Intro to Neuro: Introduction to the Brain

Orientation of the Brain


Outline the Orientation of the Brain


  • Orientation of the Brain is based on two axes:


  1. Rostral to Caudal
  • Rostral to Caudal is the Longitudinal Axis of the Forebrain


  • Above the axis is the Dorsal Side and Below the axis is the Ventral Side


  1. Brain Centre to Caudal
  • Brain Centre to caudal is the Longitudinal Axis of the Brainstem and Spinal Cord


  • Brain Centre to Caudal is based on when an individual or animal is on all fours


  • Above the axis is the Dorsal Side


  • Below the Axis is the Ventral Side


  1. Anterior and Posterior

  • Anterior is in front of


  • Posterior is behind




  1. Superior and Inferior

  • Superior is above


  • Inferior is below



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Planes of the Brain


Outline the Planes of the Brain and each view given


  1. Coronal (Frontal) Section
  • Coronal Section is the cross section of the brain


  • Coronal Section gives a Medial to Left and Right Lateral view of the Brain


  1. Mid-Sagittal Section
  • Mid-Sagittal Section separates the two Hemispheres of the Brain


  • Mid-Sagittal Section gives an Anterior to Posterior View of the Brain


  1. Horizontal Section
  • Horizontal Section of the Brain gives an Anterior to Posterior View of the Brain and a medial to Left and Right Lateral View of the Brain


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Brain lies within a cranial vaults protected by Skull bones, and Cranial Meninges, Cerebrospinal Fluid and Ventricles



Membranes covering the Brain


List the Membranes covering the Brain


  • Brain is covered by the following membranes:


  1. Dura Mater

  • Periosteal Dura Mater


  • Meningeal Dura Mater




  1. Arachnoid Mater


  1. Pia Mater

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Lobes of the Brain


List and Label the Lobes of the Brain


  1. Frontal Lobe


  2. Parietal Lobe


  3. Occipital Lobe


  4. Temporal Lobe


  5. Cerebellum


  6. Insular/Limbic Lobe




Outline the function of each Lobe


  1. Frontal Lobe
  • Frontal Lobe is responsible for high cognitive processing, motor and pre-motor action


  • Frontal Lobe has the:



    • Primary Motor and Pre-Motor Cortex


    • Pre-Frontal Cortex: Broca's Speech Area


    • Frontal Eye Fields


    • Motor Association Area




  1. Parietal Lobe
  • Parietal Lobe is responsible for Somatosensory action such as touch and vibration


  • Parietal Lobe has the:


  • Primary Somatosensory Cortex



    • Wernicke's Area


    • Sensory Association Area




  • Wernicke's Area is responsible for speech comprehension


  1. Occipital Lobe
  • Occipital Lobe is responsible for vision and visual association (Cortical vs Psychic blindness)


  • Occipital Lobe has the:



    • Primary Visual Cortex


    • Visual Association Area




  1. Temporal Lobe which is responsible for Auditory, Speech and Language


  • Temporal Lobe also has the:



    • Primary Auditory Cortex


    • Auditory Association Area


    • Wernicke's Area




  1. Cerebellum
  • Cerebellum is responsible for motor co-ordination


  1. Insular/Limbic Lobe

  • Insular Lobe is associated with tastes vestibular, visceral sensation



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Major Divisions of the Brain using embryological terms


Explain the Major Divisions of the Brain using embryological terms



  1. Brain Encephalon

  • Brain Encephalon is divided into three areas:



    • Prosencephalon (Forebrain)


    • Mesencephalon (Mid-Brain)


    • Rhombencephalon (Hindbrain)




  1. Prosencephalon
  • Prosencephalon is divided into:


  1. Telencephalon
  • Telencephalon forms the Cerebral Hemispheres which associated with the Lateral Ventricles
  1. Diencephalon
  • Diencephalon is associated with the 3rd Ventricle



  1. Mesencephalon
  • Mesencephalon forms the Mid-Brain which is associated with the Cerebral Aqueduct



  1. Rhombencephalon
  • Rhombencephalon is divided into:


  1. Metencephalon
  • Metencephalon forms the Pons and Cerebellum which are associated with the 4th Ventricle


  1. Myelacephalon

  • Myelacephalon forms the Medulla Oblongata which is associated with the 4th Ventricle



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Surface of the Brain


List and Explain the different features of the Brain Surface


  1. Gyrus
  • Bumps on the brain surface are known as Gyri


  1. Sulcus
  • Grooves in the brain surface are known as Sulci


  1. Fissures
  • Deep grooves on the brain surface are known as Fissures

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Describe the important different features on the Brain Surface


