Handout on occipital bone : helpful for viva examination

Occipital

1.       Anatomical  points:

·         Occipital condyles are directed  downwards

·         Basilar part is directed forwards and upwards

·         External surface of squamous part is convex and directed backward

2.       Morphological type : Flat bone

3.       Structure of bone : inner and outer compact and middle diploe

4.       Ossification :  area of occipital bone above the highest nuchal line  is arisen from membranous ossification and rest of the parts of occipital bone is arisen from cartilaginous ossification

5.       Development : paraxial mesoderm

6.       Parts : Squamous part , basilar part and condylar part

Squamous part :

1.       Two surfaces : external and internal

External surface of squamous part

·         External occipital protuberance : gives attachment to the highest point of the ligamentum nuchae

·         Highest nuchal line : gives attachment to epicranial aponeurosis :

·         Superior nuchal line:  its

·          medial part attached with origin of trapezius muscle and

·          lateral part from before backwards attached with origin of occipital belly of occipito frontalis muscle and insertion of sternocleidomastoid and splenius capitis

·         Inferior nuchal line: medially:  rectus capitis posterior minor and

                                     Laterally rectus capitis posterior major  

·         External occipital crest : gives attachment of ligamentum nuchae

·         Area between superior and inferior nuchal line :

·          medially insertion of semispinalis capitis and

·          laterally obliquus capitis superior  

·         Area between inferior nuchal line and foramen magnum

·         Medially attachment of rectus capitis posterior minor and

·         laterally attachment of rectus capitis posterior major

Internal surface of squamous part of occipital bone

Internal occipital protuberance : an irregular elevation opposite the external occipital protuberance

Sagittal sulcus : lodges superior sagittal sinus and its margin of sulcus attached with falx cerebri

Transverse sulcus  (right and left)  : lodges  transverse sinuses  and its margin of sulcus attached with tentorium cerebella

Right transverse sinus is the continuous of superior sagittal sinus and

left transverse sinus is the continuous of straight sinus

Internal occipital crest lodges occipital sinus and its margin attached with falx cerebelli.

Fossae :

Two upper triangular fossae : lodge occipital lobes of the cerebrum with meninges

Two lower quadrilateral fossae : lodge cerebellar hemispheres

Vermian fossa: a small depression which lodge vermis of the cerebellum

Angles:

Superior angle :  is meeting points of occipital bone and two parietal bone

Lateral angle : is the meeting points of occipital bone, parietal bone and mastoid part of temporal bone

Two lambdoid borders: they are articulates with posterior border of occipital bone

Two mastoid borders: they are articulates with mastoid part of temporal bone

Basilar part of occipital bones

Parts

2.        Three surfaces and three borders

3.       Anterior surface: articulate with body of sphenoid , forming primary cartilaginous joint , ossifies by the end of the 25^th years

4.       Smooth Superior surface (also known as clivus) it is related with meninges , ligament , lower part of pons and medulla oblongata , near the foramen magnum it is related with following structures above downward

·         Membrana tectoria

1.       Upper band of crucial ligament

2.       Apical ligament

3.       Anterior atlanto –occipital membrane

Inferior surface of basilar part of occipital bone :

Pharyngeal tubercle: a small middle bony elevation attached with fibrous raphe of pharynx and superior constrictor muscle

Lateral to pharyngeal tubercle : insertion of longus capitis muscles

Behind the attachement of longus capitis or in front of occipital condyles : insertion of rectus capitis anterior

Borders of basilar part of occipital bones

Posterior border is formed the anterior margin of foramen magnum

Two Lateral borders : articulate with petrous part of temporal bone

Condylar part of occipital bone

Parts

Superior surface : contain jugular tubercle an oval eminence overlying the hypoglossal canal

Inferior surface:

Two Occipital condyles : articulate with superior articular processes of atlas forming atlanto –occipital joint

Hypoglossal canals : they are  situated anterior part of each condyle

 transmits :

1.       Hypoglossal nerve

2.       Meningeal branch of ascending pharyngeal artery 

3.       Emissary vein connecting basilar venous plexus with pterygoid venous plexus

Condylar fossa : a depression behind the condyle

Condylar canal occationally a foramen present within the condylar fossa which transmit emissary vein connect sigmoid sinus with veins of suboccipital triangle

Jugular process : it is situated just lateral to occipital condyles

Anterior surface of jugular process bears jugular notch which form jugular foramen by articulating with petrous part of temporal bone

Jugular foramen : transmitted

1.       Anterior compartment  :  inferior petrosal sinus

2.       Middle compartment : glossopharyngeal

Vagus nerve , accessory nerve 

Meningeal branch of ascending pharyngeal artery

Emissary vein

3.       Posterior compartment :

Sigmoid sinus continued as internal jugular vein

Foramen magnum:

