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Spinal cord
- 2. GREY MATTER
- 3. 2 MIN NEUROSCIENCE: SPINAL CORD https://www.youtube.com/watch?v=MM7YNKJj_Lg https://www.youtube.com/watch?v=fbt3H3JxRMA ▸ Exterior of the Spinal Cord ▸ Spinal Cord Cross-Section
- 4. SPINAL CORD GREY MATTER: OVERVIEW ▸ The spinal cord is an important information relay and processing hub connecting the brain with the rest of the body ▸ A transverse section of the spinal cord reveals a distinct “butterfly” pattern of dark, inner “grey” matter surrounded by the lighter colour “white matter” ▸ The white matter contains the ascending and descending pathways connecting the brain and spinal cord ▸ Spinal cord grey matter can be functionally classified in three different ways: ▸ 1) into four main columns ▸ 2) into six different nuclei ▸ 3) into ten Rexed laminae
- 5. SPINAL CORD GREY MATTER: FOUR COLUMNS OF THE SPINAL CORD GREY MATTER ▸ The grey matter is divided into four main columns: the dorsal horn, the intermediate column, the lateral horn and the ventral horn: ▸ The dorsal horn (also known as the posterior horn) contains neurons that receive somatosensory information from the body, which is then transmitted via the ascending pathways, to the brain ▸ The ventral horn (also known as the anterior horn) largely contains motor neurons that exit the spinal cord to innervate skeletal muscle ▸ The intermediate column and lateral horn contains neurons that innervate visceral and pelvic organs
- 7. SPINAL CORD GREY MATTER: SPINAL CORD NUCLEI ▸ The prominent nuclei (groups of neuron cell bodies) in the spinal cord are the: ▸ Marginal zone (MZ, posterior marginalis) ▸ located at the tip of the dorsal horn ▸ important for relaying pain and temperature sensation to the brain ▸ Substantia gelatinosa (SG) ▸ located at the top of the dorsal horn ▸ SG is important for relaying pain, temperature and light touch sensation to the brain ▸ Nucleus proprius (NP) ▸ located in the ‘neck’ of the dorsal horn ▸ NP relays mechanical and temperature sensation to the brain
- 8. SPINAL CORD GREY MATTER: SPINAL CORD NUCLEI ▸ Dorsal nucleus of Clarke (DNC) ▸ the most dorso-medial nuclei ▸ DNC relays unconscious proprioceptive information to the brain ▸ only found in spinal segments C8 to L3 ▸ Interomediolateral nucleus (IMN) ▸ located in the intermediate column and lateral horn ▸ IMN relays sensory information from viscera to the brain ▸ autonomic signals from the brain to the visceral organs ▸ Lateral motor neurons and medial motor neurons (MNs) ▸ located in the ventral horn ▸ composed of motor neurons that innervate visceral and skeletal muscles
- 9. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ As an alternative to spinal cord nuclei, Bror Rexed (1950s) identified layers, or laminae, within the spinal cord where cells were grouped according to their structure and function, rather than solely on location
- 11. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ Lamina I ▸ tip of the dorsal horn ▸ cells respond to noxious or thermal stimuli ▸ sends information to the brain by the contralateral spinothalamic tract ▸ corresponds to the marginal zone ▸ Lamina II ▸ Involved in sensation of noxious and non-noxious stimuli, and modulating sensory input to contribute to the brain’s interpretation of incoming signals as painful, or not ▸ Sends information to Lamina III and IV ▸ Corresponds to substantia gelatinosa
- 12. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ Lamina III ▸ Involved in proprioception and sensation of light touch ▸ Cells in this layer connects with cells in layers IV, V and VI ▸ Partially corresponds to nucleus proprius ▸ Lamina IV ▸ Involved in non-noxious sensory information relay and processing ▸ Cells connect with those in lamina II ▸ Partially corresponds to nucleus proprius
- 13. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ Lamina V ▸ Relays sensory, including nociceptive (potentially painful), information to the brain via the contralateral and spinothalamic tracts ▸ Receives descending information from the brain via the corticospinal and rubrospinal tracts ▸ Lamina VI ▸ Contains many small interneurons involved in spinal reflexes ▸ Receives sensory information from muscle spindles (involved in proprioception) ▸ Sends information to the brain via ipsilateral spinocerebellar pathways
