Spinal cord and Periphery Flashcards
Name the components of the cross sectional anatomy anatomy of the spinal cord
- Has a central grey matter & peripheral white matter.
- The grey matter has on each side a dorsal & a ventral horn.
- The axons of sensory fibres enter through the dorsal root into the dorsal horn of grey matter.
- Motor neurons have their cell bodies in the ventral horn.
How is the white matter in the spinal cord arranged?
- The white matter is arranged in 3 columns - posterior, leteral & anterior
- Each column has various bundles (tracts) of axons
- Ascending pathways are sensory, descending pathways are motor
- Different tracts carry different information
List the Ascending tracts
- Lateral spinothalmic
- Ventral spinothalmic
- Dorsal column
- Spinocerebellar
- Cuneocerebellar
- Spinoreticular
- Spino-olivary
List the descending tracts
- Corticospnal
- Reticulospinal
- Rubrospinal
- Vestibulospinal
- Tectospinal
What are the three important spinal tracts?
- Corticospinal/pyramidal tract - carries motor impulses from motor cortex to skeletal muscles
- Posterior/dorsal column - carries touch, tactile localisation, vibration sense, proprioception
- Lateral spinothalmic tract - pain and temperature
Explain the Corticospinal/Pyramidal tract
- Control of voluntary skilled movements (i.e. motor pathway).
- Pathway starts from the motor cortex (Area 4)
- Posterior limb of Internal Capsule (blood supply Middle Cerebral Artery).
- Corticobulbar fibres go to contralateral cranial n nucleii.
- Corticospinal fibres mostly cross in decussation of pyramids (Lateral corticospinal tract).
What neurons are involved in the costicospinal/pyramidal tract?
- 2 neurons in the pathway. These are called the upper and lower motor neurons respectively.
- Decussates to the opposite side in the medulla.
Where is the site of lower motor neurons
Ventral horn= site of lower motor neurons
Describe the Posterior/Dorsal column
- Carries sensations of fine touch, tactile localisation, vibration sense, proprioception
- 1st order neuron ends by synapsing with the cell body of the 2nd neuron. This is situated in the lower part of the medulla.
- 2nd order neuron crosses over (decussates) in the medulla.
- The tract now is called medial lemniscus and passes through the medulla, pons and midbrain to reach the thalamus
- The third order neuron starts from the thalamus and axons pass through the IC and radiate to the post-central gyrus (Area 2,1,3)
Describe the Lateral Spinothalmic tract
- Pain and temperature
- First order neuron enters into the grey matter and ends at the same level.
- 2nd order neurons cross over to reach the lateral column and is now called lateral spinothalamic tract
- 2nd order neuron ends in thalamus and 3rd order passes through IC, radiation to reach post-central gyrus•
Describe the Ascending spinal tracts
Pathways reaching conscious level have common characteristics:
There are 3 neurons between peripheral receptor and cortex.
Explain what Reflexes are?
- A reflex is an involuntary stereotyped pattern of response brought about by a sensory stimulus.
- Many reflexes are mediated at the level of the spinal cord (spinal reflexes).
- Anatomically they may be monosynaptic (eg: stretch reflex) or polysynaptic (eg: flexor reflex).
Describe the steps in Stretch reflex( and reciprocal innervation)
- Tendon stretched
- Intrafusal muscle fibres stimulated
- Sensory neuron activated
- Monosynaptic reflex arc
- Polysynaptic reflex arc to inhibitory interneuron
- Muscle contraction
- Reciprocal innervation
Describe the Flexor and corssed extensor reflex
What mediated reflexes?
Lower motor neuron
What mediated reflexes?
Lower motor neuron
If lower motor neuron is not affected in an upper motor neuron lesion that causes paralysis then what happens to reflexes?
Reflexes are exaggerated in Upper motor neuron lesions
What affects tone of muscle?
- Requires Lower motor neuron
- Upper motor neuron lesion causes increased tone (spasticity) while lower motor neuron lesion causes flaccidity
Describe what happens when Left upper motor neuron lesion at internal capsule occurs?
- Right sided paralysis
- Hyper-reflexia
- Increased tone
Describe what happens when Left Upper Motor Neuron Lesion at upper cervical spinal cord occurs?
- Left sided paralysis
- Hyper-reflexia
- Increased tone
Describe what happens when Left Lower Motor Neuron lesion occurs?
- Left sided paralysis
- Absent reflexes
- Flaccid
Describe what Motor Neuron Disease (Lower Motor Neuron) is?
- Group of diseases affecting the lower motor neuron in the ventral horn of spinal cord
- The neuron dies and as a result muscle supplied by it atrophies
- Progressive, icurable disease
Describe when symptoms are Contralateral?
If lesions is above level of decussation
Describe the cause for symptoms to be Ipsilateral?
If lesions is below the level of decussation
Describe the flow diagram for contralateral and ipsilateral pathways?
Describe what happens when lesions occur at the Posterior/Dorsal column ?
Describe what happens when lesions occur at the Lateral Spinothalamic tract?
How are central grey and whiter matter tracts arranged in the spinal cord?
Peripherally
How many pathway neurons do ascending sensory tracts have?
3
How many neurons in the descending motor tract pathway?
2
What are reflexes?
Reflexes are involuntary stereotyped responses to sensory stimuli