Smaller anterior compartment transmits

1.       Apical ligament

2.       Upper band of cruciate ligament

3.       Membrane tectoria

Larger posterior compartment transmits

1.       Lower end of medulla oblongata

2.       Right and left vertebral artery

3.       Anterior and posterior spinal artery

4.       Spinal root of accessory nerve

5.       Sympathelic plexus of nerves

6.       Veins joining the venous plexus of medulla oblongata

7.       Lower part of tonsil of cerebellum

Jugular foramen:

1. glossopharyngeal nerve : mixed nerve : sensory supply motor supply
2. vagus nerve : mixed nerve : sensory supply  motor supply
3. Cranial root of accessory nerves: motor nerve. supply
4. Internal jugular vein

Summary of cranial nerves

Cranial nerves

Pure Sensory nerve: 

 olfactory nerve, optic nerve and vestibulocochlear nerve (1, 2, 8)

Function of sensory nerve in short:

1. Olfactory nerve : carry smell

1. Optic nerve : responsible for vision

1. Vestibulocochlear nerve : vestibular part responsible for balance and cochlear nerve responsible for vision

No.	Sensory nerve	Component	Name of the opening  through which nerve  enter  into the  cranium	Arises from
I	Olfactory nerve	SVA	Cribriform plate of  ethmoid	Axon of olfactory nerve   arises from the Olfactory  receptors cells which are  situated in the nasal mucosa
II	Optic nerve	SSA	Optic canal	Optic nerve fibres are arises  from  the ganglionic cells  of the retina
VIII	Vestibulocochlear  nerve	SSA	Internal acoustic meatus	Nerves are arises from inner ear

Pure motor nerve:  Oculomotor,  trochlear and abducent , accessory nerve and hypoglossal 

 nerve (3, 4, 6,   11, 12)

Oculomotor, trochlear and abducent nerves are pure motor nerve which innervate extraocular muscles

	Nerves	Functions	Nucleus	Name of the opening through which nerve exit the cranium
III	Oculomotor nerve	All extra-ocular muscles of  eye are supplied by oculomotor nerve except SO and LR	Oculomotor nucleus Edinger –Westphal  nucleus	Superior orbital fissure
IV	Trochlear nerve	SO 4: superior oblique muscle is supplied by trochlear nerve	Trochlear nucleus	Superior orbital fissure
VI	Abducent nerve	LR 6: lateral rectus muscle is supplied by abducent nerve	Abducent nucleus	Superior orbital fissure

XI	Accessory nerve	Functions	Nucleus	Name of the opening  through which nerve exit  the cranium
	Cranial root	It supplies all muscles of soft palate  ( except tensor veli  palatine)  and all muscles of  the pharynx  except stylopharyngeus	Spinal accessory nucleus	Jugular foramen
	Spinal root	This part supplies the sternocleidomastiod and trapezius muscles		Foramen magnum
XII	Hypoglossal nerve	It supplies all muscles of the tongue  except  palatoglossus	Hypoglossal nucleus	Hypoglossal canal

Mixed nerves: (V, VII, IX, X)

 Trigeminal nerve,

Facial,

Glossopharyngeal,

 Vagus 

Trigeminal nerve (V)

It has three parts

		Foramen	Nucleus of trigeminal nerve
Ophthalmic nerve	sensory nerve	Superior orbital  fissure	Motor nucleus of trigeminal  nerve Spinal nucleus of trigeminal  nerve Main sensory nucleus of  trigeminal nerve and  mesencephalic nucleus of  trigeminal nerve
Maxillary nerve	sensory nerve	Foramen  Rotundum
mandibular nerve	Mixed : both  sensory and  motor	Foramen ovale

Functions of mixed nerves in short:

Trigeminal nerve functions (in short):

Sensory function: carry sensation from face

Motor function: ---Muscles of mastication, tensor tympani, tensor veli palatine

Facial nerve (VII)Functions (in short):

Sensory function: carry taste sensation from ant 2/3 of tongue

Motor function: motor innervation of muscles of facial expression

Secretomotor function: innervate lacrimal gland through pterygopalatine ganglion 

Glossopharyngeal nerve functions(IX) (in short):

Sensory function: carry taste sensation and general sensation from pos 1/3 of tongue 

Motor function: innervate stylopharyngeus muscle

Secretomotor function: innervations of parotid gland through otic ganglion

Vagus nerve(x) function in short :

Sensory function: carry taste sensation from post most part of tongue, carry sensation from larynx, 

external ear

Motor innervations: muscles of larynx 

Male reproductive system : easy and brief handout for oral examination

Male reproductive organ

•      Epididymis

•      It is a coma-shaped body situated along the lateral part of the posterior border of testis

•      It is an organ that contains the efferent ductules and the duct of the epididymis

