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Basic Neuroanatomy:Diencephalon, Hypothalmus, Telencephalon, Frontal Lobe

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Neurological Basis of Behavior (PSY - 610)
VU
Lesson29
Basic Neuroanatomy
Objectives:
The main objective of this lesson is to study
·
The Brain and the Peripheral systems:
·
Brain: Forebrain, Mid brain, Hind Brain functioning of each anatomical location in the CNS.
Starting from the posterior located areas upto the anterior-most.
·
Cerebral Cortex: its layers, Corpus Callosum and the two hemispheres
Main purpose:
Students will come to relate the importance of location of various areas in the Diecephalon and the
Telencephalon, their functions and their relationship to other areas. The students would also understand
how control and modulation of behavior related to these neuroanatomical site takes place
Diencephalon:
This comprises of two major areas of the brain both equally important in their functions and their
involvement in a wide range of behaviors and connection, the hypothalamus and the Thalamus
Hypothalmus: it lies at the base of the brain, on both sides of the 3rd ventricle. It is very small in size a
compared to other brain areas but is very important in it s role and function. Hypothalamus is located
immediately beneath the thalamus and lies above the pituitary.
Hypothalamus is part of the Limbic system, and in all situations requiring a fight-flight or other
survival responses. There are several important fibre bundles passing through the hypothalamus,
including the-MFB Medial forebrain bundle which carries major neurotransmitters along with other
fibers to the higher areas.
Underneath the hypothalamus lies the superchiasmatic nucleus (SCN). The SCN plays an important
role in the day night cycles i.e. diurnal cycles. Within this region we also see the mammiliary bodies
which are important in memory.
The hypothalamus also secretes its own hormones which act as releasing factors for hormonal secretions
in the pituitary. The neurosecretory cells of the hypothalmic hormones are located near base of
hypothalamus, very close to the pituitary. Therefore hypothalamic-pituitary connection is important for
the neural and endocrinal connections. The brain talks to the pituitary through the hypothalamus, and
vice ­versa. All the endocrinal glands communicate for fear aggression, temperature regulation, food
and water, and mating. The Anterior hypothalamus is important in thrist regulation and there are
important sensors which continuously monitor fluid (and isotonic saline levels) of neurons. The
Ventromedial (VMH) and Lateral Hypohtalamus (LH) are involved in regulation of feeding. Research
has shown that the VMH is the satiety center (have- enough- food -stop -signal), and the lateral
hypothalamus is the center for initiation of feeding. Hypothalamus important in all major survival and
maintenance functions; it is related to the management functions of the body and survival rather than
intellectual functioning.
Thalamus: this is the largest component of Deincephalon with an ovalish shape; it has two lobes
which are connected by the mass intermedia which go through the midline of the third ventricle.
The thalamus comprises of large clusters of nuclei. The thalamus is a staging area, information
received from sensory receptors systems and other lower areas and then it is projected to the
relevant cortical areas. 1. Sensory relay nuclei: All afferent sensory input are received classified,
sorted and the passed through the thalamus, these go from the receptor to the Thalamus which then
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Neurological Basis of Behavior (PSY - 610)
VU
sends the selected projections to the related cortices. The Visual, auditory input goes through the
lateral geniculate nuclei and the medial geniculate nuclei, and somatosensory sensory fibers go to
the somatosensory cortices. There is a reciprocal one to one relationship of these connections in the
cortex. If one fiber degenerates in the cortex, it would lead to atrophy of the relevant thalamic areas.
The Dorsal group of fibers is multimodal (that is it receives and sends input to different sensory
areas). This receives input from within the thalamic regions, and project to the association cortex.
There is another group of fibers in the thalamus the Intrinsic or the non-specific. If this area is
stimulated it leads to wide spread electrical discharge in the cortex and other areas, evidence that
this bundle is important in electrical activity of the cortex. It is involved in sleep awakening as well
as attention. It is also important in affective behavior, memory (there is severe amnesia after lesions
to midline thalamic area). Thus the thalamus is important in every aspect of behavior
Telencephalon: The End brain comprises mainly of the areas of the cerebral cortex and some parts of
the Corpus striatum, the limbic system. The two hemispheres of the cerebral cortex and the other parts
are connected to each other by commissures (bands of fibers connecting the left and the right
hemispheres).
Corpus Callosum is the major band of fibers joining the two hemispheres it is wide, white and
visible to the naked eye. The commisures are mainly for interaction between the two hemispheres
and for crossing over of information (so that the two hemispheres acna coordinate decisions).
