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Anatomy

Skeletal Muscle:  1-40 cm long fibres, 10- 60 µm thick, according to myoglobin content there are:

Red fibres: lots of myoglobin, many mitochondriam slow twitching - tire slowly

White fibres:  less myoglobin,  less mitochondria, fast twitching - tire quickly

Intermediate fibres:

mixture of 2 above

Most muscles have all three - in varying ratios

Structure of skeletal muscle:

Light Microscopy:  Many nuclei - 35/mm,  Nuclei are oval - situated peripheral,  Dark and light bands

Electron Microscopy: Two types of myofilaments

Actin

- 5,6 nm

 3 components:

 -actin monomers,  

 -tropomyosin - 7 actin molecules long

- troponin

 actin monomers form 2 threats that spiral

- tropomyosin - lie in the groove of the spiral

- troponin - attach every 40 nm

- one end attach to the Z line

- other end goes to the middle of the sarcomere

- Z line consists of á actinin

Myosin:

- 15 nm

- 1,6 µm long

- The molecule has a head and a tail

- tails are parallel

- heads project in a spiral

- in the middle is a thickening

- thin threats bind the myosin at thickening (M line)

Contraction:

A - band stays the same, I - band, H - bands become narrower

Myosin heads ratchet on the actin molecule

Sarcolemma: 9 nm thick,  invaginate to form T-tubule,

 myofibrils - attach to the sarcolemma

Sarcoplasmic Reticulum:

specialized smooth EPR,  Consists of T-tubules, terminal sisternae and sarcotubules

It is speculated that there are gap junctions between the T-tubule and terminal sisterna

An impulse is carried into the fiber by the T-tubule from where it goes to the rest of the sarcoplasmic reticulum

Connective tissue coverings of the muscle

Endomycium around fibres, perimycium around bundles and epimycium around the whole muscle

Blood vessels and nerves in CT

CT goes over into tendon or aponeurosis which attaches to the periosteum

Nerves:

The axon of a motor neuron branches and ends in motor end plates on the fiber

Specialized striated fibres called spindles (stretch receptors) form sensory receptors in muscles telling the brain how far the muscle has stretched

Stylohyoid Muscle

  • Origin: Posterior border of the styloid process of the temporal bone.
  • Insertion: Body of the hyoid bone at the junction with the greater horn.
  • Nerve Supply: Facial nerve (CN VII).
  • Arterial Supply: Muscular branches of the facial artery and muscular branches of the occipital artery.
  • Action: Elevates the hyoid bone and base of the tongue.

The Oropharynx

  • The oral part of the pharynx has a digestive function.
  • It is continuous with the oral cavity through the oropharyngeal isthmus.
  • The oropharynx is bounded by the soft palate superiorly, the base of the tongue inferiorly, and the palatoglossal and palatopharyngeal arches laterally.
  • It extends from the soft palate to the superior border of the epiglottis.

 

The Palatine Tonsils

  • These are usually referred to as "the tonsils".
  • They are collections of lymphoid tissue the lie on each side of the oropharynx in the triangular interval between the palatine arches.
  • The palatine tonsils vary in size from person to person.
  • In children, the palatine tonsils tend to be large, whereas in older persons they are usual small and inconspicuous.
  • The visible part of the tonsil is no guide to its actual size because much of it may be hidden by the tongue and buried in the soft palate.

Digastric Muscle

  • Origin:
    • Anterior Belly: Digastric fossa of the mandible.
    • Posterior Belly: Mastoid notch of the temporal bone.
  • Insertion: Intermediate tendon attached to the body of the hyoid bone.
  • Nerve Supply:
    • Anterior Belly: Nerve to mylohyoid (branch of the trigeminal nerve, CN V3).
    • Posterior Belly: Facial nerve (CN VII).
  • Arterial Supply:
    • Anterior Belly: Branch of the submental artery.
    • Posterior Belly: Muscular branch of the posterior auricular artery and occipital artery.
  • Action: Raises the hyoid bone and base of the tongue, steadies the hyoid bone, and opens the mouth by lowering the mandible.

Mesodermal Origin

Muscles

Innervation

Somitomeres 1, 2

Superior, medial and ventral recti

Oculomotor (III)

Somitomere 3

Superior oblique

Trochlear (IV)

Somitomere 4

Jaw-closing muscles

Trigeminal (V)

Somitomere 5

Lateral rectus

Abducens (VI)

Somitomere 6

Jaw-opening and other 2nd arch muscles

Facial (VII)

Somitomere 7

Stylopharyngeus

Glossopharyngeal (IX)

Somites 1, 2

Intrinsic laryngeals

Vagus (X)

Somites 2-5

Tongue muscles

Hypoglossal (XII)

The Palate

  • The palate forms the arched roof of the mouth and the floor of the nasal cavities.
  • The palate consists of two regions: the anterior 2/3 or bony part, called the hard palate, and the mobile posterior 1/3 or fibromuscular part, known as the soft palate.

 

The Hard Palate

  • The anterior bony part of the palate is formed by the palatine process of the maxillae and the horizontal plates of the palatine bones.
  • Anteriorly and laterally, the hard palate is bounded by the alveolar processes and the gingivae.
  • Posteriorly, the hard palate is continuous with the soft palate.
  • The incisive foramen is the mouth of the incisive canal.
  • This foramen is located posterior to the maxillary central incisor teeth.
  • This foramen is the common opening for the right and left incisive canals.
  • The incisive canal and foramen transmit the nasopalatine nerve and the terminal branches of the sphenopalatine artery.
  • Medial to the third molar tooth, the greater palatine foramen pierces the lateral border of the bony palate.
  • The greater palatine vessels and nerve emerge from this foramen and run anteriorly into two grooves on the palate.
  • The lesser palatine foramen transmits the lesser palatine nerve and vessels.
  • This runs to the soft palate and adjacent structures.

Eye 

At week 4, two depressions are evident on each of the forebrain hemispheres.  As the anterior neural fold closes, the optic pits elongate to form the optic vesicles.  The optic vesicles remain connected to the forebrain by optic stalks. 
The invagination of the optic vesicles forms a bilayered optic cup.  The bilayered cup becomes the dual layered retina (neural and pigmented layer)
Surface ectoderm forms the lens placode, which invaginates with the optic cup.
The optic stalk is deficient ventrally to contain choroids fissure to allow blood vessels into the eye (hyaloid artery).  The artery feeds the growing lens, but will its distal portion will eventually degenerate such that the adult lens receives no hyaloid vasculature.
At the 7th week, the choroids fissure closes and walls fuse as the retinal nerve get bigger.
The anterior rim of the optic vesicles forms the retina and iris.  The iris is an outgrowth of the distal edge of the retina.
Optic vesicles induces/maintains the development of the lens vesicle, which forms the definitive lens.  Following separation of the lens vesicle from the surface ectoderm, the cornea develops in the anterior 1/5th of the eye.
The lens and retina are surrounded by mesenchyme which forms a tough connective tissue, the sclera, that is continuous with the dura mater around the optic nerve.  
Iridopupillary membrane forms to separate the anterior and posterior chambers of the eye.  The membrane breaks down to allow for the pupil
Mesenchyme surrounding the forming eye forms musculature (ciliary muscles and pupillary muscles – from somitomeres 1 and 2; innervated by CN III), supportive connective tissue elements and vasculature.


Eyelids

Formed by an outgrowth of ectoderm that is fused at its midline in the 2nd trimester, but later reopen.

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