Gray vs white rami communicans

 

Gray vs  white rami communicans

White and gray rami communicans connect the sympathetic ganglia to the spinal nerves.

They are associated with the sympathetic nervous system, which is part of the autonomic nervous system responsible for the body's fight or flight response.

White Rami Communicans:

It is myelinated so it looks white.

They situate away from the spinal cord, just lateral to gray rami communicans

They are only attached with the thoracic and upper lumbar spinal nerves.  

They contain preganglionic sympathetic fibers which is the axon of pre-ganglionic neuron located in the lateral horn of spinal cord.

This pre-ganglionic sympathetic fibers passage following pathway:

 lateral horn of spinal cord, ventral root of spinal nerve, trunk of spinal nerve, white rami communicans and synapse with sympathetic ganglion

The pre-ganglionic sympathetic fibers of white rami communicants may synapse with post ganglionic neuron at the same level , or it may ascend or descend and synapse with post ganglionic neuron.

Gray Rami Communicans:

It is un-myelinated so it looks gray .

They are situated near the spinal cord, just medial to the white rami communicants

 They are attached with all spinal nerves of spinal cord

They contain post-ganglionic sympathetic fibers which is the axons of post -ganglionic neuron located within the sympathetic ganglion  

Pathway of post ganglionic fibres

Sympathetic ganglion , gray rami communicans, trunk of spinal nerve, distributed by ventral and dorsal rami of spinal nerves and reach to the target organ (sweat gland, blood vessels etc )  

White rami communicans	Gray rami communicans
It conveys pre-ganglion sympathetic fibers	It conveys post-ganglion sympathetic fibers
Whitish in colour	Grey in colour
It contain myelinated nerve fibres	It contains unmyelinated nerve fibers
It is situated away from the spinal cord	It is situated near to the spinal cord
It is only attached with thoracic and lumbar spinal nerves	It is attached with all spinal nerves
Through white rami communicans pre-ganglionic fibers enter into the sympathetic ganglia	Through gray rami communicans post-ganglionic fibers leave the sympathetic ganglia

Anatomy of male reproductive system : important information for viva 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

 

          Section of the ductus deferens

• Section of the ductus deferens showing the mucosa formed by pseudostratified columnar epithelium with stereocilia and a lamina propria. The thick outer wall is formed of smooth muscle (brown) and collagen fibers (blue).

 

• 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

 

•         

Spinal cord : important viva questions and answers

 

Spinal Cord & Nerves

This is the viscera of spinal cord and spinal meninges

1.        Anatomical points:

            I.        anteriror median fissure lies anteriorly

          II.     cauda equina lies inferiorly

 

2.        length : 45cm                    wide 2.5 cm

3.         Extension of spinal cord:

   Adult: start at the level of foramen magnum to lower border of 1^st lumbar vertebra

   Children: at the level of the foramen magnum to the 3^rd lumber vertebra

4.        Terminal part of sub-arachnoid space of the spinal cord : lower border of 2^nd sacral vertebra

5.        termination of filum terminalis: at the 1^st coccyx

External feature of spinal cord :

i)                 anteriorly : anterior median fissure

ii)               posteriorly : posterior median septum

iii)              inferiorly : filum terminalis and cauda equine

iv)              two enlargement in cervical and lumbar region

v)               external surface is covered by spinal meninges : outer meningeal dura mater, middle arachnoid mater and  inner pia mater

vi)              ventral roots, dorsal roots and dorsal root ganglia and spinal nerve

6.        How many enlargement present within the spinal cord and why?

i)                 Cervical enlargement: extend from the foramen magnum to 1^st thoracic vertebra. Supply upper limb

ii)               Lumbar enlargement: extend from thoracic 10^th to 12^th vertebra. Supply lower limb.

7.        What is spinal segment?

 Ans: Part of the spinal cord to which one pairs of spinal nerve is attached.

