How many pairs of spinal nerves are there?
What do the dorsal and ventral root join to form? What does this structure later spilt to form?
They join to form the spinal nerve for that segment. This spinal nerve later splits to form the dorsal and ventral rami
What kind of information is transmitted through the dorsal root?
What kind of information is transmitted through the ventral root?
What are the names for the thicker sections of the spinal cord which correlate for the upper and lower limbs? Why are they thicker?
The cervical and lumbar enlargements
What is grey matter?
What is white matter?
What is the function of the dorsal horn grey matter?
Cell bodies for sensory information
What is the function of the ventral horn grey matter?
Cell bodies for motor information
What is the function of the lateral horn grey matter?
Cell bodies for autonomic function
Where is the lateral horn found?
Between the levels of T1-L2-3
What are the separations of white matter called, what makes these separations and what are the 3 regions these separations are named after?
The separations are called funiculi and are divided into these by the horns of grey matter. There are 3 funiculi: Ventral Dorsal Lateral
Briefly describe each of the Laminae of Rexed:
1: AKA marginal zone. 2nd order neurons of the ALS found here. 2: AKA Substantia gelatinosa. 2nd order neurons for ALS found here. 3,4,5,6: AKA Nucleus Proprius. Processing of sensory info, input of nociceptive and other senses from both peripheral and visceral areas. (may explain referred pain) 7: AKA Clarkes nucleus. Only in the thoracic and upper lumbar regions. Relays unconscious proprioceptive information about the limbs to the ipsilateral cerebellum. 8: Contains the interneurons for the regulation of skeletal muscle contraction. 9: LMN's for skeletal muscle contraction 10: Surround central canal and receives afferent input similar to laminae 1 and 2.
What are A delta fibres?
Myelinated nociceptive fibres
What are A beta fibres?
Large myelinated fibres from mechanoreceptors
What are C fibres?
Unmyelinated fibres from nociceptors
What does the first lamina of rexed do? What is it AKA?
AKA marginal zone. 2nd order neurons of the ALS found here.
What does the second lamina of rexed do? What is it AKA?
AKA Substantia gelatinosa. 2nd order neurons for ALS found here.
What do the 3rd-6th laminae of rexed do? What are they AKA?
AKA Nucleus Proprius. Processing of sensory info, input of nociceptive and other senses from both peripheral and visceral areas. (may explain referred pain)
What does the 7th lamina of rexed do? What is it AKA?
AKA Clarkes nucleus. Only in the thoracic and upper lumbar regions. Relays unconscious proprioceptive information about the limbs to the ipsilateral cerebellum.
What does the 8th lamina of rexed do?
Contains the interneurons for the regulation of skeletal muscle contraction.
What does the 9th lamina of rexed do?
LMN's for skeletal muscle contraction
What does the 10th lamina of rexed do?
Surround central canal and receives afferent input similar to laminae 1 and 2.
What 3 tracts ascend in the white matter?
DCML ALS Spinocerebellar tracts
What tracts descend in the white matter?
Lateral corticospinal tract Ventral corticospinal tract Medial longitudinal fasciculus Tectospinal tract Vestibulospinal tract Dorsolateral fasciculus
Label each of the tracts.
Describe the DCML system
Ascending 3 neuron pathway
Gracile & Cuneate fasciculi (cuneate above T6)
Transmits Proprioception, light touch, vibration
1st order neuron cell body in DRG
1st order neuron neuron axon enters spinal cord dorsolaterally, straight into dorsal column
Once in spinal cord axons typically branch to form collaterals
1st order neuron axon ascends in dorsal column
(Others may ascend to the brainstem in separate tracts or may synapse on to motor neurons or interneurons to mediate tendon or postural reflexes)
Ascending fibres synapse onto 2nd order neuron relative nuclei in the medulla. ( Cuneate or Gracile)
2nd order neurons from the medullary nuclei decussate in the brainstem as the internal arcuate fibres to form the contralateral medial lemniscus
Medial lemniscus ascends to synapse at the ventral posterolateral nucleus of the thalamus (VPL) which gives rise the 3rd order neuron or terminal neuron
Terminal neurons project predominantly to areas 3, 1 & 2 of the primary somatosensory cortex via the posterior limb of the internal capsule.
Describe the ALS
Ascending 3 neuron pathway
3 tracts: Spinothalamic, spinomesencephalic and spinoreticular tracts
Relays nociceptive & thermal information, as well as crude touch
1st order neuron cell body in DRG, axon enters spinal cord via dorsolateral tract of Lissauer and synapses in the dorsal horn (laminae 1& 2)
2nd order neurons originate in the dorsal horn and decussate through the ventral white commissure within a few levels of entry to enter the contralateral ALS and ascend to the brainstem and diencephalon where it’s synapses are much more diverse than the DCML
Spinothalamic synapses at the VPL of the thalamus
Spinoreticular synapses in the reticular formation of the medulla and pons
Spinomesencephalic synapses at the reticular formation and periaqueductal grey of the midbrain
The 3rd order neurons which arise from here also have wide spread terminations not only in the 1o somatosensory cortex but also in other cortical and sub cortical areas
Spinothalamic: Sharp well localised pain
Spinoreticular: Dull diffuse pain
Spinomesencephalic: Important in modulation of pain
What type of sensation does the spinathalamic tract transmit?
