• 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.

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

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

The Temporalis Muscle

• This is an extensive fan-shaped muscle that covers the temporal region.
• It is a powerful masticatory muscle that can easily be seen and felt during closure of the mandible.

• Origin: floor of temporal fossa and deep surface of temporal fascia.
• Insertion: tip and medial surface of coronoid process and anterior border of ramus of mandible.
• Innervation: deep temporal branches of mandibular nerve (CN V³).

• The temporalis elevates the mandible, closing the jaws; and its posterior fibres retrude the mandible after protrusion.

Muscles of the Soft Palate

The Levator Veli Palatini (Levator Palati)

• Superior attachment: cartilage of the auditory tube and petrous part of temporal bone.
• Inferior attachment: palatine aponeurosis.
• Innervation: pharyngeal branch of vagus via pharyngeal plexus.

• This cylindrical muscle runs inferoanteriorly, spreading out in the soft palate, where it attaches to the superior surface of the palatine aponeurosis.

• It elevates the soft palate, drawing it superiorly and posteriorly.
• It also opens the auditory tube to equalise air pressure in the middle ear and pharynx.

The Tensor Veli Palatini (Tensor Palati)

• Superior attachment: scaphoid fossa of medial pterygoid plate, spine of sphenoid bone, and cartilage of auditory tube.
• Inferior attachment: palatine aponeurosis.
• Innervation: medial pterygoid nerve (a branch of the mandibular nerve).

• This thin, triangular muscle passes inferiorly, and hooks around the hamulus of the medial pterygoid plate.
• It then inserts into the palatine aponeurosis.

• This muscle tenses the soft palate by using the hamulus as a pulley.
• It also pulls the membranous portion of the auditory tube open to equalise air pressure of the middle ear and pharynx.

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.

• Superior attachment: hard palatThe Palatopharyngeus Musclee and palatine aponeurosis.
• Inferior attachment: lateral wall of pharynx.
• Innervation: cranial part of accessory nerve (CN XI) through the pharyngeal branch of vagus (CN X) via the pharyngeal plexus.

• This thin, flat muscle is covered with mucous membrane to form the palatopharyngeal arch.
• It passes posteroinferiorly in this arch.

• This muscle tenses the soft palate and pulls the walls of the pharynx superiorly, anteriorly and medially during swallowing.

The Musculus Uvulae

• Superior attachment: posterior nasal spine and palatine aponeurosis.
• Inferior attachment: mucosa of uvula.
• Innervation: cranial part of accessory through the pharyngeal branch of vagus, via the pharyngeal plexus.

• It passes posteriorly on each side of the median plane and inserts into the mucosa of the uvula.
• When the muscle contracts, it shortens the uvula and pulls it superiorly.

NEUROHISTOLOGY

The nervous system develops embryologically from ectoderm, which forms the neural plate

Successive growth and folding of the plate results in the formation of the primitive neural tube.

The neuroblasts in the wall of the tube differentiates into 3 cell types:

Neurons:  conduction of impulses

Neuroglial cells: connective tissue and support of CNS

Ependymal cells:  Lines the lumen of the tube.

   - Specialized neuro-ectodermal cells which lines the ventricles of the adult brain

                - Essentially also a neuroglial cell

Basic Unit = neuron

Exhibits irritability (excitability) and conductivity

A typical neurons consists of:

Cell body : Has nucleus (karyon) and surrounding cytoplasm (perikaryon) which contains organelles cell's vitality

Dendrites:  Several short processes

Axon:One large process

Terminates in twig like branches (telodendrons)

May also have collateral branches projecting along its course. These exit at nodes of Ranvier

Axon enveloped in a sheath, and together forms the nerve fiber

Classification:

May be done in different ways, i.e.

Functional = afferent, efferent, preganglionic, postganglionic, etc.

Morphological = shape, processes, etc

A typical morphological classification is as follows

a. Unipolar: Has one process only Not found in man

b. Bipolar (so-called ganglion cell):Has two processes Found in sensory systems, e.g. retina olfactory system

c. Multipolar: Has several process Most common in CNS

Cell bodies vary in shape, e.g.  stellate (star) , pyramidal

d. Pseudo-unipolar: Essentially bipolar neurons, but processes have swung around cb and fused with each other. They therefore enter and leave at one pole of the cell.

Typical neuron:

- Has 2 or more dendrites

Close to the cb the cytoplasm of dendrites has Nissl granules as well as mitochondria

Only one axon Arises from axon hillock, Devoid of Nissl granules, Encased in myelin sheath

No additional covering except for occasional foot processes of neuroglial cells

May branch at right angles

Branches at a node of Ranvier is known as a collateral

Ends of axons break up into tree-like branches, known as telodendria

Axons may be short (Golgi Type II) e.g. internuncial long (Golgi Type I) e.g. pyramidal neuron

Nucleus Central position Large and spherical

Chromatin is extended and thus not seen in LM. This allows the nucleolus to be prominent

Cytoplasm (perikaryon)

Surrounds nucleus  May be large or small, shape may be round, oval, flattened, pyramidal, etc

Contains aggregates Nissl granules(Bodies) which is also sometimes referred to as rhomboid flakes

aggregation of membranes and cisternae of rough endoplasmic reticulum (RER)

numerous ribosomes and polyribosomes scattered between cisternae

(Polyribosome = aggregate of free ribosomes clumped together)

responsible for ongoing synthesis of new cytoplasm and cytoplasmic substances

needed for conduction of impulses

highly active in cell protein synthesis

resultant loss of power to divide which is characteristic of neurons

- Golgi network surrounding nucleus (seen in EM only)

- Fibrils made up of:

- neurofilaments

- microtubules

Tubules involved in:

1. plasmic transport

2. maintenance of cell shape

3. essential for growth and elongation of axons and dendrites

Neurofilament:

1. provide skeletal framework

2. maintenance of cell shape

3. possible role in axonal transport

(Axonal [axoplasmic; plasmic] transport may be antero- or retrograde. Anterograde transport via neurotubules is fast and moves neurotransmitters. Retrograde transport is slow and is the reason why viruses and bacteria can attack and destroy cell bodies. E.g. polio in the ventral columns and syphilis in the dorsal columns).