•      The efferent ductules are lined with pseudostratified columnar epithelium

•      A circular smooth muscle layer 1st appear at the beginning of the efferent ductules

      Duct of epididymis

•      It is lined with a pseudostratified columnar epithelium. It contains principal cells and basal cells

•      Numerous long, modified microvilli called stereocilia extend from the luminal surface of the principal cells

•      Epididymal cells function in both absorption and secretion

•      The smooth muscle coat of the duct of epididymis gradually increases in thickness to become three-layered in the tail

        Ductus deferens
   

         is a thick cord-like tubular structure and is about 45 cm. it is lined by pseudostratified columnar epithelium with stereocilia and a lamina propria. The thick outer wall is formed by inner and outer longitudinal and middle circular smooth muscle  cells layers. .

§  SN: In epididymis, the lumen is smooth but in d. deferens the lumen is thrown into deep longitudinal fold due to contraction of the thick muscular coat.

Course and relations of ductus deferens

•      It begins from the tail of epididymis then enters the spermatic cord and traverses the inguinal canal

•      At the deep inguinal ring the vas leaves the other constituents of the cord & ascend in front of the external iliac artery

•      Next the vas crosses above and medial to the terminal part of Ureter & passes behind the base of urinary bladder

•      Finally, approaches the base of prostate and joins with the duct of seminal vesicle to form the ejaculatory duct 

Seminal vesicle

•      They are paired, elongated and highly folded tubular glands

•      It secrete a fluid rich in fructose which is the principal metabolic substrate for sperm 

•      It is lined by pseudostratified columnar epithelium which contain tall, nonciliated columnar cells and short, rounded cells that rest on basal lamina

Prostate gland

•      This is a pyramidal-shaped, fibromuscular and glandular organ 3cm in long, which surrounds the prostatic urethra

Prostate gland: relations

•      Superiorly: it is continuous with the neck of urinary bladder

•      Inferiorly, the apex of the prostate rest on external sphincter of the bladder

•      Anteriorly, lies the pubic symphysis separated by the extraperitoneal fat of retropubic space

•      Posteriorly,lies the rectum separated by the fascia of Denonvilliers

•      Laterally, lies levator ani

The prostatic capsules

•      These are normally two

•      The true capsule – a thin fibrous sheath which surrounds the gland

•      The false capsule –condensed extraperitoneal fascia

•      Between layers 1 and 2 lies the prostatic venous plexus

•      In prostatic operation the true capsule is not disturbed because the prostatic venous plexus lying external to this. 

The prostate gland secretes prostatic acid phosphatase (PAP), fibrinolysin, citric acid & prostate specific antigen

Presenting parts of prostate 

•         The apex is directed below

•         The base is directed above and surrounds the neck of the bladder. It is pierced by the urethra in the median plane

•         Anterior surface is narrow and convex situated behind the lower part of symphysis pubis

•         Each infero-lateral surface is related to the anterior fibers of the levator ani

•         The posterior surface is broad and flat related to the ampulla of rectum. This surface is palpable by rectal examination about 4 cm.above the anus. 

The penis

•         It forms the male organ of copulation and consists of two parts – a root and a body

•         The root is situated in the superficial perineal pouch and consists of two diverging crura and a median bulb of the penis

The body of the penis

•      The body of the penis consists principally of two dorsal masses of erectile tissue the corpora cavernosa  which are the continuation of two crura and a ventral mass of erectile tissue the corpora spongiosum in which the spongy part of urethra is embedded and it is the continuation of bulb of penis .

                                     

CORPORA  CAVERNOSA

•         It is divided into number of intercommunicating cavernous spaces which is lined by endothelium

•         These spaces receive the blood from the capillaries of the helicine arteries are the branches of deep artery of penis

•         During erection the arterioles dilate and the cavernous spaces are filled with blood, at the same time the venous outflow is diminished by the pressure of the distended cavernous spaces. Therefore, erection is purely a vascular phenomenon

Coverings of penis

•         The skin

•         The superficial fascia

•         Fibrous envelope- the tunica albuginea

Ligaments of penis

•         Fundiform ligaments

•         Suspensory ligaments

•         Erection

•          It is a vascular phenomenon which occur by the action of parasympathetic nerve. The parasympathetic nerve ( S2-4 spinal segments) dilate arterioles of the corpora cavernosa

•                    

•         Ejaculation

•         It is stimulated by the sympathetic nerves (L1 spinal segment) which produce contraction of the vas deferens, seminal vesicle, ejaculatory ducts and prostate.

•         Contraction of the internal urethral orifice preventing the reflux of semen into the bladder

•         At the end of the  ejaculation, the sympathetic nerves produce vasoconstriction of penis and the penis is flaccid.

   The parasympathetic initiates the sexual act by erection & sympathetic finalizes the act by       ejaculation