Some aspects of spinal Some aspects of spinal cord and medullacord and medulla

Tract, fasciculus and lemniscusTract, fasciculus and lemniscus

Tract--- collection of nerve fibers (in the Tract--- collection of nerve fibers (in the white matter) having the same origin, white matter) having the same origin, course and termination.course and termination.

Fasciculi (bundles) and leminisci (ribbons) Fasciculi (bundles) and leminisci (ribbons) are the other names of the tracts.are the other names of the tracts.

Functionwise the tracts are sensory Functionwise the tracts are sensory (ascending, afferent (signals coming to (ascending, afferent (signals coming to CNS) and motor (descending,efferent, CNS) and motor (descending,efferent, signals going away from CNS).signals going away from CNS).

Naming the tractsNaming the tracts

Named by the grey matter which they Named by the grey matter which they connect.connect.

E.g. Corticospinal tract (from cerebral E.g. Corticospinal tract (from cerebral cortex to spinal cord (descending tract), cortex to spinal cord (descending tract), spinothalamic tract (ascending tract).spinothalamic tract (ascending tract).

nuclei and ganglianuclei and ganglia

Collections of cell bodies of neurons in Collections of cell bodies of neurons in CNS are called the nuclei (not to be CNS are called the nuclei (not to be confused with the nucleus of a cell!!).confused with the nucleus of a cell!!).

Collections of neurons in the peripheral Collections of neurons in the peripheral nervous system are called “ganglia”.nervous system are called “ganglia”.

AF

LF

PF

The term FUNICULUS or COLUMN is used for white matter in the cord

WHAT ARE THE COMMISSURES?

Major ascending tracts, their Major ascending tracts, their function and location in the cordfunction and location in the cord

Lateral spinothalamic tract—lateral white column--- pain Lateral spinothalamic tract—lateral white column--- pain and temperature from opposite side of the body.and temperature from opposite side of the body.

Spinotectal tract--- lateral white column--- visual Spinotectal tract--- lateral white column--- visual responses ie; turning of head and eyes towards the responses ie; turning of head and eyes towards the source of stimulation.source of stimulation.

Spinocerebellar (dorsal and ventral)– lateral white Spinocerebellar (dorsal and ventral)– lateral white column--- proprioception.column--- proprioception.

Fasciculus gracilis(Gall) and F.cuneatus (Burdach)--- Fasciculus gracilis(Gall) and F.cuneatus (Burdach)--- posterior white column—joint sense,vibration sense, two-posterior white column—joint sense,vibration sense, two-point discrimination. stereognosis,conscious kinesthesia.point discrimination. stereognosis,conscious kinesthesia.

Some important descending tracts Some important descending tracts in the cordin the cord

Lateral corticospinal tract (crossed Lateral corticospinal tract (crossed pyramidal tract)--- lateral white column—pyramidal tract)--- lateral white column—skilled movements especially hands and skilled movements especially hands and feet.feet.

Anterior corticospinal tract (uncrossed Anterior corticospinal tract (uncrossed pyramidal)--- anterior white column—same pyramidal)--- anterior white column—same as aboveas above

Vestibulospinal --- anterior white column– Vestibulospinal --- anterior white column– unconscious maintenance of balance.unconscious maintenance of balance.

Sensory neuronsSensory neurons

Three order of neuronsThree order of neuronsFirst order neuron– in the dorsal root First order neuron– in the dorsal root

ganglion.ganglion.Second order neuron– in the CNS.Second order neuron– in the CNS.Third order neuron– in the thalamus.Third order neuron– in the thalamus.

SYRINGOMYELIASYRINGOMYELIA

Destruction of central canal and its Destruction of central canal and its surrounding areas--- results in injury to surrounding areas--- results in injury to anterior white commissure which contains anterior white commissure which contains crossing anterior spinothalamic tracts.crossing anterior spinothalamic tracts.

This results in bilateral loss of pain and This results in bilateral loss of pain and temperature sensations below the lesion temperature sensations below the lesion but other sensations are preserved in the but other sensations are preserved in the uncrossed tracts of posterior column. uncrossed tracts of posterior column. (dissociated sensory loss)(dissociated sensory loss)

Tabes dorsalisTabes dorsalis

Tertiary syphilitic degeneration of posterior Tertiary syphilitic degeneration of posterior white columns which only sensory tracts.white columns which only sensory tracts.

