Flashcards in 10/9 - Structural Organization of the Forebrain Deck (71):
The 3 DIVISIONS of the FOREBRAIN
1. CORTICAL – Thin Outer Mantle of Grey Matter
2. SUBCORTICAL – Collection Of Nuclei In Deep White Matter Below Cortex.
These Consist Primarily Of Nuclei Called The Basal Ganglia.
3. LIMBIC – Hippocampus, Amygdala
ASSOCIATED FIBER TRACTS of the FOREBRAIN:
Superior Longitudinal Fasciculus
BORDERS of the FRONTAL LOBE
FRONTAL POLE OF BRAIN
BORDERS of the PARIETAL LOBE
LINE BETWEEN BASE OF CORTEX AND PARIETO-OCCIPITAL SULCUS
BORDERS of the OCCIPITAL LOBE
LINE BETWEEN BASE OF CORTEX AND PARIETO-OCCIPITAL SULCUS
BORDERS of the TEMPORAL LOBE
NO CLEAR DEMARCATION BETWEEN PARIETAL LOBE AND OCCIPITAL LOBE POSTERIORLY
PRIMARY MOTOR CORTEX.
Gyri immediately anterior to PRIMARY MOTOR CORTEX are supplementary motor areas.
In the Frontal Lobe.
INFERIOR FRONTAL Gyri
Includes Broca’s area for motor control of language production (on left)
DIVISIONS of the FOREBRAIN
The forebrain divides into 3 general regions including the outer mantle of grey matter called the cortex.
Internal to the cortex is the white matter consisting of axons traveling to and from the cerebral cortex. Deep in the white matter, several areas of grey matter are evident. These collectively are called subcortical nuclei.
Structures related to the limbic system include the hippocampus and amygdala, both of which are located in the temporal lobe.
Finally, there are fiber tracts that connect different parts of the cerebral cortex.
MAJOR SULCI OF LATERAL CORTEX
To define the lobes, we must identify some of the major depressions or sulci that form the borders of the different lobes.
The most obvious depression is the lateral sulcus, which seems to split the brain almost in half in the horizontal plane.
The central sulcus seems to divide the brain in half in the transverse plane. The central sulcus does not quite reach the lateral sulcus and there is always a small bridge of cortex that separates them.
The depression rostral to the central suclus is the precentral sulcus, whereas the depression immediately caudal to the central sulcus is the postcentral sulcus.
A very short, shallow sulcus near the caudal pole of the cerebral cortex is the parieto-occipital sulcus.
LATERAL CEREBRAL CORTEX - LOBES
The most anterior part of the brain is the frontal lobe. It extends from the frontal pole of the brain to the central sulcus.
The parietal lobe extends from the central sulcus to the parietal occipital sulcus. On the lateral aspect of the brain, there is no clear separation between the parietal lobe and the occipital lobe, the most caudal pole of the telencephalon. An imaginary line may be drawn from the dorsal point of this sulcus to the base of the hemisphere to better define the separation between the parietal lobe and the occipital lobe.
The temporal lobe is the area below the lateral sulcus. There is no clear demarcation between the temporal lobe and the parietal and occipital lobes posteriorly.
These areas interact to correlate visual, sensory, and auditory information to interpret the world.
Most anterior portion of the frontal lobe
PRIMARY SENSORY CORTEX
More posterior gyri are sensory association areas: spatial orientation and directing attention.
In the Parietal lobe
the central sulcus
An anatomically and functionally important infolding of the cerebral hemisphere, beginning just medial to the superior border of the hemisphere, proceeding over its superior margin, and descending obliquely forward almost to the lateral sulcus.
The central sulcus is the boundary between the frontal and parietal lobes, and the transition zone between primary motor and primary somatosensory cortex.
Primary auditory cortex
Posterior part related to interpretation of language – Wernicke’s area
In the Temporal Lobe.
LATERAL OCCIPITAL GYRI
Visual association areas
LATERAL CEREBRAL CORTEX - GYRI
Gyri extend down into the sulci.
In the frontal lobe, the prominent Precentral Gyrus is located between the central and precentral sulci. This is the primary motor cortex where voluntary movements are initiated. The area immediately anterior to this gyrus are supplementary motor areas that are involved in planning movements.
The most rostral part of the frontal lobe is the prefrontal cortex. It can be divided into inferior frontal which contains Broca’s area, which is essential for generating speech.
The most rostral part of the frontal lobe is the Orbital Cortex and is involved in decision making, memory, personality, etc.
Between the central and postcentral sulcus is the postcentral gyrus. This is primary sensory cortex. More posterior gyri are association areas and are involved in spatial orientation, and sterognosis.
The area immediately inferior to the lateral sulcus is the superior temporal gyrus which is involved in processing auditory information. The posterior portion of this gyrus is called Wernicke’s area and it is essential for interpreting speech.
