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Neuroscience: GENERAL ORGANIZATION OF THE BRAIN

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Terms

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vertical axis of neuraxis
represented by a line through the entire brainstem and spinal cord
horizontal axis
represented by a line extending from anterior to posterior in the cerebrum; that is, from the frontal to the occipital poles
nucleus, used in reference to brain
refers to a collection of neuron cell bodies, analogous to ganglia in peripheral nervous system. ndividual nuclei represent functionally separate structures
subcortical definition
meaning that it lies beneath the cortex
gray matter
Areas of the brain where the neuron cell bodies (and dendrites) lie. a nucleus is one of these since it is, by definition, a collection of cell bodies
neuropil
Areas which consist primarily of dendritic trees (where most synapses occur. may also include some neuron cell bodies, especially small, local circuit neurons or interneurons
molecular layers
these are, for example of the cerebral or cerebellar cortex, neuropil layers
white matter
Areas where axons form together into bundles. myelin (lipid) sheath surrounding axons give them a white appearance in the fresh brain; most axons in the human brain are myelinated
Groups of axons running together are called by various names, including⬦
fiber bundles, axon bundles/tracts, pathways, peduncles, funiculi, fasciculi, columns, lemnisci, capsules, brachia, nerves, fibers
hemisphere specialization of function examples
in general, the left hemisphere excels in intellectual, rational, verbal, and analytical thinking and the right hemisphere excels in emotional, non-verbal, and intuitive thinking
axon collaterals
arise from Nodes of Ranvier, projecting to many different areas or nuclei
decussate
With few exceptions, pathways in the brain do this (cross), such that each hemisphere of the brain controls (or processes information from) the opposite side of the body. Different pathways decussate in different areas of the brain
“project to”
A nucleus is said to do this another nucleus or area. always used to mean "innervates directly "; thus the motor cortex does not do this to the muscle
“descending or ascending” axons
“relative” terms used generally for pathways going in the direction “away from or to” the cortex
corticospinal tract
tract in which axonstravel all the way from the motor cortex where their cell bodies lie to the appropriate spinal cord level they innervate; the corticospinal tract is an example of a descending pathway; damage anywhere along the pathway (or in the motor cortex or spinal cord) will produce motor signs/symptoms
divisions of the cortex
1) primary sensory or primary motor areas; 2) secondary, supplementary, or “higher order” sensory or motor association areas; and 3) multimodal association areas
five major subdivisions of the adult human brain
Telenchephalon, Diencephalon, Mesencephalon (midbrain), Metencephalon (means "between" brain), Myelencephalon ("hind"-brain)
“cerebrum”
refers to structures of telencephalic origin
Components of Each cerebral hemisphere
1 cerebral cortex ("bark", as in the bark of a tree) or mantle of gray matter,
3 A core of subcortical "white" matter,
4 Deep in the interior of each cerebral hemisphere is a lateral ventricle (a "C"-shaped cavity in each hemisphere where most of the CSF is made),
5 and subcortical nuclei referred to as the basal ganglia (including the corpus striatum, amygdala, claustrum, nucleus basalis of Meynert [substantia innominata])
gyri
folds of cortex are called this
sulci
the grooves between the gyri
fissure
if a sulcus is very deep, it may be called this
term for agyric cortices;
lissencephalic (from the Greek meaning "smooth brain")
effects of cortical degenerative disease on gyri and sulci, and ventricles
cortical neurons die and gyri become smaller and the sulci between the gyri enlarge, ventricles dilate
compensatory dilation
expansion of ventricles due to neurodegenerative disease
cortical thickness
between 1-4 mm
Brodmann number
divisions of cortex based on variation in cytoarchitecture
age and number of layers of types of cortex
neo (new)-cortex (6 layers), paleo (old)- and archi (ancient)- cortex (usually 3 layers)
Projection fibers
axons of cortical neurons which leave the cortex to synapse in other subcortical areas; axons of cells lying in subcortical structures which project to the cortex
Commissural fibers
axons of cortical cells which cross the midline to connect the two hemispheres
corpus callosum
the most important commissural pathway
anterior and posterior commissures
two minor commissural pathways
Association fibers
axons of cortical cells which connect different functional areas within the same hemisphere
lateral ventricle
"C"-shaped cavity in each hemisphere where most of the CSF is made, deep in the interior of each cerebral hemisphere
basal ganglia
subcortical nuclei deep in the interior of each cerebral hemisphere
Diencephalon location
Anatomically, this area of the brain is located in each hemisphere lateral to the third ventricle
hypothalamic sulcus significance
the diencephalon is divided into two areas by this groove
Components of the Diencephalon
