Spinal cord anatomy and Ascending & Descending pathways Flashcards
How many spinal nerves are there?
31
In the spinal cord, does the grey matter lie on the outer aspect or the core
The inner core (forms an H shape)
What is in the white matter?
Axons, glial cells and blood vessels
What is in the grey matter?
Neuronal soma, cell processes, synapses, glial cells and blood vessels
Describe the blood supply to the spinal cord
A. Three major longitudinal arteries: one anterior and two posterior that originate from the vertebral arteries. These run the length of the cord.
B. Segmental arteries derived from vertebral, intercostal and lumbar arteries.
C. Radicular arteries that travel along the dorsal and ventral roots.
Where is the primary somatosensory cortex?
Postcentral gyrus
How does the information from the periphery reach the somatosensory cortex?
Travel through the spinal cord (NB not face and scalp)
Which ascending tract sends the signals allowing us fine touch and propriception?
The dorsal column/Medial lemniscus system
Where do the signals carried in the dorsal column/Medial lemniscus system cross over?
Medulla
What spinal tract carries the sensations of pain, temperature and deep pressure?
Spinothalamic tract
Where is the primary motor cortex?
Precentral gyrus
What spinal tract allows fine, precise movement?
Corticospinal tract
Where do most of the fibres of the corticospinal tract cross over?
Decussation of the pyramids
What spinal tract mediates reflex head and neck movement due to visual stimuli?
Tectospinal tract
What is the reticular formation?
A network of nerve pathways in the brainstem connecting the spinal cord, cerebrum, and cerebellum, and mediating the overall level of consciousness. Forms the central core of the brainstem
Where do the fibres of the reticular formation originate?
Pons and medulla
Do reticular fibres originating in the pons tend to facilitate extensor or flexor movements?
Extensor (Inhibit flexor)
Do reticular fibres originating in the medulla tend to facilitate extensor or flexor movements?
Flexor (inhibit extensor)
What tract provides excitatory input to antigravity muscles?
Vestibulospinal tract
Where do the fibres of the vestibulospinal tract originate?
Vestibular nuclei of the pons and medulla.
Is the dorsal column a motor or sensory pathway?
Sensory
What two fasiculi make up the dorsal column pathway?
Graclie
Cuneate
What does the dorsal column sense?
Fine touch and proprioception
What four nerve endings sense fine touch?
Meisners corpuscles
Pacinian corpuscles
Rufini endings
Merkel endings
Where do the cell body’s of sensory nerves sit? (this is before they enter the spinal cord!)
Dorsal root ganglion
Do axons from the lower limb travel in the gracile or cuniform fasiculus?
Gracile
Do axons from the upper limb travel in the gracile or cuniform fasiculus?
Cuneate
What is a nucleus?
Collection of cell bodies within the CNS
Explain the dorsal column medial lemniscus pathway
- Sensation of fine touch/proprioception perceived by sensory neurones. The cell bodies of these neurones are in the dorsal root ganglion.
- Travels up on the ipsilateral side in the dorsal column (either gracile of cuneate fasiculus)
- Reaches the gracile or cuneate nucleus in the Medulla.
- After this is crosses over at the pyramids of the medulla (after this is is referred to as medial lemniscus)
- Travels from here to the ventral posterolateral nucleus in the thalamus.
- Travels from the thalamus to the post central gyrus (primary somatosensory cortex)
What is the decussation point in the spinal cord (the fibres of the spinothalamic tract cross here) called?
Anterior white commissure
What is lissaure’s fasiculus?
The fasiculus in which the fibres of the spinothalamic ascend for 1 - 2 levels before crossing.
Explain the spinothalamic tract
- Sensory neurones pick up sensations of temperature and crude touch. The cell bodies of these neurones are located in the dorsal root ganglion.
- Travels up in lissaure’s fasiculus on the ipsilateral side for 1 - 2 levels of the spinal cord.
- Decussates at the anterior white commisure.
- Travels to the thalamus
- Travels from thalamus to the post central gyrus.
Describe the corticospinal tract.
- Arises in the primary motor cortex of the pre central gyrus.
- Axons exit through white matter and pass through the internal capsule.
- Travel down through the midbrain and the pons before crossing over at the pyramids of the medulla.
- Then enter the lateral funiculus of the spinal cord to become the lateral corticospinal tract.
(The fibres which don’t cross at the medulla continue as the ventral corticospinal tract and they cross segmentally at the spinal cord) - Exit the spinal cord
What would a stroke causing ischaemia to the internal capsule result in?
Loss of control of the corticospinal tract (spastic paralysis/decorticate posturing)
