PSYCH261 Lecture Notes - Lecture 3: Pia Mater, Olfactory Bulb, Auditory Cortex

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UNIT 3: STRUCTURE OF THE NERVOUS SYSTEM
Anatomical Directions
Directions in the nervous system are described relative to the neuraxis, an imaginary line drawn
through the length of the central nervous system, from lower end of the spinal cord up to the
front of the brain.
- Ipsilateral: refers to structures on the same side
oE.g. If we say “the olfactory bulb sends axons to the ipsilateral hemisphere” it
means that the left olfactory bulb sends axons to the left hemisphere and the
right olfactory bulb sends axons to the right hemisphere
- Contralateral: refers to structures on the opposite sides of the body
oE.g. If we say that a region of the left cerebral cortex controls movements of the
contralateral hand then it means that the region controls movement of the right
hand
We can slice the nervous system in three ways:
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1. Transversely (also known as frontal sections when referring to the brain)
2. Horizontal sections: parallel to the ground
3. Sagittal section: perpendicular to the ground and parallel to the neuraxis
a. Midsagittal plane divides brain into two symmetrical halves
Nervous System
Central Nervous System (CNS)
- Brain and spinal cord
Peripheral Nervous System (PNS)
- Cranial nerves, spinal nerves, and peripheral ganglia
CNS is encased by a bone. The brain is covered by the skull and the spinal cord is encased by the
vertebral column.
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Meninges
The protective sheaths around the brain and spinal cord are called meninges (membrane).
The meninges consist of three layers (from outer to innermost):
1. Dura mater: thick, tough, flexible but unstretchable
2. Arachnoid membrane: weblike appearance, soft and spongy
3. Pia mater: closely attached to brain and spinal cord, contains the smaller blood vessels
of the brain and spinal cord
- Between the pia mater and the arachnoid membrane is the subarachnoid space which
is filled with cerebrospinal fluid (CSF)
The PNS is covered with two layers of meninges: the middle layer (with its associated pool of
CSF) covering only the brain and spinal cord. The outer and inner layers (dura mater and pia
mater) fuse to for a sheath that covers the spinal and cranial nerves and peripheral ganglia.
The Ventricular System and Production of CSF
- The human brain floats in the CSF within the subarachnoid space which helps reduce the
net weight of the brain
- CSF also helps absorb shock
- Brain connects with series of interconnected ventricles which are filled with CSF
1. Lateral ventricles: largest chambers which are connected to the
2. Third ventricles: located at the midline of the brain, the walls dividing the brain into
symmetrical halves
3. Cerebral aqueduct: long tube that connects the third ventricle to the fourth ventricle
(constitutes first and second ventricles but rarely referred to as such)
- CSF is obtained from blood and resembles blood plasma in its composition
oMade by a tissue with rich blood supply called choroid plexus (protrudes into all
four ventricles)
- CSF is provided constantly and flows into the third ventricle  cerebral aqueduct 
fourth ventricle where CSF is still being produced. CSF leaves fourth ventricle through
small openings that connect with the subarachnoid space. CSF flows through
subarachnoid space around the CNS, where it is reabsorbed into the blood supply
through arachnoid granulations. These pouch-like structures protrude into the superior
sagittal sinus which drains into the veins serving the brain.
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