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Basic Neuroanatomy:Telencephalon, Mesencephalon. Myelencephalon

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Neurological Basis of Behavior (PSY - 610)
VU
Lesson27
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 become familiarized with the location of various brain areas, their functions and their
relationship to other areas. The students would also understand how control and modulation of
behaviour related to each neuroanatomical site takes place
Basic Neuroanatomy is based on the following assumptions:
·  The cortex is newly evolved as compared to the other structures, and it controls all major
functions (especially in the higher animals)
·  The higher areas cover the lower areas as they have grown over these areas. The lower brain
areas have to send information to the higher areas and then the commands for actions come
back from these areas ( the thalamus send all messages it receives to the relevant cortices and
receives commands)
·  The lower underlying areas are more primitive in terms of functions, their functions are more
survival functions ( the brain stem areas)
·  These lower areas are similar in locations, site and functions in lower and higher order animals
(e.g. the hypothalamus, the thalamus).
Phylogenetically, encephalization (control of the higher brain areas) has occurred leading to increased
ability to interact and respond to the environment (greater adaptability).
The greater the encephalization, the more the functions are controlled by the higher brain areas,
therefore if these areas are damaged the animals cannot function at a normal level (Bridgeman, 1988,
Thompson 1980).
The following would elaborate how the brain is located with reference to the spinal cord and how other
areas within the brain and the top of the spinal cord
Brain------------------------------------------------------------------------------spinal cord
There are three major divisions of the brain: The Forebrain, the midbrain and the hind brain.
·
The Forebrain comprises of the Telencephalon (coritcal and some subcortical structures) and
Diencephalon (the Thalamus and the hypothalamus).
·
The Mid brain consists of older structures, the Mesencephalon and
·
The Hind brain The posterior most part of the brain is called the Hind brain, which has two
sections the Metencephalon and the Myelencephalon
We will elaborate these areas further moving from the frontal and dorsal areas to the more caudal
ventral areas. The anterior most and the dorsal area is the Telencephalon, with Myelencephalon at the
caudal most end
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Neurological Basis of Behavior (PSY - 610)
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Telencephalon: comprises of the Cerebral Cortex, the Corpus Striatum, Cingulate Gyrus, Septum,
Amygdala, Hippocampus (these last three are also part of the limbic system). Therefore this is cerebral
cortex which is a phylogenetically a newer structure, and some older primitive structures which underlie
the cerebral cortex
Diencephalon: Comprises of the Thalamus which is the junction and the gateway for all sensory-motor
and association pathways and the Hypothalamus which is the primitive survival centre
Mesencephalon: has the Tectum which comprises of the Inferior (for auditory systems) and the
Superior colliculi (for visual system) Tegmentum, cerebral peduncles Metencephalon: comprises of the
Cerebellum which lies dorsally over the Pons, and the Pons
Myelencephalon comprises of the Medulla Oblangata
Brain stem: includes the Mesencephalon, Metencephalon and the Myelencephalon i.e. technically
everything between spinal cord and cerebral cortex
Myelencephalon: Medulla Oblongata ( Oblong and narrow structure) is continuation of spinal cord and
the caudal part of the brain stem .Another important structure which is located in the Brain stem are is
the reticular formation.
Medulla contains all the acending and descending fibre pathways connecting the brain and the spinal
cord. It also has nuclei for the cranial nerves especially related to the control of respiration; heart and
digestive activity enter the brain at the level of medulla. Cranial nerves for tongue, larynx, pharynx, ear,
vestibular, involved in control of breathing while sleeping (sleep apnea), sneezing, swallowing,
vomiting are also found here.
Cranial nerves:
Hypoglossal nerve (tongue) -
Cranial Nerve XII
Accessory (larynx, voice, mouth mastoid) Cranial nerve XI
Vagus (taste, larynx, pharynx, ear)
Cranial Nerve X
Glossopharyngeal (Taste, posterior part of the Tongue) Cranial IX
Vestibulocochlear related to ear and vestibular
Cranial VIII
Sneezing: when nasal mucosa is irritated. The sneezing center is located in the medial part of medulla (it
also involves the trigeminal nerve).
Vomiting is found in the Medullar Reticular Formation
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Neurological Basis of Behavior (PSY - 610)
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Reticular Formation: this is a criss cross of nerve fibres , nuclei and cell bodies ( like a net ( reticulum
means: the net). It extends from the spinal cord to the Thalamus. It is a phylogenetically older structure.
It is a well organized are with both efferent and afferent ascending and descending fibres:
Ascending fibres go to thalamus, cortex, and are involved in sleep and awakening. Raphe Nuclei
produces serotonin and extends from the lower pons, andmedulla. Analgesia is produced by the
electrical stimulation of the Periaquaductal greay (PAG), is through the Raphe nuclei. It gets input from
cerebral cortex, the cerebellum and output to cerebellum and the spinal cord. "The reticular activating
system" (RAS) which is important in arousal. Sleep, arousal, muscle tone, alertness was found to be
located here by experiments of Moruzzi and Magoun (1949) on cats. They stimulated the raphe Nuclei
of a sleeping cat which led to an arousal EEG response (low voltage, high frequency theta response), it
woke up, and when the awake cat was stimulated and it became more alert. However, when this area
was lessioned animals went into a comatose stuporous state.