Dorsally, the thalamus ("anteroom"), Ventrally, the hypothalamus
thalamus
all information destined for the cortex must be relayed (via a synapse) through this structure
hypothalamus
he general function of this structure is as a CNS center for the regulation of autonomic and endocrine functions to maintain internal homeostasis; also a major player in the limbic system (emotions)
Mesencephalon (midbrain), general location and major divisions
This General area of the brain that fits through the tentorial incisure or notch, Divided by the cerebral aqueduct of Sylvius into a "tectum" (roof) [contains superior and inferior colliculi] and a "tegmentum" (floor)
tectum location
part of midbrain superior to cerebral aqueduct of sylvius
tegmentum
part of midbrain inferior to cerebral aqueduct of sylvius
divisions of textum
superior and inferior colliculi
superior and inferior colliculus function
involved in visual and auditory reflexes, respectively; in non-mammalian vertebrates, the "optic tectum" is the major visual structure in the brain and is the homolog of the mammalian superior colliculus
tegmentum function
Most of the pathways coming down from higher structures on their way below the midbrain, and fibers from below on their way to higher levels of the brain, course in this structure
substantia nigra, location, claim to fame
the nucleus in the midbrain which degenerates in Parkinson's Syndrome)
Metencephalon (means "between" brain) components
Cerebellum and pons (“bridge”)
Cerebellum ("little cerebrum") function
a structure primarily concerned with integrating sensory information to allow for a coordinated motor response; plays a role in the proper "timing" and coordination of learned, skilled motor movement; also involved in some forms of cognitive learning
folia
folds of cerebellar cortex
components of cerebellum
1 two hemispheres,
2 cortex (folds of cerebellar cortex are called folia, not gyri; grooves between the folia are called fissures),
3 underlying white matter,
4 deep nuclei.
5 midline structure called the vermis,
6 rounded lobule on the undersurface of each hemisphere continuous with the vermis called a tonsil
vermis
midline structure in cerebellum
tonsil (CNS)
rounded lobule on the undersurface of each cerebellar hemisphere continues with the vermis. herniates thru foramen magnum in tonsillar herniation
Pons ("bridge")
connects the cerebellum to the rest of the brain
Myelencephalon ("hind"-brain) component
Medulla oblongata (meaning "long white marrow-like structure")
Medulla oblongata (meaning "long white marrow-like structure") structure
1) Long pathways course through this structure//
2) has portion of the reticular formation; nuclei involved in vital functions; in tonsillar herniation tonsil of the cerebellum presses down//
3) is continuous with spinal cord at foramen magnum //
4) many motor nuclei of cranial nerves located here, the pathways from cortex to these nuclei are referred to as the cortico-bulbar pathway
reticular formation
it is in this area that nuclei involved in vital functions such as consciousness, heart-rate and rhythm, breathing, etc. are located;
cortico-bulbar
Because many motor nuclei of the cranial nerves are located in the medulla, the pathways from the cortex to these nuclei are referred to as this
Subdivisions of CNS
Forebrain, midbrain, hindbrain, brainstem
forebrain
this would include the cerebrum (cerebral cortex and deep nuclei of the telencephalon) and the diencephalons
Midbrain
the part of the brain between the forebrain and the hindbrain
Hindbrain:
includes the pons, medulla, and cerebellum
Brainstem
midbrain, pons, and medulla
Major fissures and sulci of Cortex
Longitudinal cerebral or sagittal fissure, lateral or sylvian fissure, central sulcus or sulcus of Rolando, parieto-occipital sulcus
Longitudinal cerebral or sagittal fissure:
divides the two hemispheres; the falx cerebri fits down into this fissure to the level of the corpus callosum
Lateral or Sylvian fissure:
fissure located laterally on the surface of the cortex
Central sulcus or sulcus of Rolando
sulcus that begins slightly behind the midpoint of the brain and generally descends with a forward inclination
Parieto-occipital sulcus
sulcus located primarily on the medial surface of the hemisphere about 4-5 cm in front of the occipital pole; it is reflected for only a short distance over the superior border of the hemisphere on the lateral surface
Lobes of the cerebral cortex
Frontal lobe, Parietal lobe, Occipital lobe, Temporal lobe
Frontal lobe demarcations
demarcated by the Sylvian fissure below and the central sulcus of Rolondo caudally
major sulci and gyri of the Frontal Lobe
Precentral sulcus/precentral gyrus, Superior and inferior frontal sulci structure, location
axons of cortical cells in this area make up part of the corticospinal tract, a very important pathway in man necessary for the initiation of voluntary motor movement, somatotopically organized
The precentral gyrus also called the "primary" motor cortex (Area 4)
Superior and inferior frontal sulci structure and location
located at right angles to the precentral gyrus; these sulci of the frontal lobe form the borders of three gyri: the superior, middle and inferior frontal gyri
structure of the inferior frontal gyrus

