Download Topic 8

Biology 463 - Neurobiology
Topic 8
Structural Organization of
the Nervous System
Lange
Korbinian Brodmann (1868-1918) - responsible for establishing the
science of comparative cytoarchitecture of the mammalian cortex
Comparative
morphology of the CNS
studies the
interrelationships
between different
species of animals and
the brain and spinal
cord.
This comparative
approach reveals
significantly similarities
and several differences
between species.
Gross Organization of the Mammalian Nervous System
The Central Nervous System of the Rat
– Cerebrum, cerebellum, brain stem
– Spinal Cord
The Spinal Cord
– Location: Attached to the brain stem
– Conduit of information (brain body)
– Spinal nerves
– Dorsal root
– Ventral root
The Peripheral Nervous System
– Nervous system outside of the brain and spinal cord
– Somatic PNS: Innervates skin, joints, muscles
– Visceral PNS: Innervates internal organs, blood vessels, glands
– Dorsal root ganglia: Clusters of neuronal cell bodies outside the spinal
cord that contain somatic sensory axons
– Ventral roots: neuronal cell bodies outside the spinal cord that contain
motor neurons
Afferent and Efferent Neurons
– Afferent (carry to): Carry information toward a particular point
– Efferent (carry from): Carry information away from a point
The Cranial Nerves
– 12 nerves from brain stem
– Mostly innervate regions of the head
Note that these cranial nerves will be
further discussed in the anatomy section.
Meninges
–
Three
membranes that surround the
brain
• Dura mater
• Arachnoid mater
• Pia mater
This view of the
meninges helps to
illustrate the net-like
arrangement of the
arachnoid mater.
Brain floats in
cerebrospinal fluid (CSF)
Liquor cerebrospinalis, is a clear
bodily fluid that occupies the
subarachnoid space and the
ventricular system around and
inside the brain and spinal cord.
Essentially, the brain "floats" in
it.
– Ventricles: CSF-filled
caverns and canals inside
brain
– Choroid plexus:
specialized tissue made of
ependymal cells in
ventricles that secretes
CSF
CSF serves four primary purposes:
1. Buoyancy: the human brain is about 1400 grams; however, the net weight
of the brain suspended in the CSF is equivalent to a mass of 25 grams.
The brain therefore exists in near neutral buoyancy, which allows the brain
to maintain its density without being impaired by its own weight, which
could cut blood supply and kill neurons in the lower sections without CSF.
2. Protection: CSF protects the brain tissue from injury when jolted or hit. In
certain situations such as auto accidents or sports injuries, the CSF cannot
protect the brain from forced contact with the skull case, causing
hemorrhaging, brain damage, and sometimes death.
3. Chemical stability: CSF flows throughout the inner ventricular system in the
brain and is absorbed back into the bloodstream, rinsing the metabolic
waste from the central nervous system through the blood-brain barrier. This
allows for homeostatic regulation and distribution of neuroendocrine
factors.
4. Prevention of brain ischemia: made by decreasing the amount of CSF in
the limited space inside the skull. This decreases total intracranial pressure
and facilitates blood perfusion.
Hydrocephaly in a small child.
Hydrocephaly - known as "water on the brain," is a medical condition in
which there is an abnormal accumulation of cerebrospinal fluid (CSF) in the
ventricles, or cavities, of the brain.
The most performed treatments for hydrocephalus, the cerebral shunt, was
first developed in 1960. The shunt must be implanted through neurosurgery
into the patient's brain.
Computed Tomography (CT)
– Hounsfields and Cormack developed the device and received the
1979 Nobel Prize for this work
– Generates an image of a brain slice much like histology of
cadaver brains
– X-ray beams are used to generate data that generates a
digitally reconstructed image
Hounsfields and Cormack
Magnetic Resonance Imaging (MRI)
– Advantages of MRI over CT
• greater detail
• not a significant source of irradiation
• Brain slice image in multiple angles
– Uses iinformation on how hydrogen atoms respond in the brain to
perturbations of a strong magnetic field – signals mapped by computer
A classic MRI
device.
Functional Brain Imaging Techniques
– Positron emission tomography (PET) - a nuclear medicine imaging technique
which produces a three-dimensional image or picture of functional processes
in the body. The system detects pairs of gamma rays emitted indirectly by a
positron-emitting radionuclide (tracer), which is introduced into the body on a
biologically active molecule.
- Functional MRI (fMRI) - a type of specialized MRI scan. It measures
the hemodynamic response (change in blood flow) related to neural
activity in the brain or spinal cord of humans or other animals. It is one
of the most recently developed forms of neuroimaging.
Basic Principles
• Detect changes in regional blood flow and metabolism within the brain.
• Active neurons demand more glucose and oxygen, more blood to
active regions, techniques detect changes in blood flow.
Understanding CNS Structure Through Development
Ventricular System and the CNS
– The CNS forms from the walls of a fluid-filled neural tube
– The inside of the tube becomes ventricular system
– The neural tube
• Endoderm, mesoderm, ectoderm
• Neural plate  neural groove
• Fusion of neural folds
– Neural tube (forms CNS neurons)
– Neural crest (forms PNS neurons)
• Formation of the Neural Tube
Anencephaly - a fatal neural tube defect in which the
cerebral hemispheres do not develop.
Typically some brainstem tissue is present, but it is
anatomically highly disorganized.
Spina bifida – literally means
cleft spine, which is an
incomplete closure in the spinal
column. In general, the three
types of spina bifida (from mild
to severe) are: Spina Bifida
Occulta, Meningocele, &
Myelomeningocele
• Putting the Pieces Together
Special Features of
the Human CNS
Compared to that of
a Rodent
– Many similarities in rat
and human brain
• Basic arrangement
of various
structures
Yet, differences are
seen in:
•
•
•
•
•
Special Features of the
Human CNS
Differences
Convolutions on human
cerebrum surface called sulci
and gyri
Size of olfactory bulb
Growth of cerebral
hemisphere: Temporal,
frontal, parietal, occipital
Comparison of Three Different Mammalian Brains
END.