- Numerous mitochondria

- Neurons lack ability to store glycogen and are dependent for energy on circulating glucose

Impulses are conducted in one direction only

Dendrites conduct towards the cb

Axons conduct away from cb

Synapses:

- Neurons interconnect by way of synapses

- Normally the telodendria of an axon synapse with the dendrites of a succeeding axon

axo-dendritic synapse

This is usually excitatory

- Other types of synapses are:

 axo-axonic

May be excitatory and/or inhibitory

axo-somatic

May be excitatory and/or inhibitory

 dendrodendritic

Usually inhibitory

- Synapses are not tight junctions but maintain a narrow space the so-called synaptic cleft

- The end of an telodendron is usually enlarged (bouton) and contains many synaptic vesicles,

mitochondrion, etc. Its edge that takes part in the synapse is known as the postsynaptic membrane and no

vesicles are seen in this area

- Synapses may be chemical (as above) or electrical as in the ANS supplying smooth muscle cells subjacent to adjacent fibres

Gray and White Matter of Spinal Cord:

- Gray matter contains:

- cb's (somas) of neurons

- neuroglial cells

- White matter contains:

- vast number of axons

- no cb's

- colour of white matter due to myelin that ensheathes axons

Myelin:

- Non-viable fatty material contains phospholipids, cholesterol and some proteins

- Soluble and not seen in H&E-sections because it has become dissolved in the process, thus leaving empty spaces around the axons

- Osmium tetroxide (OsO4) fixes myelin and makes it visible by staining it black. Seen as concentric rings in cross section

- Myelin sheath (neurolemma) is formed by two types of cells

- Within the CNS by Oligodendrocytes

- On the peripheral neurons system by Schwann cells

- Sheath is formed by being wrapped around the axon in a circular fashion by both types of cells

Neuroglial Cells:

- Forms roughly 40% of CNS volume

- May function as: 1. support

2. nurture ("feeding")

3. maintain

Types of glial cells:

Oligodendrocytes:

- Small dark stained dense nucleus

- Analogue of Schwann cell in peripheral nervous system

- Has several processes which forms internodal segments of several fibres (one cell ensheathes more than one axon)

- Provides myelin sheaths in CNS

- Role in nurturing (feeding) of cells

Astrocytes:

Protoplasmic astrocytes:

- found in gray matter

- round cell body

- large oval nucleus with prominent nucleolus

- large thick processes

- processes are short but profusely branched

- perivascular and perineurial foot processes

- sometimes referred to as mossy fibres

Fibrous Astrocytes:

- found in white matter

- polymorphic cells body

- large oval nucleus

- long thin processes

Microglia:

- Neural macrophages

- smallest of the glial cells

- intense dark stained nucleus

- conspicuously fine processes which has numerous short branches

Cerebral Cortex:

Consists of six layers which are best observed in the cortex of the hippocampus

From superficial to deep:

- Molecular layer:

- Has few cells and many fibres of underlying cells

- Outer granular layer:

- Many small nerve cells

- Pyramidal layer:

- Pyramidally-shaped cells bodies

- Inner granular layer:

- Smaller cells and nerve fibres

- Internal (inner) pyramidal layer:

- Pyramidal cells bodies

- Very large in the motor cortex and known as Betz-cells

- Polymorphic layer:

- Cells with many shapes

Cerebellar Cortex:

Consists of three layers

Connections are mainly inhibitory

From superficial to deep

- Outer molecular layer:

- Few cells and many fibres

- Purkinje layer:

- Huge flask-shaped cells that are arranged next to one another

- Inner granular layer:

- Many small nerve cells

Motor endplate:

Seen in periphery on striated muscle fibres

- known as boutons

- has no continuous myelin covering from the Schwann cells

- passes through perimysium of muscle fiber to "synapse"

- multiple synaptic gutter (fold) in sarcoplasma of muscle fiber beneath bouton

- contains numerous synaptic vesicles and mitochondria

Ganglia:

- Sensory Ganglia:

(e.g. trigeminal nerve, ganglia and dorsal root ganglia)

- No synapse (trophic unit)

- pseudo-unipolar neurons

- centrally located nucleus

- spherical smooth border

- conspicuous axon hillock

- Surrounded by cuboidal satellite cells (Schwann cells)

- Covered by spindle shaped capsular cells of delicate collagen which forms the endoneurium

- Visceral and Motor Ganglia (Sympathetic and Parasympathetic):

- Synapse present

- Ratio of preganglionic: postganglionic fibres

1. Sympathetic 1:30

Therefore excitatory and catabolic

2. Parasympathetic 1:2

Therefore anabolic

Except in Meissner and Auerbach's plexuses where ratio is 1:1000 '2 because of parasympathetic component's involvement in digestion

- Preganglionic axons are myelinated (e.g. white communicating rami)

- Postganglionic axon are non-myelinated (e.g. gray communicating rami)

- small multipolar cell body

- excentrally located nucleus

- Inconspicuous axon hillock

- satellite cells few or absent

- few capsular cells