The Muscles of Facial Expression

• These lie in the subcutaneous tissue and are attached to the skin of the face.
• They enable us to move our skin and change our facial expression. They produce their effects by pulling on the skin but do not move the facial skeleton.
• These muscles surround the facial orifices and act as sphincters and dilators.
• All facial muscles receive their innervation from the branches of the facial nerve (CN VII)-temporal, zygomatic, buccal, marginal mandibular, cervical.

Classified on functional Basis

Secretion ,Protection and waterproofing, Absorbtion, Transport, Sensory

Secretion

Glandular epithelium’s 3 types:

- Exocrine - with ducts

- endocrine - without ducts

- mixed exo-endocrine

Exocrine glands: One cell

- goblet cells

- In lining epitheliums of respiratory tract and GIT

- Secretes musin (protein) Musin + water = mucus, Mucus is a lubricant

More than one cell

 Simple:  Has a single duct,

• Acinar - mucus glands of the penile urethra
• Tubular - cripts of Lieberkuhn
• Coiled tubular - sweat gland
• Spiral tubular - Gland of Moll
• Branched tubular - mucous glands of the pyloric region
• Branched acinar - sebaceous gland in the skin

Compound

• Consists of a branched duct with numerous secretory end organs
• Compound tubular - Brünners glands
• Compound alveolar - mammary, prostate, pancreas, parotid
• Compound tubuloalveolar - submandibular-, sublingual salivary glands

Endocrine glands

Secrete directly into the blood

One cell :  mast cells,  in soft CT,  near capillaries,

secrete - heparin - histamine

More than one cell

Cells can be arranged in the following ways:

• Cords - adrenal glands, parathyroid, anterior pituitary
• anastomosing cords with dilated blood capillaries in-between
• Isles - pancreas
• Follicles - thyroid
• cells line a follicle filled with non-cellular material

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

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.

Vessels of the Palate

• The palate has a rich blood supply from branches of the maxillary artery.

The Oral Cavity

• The oral cavity (mouth) consists of two parts: the vestibule and the mouth proper.

• The vestibule is the slit-like spaced between the cheeks and the lips and the teeth and gingivae.
• It is the entrance of the digestive tract and is also used for breathing.
• The vestibule communicates with the exterior through the orifice of the mouth.

• The oral cavity is bounded:
• Externally: by the cheeks and lips.
• Roof of oral cavity: formed by the palate.
• Posteriorly: the oral cavity communicates with the oropharynx.