- 14. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ Lamina VII ▸ Large, heterogenous zone that varies through the length of the spinal cord ▸ Receives information from Lamina II to VI, and from viscera ▸ Relays motor information to the viscera ▸ Gives rise to cells involved in the autonomic system ▸ Dorsal nucleus of Clarke is part of Lamina VII ▸ Lamina VIII ▸ Varies depending on spinal cord level, but is most prominent in cervical and lumbar enlargements ▸ Cells are involved in modulating motor output to skeletal muscle
- 15. SPINAL CORD GREY MATTER: REXED LAMINAE ▸ Lamina IX ▸ Size and shape varies between spinal cord levels ▸ Distinct groups of motor neurons that innervate skeletal muscle ▸ Lamina X ▸ Surrounds the central canal – the grey commissure ▸ Axons decussate (cross over) from one side of the spinal cord to the other
- 17. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ Which grey matter column contains neurons that receive somatosensory information from the body, which is then transmitted via the ascending pathways, to the brain? ▸ dorsal horn ▸ ventral horn ▸ intermediate column ▸ lateral horn
- 18. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ dorsal horn - somatosensory information transmitted via ascending pathways
- 19. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ Which of the spinal cord nuclei is located in the ventral horn and composed of motor neurons that innervate visceral and skeletal muscles? ▸ Marginal zone (MZ, posterior marginalis) ▸ Substantia gelatinosa (SG) ▸ Nucleus proprius (NP) ▸ Dorsal nucleus of Clarke (DNC) ▸ Interomediolateral nucleus (IMN) ▸ Lateral motor neurons and medial motor neurons (MNs)
- 20. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ Lateral motor neurons and medial motor neurons (MNs) - located in the ventral horn and composed of motor neurons
- 21. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ Which lamina relays sensory, including nociceptive (potentially painful), information to the brain via the contralateral and spinothalamic tracts and receives descending information from the brain via the corticospinal and rubrospinal tracts? ▸ I - II - III - IV - V - VI - VII - VIII - IX - X?
- 22. SPINAL CORD GREY MATTER REVIEW QUESTIONS ▸ Lamina V
- 23. ASCENDING TRACTS
- 24. 2 MIN NEUROSCIENCE: ASCENDING TRACTS https://www.youtube.com/watch?v=nQfRUehU4zQ▸ Touch and the Dorsal Columns-Medial Lemniscus https://www.youtube.com/watch?v=gcOqv0uzyAQ▸ Pain and the Anterolateral System
- 25. SPINAL CORD ASCENDING TRACTS: OVERVIEW ▸ The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex ▸ In some texts, ascending tracts are also known as somatosensory pathways or systems ▸ Functionally, the ascending tracts can be divided into the type of information they transmit – conscious or unconscious: ▸ Conscious tracts – comprised of the dorsal column-medial lemniscal pathway and the anterolateral system ▸ Unconscious tracts – comprised of the spinocerebellar tracts
- 26. SPINAL CORD ASCENDING TRACTS: DORSAL COLUMN-MEDIAL LEMNISCAL PATHWAY ▸ The dorsal column-medial lemniscal pathway (DCML) carries the sensory modalities of fine touch (tactile sensation), vibration and proprioception ▸ Its name arises from the two major structures that comprise the DCML ▸ In the spinal cord, information travels via the dorsal (posterior) columns ▸ In the brainstem, information travels via the medial lemniscus ▸ There are three groups of neurones involved in this pathway – first, second and third order neurones
- 27. SPINAL CORD ASCENDING TRACTS: DORSAL COLUMN-MEDIAL LEMNISCAL PATHWAY First Order Neurones ▸ The first order neurones carry sensory information regarding touch, proprioception or vibration from the peripheral nerves to the medulla oblongata ▸ There are two different pathways which the first order neurones take: ▸ Signals from the upper limb (T6 and above) ▸ travel in the fasciculus cuneatus (the lateral part of the dorsal column) ▸ then synapse in the nucleus cuneatus of the medulla oblongata ▸ Signals from the lower limb (below T6) ▸ travel in the fasciculus gracilis (the medial part of the dorsal column) ▸ then synapse in the nucleus gracilis of the medulla oblongata