Spinothalamic: Sharp well localised pain
What type of sensation does the spinoreticular tract transmit?
Spinoreticular: Dull diffuse pain
What is the function of the spinomesencephalic tract?
Spinomesencephalic: Important in modulation of pain
What are the spinocerebellar tracts? Where does the information transmitted through them come from?
They are collaterals from the proprioceptive fibres in the DCML system. They relay proprioceptive information to the cerebellum without being processed by the cortex. This is usually described as unconscious proprioception.
What does the term "unconscious proprioception" refer to? What part of the CNS uses this information and why?
The proprioceptive information transmitted to the cerebellum via the spinocerebellar tracts.
The cerebellum uses this information to monitor and rapidly adjust the accuracy of execited motor plans in action.
What is simple unconscious proprioception? How does it differ to complex unconscious proprioception?
Simple is purely sensory information
Complex also integrates descending motor information.
Does the cerebellum function ipsilaterally or contralaterally?
Describe the dorsal spinocerebellar tract:
•Collaterals of the proprioceptive fibres of fasciculus gracilis synapse at Clarke’s nucleus of lamina 7
•Simple unconscious proprioceptive information about the ipsilateral lower limb
•The axons of these 2nd order neurons then ascend in the ipsilateral DSCT
•The DSCT projects to the cerebellum and enters via the inferior cerebellar peduncle
•Fibres terminate predominantly in and around the vermis
•Clarke’s nucleus does not exist below ~L2 but still receives collaterals from the levels below making it rather large at this level
Describe the cuneocerebellar tract:
•Simple unconscious proprioceptive information from the ipsilateral upper limb supplied by collaterals from the fasciculus cuneatus
•1st order neurons don’t synapse at Clarke’s nucleus but rather ascend to the medulla to synapse at the lateral cuneate nucleus
•Lateral cuneate nucleus sits just lateral to the cuneate nucleus in the dorsal medulla
•Also projects to the cerebellum via the inferior cerebellar peduncle (2nd order neuron)
What 2 spinocerebellar tracts carry simple unconscious proprioceptive information? Which of these is for the upper limb and which is for the lower limb?
Dorsal spinocerebellar tract - lower limb
Cuneocerebellar tract - upper limb
Describe the ventral spinocerebellar tract
•More complex unconscious proprioceptive information from a combination of golgi tendon organs and muscle spindles as well as cutaneous receptors, spinal interneurons and descending fibre tracts
•1st order neurons are collaterals from the fasciculus gracilis so cell bodies are within the DRG
•Synapse at the spinal border cells of the ventral horn where we find the 2nd order neurons
•Axons of the 2nd order neuron decussate in the ventral white commissure and ascend in the contralater VSCT
•The axons of the VSCT ascend up to the level of the pons before taking a u-turn and descending into the cerebellum via the superior cerebellar peduncle
•Once inside the cerebellum the fibres decussate once more so that the information processed is ipsilateral (like the DSCT)
Describe the rostral spinocerebellar tract
•Analogous in function to the VSCT but relays information about the upper limb
•Other than this little is known about the RSCT
What 2 spinocerebellar tracts carry complex unconscious proprioceptive information? Of these 2, which is for the upper limb and which is for the lower limb?
Ventral spinocerebellar tract - lower limb
Rostral spinocerebellar tract - upper limb
Which of the 4 spinocerebellar tracts is the only one to decussate in the spinal cord? How then does this tract still end up being ipsilateral?
The ventral spinocerebellar tract
Once it reaches the pons, it enters the cerebellum via the superior cerebellar peduncle and then does a u-turn across the cerebellum to reach the opposite side, the side it originally entered the spinal cord on.
Diagram of spinocerebellar tracts
What is the lateral cortiocospinal tract also known as?
The pyramidal tract
What are the 2 corticospinal tracts
Ventral corticospinal tract
Lateral corticospinal tract
How much of the LCST and VCST arise from the primary and premotor cortices? Where does the remaining come from?
The remainder comes from the primary somatosensory cortex.
Where are the 1st order neurons for the LCST and the VCST found? What is this information commonly referred to?
In the cortex, and is commonly referred to as supraspinal
Where do the 1st order neurons for the VCST and the LCST descend in the brain? Where do they then go to?
Through the posterior limb of the ipsilateral internal capsule. They continue to descend ipsilaterally through the brainstem until they reach the pyramids found anteriorly on the medulla.
What % of axons of the corticospinal tracts decussate in the medulla? What do these fibres become?
