Neuroanatomy Practical 2 Flashcards
Which of the 5 major subdivisions of the brain make up the brainstem?
Mesencephalon, metencephalon and myelencephalon
What fibres are found in the pyramids of the medulla?
- Descending motor fibres
- White matter
What are descending tracts?
The descending tracts are the pathways by which motor signals are sent from the brain to lower motor neurones. The lower motor neurones then directly innervate muscles to produce movement.
What can the descending motor tracts be divided into?
- Pyramidal
- Extra-pyramidal
Where do the pyramidal tracts originate? What are they responsible for?
- These tracts originate in the cerebral cortex (primary motor cortex - precentral gyrus), carrying motor fibres to the spinal cord and brain stem.
- They are responsible for the voluntary control of the musculature of the body and face.
Are there any synapses in the descending motor pathways?
No:
- At the termination of the descending tracts, the neurones synapse with a lower motor neurone.
- Thus, all the neurones within the descending motor system are classed as upper motor neurones.
- Their cell bodies are found in the cerebral cortex or the brain stem, with their axons remaining within the CNS.
Where do the pyramidal tracts derive their name from?
The pyramidal tracts derive their name from the medullary pyramids of the medulla oblongata, which they pass through.
Functionally, what can the pyramidal tracts be divided into
- Corticospinal
- Corticobulbar
Course of corticospinal tract explained
- Neurones originate in cerebral cortex
- Converge and descend through the posterior limb of the internal capsule
- Then pass through the crus cerebri of the midbrain, the pons and into the medulla.
- In the most inferior (caudal) part of the medulla, the fibres decussate (cross over to the other side of the CNS) –> decussation of pyramids
- Then descend into the spinal cord
What is the internal capsule?
a white matter pathway, located between the thalamus and the basal ganglia
Why is the internal capsule clinically important?
As the internal capsule is particularly susceptible to compression from haemorrhagic bleeds, known as a ‘capsular stroke‘. Such an event could cause a lesion of the descending tracts.
What structure is this?
Olfactory bulb and tract
What structure is this?
Optic nerve (attached to eye balls)
Where do the optic nerves converge?
At the optic chiasma (crossing over of fibres from either eye)
What is this?
Infundibulum (pituitary stalk) - connects the hypothalamus and the posterior pituitary gland.
The infundibulum, optic nerves and chiasma and mamillary bodies are all extensions of what?
Diencephalon
What structure is being pointed to?
Cerebral peduncle of midbrain (one on each side)
Diagram of pons and transverse pontine fibres. What does the pons connect?
The pons is a bridge that connects the cerebellar hemispheres
What sulcus is found here? What is found either side?
- Anterior median sulcus
- Pyramids either side
What is found lateral to the pyramids?
Olives (small bumps)
What is the medulla continuous with inferiorly?
Spinal cord
How does the spinal cord exist the cranium?
Foramen magnum
What is found just inferior to middle cerebellar peduncles?
- Flocculus (one on either side)
- These are pieces of cerebellar tissue
What is this?
- Cerebellar tonsil (one on each side)
- Project inferiorly and are closely related to medulla
View of optic nerves and chiasma
What is the function of the optic chiasm?
- Allows the visual cortex to receive the same hemispheric visual field from both eyes.
- 2 optic tracts then leave the optic chiasma and travels to its corresponding cerebral hemisphere
Where do the optic tracts travel to?
- Winds around thalamus
- Reach the lateral geniculate nucleus (LGN), a relay system located in the thalamus; the fibres synapse here.
- Axons from the LGN then carry visual information via a pathway known as the optic radiation.
Clearer view of cerebral peduncles
What is the space between the 2 cerebral peduncles called?
Interpeduncular fossa
Which nerve emerges between the pyramids and olives?
Root fibres of CN XII (hypoglossal)
Telencephalon has been removed and left with diencephalon. What are these 2 egg shaped structures?
One thalamus either side (bilateral egg shaped matters that sit on top of brainstem)
Which ventricle sits between the two thalami?
3rd ventricle
What are the mamillary bodies?
- Part of diencephalon
- Found on underside/ventral side of brain
- Paired - one on either side of brain
View of interpeduncular fossa and 2 cerebral peduncles (without telencephalon)
Which CN emerges from the interpeduncular fossa?
CN III oculomotor
What nerve stump is this?
Trigeminal
Which nerves emerge from the cerebellopontine angle?
CN VII and CN VIII
Cross section of midbrain
- Mickey mouse shape –> ears are the cerebral peduncles
- Space between ears –> interpeduncular fossa
- Can see oculomotor nerves emerging
Direction of fibres in cerebral peduncle vs pons?
Cerebral peduncle: horizontal
Pons: transverse pontine fibres
What structure is this? (cross section of midbrain)
Cerebral aquaduct
What is this darker area of the midbrain called? What can be found here?
- Substantia nigra / ‘black substance’
- Considered part of the basal ganglia
- Most of dopamine neurons of the brain can be found here
Where does the anterior median fissure disappear?
At decussation of pyramids
View of cerebellopontine angle (CN VIII being pointed to)
Cranial nerves emerging diagram