PSY290H1 Chapter Notes - Chapter 3: Myelin, Dorsal Root Of Spinal Nerve, Spinal Cord

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3 Feb 2013
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Chapter 3: Anatomy of the Nervous System
Cells of the Nervous System
Neurons
Specialised for reception, conduction, and transmission of electrical signals
Cell body
Endoplasmic Reticulum
Folded membranes in the cell body
Rough areas help synthesise proteins
Smooth areas help synthesise fats
Cytoplasm
Clear internal fluid of the cell
Golgi complex
Connected system of membranes that packages molecules in vesicles
Mitochondria
Sites of aerobic (oxygen-consuming) energy release
Neuron cell membrane
Composed of a lipid bilayer
Channel proteins
Allow certain molecules to pass
Signal protein
Transfer a signal to the inside of the neuron according to which molecules bind to
them on the outside
Types of neurons
Multipolar (most neurons)
Has more than two processes extending from its cell body
Unipolar neuron
Has one process extending from its body
Bipolar neuron
Has two processes extending from its body
Interneurons
Neurons with short or no axon body whose function is to integrate neural activity
within a single brain structure, not to conduct signals from one structure to another
Neurons in neuroanatomical structure
In the CNS:
Clusters of cell bodies = nuclei
Bundles of axons = tracts
In the PNS:
Clusters of cell bodies = ganglia
Bundles of axons = nerves
Glial Cells
Ogliodendrocytes glial cells with extensions that wrap around axons of some neurons in the
CNS
Constitutes one myelin segment
Schwann cells are like ogliodendrocytes but in the PNS
Constitutes many myelin segments, often with more than one axon
Unlike ogliodendrocytes, these can guide axonal regeneration after damage (regrowth).
This is why effective regeneration in mammals is restricted to the PNS
Microglia
Smaller than glia
Respond to injury or disease by multiplying, engulfing cellular debris, and triggering
inflammatory responses
Astrocytes
Largest glial cells and star-shaped
Cover blood vessels that course through the brain and make contact with cell bodies
Allow passage of some chemicals from the blood to the CNS and blocks others
Neuroanatomical Techniques
Staining
Golgi stain
Can see individual neurons
Silver invades neurons and turns them black
Can only see neurons in silhouette though
Nissl Stain
Made it possible to see the number of neurons in an area and the nature of their inner
structure
Usually cresyl violet dye is used
Electron microscopy
Tracing techniques
Anterograde (forward)
Shows cell bodies projecting away from a certain area
Retrograde (backward)
Shows cell bodies projecting towards a certain area
Spinal Cord (cross-section)
Gray matter
Inner H-shaped core of the spinal cord
Composed mostly of cell bodies and unmyelinated interneurons
White matter
Outer area of the spinal cord
Composed mostly of myelinated axons
Dorsal horns
Dorsal arms of the spinal gray matter
Ventral horns
Ventral arms of the gray matter
Spinal nerves are attached to the cord on either side (left and right) at 31 levels of the spine
Each of the 62 spinal nerves divide as it nears the cord and its axons are joined to the cord
by the ventral or dorsal roots
Dorsal root
All dorsal root axons (somatic and autonomic both) are sensory (afferent) unipolar
neurons
The cell bodies are grouped together right outside the cord to form root ganglia
Ventral root
Motor (efferent) multipolar neurons with their cell bodies in the ventral horns
Those that project to the skeletal muscles and are part of the somatic nervous
system
Those that are part of the autonomic nervous system project in the ganglia where
they synapse onto neurons that project to the internal organs
Five Major Divisions of the Brain
In development:
There is a fluid-filled tube that starts to have 3 swellings
These turn into the forebrain, midbrain, and hindbrain eventually
Then this turns into 5 swellings when the forebrain and hindbrain each turn into two
swellings
The last four are often collectively called the “brain stem”
From front (anterior) to back (posterior), the swelling become [encephalon = in the head]:
Telencephalon (cerebral hemispheres)
Largest division of the brain and conducts the most complex brain functions
Initiates voluntary movement, interprets sensory input, and mediates complex
cognitive processes (learning, speaking, problem-solving)
Cerebral Cortex
Tissue layer covering the hemispheres
Mostly made of small, unmyelinated neurons, and therefore has a gray
colour
Fissures large furrows in the cortex; Sulci small furrows; Gyri ridges
between them
The largest fissure separates the hemispheres: longitudinal fissure and the
hemispheres are still partially connected by cerebral commissures, with the
largest being the corpus collosum
Postcentral Gyrus
Analyzes sensation from the body, like touch
Superior Temporal Gyrus
Hearing and language
Inferior Temporal Cortex
Id’s complex visual patterns