Spinal Cord Neurobiology 2217 2006 Dr Avinash Bharadwaj

Spinal Cord Neurobiology 2217 - 2006 Dr Avinash Bharadwaj

Extent and Gross Features Foramen magnum – L 1/L 2 (Adult) n Ventral median fissure n Dorsal median sulcus n Ventrolateral and dorsolateral sulci n

Spinal Segments P A A Spinal Segment : A “slice” of the spinal cord that gives out one spinal nerve (R+L pair!)

Typical Spinal Nerve Roots Rami P Posterior (dorsal) root : Sensory Dorsal root ganglion Anterior (ventral) root : Motor Note : “Rootlets” Posterior (dorsal) ramus : Mixed A Anterior (ventral) ramus : Mixed

Spinal Cord – General Features Posterior Median Sulcus D White and Grey Matter V Anterior Median Fissure 2 -D Sections and 3 -D Structure : Grey horns and columns White funiculi : Dorsal, Lateral and Ventral

Dorsal Root Fibres Continued…

Dorsal Root Fibres “Central” processes of DR ganglion cells n Ascend without synapse OR n Synapse – intermediate neurones – “Tract” cells (long axons) n

Ventral Root Fibres Axons of neurone bodies in grey matter

Spinal Grey Matter n Functionally discrete neurone groups Nuclear columns Laminae

White Matter –Tracts … MB Pons MO SC SC

Tracts…

Tracts… n n Functionally related fibres Similar origin and termination May begin or end at various levels in the cord. No distinct anatomical boundaries

Dorsal Root Fibres “Central” processes of DR ganglion cells n Ascend without synapse OR n Synapse – intermediate neurones – “Tract” cells (long axons) n

Examples of ascending tracts : Uncrossed and Crossed

More… Not all tracts are coextensive with the entire cord n Long ascending / descending tracts n Fasciculus proprius (intersegmental) n Long tracts – terminate at various levels (desc) Or Accumulate fibres at various levels (asc).

Major Descending Tracts n Corticospinal – Lateral and Ventral n Rubrospinal n Tectospinal, Vestibulospinal n Reticulospinal and others… n Motor control [somatic (voluntary movements and their fine control) and visceral] Modulation of ascending input. n

Ascending Tracts n Conscious sensory perception n Input to cerebellum n Other inputs to higher centres General principles presented here… More with “somatosensory system” The following slides are not essential for this week’s lecture.

To Thalamus and Cerebral Cortex (Conscious Sensory Perception) n General rules (But… there’s more than what meets the eye!) Three long neurones n 1 st neurone – body in DRG n Second neurone crosses, ends in the thalamus n

Dorsal Column (Lemniscal System) n n n Central processes of DRG cells… Uncrossed Modalities… Fasciculus gracilis and fasc. cuneatus Extent…

Spinothalamic (Anteolateral) System Light touch, pain, temperature n “Second order” neurones – axons of tract cells n Crossed n Anterior and lateral tracts? ?

Spinocerebellar Tracts n Dorsal n Ventral

Somatotopism FC FG C S S C C S

Spinal Cord – Editing Input “Sensory Gate” Mechanism n Different sensory modalities and preferential transmission n Evolution of the concept…discussed further with “somatosensory system”.

Spinal Cord and Reflex Activity Types of reflexes n Synapses and segments n Neurones involved n Last Slide