BMA1901

• The spinal cord is a two-way conduction highway that conducts sensory input to the brain and motor output away from the brain
• Why Study the Spinal Cord

  • As an allied health professional it is important that you understand the anatomy and functions of the spinal cord to successfully assess, treat and rehabilitate patients with spinal cord injuries

  
• Autonomic nervous system


  • Dual innervation - most effector organs are innervated by both sympathetic and parasympathetic divisions
  • Divisions can work independently or together
  • Divisions generally have opposing effects
  • One division predominates in specific circumstances
  • Divisions counterbalance to control organ function and maintain homeostasis

  
• Spinal cord


  Long, thin, delicate tubular structure protected by the vertebral column

  
• Sympathetic division


  • Prepares the body for heightened activity, i.e. exercise, excitement, emergency, embarrassment → fight-or-flight
• Regions of the spinal cord

  • Cervical (C1-C8)
  • Thoracic (T1-T12)
  • Lumbar (L1-L5)
  • Sacral (S1-S5)
  • Coccygeal

  
• Sympathetic response in organs

  • Increased heart rate and strength of contraction
  • Vasodilation in cardiac & skeletal muscle, vasoconstriction in non-essential areas
  • Bronchiole dilation
  • Stimulates release of glucose into blood
  • Stimulates sweating
  • Stimulates secretion of thick saliva
  • Decreased secretion and motility in stomach and intestine
  • Reduced blood flow and urine formation in kidney
  • Micturition (urination) inhibited
  • Secretion of adrenalin, noradrenalin
  • Release of stored blood from spleen
  • Defecation inhibited
  • Iris (pupil) dilates, lens flattens: adjusts for distance vision
• Spinal nerves


  A pair of spinal nerves connects to each segment of the spinal cord
• Parasympathetic division


  • Stimulates abdominal visceral activity, conserves energy à rest and digest
• Parasympathetic response in organs

  • Decreased heart rate
  • Bronchiole constriction
  • Increases glucose uptake from blood
  • Increased secretion of watery saliva
  • Increased secretion and motility in stomach and intestine
  • Increased blood flow and urine formation in kidney
  • Micturition promoted
  • Defecation promoted
  • Iris (pupil) constricts, lens thickens: adjusts for near vision
• Spinal nerves by region

  • 8 Cervical nerves
  • 12 Thoracic nerves
  • 5 Lumbar nerves
  • 5 Sacral nerves
  • 1 Coccygeal nerve

  
• Dorsal root


  Contains the axons of sensory neurons
• Somatic nervous system


  Voluntary movement, somatic reflexes

  
• Ventral root


  Contains the axons of motor neurons (somatic & autonomic)
• Autonomic nervous system


  Involuntary control of visceral organ function, glandular activity, visceral reflexes

  
• Cauda equina


  The lumbar, sacral and coccygeal nerve roots that travel beyond the conus medullaris

  
• Differences between somatic and autonomic nervous systems

  • Neural (efferent) pathways
  • Effectors (target organs)
  • Organ response
  • Neurotransmitters

  
• Structures that protect the spinal cord

  • Vertebral column
  • Cerebrospinal fluid
  • Spinal meninges
• Somatic motor neuron


  Lower motor neuron, cell body in spinal cord motor nucleus or brainstem nucleus, axon exits CNS via ventral root of spinal nerve or cranial nerve, releases acetylcholine which is always excitatory
• Spinal meninges


  Continuous with the cranial meninges and extend beyond the spinal cord to the second sacral vertebra (S2)

  
• Autonomic motor neuron


  • Preganglionic neuron, cell body in motor nucleus in lateral grey matter of spinal cord or brainstem, axon exits CNS via ventral root of spinal nerve or cranial nerve, releases acetylcholine which is always excitatory
  • Postganglionic neuron, cell body in peripheral ganglion, releases acetylcholine or noradrenalin which may be excitatory or inhibitory
• Lumbar puncture


  Insertion of a needle into the subarachnoid space beyond L3 to withdraw CSF fluid or administer medications
• Parasympathetic division


  • Preganglionic neurons arise from opposite ends of the CNS - brainstem and sacral region of spinal cord
  • Ganglia located close to or within target organ
  • Preganglionic axon is long, postganglionic axon is short
  • Innervates cranial and pelvic organs
• Sympathetic division


  • All preganglionic fibres arise within spinal cord segments T1 - L2
  • Ganglia located close to spinal cord
  • Preganglionic axon is short, postganglionic axon is long
  • Innervates head, thorax, abdomen and pelvis
• Epidural space


  Space between the outer dura mater and the vertebral column, site of anaesthetic administration
• Sympathetic preganglionic neuron


  • Synapses with adrenal medullary cells
  • Releases acetylcholine which binds to nicotinic receptors on adrenal medulla cells
  • Acetylcholine stimulates medullary cells to release adrenalin and noradrenalin into bloodstream
• Denticulate ligaments


  Extensions of the pia mater that prevent lateral movements of the spinal cord
• Sympathetic effects are widespread as adrenalin and noradrenalin released into blood can affect any cell bearing adrenergic receptors, enhancing and prolonging the sympathetic response
• Organs/structures


  • Skin (arrector pili muscles and sweat glands)
  • Salivary glands
  • Heart
  • Lung
  • Rectum
• Gray matter


  Composed of neuron cell bodies (mainly), unmyelinated axons & neuroglia
• Preganglionic

  Neuron that synapses with a ganglion

  
• White matter


  Composed of myelinated (mainly) & unmyelinated axons
• Postganglionic


  Neuron that extends from a ganglion to a target organ
• Gray commissure


  Site where axons cross from one side of the CNS to the other
• Gray horn subdivisions


  • Posterior gray horns - sensory function
  • Anterior & lateral gray horns - motor function
• Spinal cord regions


  • Thoracic
  • Lumbar
• Sensory nuclei


  Contain the cell bodies of spinal cord interneurons that receive and process incoming sensory input
• Sympathetic


  Preganglionic neurons synapse with adrenal medullary cells

  
• Somatic motor nuclei


  Contain the cell bodies of lower motor neurons that receive outgoing somatic motor output
• Sympathetic response


  1. Preganglionic neuron releases ACh

  2. ACh binds to nicotinic receptors on adrenal medulla cells

  3. ACh stimulates medullary cells to release A and NA into bloodstream