Destruction of the Raphe Nuclei led to Insomniac cats thus it was found that the RAS is important in
sleep and attention.
Metencephalon. Has many tracts going up and down,and contains two important brain areas the
Cerebellum and the POns.
Cerebellum: lies over Pons, it is a phylogenetically older structure, for sensory motor coordination,
movement and balance. It has two lobes like the CC with a large number of lobules separated by
fissures ( vermis, smaller grooves) with a large number of convulations, but these are similar all over
(unlike the cerebral cortex in which there is a difference). The nerve cell layer is 2mm thick below
which lies the white matter under which lies the cerebellar nuclei
Cerebellum receives inputs from the vestibular system, auditory and visual system, reticular formation,
and various regions of the cerebral cortex. It sends out fibers to the reticular formation, thalamus and the
vestibular system
Damage to the cerebellum leads to disturbances of gait in all regions. If one lobe is damaged then there
is postural imbalance. If both cerebellar poles are damaged there is tendency to fall backwards because
of the inability to maintain upright postures and gait disturbance with damage to the posterior region
In Humans, Ataxia, characterized by unsteadiness of gait is seen, this is with anterior lobe syndrome:
with the following symptoms:
·
Abnormalities in force, rate, and direction of rapid movements a) overshooting while reaching
targets b) jerky not smooth movements. Damage to the cerebellum impairs standing, walking
and performance of coordinated movements
·
Birds and reptiles have large cerebellums? Why?? To maintain balance during flight and since
sensory ­motor fibers are coming and going out to various areas, coordination of smooth
movements takes place in this area.
The oculomotor signs of cerebellar damage are: Nystagamus (rythmic and involuntary oscillatory
movements of the eyes)
Cerebellectomy (removal of the cerebellum) lead to inability to maintain gaze, defective smooth pursuit
movements, difficulty of fixation
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Neurological Basis of Behavior (PSY - 610)
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Cerebellar neurons: Purkinje cells (long dendritic trees), Basket cells (short axons, dendrites cover
Purkinje cells), Stellate Cells (axons terminate on Purkinje cells), granule cells (smallest, go vertical
for communication)
Pons: Bridge between the medulla, midbrain, and the cerebellum. The medulla is caudally located
with refernce to POns and the midbrain is rostrally located. The Dorsal surface of PONS is covered
by the cerebellum. Large rounded pontine nuclei contain ascending and descending fibre bundles.
One such bundle connects the rbain stem and the cerebellum and contains the Pyramidal fibres from
Cerebral cortex to the spinal cord (part of the cortico-spinal tract). The Trigeminal cranial nerve
enters and leaves the brain at the level of POns. Further the Cranial nerves for feeding, facial
expression, respiratory nuclei, relay nerves for auditory systems are also located here.
The cortico-ponto-cerebellar tract is the largest group of fibres which originate form a wide area of
the cerebral cortex 9 has over 19 million fibres on each side). These rises from the primary cortical
areas are involved in rapid correction of movements.
PONTINE NUCLEI, THE GIANT PONTINE CELLS play an important role in rapid eye
movement sleep by inhibiting the movement of body muscles to prevent damage which could occur
due to activation of the body (as the brain is active)
Mesencephalon is a small portion between the hind brain and the diencephalons- the anterior
section of the brain stem, it is tubular in form. It has three main areas: tectum, tegmentum, and basis
pedunculi
Tectum comprises of two pairs of relay nuclei, which look like 4 little lumps on the surface of the
brain stem. These are the Superior Colliculi and the Inferior Colliculi
Superior Colliculi: laminated grey and white matter important in visual reflexes and eye movement,
well defined and organized in terms of receptive fields and maps of visual space. It is part of the
pathway coming from the optic tract to the visual cortex for eye movement and gross spatial
localization. This is important for vertical gaze and pupillary reflexes. It receives inputs from retina
of eyes, thalamus, and inferior colliculus and sends outputs to thalamus and frontal and visual
cortices.
Inferior colliculi: it is an oval mass of small and medium sized neurons and is major relay nuclei for
the auditory pathway. Fibres come in from the Thalamus (Medial Geniculate Nuclei), auditory
cortex and cerebellar cortex, and fibres from Inferior colliculi project to the MGN, superior
Colliculi and the cerebellum... turn to look at sound reflex and localizing the source of sound.
Therefore both the inferior and superior colliculi work together as part of the reflex system which
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Neurological Basis of Behavior (PSY - 610)
VU
take care of attending and turning to wards the direction of a sound ( This is why we see extensive
connection with the thalamus, the cerebellum and the relevant cortices)
We would be continuing discussion on location of various brain areas and their connections and
functions in the next class.
References:
1.
Kalat J.W (1998) Biological Psychology Brooks/ Cole Publishing
2.
Carlson N.R.(2005) Foundations of Physiological Psychology Allyn and Bacon, Boston
Pinel, John P.J. (2003) Biopsychology (5th edition) Allyn and Bacon Singapore
3.
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