Gray and white rami communicans of spinal nerves

Gray and white rami communicans 
Gray and white rami communicans are related with sympathetic system.

Both gray and white rami communicans are attached with ventral ramus of thoracic and lumbar spinal nerves. Only gray rami communicans are attached with ventral ramus of cervical, sacral and coccygeal spinal nerves.

Through white rami communicans pre-ganglionic sympathetic fibre leave the spinal nerves and enter into sympathetic ganglia . pre- ganglionic fibres are myelinated so it looks white. Through gray rami communicans post-ganglionic sympathetic fibre again enter into the spinal nerve , leave the sympathetic ganglia. Post ganglionic sympathetic fibres are non- myelinated so it looks gray.

Gray and white rami communicans are the lateral branch of sympathetic ganglia which connect ventral ramus of corresponding spinal nerve. White rami communicans has distal connection with ventral ramus of spinal nerve. Gray rami communicans has proximal connection with ventral ramus of spinal nerve. In thoracic and lumbar region pre-ganglionic fibres reach to sympathetic ganglia by using white rami communicans and corresponding ventral ramus of spinal nerve . in cervical and sacral region there are no corresponding white rami communicans of ventral ramus of spinal nerves . pre- ganglionic fibres enter into the corresponding sympathetic ganglia , some are ascend to cervical sympathetic ganglia and some fibres are descend to the sacral sympathetic ganglia. So cervical and sacral region lacks white rami communicans .

 pre-ganglionic sympathetic neurons are present in the lateral horn of gray matter of spinal cord ... pre-ganglionic fibres leave the spinal cord through the ventral root  of spinal nerve, spinal nerve trunk,.... through white rami communicans they enter into the sympathetic ganglion   

Post ganglionic neurons are present within the sympathetic ganglia ---- post -ganglionic fibres leave the sympathetic ganglia through gray rami communicans --- again enter into the ventral ramus of spinal nerve and distributed along the ventral and dorsal ramus of spinal nerve --- they innervate smooth muscle cells of vessel, sweat gland , arrector pili muscle(smooth muscle )  of the skin

Dilator pupillae

Dilator pupillae

They are involuntary  muscle fibers of the iris , which running radially from papillary margin to periphery .

It is supplied by sympathetic nerves from the superior cervical ganglion. It is widening the pupil and allowing for more light to pass through the eye.

Some condition like carcinoma of the lung, thyroid or oesophagus or metastatic lymph nodes may involve sympathetic trunk and give rise Horner’s syndrome,. One of the  characteristic feature of Horner’s syndrome is  slight constriction of pupil because dilator papillae muscle  losses it innervations  so fail to dilate pupil .  

Sphincter pupillae

Sphincter pupillae

Pupil is the central small aperture situated within the iris of eye. The size of it control by two muscles one is sphincter papillae and dilator papillae. So through pupil only the appropriate amount of light enters the eye .

    They are involuntary muscle fibers of the iris, which arranged circularly.

It is only present in papillary margin of iris. It is supplied by parasympathetic fibers from Edinger-westphal nucleus of oculomotor nerve.

Function: constrictor of the pupil in response to bright light. Failure of pupil to respond to light is an important clinical sign of the lack of nerve or brain function.

Erb's paralysis : brief and easy handout

Erb’s paralysis : it is also known as upper trunk plexus injury.

Cause of injury:  Upper trunk is ruptured due to forceful widening of the angle between the head and shoulder . traction of the arm during child birth and or by fall on the shoulder causes widening of angle between the head and shoulder. The root value of upper trunk is C5,6 .

In this paralysis, nerve roots involved: Mainly C5 and partly C6.

Muscles paralysed: Mainly biceps, deltoid,brachilais and brachioradialis.Partly supraspinatus, infraspinatus and supinator

Deformity: The deformity is known as "Policeman's tip hand" or "Porter's tip hand".

Loss of function:

Motor loss:

Arm: Hangs by the side, it is adducted due to paralysis of deltoid muscle. It is also medially rotated due to paralysis of supraspinatus, infraspinatus  and teres minor muscles

Forearm: Extended and pronated due to paralysis of biceps brachii.

Sensory loss:

The sensory loss of this clinical condition is minimal, only along the outer aspect of arm due to involvement of roots of C6 spinal nerve.