  1. Central Sulcus
  • Central Sulcus extends from the Superior most Medial position on the Brain all the way down to the Lateral sides of the Brain


  • Central Sulcus separates the Frontal Lobe from the Parietal Lobe


  1. Pre-Central Gyrus
  • Pre-Central Gyrus is located anterior to the Central Sulcus


  • Pre-Central Gyrus is the Primary Motor Area of the Brain


  • It is responsible for the control of motor and pre-motor (voluntary) movement


  1. Post-Central Gyrus
  • Post-Central Gyrus is located posterior to the Central Sulcus


  • Post-Central Gyrus is known as the Primary Somatosensory area


  • It is responsible for somatosensory action such as vibration and touch


  1. Lateral (Sylvia) Fissure
  • Lateral (Sylvian) Fissure is a deep groove which separates the Frontal and Parietal Lobe from the Temporal Lobe


  1. Superior Temporal Gyrus
  • Superior Temporal Gyrus


  • Superior Temporal Gyrus is the Primary Auditory Area of the Brain


  • Superior Temporal Gyrus is responsible for hearing, speech and language


  1. Cingulate Gyrus
  • Cingulate Gyrus is located above the Corpus Callosum


  • Cingulate Gyrus is responsible for Limbic Function


  1. Calcarine Sulcus
  • Calcarine Sulcus separates the Primary Visual Area pf the Occipital Lobe from the other Occipital Areas


  1. Parieto-Occipital Sulcus
  • Parieto-Occipital Sulcus separates the Parietal Lobe from the Occipital Lobe


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Major Sub-divisions of the CNS in Humans


List the major sub-divisions of the CNS in Humans


  1. Cerebral Hemisphere
  • Cerebral Hemisphere is the folded and highly convoluted area of the Brain


  1. Diencephalon: Thalamus and Hypothalamus
  • Diencephalon is located below the Cerebral Hemispheres


  1. Cerebellum


  1. Brain Stem:



    • Midbrain


    • Pons (Bulge on the Ventral aspect)


    • Medulla Oblongata (Houses many Autonomic Sensors)




  1. Spinal Cord



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Divisions of the Nervous System


Outline the decisions of the Nervous System


  1. Central nervous System

  • Brain


  • Spinal Cord




  1. Peripheral Nervous System

  • Somatic: Involuntary Action


  • Autonomic: Voluntary Action



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Cells in the Central Nervous System


List the Cells of the CNS


  • Neural Tissue is made up of the following cells:
  1. Neurons
  • Neurons are the functional units of the CNS


  • Neurons transfer stimuli between different places


  1. Glial (Support) Cells

  • Glial Cells serve to support the functioning neurons



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Typical Structure of a Neuron


Describe the morphological features of a typical Neuron


  • A typical Neuron has the following features:


  1. Dendrites
  • Dendrites are the extensions which receive information


  • Dendrites transmit the information towards the Cell Body


  1. Cell Body


  1. Axons and Axon Terminals
  • Axons transmits information away from the Cell Body towards the Muscle


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Neurons


  • Neurons are the individual functional Units


  • A Group of Neurons is collectively called a Nucleus in the CNS


  • There are many Nuclei in the Brain


Classification of Neurons


List the classification categories of Neurons


  • Neurons can be classified according to:

  1. Number of Processes


  2. Function


  3. Mode of Function


  4. The Length of Axons




Describe the classification categories of Neurons


  1. According to the Number of Processes

  • Unipolar


  • Bipolar


  • Pseudo-Unipolar


  • Multipolar




  1. According to the Function

  • Sensory (Afferent)


  • Motor (Efferent)


  • Interneurons




  1. According to the Mode of Action

  • Excitatory


  • Inhibitory




  1. According to the Length of the Axons

  • Long Axons (Golgi Type 2)


  • Short Axons (Golgi Type 1)

  1. Afferent (Sensory) Neurons
  • Afferent Neurons bring impulses to the CNS


  1. Efferent (Motor) Neurons
  • Efferent neurons carry impulses away from the CNS


  1. Interneurons
  • Interneurons are located between the Sensory and Motor Neuron


  • Interneurons are ONLY found in the CNS


  • Interneurons can be Sensory or Motor in function


  • The more complex the required action, the more greater the number of interneurons involved


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Types of Neurons According to the Number of Processes


Describe the Types of Neurons according to the Number of Processes


  1. Unipolar Neurons
  • In Unipolar Neurons the Axons and Dendrites move towards the Cell Body


  • Unipolar neurons are usually found in invertebrates



  1. Bipolar Neuron
  • In Bipolar Neurons the Cell Body is located between the Axons and Dendrites


  • Dendrites carry information towards the Cell Body and Axions carry information away from the Cell Body


