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
What nerve is being pointed to?
spinal accessory - travels upwards to join with cranial accessory (receives spinal nerve roots from spinal cord)
How does CN XI leave the cranium?
jugular foramen
Which nerve is this emerging from the dorsal aspect of the brainstem?
CN IV - trochlear
Which vessel is located besides the optic chiasm?
Internal carotid
Cranial nerves diagram 2
Clear view of cerebral aquaduct
Where does CN VI emerge?
At junction between pons and medulla - pontomedullary junction
What 2 main parts can the midbrain be divided into?
- Tectum –> located posterior to the cerebral aqueduct
- Paired cerebral peduncles –> located anteriorly and laterally
What four rounded prominences does the tectum house?
The superior and inferior colliculi
Which nerve emerges inferior to colliculi?
Trochlear nerve - wraps itself round brainstem to move anteriorly
View of floor of 4th ventricle –> if you follow probe it will connect to cerebral aquaduct
N.B. this is dorsal aspect of brainstem
What is the 4th ventricle continuous with inferiorly?
Central canal of medulla and spinal cord
What is point called where 4th ventricle ends and continous with central canal?
Obex
What is the midline structure of the posterior surface of the medulla?
Posterior median sulcus (continuous below as the posterior median sulcus of the spinal cord)
Where does the posterior median sulcus end superiorly?
at the point in which the fourth ventricle develops.
Open vs closed medulla
As we move lateral from the posterior median sulcus, what bumps are seen?
- Gracile fasciculus
- Brings ascending sensory fibres from body
- Dilates rostrally to form gracile tubercle
- Underlying this area is a nucelus (where ascending fibres connect and synapse)
- Cuneate fasciculus
- Contains ascending sensory fibres
- Dilates rostrally to form cuneate tubercle
What is a fasciculus?
bundle of white matter fibres
view of cuneate and gracile fasciculi
Are the cerebellar peduncles seen in doral or ventral view?
Ventral
When there is increased intracranial pressure, structures of the brain may be distorted and displaced.
- Herniation of the cerebellar tonsils would occur through which foramen?
- What brainstem structures would be compressed?
- Foramen magnum
- Medulla
How is the brainstem connected to the cerebellum?
Via 3 paired cerebellar peduncles
What structure is this? What does it connect?
Superior cerebellar peduncle –> connects cerebellum to midbrain
What structure is this? What does it connect?
Middle cerebellar peduncle - connects cerebellum to pons
What structure is this? What does it connect?
Inferior cerebellar peduncle - connects cerebellum to medulla
What structure is seen in midline of ventral cerebellum?
Vermis
More ventrally, what is this aspect of the vermis called?
Nodule
- The cerebellum is located at the back of the brain, immediately inferior to which lobes?
- How is it separated from these lobes?
- Which cranial fossa is it in?
- How is it separated from the pons?
- occipital and temporal lobes
- separated from these lobes by the tentorium cerebelli, a tough layer of dura mater.
- within the posterior cranial fossa
- ies at the same level of and posterior to the pons, from which it is separated by the fourth ventricle.
The cerebellum consists of two hemispheres which are connected by which structure?
Vermis (a narrow midline area)
The cerebellum can be divided into 3 anatomical lobes. What lobes are these? How are these lobes divided?
- Anterior
- posterior
- flocculonodular
These lobes are divided by two fissures – the primary fissure and posterolateral fissure.
What fissure is this? What does it separate?
NB. this is superior surface of cerebellum
Primary fissure - separates anterior and posterior lobe of cerebellum
Tonsils compressing medulla if herniation occurred
View of 2 vertebral arteries joining on ventral surface of pons to form basilar artery
Which arterial branches supply the cerebellum?
- PICA
- AICA
- SCA
Which branch is this? Where does it arise from?
PICA - arises from vertebral artery (paired) to supply posterior and inferior cerebellum
Which branch is this? Where does it arise from?
AICA - arises from basilar artery
Which branch is this? Where does it arise from?
SCA - arises from basilar artery
What does PICA supply?
- posteroinferior cerebellar hemispheres
- lower part of the medulla
Cross-section of upper midbrain (at level of superior colliculus)
Cross-section of lower midbrain (at level of inferior colliculus)
Cross section of upper pons
Cross section of mid pons
Cross section of lower pons
Cross section of upper medulla
Cross section of mid medulla
Cross section of lower medulla
What is this a cross section of?
- Midbrain
- Ventral region is interpeduncular fossa
- CN III emerges ventrally
- CN IV emerges dorsally
- Dorsal region is cerebral aquaduct
- Colliculi found dorsally
- Mickey mouse ears are cerebral peduncles
What is this a cross section of?
- Pons
- Basilar groove found ventrally (where basilar artery sits)
- 4th ventricle found dorsally
- Cerebellar peduncles found
- More caudal aspect of pons
What is this a cross section of?
- Open/rostral medulla
- 4th ventricle dorsally
- Pyramids and olives found ventrally
- Olives have characteristic squiggly squished feature
- Inferior cerebellar peduncle –> white matter found laterally dorsally
What is this a cross section of?
- Caudal/closed medulla
- Central canal
- Pyramids ventrally
- Cuneate tubercle dorsally and laterally to gracile tubercle
- Cranial CT shows a basal skull fracture extending through the jugular foramen
- Assuming that the nerve(s) that transverse this opening are damaged, what deficits are likely to be seen?
- CN IX, CN X and CN XI pass through jugular foramen
- Drooping and difficulty elevating shoulder (CN XI)
In a presentation of:
- Dilated right pupil
- Loss of most eye movement on right
- No other motor or sensory difficulties
What nerve is likely to be damaged?
Oculomotor CN III
The patient is attempting to retract both angles of the mouth and raise both eyebrows. Which cranial nerve has been damaged?
Right facial nerve
Which cranial nerve is damaged?
Left hypoglossal nerve
In the tearing/lacrimal reflex, where is the location of the postganglionic cell bodies that innervate the lacrimal gland?
Pterygopalatine ganglion
Which cranial nerves pass through the cribriform plate of the ethmoid mode?
CN I olfactory
Where are the true olfactory nerves (olfactory receptors) located?
Nasal epithelium
Which cranial nerves pass through the optic canal?
CN II optic nerve - passes through orbit
Which cranial nerves pass through the superior orbital fissure?
- CN III oculomotor
- CN IV trochlear
- CN V1 opthalmic branch
- CN VI abducens
Enter/leave the orbit
Which cranial nerves pass through the foramen rotundum?
CN V2
Which cranial nerves pass through the foramen ovale?
CN V3
Which cranial nerves pass through the internal acoustic meatus?
CN VII and CN VIII
- CN VIII then stays in petrous bone (here is where tiny structure of inner aer are located)
- CN VII then takes path within petrous temporal bone (giving off branches) and then leaves skull via stylomastoid foramen
Stylomastoid foramen
Which cranial nerves pass through jugular foramen?
CN IX, CN X, CN XI
Which cranial nerves pass through the hypoglossal canals?
CN XII
View of ventral surface of brain
What limb of the internal capsule do corticospinal fibres pass through?
Posterior limb
What is the crus cerebri?
the anterior portion of the cerebral peduncles which contains the motor tracts, travelling from the cerebral cortex to the pons and spine
