MBBS Pathways 2024 PDF

Institute of Psychology, Psychiatry and Neuroscience 18th March 2024 Dr Suba 4MBBS103 Poopalasundaram Neuroscience Education Major ascending and descending pathways Learning outcomes By the end of thi...

Institute of Psychology, Psychiatry and Neuroscience 18th March 2024 Dr Suba 4MBBS103 Poopalasundaram Neuroscience Education Major ascending and descending pathways Learning outcomes By the end of this lecture, you should: be able to describe the major ascending and descending pathways (including their central connections): spinothalamic, dorsal column, spinocerebellar and corticospinal tracts have heard of the reticulospinal, rubrospinal, tectospinal and vestibulospinal tracts understand how these pathways function together to maintain balance and posture and regulate movement 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways The spinal cord 31 pairs of spinal nerves: 8 cervical 12 thoracic 5 lumbar 5 sacral 1 coccygeal The spinal cord is shorter than the vertebral column (usually ends between L1/2. Lumbar puncture at L3/4. 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 3 Cauda equina (horse’s tail) 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 4 Filum terminale – anchors the spinal cord to the vertebrae 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 5 Spinal nerves are ‘mixed’ – they contain sensory and motor fibres 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 6 Weigert – Pal stained sections of human spinal cord The sections shown represent photographs of stained sections from human spinal cord using Weigert-Pal (stains myelin), which means that nuclear areas (i.e. zones consisting predominantly of cell bodies) stand out as pale islands of unstained tissue, whereas myelinated tracts appear dark grey to black. Where these micrographs appear, the ventral surface is always closer to the bottom of the screen. Note the cervical and lumbar enlargements and the ventral horns of the spinal cord.​ 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 7 The patellar tendon (knee-jerk) reflex (Backyardbrains.com) 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 8 Integration of general and special sensation and motor output Ascending pathways (spinal cord, cranial nerves) – general somatic afferents (GSAs) and general visceral afferents (GVAs) Conscious: pain, temperature, crude and fine touch Conscious proprioception Subconscious proprioception Special senses: cranial nerves Descending pathways (spinal cord, cranial nerves) – general somatic efferents (GSEs) and general visceral efferents (GVEs) 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 9 The organization of the spinal nerves Dorsal root Ventral root Grey and white ramus communicans Dorsal root ganglion Spinal nerve Sympathetic chain ganglion Posterior ramus Anterior ramus [Drake et al. (2015) Gray’s Anatomy for Students. Elsevier.] 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 10 Organisation of the CNS Cerebral cortex Forebrain Thalamus Midbrain Pons Brain stem Medulla oblongata Dorsal root ganglion Spinal cord Spinal nerves 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 11 Ascending pathways Cerebral cortex Forebrain Thalamus Midbrain Pons Brain stem Medulla oblongata Dorsal root ganglion Spinal cord Spinal nerves 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 12 1) Pain/temperature: spinothalamic tract Somatosensory cortex Thalamus DRG Sensory neuron synapses onto second order neurons in the spinal cord, these decussate at the level of the Sensory nerve ending spinal cord. 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 13 2) Fine touch/two-point discrimination/vibration/conscious proprioception: dorsal column-medial lemniscus pathways Somatosensory cortex thalamus medulla oblongata Sensory neuron synapses onto second order neurons in the medulla oblongata, these decussate in the sensory medulla oblongata. nerve ending 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 14 The dorsal column pathways and their brain stem nuclei us) eat s ct s cul tract cun tra us gracile tracts (fa ate cile e (fasciculus gracilis) gra cun s ci N N N N lumbar cervical medulla oblongata 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 15 3) Subconscious proprioception: spinocerebellar tracts Motor cortex cerebellum DRG muscle spindles Golgi tendon organs 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 16 The cerebellum as a comparator alcohol poisoning (GABA receptors), heavy metal poisoning congenital agenesis or hypoplasia degenerative diseases (e.g. Friedreich’s Ataxia) trauma, infections, tumours (e.g. medulloblastoma), MS, thrombosis of cerebellar arteries (SCA, AICA, PICA) aging  muscular hypotonia, changes of posture and gait, intention tremor, decomposition of movement, disturbed reflexes (e.g. pendular knee Snell, Clincal Neuroanatomy, 7 ed. (2010) Wolters Kluwer jerk reflex), dysarthria 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 17 The ascending pathways in situ us) eat s ct s cul tract cun tra us gracile tracts (fa eate cile (fasciculus gracilis) gra cun s ci post. spinocerebellar tract post. spinocerebellar tract spinothalamic tract spinothalamic tract ant. spinocerebellar tract ant. spinocerebellar tract lumbar cervical 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 18 Descending motor control pathways 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 19 1) Voluntary control of skilled movements: corticospinal tract Primary motor cortex Thalamus Internal capsule Basal ganglia Pons 85% Medulla 15% Muscle 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 20 2) Posture and locomotion: reticulospinal tract reticular formation medullary medullary pontine Muscle 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 21 3) Balance, posture, ‘antigravity’: vestibulospinal tract vestibular nuclei Muscle 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 22 4) Facilitation of flexion: rubrospinal tract red nuclei Muscle 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 23 5) Coordination of head and eye movements: tectospinal tract superior colliculi Muscle 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 24  Multiple descending systems control motor output Only the corticospinal tract originates in the cortex, all other descending tracts originate from the brain stem. 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 25 Different pathways decussate at different levels dorsal column pathways spinothalamic tract corticospinal tract 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 26 Recommended reading Bear, Connors, Paradiso (2016) Neuroscience: Exploring the Brain. 4th ed. Wolters Kluwer. Kiernan & Rajakumar (2014) Barr’s the Human Nervous System: An Anatomical Viewpoint. 10th ed. Wolters Kluwer. Snell (2009) Clinical Neuroanatomy. 7th ed. Lippincott Williams & Wilkins. 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 27 Thank you for your attention [email protected] © King’s College London. All rights reserved Comparison at the cervical and thoracic levels of the spinal cord Spinal cord (cervical level) Spinal cord (thoracic level) 18/March/2021 Dr Clemens Kiecker Major ascending and descending pathways 29