Download Parts of the Peripheral Nervous System

Test Review 1: Lecture
Nervous System Review
Anatomical Subdivisions of Nervous System:
Central nervous System (CNS): Brain + Spinal cord, parts encased in bone
Peripheral Nervous System (PNS) = 12 pairs of cranial nerves + 31 pairs of spinal nerves, everything BUT
the brain and spinal chord
Parts of the Peripheral Nervous System
Somatic nervous System (Voluntary): Innervates structures of the body wall and appendages (muscles,
skin, ect)
Autonomic Nervous System (ANS, Visceral nervous system, “involuntary”)- Innervates and controls the
smooth muscle and glands of the internal organs and blood vessels and returns sensory information to
CNS.
 ANS axons bring info to the CNS such as the pressure and oxygen content of the blood in
the arteries. Visceral motor fibers command contraction and relaxation of muscles
(intestines, and blood vessels, smooth muscles, rate of cardiac muscle contraction and
secretary function of glands
Has components of CNS and PNS. ANS subdivides into the Sympathetic (“Flight or fight”) and
Parasympathetic (“resting and digesting”) Systems
Brain Divisions:
Cerebrum (forebrain)- Consists of telencephalon and diencephalon. The largest part of the brain, Two
hemispheres separated by deep sagittal fissure.
Telencephalon: End brain, includes cerebral cortex (most evolved part of the brain, called gray matter),
subcortical white matter and basal ganglia (gray mass within the hemispheres, “basal nuclei”). “White
matter” named because has glistening white appearance in freshly section brain, due to lipid rich myelin
Diencephalon (in between brain): Thalamus, hypothalamus and epithalamus (contains pinal gland and
habenula)
Brain stem- composed of midbrain (mesencephalon), pons and medulla Oblongata
 Relay information from cerebrum to the spinal cord and vice versa, complete nexus of
fibers and cells. Also site of vital function regulation (breathing, consciousness, and boy
temp)
Cerebellum (little brain) Behind the cerebrum, includes vermis and two cerebellar hemispheres. Part of
metencephalon
o Primary movement control center that connects with the cerebrum (forebrain) and the
spinal cord
o In contrast to the cerebrum, the left of the cerebellum controls the left side of the body
and the right side of the cerebellum controls the right side of the body
Collections of Neurons
A term for a collection of neuronal cell bodies in
the CNS. When a fresh brain is cut open, neurons
seem gray
Any collection of neurons that form thin sheets,
usually at the brains surface. (cortex = Latin for
bark)
A clearly distinguishable mass of neurons, deep in
the brain.
A group of related neurons deep within the brain,
but sually with less distinct borders than those of
nucli. Ex. Substantia nigra (Latin for black
substance), a brain stem cell group involved in the
control of voluntary movement
A small well defined group of cells
A collection of neurons in the PNS. Ex. The dorsal
root ganglia, contains the cell bodies of sensory
axons entering the spinal cord via the dorsal roots.
Only one cell group in the CNS goes by this name:
the basal ganglia, which are structures lying deep
within the cerebrum that control movement.
Gray Matter
Cortex
Nucleus
Substantia
Locus
Ganglion
Formation of the neural Tube (brief)
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Embryo begins as a flat disk with 3 germ layers (endo, meso and ecto-derm)
At about 17 days from conception in humans, the brain is a flat sheet of cells. Then
theres a formation of a groove in the neural plate that runs rostral to caudal, called the
neural groove
The entire Central Nervous System develops from the walls of the Neural Tube
Folds come together, and some ectoderm is pinched off and lies lateral to the neural
tube. (this tissue called neural crest)
All neurons with cell bodies in the peripheral Nervous System derive from the neural
crest
The mesoderm makes bulges on the sides of the neural tube called somites, from them
33 individual vertebrae of the spinal column and skeletal muscles develop (nerves that
innervate the skeletal muscles are therefore called somatic motor nerves)
Brain Vesicles
The entire brain derives from the three primary vesicles of the neural tube
Prosencephalon (Pro- greek for before, aka forebrain) Behind it lie,
Mesencephalon (midbrain) and Caudal to that is the
Rhombencephalon (hind brain) The rhombencephalon connects with the caudal neural tube, which
gives rise to the spinal cord
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2 vessicles grpw out of the prosencephalon 1. Optic Vessels and 2. Telencephalic vesciles. What
remains after is the diencephalon, or the “in between brain”. Thus, the forebrain consists of 2
optic vesicles, 2 telencephalic vesicles and the diencephalon.
