Some main regions of the brain:
Cerebrum (two hemispheres)
Diencephalon (contains thalamus and hypothalamus)
Brainstem (Midbrain - Pons - Medulla)
Where are the ventricles found in the brain?
2 Lateral Ventricles are found within the cerebral hemispheres
The 3rd ventricle is found within the diencephalon
The cerebral aqueduct is contained within the midbrain
The 4th Ventricle is post to the pons & medulla and anterior to the cerebellum
What is contained within the ventricles?
Where is CSF made, travel and absorbed
- Produced in choroid plexus of ventricles
- Passes into subarachnoid space through foramina in the roof of the 4th ventricle
- Absorbed by arachnoid villi
- Passes into the sagittal sinus
What arteries supply the brain?
The ICAs & Vertebral Arteries
What is the function of the circle of willis and what arteries feed into it?
The circle of willis compensates for one vessel to the brain being blocked by allowing others to supply the same area.
Its fed by the two ICAs and the basilar artery (which is made by the 2 vertebral arteries)
What major vessels come off the circle of willis?
Anterior Cerebral Artery
Middle Cerebral Artery
Posterior Cerebral artery
Its worth noting there is no more anastomosis after the circle of willis (they are end arteries), so any blockage in this arteries or their branches will cause ischaemic stroke
Which artery supplies which part of the brain?
Brainstem - Basilar Art
Cerebellum - Basilar Art
- Ant Cerebral Art supplies the medial aspect
- Middle Cerebral Art Supplies the lateral aspect
- Posterior cerebral Art supplies the occipital lobe and much of the inferior aspect
Describe the venous drainage of the brain?
- > Deep Veins
- > Venous Sinuses
- > Internal Jugulars
Where do the venous sinuses lie?
Between layers of dura mater
Dura mater is two layers its just they’re always fused except at venous sinuses
What are the major venous sinuses of the brain?
Cavernous sinus Superior & Inf Sagittal Sinuses Transverse Sinus Straight Sinus Sigmoid Sinus Sup & Inf Petrosal Sinuses
Can you locate them all?
Where is the cavernous sinus?
Between the sphenoid and temporal bones.
Basically just under/lateral to the sella turcica
Where is the transverse sinus?
Runs in a transverse plane against the inf surface of the occipital bone
Where is the sigmoid sinus?
Curves in an S shape behind the petrous temporal bone.
It drains from the transverse sinus and becomes the IJV at the jugular foramen
What cranial nerves are given off by the brainstem?
III –> XII
What is the function of the brainstem?
- Give off cranial nerve 3-12
- Pathway for tracts running from higher brain centres
- Contains vital centres (Respiratory, cardiovascular)
How is the brainstem attached to the cerebellum?
By the Cerebellar Peduncle which is split into 3:
- Meddulla = Inf Cerebral Peduncle
- Pons = Middle Cerebral Peduncle
- Midbrain = Sup Cerebral Peduncle
Which section of the brainstem gives out which cranial nerves?
Higher the brainstem lower the cranial nerve.
Midbrain - 3 & 4
Pons - 5 –> 8
Medulla - 9 –> 12
What are the important surface features of the medulla?
Pyramidal projections run down the front of the medulla, they are motor fibre tracts.
The olives lateral to the pyramids at the top of the medulla
What happens to the medullla’s pyramids near the bottom?
Near the bottom of the medulla the pyramids cross over.
This is called the Decussation of the Pyramids
What ventricle is related to the brainstem?
Midbrain contains the cerebral aqueduct
The pons & medulla are ant to the 4th ventricle
Which cranial nerve is the only one to originate posteriorly?
The 4th (Trochlear) from the midbrain
What is the important surface anatomy of the midbrain?
Posteriorly you can see the sup & Inf Colliculi which are involved in the visual and auditory reflex
Function of the cerebellum?
Co-ordination and movement
Function of the Diencephalon?
Thalamus - Acts as a sensory relay centre
Hypothalamus - Involved in regulating the ANS, hormones, temperature and circadian rhythm
What makes up the Diencephalon?
A number of paired structures:
- Epithalamus (pineal Gland)
Whats the function/location of the thalamus
Its egg shaped on either side of the 3rd ventricle
Made up of ant/medial/lateral nuclei groups
Acts as a sensory relay station
Whats the function of the hypothalamus?
Below thalamus separated by the hypothalamic sulcus
Its essential for homeostasis:
- Controls the autonomic system
- Regulates body temp
- Regulates hunger and thirst
- Regulates sleep-wake cycle
- Controls the endocrine system
Describe the structure of the cerebellum?
- Connections to rest of brain
- Two hemispheres connected by a vermis
- Each hemisphere is split into ant/post/flocculonodular lobe
- Surface covered in sulci & Folia (Gyri)
- Connected to brainstem by inf/middle/sup cerebellar peduncles
- Undersurface has attached cerebellar tonsils
Whats the function of the cerebellum?
It gets info on proprioception, balance, posture and from the brain motor intention
Then it works out force, direction, extent of contraction to ensure smooth coordinated movement while maintaining posture and feeds it back to the cerebral cortex.
I.e. it fine tunes movement and maintains posture
What happens if theres damage to the cerebellum?
Ataxia - A lack of smooth voluntary muscle contraction
So the person can still make movements but without fine control so cant do:
- Finger Nose test
- Knee Heel Test
- Walking in a straight line
What connects the brainstem and the cerebrum?
The midbrain includes the cerebral peduncles which connect the pons to the thalami (and through that to the cerebrum)
What vessels come off the basilar artery?
The Superior cerebellar and Anterior Inferior Cerebellar come of the Basilar itself
The Posterior Inferior comes off the vertebral arteries prior to fusing to form the basilar artery