ZeePedia

Basic Neuroanatomy:Brain and spinal cord, Glial cells, Oligodendrocytes

<< DEVELOPMENT OF THE NERVOUS SYSTEM:Oxygen level
Basic Neuroanatomy:Neuron Structure, Cell Soma, Cytoplasm, Nucleolus >>
img
Neurological Basis of Behavior (PSY - 610)
VU
Lesson24
Basic Neuroanatomy
Objectives:
These lessons would familiarize the students with
·  Systems, structure, Cells of the NS Neurons, Types of neurons, axonic and dendritic
communications,
·  Neuronal conduction and functioning, ionic and electrophysiological properties,
·  Localizing brain areas planes of reference (anterior-posterior etc).
·  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.
Brain and spinal cord:
When we study the brain and the spinal cord we will first study the basics of neuroanatomical structure
and systems. The basic component, like all systems in the body is the cells. The building blocks which
the Nervous System is composed of are the neurons, the brains cells and the glial cells. There is also the
cerebrospinal fluid (CSF) which cleans and insulates the brain.
Neurons:
Neurons are the specialized cells of the Nervous System. They are critical in the reception, conduction
and transmission of information (many things in between, like chemical processes). There are about 10-
12 billion neurons in the adult brain (as many stars in the Milky Way). For each neuron there are about
10-12 Glial cells. Make a very crowded brain, especially if their processes are also included.
We would be discussing these first followed by the cerebrospinal fluid, the blood brain barrier and lastly
the neuron.
Glial cells
These are the supportive cells found in the brain. They have many important functions. A) They hold
neuronal systems together. The synapse, the neuron, the synapse, and the dendrites are supported and
held in position by the glial cells. B) They do the housekeeping chores such as moving out the dead cells
and, keep the intra and extracellular space clean of debris c) they also provide nutrients to the cell and
its processes.
There are three major types of glial cells, the astrocytes, the oligodendrocytes, phagocytes, and
microglia.
Astrocytes:
The Astroglial extensions cover blood vessels and capilliaries (as insulation); these glial cells form the
blood brain barrier (V.IMP). Astrocytes cover the neuronal cell bodies and their branches to keep them
in place as well as separated from the fine branches. These also provide nutrients and chemicals which
pass through blood into the cell.
Oligodendrocytes:
This is a glial cell which sends out several layered extensions which wrap around the axons. These are
rich in myelin which is a fatty sheath. This sheath provides insulation and support to the axons and the
dendrites. This increases the efficiency and speed of transmission. In axonal processes, the gaps
between the folds are known as the Nodes of Ranvier, for messages to renew and jump across. One
Oligodendrocyte can send extensions to many axons at the same time.
Microglia:
79
img
Neurological Basis of Behavior (PSY - 610)
VU
Smaller glial cells which keep the cells clean by moving debris out of the cell and move them out of the
cell.
Phagocytes:
These are like the little Pac-man eating away all debris unattended and dead cells. They go around
eating up and removing them.
Glial cells not passive providers or caretakers; they are actively involved in chemical transmission. They
control, establish, and maintain synapses.
Protection of the brain
Brain is a highly protected area; there are many levels of protection. Firstly, the brain is encased by a
bony skull case covering, Additionally three coverings known as the 3 meninges, which are connective
tissues holding the brain in a protective net covering? The outer most menix is known as the Dura
mater (translated from Arabic "tough mother"). This is the tough outer most covering of the brain,
white colored. The second layer lying inside the Dura mater is the arachnoid membrane a web like
structure (made of spongy filaments like a wire mesh). Beneath arachnoid membrane lies subarachnoid
space where many large blood vessels (part of the vascular system) and the cerebrospinal fluid (CSF)
floating around. This provides protection and the blood supply. A network of blood vessels can be seen
if we open this space. The inner most covering­ the most delicate membrane is known as the Pia Mater
(Arabic translated into Latin= the soft or pious mother). This sticks to every convulation, every groove,
thereby ensuring covering is comprehensive. As can be seen the brain is extremely well protected
against injury (protection against jolts).
Cerebrospinal fluid: CSF:
This fluid fills the arachnoid space, the spinal cord (central canal) and the ventricles of the brain. These
connected through a series of opening, and the CSF travels through the brain and the spinal cord.
Essentially it is one big fluid reservoir. This fluid supports the form and shape of the brain (brain is very
soft tissue), from inside and outside.
The cerebrospinal fluid traverses through the brain using the ventricular system. There are four
ventricles. The first two (laterally placed) are very large cavities continuing in both hemispheres. The
third ventricle lies in the mid brain at the level of diencephalic area. The fourth ventricle is found lower
at the brain stem/cerebellar level. This is connected to the central canal of the spinal cord. The Choroid
plexuses in the PIA mater produce the CSF. Small capillaries that get through the PIA mater lining
produce the fluid. This is constantly being produced and circulated. It is about 125 milli litres and
replacement of half of it takes place every 3 hours, indicating a continuous circulation. Blocking of the
fluid or any infections may alter the level of functioning:
Cerebral aquaduct is the link between the 3rd and 4rth ventricles. The CSF is made up of water, proteins,
gases glucose, and other chemical ingredients (Carlson, Pinel)
Blood brain barrier:
This is not a fence or a barrier which is visible, it is essentially cerebral blood vessels and the glial cells
in the brain very tightly and densely packed together. These provide protection through the insulating
glial cells, creating difficulty for large molecules to pass through such as some Proteins, but large
glucose molecules to actively transport through blood vessel walls. The Blood brain barrier is also
selective depending on the locations. It makes some substances easier to pass than others at some
specific locations.