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Unlike the forebrain, the midbrain doesn’t differentiate that much. The dorsal surface of the
mesencephalic vesicle becomes known as the tectum (latin for “roof”). The floor of the midbrain
becomes the tegmentum. The CSF filled space between constricts into a narrow channel called
the cerebral aqueduct. The aqueduct connects rostrally with the 3rd ventricle of the
diencephalon. The aqueduct is a good landmark for identifying the midbrain
The hindbrain turns into 3 important structures: the cerebellum, pons and the medulla
oblongata
The myelencephalon forms the medulla oblongata in the adult brain
The Metencephalon forms the Pons and Cerebellum
Notes
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Cerebellum and pons comprise the metencephalon. Medulla oblongata is the myelencephalon
Brain has 4 ventricles filled with CSF
Brain weight is 3 pounds
CNS is wrapped in protective coverings (meninges): Dura mater (tough mother) arachnoid
(spider), Pia mater (gentle mother)
5. Nervous tissue is one of the 4 basic tissues
6. Nervous tissue comprised of neurons and glial cells
7. CSF is clear, interstitial fluid made by choroid plexus. Found in all ventricles. CSF floats the brain
History of Neuroscience
Trepanation (penetrated the skull)
7,000 years old
Not known why, but thought for headaches or mental disorders to allow evil spirits to escape
Evidence of healing indicates it was preformed on live people
Egyptians
5,000 years ago
Writings of physicians were aware of symptoms of brain damage
Believed heart repository of memories, consciousness and soul
Carefully preserved other organs for afterlife, but scooped brain out through nostrils and threw away
Hippocrates
Greek Scholar, 460-379 BC, the father of western medicine who stated his belief that the brain not only
was involved in sensation but also was the seat of intelligence. This view wasn’t accepted universally
Aristotle
384-322 BC said that the heart was the center of intellect. He said the brain was the radiator for the
cooling of blood that was overheated by the heart.
Galen 130-200 AD
Greek Physician, who embraced Hippocratic view of brain function
A physician to the gladiators, saw brain and spinal injury
Did some animal dissections (loved the sheep brain)
Discovered the cavities of the brain “ventricles” containing fluid
Observed that the cerebrum must be the recipient of sensations and that cerebellum must
command the muscles
Theory that the body functioned according to balance of the 4 vital fluids, or humors. Sensations were
registered and movements initiated by the movement of humors to or from the brain ventricles via
the nerves, which were believed to be hollow tubes, like blood vessels
His view prevailed for almost 1500 years
Andreas Vesalius
Anatomist (1514-1564) During the Renaissance
Father of modern anatomy
Added more detail to Galen’s descriptions
Held fluid mechanical view more strongly due to French hydraulics
These devices supported the notion that the brain could be machinelike in its function: Fluid forced out of
the ventricles through the nerves might literally “pump you up” and cause the movement of limbs.
(muscles bulge when they contract, is what they noticed)
Rene Descartes
French Mathematician and philosopher 1596-1650
Reasoned that unlike other animals, people possess intellect and a soul. Proposed that the brain
mechanisms control human behavior only to the extent that the behavior resembles that of the
animals.
Uniquely, human mental capabilities exist outside the brain in the “mind”.
He believed that the mind is a spiritual entity that receives sensations and commands movements by
communicating with the machinery of the brain via the pineal gland
 Note: Scientists believed white matter was continuous with the nerves of the body and was
believed to contain the fibers that bring information to and from the gray matter
Review of the Understanding of the nervous system at the
end of the 18th Century
 Injury to the brain can disrupt sensation, movement and
thought and can cause death
 The brain communicates with the body via the nerves
 The brain has different identifiable parts, which can
function differently
 The brain operates like a machine and follows the laws of
nature
Benjamin Franklin
1751, published a pamphlet titled Experiments and Observations on Electricity, w/ new understandings of
electricity
Luigi Galvani and Emil du Bois-Reymond
German Biologists, shown that muscles can be caused to twitch when nerves were stimulated electrically
and that the brain can generate electricity
Discoveries displaced the notion that nerves communicated with the brain by movement of fluid. New
concept that nerves were “wires” that conducted electrical signals to and from the brain
Charles Bell 1810 and Francois Magendie
Scottish Physician and French physiologist
Just before the nerves attach to the spinal cord, the fibers divide into two branches or roots. The dorsal
root enters toward the back of the spinal cord, and the ventral root enters toward the front
Bell tested the possibility that these two spinal roots carry info in different directions
Bell found that cutting only ventral roots caused muscle paralysis
Magendie showed that dorsal roots carry sensory information into the spinal cord
 In each sensory and motor nerve fiber, transmission is strictly one way. The two kinds of fibers
are bundled together for most of their length, but they are anatomically segregated when they
enter or exit the spinal cord
 Approach where parts of brain are destroyed to determine their function is termed: experimental
ablation method
Marie Jean Pierre Flourens 1823
French physiologist used this method on animals (birds) to show that the cerebellum does indeed play a
role in coordination
He concluded that cerebrum involved in sensations and perceptions
Unlike before him, Flourens provided solid experimental support for conclusions
Flourens, the pioneer of brain localization of functions was misled into believing that the
cerebrum acted as a whole and could not be subdivided
Franz Joseph Gall
Austrian Medical Student, believed bumps on the surface of the skill reflect bumps on the surface of the
brain
Proposed that personality traits could be related to the dimensions of the head
Phrenology: bumps on the skull reflect surface of the brain
Divisions of Labor in the brain
Paul Broca
French neurologist, credited w/ tilting the scales of scientific opinion toward localization of function in
the cerebrum
Had a patient who could understand language but could not speak. After examining his brain, he found a
lesion in the left frontal lobe. Based on this, Broca concluded that this region of the human cerebrum
was specifically responsible for the production of speech
“broca’s area” = left frontal lobe
Gustav Fritsch and Eduard Hitzig
German physiologists (1870) showed that applying small electrical currents to a region of the exposed
surface of the brain (of a dog) could elict discrete movements
Low level electric stimulation (precentral gyrus of frontal lobe equivalent)
David Ferrier
Scottish neurologist 1881
Repeated same experiment with monkeys, showed that the removal of the same region of the
cerebrum causes paralysis of the muscles
Hermann Munk
German Physiologist, using experimental ablation presented evidence that the occipital lobe of the
cerebrum was required for vision
Evolution of Nervous Systems
Charles Darwin (1859)
English biologist, published On the Origin of Species
Theory of evolution: that species of organisms evolved from a common ancestor
Natural Selection: differences among species
Darwin included behavior among the heritable traits that could evolve, ex. Noticed mammalian species
show same reactions when frightened.
