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

Temporal bone: easy handout covering only important topics

Temporal: It is an important bone because

·        Whole internal ear

·        Whole middle ear

·        Bony part of external auditory meatus lies within it .

SN: Only cartilaginous part of external auditory meatus and auricle lies outside the temporal bone 

1.   Anatomical  point :

·        Convex squamous part is directed laterally

·        Apex of petrous part is directed medially , forward, and upward

·        Zygomatic process is directed anteriorly

2.   Morphological type : pneumatic irregular bone

3.   Ossification : both intramembranous and intracartilaginous

·        Squmous part and tympanic part is ossify from membrane

·        Rest of the temporal bone is ossify from cartilage

4.   Development :

     Petrous part of temporal bone is derived from paraxial mesoderm

    Rest of the part of temporal bone is derived from neural crest

5.   Parts: It has

Three parts:

                     i.        Squamous part

                    ii.        Petro-mastoid part

                   iii.        Tympanic part

Three processes:

It has three processes :

                     i.        Zygomatic process

                    ii.        Mastoid process

                   iii.        Styloid process

Squamous part : it has two surfaces

External surface: 

i)             whole external  surface is attached by origin of temporalis muscle except mandibular fossa and zygomatic process

ii)            external surface bears groove for middle temporal artery

iii)        Suprameatal triangle : this triangle situated just above and posterior part of  the external auditory meatus

iv)        Importance of suprameatal triangle : mastoid antrum lies 1.25 cm deep to it

Internal surface:

Impressions of temporal lobe of cerebrum

Groove for middle meningeal artery

Squamous part has two borders

·        Superior border articulate with inferior border of parietal bone

·        Antero-inferior border : articulate with greater wing of sphenoid bone

Petrous part:    It has

Apex: is directed medially, forward and upwards

Base: attached with squamous and mastoid part

Petrous part : 3 borders:

1.   Anterior border: articulate with greater wing of sphenoid   

2.   Superior border:  lodges superior petrosal sinus and attachment of tentorium cerebella except medial part

3.   Posterior border:

Medial part of posterior border is lodge by inferior petrosal sinus  and

Lateral part of posterior border forms jugular foramen by articulating with condylar part of occipital bone

3 surfaces of petrous part : anterior, posterior and inferior

Anterior surface of petrous part :

1.   This surface  is irregular for sulci and gyri of temporal lobe of cerebrum

2.   Trigeminal impression ( a depressed area near the apex ): lodge trigeminal ganglion

3.   Arcuate eminence: an elevated area behind the trigeminal impression, it is caused by superior semicircular canal of internal ear

4.   Tegmen tympani:  a thin plate of bone situated in between arcuate eminence and squamous part of temporal bone.

From antero- posteriorly , tegment tympani forms

1.   Roof of tensor tympani

2.   Roof of middle ear cavity

3.   Roof of mastoid antrum

Posterior surface of petrous part of temporal bone:

Bear orifice of internal auditory meatus :  Structure passing through the foramen

Structures entrance into internal auditory meatus :

·        Motor root of facial nerve

·        Labyrinthine artery

Structures exit from the internal auditory meatus:

·        sensory root of facial nerve

·        vestibulocochlear nerve

·        labyrinthine vein

Inferior surface of petrous part of temporal bone:

From antero posteriorly

1.   Near apex: attachment of levator veli palatine muscle and cartilaginous part of auditory tube

2.   External or lower opening of carotid canal

3.   Jugular fossa

Mastoid part

It forms the posterior part of temporal bone

It has

Two surfaces: external and internal

Two borders: superior and posterior

1 process: mastoid process

                                               External surface of mastoid part

It is attached with following muscles : muscles are arrange from above , downwards and forwards

                     i.        Auricularis posterior

                    ii.        Origin of occipital belly of occipito frontalis muscle

                   iii.        Insertion of sternocleidomastoid

                  iv.        Insertion of splenius capitis

                   v.        Insertion of longissimus capitis

internal surface of mastoid part

Sigmoid sulcus : a deep groove which lodge sigmoid sinus

Two borders of mastoid part  :

·        superior border articulate with inferior border of parietal bone

·        posterior border articulate with inferior border of squamous part of occipital bone

Tympanic part

·        A thin plate of bone lies between the squamous and mastoid parts

·        Anterior surface form non articular part of mandibular fossa

·        Posterior surface forms greater part of external auditory meatus

Processes of temporal bone

                                                                                                          i.        Zygomatic process :

·        medial surface and lower border of zygomatic process give origin of masseter muscle

·        Superior border of zygomatic process attached with temporal fascia

·        Anterior end of zygomatic process articulate with temporal process of zygomatic bone

                                                                                                             ii.        Mastoid process :

External surface of mastoid process is attached with

a)   Insertion of sternocleidomastoid

b)   Insertion of splenius capitis

c)   Insertion of longissimus capitis

Mastoid notch : a deep notch at the medial surface of mastoid process gives origin of posterior belly of digastric muscle

Mastoid foramen near the posterior border of mastoid part of temporal bone : it transmit an emissary vein which connect sigmoid sinus with posterior auricular vein

                                                                                                              iii.        Styloid process

Muscles :

·        origin of styloglossus,  stylohyoid and stylopharyngeus

Ligaments :

·         stylohyoid and stylomandibular ligament

Stylomastoid foramen :

·        It is situated in between mastoid process and styloid process

It transmitted

·        Facial nerve exit

·        Entrance stylomastoid branch of posterior auricular artery