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Lecture VIII. The Spinal Cord, Reflexes and Brain Pathways Bio 3411 Monday September 21, 2009 Readings NEUROSCIENCE 4th ed: Review Chapter 1 pp. 11-22; Read Chapter 9 pp. 207-212, 218 Study Box 9A, Figure 9.8 & Refer to Table 9.1; Read Chapter 16 pp. 399–414 Study figures 16.2,16.3,16.4, 16.14 Read Chapter 17 pp. 432–436 Study figure 17.9 THE BRAIN ATLAS 3rd ed: Read pp. 4-17 on class web site Look at pp 36, 43, 49, 75-76, 140, 151, 154, 170-171, 182-183, 200201. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 2 What the last Lecture was about • The Initiation of the Central Nervous System • CNS Growth and Pattern Development • Bug Brains • Several Mechanisms for Directing the Show (scripts conserved) • How did vertebrate and invertebrate patterns arise? • Reprise and overview the discussions of developmental sequences and mechanisms in the nervous system September 16, 2009 Lecture VII. CNS Patterning 3 Overview for this Lecture Spinal Cord Columns, Horns, Spinal Segments Spinal Nerves Dermatomes, Motor Units Reflexes “Knee Jerk”- Myotatic or Stretch Reflex Withdrawal & Crossed Extensor Reflexes Two Spinal Pathways Sensory - Dorsal Column/ Medial lemniscus Motor - Cortico-spinal Tract September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 4 (The Brain Atlas 3rd ed, p. 8) Cervical (C) - Neck Thoracic (T) - Chest Segments of spinal cord, spinal nerves and vertebrae Lumbar (L) - Back Sacral (S) - Pelvis September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 5 Human spinal cord from side, front and back ≈ 50 cm September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 6 Internal Structure • Canal = tube • White Matter - columns, tracts anterior up and down to and from brain lateral down from brain (>>up) posterior mainly up to brain • Gray Matter - posterior (dorsal) horn “sensory”, anterior (ventral) horn “motor” September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 7 Anterior Column (white matter) Front (anterior/ventral) Anterior Horn (gray matter) Section of human spinal cord (C8) myelin stain Lateral Column (white matter) Posterior Horn (gray matter) Posterior Column (white matter) September 21, 2009 Back (posterior/dorsal) Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 8 Anterior Anterior Horn Column Front (anterior/ventral) Section of human spinal cord (C8) cell body stain Lateral Column Posterior Horn September 21, 2009 Posterior Back Column (posterior/dorsal) Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 9 Cervical Cord Sacral Cord (The Brain Atlas 3rd ed, p.151) (The Brain Atlas 3rd ed, p.154) The size of white matter tracts (posterior, lateral and anterior columns) increases as more axons are added on the way TO the brain and decreases as axons end on the way FROM the the brain. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 10 Spinal Nerves • Intervertebral foramen • Segmental spinal nerve • Compound action potential September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 11 The Brain Atlas 3rd ed, p. 49. Spinal canal Intervertebral foramen Left - Vertebral bones. Right - Human spinal cord in cross–section showing anterior (ventral) and posterior (dorsal) spinal roots and spinal or posterior (dorsal) root ganglion (posterior to right). September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 12 Segmental nerve: (posterior (dorsal) root = sensory - touch; anterior (ventral) root = motor -movement; spinal or posterior (dorsal) root ganglion = sensory nerve cell bodies) Periphery (skin, muscle, etc.) Spinal cord Mixed spinal nerve front = anterior back = posterior September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 13 Joseph Erlanger Herbert Spencer Gasser George H. Bishop 1874 - 1965 1888 - 1965 1889 - 1973 (Prix Nobel 1944) (Prix Nobel 1944) September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 14 Periphery (skin, muscle, etc.) Spinal cord Mixed spinal nerve front = anterior back = posterior Stimulate (Shock) September 21, 2009 Record Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 15 Discriminative Touch Conduction Velocity m/s Fast pain & Temperature (cold) Slow pain & Temperature (warm) Compound action potential Erlanger, Gasser (Bishop) September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 16 Axon diameters differ in motor and sensory nerves Cross section of human muscle (motor) nerve – myelin stain September 21, 2009 Cross section of human sensory nerve – myelin stain Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 17 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 18 Segmental Nerves Spinal or Posterior (dorsal) Root, Ganglion Cells & Sensory Nerves (axons in from posterior (dorsal) root ganglia) Dermatomes Anterior (ventral) Root & Motor Nerves (axons out from motor neurons) Motor Units September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 19 Spinal or Posterior (dorsal) Root Ganglion Cells Pseudo-Unipolar Neurons (neurons start as bipolar cells and become “unipolar” during development) Single sensory endings light & crude touch, pain, temperature and muscle senses Axons diverge to multiple spinal targets motor neurons - c, interneurons - c, spinal cord - b, and brain -a September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 20 Segmental nerve (posterior (dorsal) root = sensory - touch; ventral root = motor -movement; spinal or posterior (dorsal) root ganglion = sensory nerve cell bodies) Mixed spinal nerve front = ventral back = dorsal Periphery (skin, muscle, etc.) September 21, 2009 Spinal cord Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 21 Dermatome = The region (slice) of skin innervated by a single spinal or posterior (dorsal) root ganglion September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 22 Motor Units, Motor Neuron Pools & Somatotopy September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 23 Spinal Motor Neurons • Multipolar • Output Diverges to several or many muscle cells: motor unit • Input Converges from – spinal or posterior (dorsal) root ganglion cells spinal interneurons long tracts from from brain • Integrate • Map flexors, extensors, proximal, distal September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 24 Section of human spinal cord (C8) myelin stain – anterior horn September 21, 2009 Section of human spinal cord (C8) cell body stain – anterior horn Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 25 Motor Unit - A motor neuron and the muscle fibers it innervates. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 26 Motor Neurons to Distal (farther) Extensor muscles Motor Neurons to Proximal (nearer) Extensor muscles Motor neuron “Quads” Proximal (nearer) Extensor muscles pools (nuclei) are Motor Neurons to Proximal (nearer) Flexor muscles Motor Neurons to Distal (farther) Flexor muscles “Shin” Distal (farther) Extensor muscles “Hamstrings” Proximal (nearer) Flexor muscles “Calf” Distal (farther) Flexor muscles September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways organized systematically according to the body plan somatotopically 27 Demonstration “Knee Jerk” Stretch Reflex & Antagonist Inhibition September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 29 When the knee is struck… Ia muscle afferents fire… there is monosynaptic activation of the extensor -motor neuron… and the (agonist) muscle(s) contracts. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 30 When the knee is struck… Ia muscle afferents fire… there is monosynaptic activation of the extensor -motor neuron… and the (agonist) muscle(s) contracts. The knee extends. Glycinergic (inhibitory) interneurons are also activated… …which inhibit motor neurons to the flexor (antagonist) muscle. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 31 “Stepping on a Nail” Withdrawal & Crossed Extensor Reflexes September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 32 Stepping on a sharp object activates pain afferents in the skin… activating interneurons in the dorsal horn… that excite flexors and inhibit extensors… September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 33 Stepping on a sharp object activates pain afferents in the skin… activating interneurons in the dorsal horn… that excite flexors and inhibit extensors… and the leg flexes “withdraws.” September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 34 But the person would fall… if the crossed extensors weren’t activated… and the crossed flexors weren’t inhibited to extend the other (contralateral) leg to stand on. September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 35 Pathways • Subserve a particular function • Axons travel together in specific locations (i.e., tracts) in a particular order (topography) • Always consider: cell body (soma) location, axon course, synapses and side relative to origin and destination • Nomenclature often origin and target, i.e., CorticoSpinal Tract = from cortex to spinal cord September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 36 Path Finding • Loss of a particular function after damage (lesion) • Stimulation (natural/electrical) with recording • Pathology - degeneration of cells and axons with secondary loss of myelin • Experiments - special stains and tracers that take advantage of physiological processes September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 37 Pathway Conventions • Related to whole brain through “sections” – gross, histological, imaging • Related to fiber bundles (fasciculi; i.e., lateral columns, internal capsule, corpus callosum) • Related to nuclei, ganglia, areas, layers • Related to transmitters and effects: excitatory, inhibitory, modulatory; fast, slower, slow September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 38 THE BRAIN ATLAS 3nd ed, pp. 5, 7 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 39 Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number) Intraspinal “Pathways” Midline Midline 2 1 1 Knee Jerk Antagonist Inhibition 1 2 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 40 THE BRAIN ATLAS 3nd ed, p. 8 Brainstem September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways Cerebellum 41 THE BRAIN ATLAS 3nd ed, p. 151 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 42 THE BRAIN ATLAS 3nd ed, p. 140 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 43 THE BRAIN ATLAS 3nd ed, p. 75-76 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 44 Dorsal Column/Medial Lemniscus (a ribbon) Pathway This pathway carries fine discriminative and active touch, body and joint position, and vibration sense. THE BRAIN ATLAS 3nd ed, p. 185 Face Hand Body Foot September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 46 Pathways - “Primitive” ––––> “Evolved” (Synapse & Synapse Number) Intraspinal “Pathways” Midline Ascending Sensory Pathway Midline Midline 2 1 2 1 1 Knee Jerk Antagonist Inhibition Dosal Column/ Medial Lemniscus Pathway 1 2 2 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 47 Corticospinal (Pyramidal) Pathway This is the direct connection from the cerebral cortex for control of fine movements in the face and distal extremities, e.g., buttoning a jacket or playing at trumpet. THE BRAIN ATLAS 3nd ed, pp. 36, 43 Corticospinal Tract (Pyramid) at Medulla September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 49 THE BRAIN ATLAS 3nd ed, p. 201 Foot September 21, 2009 Hand Face Lecture VIII. The Spinal Cord, Relexes and Brain Pathways All 50 THE BRAIN ATLAS 3nd ed, p. 201 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 51 Pathways - “Primitive” ––––> “Evolved’ (Synapse & Synapse Number) Intraspinal “Pathways” Midline Ascending Sensory Pathway Midline Midline Descending Motor Pathway Midline 2 1 2 1 1 1 Knee Jerk Antagonist Inhibition Dosal Column/ Medial Lemniscus Pathway Corticospinal Pathway 1 2 2 1 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 52 The left hemisphere of the monkey brain - Motor (Ms) and Somatosens ory (Sm) maps September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 53 What this lecture was about: Spinal Cord - Segmental organization Peripheral Nerves - Compound action potential (Erlanger & Gasser Prix Nobel 1944) Spinal Nerves - Dermatomes, motor neuron pools (nuclei) and motor units Spinal reflexes - stretch (knee jerk); withdrawal/ crossed extensor Introduction to Pathways - 1 sensory (DC-ML); 1 motor (CST) September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 54 For Review Use the Bio 3411 Work Sheet 082809 (handout and posted on the course web site) to get comfortable with the neuroanatomy. It’s neither rocket science nor is it neurosurgery, it just takes a little practice! September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 55 The New Yorker, 7/10-17/2006, p. 110 September 21, 2009 Lecture VIII. The Spinal Cord, Relexes and Brain Pathways 56