The spinal cord

What is the spinal cord?

~the spinal cord is the lower elongated, cylindrical part of the CNS. It occupies the upper two-thirds of the vertebral canal.it extends from the level of the upper border of the atlas to the lower border of vertebra L1 or the upper border of vertebra L2.

~it is about 45 cm long. the lower end is conical and is called the Conu medullaris.

~the apex of the conus is continued down as the filum terminale.

~along its length,the cord presents two thickenings,the cervical and lumbar enlargements,which give rise to large nerves for the limbs.

~the spinal cord gives off 31 pairs of spinal nerves.

Meningeal layers around the spinal cord:-

~duramater S2
~arachnoidmater S2
~piamater L1
~filum terminale
~linea splendens
~ligamenta denticulata

spinal nerves & spinal segments:-

~gives off 31 pairs of nerves
~C8 T12 L5 S5 CO1
~Cervical & lumbar enlargements
~cauda equina

Gray mater:-

~H-shaped pillar with anterior & posterior gray mater horns.
~united by gray commisure containing the central canal.
~lateral gray column (horn)present in thoracic & upper lumbar segments.
~amount of gray mater related to the amount of muscle innervated.
~consists of nerve cells ,neuroglia,blood vessels.

nerve cells in the anterior gray columns:-

~large & multipolar
~axons pass out in the anterior nerve roots as efferents.
~smaller nerve cells are multipolar.
~axons pass out in anterior roots as effrents.

nerve cells in the posterior gray columns.

~4 nerve cell groups:-
~substania gelatinosa:-
~situated at the apex.
~throughout the length of spinal cord.
~composed mainly of golgi type || neurons.
~recevies afferent fibers concerning with pain,tempreture & touch from posterior root.

Nucleus proprius:-

~anterior to substania gelatinosa.
~present throughout the length of spinal cord.
~main bulk of cells in posterior gray column.
~recevies fibers from posterior white column that are assoc with proprioception ,2-point discrimination,vibration.

Nucleus dorasalis:-

~base of posterior column
~C8-L3/L4
~associated with proprioceptive endings.(neuromuscular spindles & tendon spindles)

Visceral afferent nucleus:-

~lateral to nucleus dorsalis.
~T1-L3
~receives visceral afferent info

Nerve cells in the lateral gray columns.

~formed by the intermediolateral group of cells.
~T1-L2/L3
~cells give rise to preganglionic sympathetic fibers.
~in S2,S3,S4 ,they give rise to preganglionic parasympathtic fibers.

The gray commissure & central canal:-

~connects the gray on each side.
~central canal in the centre
~posterior gray commissure
~anterior gray commissure
~cental canal present throughout
~superiorly continous with the central canal of medulla oblongata
~inferiorly,expands as terminal ventricle
~terminates within the root of filum terminale.

White matter:-

~devided into:-
~anterior white column
~posterior white coumn
~lateral white column
~consists of nerve fibers,neurolgia,blood vessels
~white due to myelinated fibers.

Internal structure:-

~When seen in transverse section the grey matter of the spinal cord forms an H-shaped mass.in each half of the cord the grey matter is divisible into

1.the anterior grey column(or horn)
2.the posterior grey column(or horn)

~in some parts of the spinal cord a small lateral grey column is also present.
~the grey matter of the right and left halves of the spinal cord is connected across the midline by the grey commissure which is traversed by the central canal.
~the white matter of the spinal cord is divisible into right and left halves,in front by a deep anterior median fissure and behind by the posterior median septum.
~in each half the white matter is divided into:-

1.the posterior white column or posterior funiculus.
2.the lateral white column or lateral funculus nd
3.the anterior white column or anterior funiculus.

~the white matter of the right and left sides is continuous across the midline through the white commissure which lies anterior to the grey commissure.
~the spinal cord gives attachment ,on either side,to a series of spinal nerves.

~each spinal nerve arises by two roots:-
1.anterior (or ventral)
2.posterior(or dorsal)

~each root is made up of a number of rootlets.the length of the spinal cord giving origin to the rootlets for one spinal nerve constitutes one spinal segment.

~as the spinal cord is much shorter than the length of the vertebral column the spinal segments do not lie opposite the corresponding vertebrae.

~in estimating the position of a spinal segment in relation to the surface of the body it is important to remember that a vertebral spine is always lower than the corresponding spinal segment.

~as a rough guide it may be stated that in the cervical region there is a difference of one segment,in the upper thoracic region there is a difference of two segment ,and in the lower thoracic region there is a difference of three segments.

