Organization and Basic Anatomy of the CNS - Lecture 1 (Neurophysiology)

What is the main function of the Cell Body of a Neuron?

Dendrites?

Axon (Nerve Fiber)?

Axon Collaterals?

Terminals?

Synapses / Varicosities?

Cell Body — cell maintenance

Dendrites — responsible for most receiving synaptic contact between neurons

Axon (Nerve Fiber) — carries information from the Cell Body to the Target

Terminals — specialized structures at the end of Axons that terminate at the Synapse and release NTs

Synapses / Varicosities — seng signals to target cells via release of NTs

What two cell types make up the Myelin?

What is located in between these cells?

1. Schwann Cells (PNS)

2. Oligodendrocytes (CNS)

In between Myelin-forming cells, there are Nodes of Ranvier

What does Myelin do to conduction velocity?

What determines the rate at which this occurs?

Myelin accelerates the conduction velocity along the Axon

The amount of acceleration is dependent upon the size of the Axon

What are the four Morphological classes of Neurons?

1. Multipolar

2. Pseudounipolar

3. Bipolar

4. Unipolar

What are the characteristics of Multipolar Neurons?

1. Have multiple dendritic processes

2. Mostly made up of Tract Neurons and Neurons with Peripheral Processes in the CNS

What are the characteristics of Pseudounipolar Neurons?

1. Have a single ‘stem’ that bifurcates to make:

• A Peripheral (Distal) Process — projects to the target organ

• A Central (Proximal) Process — projects to the CNS

2. Typical cell type in the Dorsal Root and Cranial Nerve Ganglia (sensory neurons)

3. Innervates all skin cells

What is a Peripheral Process?

Central Process?

What are other names for both types?

Peripheral Process — also called a Distal Process; projects to the target organ

Central Process — also called a Proximal Process; projects to the CNS

What are the characteristics of Bipolar Neurons?

1. Have two processes

2. Mainly associated with the special senses (commonly found in sensory systems)

3. Example includes Retinal Bipolar Cells

What are the characteristics of Unipolar Neurons?

1. Only one process extends from the cell body

2. Composed of only the Axon and Cell Bodies, but NO Dendrites

3. Example includes Brush Cells in the Cerebral Cortex

What determines the specific morphology of each neuron?

Function determines morphology

What are the four Functional classes of neurons?

1. Afferent (Sensory) Neurons

2. Efferent (Motor) Neurons

3. Interneurons (aka Local Circuit Neurons)

4. Projection Neurons

What is the main function of Afferent (Sensory) Neurons?

Efferent (Motor) Neurons?

Interneurons (Local Circuit Neurons)?

Projection Neurons?

Afferent (Sensory) — projects from the PNS to the CNS

Efferent (Motor) — projects from the CNS to PNS (Viscera effectors)

Interneurons (Local Circuit Neurons) — connect neurons within the CNS

Projection Neurons — long axons that stretch from the Site of Origin to the Distant Target within the CNS (SC —> Brain or vice versa)

What functional class are Postganglionic Neurons?

Efferent Neurons

What does it mean when a Cell Body is Ipsilateral to the end of an Axon?

Contralateral?

What is this in relation to?

Ipsilateral — Cell body and Axon are on the same side

Contralateral — Cell and Axon are on the opposite side

This is in relation to the Midline of the body

What is a Nerve?

Bundle of axons in the PNS that usually contains both Afferent and Efferent fibers

What is a Ganglion?

Nucleus?

What is an example of each?

Ganglion — group of neurons in the PNS, ex. Dorsal Root Ganglion

Nucleus — group of neurons in the CNS, ex. Basal Ganglia (group of nuclei in the CNS)

What is a Fasciculus?

Part of the CNS containing a discrete collection of axons

What is a Tract?

How do they pass?

Collection of axons where cell bodies are located in ONE area of the CNS and projections are sent to another CNS area

Can pass via several Fasciculi

What is a Funiculus?

