Topography of the Brain Flashcards
Neurulation
The process by which the neural plate becomes the neural tube. The mesoderm and the ectoderm form the neural tube
- folding occurs in the middle then anteriorly than posteriorly
- during folding the mesoderm forms somites which develop into the 33 individual vertebrae of the spinal column and related skeletal muscles
- nerves that innervate these skeletal muscles are called somatic nerves
- Folic acid is essential for this process
What are the layers of the Neural tube?
- Neural Crest cells
- Mantle Layer
- Ependymal layer
- Lumen
Anencephaly
- the failure of the anterior neural tube to close
- results in the degeneration of the forebrain, as it herniates out of the foetus
- always fatal
Spina bifida
- Failure of the posterior neural tube to close
- leads to an open vertebral canal
- Failure of the posterior neural tube to close
- most severs is when posterior spinal cord fails to form from the neural plates (Spina Bifida Cystic)
- the meninges projects out posterior from the spinal cord: can be filled the cerebrospinal fluid
- less severe cases present as defects in the meninges and vertebrae overlying the posterior spinal cord (Spina Bifida Occulta)
Primary Brain Vesicles
These develop at the rostral end of the neural tube
- Prosencephalon (forebrain)
- Mesencephalon (midbrain)
- Rhimbencephalon (hindbrain)
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Secondary brain Vesicles
From the Prosencephalon
- Telencephalon
- Cerebrum
- Diencephalon
- Eye Cup
- Thalamus (hypo, epi)
From the Mesencephalon
- Mesencephalon
- Midbrain
From the Rhomencephalon
- Metencephalon
- Pons
- Cerebellum
- Myecenphalon
- Medulla oblongata
the Adult Brain
- Frontal Lobe
- Parietal Lobe
- Temporal Lobe
- Occipital Lobe
- Cerebellum
Grey Matter
- mainly neuronal cell bodies i.e cereberal cortex, brain nuclei
White Matter
- myelinated neurons
Telencephalon- Cerebral hemispheres
- Frontal Lobe
- Parietal Lobe
- Occipital Lobe
- Temporal Lobe
- folded to form gyri and sulci
The Cerebral cortex
- Central Sulcus
- Lateral Sulcus
- Precentral gyrus
- Postcentral gyrus
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Corpus callosum
- Seen as a large C-shaped tract of white matter when a midsagittal cut is made
- connects the two cerebral hemispheres of the brain
- the Coronal radiator is seen in a coronal view of the brain
- all the wires connecting the brain together
- has a Genu, Body and Splenium
- Genu- many motor axons, connecting the motor regions
- Body- many sensory axons, connecting the sensory areas of the brain
Limbic System
a deep brian structure which controls memory and emotion
- spans the telencephalon and diencephalon*
- Cingulate cortex
- Fornix
- Amygdala
- Hippocampus
- Thalamus*
- Hypothalamus*
- Mamillary bodies*
Fornix
- a semicircular white matter tract that connects hippocampus and the mamillary bodies
- from the hippocampus passes posteriorly in a curve then superiorly through the third ventricle, over the top of the third ventricle then drops down anteriorly to join with the mammillary bodies
- it is part of the limbic system (the telencephalon part)
Basal Ganglia
sits in the base of the forebrain
a deep brain structure involved in the control of posture and voluntary movement
the Corpus striatum refers to the two main nuclei that forms the basal ganglia
- lentiform nucleus (lens shaped)
- Putamen: the outer part
- Globus pallidus: the inner part
- caudate nucleus (C-shaped)
- follows the shape of the lateral ventricle wall
- moves anteriorly to the inferior horn of the lateral ventricle
The Capsules
- Internal Capsule
- major white matter tracts in the brain that connects the cerebral cortex to the brainstem
- internal to the lentiform nucleus
- External capsules
- external to the lentiform nucleus
- The Extreme capsule is really small and is after the external capsule closer to the lateral sulcus
Diencephalon
Sits in the middle of the brain
- Thalamus
- Hypothalamus
Thalamus
a paired structure that is part of the diencephalon
- the paired structures are connected by an inter-thalamic adhesion through the third ventricle
- relays sensory info to the cortex
- olfactory information doesn’t go through the thalamus
- involved in voluntary movement, personality and consciousness
Hypothalamus
part of the diencephalon found inferior to the thalamus
- involved in homeostasis
- coordinates ANS and endocrine response
- connected directly to the pituitary gland (infundibulum connects them)
- thermoregulation, feeding, drinking, circadian rhythms
- near the pineal gland (melatonin released)
- receives inputs from the limbic system
