Spinal Cord

Question 1

Identify the gross anatomy of the spinal cord

Answer 1

• goes from brainstem to IV disc at L1/L2
• has cervical and lumbosacral enlargements
• tapers to form conus medullaris
• 31 spinal cord segments give rise to 2 spinal nerves each
• rootlets (6-8) form nerve roots
  
  • roots are both dorsal and ventral, merging on each side of the spinal cord to form the spinal n. which exits through the vertebral canal through intervertebral foramen
  • proximal to merger, dorsal root exhibits a swelling - dorsal root ganglion
  • spinal roots in the lumbar and upper sacral region are called cauda equina

Question 2

Describe the formation, distribution, and nomeclature of the spinal nerves.

Answer 2

• named for the vertebrae for which they are related
  
  • C8 is exception
  • C1 -C7 spinal n. exit the intervertebral foramen above the same numbered vertebra
  • C8 goes between C7 and T1
  • T1 to S5 exit below the same numbered vertebra
• spinal cord segment
  
  • area of the spinal cord that originates dorsal and ventral spinal rootlets, roots, and spinal n.
  • spinal cord segments equal the number of spinal nerves on each side
  • lumbar spinal cord segments are located T11-T12
  • sacral spinal cord segments are located at L1-L2

Question 3

List the spaces and meninges between vertebra and spinal cord - from bone to spinal cord

Answer 3

• bone of vertebra
• epidural space (contains fat and internal vertebral venous plexus)
• dura mater
• subdural space (virtual/potential space)
• arachnoid mater
• subarachnoid space (CSF within)
• in lumbar cistern, spinal roots - cuada equina and filum terminale
• pia mater
• spinal cord

Question 4

Describe dura mater

Answer 4

• outermost covering of spinal cord
• extends above at the foramen magnum and is continuous with the dura mater lining the intracranial space
• extends caudally, ending in the sacral canal at S2
• represented beyond S2 caudally to the coccyx by the coccygeal ligament (dural portion of teh filum terminale)
• dura mater at intervertebral foramen fuses to the spinal nerves

Question 5

Describe arachnoid membrane.

Answer 5

• separtated from pia mater by subarachnoid space
  
  • has about 150 ml of CSF which is produced in the ventricles of the brain by the choroid plexus and is reabsorbed into the venous system
• a delicate, spider web-like structure

Question 6

Describe pia mater

Answer 6

• innermost layer of meninges which directly covers spinal cord
• is intimately associated with nervous tissue
• denticulate ligaments are lateral extensions of pia mater that anchor the spinal cord to the dura mater
  
  • separates dorsal and ventral roots
• filum terminale is an extension of pia from the conus medullaris, which extends to the end of teh subarachnoid/dural space at S2
  
  • continues as the coccygeal ligament which is dura and attaches to the coccyx

Question 7

Describe the main blood vessels of the spinal cord and spinal nerves, both arterial and venous

Answer 7

• unpaired anterior spinal artery (branch at union of vertebral arteries)
• paired posterior spinal arteries (branch of vertebral arteries)
• segmental arteries (branches of variety of arteries)
  
  • supply nerve roots as radicular arteries
• veins are present as plexuses that invest the verebrae (external and internal vertebral plexuses) and spinal cord (external spinal veins)
  
  • internal vertebral venous plexus is located in the epidural space in the vertebral column
  • external vertebral venous plexus is located outside the vertebrae
  • contains no valves

Question 8

Differentiate between gray matter and white matter

Answer 8

• gray matter
  
  • collection of nerve cell bodies
  • cortex and nucleus
  • ganglion
• white matter
  
  • axons with glial sheaths (myelin)
  • pathways (tracts, fascicles)
  • nerve

Question 9

List the spinal cord tracts of greatest functional relevance and what kind of information they carry.

Answer 9

• dorsal columns
  
  • sensory information
    
    • touch, vibration, proprioception
• spinothalamic tract
  
  • sensory information
    
    • pain and temperature
• lateral corticospinal tract
  
  • motor impulse

Question 10

Describe the dorsal column pathway

Answer 10

• three neuron circuit, subserving the transmission of tactile, vibration, and proprioceptive information
• carry central processes of sensory first order neurons
  
  • peripheral process connected to receptors
  • neural soma in dorsal root ganglion
  • central process enters spinal cord through dorsal root
• first order neuron reaches second order neuron
  
  • in the brain stem (medulla oblongata)
  • second order neuron crosses midline here
• second order neuron synapses with the third order neuron
  
  • in the thalamus and go to the contralateral cerebral cortex
  • stimuli was carried through the spinal cord ipsilaterally to the position of the receptor/origination
• has 2 fasciculi
  
  • fasciculus gracilis
    
    • more medial
    • stimuli from below mid thoracic
  • fasciculus cuneatus
    
    • more lateral
    • stimuli coming from above mid thoracic

Question 11

Describe the Spinothalamic tract

Answer 11

• position of the tract is anterolateral within the spinal cord
• three neuron circuit, subserving transmission of pain and temperature where the stimulus is received in the side opposite the pathway
  
  • meaning cross the spinal cord, then ascend
• first order neuron is continuous with stimulus receptor and enters the spinal cord through the dorsal root
• first order neuron synapses with second order neuron
  
  • within the dorsal horn
  • crosses over here to reach the spinothalamic tract on the opposite side
• second order neuron ascends through the brainstem to the thalamus where it synapses with the third order neuron
  
  • ascends further to the cerebral cortex

Question 12

Describe the lateral corticospinal (pyramidal tract)

Answer 12

• motor pathway originating in cerebral cortex
• descends through white matter of cerebrum and brainstem
  
  • 90% of its fibers crossover here and then reach the spinal cord
• within spinal cord, it is located in the lateral column of white matter
• carries axons from the Upper motor neurons to lower motor neurons in the ventral horn
• lowern motor neurons send axons through the ventral roots and are distributed to the myotome of each specific spinal cord segment

Question 13

Describe the 5 stages of the Reflex Arc

Answer 13

1. receptors - detect specific environment changes\
   
   • exteroreceptors - change in external environment (skin for touch, vibration, pain, or temp; vestibular apparatus for acceleration of teh head, pull of gravity)
   • proprioceptors - change in skeletal position (muscle spindle and Golgi tendon organs)
2. Afferent neuron - psuedounipolar with cell bodies located in dorsal root ganglia
   
   • peripheral process is distal to the cell body
   • central process is between cell body and dorsal horn
3. Synapse - transmission from afferents to efferents
   
   • can have direct synaptic contact - monosynaptic
   • can have one or more intermediate neurons incorporated - disynaptic or polysynaptic
   • interneurons are multipolar, cell body and dendrites are located in the dorsal gray horn and the very short axon terminates on the efferent neuron
4. Efferent neuron - multipolar neurons with cell bodies and dendrites located in the gray matter
   
   • axons cross the ventral rootlets, root, spinal nerves, and primary rami to reach an effector
5. Effector
   
   • target of the efferents
   • for somatic response, skeletal muscle
   • for visceral response, smooth muscles, cardiac muscles, erector pili/glands