Thus we see the complexity of the brain emerging through the various specialized parts, the glials, the
CSF, the Protection of the brain, and the glial cells. They all work to keep the complex system of the
brain functioning smoothly.
80
img
Neurological Basis of Behavior (PSY - 610)
VU
Neurons:
There are many types of neurons which have been identified using the a) silver staining b) electron
microscopic techniques c) the golgi and other histological/cytological techniques.
The neuron mainly has three distinct features a) the cell soma, the cell body b) the axon one and only
output end which carries the commands out of the cell c) the dendrites which bring in messages and
information to the cell.
Types:
The neurons fall in three major categories, the Unipolar, Bipolar and Multipolar.
i)
Unipolar: The Unipolar is the neuron which has only one process emerging out of the cell body and
extending to both ends for quicker communication.
ii) Bipolar: the Bipolar neurons are neurons with two poles, one axon ( output end ) and dendrite (
input end) and these are mainly for horizontal communication as the sensory neuron, found in the
eye and the ear
iii) Multipolar: This is the most commonly found neuron. This type of neuron has more than more than
two processes i.e. there is always one axon but multiple dendritic connections. These again fall into
different categories, there are neurons with short branches (such as the Astro type cells), these are
the Interneurons with shorter or no axons, for quick integration and processing of information, The
Pyramidal cell which have very long Apical dendrites but short axon.
Neurons: Special Characteristics
Neurons are different from the cells in the body because of two main properties.
a) They can conduct bioelectric signals over long distances without loss in signal strength, unlike the
sound waves which become dimmer and dimmer with distance. These carry signals at exactly the same
strength from the point of beginning to the end
b) The Intercellular connections with other cells and tissues such as muscles and glands are multiple.
The information which can be sent out and which can be received by the neurons is determined by the
connections it has. There are many connections and for each there are specialized neurons and groups of
neurons. When neurons group together they are known as nuclei. Neurons clustered into bunches of
nuclei, tracts are fiber systems connecting these nuclei
Neurons Types:
Neurons are heterogeneous with respect to cell size, shape etc. because the kind of work the cell has to
do depends on the location, the systems, the connections and the neurotransmitters that it is specialized
in. ( motor neurons are different from the sensory neurons, visual cells are different form the auditory
cells)
Cells in all cases are composed of the soma -perikaryon (surrounding the nucleus), the axon (efferent:
output) the dendrites (receiving and input), and majority of the neurons are multipolar.
Neuronal Codes of communication:
How does information get processed and transmitted by the neurons. Information is coded in two
different codes the Digital code and the Analog code.
Digital code:
81
img
Neurological Basis of Behavior (PSY - 610)
VU
This is the code used by the neuron to pass information from one end to of the neuron to the other. This
is like the Morse code, where the changing number of dots and dashes change the message sent out. In
this the Rate of change is constant and in the same unit when the axonal end talks to the soma and the
dendritic ends. This determines how and what message sent. This is the electrical in nature; the
electrical impulse is generated and sent.
Analog code:
This is the code used when two neurons are communicating with each other. This is a biochemical
signal, varies with the intensity of the message. The more intense the message the more
Neurotransmitter released (Chemical)
Can the two codes be linked/ transformed one into other? Yes, this is happening constantly. Neurons are
communicating to each other as well as passing information within the neuron. The frequency or rate of
information in the digital would lead to amount of neuro-chemical released in the synapse and when the
neurotransmitter molecules crosses over to the other neuron, their contact transforms into an electrical
signal. Therefore it is a continuous Electrical---chemical---electrical change taking place. The neuron
can communicate effectively in both information systems.
The transmission of a neuron takes place when the axon sends in the impulse to the cell soma, and then
the cell responds by triggering a message to the dendritic synapse ( with axons /somas of other cells).
This is known as the axonal transmission and the junctional transmission.
Axonal transmission:
a) In this transmission the impulse travels both ways i.e. from the cell body to terminal is known as
orthodromic or anterograde, and if the impulse travels from the Terminal to cell body it is known as
antidromic or retrograde.
b) In the axonal transmission there is no time delay
c) This is not affected by drugs or other substances
d) This is an all or none firing. Firing begins and ends with stimulation, there is no after discharge
Junctional Transmission:
a) Junctional Impulse travels only in one direction from the presynapse to the post synapse.
b) There is time delay between transmissions. Neuro Transmitter molecules travel across synapse .1 to.2
milli seconds.
c) Spatial and temporal summation. In this transmission, the messages get summated at the axonal
hillock before a decision is made to fire or not i.e. they reach threshold where the cell fire an action
potential.
d) Affected by drugs, as drugs can be used to change the rate of transmission.
e) It is not all or none transmission it is graded response
In the next lesson we would discuss more about the neuron and the processes which take place within
the neuron.
82
img
Neurological Basis of Behavior (PSY - 610)
VU
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.JohnWiley &Sons. N.Y
6. Brown,T.S. and Wallace. (1980) P.M Physiological Psychology
Academic Press New York
83
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