Cerebral Cortex: (cortex means outer covering: bark of the brain). This is made up of layers of
grey matter which covers the white matter. The thickness of the cerebral cortex varies from 1.5 to
4.5 mm; the average is about 2.00 mm. It is thickest in the primary motor cortex about 4.5 mm thick
and thinnest about 1.5 mm at the primary visual cortex. It is laid out in a straight line; the total
surface of the cerebral cortex would be about 20 sq.foot. How does this fit into the cranium, it is
sqeezed into folds. These folds are irregular convulations and grooves called sulci (for smaller size)
and fissures (for large sized). The area lying between two fissures is called gyrus and there is 2/3rds
of the cerebral collosum is these gyri. The two major fissures which are used as the
dividing/identifying borders are the Central fissure or the Fissure of Rolando separates the Frontal
from the Parietal Lobe and Temporal Fissure (or the Sylvian fissure) which separates the Frontal
from the Temporal Lobe. The Central Fissure divides Cerebral Cortex into the anterior-posterior
(frontal parietal).
There are several types of cortices the neo cortex- the newly evolved areas of cortex, and the allocortex
- the older cortex
The allocortex or the paleocortex (/archicortex) is a three layered older cortical structure subdividied
into the apleo cortex and the archicortex. These two have very close ties with the kinbic system and
the olfactory system.
Paleocortex: (Have the primary olfactory cortex and other areas)
Archicortex (consists of the hippocampal formation) this is similar to the human cerebral cortex in
terms of a) connections b) characteristics, c) kinds of neurons found in these areas.
Mesocortex: the middle cortex is found in the cingulate gyrus, parahippocampal areas and also between
the iso cortex and the allocortex
Neocortex: the new cortex, the iso cortex, consists of 6 layers which are more recent evolution:
organized in one-one: incoming in specific areas. Outgoing in others, association cortex takes care of
higher order functions
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Neurological Basis of Behavior (PSY - 610)
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The higher the evolutionary scale, the greater the neocortical development to the extent that in humans
where cortical development is maximal, 90% of the cortex is neocortex. In the primitive or less
developed animals the cortical surface is smooth, whereas in the more evolved and sophisticated
animals the surface is rough and convulated. In rats the cortical surface is relatively smooth, in the
squirrel monkeys it is somewhat rougher and the cortex of the chimpanzees and humans increase in
convulations. In humans, rhesus monkeys or chimpanzees have a very large disproportionate, rough
surface of the cerebral cortex.
The cortex is organized in a one-to-one manner a) incoming information goes to specific areas ( most of
the cortex is receiving information) b) Outgoing information is sent out from motor cortex and other
relevant areas ( visual information sent out by visual cortex) c) Association cortex takes place of other
important and higher order functions.
Lobes of the cerebral Cortex:
Frontal Lobe: lies rostrally to the Central fissure, and caudally to the precentral fissure are the primary
motor area. The primary motor area is most important in movement of the body. The motor homunculus
is the dictionary of motor movements, where each motor movement and muscle is mapped. The body
parts are represented in well defined but a disproportionate manner. For, example the tongue and the
thumb gets greater representation as compared to the body torso and the extremeties ( depending on the
evolutionary importance of the areas) Electrical stimulation of specific areas in the primary motor cortex
leads to movement in the contralateral area of the body, and lesions lead to contralateral paralysis ( as
in stroke). Rostral to the precentral sulcus is the premotor area; this is involved in initiating of a
movement and changes in the already ongoing movement. Rostral to premotor is the Bordmanns area 8
which is has the frontal eye fields, (for conjugate eye movements). There are other important areas such
as the Brocas area which is important in speech articulation and production. If this area is lesioned it
leads to aphasia.
Parietal:lies caudally ( behind) the central sulcus, and primary somatosensory cortex is located here.
The sensory homunculus is mapped in the same manner as the motor humonculus (not in proportion to
the size of the body part, but in direct proportion to the needs). Stimulation of the areas leads to
sensations of tingling and numbness in the contralateral part. The parietal lobe is also involved in the
behavioral interaction of individual with the space around him. If lesioned these lead to sensory neglect
of contralteral space (e.g. the patient would shave contralteral half of face, eat half the plate, and not
respond to chairs and tables in contralateral half of damage). The parietal is also involved in object
recognition, and language comprehension.
Temporal: lies caudal to the lateral gyrus in the superior area and is primary auditory cortex,
Wernicke's area important for speech comprehension. The spoken language is comprehended here.