Large collection of axons (within a defined CNS region) that may contain multiple fasciculi or tracts

What are the three major planes of the brain?

1. Sagittal — front to back

2. Coronal — side to side

3. Horizontal — horizontal 

What does Superior mean in anatomical terminology?

Inferior?

Posterior?

Anterior?

Superior — higher

Inferior — lower

Posterior — back

Anterior — front

What type of cell makes up the majority of cells in the nervous system?

What ratio does it compose in the CNS?

Glial Cells

For every 1 neuron in the CNS, there is 9 Glial Cells

What is the main function of Glial Cells?

Support neurons and maintain the extracellular fluid (absolutely necessary for neuron function)

What is the main function of Oligodendrocytes (CNS) and Schwann Cells (PNS)?

Form the myelin sheath around neurons

What is the main function of Astrocytes?

How does it accomplish this?

Maintains the extracellular fluid and supports metabolic activity of neurons

Removes excess K+ and NTs from the extracellular space

What is the main function of Microglia?

Macrophage-like cell that participates in immune function

What is the main function of Ependymal Cells?

Where is it located?

Comprise the lining of cerebral ventricles and produce / regulate cerebrospinal fluid that fills the ventricles

Located in the Choroid Plexus

What happens if an Axon is severed in the PNS?

CNS?

PNS — axon can partially regrow and reinnervate the original target

CNS — axon will NOT regrow; can sprout new endings, but axon function is never regained

What is Gray Matter?

Why does it appear gray?

Gray Matter — central, butterfly-shaped spinal cord region that contains the cell bodies of Neurons and Glia

Located in the Spinal Cord

Appears gray because of lack of Myelin

What is White Matter?

Where does it get its color from?

White Matter — tracts consisting of primarily axons that surround gray matter and connect regions of the SC or the SC to the brain

Gets the color from axons that have Myelin

What are Dorsal Roots?

What is their main function?

Dorsal Roots — consist of the axons of sensory neurons

Takes in sensory input and sends it to the spinal cord

What is the main function of the Dorsal Root Ganglia?

Contains the cell bodies of the Pseudounipolar Sensory Neurons

What are Ventral Roots?

What is their main function?

Ventral Roots — consist of the axons of Motor Neurons

Location where Motor output leaves the Spinal Cord

What is another name of the Telencephalon?

What does it contain?

Another name is the Cerebrum

Contains the Cerebral Cortex, Basal Ganglia, etc.

What does the Diencephalon contain?

Contains the Hypothalamus, Thalamus, etc.

What two things make up the Forebrain?

The Brainstem?

Forebrain is made up of the Telencephalon and the Diencephalon

Brainstem is made up of the Midbrain, Pons, and Medulla Oblongata

What are the main functions of the Brainstem?

Responsible for:

• Regulation of cardiovascular and respiratory function

• Sleep and wakefulness

• Posture and Balance

• Relay and integration of information from the PNS to the CNS, and vice versa

Where are the nuclei of most Cranial Nerves located?

Nuclei of Biogenic Amines?

Nuclei of Cranial Nerves — in the Brainstem

Nuclei of Biogenic Amines — in the Reticular Formation

What is the central core of the Brainstem?

What is its main function?

Central Core of the Brainstem is the Reticular Formation

Reticular Formation is responsible for integrating information from all sensory modalities and shifting motor outflow (in response)

What is the main function of the Cerebellum?

Coordinates ongoing movements and learns new movements; receives input from all muscles and any other brain regions responsible for movement

What are the two major components of the Cerebellum?

1. Cerebellar Cortex — located near the surface; output cells project to the Deep Nuclei

2. Deep Nuclei — located deeper in the Cerebellum; its neurons produce output from the Cerebellum

What are Cerebral Hemispheres?

Cerebral Hemispheres — major divisions of the brain

What is the Cerebral Cortex?

What is its main function?

Outer shell of each cerebral hemisphere that is made up of gray matter (3 mm thick)

Main function is to be the major integrating region of the brain, making humans human

What connects the Cerebral Cortex to other regions of the Brain?

