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

Gross Features of the Tongue

• The dorsum of the tongue is divided by a V-shaped sulcus terminalis into anterior oral (presulcal) and posterior pharyngeal (postsulcal) parts.
• The apex of the V is posterior and the two limbs diverge anteriorly.
• The oral part forms about 2/3 of the tongue and the pharyngeal part forms about 1/3.

Oral Part of the Tongue

• This part is freely movable, but it is loosely attached to the floor of the mouth by the lingual frenulum.

• On each side of the frenulum is a deep lingual vein, visible as a blue line.
• It begins at the tip of the tongue and runs posteriorly.
• All the veins on one side of the tongue unite at the posterior border of the hyoglossus muscle to form the lingual vein, which joins the facial vein or the internal jugular vein.

• On the dorsum of the oral part of the tongue is a median groove.
• This groove represents the site of fusion of the distal tongue buds during embryonic development.

The Lingual Papillae and Taste Buds

• The filiform papillae (L. filum, thread) are numerous, rough, and thread-like.
• They are arranged in rows parallel to the sulcus terminalis.

• The fungiform papillae are small and mushroom-shaped.
• They usually appear are pink or red spots.

• The vallate (circumvallate) papillae are surrounded by a deep, circular trench (trough), the walls of which are studded with taste buds.

• The foliate papillae are small lateral folds of lingual mucosa that are poorly formed in humans.

• The vallate, foliate and most of the fungiform papillae contain taste receptors, which are located in the taste buds.

The Pharyngeal Part of the Tongue

• This part lies posterior to the sulcus terminalis and palatoglossal arches.
• Its mucous membrane has no papillae.

• The underlying nodules of lymphoid tissue give this part of the tongue a cobblestone appearance.
• The lymphoid nodules (lingual follicles) are collectively known as the lingual tonsil.

• Ossification

• Intramembranous-found in the flat bones of the face
  • Mesenchymal cells cluster and form strands
  • Strands are cemented in a uniform network. Which is known as osteoid
  • Calcium salts are deposited; osteoid is converted to bone
  • Trabeculae are formed and make cancellous bone with open spaces known as marrow cavities
  • Periosteum forms on the inner and outer surfaces of the ossification centers
  • Surface bone becomes compact bone
• Endochondral-primary type of ossification In the human

• This is the second cranial nerve (CN II) and is the nerve of sight.

Nerves of the Palate

• The sensory nerves of the palate, which are branches of the pterygopalatine ganglion, are the greater and lesser palatine nerves.
• They accompany the arteries through the greater and lesser palatine foramina, respectively.

• The greater palatine nerve supplies the gingivae, mucous membrane, and glands of the hard palate.

• The lesser palatine nerve supplies the soft palate.

• Another branch of the pterygopalatine ganglion, the nasopalatine nerve, emerges from the incisive foramen and supplies the mucous membrane of the anterior part of the hard palate.

• The tongue is divided into halves by a medial fibrous lingual septum that lies deep to the medial groove.
• In each half of the tongue there are four extrinsic and four intrinsic muscles.

• The lingual muscles are all supplied by the hypoglossal nerve (CN XII).
• The only exception is palatoglossus, which is supplied by the pharyngeal branch of the vagus nerve, via the pharyngeal plexus.