- 28. SPINAL CORD ASCENDING TRACTS: DORSAL COLUMN-MEDIAL LEMNISCAL PATHWAY Second Order Neurones ▸ The second order neurones begin in the cuneate nucleus or gracilis ▸ The fibres receive the information from the preceding neurones, and delivers it to the third order neurones in the thalamus ▸ Within the medulla oblongata, these fibres decussate (cross to the other side of the CNS) ▸ They then travel in the contralateral medial lemniscus to reach the thalamus. Third Order Neurones ▸ Lastly, the third order neurones transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain ▸ They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex
- 30. SPINAL CORD ASCENDING TRACTS: ANTEROLATERAL SYSTEM ▸ The anterolateral system consists of two separate tracts: ▸ Anterior spinothalamic tract – carries the sensory modalities of crude touch and pressure. ▸ Lateral spinothalamic tract – carries the sensory modalities of pain and temperature. ▸ Much like the DCML pathway, both tracts of the anterolateral system have three groups of neurones
- 31. SPINAL CORD ASCENDING TRACTS: ANTEROLATERAL SYSTEM First Order Neurones ▸ The first order neurones arise from the sensory receptors in the periphery ▸ They enter the spinal cord, ascend 1-2 vertebral levels, and synapse at the tip of the dorsal horn – an area known as the substantia gelatinosa
- 32. SPINAL CORD ASCENDING TRACTS: ANTEROLATERAL SYSTEM Second Order Neurones ▸ The second order neurones carry the sensory information from the substantia gelatinosa to the thalamus ▸ After synapsing with the first order neurones, these fibres decussate within the spinal cord, and then form two distinct tracts: ▸ Crude touch and pressure fibres – enter the anterior spinothalamic tract ▸ Pain and temperature fibres – enter the lateral spinothalamic tract ▸ Although they are functionally distinct, these tracts run alongside each other, and they can be considered as a single pathway ▸ They travel superiorly within the spinal cord, synapsing in the thalamus
- 33. SPINAL CORD ASCENDING TRACTS: ANTEROLATERAL SYSTEM Third Order Neurones ▸ The third order neurones carry the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain ▸ They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex
- 35. SPINAL CORD ASCENDING TRACTS: SPINOCEREBELLAR TRACTS Unconscious Sensation ▸ The DCML and the anterolateral tracts transmit conscious sensations, such as pain, touch and temperature ▸ The tracts that carry unconscious proprioceptive information are collectively known as the spinocerebellar tracts ▸ Although we cannot physically acknowledge these signals, they help our brain co-ordinate and refine motor movements
- 36. SPINAL CORD ASCENDING TRACTS: SPINOCEREBELLAR TRACTS ▸ They transmit information from the muscles to the cerebellum ▸ Within the spinocerebellar tracts, there are four individual pathways: ▸ Posterior spinocerebellar tract ▸ Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum ▸ Cuneocerebellar tract ▸ Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum
- 37. SPINAL CORD ASCENDING TRACTS: SPINOCEREBELLAR TRACTS ▸ Anterior spinocerebellar tract ▸ Carries proprioceptive information from the lower limbs ▸ The fibres decussate twice – and so terminate in the ipsilateral cerebellum ▸ Rostral spinocerebellar tract ▸ Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum
- 43. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ Which of the following sensory modalities is transmitted by the dorsal column-medial lemniscus pathway? ▸ Crude touch ▸ Temperature ▸ Pain ▸ Proprioception
- 44. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ The DCML transmits touch (tactile sensation), vibration and proprioception
- 45. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ Which tracts carry unconscious proprioceptive information? ▸ DCML ▸ Spinocerebellar tracts ▸ Anterior spinothalmic tract ▸ Lateral spinothalmic tract
- 46. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ The tracts that carry unconscious proprioceptive information are collectively known as the spinocerebellar tracts
- 47. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ Complete the sentence: The third order neurones of the DCML ascend from the ___________ and synapse in the sensory cortex ▸ Cuneate nucleus ▸ Gracile nucleus ▸ Thalamus ▸ Medulla oblongata
- 48. SPINAL CORD ASCENDING TRACTS REVIEW QUESTIONS ▸ The 3rd order neurones of the DCML ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex
- 50. 2 MIN NEUROSCIENCE: DESCENDING TRACTS https://www.youtube.com/watch?v=Ma4i6nH3qMQ▸ Corticospinal Tract
- 51. SPINAL CORD DESCENDING TRACTS: OVERVIEW ▸ The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones ▸ The lower motor neurones then directly innervate muscles to produce movement
- 52. SPINAL CORD DESCENDING TRACTS: OVERVIEW ▸ The motor tracts can be functionally divided into two major groups: ▸ Pyramidal tracts ▸ These tracts originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem ▸ They are responsible for the voluntary control of the musculature of the body and face ▸ Extrapyramidal tracts ▸ These tracts originate in the brain stem, carrying motor fibres to the spinal cord ▸ They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
- 53. SPINAL CORD DESCENDING TRACTS: OVERVIEW ▸ There are no synapses within the descending pathways ▸ At the termination of the descending tracts, the neurones synapse with a lower motor neurone ▸ Thus, all the neurones within the descending motor system are classed as upper motor neurones ▸ Their cell bodies are found in the cerebral cortex or the brain stem, with their axons remaining within the CNS
- 54. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS ▸ The pyramidal tracts derive their name from the medullary pyramids of the medulla oblongata, which they pass through ▸ These pathways are responsible for the voluntary control of the musculature of the body and face ▸ Functionally, these tracts can be subdivided into two: ▸ Corticospinal tracts – supplies the musculature of the body ▸ Corticobulbar tracts – supplies the musculature of the head and neck
- 55. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS - CORTICOSPINAL TRACTS ▸ The corticospinal tracts begin in the cerebral cortex, from which they receive a range of inputs: ▸ Primary motor cortex ▸ Premotor cortex ▸ Supplementary motor area ▸ They also receive nerve fibres from the somatosensory area, which play a role in regulating the activity of the ascending tracts
- 56. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS - CORTICOSPINAL TRACTS ▸ After originating from the cortex, the neurones converge, and descend through the internal capsule (a white matter pathway, located between the thalamus and the basal ganglia) ▸ This is clinically important, as the internal capsule is particularly susceptible to compression from haemorrhagic bleeds, known as a ‘capsular stroke’ ▸ Such an event could cause a lesion of the descending tracts ▸ After the internal capsule, the neurones pass through the crus cerebri of the midbrain, the pons and into the medulla
- 57. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS - CORTICOSPINAL TRACTS ▸ In the most inferior (caudal) part of the medulla, the tract divides into two: ▸ The fibres within the lateral corticospinal tract decussate (cross over to the other side of the CNS) ▸ They then descend into the spinal cord, terminating in the ventral horn (at all segmental levels) ▸ From the ventral horn, the lower motor neurones go on to supply the muscles of the body ▸ The anterior corticospinal tract remains ipsilateral, descending into the spinal cord ▸ They then decussate and terminate in the ventral horn of the cervical and upper thoracic segmental levels
- 59. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS - CORTICOBULBAR TRACTS ▸ The corticobulbar tracts arise from the lateral aspect of the primary motor cortex ▸ They receive the same inputs as the corticospinal tracts ▸ The fibres converge and pass through the internal capsule to the brainstem ▸ The neurones terminate on the motor nuclei of the cranial nerves ▸ Here, they synapse with lower motor neurones, which carry the motor signals to the muscles of the face and neck
- 60. SPINAL CORD DESCENDING TRACTS: PYRAMIDAL TRACTS - CORTICOBULBAR TRACTS ▸ Clinically, it is important to understand the organisation of the corticobulbar fibres ▸ Many of these fibres innervate the motor neurones bilaterally ▸ For example, fibres from the left primary motor cortex act as upper motor neurones for the right and left trochlear nerves ▸ There are a few exceptions to this rule: ▸ Upper motor neurones for the facial nerve (CN VII) have a contralateral innervation to the upper quadrants of the face ▸ Therefore an UMN lesion will only affect the muscles in the contralateral lower quadrant of the face – below the eyes ▸ Upper motor neurons for the hypoglossal (CN XII) nerve only provide contralateral innervation