There is loss of tactile There is loss of tactile discrimination,vibration and position discrimination,vibration and position sense. (Rhomberg’s sign is positive).sense. (Rhomberg’s sign is positive).

Medulla oblongataMedulla oblongata

Medulla oblongataMedulla oblongata

Lower part of brainstem.Lower part of brainstem.Contains central canal in the lower part Contains central canal in the lower part

and its upper part contains IV ventricle.and its upper part contains IV ventricle.Presents pyramids on either side of the Presents pyramids on either side of the

midline anteriorly (formed by corticospinal midline anteriorly (formed by corticospinal tracts on their way to spinal cord) and olive tracts on their way to spinal cord) and olive produced by underlying inferior olivary produced by underlying inferior olivary nucleus.nucleus.

Gross features

On the back of medulla On the back of medulla are gracile and cuneate are gracile and cuneate tubercles which contain tubercles which contain nuclei of the same nuclei of the same name(2nd order neurons) name(2nd order neurons) for the fasciculi of the for the fasciculi of the same name.same name.

structurestructure

The characteristic appearance of grey The characteristic appearance of grey matter in spinal cord is lost in medulla.matter in spinal cord is lost in medulla.

The grey matter contains the nuclei of last The grey matter contains the nuclei of last four cranial nerves and reticular formation.four cranial nerves and reticular formation.

For the arrangement of grey and white For the arrangement of grey and white matters medulla is studied at 3 levels.matters medulla is studied at 3 levels.

Medulla at the level of pyramidal Medulla at the level of pyramidal decussationdecussation

Important features are:Important features are: 1.Spinal nucleus and tract 1.Spinal nucleus and tract

of V in line with the of V in line with the posterior horn of spinal posterior horn of spinal cord.cord.

2.Pyramidal 2.Pyramidal decussation(75%of fibers decussation(75%of fibers cross the midline and cross the midline and descend to the cord as descend to the cord as lat.corticospinal tracts.lat.corticospinal tracts.

continuedcontinued

3.corresponding to 3.corresponding to the anterior horn is the anterior horn is the spinal nucleus of the spinal nucleus of accessory.accessory.

4.diffuse zone of 4.diffuse zone of nerve cells and fibers nerve cells and fibers corresponding to the corresponding to the lateral white column lateral white column called the reticular called the reticular formation. formation. The reticular formation

SPECIAL FEATURES OF V nerveSPECIAL FEATURES OF V nerve

Has a large sensory nucleus (V1,V2 and Has a large sensory nucleus (V1,V2 and V3) and a smaller motor nucleus.V3) and a smaller motor nucleus.

Hence it extends throughout the brain Hence it extends throughout the brain stem (mesencephalic nucleus, principal stem (mesencephalic nucleus, principal nucleus and spinal tract and nucleus).nucleus and spinal tract and nucleus).

Perhaps the only cranial nerve nucleus to Perhaps the only cranial nerve nucleus to do so.do so.

Medulla at the level of sensory decussationMedulla at the level of sensory decussation

Fasciculi gracilis and Fasciculi gracilis and cuneatus end in cuneatus end in corresponding nuclei.corresponding nuclei.

Second order neurons Second order neurons begin as internal arcuate begin as internal arcuate fibres,cross the midline fibres,cross the midline and form the medial and form the medial lemniscus.lemniscus.

Olivary nucleus makes its Olivary nucleus makes its appearance.appearance.

Pyramids on either side Pyramids on either side of midline.of midline.