Finally most caudally are lateral occipital gyri. These are visual association areas.
BURIED DEEP IN THE LATERAL SULCUS. COVERED BY GYRI FROM THE TEMPORAL, PARIETAL AND FRONTAL LOBES.
CONTAINS GUSTATORY, AUTONOMIC, PAIN, VESTIBULAR AREAS.
Area of cortex on the lateral surface. This part of the cortex is not visible unless the temporal and parietal lobes are separated. This deeply buried cortex is the Insular cortex. In transverse/horizontal sections, it can be recognized as the deep cortex covered by the temporal and parietal lobes.
MAJOR SULCI OF MEDIAL CORTEX
The medial surface of the cortex.
The cingulate sulcus defines cortical tissue immediately above the corpus callosum.
Caudally, we now see a defined parieto-occipital sulcus that separates the parietal and occipital lobes.
In the occipital lobe, the large calcarine sulcus divides the lobe into dorsal and ventral halves.
MEDIAL CEREBRAL CORTEX LOBES
The lobe located immediately below the cingulate sulcus is the Cingulate or limbic lobe. This is part of the allo or old cortex.
This is the only new addition with respect to lobes.
MEDIAL CEREBRAL CORTEX
The cingulate lobe is also called the cingulate gyrus. It is related to the frontal lobe, the parietal lobe and the temporal lobe. Functionally, it is part of the limbic system.
The portion in the temporal lobe is the parahippocampal gyrus. Para means “next to,” and it is next to a limbic structure called the hippocampus.
At the rostral end of the parahippocampal gyrus there is a swelling called the uncus. This is related to the amygdala, another part of the limbic system. This bump is clinically important.
In the occipital lobe, 2 gyri may be identified on either side of the calcarine sulcus: the cuneus and the lingual gyri. These are visual association areas. So where is primary visual cortex? It is buried deep in the calcarine sulcus.
Related to limbic system
Related to the frontal lobe, the parietal lobe, and the temporal lobe
Is continuous with cingulate gyrus at posterior end of corpus callosum.
parahippocampal gyrus: portion of the temporal lobe. Para means “next to,” it is next to a limbic structure called the hippocampus.
At the rostral end of the parahippocampal gyrus, there is a swelling called the uncus.
Anterior End Parahippocampal Gyrus
Visual association cortex
In the occipital lobe, 2 gyri may be identified on either side of the calcarine sulcus – the cuneus and the lingual gyri. These are visual association areas.
Primary visual cortex
located on walls calcarine sulcus
buried deep in the calcarine sulcus and not visible on the gross brain.
HISTOLOGY OF CEREBRAL CORTEX:
NEURONAL ORGANIZATION OF CEREBRAL CORTEX
The outer mantle, consisting of neurons that are distributed in 3-6 layers, is very thin measuring 1.5-4.5 mm.
There are 10-15 billion neurons, 50 billion glial cells, 100,000 km of axons, and 10^14 synapses in the cerebral cortex.
Highly infolded. If laid out flat it would be ~2 square feet. About 1/3 of cortex is visible and 2/3 is located in sulci and fissures
DIVISIONS OF THE CORTEX
Neocortex: Represents 90 -95% Of The Cortex In Humans. All Of The Cortex That Is Seen On Outside Of Brain.
Most Recently Evolved Cortex; Plays a critical role in abilities and activities that reach highest level of development in humans.
Archicortex: (i.e., Hippocampus)
Paleocortex: Parahippocampal Gyrus Of Temporal Lobe, Olfactory Cortex, Cingulate Cortex.
found in more primitive species.
It basically consists of limbic and olfactory centers, including the hippocampus and cingulate cortices.
Represents 90 -95% Of The Cortex In Humans.
All Of The Cortex That Is Seen On Outside Of Brain.
Most Recently Evolved Cortex: Plays a critical role in abilities and activities that reach highest level of development in humans.
that part of the cerebral cortex that, with the palaeocortex, develops in association with the olfactory system and is phylogenetically older than the neocortex and lacks the neocortex's layered structure.
Parahippocampal Gyrus Of Temporal Lobe,
that portion of the cerebral cortex that, with the archicortex, develops in association with the olfactory system and is phylogenetically older and less stratified than the neocortex.
It is composed chiefly of the piriform cortex and the parahippocampal gyrus.
The phylogenetically oldest part of the cortical mantle of the cerebral hemisphere, represented by the olfactory cortex.
The cerebral cortex is the outermost part of the telencephalon. It is very thin, measuring only 1.5-4.5 mm. This area contains all of the neurons that are essential for interpreting sensory information, generating voluntary motor activity, speaking, personality, making executive decisions, memory, etc. There are 10-15 billion neurons and 50 billion glial cells in the cerebral cortex. Appreciate that there are a lot of neurons and glia in the telencephalon. Given the large number of neurons, one might wonder how they all fit. It turns out nature solved that problem by highly infolding the cerebral cortex giving it the bumpy appearance. If it was laid out flat, it would measure 2 sq feet, about the size of a open newspaper. Only 1/3 of the cortex is visible, the rest is buried in the trenches or sulci.
