Spinal Cord and Periphery Flashcards
Describe dorsal and ventral horn?
Sensory axons for dorsal root and Motor neurons for ventral root
What are the columns of white matter arranged into?
Posterior, lateral and anterior
Each column has various tracts of axons
What is the difference between ascending and descending tracts?
Ascending - sensory
Descending - motor
What are some ascending tracts?
Lateral spinothalamic, medial spinothalamic, dorsal column, spinocerebellar, cuneocerebellar, spinoreticular, spino-olivary
What are some descending tracts?
Corticospinal, reticulospinal, rubrospinal, vestibulospinal, tectospinal
Where is the dorsal column?
Dorsal or posterior part of the spinal cord behind the grey matter
What does the corticospinal/ pyramidal tract carry?
Motor impulses from motor cortex to skeletal muscles
What does the posterior/ dorsal column carry?
Carries touch, tactile localisation, vibration sense and proprioception (sensory impulse from muscles)
What does the lateral spinothalamic tract carry?
Pain and temperature
What is the blood supply for the internal capsule?
Middle cerebral artery - direct continuation of ICA (frequently implicated by occlusion leading to strokes)
Lead to dense stroke as projection fibres of corticospinal tract are here
What is the function of the corticospinal tract?
Control of voluntary skilled movements - motor pathway
Where does the corticospinal tract start and where does the projection fibres lead into?
Motor cortex - area 4
Leads into the posterior limb of the internal capsule
What are corticobulbar fibres?
Fibres which are coming from precentral gyrus and ten leave tract to go to
contralateral cranial nerve nuclei
These fibres do not go into spinal cord
Where do corticospinal fibres mostly cross?
Decussation of pyramids as 10 crania nerves leave the brainstem
Where do the rest of fibres from corticospinal tract (not corticobulbar) go?
Down medulla - forming projection - pyramids
At lower part of pyramid they cross - decussation
Tract to lie now in lateral column of spinal cord forming the lateral corticospinal tract
How does lateral corticospinal tract synapse with skeletal muscles?
Axon enters into grey matter where it synapses - impulse assed through ventral root to spinal nerve then spinal muscles
Where do the corticospinal fibres sit in midbrain?
Motor fibres at very front of midbrain
In the crus cerebri - in front of the substantia nigra (part of basal ganglia)
Where does the corticospinal fibres lie in the pons?
Anterior region but are separated - not one bundle, broken up
Describe where the corticospinal fibres are in the medulla
Anterior and back in a bundle
Form projections called pyramids - at lower part of pyramids is where the fibres cross over
How many neurons in the corticospinal pathway?
2 neurons - upper and lower motor neurons
1st neuron at cell body in grey matter of precentral gyrus
Synapses in ventral horn of grey matter - depending on which muscle
Describe the first and second neurons in the posterior column
1st neuron ends by synapsing with cell body of 2nd neuron - situated in lower par of medulla
2nd order neuron crosses over at medulla
What is the medial lemiscus?
When 2nd order neuron crosses over in medulla
This tract passes through the medulla, pons and midbrain to reach the thalamus
Where is the 3rd order neuron of medial lemniscus?
Starts from thalamus and axons pass through internal capsule and radiate to post-central gyrus
Where does the posterior column fibre synapse in medulla?
Gracile and cuneate nuclei
Where does the first order neuron enter in lateral spinothalamic tract?
Neurons of pain and temperature enters into grey matter of spinal cord and ends at same level that it entered
Describe the 2nd and 3rd order neuron of the lateral spinothalamic tract
Crosses over to reach lateral column in grey matter and now is lateral spinothalamic tract
Ends in thalamus
3rd order neuron passes through IC, coronal radiator to reach post-central gyrus
Where is decussation happening in lateral spinothalamic tract?
At level of entry
What is the definition of reflexes?
Involuntary stereotypes pattern of response brought about by sensory stimuli
Many reflexes are mediated at level of spinal cord - spinal reflexes
Can be monosynaptic or polysynaptic
Describe the stretch reflex
Tenon is stretched - muscle fibres stretched so intrafusal muscle fibres stimulated
Sensory neuron is activated - dorsal root ganglion to come to synapse in ventral horn - effector neuron (motor)
Spinal nerve back to that muscle
What other muscles are innervated in stretch reflex?
Some fibres go to other segments of the spinal cord to inhibit neurons - innervates muscle to relax
This is reciprocal innervation causing relaxation
Why is the stretch reflex important?
Control of muscle tone and posture
Why is the flexor reflex important?
protects the body from painful stimuli
Describe the flexor reflex and crossed extensor
Pain receptors stimulated - activate sensory neuron which goes through dorsal root into dorsal grey matter of spinal cord
Acts on inhibitory neuron on ventral horn - contraction of muscle
Crossed extensor response to stimulate muscle for balance
What are reflexes mediated by?
Lower motor neurons
What happens to reflexes in upper motor neuron lesions?
Reflexes are exaggerated
LMN is compensating for firing excessively
What controls tone of muscle?
Requires LMN
UMN lesion causes increased tone (spasticity) while LMN lesion causes flaccidity
What happens if here is a left UMN lesion in internal capsule?
Right sided paralysis
Hyper-reflexia
Increased tone
What happens if there is a lesion in left UMN at upper cervical spinal cord?
Left sided paralysis as crossed over
Hyper-reflexia
Increased tone
What happens if lesion in left LMN?
Left sided paralysis
Absent reflexes
Flaccid muscles
Describe motor neuron disease
Group of diseases affecting the lower motor neuron in ventral horn of spinal cord
Neuron dies and as a result the muscle supplied by it atrophies
Progressive and incurable disease
