Chapter 12 part 3) Spinal Chord

Question 1

Spinal Chord Location and Function

Answer 1

• Enclosed in the vertebral column (through froamen of vertebrae)
• Begins at Foramen Magnum (occpital bone)
• Ends at L1 or L2 verebra (nerves extend beyond)
• Funtions
  
  • Provide two-way communication to and from brain and body
  • Major reflex center (initiate and complete)

Question 2

Protection of Spinal Chord

Answer 2

• Protected by bone, meniniges and CSF
• Menigines
  
  • Dura>Arachnoid>Pia
  • Dura mater is one thick layer that does not attach to vertebrae
  • Dural and Arachnpid Matter extend beyond end of spine at L1 or L2. Provides point for lumbar puncture without risk of damaging nerves
• Epidural Space
  
  • Cushion of Fat and Network of Veins in space between vertebrae and spinal dura mater
• CSF
  
  • Fills subarachnoid space between arachnoid and pia mater.

Question 3

Conus Medullaris

Answer 3

• Spinal Chord Terminates in cone-shaped structure called Conus Medullaris
• Filum Terminale
  
  • Fibrous extension of Conus covered in pia mater,
  • Extends to coxyx to anchor spinal chord
• Denticulate Ligaments
  
  • Extensions of pia mater that secure spinal chord to dura mater.

Question 4

Spinal Nerves

Answer 4

• Part of the PNS (peripheral)
• Attached to spinal chord via 31 paired roots
  
  • Spinal chord segmants are designated by paired spinal nerves that arise from it.
• Cervical and Lumbar Enlargments
  
  • Areas where nerves servicing upper and lower limbs arise from spinal chord
  • Cervical) upper
  • Lumbar) lower
• Cauda Equine
  
  • Collection of nerve roots at infrior end of vertebral canal
  • (Looks like a horses tail)

Question 5

Cross Sectional Anatomy

Answer 5

• Two Grooves run the Length of the chord and divide it into left and right halves
  
  • Ventral (anterior) median fissure
  • Dorsal (Posterior) median Sulcus
• Grey Matter (located in core)
  
  • Grey Commisure) connects masses of grey matter
    
    • Encloses central canal
  • Dorsal Horns) Internuerons that reveive somatic and visceral input
  • Ventral Horns) Somatic Motor nuerons
  • Lateral Horns) Sympathetic Nuerons
    
    • Only found in thoracic and superior lumber regions
• Spinal Nerves (fusion of ventral and dorsal roots)
  
  • Ventral Roots) Motor Nuerons exiting the spinal chord.
  • Dorsal Roots) Sensory input to spinal chord
  • Spinal Ganglia (dorsal) cell bodies of sensory nuerons

Question 6

Spinal Gray Matter Zones (four)

Answer 6

• Somatic sensroy and Visceral Sensory
  
  • Located in Dorsal Horn
  • Sensroy nuerons
  • Somatic Sensory is more Dorsal
• Somatic Motor and Visceral Motor
  
  • Located in Ventral horn
  • Motor nueron
  • Somatic Motor is more ventral

Question 7

White Metter Collums in Spinal Chord

Answer 7

• Myelinated and Nonyelinated fibers allow communication between spinal chord and brain and diffrent parts of the spinal chord
• Three Directions
  
  • Ascending) To higher centers (sensory input)
  • Descenting) from brain to chord or lower levels (motor output)
  • Transverse) From one side to another (commisural fibers)
• In Chord White matter is divided into three collums (funiculi)
  
  • Dorsal, Lateral and Ventral Funiculi
  • Each contains several fiber tracts. Each tract is made of axons with similar destinations and functions.

Question 8

Spinal Chord Trauma

Answer 8

• Localized injury to spinal chord or roots which leads to funtional loss
• Paresthesias
  
  • Damage to dorsal roots or sensory tracts
  • Leads to sensory function loss
• Paralysis
  
  • Damage to ventral roots or motor tracts
  • Leads to motor loss
• Two types of paralysis
  
  • Flaccid) Severe damage to ventral root so no signals reach. No muscular control at all
    
    • muscles begin to atrophy
  • Spastic) Nuerons are intact to spinal reflexes occur. No voluntary control
    
    • Muscles begin to shorten permanently.

