Note: Important for OSPE & read up foundation 1!

Peripheral nervous system

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  • Made up of
    • nerve cell bodies
    • nerve fibres
      • cranial nerves
      • spinal nerves
  • Connects
    • CNS with peripheral structure
  • Function
    • afferent (sensory) neuron
      • carry impulse from sensory receptors to CNS
    • efferent (motor) neuron
      • carry information from CNS to muscles/glands

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  • Accessory nerve
    • 2 parts
      • cranial part
      • spinal part
        • arise from C5, C6
    • Injury is possible

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Spinal cord

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  • It is the major reflex centre & conduction pathway
    • Length: 45 cm
    • Extent:
      • from foramen magnum
      • to lower border of L1
        • newborn: upper border of L3
  • 2 enlargements
    • cervical
    • lumbar
  • Midline demarcation
    • anterior median fissure
    • posterior median sulcus
  • Cross section
    • Gray mater
      • anterior gray column
      • posterior gray column
      • gray commissure (central canal)
      • lateral gray column
        • T1 – L2
        • S2,3,4
    • White mater
      • anterior funiculus
      • lateral funiculus
      • posterior funiculus

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  • Spinal meninges
    • Dura mater
      • dense, fibrous
      • from foramen magnum –> S2
      • above it epidural space
      • below it subdural space (negligible)
    • Arachnoid mater
      • delicate, impermeable
      • from foramen magnum –> S2
      • Subarachnoid space
        • cerebrospinal fluid here
    • Pia mater
      • fine, vascular
      • from foramen magnum –> coccyx
        • as filum terminale
      • thickened on either side of nerve roots
        • pairs of ligamentum denticulatum

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  • Denticulate ligament
    • attached to pia mater
      • actually pia mater extension
    • helps in fixation of spinal cord
  • Cauda equina
    • bundle of lumbar & sacral nerve roots
      • in the subarachnoid space
      • caudal to termination of spinal cord
    • looks like horse tails
  • Conus medullaris
    • ending of spinal cord
      • lower tapering of spinal cord
      • at lower border of L1
    • from L2 – coccyx
      • just spinal nerve roots
      • extensions
  • Filum terminate
    • condensation of pia mater
      • from lower end of spinal cord to coccyx
    • attached to sacral
      • fixation

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Spinal column

  • circular part of spinal cord
    • Rootlets of 1 spinal nerve emerge
  • 31 spinal segments – corresponding to spinal nerves
    • 8 cervical
    • 12 thoracic
    • 5 lumbar
    • 5 sacral
    • 1 coccygeal

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Blood supply

  • Anterior spinal artery
    • from vertebral artery
    • supply anterior 2/3 of spinal cord
  • Posterior spinal artery
    • from posterior inferior cerebellar artery
    • supply posterior 1/3 of spinal cord
  • Radicular arteries
    • reinforce the anterior & posterior spinal artery
    • enter via intervertebral foramina
    • from
      • deep cervical artery
      • intercostal artery
      • lumbar artery
    • running along spinal nerve roots
    • mostly supply lower spinal cord
    • Arteria Radicularis Magna (Artery of Adamkiewicz)
      • major source of blood supply to
        • lower 2/3 of spinal cord

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  • Clinical signs of spinal cord ischaemia
    • flaccid
    • paraplegia
      • both lower limbs paralysed
    • areflexia
      • Absence of neurologic reflexes
        • eg. knee jerk
    • loss of pain
    • loss of temperature sensation
    • autonomic deficits
      • atonic bladder

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  • Spinal cord is short , vertebral column is long
    • spinal segment not the same level as vertebrae
VERTEBRAE SPINAL SEGMENT EXAMPLE
Cervical vertebrae Add 1 C3 vertebrae – C4 spinal segment
Upper thoracic (T1 – T6) Add 2 T4 vertebrae – T6 spinal segment
Lower thoracic (T7 – T9) Add 3 T9 vertebrae – T12 spinal segment
T10 thoracic L1 & L2  
T11 thoracic L3 & L4  
T12 thoracic L5  
Lumbar 1 Sacral & coccygeal spinal segment  
  • How spinal cord can be affected?
    • compression
    • metastasis
    • Intervertebral disc prolapse
    • fracture
  • Most common cervical spinal injuries involve C4/C5
    • A person who has had a burst fracture of the C5 vertebral body
      • injures C6 spinal segment
        • wrist extensors weak
        • sensation below C6 severely compromised
      • injures C4 spinal roots
        • exits the spinal column btwn C4 & C5 vertebrae
        • loss of sensation in C4 dermatome
        • weak deltoids (supplied by C4)

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  • Dermatome
    • area of skin supplied by a single spinal nerve
    • loss of sensation on a certain dermatome
      • able to tell which spinal nerve affected

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How are spinal nerves formed?