In the inferior temporal lobe, the perception of visual form and color is located (this is in the close
vicinity of the occipital and the parietal lobes.
Occipital Lobe: The primary and secondary visual cortex visual processing is carried out here. This is
laid out in very well organized layers, in Brodmanns areas 17, 18, 19. This is the striated cortex, i.e. the
layered cortex, where both the left and the right eye images get represented in these layers. Hubel and
weasel have identified coular dominance columns.
Cytoarchitectonics: The cellular architecture of the cerbal cortical layers. There are six layers in which
cortex can be divided (not on an all or none basis), but it is mainly in terms of the organization of cell
layers.
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Neurological Basis of Behavior (PSY - 610)
VU
Table: Layers of cerebral cortex
Lay
Cytoarchitecture,
network
Area
Order
of
er
name
migration
I
Molecular layer
Fibers  going  in  a Primary area for Oldest (cellular)
network
fewer synapses
interneurons and glial
cells
granular Dense packing of small Dendrites of the 5th   wave  of
II
External
layer
and medium pyramidal pyramidal
neuronal
cells and interneurons project to layer 5 development
from other layers.
and
other
extensions
go
deeper
Pyramidal cells which Dendrites  send 4th wave of the
III
External Pyramidal
to neuronal
( medium and large)
increase in size as the extensions
layers 1, axons migration
cell layers deepens
extend to other
deeper layers in
the  same  and
contralateral
hemisphere
densely 3rd   wave  of
granular Pyramidal  cells  are Most
IV
Internal
densely packed. There is packed,  project neuronal
layer
and stellate  and  granular to deeper layers, migration
(
pyramidal
cells terminating in this thalamocortical
granular)
fibers end here
layer
Large and medium sized Lowest  density 2nd   wave  of
V
Internal Pyramidal
pyramidal stellate cells. as  cells  sends neuronal
Betz  cells  (  apical out  projections migration
to other areas.
dendrite)
VI
Multiform layer
Varying  shapes  and
1st  wave  of
sizes short axons and
neuronal
dendrites
migration
·
The first layer contains cells with horizontal fibres and horizontal cells of Cajal
·
Granule cells- Short branching axons and amny dendritic branches
·
Pyramidal cells shaped like a pyramid, send axons to layers below cortex. They also have long
Apical dendrite which extend to other layers ( and even down to the spinal cord) therefore a bigger
cell body is need to energize the cell to send messages out for longer extensions and carry messages
effectively.
Cerebral Cortex: Two Lobes
There are two independent lobes connected with the commissures. Many researchers have worked on
the question do we have two brains or one. Are there two independently functioning brains or do they
coordinate as one. Research by Gazzaniga, Milner, Sperry and others has shown that the two
hemispheres are specialized for different functions, Speech in left hemisphere (first identified by Broca)
and spatial functioning in right hemisphere. Milner carried out the WADA TEST on patients, in this test
one side of the brain is anesthetized with slow infusion of sodium amytal through the carotid artey
(major artery of the brain). It was reported by Milner that all right handed persons have left hemisphere
speech dominance (92%), as their speech stopped with the anesthetization of the left hemisphere.
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Neurological Basis of Behavior (PSY - 610)
VU
There are specific disorder known as Aphasias, which are language and speech disorders with left
hemisphere damage
The Apraxias are movement disorders which occur when patient is required to perform on a verbal
command and fails to do so, even though spontaneously it can be performed.
(Additional references, Graham 735, Gazzaniga, Pinel, Kolb and Wishaw)
In order to explain the cerebral differences, there are several theories of cerebral asymmetry: Levy
and Sperry state that there are two basic modes of thinking: the analytical (LH)/synthetic and the
(RH) more gestalts more organized therefore the neural circuitry is differently wired.
Both hemispheres are equipotential upto two years states Lenenberg, that each hemisphere can take
on any role of specialization. However, Kinsberg states that each child is born with specialized
functions of the two hemispheres (the planum temporale, in the temporal lobe is large in the left side
in the fetus)
The research is ongoing and continues to this day to identify the specializations and roles of the two
Hemispheres.
The complexity of the cerebral cortex and that of the mysteries of how each neuron adds up to the
behaviours we exhibit are an interesting ongoing journey.
