Topography of the Brain Flashcards
How is the structure of the brainstem similar to the structure of the spinal cord?
Like the spinal cord, the brainstem has central grey matter surrounded by peripheral white matter
What cranial nerve do not come off the brainstem?
Cranial Nerves 1 and 2
- Olfactory nerve
- Optic nerve
What (very basically) does the brainstem do/ give off?
Cranial nerves III-XII
-Brainstem uncle are involved with 10 of the 12 cranial nerves, so innervation of head and neck.
Tracts from Spinal Cord
-Pathway for fibre tracts running between higher and lower centres
Vital centres e.g. cardiorespiratory centre:
-BRAINSTEM CENTRES PRODUCE THE RIGIDLY PROGRAMMED AUTOMATIC BEHAVIOUS ESSENTIAL FOR SURVIVAL
What makes up the brainstem?
Medulla (inferiorly)
Pons (middle)
Midbrain (superiorly)
Where does the Medulla (oblongata) come from and what is its position?
Develops from hindbrain vesicle.
Cavity is the 4th ventricle
Continues as spinal cord at foramen magnum of cranium.
Lower part of medulla resembles spinal cord in structure
What are the surface features of the Medulla?
Pyramids (elevation of motor tract fibres)
Motor fibres start to cross lower down pyramid = decussation (crossing over)
Olives laterally
Connected to cerebellum by inferior cerebellar peduncle.
Cranial nerves IX, X, XI and XII from its surface
What are the 2 cross sectional parts of the medulla?
Caudal part = closed part
-Closed around IV ventricle
Cranial part = open part
-Open with IV ventricle posteriorly
What is contained in the white matter of the medulla?
-Pyramidal tract:
(tract with fibres going down)
-Medial lemniscus:
(tract with fibres going up)
Inferior cerebellar penduncle
Other tracts
What is contained within the grey matter of the medulla?
Cranial nerve nucleii
Inferior olivary nucleus
Nucleii of the reticular foramen
Sensory nucleii
(gracile and cuneate)
What are the Nucleii of the reticular foramen?
Contain vital centres
Set of interconnected nuclei that are located throughout the brainstem.
The neurons of the reticular formation all play a crucial role in maintaining behavioral arousal and consciousness
What is the inferior olivary nucleus?
Major source of input for the cerebellum
Where does the pons develop from?
Develops from the metencephalon part of hindbrain vesicle
What relation is the pons to the IV ventricle?
Pons is anterior to the IV ventricle
What are the surface features of the pons?
Middle cerebellar peduncle
Cranial nerves V, VI, VII and VIII originate from its surface
How does the middle tract differ in the pons compared to the medulla?
Tracts aren’t one complete structure
Motor fibre bindles separated by pontine nucleii
What are the contents of the pons white matter?
Middle cerebellar peduncle
Medial lemniscus (sensory)
Pyramidal tract (motor)
What are the contents of the grey matter of the pons?
Cranial nerve nucleii
Pontine nucleii
(involved in learning motor skills)
Nucleii of reticular formation
What does the midbrain develop from and what is in its central cavity?
Develops from the mesencephalon
Central cavity has the cerebral aqueduct
What are the surface features of the midbrain?
Cerebral peduncle
Superior cerebellar peduncle
Corpora quadrigemina
(superior and inferior colliculus)
Origin of Oculomotor (CN III) and Trochlear (CN IV)
How does the trochlear nerve (CN IV) differ from all the other nerve routes?
Only nerve to originate posteriorly
What is the corpora quadrigemina?
Made up of:
- Superior colliculi
- –Visual reflex
- Inferior colliculi
- –Auditory reflex
4 nodules at the posterior of the midbrain (bellow diencephalon and above superior cerebellar peduncle
What are the features of the midbrain section?
Central cavity contains the cerebral aqueduct (connects III and IV ventricles)
Periaqueductal grey matter with nucleus for III and IV cranial nerves
White matter embedded Nucleii surrounds the periaqueductal grey matter
Red nucleus (containing lots of iron)
Black bands of the substantial nigra can be seen in specimen
Give an introduction to the structure of the cerebellum
Right and left hemispheres separated by Vermis
Each hemisphere has an anterior, posterior and tiny flocculonodular lobe
Surface has sulci and folia
Three cerebellar peduncles connect it to brainstem
Cerebellar tonsils also present
What forms the grey and white matter of the cerebellum?