  • Bipolar Neurons are found in Cells in the Retinal layer of the Eye


  1. Pseudo-Unipolar Neuron
  • In Pseudo-Unipolar Neurons the Cell Body sits a distance away from the Axons and Dendrites


  • Cell body connects to a process, the process then bifurcates and gives rise to the Axon and the Dendrite


  • Pseudo-Unipolar Neurons are found in the Ganglion Cell of the Dorsal Root


  1. Multipolar Neuron
  • Multipolar Neurons have many different Dendrites and usually a one single Axon or two Axons


  • Multipolar neurons are found in the Motor Neuron of the Spinal Cord


  • Multipolar Neurons are the most common type of Neurons in the Brain


  1. NOTE: Ganglia are a collection of Cell Bodies in the Peripheral Nervous System (PNS)



    • E.g: Dorsal Root Ganglion

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Ganglia vs Nuclei


List the differences between the Ganglia and Nuclei


  • Ganglia

  1. Ganglia refers to a structure which contains a number of Cell Bodies in the PNS


  2. Ganglia occur in the PNS


  3. Ganglia form Plexuses


  4. Examples of Ganglia: Dorsal Root Ganglia




  • Nuclei

  1. Nuclei refers to a structure which contains a number of Cell Bodies in the CNS


  2. Nuclei occur in the CNS


  3. Nuclei occurs in Grey matter


  4. Examples of Nuclei: Caudate



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Communication between Neurons


Outline the Two Types of Communication between Neurons


  • Neurons can communicate via two types of communication:


  1. Electrical Communication using Action Potentials
  • Information is received by the Dendrites


  • Dendrites then transmit the information to the Cell Body


  • Cell Body then converts the information into an Action Potential


  • Then Action Potential is the transmitted by the Axons away from the Cell Body to the Effector


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  1. Chemical Communication using Neurotransmitters
  • Chemical Communication occurs at the end of the Axons


  • Axons have Neurotransmitters


  • Neurotransmitter are stored with the Synaptic Vesicles


  • Arrival of an Action Potential at the Axon stimulates the release of Neurotransmitter into the Synaptic Cleft



    • Synaptic Cleft is the small space between an Axon and Dendrite/Cell Body


  • Neurotransmitters are then picked up by the Dendrites


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Glial (Support) Cells


Outline the function of the Glial (Support) Cells


  • Glial (Support) Cells are responsible for the following:

  1. Structural and Metabolic Support


  2. Protection


  3. Guidance of Axonal Growth during development


  4. Role in repair process




Glial Cells of the Nervous System


List the types of Glial Cells of the Nervous System


  • There are two types of Glial Cells of the Nervous System:


  • Glial Cells in the CNS

  1. Oligodendrocytes


  2. Astrocytes


  3. Microglia


  4. Ependymal Glia




  • Glial Cells in the PNS

  1. Schwann Cells (Neurolemmocytes)


  2. Satellite Cells (Non-myelinating Schwann Cells)

Oligodendrocytes


Describe the features and functions of Oligodendrocytes


  • Oligodendrocytes are responsible for myelinating several segments of the Axon


  • This results in the formation of the Nodes of Ranvier


  • Nodes of Ranvier are the segments of the Axon which are unmyelinated


  • Node of Ranvier contains membrane channel proteins that assist in this process


  • Nodes of Ranvier increase the speed of Action Potential transmission from the Cell Body through the Axon to the periphery



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Astrocytes


Describe the functions of the Astrocytes


  • Astrocytes are star-shaped Glial Cells


  • Astrocytes are in contact with Neurons and Capillaries


  • Astrocytes are the most common Cells int he CNS


  • Astrocytes are responsible for the following:
  1. Providing structural and trophic support


  1. Regulating the composition of the ECF


  1. Contributing to the Blood-Brain-Barrier


  1. Replace damaged neurons


  1. Provide guidance of axonal growth during development



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Microglia


Describe the features and functions of the Microglia Cells


  • Microglia Cells are derived from the Monocyte lineage


  • Microglia are the equivalent of the Macrophages in the Nervous System


  • Microglia are responsible for:
  1. Mediate immune function


  1. Clearing cellular debris


  1. Clearing dead neurons

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Ependymal Glial Cells


Describe the features and functions of the Ependymal Glial Cells


  • Ependymal Glial Cells range in shape from squamous to columnar shaped cells


  • Ependymal Glial Cells have Cilia


  • Ependymal Glial Cells are located in the:

  1. Ventricles of the Brain


  2. Central Canal


  3. Spinal Cord




  • Some Ependymal Glial Cells are specialized and form the Choroid Plexus in the Ventricles


