Scenario (3)brain -stroke Flashcards
(41 cards)
Venous drainage of the brain
Deep veins
Superficial veins
Dursley’s venous sinuses
None have valves
What is the function of the Ascending tracts
neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex.
What type of information do ascending tracts carry
Sensory information
1) Conscious tracts - comprised of the dorsal column-medial lemniscal pathway and the anterolateral or spinothalamic system.
2) Unconscious tracts - comprised of the spinocerebellar tracts.
Name the ascending tracts
Dorsal Column-Medial Lemniscal Pathway
(Spinothalamic)or(Anterolateral) system
Spinocerebellar Tracts - Unconscious Sensation
Dorsal Column-Medial Lemniscal Pathway
Carries sensory modalities of fine touch (tactile sensation), vibration and proprioception.
> spinal cord:information travels via the dorsal (posterior) columns.
> brainstem, it is transmitted through the medial lemniscus.
First, second and third order neurones are involved in this pathway
DC First order neurones
Carry sensory information= touch, proprioception or vibration from the peripheral nerves to the medulla oblongata.
X2 pathways first order neurones take:
Signals from the upper limb (T6 and above) - travel in the fasciculus cuneatus (the lateral part of the dorsal column). They then synapse in the nucleus cuneatus of the medulla oblongata.
Signals from the lower limb (below T6) - travel in the fasciculus gracilis (the medial part of the dorsal column). They then synapse in the nucleus gracilis of the medulla oblongata.
DC Second order neurones
Begin in the cuneate nucleus or gracilis.
The fibres receive the information from the preceding neurones, and delivers it to the third order neurones in the thalamus.
Within the medulla oblongata, these fibres decussate to the other side of the CNS.
They then travel in the contralateral medial lemniscus to reach the thalamus.
DC Third order neurones
Transmit the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain.
They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.
What the 2 tracts of the anterolateral tract
1) Anterior spinothalamic tract - carries the sensory modalities of crude touch and pressure.
2) Lateral spinothalamic tract - carries the sensory modalities of pain and temperature.
Also have first,second and third order neurones
AL First order neurones
Arise from the sensory receptors in the periphery.
They enter the spinal cord, ascend 1-2 vertebral levels, and synapse at the tip of the dorsal horn - an area known as the substantia gelatinosa.
AL Second order neurones
Carry the sensory information from the substantia gelatinosa to the thalamus.
After synapsing with the first order neurones, these fibres decussate within the spinal cord, and form two distinct tracts:
- Crude touch and pressure fibres - enter the anterior spinothalamic tract.
- Pain and temperature fibres - enter the lateral spinothalamic tract.
Functionally distinct, these tracts run alongside each other, and they can be considered as a single pathway.
Travel superiorly within the spinal cord, synapsing in the thalamus.
AL Third order neurones
Carry the sensory signals from the thalamus to the ipsilateral primary sensory cortex of the brain.
They ascend from the ventral posterolateral nucleus of the thalamus, travel through the internal capsule and terminate at the sensory cortex.
Name the Spinocerebellar tracts
1) Posterior spinocerebellar tract - Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum.
2) Cuneocerebellar tract - Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
3) Anterior spinocerebellar tract - Carries proprioceptive information from the lower limbs. The fibres decussate twice - and so terminate in the ipsilateral cerebellum.
4) Rostral spinocerebellar tract - Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
What does the Spinocerebellar tract transmit
Transmit unconscious information/ proprioception
Although we cannot physically acknowledge these signals, they help our brain co-ordinate and refine motor movements.
They transmit information from the muscles to the cerebellum.
What does the descending tracts carry
Motor signals are sent from the brain to lower motor neurones.
The lower motor neurones directly innervates muscles producing movement.
2 categories of descending tract
Origin and function
1)Pyramidal tracts - originate in cerebral cortex, carry motor fibres to the spinal cord and brain stem.
Responsible for voluntary control of musculature of the body and face.
2)Extrapyramidal tracts - originate in the brain stem, carry motor fibres to the spinal cord.
Responsible for the involuntary and automatic control of all musculature, such as muscle tone, balance, posture and locomotion
Do the descending tracts have synapses
What are the neurones in the descending tracts classified as
There are no synapses within the descending pathways.
At the termination of the descending tracts, the neurones synapse with a lower motor neurone.
Therefore: the neurones within the descending motor system= upper motor neurones.
Their cell bodies are found in the cerebral cortex or the brain stem, with their axons remaining within the CNS.
Pyramidal tracts function and 2 categories
Responsible for the voluntary control of the musculature of the body and face.
1) Corticospinal tracts - supplies the musculature of the body.
2) Corticobulbar tracts - supplies the musculature of the head and neck.
Corticospinal tract
- Begins in cerebral cortex = primary motor cortex
- Terminate spinal grey matter
75% decussate
Nerve fibres from the somatosensory area =regulate the activity of the ascending tracts.
Originate cerebral cortex, the neurones converge, and descend through the internal capsule (a white matter pathway, located between the thalamus and the basal ganglia).
What happens in the most inferior (caudal) part of the medulla
Tract divides into two:
Lateral corticospinal tract
Anterior corticospinal tract
1) Lateral = desiccated mainly one that crosses
2) Anterior = ipsalateral
Corticobulbar tract
Arises from the lateral aspect of the primary motor cortex.
Receive the same inputs as the corticospinal tracts.
The fibres converge and pass through the internal capsule to the brainstem.
Neurones terminate on the motor nuclei of the cranial nerves within brain stem:
synapse with lower motor neurones=carry the motor signals to the muscles of the face and neck.
Clinical importance corticospinal tract
Internal capsule is susceptible to compression from haemorrhagic bleeds, known as a -capsular stroke-.
Could cause a lesion of the descending tracts.
Clinical importance corticobulbar tract
Fibres innervate the motor neurones bilaterally.
E.g fibres from the left primary motor cortex act as upper motor neurones for the right and left trochlear nerves.
Exceptions to this rule:
Upper motor neurones for the facial nerve (CN VII) have a contralateral innervation. This only affects the muscles in the lower quadrant of the face - below the eyes.
Upper motor neurons for the hypoglossal (CN XII) nerve only provide contralateral innervation
Name the 4 extrapyramidal tracts
vestibulospinal
reticulospinal
rubrospinal
tectospinal