Tracts of the spinal cord:-

~A collection of nerve fibers that connects two masses of grey matter within the central nervous system is called a tract.tracts may be ascending or descending.
~they are usually named after the masses of grey matter connected by them.some tracts are called fasciculi or lemnisci.

*Lateral spinothalamic tract:-
~Pain & T

*Anterior spinothalamic tract:-
~Light(crude) touch & pressure

*Fasciculus cuneatus

*Fasciculus gracilis
~discriminatory touch,vibration,info from muscles & joints.

*Anterior spinocerebellar tract

*Posterior spinocerebellar tract
~unconscious info from muscles,joints,skin,subcut

*Spinotectal tract:-
~spinovisual reflexes

*spinoreticular tract:-
~info from muscles, joints & skin to the reticular formation

*spino-olivary tract:-
~indirect pathway to cerebellum

*Lateral spinothalamic tract:-
~pain & temp pathways

*1st order neurons:-
*pain conducted by A type fibers & C type fibers

*2nd order neurons:-
~deccussate to the opposite side
~ends in thalamus(ventral posterolateral nucleus)

*3rd order neurons:-
~ends in sensory area in postcentral gyrus
*Anterior spinothalamic tract:-
~light (crude) touch & pressure pathways

*Posterior white column:-
~discriminative touch,vibratory sense,consious muscle joint sense(conscious proprioception)

*Posterior spinocerebellar tract:-

~muscle joint sense pathways to cerebellum.
~unconscious proprioception
~muscle joint info from muscle spindles,GTO,joint receptors of the trunk & lower limbs.
~info is used by the cerebellum in the coordination of movements & maintenance of posture.

*Anterior spinocerebellar tract:-

~majority of 2nd order neurons cross to the opposite side.
~enter cerebellum through superior cerebellar peduncle.
~info from trunk ,upper & lower limbs.
~also carries info from skin & subcut tissue.

*Descending tracts:-

~upper motor neurons
~lower motor neurons
~corticospinal tracts:-
~concerned with voluntary,discrete,skilled movements.

*Reticulospinal tract:-
~facilitates or inhibits voluntary movement or reflex activity.

*Tectospinal tract:-
~reflex postural movements in response to visual stimuli.

*Rubrospinal tract:-
~fascilitates activity of flexor muscles & inhibits activity of extensor muscles.

*Vestibulospinal tract:-
~fascilitates extensor muscles,inhibits flexor muscles.

Blood supply:-

*Arteries of spinal cord:-

1.anterior spinal artery

2.posterior spinal artery

3.segmental spinal arteries

*Anterior spinal artery:-

~formed by the union of 2 arteries.
~from vertebral artery
~supply anterior 2/3 of spinal cord.

*Posterior spinal arteries:-

~arises from vertebral artery or posterior inferior cerebellar arteries(PICA)
~Descend close to the posterior roots.
~supply posterior 1/3 of spinal cord.

*Segmental spinal arteries:-

~Branches of arteries outside the vertebral column.
~gives off the anterior & posterior radicular arteries.
~great anterior medullary artery of adamkiewicz.
~arise from lateral intercostal artery or lumbar artery at any level from T8-L3

*main source of blood is the vertebral arteries…cervical
~radicular arteries ..spinal branch of vertebral ,asc cervical,deep cervical    ,inercostal,lumbar and sacral art
~arteria radicularis magna

*Distribution of blood supply:-

~radicular art:-grey & white matter
~anterior spinal :-ant two-third ventral grey matter,part of dorsal grey matter,ant and lat feniculi

~posterior spinal:-post one third posterior horn and posterior feniculus

Meninges:

*Dura mater:-

~dense,strong fibrous membrane.
~encloses the spinla cord & cauda equina
~continous above with the meningeal layer of dura covering the brain.
~ends at the level of S2.
~separated from wall of vertebral canal by the extradural space
~contains loose areolar tissue & internal vertebral venous space

*Arachnoid mater:-

~delicate impermeable membrane.
~lies between pia and dura mater.
~separated from pia mater by subarchanoid space.
~continous above with archanoid mater covering the brain.
~ends on filum terminale at level of S2.

*Pia mater:-

~vascular membrane
~closely covers spinal cord
~thickened on either side between nerve roots to form the ligamentum denticulatum

Clinical importance:-

*Spinal shock:-

~follows acute severe damage to the spinal cord.
~all cord functions below the level of the lesion become depressed lost.
~sensory impairment and flaccid paralysis occur.
~segmental spinal reflexes are depressed
~persists for less than 24 hours (may be as long as 1-4 weeks)

*Poliomyelitis:-

~acute viral infection of the neurones of anterior gray column.
~motor nuclei of cranial nerves.
~death of motor neurons cells-paralysis & wasting of muscles.
~muscles of lower limb more often affected.

