0729 - TEXT Spinal Cord Pathways Flashcards
What are the key features of the Gross anatomy of spinal cord?
Nerves (pairs at each level) - defined by level of exit of vertebrae Cervical and lumbar enlargements Grey and white matter Conus medullaris Filum terminale Cauda equina
What are the Spinal cord coverings?
Bony - vertebral coverings
Meninges - Dura/arachnoid/pia mater. with dentate ligs (thickening of pia) anchoring spinal cord into dural sheath (dura mater). Filum terminale (extension of pia) anchoring spinal cord to end of vertebral column.
Cushioned by CSF in arachnoid.
What do you see in a spinal cord cross section?
Posterior median sulcus, anterior median fissure
Nerve roots attach at posterolateral sulcus either side of posterior median sulcus.
Mixed spinal nerve splits as it approaches cord - sensory goes in dorsally, motor comes out ventrally.
Grey and white matter.
What is a fasciculus?
A group of neurons travelling from or going to similar locations.
What are the functional divisions of grey matter? How can inputs and outputs arise?
Dorsal horn (input), intermediate grey (processing), ventral horn (output). Inputs can be peripheral, intrasegmental, descending, or intrasegmental. Outputs can be peripheral (innervating somatic/visceral depending on whether more or less down the horn) or ascending. Proximal muscles innervated by medial areas of ventral horn, distal by lateral areas.
Outline the segmental organisation of White and grey matter in the spinal cord:
Outline the segmental organisation of White and grey matter in the spinal cord:
Posterior dorsal funiculus -
Lateral funiculus
Anterior/ventral funiculus
Grey - dorsal horn, intermediate grey and ventral horn. Lateral horn (predominantly thoracic).
Large fibres vs small fibres synapse at different layers. (options for fibres)
What are Rexed’s Laminae?
Divisions of the Grey matter based on cell types and thus functional characteristics. Different laminae are found on different levels (I-VI, X found on all levels). Starts with layer I at dorsal horn (just after entry), proceeding ventrally and increasing in size (generally) to VIII at ventral horn. IX forms ‘islands’ in VII and VIII, with X surrounding the central canal.
How are the dorsal columns mapped?
Leg, Hip, Trunk, Arm - medial to lateral.
How is the grey matter mapped (somatic and visceral as well as body region)?
Somatic/visceral - Sensory more dorsal, motor more ventral. Somatic/visceral/visceral/somatic occupying from dorsal horn, through lateral horn to ventral horn.
Body region - Medial-lateral is proximal-distal - e.g. extensors of trunk, shoulder, arm, forearm, hand in dorsal horn.
Where is the marginal zone in terms of Rexed’s Laminae and spinal level?
All levels, laminae I. Contains some spinothalamic tract cells.
Where is the substantia gelatinosa in terms of Rexed’s Laminae and spinal level?
All levels, laminae II. Modulates transmission of pain and temperature information.
Where is the body of the posterior horn in terms of Rexed’s Laminae and spinal level?
All levels, laminae III-VI - Sensory processing.
Where is the Clarke’s Nucleus in terms of Rexed’s Laminae and spinal level?
T1-L2, Laminae VII. Contains posterior spinocerebellar tract cells.
Where is the intermediolateral column in terms of Rexed’s Laminae and spinal level?
T1-L3, Lamina VII. Contains preganglionic SY neurons.
Where is the sacral parasympathetic nucleus in terms of Rexed’s Laminae and spinal level?
S2-S4, Lamina VII. Contains preganglionic parasympathetic neurons to the pelvic viscera.
Where is the Accessory Nucleus in terms of Rexed’s Laminae and spinal level?
Medulla-C5, lamina IX. Contains motor neurons to SCM and trapezius.
Where is the Phrenic nucleus in terms of Rexed’s Laminae and spinal level?
C3-5, lamina IX. Contains motor neurons to diaphragm.
Describe the Stretch (myotatic reflex) with reference to all neurons involved.
Tap patellar tendon to stretch quads. Stretch is sensed by afferent fibres from muscle spindles (Group Ia proprioceptors). Large myelinated axons with a very fast rate of conduction. Ia fibres synapse directly on alpha motor neurons innervating the same muscle group as that stretched, contracting to counteract the passive stretched.
Describe Reciprocal inhibition with reference to all neurons involved.
The stretch information carried by Ia afferent fibres also passes onto interneurons in lamina VI. These inhibit the alpha motor neurons innervating the opposing muscles (e.g. hamstrings), so that affected muscle can act properly.
Describe the Autogenic inhibition (reverse myotatic reflex) with reference to all neurons involved.
Golgi tendon organs are a second class of proprioceptors. Located in muscle tendons and sense tension. Information is transmitted via large, fast 'Ib' afferents. Ib inhibit agonist muscles (and excite antagonist muscles via alpha motor neurons). Sudden relaxation of muscle upon high tension (protect from a tear)
Describe the Withdrawal reflex with reference to all neurons involved.
Consists of flexor and crossed extensor reflexes. Eg when stepping on then withdrawing from a tack.
Flexor - initiated by cutaneous receptors, involving many levels of spinal cord to coordinate flexor stimulation across the limb and reciprocal inhibition of extensors.
Crossed-extensor reflex - flexor reflex accompanied by the simultaneous and opposite pattern in other lumb, so it can support body’s weight.
How does clasp knife spasticity arise?
When bending the extensors, poorly-controlled myotatic (1a) and autogenic inhibition (Ib) reflexes don’t behave properly due to UMN lesion. The stretch reflex is prolonged and exaggerated, but eventually overcome by a prolonged and exaggerated reverse myotatic reflex
What muscle group, spinal level, and peripheral nerve is tested by the Jaw Jerk reflex?
Masseter, brainstem, V3 nerve
What muscle group, spinal level, and peripheral nerve is tested by the Biceps reflex?
Biceps brachii, C5, Musculocutaneous nerve
