Pelvic splanchnic nerve : easy and brief discussion

Pelvic splanchnic nerve :

Pelvic splanchnic nerves is also known as  nervi erigentes

Pelvic splanchnic nerves are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the hindgut.

The splanchnic nerves are paired visceral nerves (nerves that contribute to the innervation of the internal organs, carrying fibers of the autonomic nervous system (visceral efferent fibers)   as well as sensory fibers from the organs (visceral afferent fibers. All carry sympathetic fibers except for the pelvic splanchnic nerves, which carry parasympathetic fibers.

      The parasympathetic nervous system is referred to as the craniosacral outflow;

       the pelvic splanchnic nerves are the sacral component.

       They are in the same region as the sacral splanchnic nerves,

        which arise from the sympathetic trunk and provide sympathetic efferent fibers.

Splanchnic nerve carrying sympathetic fibres  

·         Cardiopulmonary nerves

·         Thoracic splanchnic nerves (greater, lesser, and least)

·         Lumbar splanchnic nerves

·         Sacral splanchnic nerves

    Splanchnic nerve carrying parasympathetic fibres  

·         Pelvic splanchnic nerve

Plexuses and pelvic splanchnic nerves :

1.    Sacral plexus

2.    Inferior hypgastric plexus

3.    Superior hypogastric plexuses

4.    Inferior mesenteric plexuses

·         Formation of  Pelvic splanchnic nerves

The pelvic splanchnic nerves arise from the anterior rami of the sacral spinal nerves S2-S4 and enter the sacral plexus. They travel to their side's corresponding inferior hypogastric plexus, located bilaterally on the walls of the rectum.

Functional component of pelvic splanchnic nerve :

1.    GVA: general visceral afferent : collect sensation from pelvic viscera and hindgut

2.    GVE: general visceral efferent : innervate smooth muscle cells and gland

Distribution of

1.    GVA: general visceral afferent: location of cell body in dorsal root ganglia of 2-4 sacral spinal nerve . central process enter the cord by posterior nerve root .

Two fates of GVA fibres :    

                                            i.            some GVA fibres make local synaptic connections .  they are responsible for bladder reflexes

                                          ii.            Other GVA fibres   collect sensory information from pelvic viscera and convey these information to higher cortical center .         

SN: both sympathetic and parasympathetic pathway collect pain sensation from urinary bladder and rectum                                        

2.    GVE: general visceral efferent

Pre-ganglionic  fibres arises from pre-ganglionic neurons which are located in the 2-4 sacral segments of spinal cord

Then pre-ganglionic fibres leave the spinal cord through anterior root of spinal nerve, trunk of spinal nerve then leave the spinal nerve when they exit anterior sacral foramina  and form pelvic splanchnic nerves . The preganglionic fibres of pelvic splanchnic nerves synapse with  Intrinsic ganglia of descending and sigmoid colon, rectum and other the pelvic viscera  

 these fibres innervate smooth muscles of hindgut and urinary bladder

Three distribution of pelvic splanchnic nerve

1.      Anterolateral branch

2.      Branches join with hypogastric nerves

3.      Superolateral branch

Distribution of three branches

1.      Anterolateral branch : join with inferior hypogastric plexuses and then distributed into pelvic viscera

2.      Branches join with hypogastric nerves: after joining with the hypogastric nerve these branch ascend and join with superior hypogastric plexuses and distributed in to the inferior mesenteric artery  

3.      Superolateral branch : it passes directly into the tissue of the retroperitoneum and the mesentery of sigmoid and descending colon

Functions of pelvic splanchnic nerve :

1.    Pelvic splanchnic nerve  the innervation of smooth muscle cells of the pelvic and genital organs.

2.    It relaxes the smooth muscle cells of sphincter vesicae but contract detrusor muscle (smooth muscle cells) of urinary bladder   

3.    It influences motility in the rectum 

4.    In the distal 1/3 of the transverse colon, and through the sigmoid and rectum, and the cervix  in females,

5.     The pelvic splanchnic nerves collect the sensation of pain from the hindgut & pelvic organ but  the rest of the proximal gastrointestinal tract sensation is collected  by the vagus nerve .

6.      Vasodilator fibres to the erectile tissue of the penis and clitoris

7.      Secretomotor fibres to the hindgut

Peculiarities of 1st rib : easy and brief discussion

Peculiarities of 1^st rib

1.    It is the shortest, broadest and more curved rib

2.    The shaft is not twisted

3.    Tubercle present near the angle of shaft

4.    It is flattened from above downward

5.    It has no costal groove

6.    Upper surface is marked by two grooves

7.    Inner border is marked by scalene tubercle

8.    Head of 1^st rib contain one costal facet

9.    The scalene muscles are very strong and they have the ability to pull the first rib up if they shorten for any reason. 