Fiber Bundles allow for sending of information from the Cerebral Cortex to other regions of the Brain

What is the main function of the Corpus Callosum?

Pyramidal Cells?

Corpus Callosum — connects two sides of the Cerebral Cortex

Pyramidal Cells — provide output from the Cerebral Cortex

What are the four lobes of the Cerebral Cortex?

1. Frontal Lobe

2. Parietal Lobe

3. Occipital Lobe

4. Temporal Lobe

Which three regions do inputs to the Cortex arise from?

1. Thalamus — major relay station

2. Other regions of the Cortex

3. Reticular Formation of the brainstem

What are Subcortical Nuclei?

Which is the most prominent type?

Groups of cell bodies deep within hemispheres

Most prominent are Basal Ganglia

What is the main function of the Basal Ganglia?

What three components are they separated into?

Main function is to help in control of movements and higher cortical functions related to motor activities (cognition, learning, and non-declarative memory)

Three components:

1. Caudate Nucleus

2. Putamen

3. Globus Pallidus

What is the main function of the Thalamus?

Major relay station of the Cortex; relays most sensory inputs from the body before they reach the cortex

Also involved in arousal and attention

What is the main function of the Hypothalamus?

Major endocrine center that is responsible for controlling body homeostasis

What are the main responsibilities of the Limbic System?

Responsibilities include:

• Emotional Responses

• Learning and Memory

• Integration of Autonomic Responses with Emotional Stimuli

What are the Cerebral Ventricles?

What are they covered by?

Cerebral Ventricles — four CSF-filled, interconnected cavities

They are covered on the surface by Ependymal Cells

What are the Lateral Ventricles?

Third Ventricle?

Fourth Ventricle?

Lateral Ventricles — right and left ventricles that are deep in the Cortex; connected to the Third Ventricle

Third Ventricle — located in the Diencephalon; connected to the Fourth Ventricle in the Midbrain

Fourth Ventricle — located between the Cerebellum and the Brainstem (including the Pons and Medulla Oblongata)

What are the three main membranous coverings of the brain?

Where are they located?

1. Dura Mater (Outer) — thickest and toughest covering that is adjacent to the skull

2. Arachnoid — middle layer

3. Pia Mater (Inner) — adjacent to the Brain and Spinal Cord

What is the Subarachnoid Space?

Area between the Arachnoid and Pia Mater layers where CSF circulates

What is the Choroid Plexus?

Part of the lining of ventricles, which appears tufted

What secretes CSF?

Where does CSF circulate?

Where does it eventually return to the blood at?

Ependymal cells secrete CSF

CSF circulates through the Ventricles and Spinal Cord, before eventually returning to the Blood at the Arachnoid Villi

What are Arachnoid Villi?

What are they the main location of?

Structures that project from the Arachnoid to Venous Sinuses

Main location of CSF returning to the Blood

What are the main functions of Cerebrospinal Fluid (CSF)?

1. Regulates extracellular environment of Neurons

2. Protective function during brain injuries

How much of the total blood supply does the Brain receive?

15% of the total blood supply

What is required by the CNS / Brain to produce energy?

What happens when there is a lack of this resource?

Glucose is required by the CNS to produce energy

When there is short term lack of Glucose, this causes Neuronal Death

What is the Blood-Brain Barrier?

Why is it unique?

What is its main function?

Unique property of the vascular system in the body; it is found ONLY in the Brain

Serves to protect the Brain / CNS by preventing large molecules from entering the Extracellular Fluid

What two layers make up the Blood-Brain Barrier?

1. Endothelial Cells of brain / spinal cord capillaries

2. Glial Cells (Astrocytes)

What substances can cross the BBB?

Which cannot?

How does this impact our profession?

Lipid soluble substances can cross the BBB

Lipid insoluble substances cannot cross the BBB

This impacts drug permeability (many drugs cannot cross BBB)