  • At each spinal segment
    • 1 pair of nerves exit to the left
    • 1 pair of nerves exit to the right
  • Dorsal root & ventral root meet
    • forming spinal nerve
  • Comes out through intervertebral foramina
  • Spinal nerve divides into
    1. Dorsal ramus
    2. Ventral ramus
    3. Meningeal ramus
    4. Rami communicating to sympathetic chain

 

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What are plexuses?

  • Ventral rami of spinal nerves interconnect to form several networks of nerves
    • Plexuses (5 in total)
      • Cervical
        • C1 – C4
      • Brachial
        • C5 – C8, T1
      • Lumbar
        • L1 – L4
      • Sacral
        • L4 – L5, S1 – S3
      • Coccyx
        • S4 – S5, Coccygeal 1
  • T2 – T12 do not form plexus
    • innervate muscles & skin of thoracic, abdominal wall
      • as intercostal nerves
  • In a plexus, nerve fibres of different spinal nerves are sorted & recombined
  • Peripheral nerves coming out of plexuses are composed of
    • fibres from several spinal nerve rami
    • eg median nerve made up of
      • C5, C6, C7, C8, T1

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  • Question:
    • What are the roots forming the brachial plexus?
    • Ventral rami of
      • must mention this
    • C4 5 6 7 and T1

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  • Components of a typical spinal nerve
    • general somatic afferent
    • general somatic efferent
    • general visceral afferent
    • general visceral efferent

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Branches of spinal nerve communicating to sympathetic trunk

  • Gray rami communicantes
  • White rami communicantes
  • Posterior primary ramus
    • dorsal cutaneous branch
    • muscular branch to erector spinae
    • articular to joints of vertebral column
  • Anterior primary ramus
    • lateral cutaneous branch
    • anterior cutaneous branch
    • proximal muscular branch
    • distal muscular branch

Coverings

  • Epineurium
    • outer
  • Perineurium
    • middle
  • Endoneurium
    • inner

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  • 3 layers
    • neuroepithelial layer
    • mantle layer
    • marginal layer
  • Ventral thickening
    • basal plate –> anterior horn cells
  • Dorsal thickening
    • alar plate –> posterior horn cells
  • Boundary (centre)
    • sulcus limitans

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  • Neural crests
    • detached from neural tube ectoderm
    • forms dorsal root ganglion

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Lumbar puncture

  • Between L3 & L4 vertebrae
  • Structures pierced
    • skin
    • thoracolumbar fascia
    • interspinous, supraspinous ligament
    • ligamentum flavum
    • dura mater
    • arachnoid mater
    • subarachnoid space

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http://rch.org.au/clinicalguide/cpg.cfm?doc_id=5178
*lumbar puncture – read up for OSPE

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Questions

  • The following statements concerning meninges of the spinal cord are correc EXCEPT:
    • Dura mater is a delicate impermeable membrane F
    • Pia mater is a vascular membrane that closely invests the cord T
    • Arachnoid mater continues along spinal nerve roots for a short extent T (until S2)
    • Dura mater is continuous above through foramen magnum with cranial dura T
    • Extradural space contains internal vertebral venous plexus T
  • The following statements concerning the arterial supply of the spinal cord are true EXCEPT:
    • Posterior spinal arteries supply posterior 3rd of spinal cord T
    • Veins communicate with veins of brain and venous sinuses
    • Arteria radicularis magna (Artery of Adamkiewicz) arises in the upper thoracic region of from arch of aorta F
    • Anterior spinal artery is single but usually arises from vertebral artery T
    • Spinal arteries are reinforced by radicular arteries, which are branches of local arteries T
  • The following statements concerning the spinal cord are correct EXCEPT:
    • Spinal cord has a cervical enlargement for the brachial plexus T
    • It possess 34 pairs of spinal nerve F (31 pairs)
    • In the adult it ends at lower border of 1st lumbar vertebra T
    • Ligamentum denticulatum anchors spinal cord to the dura mater along each side T
    • Central canal communicates with the 4th ventricle of brain T
  • The following statements concerning CSF are correct EXCEPT:
    • Normal pressure is between 60 & 150 mm of water T
    • Normal glucose content is 50 to 85 mg per 100 ml T
    • It is a clear colorless fluid T
    • The cells are polymorphonuclear leucocytes F (mononuclear)
    • Compression of internal jugular vein (Queckenstedt sign) can diagnose blockage of subarachnoid space by tumour T
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Terri is obsessed with making medical school as painless as possible. She studies and compiles medical school notes in a concise, easy-to-understand format. She also enjoys reading contributions by others. She is an investor in sustainability projects. Her ideal weekend is wine tasting and experimenting on bread-making. She has yet to master the art of Sourdough baking.

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