Base of the skull : all important viva questions

Viva question of Base of the skull:

1. Define skull:  cranium with mandible is known as skull

Parts of the skull : base of the skull and cranial vault

Ossification : base of the skull : intracartilaginous ossif) & cranial vault : intramembranous ossification

Anatomical points:

1. infraorbital margin and and upper border of external auditory meatus lies in same horizontal line , this line is known as  Frankfort  line

2. orbital cavity directed anteriorly

3. foramen magnum lies horizontally and directed  inferiorly

q. show different view of skull :

norma verticalis : viewed from above

norma frontalis  from front

norma basalis from below

norma occipitalis from behind

norma lateralis from sides

Identification and definition of: bregma, lambda , asterion, pterior  

** pterior: it is the meeting point of 4 bones frontal , squamous part of temporal bone, parietal bone and greater wings of sphenoid clinical important : deep to this point branches of middle meningeal vessels are present . this vessel torn in accident , barr hole operation done here

Cranial fossa : three in number anterior, middle and posterior

Learn Boundary and content of each cranial fossa :

 *** foramen through which cranial nerves are passage 

 

Identify the sulcus which lodges cranial dural sinus

Cranial dural sinus

Cranial dura has two layer : endoesteum layer and meningeal layer

The sinuses of the dura mater are venous channels which drain the blood from the brain;

They are situated between the two layers of the dura mater

They are devoid of valves, and and lined by endothelium but no smooth muscle cells layer.

Different types of dural venous sinus:

1. Pair: cavernous sinus, transverse sinus, sigmoid sinus etc.
2. unpair: superior sagittal sinus, inferior sagittal sinus, straight sinus etc.

Superior sagittal sinus > right transverse sinus > right sigmoid sinus > right internal jugular vein

 Inferior sagittal sinus > straight sinus > left transverse sinus > left  sigmoid sinus > left internal jugular vein

 The cavernous sinuses are placed one on either side of the body of the sphenoid bone, extending from the superior orbital fissure to the apex of the petrous portion of the temporal bone.

 Medial wall (central part) is related to –

1. the internal carotid artery,
2. abducent nerve.

Lateral wall : is related to

1. the oculomotor
2. trochlear nerves,
3. the ophthalmic nerves
4. maxillary divisions of the trigeminal nerve  

The cavernous sinus : tributaries :

1. the superior ophthalmic vein
2. superior and inferior  petrosal sinus
3. pterygoid venous plexus veins
4. The two sinuses also communicate with each other by means of the anterior and posterior intercavernous sinuses.

Sulcus (a bony impression)	Structure lodge on sulcus	Bone
Sagittal sulcus	Superior sagittal sinus	Frontal bone, parietal bone, occipital bone
Transverse sulcus	Transverse sinus	occipital bone
Sigmoid sulcus	Sigmoid sinus	Mastoid part of temporal bones

 

q. Identify the Suture :  coranal , sagittal, lamdoid suture

q:  Suture,  what type of joint: fibrous variety

Location of anterior and  posterior frontanelle and their time of closer

Anterior frontanelle : located in between coronal and sagittal suture close : 8–24 months after birth

Pos frontanelle : located in between coronal and lambdoid suture. close : 6–8 weeks after birth

 

 

Summary of development of skeletal system

Summary of development of skeletal system 

The skeletal system develops from paraxial, somatic layer of lateral plate mesoderm and neural crest

 Neural crest: develops facial skeleton, and most of the vault of cranium and prechordal part of  base of the skull (area of base of the skull just rostral to the rostral half of the sella turcica)

Paraxial mesoderm: parietal bone, occipital bone, petrous part of temporal bone, vertebrae, ribs

Somatic layer of lateral plate mesoderm: develops all  bones of upper and lower limb

 

Lecture note: gastroschisis

Gastroschisis

Gastroschisis Ventral body wall defect resulting from a lack of closure of the lateral body wall folds in the abdominal region resulting in protrusion of intestines and sometimes other organs through the defect.

It occurs lateral to the umbilicus usually on the right

Cause : abnormal closure of body wall around the connecting stalk

Content:  intestines, other organs including the stomach and liver  protruded, which  are not covered by peritoneum or amnion

Out come : the bowel may be damaged by  exposure to amniotic fluid

Diagnosis : like omphalocele it can be diagnosed later part of pregnancy by ultrasound

Incidence : 1/10000 birth but is increasing in frequency especially among young women <20 years old.

It is not associate with chromosomal abnormality or other birth defect like omphalocele so the survival rate is excellent

Death usually occurs due to volvulus formation (rotation of bowel ) resulting in compromised blood supply may kill large regions of the  intestine and lead to fetal death . 

 

Afferent fibers of cerebellum : climbing and mossy fiber

 Afferent fibers of cerebellum : climbing and mossy fiber 

climbing fiber 

Climbing fibers  are the terminal fibers of the olivocerebellar tracts

One climbing fiber makes synaptic contact with

1-10  purkinje neuron

Climbing fiber arises from

·         the inferior olivary nucleus located in the medulla oblongata

They passes through the granular layer and purkinje layer and terminate into  the molecular layer

These axons pass through the pons and enter the cerebellum via the inferior cerebellar peduncle

These fibers provide very powerful, excitatory input to the cerebellum which results in the generation of complex spike excitatory postsynaptic potential (EPSP) in Purkinje cells

 In this way climbing fibers (CFs) perform a central role in motor behaviors.

They influence 

·         Motor timing.

·         the control & coordination of movements

·         They contribute to sensory processing and cognitive tasks likely by encoding the timing of sensory input independently of attention or awareness

Climbing fibers cross the midline in the brain stem, enter the cerebellum through the inferior cerebellar peduncle, and terminate contralaterally within the cerebellum.

In the central nervous system, these fibers are able to undergo remarkable regenerative modifications in response to injuries, being able to generate new branches by sprouting to innervate surrounding Purkinje cells if these lose their CF innervation.

This kind of injury-induced sprouting has been shown to need the growth associated protein GAP-43

Climbing fiber cannot have rosettes

A single purkinje neuron makes synaptic contact with only one climbing fiber

Climbing fiber > purkinje fiber

Mossy fiber 

 

Mossy fibers are the termical fibers of all other cerebellar afferent tract

One mossy fiber makes synaptic contact with 1000 purkinje neuron through granule cells of cerebellum

Mossy fiber arises from many sources

·         cerebral cortex ( largest),

·         the vestibular nerve and nuclei,

·         the spinal cord,

·         the reticular formation, and

·         feedback from deep cerebellar nuclei

They terminate in the granular layer of the cortex within the glomeruli

Axons of mossy fiber enter the cerebellum via the superior , middle and inferior cerebellar peduncles

They serve as inhibitory interneuron , they influence the degree of purkinje cell excitation

They  modify muscle activity through the motor control areas of the brain stem and cerebral cortex

Depending on the source of the mossy fibers, their termination within the cerebellum can be predominantly ipsilateral or contralateral and is restricted to particular lobules.

Keratan sulfate proteoglycan phosphacan regulates mossy fiber outgrowth and regeneration

Each mossy fiber can have up to 50 rosettes

unlike climbing fibers, mossy fibers DO NOT go directly to the Purkinje cell.

Mossy fiber > granule cell > purkinje fiber