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Flashcards in Development and External Features of the Brain Deck (21)
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Gastrulation (week 3)

-Proliferation and migration of the epiblast to create the endoderm (first wave), mesoderm (second wave) and ectoderm (remainder)
-Brain and spinal cord from ectoderm


Neurulation (week 4)

-Mesoderm condenses to form notochord, which induces the overlying ectoderm to become the neural plate
-Neural plate will give rise to CNS
-Neural plate forms groove in middle and folds in on itself to form neural tube (becomes brain and spinal cord)
-Cavity in center of tube represents the future ventricular system
-Neural crest cells (multipotent) are from the dorsal-most portion of the neural folds and migrate away to become a variety of structures


Development of brain and brain stem: 3 vesicle stage

-The immature neural tube becomes segmented into the 3 vesicle stage: forebrain (prosencephalon), midbrain (mesencephalon), and hindbrain (rhombencephalon)
-The spinal cord is the remaining portion of the neural tube


Development of brain and brain stem: 5 vesicle stage

-At 5 weeks the neural tube becomes segmented into 5 parts (not including spinal cord)
-Forebrain becomes the telencephalon and diencephalon
-Mesencephalon is unchanged
-Hindbrain becomes the metencephalon and myelencephalon
-In the fully developed brain, the brain stem and spinal cord division is at the foramen magnum


Details of the 5 vesicle stage

-Telencephalon contains both cerebral hemispheres and the lateral ventricles. Becomes the cerebral cortex and basal ganglia
-The diencephalon contains the optic vesicle and third ventricle. Becomes the retina, thalamus, hypothalamus, and subthalamus
-The mesencephalon contains the cerebral aqueduct. Becomes the midbrain, superior and inferior collicullus
-The metencephalon and myelecephalon both contain the fourth ventricle
-Metencephalon becomes the pons and cerebellum
-Myelencephalon becomes the medulla


Surface anatomy of cerebral cortex

-Frontal cortex and parietal cortex separated by central sulcus
-Immediately anterior to the central sulcus is the precentral gyrus (part of frontal cortex), which is the primary motor cortex
-Immediately posterior to the central sulcus is the postcentral gyrus (part of parietal cortex), which is the primary sensory cortex
-Frontal cortex responsible for motor, judgement, abstract reasoning, and socially appropriate behavior
-Parietal cortex responsible for sensory integration
-Occipital cortex houses the visual cortex
-Temporal cortex associated w/ learning, memory, and emotion


Sulci separating the lobes

-Longitudinal fissure separates the L from the R side of the parietal, frontal, and occipital lobes
-Central sulcus separates the frontal and parietal lobes
-Lateral (horizontal) fissures separate the temporal lobe from the frontal and parietal lobes
-Parieto-occipital sulcus separates the occipital lobe from the parietal and temporal lobes



-Located btwn the cortex and brain stem, divided into 4 parts
-Thalamus: relays sensory info from PNS to cortex, integrates motor function of cortex w/ cerebellum and basal ganglia
-Hypothalamus: major role in regulating homeostasis
-Subthalamus: involved in motor control
-Epithalamus (pineal gland): circadian rhythms (melatonin)


Brain stem

-Composed of the midbrain, pons, and medulla
-Contains cranial nerve nuclei, ascending sensory tracts, descending motor tracts, and the reticular formation (RF, keeps us awake)



-Coordinates motor activity and is involved in motor learning
-Made up of 2 hemispheres and a midline vermis
-Separated from cortex by the tentorium
-Most inferior part is the tonsil, can become herniated w/ increased inter cranial pressure and compress part of the brainstem



-Cavity contained w/in each hemisphere is the lateral ventricle (LV)
-LV is continuous w/ the 3rd ventricle (in diencephalon) and the cerebral aqueduct/4th ventricle (in the brainstem)
-LV is divided into anterior horn (frontal lobe), body (parietal lobe), posterior horn (occipital lobe), and inferior horn (temporal lobe)
-Both LVs communicate w/ the single midline 3rd ventricle through the interventricular foramen (IVF, monro)
-Choroid plexus is present in body, atrium (near posterior horn), and inferior horn of LV


