Central Nervous System Part 2 PDF

CNS Part 2 – Spinal Cord Unless otherwise indicated, image source for all slides: Human Anatomy, 8th edition Marieb, et.al. (Pearson, 2017) PARA 1002 1 Spinal Cord Vertebral canal, 31 pairs of spinal...

CNS Part 2 – Spinal Cord Unless otherwise indicated, image source for all slides: Human Anatomy, 8th edition Marieb, et.al. (Pearson, 2017) PARA 1002 1 Spinal Cord Vertebral canal, 31 pairs of spinal nerves Continuous with medulla oblongata Exits skull at Foramen magnum (occipital) Extends inferiorly to L1-L2 level Cervical + lumbar enlargements Centre for spinal reflexes PARA 1002 2 1  Meninges Meninges extend to spinal cord This arrangement results in the following spaces: epidural, potential subdural, subarachnoid Dura has no periosteal layer CSF: Circulates thru brain and spinal cord in subarachnoidPARA space 1002 3 Arachnoid Pia mater Dura mater PARA 1002 4 2  Anatomical Features Filum terminale anchors the spinal cord to the coccyx Why is it important to know the level of the conus medullaris and cauda equina? PARA 1002 5 Lumbar Puncture (Spinal Tap) Lumbar puncture can safely be performed inferior to midlumbar region after spinal cord terminates Needle is inserted into the subarachnoid space between L3-L4 or L4-L5 PARA 1002 6 3  Anatomy Anterior median fissure Posterior median sulcus Posterior Median Sulcus (more shallow) Grey matter White matter Anterior Median Fissure PARA 1002 7 Components of the Cord Dorsal root Dorsal root ganglion Rami Spinal Nerve Ventral root Central area of gray matter shaped like a butterfly and surrounded by white matter in 3 columns Bundles of myelinated axons that run up & down cord (white matter) PARA 1002 8 4  Spinal Grey Matter (Horns) Dorsal (posterior) horns Afferent fibres (sensory) enter through dorsal root Cell bodies in dorsal root ganglion (outside CNS) Ventral (anterior) horns Cell bodies of somatic motor neurons Axons exit through ventral root PARA 1002 9 Gray Matter Dorsal Horn Somatic Sensory Somatic Motor Ventral Horn PARA 1002 10 5  White Matter Tracts Classified as: Ascending – sensory neurons Descending – motor neurons Commissural – cross from one side of the cord to the other Posterior Myelinated fiber tracts Column 3 regions: Posterior, lateral and anterior Anterior Column PARA 1002 11 Somatic Sensory Pathways (CNS) Sensory pathways carry impulses from receptors to the sensory areas of the cerebral cortex Impulses generally travel through 3 “pools” of sensory neurons:primary, secondary, tertiary (how are they different?) – 1º: periphery to CNS – 2º: CNS (cord or brainstem) to thalamus via ascending tracts – 3º: thalamus to somaticosensory area of parietal lobe (thalamocortical tracts) These pathways decussate (cross) at the level of the 2º neurons What effect does this have? PARA 1002 12 6  Somatic Sensory Pathways (CNS) Medial Lemniscal Pathway: Conducts impulses along the medial lemniscus through medulla, pons and midbrain Fibres enter medulla and decussate before thalamus Fine pressure and touch (stereognosis, precise localization, vibration) Spinothalamic Pathway: Crude touch and pressure sensation not involving precise discrimination PARA 1002 13 Somatic Motor Pathways (CNS) Motor function is controlled by impulses from motor areas of cerebral cortex conducted along somatic motor pathways (What about reflexes?) Each single motor neuron from the anterior grey horn of the spinal cord conducts impulses to a specific motor unit of a skeletal muscle (principle of the final common pathway) (What are the implications of this arrangement?) Various somatic motor pathways conduct impulses to the anterior grey horn: – Pyramidal tracts vs Extrapyramidal tracts – Facilitatory tracts vs Inhibitory tracts PARA 1002 14 7  Somatic Motor Pathways (CNS) Pyramidal (corticospinal) Tracts: Fibres for pyramids in the medulla Most synapse with interneurons in spinal cord before the anterior horn Impulses are summative and cause stimulation of individual muscle groups (mainly feet and hands) True “willed” movements Stroke relate paralysis PARA 1002 15 Somatic Motor Pathways (CNS) Extrapyramidal Tracts: More complex and includes all other motor tracts Involve many more relays between various motor areas (more integration) Both facilitatory & inhibitory tracts act on anterior horn in a summative manner Responsible for contraction of muscle groups in complex gross movement (walking) Emotional expressions, body language and “programmed” motor responses PARA 1002 16 8