Reflexes and Brain Bio 3411! Monday!! 1! Readings! NEUROSCIENCE 5 th ed: Review Chapter 1 pp. 11-21;!!Read Chapter 9 pp. 189-194, 198! THE BRAIN ATLAS 3 rd ed:! Read pp. 4-17 on class web site! Look at pp 36, 43, 49, 75-76, 140,!!Study Box 9A, Figure 9.8 & Refer to!table 9.1;! 151,154,170-171, 182-183, 200-201.!!Read Chapter 16 pp. 355 367!!!Study figures 16.2,16.3,16.4, 16.14!!Read Chapter 17 pp. 375-380!!!Study figure 17.4! NEUROSCIENCE 4 th 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!! 2! 1!
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 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!Sensory - Dorsal Column/ Medial lemniscus!!motor - Cortico-spinal Tract!!! 4! 2!
(The Brain Atlas 3 rd ed, p. 8)! Cervical (C) - Neck! Thoracic (T) - Chest! Lumbar (L) - Back! Segments of spinal cord, spinal nerves and vertebrae! Sacral (S) - Pelvis! 5! 50 cm Human spinal cord from side, front and back! 6! 3!
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!! 7! Anterior Column (white matter)!! Front! (anterior/ventral)! Anterior! Horn! (gray! matter)! Lateral! Column! (white! matter)! Posterior! Horn! (gray! matter)! Posterior Column (white matter)!! Back! (posterior/dorsal)! Section of human spinal cord (C8) myelin stain! 8! 4!
Anterior! Horn! Anterior! Column!! Front! (anterior/ventral)! Lateral! Column! Section of human spinal cord (C8) cell body stain! Posterior! Horn! Posterior! Column!! Back! (posterior/dorsal)! 9! Cervical Cord (The Brain Atlas 3 rd ed, p.151)! Sacral Cord (The Brain Atlas 3 rd 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.! 10! 5!
Spinal Nerves! Intervertebral foramen! Segmental spinal nerve! Compound action potential! 11! The Brain Atlas 3 rd 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).! 12! 6!
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! 13! Joseph Erlanger!! 1874-1965! (Prix Nobel 1944)! Herbert Spencer Gasser! 1888-1965! (Prix Nobel 1944)! George H. Bishop! 1889-1973! 14! 7!
Periphery (skin, muscle, etc.)! Spinal cord! Mixed spinal nerve! front = anterior! Stimulate (Shock)! Record! back = posterior! 15! Discriminative Touch! Fast pain & Temperature (cold)! Slow pain & Temperature (warm)! Conduction Velocity m/s! Compound action potential! Erlanger, Gasser (Bishop)! 16! 8!
Axon diameters differ in motor and sensory nerves! Cross section of human muscle (motor) nerve myelin stain! Cross section of human sensory nerve myelin stain! 17! 18! 9!
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!! 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! 20! 10!
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! Periphery (skin, muscle, etc.)! Spinal cord! back = dorsal! 21! Dermatome =! The region (slice) of skin innervated by a single spinal or posterior (dorsal) root ganglion! 22! 11!
Motor Units, Motor Neuron Pools & Somatotopy! 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! 24! 12!
Section of human spinal cord (C8) myelin stain anterior horn! Section of human spinal cord (C8) cell body stain anterior horn! 25! Motor Unit - A motor neuron and the muscle fibers it innervates.! 26! 13!
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! organized systematically Shin! Distal (farther)! Extensor muscles! Hamstrings! Proximal (nearer)! Flexor muscles! Calf Distal (farther)! Flexor muscles! Motor Neurons to! Distal (farther)! Flexor muscles! according to the body plan - somatotopically! 27! Demonstration! 28! 14!
Knee Jerk Stretch Reflex & Antagonist Inhibition! 29! When the knee is struck Ia muscle afferents fire there is monosynaptic activation of the extensor α-motor neuron and the (agonist) muscle(s) contracts. 30! 15!
When the knee is struck Ia muscle afferents fire there is monosynaptic activation of the extensor α-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.! 31! Stepping on a Nail Withdrawal & Crossed Extensor Reflexes! 32! 16!
Stepping on a sharp object activates pain afferents in the skin! activating interneurons in the dorsal horn! that excite flexors and inhibit extensors! 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.! 34! 17!
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.! 35! 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., Cortico- Spinal Tract = from cortex to spinal cord! 36! 18!
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! 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! 38! 19!
THE BRAIN ATLAS 3 nd ed, pp. 5, 7! 39! Pathways - Primitive > Evolved! (Synapse & Synapse Number)! Intraspinal Pathways! Midline! Midline! Knee Jerk! 1! 1 1 Antagonist Inhibition! 2 2! 40! 20!
THE BRAIN ATLAS 3 nd ed, p. 8! Brainstem! Cerebellum! 41! THE BRAIN ATLAS 3 nd ed, p. 151! 42! 21!
THE BRAIN ATLAS 3 nd ed, p. 140! 43! THE BRAIN ATLAS 3 nd ed, p. 75-76! 44! 22!
Bio 3411!!Dorsal Column/Medial Lemniscus (a ribbon) Pathway! This pathway carries fine discriminative and active touch, body and joint position, and vibration sense.! 45! THE BRAIN ATLAS 3 nd ed, p. 185! Face Hand Body Foot 46! 23!
Pathways - Primitive > Evolved! (Synapse & Synapse Number)! Intraspinal Pathways! Ascending Sensory Pathway! Midline! Midline! Midline! 1 2 Knee Jerk! 1! 1 1 Antagonist Inhibition! 2 2! Dosal Column/ Medial Lemniscus Pathway! 2! 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.! 48! 24!
THE BRAIN ATLAS 3 nd ed, pp. 36, 43! Corticospinal Tract (Pyramid) at Medulla! 49! THE BRAIN ATLAS 3 nd ed, p. 201! Foot Hand Face All 50! 25!
THE BRAIN ATLAS 3 nd ed, p. 201! 51! Pathways - Primitive > Evolved! (Synapse & Synapse Number)! Intraspinal Pathways! Ascending Sensory Pathway! Descending Motor Pathway! Midline! Midline! Midline! Midline! 1 2 Knee Jerk! 1! 1 1 Antagonist Inhibition! 2 2! Dosal Column/ Medial Lemniscus Pathway! 2! 1 Corticospinal Pathway! 1! 52! 26!
The left hemisphere of the monkey brain - Motor (Ms) and Somatosens ory (Sm) maps! 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)!! 54! 27!
For Review! Use the Bio 3411 Brain Practice Sheet 083112 (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!! 55! The New Yorker, 7/10-17/2006, p. 110! 56! 28!