To Darwin, similarities of this response pattern indicated that these different species evolved from a
common ancestor, which possessed the same behavioral trait.
B/c Behavior reflects the activity of the nervous system we can infer that the brain mechanisms that
underlie this fear reaction may be similar, if not identical across these species
Neurons and Glia
Minor Notes:
Glia outnumber neurons by tenfold. However, neurons are the most important cells for the unique
functions of the brain. It is the neurons that sense changes in the environment communicate these
changes to other neurons and command the body’s Reponses to these sensations
Glia or glial cells, are thought to contribute to brain function mainly by insulating, supporting and
nourishing neighboring neurons
Neurons perform the bulk of information processing in the brain
Tissue Fixing: hardening the brain tissues to make thin slices, by immersing them in formaldehyde and
using a special device called a microtome to make the slices.
These advanced made the field Histology, the microscopic study of tissues
Franz Nissl: Late 19th century, Nissl showed that a class of basic dyes would stain the nuclei of all cells
and also stain clumps of material surrounding the nuclei of neurons. These clumps are Nissl bodies, and
the stain is known as the Nissl Stain. Useful for
1.Distinguishing neurons and glia from one another
2. Histologists can study the arrangement, or cytoarchitecture, of neurons in the brain
 Do not see axons w/ Nissl Stain
 Cresyl Violeet NOT Crystal Violet
 ACHettylcholine?
Theodore Schwann
German Zoologist, 1839
Profited from refinement of microscope in early 1800’s
Proposed “Cell theory” i.e all tssues composed of cells
Jan purkinje
Czech physiologist, 1936
Observed cells in the cerebellum
Otto Deiters
German anatomist, 1865
Diagram of large motor nerve cell in anterior horn
First to describe nerve cell fibers
Protoplasmic Prolongations – named “dendrites”
“Axis Cylinder” termed “Axon”
“nerve Cell” (Cell Theory) vs. “Nerve Net” (reticular Theory)
Controversy
Despite above, many believed axons and dentdrites contiguous
In each nerve cell is separate entity whos branches terminate in “free nerve endings?”
Needed better methods to reesolv cells
Camillo Golgi
Italian histologist, 1872
Discovered that by soaking brain tissue in silver chromate solution, known as the Golgi Stain, a small
percentage of neurons became darkly colored in their entirety.
Revealed that the neuronal cell body, the region of the neuron around the nucleus that is shown w/
the Nissl stain, is actually only a small fraction of the total structure of a neuron
*Potassium Dichromate fix?
Showed neurons have 2 parts, region of the cell nuclus and the numerous thin tubes that radiate away.
Santiago Ramon y Cajal
Spanish histologist and artist who used Golgi stain to work out the circuitry of many regions of the brain.
Cajal and Golgi had opposite conclusions about neurons.
o Golgi said that neuritis of different cells are fused together to form a continous reticulum,
or network like the arteries and veins of the circulatory system. According to the reticular
theory, the brain is an exception to the cell theory, which states that individual cell is the
elementary functional unit of all tissues
o Cajal said that neuritis of different neurons are not continuous, and must communicate by
contact not continuity. The idea that the neuron adhered to the cell theory came to be
known as the neuron doctrine.
 Research showed that neuritis of enruons are not continuous with one another.
Wilhelm Waldeyer
German Prof. 1891
Published case that cell theory applied to nervous system
Coined the term Neuron for the nerve cell
Fun Facts:
Cajal never forgave Waldeyer for being credited with the neuronal Doctrine
Golgi never accepted the neuron Doctrine and clung to reticular theory
Waldeyer never shared his prize
Rudolph Virchow
German microscopist and founder of cellular pathology,1860
Nerve cells not embedded in amorphous ground substances
Substance is glue-like and cellular, “Neuroglia”
Cajal subsequently identified several distinct glial cell types
 Read Packet about Neuroscience Today
Others who were mentioned
Luigi Galvani
Discovered “Animal Electricity” 1781
Flow through bodily solutions caused muscle twitch in frogs