Descending/Ascending Spinal Cord Tracts Flashcards
What are the two enlargements in the spinal cord and what do they mean?
Cervical - related to upper limb
Lumbar - related to lower limb
At what level does the spinal cord end?
L1/L2
What is the end of the spinal cord called?
Conus medullaris
What projects from the conus medullaris?
Thin connective tissue called filum terminale, which is anchored to the dorsum of the coccyx
Are the cranial meninges continuous with the cranial meninges?
Yes, via the foramen magnum
How is the spinal cord suspended in the spinal canal?
Denticulate ligament - ribbon of tissue on the lateral aspects of the cord
What is the denticulate ligament made of?
Pia and arachnoid tissue and attaches to the dura at points along the length of the cord
What fills the subarachnoid space?
CSF - just like the brain
What is the central canal?
Extension of the 4th ventricle - extends the length of the canal
What is the white matter of the spinal cord made up of?
Posterior, Lateral and Anterior fasciculi
What is the grey matter in the spinal cord divided into?
4 Left and Right Posterior and Anterior Horns Make up letter H
What does the horizontal bit of the grey matter H represent?
Dorsal and ventral commisures which surround the central canal
Arterial Supply of the spinal cord
3 major longitudinal arteries
Segmental arteries
Radicular arteries
Describe the 3 major longitudinal arteries
one anterior and two posterior that originate from the vertebral arteries. These run the length of the cord.
What are the segmental arteries derived from?
Vertebral, intercostal and lumbar arteries
How do radicular arteries travel?
Along the dorsal and ventral roots. Arteries follow roots
Describe venous drainage of the spinal cord?
The venous drainage of the cord follows a similar pattern to the supply, with both longitudinal and segmental veins.
Venous drainage also occurs in spaces around the dura. The dura mater in cranial cavity is adherent to cranial bones, in vertebral canal typically epidural fat pad which separates canal and dura, in fat pad is venous plexus - epidural anaesthetic occurs here as bathes outer layers or roots at exit intervertebral foramen.
Where is the first stop for sensory information?
Postcentral gyrus
Where in the brain is the sensory area for left sided sensation of the body
Right cortex - postcentral gyrus
Where is there least white matter in the length of the spinal cord?
White matter occupies a smaller proportion of the cord as you descend the cord.
Which are the ascending tracts of the spinal cord? Name 2
- Dorsal column; fasciculus gracilis and fasciculus cuneatus
- Spinothalamic tract
Which are the descending tracts of the spinal cord? Name
- Lateral and ventralcorticospinal
- Medial longitudinal fasciculus
- Rubrospinal
- Reticulospinal (pontine and medullary)
- Vestibulospinal
What does the dorsal column/medial lemniscus system do?
Fine touch and proprioception (particularly from upper limb)
Describe the ascending action potential after stubbing your toe
stub toe, action potential into dorsal posterior column until reach lower portion of medulla where they synapse, one neuron, one synapsis - until reaches brainstem is ipsilateral - crosses midline at medulla. The second order neutron they synapse onto cross midline and join white matter track on OTHER side called the medial lemniscus (“ribbon like” white matter) then ascends rest of brainstem to internal capsule and enters thalamus. 3rd order neutron will then send its axon into internal capsule to appropriate part of primary somatosensory cortex.
in medulla…..2 nuclei - represent lower input (from lower limb) and upper (upper limb) - nucleus gracilis is receiving information from lower limb and nucleus cuniatus from upper limb/upper half of body. Gracilis is medial as fibres from leg enter and go in and as they ascend other fibres are coming in.
Dorsal Column - do fibres cross/where
YES cross in medulla
What does the spinothalamic tract do?
Pain, temperature, deep pressure
Spinothalamic tract - do fibres cross/ where
YES fibres cross segmentally
Describe the action potential journey when someone steps on your foot
anterolateral tract
stamp on toe - pain carried into spinal cord - immediately synapses, 2nd order neutrons send axon across midline and join anterolateral tract on other side, segmentally crossing. Track upwards to brainstem, join spinal lemniscus (white matter track )taking them all the way up to thalamus and 3rd neuron synapses to appropriate primary cortex.
Where is the primary motor cortex?
PRE central gyrus
Where will the signal to move your right arm come from?
Left cortex - pre central gyrus
What does the corticospinal tract do?
Fine precise movement - particularly of distal limb muscles eg digits
What is the decussation of the pyramids?
Corticospinal tract - Tract forms visible ridges referred to as the ‘pyramids’ on the anterior surface of the medulla, so also called the pyramidal tract. About 85% of fibres cross in the caudal medulla at the decussation of the pyramids.
Where do fibres from the corticospinal tract cross to the other side?
Medulla
Describe what happens if a CVA of the internal capsule results in a lack of descending control of the corticospinal tract
Spastic paralysis with hyperflexion of the upper limbs - decorticate posturing
Not paralysed as other tracts can take over
What are pyramidal and extrapyramidal tracts?
Corticospinal tracts = pyramidal
All other motor systems collectively called = extrapyramidal
What does the tectospinal tract do?
Mostly cervical segments - mediates reflex head and neck movements due to visual stimuli eg watching bus go past head moves
What does the reticulospinal tract do?
Voluntary movement
Fibres originating in which parts of the brain cause extension/flexion
PONS = EXTENSOR MEDULLA = FLEXOR
What does the vestibulospinal tract do?
Detects falling and activates anti gravity extensors eg arms and legs out to balance
Where do fibres of the vestibulospinal tract originate?
Vestibular nuclei of the pons and medulla (these in turn receive input from vestibular apparatus and cerebellum)