Ascending rami of the lateral fissure divide this gyrus into three smaller areas: the pars orbitalis, pars triangularis, and pars opercularis; the posterior part consisting of the pars triangularis and pars operularis (Areas 45 and 44)
In the dominant hemisphere (usually the left hemisphere), Areas 44 and 45 (also called Broca's Area) function

brain regions critically involved in the motor control of language
Damage to or compromise of the blood supply to Broca's area results
damage to this area results in an individual who can understand spoken language, but has difficulty in speaking language fluently; if severe enough, the person will become mute
aphasia
cquired disorders of language are referred to as this
Prefrontal cortex location
anterior-most part of the frontal lobes (rostral to Areas 6 and 8; made up of a number of distinct areas);
important multimodal association areas which involve frontal lobe areas
Prefrontal association area, Limbic association cortex
Prefrontal association area
is entirely within the frontal lobe; believed to play a role in some aspects of cognitive and motor behavior; Broca’s area is generally considered part of this
Limbic association cortex
Areas of the prefrontal cortex, in particular, appear to be critically involved in the abstraction of cultural mores, rules of social interaction, judgment, and the ability to perceive and to reflect on the consequences of one's actions; other specific areas in the prefrontal cortex play a role in appropriately associating “affect” with “experience”; these areas are linked to the most complex intellectual functions and imagination
Prefrontal lobotomy
removal of the prefrontal lobes
leukotomy
cutting of the axons beneath the prefrontal area
There is also lateralization of function in the limbic cortex
serious depression occurs more often following left frontal lobe lesions; mania occurs more often from right frontal lobe lesions
Parietal lobe demarcations
demarcated anteriorly by the central sulcus of Rolando, inferiorly by the lateral fissure, and posteriorly by an imaginary line extending from the parieto-occipital sulcus to the top of the Sylvian fissure
the main sulci and gyri of the parietal lobe
Postcentral sulcus/postcentral gyrus, Intraparietal sulcus, Occipital lobe, Calcarine cortex, components
Area 17 visuotopically organization
each point on the retina represented in this area so that a "map" of visual space (retina) is represented in the brain; again, there is a disproportionate representation, with the greatest cortical area being devoted to macular or central vision
cuneus location
gyrus of calcarine cortex above the calcarine fissure
lingual gyri location
gyri of calcarine cortex below the calcarine fissure
scotomas

blind spots produced by lesions of area 17
visual association areas

Areas anterior to primary visual cortex; Areas 18 and 19 in the occipital lobe
visual agnosias
the individual is not blind, but cannot recognize an object or its “significance” by sight alone, produced by lesions of the visual association areas
Temporal lobe demarcations
demarcated by the Sylvian fissure dorsally and the parieto-occipital sulcus/preoccipital notch "line" caudally
major sulci and gyri of temporal lobe
Superior and inferior temporal sulci,
Superior and inferior temporal sulci location, structure
sulci which run parallel with the Sylvian fissure and divide the temporal lobe into three major gyri: the superior, middle, and inferior temporal gyri
transverse temporal gyri of Heschl, location importance

gyrus on the superior aspect of the superior temporal gyrus where Area 41 is located; this area constitutes the "primary" auditory cortex
unilateral lesions of primary auditory cortex results
lesions of this area do not produce deafness; rather the individual will show a bilateral diminution in hearing, with a greater loss contralaterally, and some difficulty in the localization of the source of sounds contralaterally; bilateral lesions this area, which would be extremely rare, would produce deafness
higher order auditory areas example, location, lesion results
these areas (for example, Area 42) also surround the primary auditory cortex; because of the bilaterality of auditory connections, lesions in these areas do not generally produce auditory agnosias
Wernicke's Area

