of glycogen and intercalated discs

Connective tissue coverings:

Only endomycium in cardiac muscle,  Blood vessels, lymph vessels and nerves lie in the endomycium

Extrinsic Muscles of the Tongue (p. 746)

The Genioglossus Muscle

• This is a bulky, fan-shaped muscle that contributes to most of the bulk of the tongue.
• It arises from a short tendon from the genial tubercle (mental spine) of the mandible.
• It fans out as it enters the tongue inferiorly and its fibres attach to the entire dorsum of the tongue.
• Its most inferior fibres insert into the body of the hyoid bone.
• The genioglossus muscle depresses the tongue and its posterior part protrudes it.

The Hyoglossus Muscle

• This is a thin, quadrilateral muscle.
• It arises from the body and greater horn of the hyoid bone and passes superoanteriorly to insert into the side and inferior aspect of the tongue.
• It depresses the tongue, pulling its sides inferiorly; it also aids in retrusion of the tongue.

The Styloglossus Muscle

• This small, short muscle arises from the anterior border of the styloid process near its tip and from the stylohyoid ligament.
• It passes inferoanteriorly to insert into the side and inferior aspect of the tongue.
• The styloglossus retrudes the tongue and curls its sides to create a trough during swallowing.

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.

The Sublingual Glands

• These are the smallest of the three paired salivary glands and the most deeply situated.
• They are almond-shaped and lie in the floor of the mouth between the mandible and the genioglossus muscle.
• The paired glands unite to form a horseshoe-shaped glandular mass around the lingual frenulum.

• Numerous small ducts (10 to 12) open into the floor of the mouth.
• Sometimes one of the ducts opens into the submandibular duct.

• The nerves the accompany the submandibular and sublingual glands are derived from the lingual and chorda tympani nerves and from the sympathetic nerves.
• The parasympathetic secretomotor fibres are from the submandibular ganglion.

The Ear

• The ear contains the vestibulocochlear organ and consists of three main parts: external, middle, and internal.
• It has two functions, balance and hearing.

• The tympanic membrane (eardrum) separates the external ear from the middle ear.
• The auditory tube joins the middle ear or tympanic cavity to the nasopharynx.

Walls of the Tympanic Cavity or Middle Ear

• This cavity is shaped like a narrow six-sided box that has convex medial and lateral walls.
• It has the shape of the biconcave lens in cross-section (like a red blood cell).

The Roof or Tegmental Wall

• This is formed by a thin plate of bone, called the tegmen tympani (L. tegmen, roof).
• It separates the tympanic cavity from the dura on the floor of middle cranial fossa.
• The tegmen tympani also covers the aditus ad antrum.

The Floor or Jugular Wall

• This wall is thicker than the roof.
• It separates the tympanic cavity from the superior bulb of the internal jugular vein. The internal jugular vein and the internal carotid artery diverge at the floor of the tympanic cavity.

• The tympanic nerve, a branch of the glossopharyngeal nerve (CN IX), passes through an aperture in the floor of the tympanic cavity and its branches form the tympanic plexus.

The Lateral or Membranous Wall

• This is formed almost entirely by the tympanic membrane.
• Superiorly it is formed by the lateral bony wall of the epitympanic recess.
• The handle of the malleus is incorporated in the tympanic membrane, and its head extends into the epitympanic recess.

The Medial or Labyrinthine Wall

• This separates the middle ear from the membranous labyrinth (semicircular ducts and cochlear duct) encased in the bony labyrinth.
• The medial wall of the tympanic cavity exhibits several important features.

• Centrally, opposite the tympanic membrane, there is a rounded promontory (L. eminence) formed by the first turn of the cochlea.
• The tympanic plexus of nerves, lying on the promontory, is formed by fibres of the facial and glossopharyngeal nerves.

• The medial wall of the tympanic cavity also has two small apertures or windows.

• The fenestra vestibuli (oval window) is closed by the base of the stapes, which is bound to its margins by an annular ligament.
• Through this window, vibrations of the stapes are transmitted to the perilymph window within the bony labyrinth of the inner ear.

• The fenestra cochleae (round window) is inferior to the fenestra vestibuli.
• This is closed by a second tympanic membrane.

The Posterior or Mastoid Wall

• This wall has several openings in it.
• In its superior part is the aditus ad antrum (mastoid antrum), which leads posteriorly from the epitympanic recess to the mastoid cells.

• Inferiorly is a pinpoint aperture on the apex of a tiny, hollow projection of bone, called the pyramidal eminence (pyramid).
• This eminence contains the stapedius muscle.
• Its aperture transmits the tendon of the stapedius, which enters the tympanic cavity and inserts into the stapes.

• Lateral to the pyramid, there is an aperture through which the chorda tympani nerve, a branch of the facial nerve (CN VII), enters the tympanic cavity.

The Anterior Wall or Carotid Wall

• This wall is a narrow as the medial and lateral walls converge anteriorly.
• There are two openings in the anterior wall.

• The superior opening communicates with a canal occupied by the tensor tympani muscle.
• Its tendon inserts into the handle of the malleus and keeps the tympanic membrane tense.

• Inferiorly, the tympanic cavity communicates with the nasopharynx through the auditory tube.

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