The cortex may be divided into neocortex, which is the most recently evolved and is essential for allowing us to do those things only humans do. Neocortex consists of 6 layers.
The allocortex is much older and is found in more primitive species. It basically consists of limbic and olfactory centers including the hippocampus and cingulate cortex.
_______ IS THE PRIMARY OUTPUT NEURON OF THE CORTEX
CORTEX IS MADE UP OF PYRAMIDAL AND NON-PYRAMIDAL CELLS
PYRAMIDAL CELLS ARE THE PRIMARY OUTPUT NEURONS OF THE CORTEX
There are many different types of neurons in the cerebral cortex organized into ____ layers.
There are many different types of neurons in the cerebral cortex organized into 3-6 layers.
There are ___ layers in the neocortex and ___ layers in the allocortex
There are 6 layers in the neocortex and 3 layers in the allocortex
Across the neocortex, layers ____ equal. This leads to ______.
Across the neocortex, layers are not equal. This leads to cytological differences.
AFFERENTS TO CEREBRAL CORTEX
1. association fiber
2. commissural fiber
3. specific thalamocortical fiber
4. non-specific thalamocortical fiber
Input from the thalamus carrying specific sensory information terminates in layer _____.
Thus, areas of the cortex that receive primary sensory information will have a proportionally ___ layer ___ than association areas.
Input from the thalamus carrying specific sensory information terminates in layer IV. Thus, areas of the cortex that receive primary sensory information will have a proportionally larger layer IV than association areas.
EFFERENTS FROM THE CEREBRAL CORTEX
1. Corticofugal Fiber: Projection Fiber
2. Corticocortical Fiber
Corticofugal Fiber - Projection Fiber
Projections to other parts of the CNS arise from neurons in layer ___ including corticospinal/bulbar, corticopontine, and cortcostriate.
Thus, areas that give rise to major ____ (i.e., motor cortex) will have a larger layer ____ .
Projections to other parts of the CNS arise from neurons in layer V including corticospinal/bulbar, corticopontine, and cortcostriate.
Thus, areas that give rise to major outputs (i.e., motor cortex) will have a larger layer V.
Projections to other parts of the cerebral cortex arise from neurons in layer ____, including association and commissural fibers.
Projections to other parts of the cerebral cortex arise from neurons in layer III including association and commissural fibers.
ALL AFFERENTS AND EFFERENTS RELATED TO THE CORTEX TRAVERSE THE ______ .
ALL AFFERENTS AND EFFERENTS RELATED TO THE CORTEX TRAVERSE THE INTERNAL CAPSULE.
DESCENDING FIBERS INCLUDE:
Corticospinal/bulbar Axons Corticopontine
ASCENDING FIBERS INCLUDE:
Tracts Terminating In Thalamus
INTERNAL CAPSULE AND CORONA RADIATA
The last major fiber tract to define is the internal capsule. It is the pathway used by all afferent and efferent axons related to the cerebral cortex. The internal capsule separates the caudate and putamen rostrally. This is called the anterior limb of the internal capsule. Caudally, the internal capsule separates the thalamus from the basal ganglia. This is called the posterior limb of the internal capsule. Within the internal capsule, axons descend from the cortex to the brainstem or spinal cord or to the subcortical nuclei such as those to the basal ganglia (called corticstriatal).
Also present are ascending axons from the thalamus to the cortex. Tracts that terminate in the thalamus will also be present in this large fiber bundle.
The portion of the internal capsule between the anterior and posterior limbs is called the genu, as there is a slight bend here. Axons that course posterior to the globus pallidus are referred to as retrolenticular.
THINK OF A FUNNEL FROM THE CORTEX TO THE BRAINSTEM
The internal capsule separates the ___ and ____ rostrally.
The internal capsule separates the caudate and putamen rostrally.
KORBINIAN BRODMANN 1868-1918
USED DIFFERENCES IN CYTOLOGICAL ORGANIZATION OF THE CORTEX TO DEFINE AREAS – BRODMANN AREAS
a neurologist in the late 1800s.
He organized the brain into functional areas based on the thickness of the various layers in different regions. Based on this analysis he came up with approximately 46 specific regions. Some are used commonly in clinical settings as well as in other presentations in this block. You will not be asked to identify a specific area on an exam; but be familiar with some of these numbers, as they will come up again.
link similar parts of the cortex on two sides.
They cross the midline, linking the right and left hemispheres.
Generally, they link related areas.
The major fiber bundle that mediates these linkages is the corpus callosum.