Area 22: this area is necessary for the interpretation of spoken language; individuals with lesions in this area cannot understand spoken language and said to have or receptive aphasia. such patients speak language fluently, but what they say is nonsense; because this area is very close to other language areas in the parietal lobe (the supramarginal and angular gyri), patients may also have problems with written language functions as well; patients may become increasingly paranoid over time
prosopagnosia, cause
inability to match a “face” with an “identity”, caused by lesions of the temporal lobe
Primary visual cortex lobe(s) and brodmann number(s)

Occipital, Area 17
Visual association cortex lobe(s) and brodmann number(s)

Occitipatl, Temporal: Areas 18, 19, rostral to 19, areas in temporal lobe // Parietal: Area 7
Primary Auditory Cortex lobe(s) and brodmann number(s)

Temporal, Area 41
Auditory Association Cortex lobe(s) and brodmann number(s)

Temporal, Areas 42, 22
Primary somatosensory complex lobe(s) and brodmann number(s)

Parietal, Areas 3, 1, and 2
Somatosensory Association Cortex lobe(s) and brodmann number(s)

Parietal, Part of area 2, Area 5
Primary motor cortex lobe(s) and brodmann number(s)

Frontal, Area 4
Motor Association cortex lobe(s) and brodmann number(s)

Frontal, Areas 6, 8
Name the multimodal association cortices
1 prefrontal association cortex,
2 limbic association cortex,
3 parietal-temporal-occipital association cortex
Function of prefrontal association cortex
This multimodal association cortex is involved in some cognitive behavior (i.e. motor speech and some “verbal” memory”, planning of motor movement, and “working” motor memory (like RAM), many individual areas primarily rostral to areas 6 and 8
Limbic Association Cortex function
this multimodal association cortex is involved in emotion and memory, numerous areas in frontal, parietal, and temporal lobes
Parietal-Temporal-Occipital Association Cortex
This multimodal association cortex is involved in poly- or multi-modal sensory, language functions, numerous areas in parietal, temporal, and occipital lobes
postcentral sulcus location
this sulcus lies posterior to and parallel with central sulcus of Rolando in parietal lobe
postcentral gyrus function, location, Area(s)
constitutes primary somatosensory cortex: important for apprectiation of pain, temperature, pressure, touch, and propioception. (areas 3, 1 and 2)Between central sulcus of Rolando and postcentral sulcus
somatosensory cortex function
constitutes primary somatosensory cortex: important for apprectiation of pain, temperature, pressure, touch, and propioception. has a somatotopic organization similar and parallel to the representation in motor cortex, with the face represented on the inferior lateral surface and the leg represented over the dorsal ridge or crown on the medial surface
Intraparietal sulcus location
at right angles and posterior to the postcentral gyrus; between the superior parietal lobule and the inferior parietal lobule
somatosensory agnosias
condition where the individual cannot recognize something on the basis of touch alone
Result of lesion of Part of the postcentral gyrus (part of Area 2) and part of the superior parietal lobule (Area 5) [somatosensory association areas ]
somatosensory agnosia is a result of lesions in these locations
Areas 5 and 7 function

posterior parietal cortex); these areas are believed to play a major role in coordinating visual and somatosensory information
inferior parietal lobule component gyri
the supramarginal (Area 40) and angular gyri (Area 39) comprise this area

supramarginal (Area 40) and angular gyri (Area 39) function

these two gyri are important for the perception and interpretation primarily of written language – and also for sight-reading of music
result of lesions of Areas 39 and 40

patients with lesions here in the dominant hemisphere have aphasias characterized by difficulties in reading (called alexia) and writing (called agraphia)
what is amygdala
subcortical nucleus in temporal pole of brain
what is lateral geniculate nucleus
nucleus located in the thalamus which recieves input from parts of both eyes and projects to a number of other ares, including primary visual cortex (area 17)
what is medial geniculate nucleus
nucleus located in thalamus which receives input from the inferior colliculus and projects to structures involved in the processing of auditory inforation, including primary auditory cortex (area 41)
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