  • Choroid Plexus produces the Cerebrospinal Fluid (CSF)


  • Ependymal Glial Cells help circulate the CSF using Cilia



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Schwann Cells


Describe the functions of the Schwann Cells


  • Schwann Cells are found in the PNS


  • A single Schwann Cell is equal to a single Myelin Sheath segment on the Axon


  • Schwann Cells have the following functions:
  1. Myelinating several segments of Axons in the PNS


  1. Secreting Neurotrophic Factors

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Satellite Cells


Describe the functions of the Satellite Cells


  • Satellite Cells are non-myelinating Schwann Cells


  • Satellite Cells surround the Cell Bodies of Neurons in Ganglia (PNS)


  • Satellite Cells provide support and nutrients



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Development of the Nervous System


Outline the Development of the Nervous System


  • Nervous System develops from the Ectoderm


  1. Ectoderm then forms a Neural Plate and Epidermis


  1. Epidermis is located on either side of the Neural Plate


  1. Epidermis and the Neural Plate are separated by a Neural Plate Border


  1. Neural Plate converges inwards to form a Neural Groove


  1. Neural Plate Borders then become the Neural Folds


  1. Eventually, the Neural Folds join together and separate from the Epidermis


  1. Neural Folds become Neural Crest Cells and the Neural Groove becomes the Neural Tube


  1. Neural Tube becomes the Brain and the Spinal Cord


  1. Neural Crest Cells become the PNS



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Grey Matter vs White Matter of the Brain


Differentiate between the Grey Matter and the White Matter of the Brain


  • Grey Matter of the Brain:
  1. Grey matter of the Brain makes up 40% of the Brain


  1. Grey matter of the Brain contains ALL the Neurons


  1. Grey Matter of the Brain is the place where Neurons receive information and respond



  • White Matter of the Brain
  1. White Matter makes up 60% of the Brain


  1. White Matter ONLY contains Myelinated and Unmyelinated Axons


  1. White Matter connects different parts of the brain


  • NOTE: ALL Brains have Grey matter and White matter



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Types of White Matter in the Brain


List the Types of White Matter in the Brain


  • There are 3 Types of White Matter in the Brain:

  1. Commissural Fibres


  2. Association Fibres


  3. Projection Fibres



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Describe the Types of White Matter in the Brain


  1. Commissural Fibres
  • Commissural Fibres allow for inter-hemispheric communication


  • An example of a Commissural Fibre is the Corpus Callosum


  • Corpus Callosum allows for inter-hemispheric communication


  1. Association Fibres
  • Association Fibres allow for intra-hemispheric communication


  • An example of an Association Fibre is the Cingulum


  • Cingulum allows for intra-hemispheric communication


  1. Projection Fibres
  • Projection Fibres connect different parts of the brain


  • An example of the Projection Fibre is the Internal Capsule


  • Internal Capsule connects different parts of the Brain



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Spinal cord Tracts: Sensory and Motor Pathways


Explain how does communication occur between the Limbs of the Body and the Cerebral Cortex


  • Spinal Cord houses Spinal Cord Tracts called the Ascending Sensory Tracts and the Descending Motor Tracts


  • Ascending Sensory Tracts and the Descending Motor Tracts in the CNS decussate (cross over) to various degrees along their course


  • So that each side of the brain is functionally associated with the contralateral half of the body


  • This means that if a stimulation occurs on the Right Side of the Body, the stimulation will be processed on the Left Side of the Brain



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Peripheral Nervous System


Outline the features of the Peripheral Nervous System


  • Peripheral Nervous System refers to the Nerves outside the Brain and Spinal Cord


  • PNS consists of:

  1. Nerve Endings


  2. Peripheral Nerves


  3. Plexuses


  4. Peripheral Ganglia





Describe what structures occur in the PNS


  1. Nerve Endings
  • Sensory Nerve Endings which detect changes


  • Motor Nerve Endings which control action and activity


  1. Peripheral Nerves
  • Peripheral nerves refer to Spinal and Cranial Nerves


  1. Plexuses

  • Plexuses are structures where spinal and cranial nerves are redistributed



    • eg: Brachial Plexus


  1. Peripheral Ganglia

  • Peripheral Ganglia are structures in the PNS outside the CNS that contain a number of cell bodies



    • eg: Dorsal Root Ganglion

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Functional Division of the Peripheral Nervous System: Autonomic Nervous System (ANS)


  • ANS is responsible for maintaining homeostasis of the internal environment


  • ANS forms part of the PNS


  • ANS is divided into:
  1. Parasympathetic Division which performs rest and digest


  1. Sympathetic Division which performs flight or fight



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