85-90% decussate via the pyramidal decussation to descend in the contralateral pyramid, and these fibres are the LCST
What % of the corticospinal tracts do not decussate in the medulla? What do these fibres become?
10-15% do not decussate in the medulla, and continue to descend as the VCST.
Where do the axons of the LCST leave the LCST and enter the grey matter of the spinal cord?
At the level of supply
Do the axons from the LCST always synapse directly with their LMN?
No. Some will synapse with the LMN in the anterior horn of the grey matter, and some till synapse with an interneuron in the ventral horn, which will then go on the synapse with the LMN.
At what level do the axons of the VCST enter the grey matter? Where do they decussate? On which side do they synapse? (do they synapse before or after the decussate?)
They enter the grey matter at the level of supply, and then decussate through the anterior white commisure to synapse with their LMN in the contralateral ventral horn
What is the supply of the LCST?
Muscles of the limbs
What is the supply of the VCST?
Muscles of the trunk and girdles.
How do the LMN's of the LCST tract exit the spinal cord? Is this the same for the VCST?
Via the ventral root. The VCST also exit through here.
What is the cranial nerve equivalent of the cortiocospinal tract called?
The corticobulbar tract
Describe the pathway of the corticobular tract
Upper motor neurons arising from the lateral aspect of the primary motor cortex descend via the internal capsule, to the ipsilateral brainstem.
At the level of the nucleus to be supplied the upper motor neurons decussate to terminate on the lower motor neurons of the contralateral nucleus.
Which areas supplied by CN's receive UMN innervation from both hemispheres? What does this mean clinically?
The forehead, larynx and pharynx receive UMN supply from both hemispheres and are therefore more likely to be clinically spared in pathology.
What area have the most common presentations of corticobulbar lesions?
Contralateral lower face and tongue
Where does the rubrospinal tract originate?
The red nucleus
Where is the red nucleus located?
In the midbrain
In lower mammals, which pathway is the main supraspinal motor output pathway?
The corticorubrospinal tract
What is the function of the rubrospinal tract?
Many of the functions of the rubrospinal tract in the evolved human have been taken over by the more direct LCST but its projection to the dorsal aspect of the ventral horn means it still plays a role particularly in the flexor muscles
The more primitive function of the rubrospinal tract can be regained however in cases of disease of the LCST although the degree of dexterity is far less and fine hand coordination does not appear to be regained
Where do the axons from the red nucleus descend?
In the contralateral rubrospinal tract which lies anterior to the LCST but partially mixes with it.
At what level of the CNS do the axons from the rubrospinal tract enter the grey matter of the spinal cord and do they always synapse directly onto their LMN?
They enter at the level of supply, similar to the LCST. They can synapse directly onto the LMN or they can synapse onto the interneuron which then synapses onto the LMN.
Where does the tectospinal tract originate?
The superior colliculis of the midbrain
Where does the tectospinal tract receive inputs from?
The retina, visual cortex, somatosensory afferents and the auditory afferents
Where do the descending fibres of the tectospinal tract terminate?
In the cervical region of the spinal cord
What is the function of the tectospinal tract?
•Coordinates head, neck and eye movements according to sensory stimuli
•Important for maintaining stable retinal image
Where do the vestibulospinal tracts arise from?
From the vestibular nuclei of the pons and medulla.
Where does the vestibulospinal tract receive its input from?
Receive inputs from the labyrinth and cerebellum via the vestibular nerve
What does the lateral vestibular nucleus give rise to?
The lateral vestibulospinal tract
What does the medial vestibular nucleus give rise to? What is this also known as?
The medial vestibulispinal tract. AKA the MLF
Where does the lateral vestibulospinal tract project within the spinal cord? What is its major role?
It projects ipsilaterally down the anterious funiculus of the spinal cord.
It plays a role in the control of extensor tone in antigravity muscles and is required for erect posture.
Does the MLF (AKA the medial vestibulospinal tract) have both ascending and descending fibres, or just one of these?
Both ascending and descending.
What is the function of the MLF. Describe in terms of the different fibre directions.
The ascending fibres project to the oculomotor nuclei of CN III, IV and VI for the coordination of conjugate gaze.
The descending fibres project to the cervical spine and upper thoracic levels for the coordination of head and neck movements to eye movements.
There reticulospinal tracts, each arising from a different area. What are these areas and what is the name of the tract coming from each?
Pontine - gives rise to the medial reticulospinal tract
Medullary - gives rise to the lateral reticulospinal tract
What is the function of the medial reticulospinal tract? Where does it arise from?
It arises from the reticular formation of the pons and enhances the antigravity functions of the spinal cord by enhancing tone in the lower limb extensors and upper limb flexors.
Where does the lateral reticulospinal tract arise from? What is its function?
It arises from the reticular formation in the medulla and liberates the antigravity muscles from the pontine reflex control (the medial reticulospinal tract). A fine balance between the medial and lateral reticulospinal tracts is required to initiate new movements and this balance is controlled by descending signals from the cortex.
Diagram of the reticulospinal tracts