- coordinates ANS and endocrine response
- Sits between he optic chiasm ad the mammillary bodies
Mamillary bodies
- brainstem nuclei on the posteroinferior aspect of the hypothalamus
- attaches tot he fornix
- associated with recollective memory
Mesencephalon and Rhombencephalon
together they form the brainstem and cerebellum
- Metencephalon
- forms the Pons/ Cerebellum
- A pontine flexure causes the cerebellum to be posterior to the brainstem around day 36 of embryonic development
- forms the Pons/ Cerebellum
- Myelencephalon
- forms the Medula
are both part of the rhombencephalon
Brainstem (Medulla)
Contains:
- cranial nerve nuclei within all three regions
- vital respiratory and cardiovascular centres
- vomiting centre
- nuclei involved with motor control, sleep
- white matter tracts
The Telencephalic and the Diencephalon Differentiation
the telencephalon is the anterior part of the brain, which is also called the cerebrum, while the diencephalon is the part of the brain that is placed between the telencephalon and the midbrain
The Lateral Ventricles
- there are two c-shaped ventricles, one for each ventricle
- Formed of
- Body: occupies the parietal lobe
- Anterior horn: frontal lobe
- Posterior horn: occipital lobe
- Inferior horn: temporal lobes
- The Septum pellucidum separates the lateral ventricles
- and the Corpus Callusom sits in the roof
Borders of the lateral ventricles
- Caudate nucleus sits in the lateral wall
- the hippocampus sits in the floor of the inferior horn
What is the Intraventricular foramen
- the communication centre between thew lateral ventricles and the third ventricle
- aka Foramen of Monro
The Third Ventricle
(position)
The third ventricles appear as a slit-like cleft
- the Thalami sit in the lateral walls
- the Fornix forms the roof
What is the Cerebral aqueduct
- The communication channel between the third and fourth ventricle
- aka Aqueduct of Sylvius
- this structure is surrounded by the midbrain
Borders of the Fourth Ventricle
- surrounded by the hindbrain
- The cerebellum is bordering it posteriorly
- Pons and the Medulla border it anteriorly
- Cerebellar peduncles border it laterally
- it is continuous with the central canal of the spinal cord and the subarachnoid space
Communication in the Fourth ventricle
- three foramen exit into the subarachnoid space into the Cisterna Magna
- two Foramen of Luschka (laterally, posterior to the cerebellar peduncles)
- one Foramen of Magendie (in the middle)
What is the Choroid plexus?
- the choroid plexus produces CSF
- the choroid plexus presents throughout the ventricles
- it is a capillary network surrounded by cuboidal epithelium
- filters blood from branches of the internal carotid and basilar arteries
- blood is filtered through fenestrated capillaries
- components transported through the cuboidal epithelium into ventricles
Structure of the choroid plexus
- Fenestrated capillaries: act as a filter
- Cuboidal epithelium: act as transport
- Tight junctions between epithelial cells
- prevent macromolecules from entering the CSF
- permeable to water and CO2
- This forms part of the blood-CSF barrier
The composition of CSF and it’s difference from blood plasma
- the CSF has a significantly lower protein content
- slightly lower pH, glucose content, Ca2+ and K+
- slightly higher, Mg2+, Cl-
- these conditions are ideal for the functioning of neurons.
Describe the direction of circulation in the CSF within the ventricles
- From the lateral ventricles, through the interventricular foramen to the
- Third ventricle, then through the Cerebral Aqueduct to the
- The fourth ventricle, then through the Luschka and Magendie foramina to the
- Cisterna manga (the Subarachnoid space)
Describe the CSF circulation within the subarachnoid space
The Arachnoid Granulations
- Herniations of arachnoid membrane (villi) through dura mater into venous sinuses
- Mainly within the superior sagittal and transverse venous sinuses
What is non-communicating hydrocephalus?
- Blockage within the ventricular system
- Due to tumour, cyst, stenosis (e.g. narrowing of the cerebral aqueduct)
- CSF does not circulate over the surface of the brain
Treatment:
- Surgery: insert a shunt to reduce intracranial pressure
What is Dandy-Walker Syndrome?
- Congenital malformation of the cerebellum (1:30,000 births)
- Obstruction within foramina of the fourth ventricle:
- Symmetrical dilation of lateral, third and fourth ventricles
- In infancy, head may become enlarged
What is communicating hydrocephalus
- Obstruction in the arachnoid villi
- Movement of CSF into venous sinuses is impeded
- E.g. Impaired absorption following subarachnoid haemorrhage, trauma or bacterial meningitis