- 62. SPINAL CORD DESCENDING TRACTS: EXTRAPYRAMIDAL TRACTS ▸ The extrapyramidal tracts originate in the brainstem, carrying motor fibres to the spinal cord ▸ They are responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion ▸ There are four tracts in total: ▸ The vestibulospinal and reticulospinal tracts do not decussate, providing ipsilateral innervation ▸ The rubrospinal and tectospinal tracts do decussate, and therefore provide contralateral innervation
- 63. SPINAL CORD DESCENDING TRACTS: EXTRAPYRAMIDAL TRACTS - VESTIBULOSPINAL TRACTS ▸ There are two vestibulospinal pathways; medial and lateral ▸ They arise from the vestibular nuclei, which receive input from the organs of balance ▸ The tracts convey this balance information to the spinal cord, where it remains ipsilateral ▸ Fibres in this pathway control balance and posture by innervating the ‘anti-gravity’ muscles (flexors of the arm, and extensors of the leg), via lower motor neurones
- 64. SPINAL CORD DESCENDING TRACTS: EXTRAPYRAMIDAL TRACTS - RETICULOSPINAL TRACTS ▸ The two recticulospinal tracts have differing functions: ▸ The medial reticulospinal tract arises from the pons, facilitating voluntary movements, and increasing muscle tone ▸ The lateral reticulospinal tract arises from the medulla and inhibits voluntary movements, and reduces muscle tone
- 65. SPINAL CORD DESCENDING TRACTS: EXTRAPYRAMIDAL TRACTS - RUBROSPINAL TRACTS ▸ The rubrospinal tract originates from the red nucleus, a midbrain structure ▸ As the fibres emerge, they decussate (cross over to the other side of the CNS), and descend into the spinal cord ▸ Thus, they have a contralateral innervation ▸ Its exact function is unclear, but it is thought to play a role in the fine control of hand movements
- 66. SPINAL CORD DESCENDING TRACTS: EXTRAPYRAMIDAL TRACTS - TECTOSPINAL TRACTS ▸ This pathway begins at the superior colliculus of the midbrain ▸ The superior colliculus is a structure that receives input from the optic nerves ▸ The neurones then quickly decussate, and enter the spinal cord ▸ They terminate at the cervical levels of the spinal cord ▸ The tectospinal tract coordinates movements of the head in relation to vision stimuli
- 71. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ The corticobulbar tracts provide innervation to the musculature of which region of the body? ▸ Head and neck ▸ Upper limbs ▸ Lower limbs ▸ Neck
- 72. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ The corticobulbar tracts pass through the medullary pyramids, and then provide innervation to the head and neck
- 73. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ The medial reticulospinal tract is an extrapyramidal tract, responsible for involuntary and automatic control of all musculature. Which region of the brainstem does it originates from? ▸ Cerebellum ▸ Pons ▸ Medulla ▸ Midbrain
- 74. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ The medial reticulospinal tract arises from the pons ▸ It facilitates voluntary movements, and increases muscle tone
- 75. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ Which of the following statements most accurately describes the function of the tectospinal tracts? ▸ Increase muscle tone and facilitate voluntary movements ▸ Coordinate movements of the head ▸ Decrease muscle tone and inhibit voluntary movements ▸ Fine control of hand movements
- 76. SPINAL CORD DESCENDING TRACTS REVIEW QUESTIONS ▸ The tectospinal tract coordinates movements of the head in relation to visual stimuli
- 77. REVIEW
- 79. Berger, Warren. Case Closed! Neuroanatomy (p. 11). CRC Press. Kindle Edition.
- 80. References ▸ These slide reflect a summary of the contents of TeachMeAnatomy.info and are to be used for educational purposes only in compliance with the terms of use policy. Specific portions referenced in this summary are as follows: ▸ https://teachmeanatomy.info/neuroanatomy/structures/spinal- cord-grey-matter/ ▸ https://teachmeanatomy.info/neuroanatomy/pathways/ascending- tracts-sensory/ ▸ https://teachmeanatomy.info/neuroanatomy/pathways/ descending-tracts-motor/ Additional sources are referenced on the slide containing that specific content.