Grey matter:
- Cortex on surface
- Deep nucleii
White matter:
- Arbor vitae
- Cerebellar peduncles
What are the functions of the cerebellum?
Posture maintenance
Fine tuning motor activity
How does the cerebellum carry out its functions?
Information from:
- Pyramidal tracts (motor intention of brain)
- Ipsilateral proprioceptors from periphery
- Vestibular nucleii (regarding balance and posture)
Calculates best way to coordinate force, direction, extent of muscle contraction to maintain posture, prevent overshoot and ensure smooth coordinated muscle contraction.
Sends “blueprint” back to cerebral cortex via superior cerebellar peduncle
What will an abnormality/ damage to the cerebellum cause?
How do you clinically test this?
Ataxia = loss of control of co-ordination and balance
- Finger- nose test
- Knee-heel test
- Walking in a straight line
Where is the diencephalon?
Deep within cerebral hemispheres, around the III ventricle
What does the diencephalon develop from?
Diencephalic vesicle (part of forebrain vesicle)
What are the paired structures of the diencephalon?
Thalamus
Hypothalamus (and pituitary)
Epithalamus (pineal gland)
All are mainly grey matter
Where is the thalamus found?
Egg shaped body in either side of III ventricle.
Makes up 80% of diencephalon
Identify 3rd ventricle
Go outside of that
Thats the thalamus
What is the thalamus?
Mainly contains groups of nucleii
(anterior, medial and lateral group)
-A lot of synapsing
Lateral group are involved in processing sensory information
IT IS A SENSORY RELAY STATION
-all sensory information going to cerebral hemisphere has to synapse in the thalamus
Decides what to pay attention to and what to ignore
-Senses overloaded so thalamus decides what to zone in on
What is the hypothalamus?
It lies below the thalamus, separated from it by the hypothalamic sulcus.
Despite its small size, it is the main visceral control centre and is essential for overall homeostasis
What is the homeostatic role of the hypothalamus?
- Autonomic control centre
- Body temperature regulation
- Regulation of food intake
- Regulation of sleep wake cycle
- Control of endocrine system functioning
What arteries enter the skull to supply the brain?
The two internal carotid arteries enter the skull through the carotid canal (Foramen lacerum) to supply the brain.
The two vertebral arteries (branches of the subclavian artery) also enter the skull through the foramen magnum to supply the brain.
What branches of the internal carotid artery supply the brain?
The ICA gives off:
- Anterior cerebral artery
- Middle cerebral artery
- Posterior Communicating arteries
The ACA and MCA supply a large part of the cerebral hemisphere.
Describe the two vertebral arteries and its branches
The two vertebral arteries join together to form a basilar artery on the ventral surface of the brainstem.
The vertebro-basilar system gives branches that supply the brainstem and cerebellum.
The basilar artery finally ends at the level of the midbrain by dividing into 2 posterior cerebral arteries (PCA) which supplies the posterior part of the cerebral hemispheres
What is the circle of willis?
Branches of the ICA join with those of the opposite side and with the PCA (branch of the basilar artery) to form a continuous circle at the base of the brain.
This is a protective feature against vaso-occlusion of large arteries.
However the branches supplying the cerebral hemispheres, distal to the Circle of Willis are effectively “end-arteries”
What is the clinical significance of the circle of villi?
Helps against vast-oclusinve phenomena.
Proximal to the circle of Willis, vaso-occlusive phenomena can be bypassed by circle.
Distal to circle of villus the arteries are end arteries (do not anastomose).
A block here will cause that part of the brain to die.
Describe the cerebral blood supply
Anterior cerebral:
-Medial aspect of cerebral hemispheres excluding Occipital lobe
Middle cerebral:
-Lateral aspect of cerebral hemispheres
Posterior cerebral:
Inferior aspect of cerebral hemispheres and Occipital lobe
What is the venous drainage of the of the brain?
Superficial and deep veins of the brain drain into venous sinuses which lie between 2 layers of dura mater
The dural venous sinuses join together to ultimately drain into the Internal Jugular Veins
What is the cavernous sinus and why does it matter?
The cavernous sinus, is a large collection of thin-walled veins creating a cavity bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica.
A lot of nerves plus the ICA pass through here so if this area thromboses these structures could be affected