*Spinal cord pathology:-

*Vertebral cause:-

1.trauma
2.disc prolapse
3.tumor-primary,eg-MM,secondary-eg.breast,thyroid,prostate,bronchus
4.spinal TB-(potts diease)

*Meningeal cause:-

1.epidural abcess
2.tumor-meningioma,neurofibroma,lymphoma,leukaemia

*Spinal cord itself:-

*Developmental:-

~syringomyelia
~meningomyelocoele
~tetherd cord syndrome

*Degenerative:-

~MND
~FA
~SCD
~HSP

*Demyelinating/inflammatory:-

~transverse myelitis
~multiple sclerosis
~neuromyelitis optica

*Infective:-

~bacterial-TB,Syphilis
~viral-EBV,polio,HIV,VZV,HSV
~parasitic-schistosomiasis,toxoplasmosis

*Deficiency:-

~vitamin B12 Deficiency
~vitamin E deficiency
~copper deficiency
~lathyrism

*Vascular:-

~vasculitis
~infraction
~haemorhage
~AVM

*Physcial agents:-

~radiation
~lightening injury

*Paraneoplastic

Localization of spinal cord diease:–

~presence of horizontally defined level below which there will be impairment of sensory,motor,and autonomic function.

*Cervical cord:-

~above C5-spastic qaudriplegia,and diaphgram weakness
~C5-T1:-(qaudriplegia,(LMN signs and segmental sensory loss in the arms & UMN signs in the legs)& respiratory(intercostal) muscle weakness.
~at C5-C6:-loss of power & reflex of biceps
~at C7:-weakness in fingers & wrist extensors & triceps.
~at C8:-finger & Wrist flexion are impaired.
~horners syndrome may accompany

*Thoracic cord:-

~spastic paraplegia with a sensory level on the trunk.
~bowel & bladder involvement
~abdominal reflex(T8-T12)lost above T8 lesion
(segmental lesion T8-T9:above the umbilicus)
(T10-T12:Below the umbilicus)

*Lumbar cord:-

~L2-L4:-
weakness of flexion & adduction of thigh
weakness in leg extension at knee
absent knee jerks(L3-L4)

*L5-S1:-
~weakness of foot & ankle and flexion at the knee & extension of the thigh
~absent ankle jerks(S1)

*Sacral cord:-

~saddle anesthesia(S3-S5)
~prominent bowel & bladder dysfunction & impotence.
~absent bulbocavernous (S2-S4) & anal reflex(S4-S5)

Types of spinal cord lesion:-

*complete or transverse lesion

*Incomplete lesion:-

~anterior cord syndrome
~posterior cord syndrome
~hemi cord syndrome
~central cord syndrome
~foramen magnum syndrome
~conus medullaris syndrome
~cauda equina syndrome

*Complete cord transection syndrome:-

~bilateral spastic(paraparesis/quadriparasis)
~bilateral loss of all moodalities of sensation
~bowel & bladder dysfunction
~LMN feature at the level of lesion
~cause:-trauma,vasculitis

*Brown sequard syndrome:-

*Anterior cord syndrome:-

*Posterior cord syndrome:-

*Central cord syndrome:-

*Foramen magnum syndrome:-

*C/F:-
~neck pain-radiating to shoulder
~occipital H/A
~variable sensory loss
~weakness & wasting of hand & neck muscles
~qaudriparesis(round the clock)

*Cause:-
~compressive lesion(meningioma,neurofibroma)in the region of foramen magnum

*Spinal shock syndrome:-

~this clinical condition follows acute severe damage to the cord.
~all cord function below the level of lesion becomes depressed or lost.
~usually last less than 24 hrs bt may last for 4-6 weeks.
~on recovery:-reflex-power-tone may regain this fashion
~5-10% patients may not recover from spinal shock.

*Conus medullaris syndrome:-

~bilateral saddle anesthesia
~prominent bowel & bladder dysfunction(urinary retention & anal incontinence)
~impotence
~absent anal reflex

*Cauda equina syndrome:-

~radicular low back pain
~asymmetrical lower limb weakness & sensory loss
~variable areflexia
~relative sparing of bowel & bladder
~planter may be flexor or absent
*cause:-
~disc prolapse
~tumor
~trauma