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Chapter 2

NROC93H3 Chapter Notes - Chapter 2: Midbrain Tectum, Brainstem, Dura Mater


Department
Neuroscience
Course Code
NROC93H3
Professor
S
Chapter
2

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Chapter 7: The Structure of the Nervous System
Gross Organization of the Mammalian Nervous System
NS of all mammals has two division: the CNS and the PNS
Anatomical References
o Read Page 169 and 170
The Central Nervous System
o Consists of the parts of the nervous system encased in bone: the brain and the spinal
cord
o Three parts of the brain are common to all mammals: the cerebrum, the cerebellum,
and the brain stem
o The Cerebrum
Rostral-most and largest part of the brain
It is split down the middle into two hemispheres; separated by the deep sagittal
fissure.
The right hemisphere receives information and controls the left side of the
body; the left hemisphere receives information and controls the right side of the
body
o The Cerebellum
Lies behind the cerebrum
It contains as many neurons as both cerebral hemispheres combined
It is primarily a movement control center with extensive connections to the
cerebrum and spinal cord
Left side of the cerebrum is concerned with the left side of the body and the
same applies to the right portion.
o The Brain Stem
The remaining part of the brain
Forms the stalk from which the cerebral hemispheres and the cerebellum sprout
A complex nexus of fibers and cells that in part serves to relay information from
the cerebrum to the spinal cord and cerebellum; and vice versa
Also the site where vital functions are regulated (e.g. breathing, consciousness,
and the control of body temp.)
Considered the most primitive part of the mammalian brain but also the most
important to life
o The Spinal Cord
Encased in a bony vertebral column and is attached to the brain stem
Is the major conduit of info from skin, joints, and muscles of the body to the
brain and vice versa
It communicates with the body via the spinal nerves (part of PNS).
Each spinal nerve attaches to the spinal cord by means of two branches:
the dorsal root and the ventral root
The Peripheral Nervous System
o Has two parts: the somatic PNS and the visceral PNS

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o The Somatic PNS
All the spinal nerves that innervate the skin, the joints, and the muscles that are
under voluntary control are part of this PNS
The somatic motor axons (command muscle contraction) derives from motor
neurons in the ventral spinal cord
The cell bodies of the motor neurons lie within the CNS, but their axons are
mostly in the PNS
The somatic sensory axons enter the spinal cord via the dorsal roots; the cell
bodies of these neurons lie outside the spinal cord in clusters called dorsal root
ganglia
o The Visceral PNS
Also called autonomic nervous system (ANS)
Consists of neurons that innervate the internal organs, blood vessels, and glands
Information such as the pressure and oxygen content of the blood in the
arteries are brought to the CNS
Visceral motor fibers command the contraction and relaxation of muscles that
form the walls of the intestines and the blood vessels, the rate of cardiac
contraction, and the secretory function of various glands
o Afferent and Efferent Axons
Afferent means to carry to
Efferent is to carry from
The Cranial Nerves
o There are 12 pairs of cranial nerves that arise from the brain stem and innervate
(mostly) the head
o Some are part of the CNS and others are a part of the two divisions of the PNS
o Contain a complex mixture of axons that perform different functions
The Meninges
o The CNS is protected by three membranes collectively called Meninges
Dura mater
Outermost covering
Leatherlike
Forms a tough, inelastic bag that surrounds the brain and spinal cord
Arachnoid membrane
Just under the dura mater
Has an appearance and consistency resembling a spider web
Pia Mater
A thin membrane that adheres closely to the surface of the brain
Along it many blood vessels that ultimately dive into the substance of
the underlying brain
Separated from the arachnoid by a fluid-filled space
Filled with salty clear liquid called cerebrospinal fluid (CSF)
The Ventricular System
o The fluid-filled caverns and canals inside the brain constitute the ventricular system
o The fluid that runs in the systems is the CSF
CSF is produced by the choroid plexus, in the ventricles of the cerebral
hemispheres
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CSF flows from the paired ventricles of the cerebrum to a series of connected,
unpaired cavities at the core of the brain stem
CSF exits the ventricular system and enters the subarachnoid space through the
small openings located near where the cerebellum attaches to the brain stem
o The in the subarachnoid space, CSF is absorbed by the blood vessels at special structures
Imaging the Living Brain
o Read Pages 174 to 176
Understanding CNS Structure through Development
The entire CNS is derived from the walls of a fluid-filled tube that is formed at an early stage in
embryonic development
o The tube becomes the adult ventricular system
Read Table 7.1 and 7.2
Formation of the Neural Tube
o Embryo begins as a flat disk with three distinct layers of cells called the endoderm,
mesoderm and the ectoderm
The endoderm gives rise to the lining of many of the internal organs (viscera)
The mesoderm arise the bones of the skeleton and the muscles
The nervous system and the skin derive entirely from the ectoderm
The ectoderm gives rise to the nervous system: the neural plate
o At about 17 days from conception (in humans), the brain consists only of a flat sheet of
cells.
Next is the formation of a grove in the neural plate that runs rostral to caudal
neural groove
The walls of the groove are called the neural folds
o The move and fuse together to form the neural tube
o The entire nervous system develops from the walls of the neural
tube
As the neural folds come together, some neural ectoderm is pinched off
and comes to lie just lateral to the neural tube neural crest
o
o All neurons with cell bodies in the peripheral nervous system
derive from the neural crest
o The neural crest develops in close association with the underlying mesoderm
The mesoderm at this stage forms prominent bulges on either side of the neural
tube called somites
From these somites, 33 individual vertebrae of the spinal column and
the related skeletal muscles will develop
The nerves that innervate these skeletal muscles are called somatic
motor nerves
o The process by which the neural plate becomes the neural tube is called neurulation
Occurs very early in embryonic development (22 days after conception)
The Primary Brain Vesicles
o The process by which structures become more complex and functionally specialized
during development differentiation
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