Question 9

Poliomyelitis

Answer 9

• Destruction of ventral horn motor nuerons by poliovirus
  
  • Muscles will atrophy
  • Death may occur if cardiac or respritory muscles are affected.

Question 10

Four Points About Spinal Tracts

Answer 10

• Decussation) Spinal pathways cross from one side of the body to the other
• Relay) Most Pathways consist of a chain of two or three nuerons
• Somatotopy) Precise spation relationship in CNS corresponds to spational relationship in body
  
  • Precice parts of brain control precise parts of the body
• Symmetry) all pathwyas are paired symmetirically

Question 11

Ordering Nuerons

Answer 11

• First Order Nuerons
  
  • Cell bodies Reside in a Ganglion (dorsal root or Dorsal cranial)
  • Conduct impulses from receptors to spinal chord or brain stem
• Second Order nuerons
  
  • Internuerons
  • Cell body in doral horn
  • Axon extends and transmits impules to thalamus or cerebellum
• Third Order Nuerons
  
  • Internueron
  • Cell body in Thalamus
  • Extends to somatosensory cortex (none to cerebellum)

Question 12

Dorsal Column-Medial Leminiscal Pathways

Answer 12

• Transmits input to Somatosensoru Cortex via Thalamus
• Responsible for detecting discriminative (specific) touch and vibrations
• First order nuerons
  
  • Fasciculus centeanus
  • Fasciculus gracilis
  • Located in spinal chord
• Second Order Nuerons
  
  • Medial leminiscus (medulla to thalamus)
• Third Order
  
  • Thalamus to somatosenory cortex
• (Decussates in Medulla)

Question 13

Spinothalamic Pathways

Answer 13

• Transmit Impules for Pain ,Temprature, Pressure and Course Sensation
  
  • Aware of sensations but difficult to localize precisely
• First Order Nuerons
  
  • From Receptors in body
• Second Order Nuerons
  
  • Found in Lateral and Ventral Spinothalamic Tracts
  • Fibers Descuciate here (cross over)
• Third Order Nuerons
  
  • Thalamus to somatosensory cortex

Question 14

Spinocerebellar Tracts

Answer 14

• Convayes info about muscle or tendon stratch to cerebellum which cordinates skeletal activity
• First Order Nuerons
  
  • Convay info from muscles
• Second order nuerons
  
  • Consists of Dorsal and Ventral Spinocerebellar Tracts
• (No Third order nuerons, goes directelly to cerebellum)
• (Does not decussate)

Question 15

Descending Pathways and Tracts

Answer 15

• Deliver Effrent Pathway (effect) iimpules from brain to spinal chord.
• Two Groups
  
  • Direct Pathways) Pyramidal tracts
  • Indirect Pathways) all other type of tracts
• Motor Nueron Types
  
  • Upper Motor Nuerons) from motor cortex and pyrmidal cells in cortex
  • Lower Motor Nuerons) from Ventral horns
    
    • Innervate skeletal muscles.

Question 16

Direct (Pyramidal) Pathways

Answer 16

• Originate mainly from pyramidal nuerons located in precentral gyri (motor cortex)
• Nuerons send impulses through large pyramidal tracts
  
  • Lateral and Ventral corticospinal Tracts
• Descned directely with No synapse until axon reaches the end of its tract in spinal chord
  
  • Synapse with internuerons (lateral tract)
  • Synapse with ventral horn motor nuerons
• Regulates fine and fast movments

Question 17

Indirect (multinueral) pathways

Answer 17

• Complex pathways with multiple synapses
• Include brain stem motor nuclei and below
  
  • everything excempt pyramidal pathways
• Pathways regulate
  
  • Axial Muscles) balance and posture
  • Muscles controling coarse (not fine) limb movments
  • Head, Neck, and Eye movments when tracking an onject
• Four Pathways
  
  • Reticulospinal and Vestibulospinal tracts
    
    • Mantain balance by controling muscle tone
  • Ruberospinal
    
    • Control Flexor muscle
  • Tectospinal
    
    • Mediate head movment
    • orginate from superior colliculi