8.        How many spinal segments present in the spinal cord? – 31 spinal segments

9.        What is conus medullaris? – cone shaped terminal part of spinal cord

10.     What is filum terminalis ? – it is the prolongation of pia mater which extend from the cunus medullaris to 1^st coccyx

11.     What is cauda equine: the lumbar and sacral roots below the termination of spinal cord continue as a leash of nerve roots known as cauda equine.

12.     What is legamentum denticulate: it is the thickening of pia mater situated on either side of spinal cord between nerve roots. (Figure ellis 364)

Spinal nerve

How many Spinal nerves present in our body? Number: 31 pairs. 8 cervical spinal nerve, 12 thoracic spinal nerve, 5 lumbar spinal nerve, 5 sacral spinal nerve and 1 coccygeal spinal nerve

How a spinal nerve is formed? :  Spinal nerve form by union of ventral and dorsal nerve roots

Location of spinal nerve: within the intervertebral foramen

Exit : C1-C7 spinal nerves exit ABOVE C1-C7 vertebrae

                         C8 spinal nerve projects below C7 vertebra

                         T1-S5 spinal nerves project BELOW T1-S5 vertebrae

 Branches of a Spinal Nerve:

                        1. dorsal ramus – supply deep muscles and skin of back

                        2. ventral ramus – supply upper and lower extremities, ventrolateral trunk

                        3. meningeal branch - back into the spinal column

                        4. rami communicantes - for autonomic nerve fibers

Type of spinal nerves: they are mixed nerve (both sensory and motor ).

Component: GSA (general somatic afferent –carry impulse from periphery to CNS) and GSE( general somatic efferent- impulse goes from CNS to skeletal muscle)

Plexus of spinal nerve: plexus of spinal nerve is formed by ventral rami of different spinal nerves. There are four spinal nerve plexus  present within the body.

Name of plexus	Formation	Supplied area	Important nerve of the plexus
1. cervical plexus	ventral rami of C1-C4 with some C5	a. muscles/skin of head, neck, some shoulder b. phrenic nerve - diaphragm muscle (breathing)	phrenic nerve -
2. brachial plexus	ventral rami of C5-C8 and T1	Upper limb and shoulder	Axillary N, musculocutanous  N, Radial N, median N, Ulnar N
3. lumbar plexus	- ventral rami of L1-L4	a. abdominal wall, genitals, part of lower limb	Femoral N, Obturator N
4. sacral plexus	ventral rami of L4-L5 and S1-S4	a. buttocks, perineum, part of lower limb b. sciatic nerve	Sacral n- largest nerve of body,  pudendal n, Sup and inf Gluteal n

                       

 Dermatomes: area of skin is supplied by single spinal nerve

           

Internal feature of spinal cord:

Inner grey matter contains a central canal. Parts of grey matter, ant horn and pos horn and lateral horn only in thoracic and lumbar region

Grey matter contain motor and internuncial neuron

Parts of outer white matter: 1. anterior (ventral) column

                        2. posterior (dorsal) column

                        3. lateral (intermediate) column

white matter contain ascending and descending tracts:

fasciculi/tracts –they are collection  axon bundles within the CNS. They are two types:                               a. ascending tracts – carry sensory impulse to the brain. Spinothalamic tract

            b. descending tracts – carry motor impulse from brain to the effector organ (skeletal muscle). corticospinal tract

Important tract within the spinal cord :

ASCENDING TRACTS (SENSORY)
anterior (ventral) spinothalamic	touch and pressure to thalamus
lateral spinothalamic tract	pain & temperature to thalamus
fasciculus gracilis	touch, 2-pt. discrimination,
fasciculus cuneatus	conscious proprioception,         vibration
posterior spinocerebellar                        anterior spinocerebellar	subconscious proprioception

 

DESCENDING TRACTS (MOTOR)
lateral corticospinal                                           anterior corticospinal tract	Carry motor output from cortex to motor neuron of ant. Grey horn which stimulate the skeletal muscles

Blood supply: one ant and two posterior spinal arteries. Other branches: ascending cervical a, pos intercostals a, and the lumbar a

Vein: ant and pos spinal vein.

Development : caudal part of neural tube (neuroectodarm)