References:
1. Kalat J.W (1998) Biological Psychology Brooks/ Cole Publishing
2. Carlson N.R. (2005) Foundations of Physiological Psychology Allyn and Bacon, Boston
3. Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore
4 Bloom F, Nelson and Lazerson (2001), Behavioral Neuroscience: Brain, Mind and Behaviors (3rd
edition) Worth Publishers New York
5. Bridgeman, B (1988) The Biology of Behaviour and Mind. John Wiley and Sons New York
6. Brown,T.S. and Wallace.(1980) P.M Physiological Psychology
Academic Press New York
Note: References 2, 3, 4, 7 more closely followed in addition to the references cited in text.
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Table of Contents:
  1. INTRODUCTION:Descriptive, Experimental and/ or Natural Studies
  2. BRIEF HISTORICAL REVIEW:Roots of Behavioural Neurosciences
  3. SUB-SPECIALIZATIONS WITHIN THE BEHAVIORAL NEUROSCIENCES
  4. RESEARCH IN BEHAVIOURAL NEUROSCIENCES:Animal Subjects, Experimental Method
  5. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Species specific
  6. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Decent With Modification
  7. EVOLUTIONARY AND GENETIC BASIS OF BEHAVIOUR:Stereoscopic vision
  8. GENES AND EXPERIENCE:Fixed Pattern, Proteins, Genotype, Phenotypic
  9. GENES AND EXPERIENCE:Mendelian Genetics, DNA, Sex Influenced Traits
  10. GENES AND EXPERIENCE:Genetic Basis of behavior, In breeding
  11. GENES AND EXPERIENCE:Hybrid vigor, Chromosomal Abnormalities
  12. GENES AND EXPERIENCE:Behavioral Characteristics, Alcoholism
  13. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION
  14. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Activating brain
  15. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Macro electrodes
  16. RESEARCH METHODS AND TECHNIQUES OF ASSESSMENT OF BRAIN FUNCTION:Water Mazes.
  17. DEVELOPMENT OF THE NERVOUS SYSTEM:Operation Head Start
  18. DEVELOPMENT OF THE NERVOUS SYSTEM:Teratology studies, Aristotle
  19. DEVELOPMENT OF THE NERVOUS SYSTEM:Stages of development, Neurulation
  20. DEVELOPMENT OF THE NERVOUS SYSTEM:Cell competition, Synaptic Rearrangement
  21. DEVELOPMENT OF THE NERVOUS SYSTEM:The issues still remain
  22. DEVELOPMENT OF THE NERVOUS SYSTEM:Post natal
  23. DEVELOPMENT OF THE NERVOUS SYSTEM:Oxygen level
  24. Basic Neuroanatomy:Brain and spinal cord, Glial cells, Oligodendrocytes
  25. Basic Neuroanatomy:Neuron Structure, Cell Soma, Cytoplasm, Nucleolus
  26. Basic Neuroanatomy:Control of molecules, Electrical charges, Proximal-distal
  27. Basic Neuroanatomy:Telencephalon, Mesencephalon. Myelencephalon
  28. Basic Neuroanatomy:Tegmentum, Substantia Nigra, MID BRAIN areas
  29. Basic Neuroanatomy:Diencephalon, Hypothalmus, Telencephalon, Frontal Lobe
  30. Basic Neurochemistry:Neurochemicals, Neuromodulator, Synaptic cleft
  31. Basic Neurochemistry:Changes in ionic gates, The direct method, Methods of Locating NT
  32. Basic Neurochemistry:Major Neurotransmitters, Mesolimbic, Metabolic degradation
  33. Basic Neurochemistry:Norepinephrine/ Noradrenaline, NA synthesis, Noadrenergic Pathways
  34. Basic Neurochemistry:NA and Feeding, NE and self stimulation: ICS
  35. Basic Neurochemistry:5HT and Behaviors, Serotonin and sleep, Other behaviours
  36. Basic Neurochemistry:ACH and Behaviors, Arousal, Drinking, Sham rage and attack
  37. Brain and Motivational States:Homeostasis, Temperature Regulation, Ectotherms
  38. Brain and Motivational States:Biological Rhythms, Circadian rhythms, Hunger/Feeding
  39. Brain and Motivational States:Gastric factors, Lipostatic theory, Neural Control of feeding
  40. Brain and Motivational States:Resting metabolic state, Individual differences
  41. Brain and Motivational States:Sleep and Dreams, Characteristics of sleep
  42. Higher Order Brain functions:Brain correlates, Language, Speech Comprehension
  43. Higher Order Brain functions:Aphasia and Dyslexia, Aphasias related to speech
  44. Higher Order Brain Functions:Principle of Mass Action, Long-term memory
  45. Higher Order Brain Functions:Brain correlates, Handedness, Frontal lobe