Sensory decussation

continuedcontinued

Central grey matter Central grey matter (close to the central (close to the central canal) containscanal) contains

1.hypoglossal nucleus 1.hypoglossal nucleus (close to the midline)(close to the midline)

2.dorsal nucleus of 2.dorsal nucleus of vagus vagus (parasympathetic)(parasympathetic)

3.nucleus of tractus 3.nucleus of tractus solitarius (taste)solitarius (taste)

Purely motor cranial nervesPurely motor cranial nerves

3rd,4th,6th and 12th 3rd,4th,6th and 12th cranial nerves lie in cranial nerves lie in the same line and the same line and have their nuclei have their nuclei close to the midline of close to the midline of the brain stem.the brain stem.

continuedcontinued

4.MLF appears just posterior to medial 4.MLF appears just posterior to medial lemniscus (this is connected to 3lemniscus (this is connected to 3rdrd,4,4thth,6,6thth,8,8thth and spinal nucleus of XI)and spinal nucleus of XI)

Spinocerebellar and lateral spinothalamic Spinocerebellar and lateral spinothalamic tracts move laterally to the lateral white tracts move laterally to the lateral white column.column.

Lateral and anterior spinothalamic tracts Lateral and anterior spinothalamic tracts lie close to each other and form “spinal lie close to each other and form “spinal lemniscus”.lemniscus”.

Upper medulla (open part)Upper medulla (open part)

central canal opens central canal opens into IV ventricle.into IV ventricle.

along with XII, along with XII, vestibular nuclei(2 of vestibular nuclei(2 of the 4) appear here.the 4) appear here.

nucleus ambiguus nucleus ambiguus (common motor (common motor nucleus for 9nucleus for 9thth,10,10thth and 11and 11thth cranial cranial nerves) is present.nerves) is present.

Medulla (clinical aspects)Medulla (clinical aspects)

Cranial nerves IX, X, XI and XII originate from the medulla.

2) control of visceral motor reflexes, e.g., coughing, swallowing, salivating,

vomiting, secretion, sneezing; the medulla also receives taste and other

visceral sensations.

Functions of the medulla include: 1) control of somatic motor reflexes

of the larynx, pharynx and tongue which are important in speech and swallowing. (nucleus ambiguus)

3) the MLF contains fibers for the regulation of the position of the head and neck and for coordinated eye movements;

4) the medulla is a relay for the cochlear and vestibular responses;

5) the reticular formation regulates a variety of functions including skeletal motor activity, consciousness, visceral functions, conduction of sensation, etc.

The features of medullary syndromes reflect its anatomy and physiology, i.e., the ascending sensory tracts, the descending motor systems, cranial nerves IX - XI exiting at this level, and the cranial nerves that are associated at or near this level, viz., CN VIII

Lateral medullary syndromeLateral medullary syndrome(PICA) of Wallenberg (PICA) of Wallenberg

Dorsolateral aspect of Dorsolateral aspect of medulla is supplied by medulla is supplied by PICA.PICA.

In this area In this area spinothalamic tract, spinothalamic tract, spinal nucleus and spinal nucleus and tract of V, nucleus tract of V, nucleus ambiguus, inferior ambiguus, inferior cerebellar peduncle, cerebellar peduncle, vestibular nuclei are vestibular nuclei are situated.situated.

Effects

Nucleus ambiguus Paralysis of vocal cord and pharyngeal muscles on the side of the lesion

Inferior cerebellar peduncle

Ipsilateral ataxia; also vertigo from interruption of connections of vestibular nuclei

Spinal tract of trigeminal Loss of pain and temperature sensation, same side of face

Spinothalamic tract Loss of pain and temperature sensation, opposite side of the body

Medial medullary syndromeMedial medullary syndrome(hypoglossal alternating hemiplegia)(hypoglossal alternating hemiplegia)

Due to thrombosis of Due to thrombosis of vertebral artery vertebral artery branches supply branches supply paramedian regions paramedian regions of medulla.of medulla.

Structures present Structures present here are: pyramid, here are: pyramid, hypoglossal nerve, hypoglossal nerve, medial lemniscus.medial lemniscus.

Effects

Medial Medial lemniscuslemniscus

Contralateral loss of Contralateral loss of position and vibration senseposition and vibration sense

pyramidpyramid Contralateral hemiplegiaContralateral hemiplegia

Hypoglossal Hypoglossal nucleusnucleus

Ipsilateral paralysis and Ipsilateral paralysis and atrophy of atrophy of halfhalf of tongue of tongue (when protruded, the tip (when protruded, the tip deviates to the same side of deviates to the same side of lesion)lesion)