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SPINAL CORD - Coggle Diagram

- - - - stimulates alpha motor neuron to cause agonist contraction
        
        withdrawal of limb from stimulus
      - inhibits antagonist muscle contraction
  - - - sensory neuron synapses directly onto alpha motor neuron (not interneuron) to cause slight contraction to maintain tone
        
        also synapses onto inhibitory interneuron to inhibit antagonist contraction
        
        reflex contraction of deep tendon
  - - - activates spindles in muscle to trick it into activating stretch reflex
        
        prompted contraction/tone
  - - - sensory neuron synapses onto inhibitory interneuron
        
        stops contraction and releases tension
  - - - bladder filling causes firing from stretch receptor afferents in detrusor
        
        synapse on interneurons in dorsal horn
        
        ascend to activate sympathetic preganglionic neurons in lumbar SC
        
        reflex sympathetic stimulation
        
        detrusor relaxation and internal sphincter contraction (hypogastric nerve, NA)
        
        interneurons in sacral spinal cord
        
        reflex and voluntary somatomotor outflow via pudendal nerve to external sphincter
        
        continence
    - - firing from detrusor stretch receptors increases
        
        activates pontine micturition centre via midbrain PAG
        
        reflex inhibition of sympathetic outflow, reflex stimulation of parasympathetic outflow
        
        detrusor contraction and internal sphincter relaxation (ACh)
        
        also inhibits somatomotor fibres innervating external sphincter
        
        external sphincter relaxation
        
        micturition
        
        also contributed to by conscious sensation and voluntary decision to void
      - interneurons in sacral spinal cord excited by afferents from either bladder or colorectal region inhibit preganglionic neurons innervating the other
        
        micturition and defecation cannot occur simultaneously
    - - distension of rectum causes firing of rectal stretch receptors
        
        reflex stimulation of parasympathetic outflow to sigmoid, rectum, internal anal sphincter (external sphincter remains contracted)
        
        contraction of sigmoid colon and rectum, and relaxation of internal sphincter
        
        conscious sensation of increased pressure in rectum
        
        decision to defecate
        
        relaxation of external sphincter
        
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        decision to delay
        
        contraction of external sphincter
        
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- - - - C fibres (deeper) or A∂ fibres (superficial) from nociceptors or thermoceptors have cell bodies in DRG and synapse in dorsal horn of spinal cord
        
        2º neuron crosses midline in ventral white commissure to ventrolateral column
        
        lateral spinothalamic = pain and temp, ventral spinothalamic = crude touch
        
        ascend contralaterally and most synapse in VP nucleus of thalamus
        
        3º neurons synapse in S1
        
        some synapse in reticular formation in brainstem
    - - transmits fine touch, vibration and conscious proprioception
        
        cell bodies in DRG and sensory neurons enter dorsal horn but enter dorsal column tract (do not synapse)
        
        gracile fasciculus (medial) = lower body, cuneate fasciculus (lateral) = upper body
        
        ascends ipsilaterally
        
        synapse on ipsilateral gracile and cuneate nuclei in medulla
        
        2º neurons cross midline via sensory decussation (internal arcuate fibres)
        
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    - - unconscious proprioception (spindles, Golgi tendon organs, joint receptors)
        
        sensory neurons synapse in dorsal horn
        
        2º neurons ascend ipsilaterally in spinocerebellar tract
        
        dorsal spinocerebellar = no decussation, ventral spinocerebellar = fibres decussate but then cross back
        
        synapse in ipsilateral cerebellum
  - - - vestibulospinal tract
        
        originates at vestibular nucleus in brainstem
        
        descends ipsilaterally to ventral horn of spinal cord
        
        synapses onto ipsilateral motor neuron innervating muscles important for balance (mostly extensors)
        
        stimulates γ reflex loop
      - reticulospinal tract
        
        originates at reticular formation in brainstem
        
        descends ipsilaterally to ventral horn of spinal cord
        
        synapses onto ipsilateral motor neuron innervating somatic muscles
        
        synapses onto ipsilateral motor neurons innervating visceral smooth muscle
        
        ipsilateral visceral control
    - - corticospinal tract
        
        originates in M1
        
        neuron travels through corona radiata, internal capsule, cerebral peduncle and then to medullary pyramid (pyramidal tract)
        
        90% of fibres decussate in motor/pyramidal decussation, while 10-15% remain ipsilateral
        
        the ones that decussate form lateral corticospinal tract
        
        enter ventral horn of spinal cord and synapse on alpha motor neurons
        
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        the ipsilateral fibres form ventral corticospinal tract
        
        cross midline later in ventral white commissure
        
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      - rubrospinal tract
        
        originates in red nucleus
        
        neurons cross midline at ventral tegmental decussation
        
        descend contralaterally to ventral horn of spinal cord
        
        synapse onto motor neuron
        
        assist corticospinal tract in skilled movements
- - - - ectoderm thickens to develop neural plate
        
        neural plate forms neural groove
        
        closes to form neural tube (both ends open dependent on cadherins)
        
        anterior opening of neuropore closes first, followed by posterior
        
        3-vesicle stage (prosencephalon, mesencephalon, rhombencephalon)
        
        5-vesicle stage (telencephalon, diencephalon, mesencephalon, metencephalon, myelencephalon)
        
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