3rd, 4th ventricles and cerebral aqueduct

-3rd ventricle: slit-like cavity btwn the thalami and hypothalami of the two sides
-CSF in 3rd ventricles enters the 4th ventricle through the cerebral aqueduct
-4th ventricle is anterior to cerebellum and posterior to brainstem
-From the 4th ventricle the CSF leaves into the subarachnoid space through 3 different openings (1 midline and 2 lateral apertures)


Formation of the CSF

-CSF is an ultrafiltrate of plasma mostly formed by the choroid plexus (capillaries and pial connective tissue)
-Choroid plexus is found in every ventricle
-CSF made from choroid plexus involves passive diffusion and active secretion by choroid epithelial (ependymal) cells
-Flow of CSF: LV-> IVF-> 3rd V-> CA-> 4th V-> apertures-> subarachnoid space
-Drainage of CSF: in subarachnoid space CSF flows in an upward direction toward superior sagittal sinus (SSS), it is absorbed mostly by arachnoid granulations into cerebral venous sinuses


Function of CSF

-Prevent injury
-Maintain microenvironment for CNS, due to Blood-CSF barrier (BCB), which is the product of ependymal cell tight junctions in the choroid plexus (choroid plexus capillaries are fenestrated)
-BBB is tight junctions of endothelial cells lining capillaries (everywhere but choroid plexus)
-CSF transports elements to and from the brain (vitamins, glucose, waste products)


Hydrocephalus (water brain)

-Results from an obstruction to the flow of CSF
-Results in dilation of all ventricles and subarachnoid space proximal to the obstruction
-Obstruction can be in the ventricular system or in the subarachnoid space impairing CSF absorption


Wernicke's and Broca's areas

-Broca's area in the lateral part of the frontal lobe, just anterior to temporal lobe (usually left side of brain)
-Broca's area is the motor component of speech, damage causes broca's aphasia (can understand but not produce speech)
-Wernicke's area is in superior posterior temporal lobe, is the auditory association cortex (usually left side of brain)
-Damage to it produces wernicke's aphasia (cannot understand or produce speech)


Cingulate gyrus and corpus callosum

-On a saggital view of a full brain, the corpus callosum is on the superior surface of the lateral ventricle
-Directly superior to the corpus callosum is the cingulate gyrus, which is bordered on the superior side by the cingulate sulcus
-The corpus callosum is divided into 3 parts (from anterior-> posterior): genu, trunk, splenium


Fornix and anterior commissure

- Is the white matter tract that extends from the hippocampus to go underneath the corpus callosum and continue anterior/inferior to be the medial wall of the lateral ventricle
-The anterior commissure looks like a small round bulb at the end of the columns of the fornix, it connects the two anterior temporal lobes on each side


Primary visual cortex

-Within the occipital lobe, just deep to both sides of the calcarine sulcus
-The calcarine sulcus and the parieto-occipital sulcus form a Y-shape as the calcarine sulcus meets up w/ the parieto-occipital sulcus
-Just deep to both sides of the calcarine sulcus (both superior and inferior gyri) lies the primary visual cortex


Diencephalon location

-Thalamus is inferior to the body of the fornix, it is the largest part of the diencephalon
-Thalamus is on the inferior border of the body of the lateral ventricle
-The intraventricular foramen separates the thalamus from the hypothalamus, which lies just below and anterior to the thalamus



-Notable information about the brainstem
-Superior and inferior colliculi in the midbrain
-Decussation of cerebellar peduncles in lower midbrain (level of inferior colliculi)
-Middle cerebellar and superior cerebellar peduncles in the pons
-Once in the pons (at the level of the superior cerebellar peduncles) the STT and ML are located right next to each other (also are pretty close at level of middle cerebellar peduncles)
-Medullary pyramids (where CST/CBT decussate) in lowest level of medulla (where it joins the SC)

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