This fiber tract links the frontal, parietal, caudal temporal, and occipital lobes.
The rostral and inferior parts of the temporal lobe have their own fiber tract to link them called the anterior commissure.
Links related areas of inferior temporal lobe
CORPUS CALLOSUM – DIFFUSION TENSOR IMAGING
Largest fiber bundle:
250 million axons
Nearly all cortical areas contribute axons
Intrahemishperic tracts link cortical areas on the same side.
SUPERIOR LONGITUDINAL FASCICULUS
Links Broca’s and Wernicke’s language areas
Links Broca’s and Wernicke’s language areas
SUPERIOR LONGITUDINAL FASCICULUS
The area Carl Wernicke discovered was located in the junction of the parietal lobe and the temporal lobe. This is Wernicke’s area. Given it’s relationship to the primary auditory cortex, damage to this region results in the patient’s not being able to recognize the spoken word. In some cases, if more of the visual cortex is involved, they may not be able to recognize written words, which is called alexia.
GLOBUS PALLIDUS, INTERNAL SEGMENT
GLOBUS PALLIDUS, EXTERNAL SEGMENT
Nuclei located below the cerebral cortex are the subcortical nuclei. For the most part, these nuclei are all related to a complex called the basal ganglia which are part of the motor system. These are the nuclei that are involved in Parkinson’s and Huntington’s disease. They also play a critical role in addiction.
Another group is related to the limbic system which is involved in memory, learning, and emotions. The hippocampus is located deep in the temporal lobe.
1. CAUDATE NUCLEUS
3. GLOBUS PALLIDUS, INTERNAL SEGMENT
4. GLOBUS PALLIDUS, EXTERNAL SEGMENT
The basal ganglia are part of the motor system. These are the nuclei that are involved in Parkinson’s and Huntington’s disease. They also play a critical role in addiction.
The limbic system is involved in memory, learning, and emotions. The hippocampus is located deep in the temporal lobe.
Collection Of Nuclei That Modulate The Output Of The Frontal Cortex Including Areas Related To Movement (Motor Cortex) As Well As Cognition And Motivation (Prefrontal Cortex)
These nuclei are involved primarily in controlling motor activity. They include:
the caudate nucleus, located just lateral to the lateral ventricle.
The putamen, which is separated from the caudate by the internal capsule.
The Globus Pallidus which is immediately medial to the putamen. The Globus Pallidus is divided into 2 divisions: the Globus pallidus external segment and the globus pallidus internal segment.
The subthalamus, located most caudally, is part of the basal ganglia.
HIPPOCAMPUS, AMYGDALA, CINGULATE GYRUS
The hippocampus is buried deep in the temporal lobe. At its most rostral end is another nucleus called the amygdala. This is the structure that forms the bump on the temporal lobe called the uncus.
The fornix originates from the caudal end of the hippocampus and loops rostrally just below the corpus callosum.
The cingulate gyrus is part of the limbic system.
The thalamic nuclei related to the limbic system are the dorsomedial nucleus and the anterior nucleus.
What structure forms the bump of the uncus?
HIPPOCAMPUS AND FORNIX
The hippocampus is part of the limbic system. It has a characteristic “c” shape and is located deep in the temporal lobe.
Axons leaving or entering the hippocampus form a fiber tract called the fornix. Note the fornix leaves the hippocampus at the posterior end of the temporal lobe. It then courses rostrally, just below the corpus callosum in the parietal lobe and then return ventrally to terminate in structures such as the mammillary bodies. Because of this course, the fornix is visible at two different levels in this horizontal section: at its origin from the hippocampus as well as rostrally.
BLOOD SUPPLY TO THE CEREBRAL CORTEX
The medial side of the cerebral cortex receives it’s blood supply from 2 major branches:
The Posterior Cerebral is the terminal branch of the basilar artery. The posterior cerebral supplies the occipital lobe and medial portions of the temporal lobe.
The Anterior Cerebral is a branch of the internal carotid artery. The anterior cerebral artery supplies the frontal and parietal lobes.
There is an area of overlap at the border of the parietal and occipital lobes. Note that both arteries extend over the dorsal surface of the brain to reach the lateral side.
2 VESSELS SUPPLY MEDIAL ASPECT OF CORTEX:
ANTERIOR CEREBRAL (BRANCH OF INTERNAL CAROTID ARTERY)
POSTERIOR CEREBRAL (BRANCH OF BASILAR ARTERY)
BLOOD SUPPLY TO THE CEREBRAL CORTEX
The lateral side of the cerebral cortex receives it’s blood supply from the Middle Cerebral Artery, a branch of the internal carotid.
Also, the branches of the anterior and posterior cerebral arteries that wrap around from the medial side supply portions of the lateral cortex.
What Artery are the Middle Cerebral Artery and the Anterior Cerebral Artery branches of?
INTERNAL CAROTID ARTERY