Topography of the Brain

Question 1

What are the parts of the brain?

Answer 1

cerebral hemispheres, cerebellum, diencephalon and brainstem (midbrain, pons, medulla oblongata)

Question 2

Where does the neural tube develop from?

Answer 2

the dorsal surface ectoderm and the cranial end forms vesicles each of which develop into different parts of the brain

Question 3

what are the 3 primary vesicles of the neural tube and what do they form?

Answer 3

forebrain= diencephalon and cerebral hemispheres - grows a lot more than the other vesicles 
midbrain= doesn’t grow a lot - forms the midbrain of the brainstem
hindbrain= pons, medulla and cerebellum

Question 4

What cranial nerves emerge from the brainstem and what does this mean?

Answer 4

3-12 which means that in the brainstem are cranial nerve nuclei and tracts passing up and down the spinal cord also pass through the brainstem

Question 5

What else does the brainstem contain?

Answer 5

vital centres which produce the rigidly programmed automatic behaviours essential for survival eg cardiorespiratory centres

Question 6

Where is and what are the features of the medulla?

Answer 6

lowest part of the brainstem and at the foremen magnum becomes the spinal cord- contains the 4th ventricle
has a groove down the anterior midline and pyramids (descending motor fibres) on either side with decussation at the lower part of the pyramids and olives laterally
it is connected to the cerebellum posteriorly by the inferior cerebellar peduncle and cranial nerves 9,10,11 and 12 arise from its surface

Question 7

Where is and what are the features of the pons?

Answer 7

middle part of the brainstem which is part of the hindbrain embryologically and so IV ventricle sits behind it
the middle cerebellar peduncle connects it to the cerebellum (the biggest of the peduncles) and cranial nerves 5,6,7 and 8 originate from its surface - 5=largest and 6,7,8 emerge from the pontomedullary junction

Question 8

Where is and what are the surface features of the midbrain?

Answer 8

most superior part of the brainstem - contains the cerebral aqueduct which connects the 3rd and 4th ventricles - posteriorly there are 4 colliculi: superior 2= visual reflex and inferior 2= auditory reflex - cranial nerves 3 and 4 originate from it and 4 is the only nerve to originate posteriorly- 2 bands of fibres anteriorly are they cerebral peduncles and carry the same motor fibres as the pyramids and it is attached to cerebellum by the superior cerebellar peduncle

Question 9

How is the cerebellum connected to the brainstem?

Answer 9

3 cerebellar peduncles connect the anterior brainstem to the posterior cerebellum

Question 10

Describe the distribution of grey and white matter in the cerebellum.

Answer 10

grey matter is on the surface and surrounds the central white matter but within this white matter are collections of grey matter called deep cerebellar nuclei and there are branches of white matter which project outwards which are called arbor vitae

Question 11

What are the lobes and hemispheres of the cerebellum and what separates them and what are the groove and elevations called?

Answer 11

2 cerebellar hemispheres which are connected by the vermis- each hemisphere has an anterior and larger posterior lobe and very small flocculonodular lobe - grooves= sulci and elevations= folia

Question 12

What is the part of the cerebellum that protrudes underneath the rim of the foramen magnum?

Answer 12

cerebellar tonsil which can herniate if there is increased ICP

Question 13

what are the functions of the cerebellum?

Answer 13

posture maintenance and fine-tuning motor activity —> information from the pyramidal tracts tells the cerebellum what the cerebrum is planning, information from the ipsilateral proprioceptors from the periphery and information from the vestibular nuclei giving information on balance and posture —> calculates best way to coordinate force, direction and extent of muscle contraction to maintain posture, not to overshoot and ensure smooth muscle contraction —> sends blueprint back to the cerebral cortex via the superior cerebellar peduncle to correct information leaving

Question 14

What happens if the cerebellum is not functioning properly?

Answer 14

the patient will not have smooth, coordinated movement = ataxia

Question 15

Where is the diencephalon found and what are its features?

Answer 15

deep within the cerebral hemispheres around the 3rd ventricle and just superior to the brainstem- it is made up of the thalamus, hypothalamus just inferiorly and pineal gland - there is no white matter only grey

Question 16

What is the role of the thalamus?

Answer 16

lots of things are happening at the same time and the thalamus decides which of these are important and need to be sent to the cerebral hemispheres for attention immediately- both special and general sensory information always synapse in the thalamus

Question 17

How are the thalamus and hypothalamus separated?

Answer 17

hypothalamic sulcus

Question 18

What connects the hypothalamus to the pituitary gland?

Answer 18

the pituitary stalk

Question 19

What is the role of the hypothalamus?

Answer 19

main visceral control centre and is essential for overall homeostasis- body temperature regulation, regulation of food intake etc

Question 20

Where do the 2 ICA enter the skull?

Answer 20

through the carotid canals which are in the smooth part of the foramen lacerum

Question 21

Where do the 2 vertebral arteries enter the skull and what do they join to form?

Answer 21

through the foramen magnum and form the basilar artery which passes up the anterior border of the brainstem giving off many arteries which supply the it before splitting into the 2 posterior cerebral arteries

Question 22

What are the vertebral arteries branches of?

Answer 22

The subclavian arteries

Question 23

What is the circle of Willis?

Answer 23

continuous circle at the base of brain made of arteries supplying the brain- it is a protective feature against vaso-occlusion of large arteries as if one gets blocked then the circle will compensate and still supply the brain with blood unless “end-arteries” which are distal to the circle which lead to ischaemia and brain damage as there is no circle to compensate

Question 24

Describe the circle of Willis.

Answer 24

the basilar artery formed by the 2 vertebral arteries splits into the 2 posterior cerebral arteries and the 2 ICAs become the anterior and middle cerebral arteries- the ACA and PCA are joint by the posterior communicating artery and the 2 ACAs are joint anterioly by the small anterior communicating artery

Question 25

where does the anterior cerebral artery supply?

Answer 25

the medial aspect of the cerebral hemispheres excluding the occipital lobe

Question 26

where does the middle cerebral artery supply?

Answer 26

the lateral aspect of the cerebral hemispheres

Question 27

where does the posterior cerebral artery supply?

Answer 27

the inferior aspect of the cerebral hemispheres and the occipital lobe

Question 28

where do both the deep and superficial veins of the brain drain?

Answer 28

the venous sinuses which lie between the 2 lates of dura matter - these dural venous sinuses join together to ultimately drain into the IJVs

Question 29

what are the sinuses of the brain and where are they found?

Answer 29

the superior sagittal sinus= upper border of the falx cerebri
inferior sagittal sinus= lower border of falx cerebri where it is continuous with the tentorium cerebelli and takes you posteriorly to the confluence of the 2 sinuses
cavernous sinus= sits either side of the pituitary body which cranial nerves and the ICA pass through