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Superficial cardiac plexus : easy and brief description

Superficial cardiac plexus

The superficial cardiac plexus is an anatomical division of the cardiac plexus; it is smaller than the more posterior deep cardiac plexus.

Physiologically, the superficial and deep plexuses are in continuity via fine nerve fibres.

The superficial cardiac plexus is sited on the inferior surface of the arch of the aorta. It is contributed to by both post-ganglionic sympathetic and pre-ganglionic parasympathetic nerves:

• left inferior cervical cardiac nerve, a branch of the left vagus nerve
• left superior cervical sympathetic nerve derived from the left cervical sympathetic ganglia

These fibres pass inferiorly over the arch of the aorta before a massing inferior to it and slightly anteromedial to the ligamentum arteriosum within the ganglion of Wrisberg.

At this point, the left phrenic nerve lies medially and the vagal nerve lies laterally. The pulmonary artery lies posteriorly.

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Dorsal root ganglion easy and brief discussion

Dorsal root ganglia

Dorsal root ganglion has different name like :  spinal ganglion/ posterior root ganglion

It is  a cluster of neuron (a ganglion) in a dorsal root of a spinal nerve.

The cell bodies of sensory neurons known as first-order neurons are located in the dorsal root ganglia

Gross information

The axons of dorsal root ganglion neurons are known as afferents.

 In the peripheral nervous system, afferents refer to the axons that relay sensory information into the central nervous system (i.e. the brain and the spinal cord).

These neurons are of the pseudo-unipolar type, meaning they have an axon with two branches that act as a single axon, often referred to as a distal process and a proximal process.

Unlike the majority of neurons found in the central nervous system, an action potential in posterior root ganglion neuron may initiate in the distal process in the periphery, bypass the cell body, and continue to propagate along the proximal process until reaching the synaptic terminal in the posterior horn of spinal cord.

Histology of dorsal root gangliaon

Connective tissue capsule 

The sensory ganglion is covered by the vascular connective tissue capsule which also envalops its sensory root . the collagenous connective tissue septa penetrate the ganglion.

Neurons

The somata of these cells are pseudounipolar which is spherical in shape with large nuclei and nucleoli

Note that some somata are large and while others are small . so nuclei of somata are not always in the plane of section.

 In hematoxylin and eosin stain the somata is more or less homogenous and pink so the organelles such as Nissl substance are not visible.

Each soma is surrounded by neuroectodermally derived capsule cells.

Capsular cells are much smaller than small sized somata of neuron and contain small , round nuclei.

The smallest cells of ganglion are Satelline cells or fibroblast  are also evident . they are small , elongated contain densely stain nuclei  and situated peripheral to the capsular cells

Synapses do not occur in the ganglion

Fibres

Fibres are mostly myelinated and travel in bundles through the sensory ganglion. They belong to the large pseudounipolar neurons.

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Embryology of cloaca : derivative and easiest summary

Fate of cloaca

What is cloaca ?

Cloaca : part of hindgut (derived from endoderm) caudal to attachment of allantois, which is common chamber for hindgut & urinary system

It is divided into two parts ventral and dorsal by urorectal septum
ventral part is called primitive urogenital sinus
dorsal part is called primitive rectum

What are the parts of primitive urogenital sinus ?

Vesico-urethral canal and definitive urogenital sinus

From above down ward different parts of primitive urogenital sinus

1.      Upper part of vesico-urethral canal

2.      Lower part of vesico-urethral canal

3.      Pelvic part of definitive urogenital sinus

4.      Phallic part of definitive urogenital sinus

Cloaca

         Primitive urogenital sinus                                               Primitive rectum

                                                                                                     Rectum & upper part of anal canal

Upper part of primitive urogenital sinus is

 known as Vesico-urethral canal : it has 2 part 

Upper part of vesico-urethral canal develops urinary bladder 

Lower part of vesico-urethral canal  upper part of prostatic 

urethra of male & most of the proximal part of female urethra

Lower part of primitive urogenital sinus is 

known as  Definitive urogenital sinus: it has 2 part 

Pelvic part of definitive urogenital sinus: prostaic urethra &

 membrous urethra in male and lower small part of female urethra 

Phallic part of definitive urogenital sinus: penile part of male urethra &

terminal part of female urethra which open into the vestibule of  valva

Cloacal malformation : In rare cases (1 in every 50,000 babies), this process does not work properly and these tracts do not separate from one another completely. A female is said to have developed a “persistent cloaca” when these three tracts open into one common cavity, with one opening from the body.

The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois.

This bend becomes dilated into a pouch, which constitutes the endodermal cloaca; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward.

At a later stage the Wolffian duct and Müllerian duct open into its ventral portion.

The cloaca is, for a time, shut off from the anterior by the cloacal membrane, formed by the apposition of the ectoderm and endoderm, and reaching, at first, as far forward as the future umbilicus.

Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and pubic symphysis.

By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca.