PSYC 2410 Lecture 4: Unit 04 notes
27 Jun 2018
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General Layout of the Nervous system:
The nervous system is a system of cells, tissue and organs that regulate the body's responses to
internal and external stimuli
The vertebrate nervous system consists of the Central Nervous System (CNS) and the Peripheral
Nervous System (PNS)
The CNS is divided into two divisions: the brain (in the skull) and the spinal cord (in the spine)
The PNS is the part of the nervous system that is located outside of the spine and skull
The CNS division of the nervous system is simple to define in comparison to the PNS which is
somewhat more complex
Like the CNS, the PNS is divided into two divisions: the somatic nervous system and the
autonomic nervous system
oBoth of these divisions are composed of afferent and efferent nerves
Afferent nerves carry sensory signals from the PNS to the CNS
Efferent nerves carry motor signals from the CNS to the PNS
The autonomic nervous system is responsible for regulating the internal environment
Its is further divided into the parasympathetic nervous system and the sympathetic nervous
system which are both efferent
oThese two systems differ from each other in how they 'communicate' with the body
The sympathetic efferent nerves synapse on neurons that are far away from their targets while
the parasympathetic efferent nerves synapse with neurons very close to their target
Three basic principles:
oSympathetic nerves mobilize energy resources; parasympathetic nerves conserve
energy
oEach autonomic target receives signals from both systems
oSympathetic activation indicates arousal while parasympathetic activation indicates
relaxation
The cranial nerves are a special group of nerves that project directly from the brain and through
the skull
oThey have specific sensory and/or motor functions and disruption of these functions is
one neurological assessment tool for accurate determination of the location and size of
tumors and other types of brain pathology
Meninges, ventricles, and cerebrospinal fluid
oThe brain and spinal cord are well protected by the skull and the vertebrae, but there
are also three membranes called the meninges that further protect this delicate system
In order from outside to inside the membranes are called: dura mater (tough
mother), arachnoid mater(spidery mother), and pia mater (pious/gentle mother)
The dura meninx is like a bathing cap, tough and tight fitting
The arachnoid meninx is immediately below the dura and above the
subarachnoid space that contains large blood vessels and cerebrospinal fluid (CSF)
The inner pia meninx adheres directly to the surface of the CNS
oCerebrospinal fluid fills the subarachnoid space, central canal of the spinal cord and the
cerebral ventricles of the brain
It is produced by the choroid plexuses (small blood vessels in the pia meter that
protrude into the ventricles)
Excess fluid is absorbed from the subarachnoid space into large sinuses in the
dura mater and drained into the blood stream
Blockage of the flow of CSF results in hydrocephalus, literally translated as water
head
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Blood-brain barrier
oThe passage of large molecules from the generally circulating blood stream to the brain
is collected by the blood-brain barrier (BBB)
oCells of the blood vessels in the brain are much more tightly packed thereby impeding
the passage of many large molecules through this protective barrier
Cells of the Nervous System:
Of the hundreds of billions of different cells in the nervous system there are two types: neurons
and glial cells. Neurons are specialized cells for the reception, conduction, and transmission of
electrochemical signals and are found in many sizes and shapes. Glial cells outnumber neurons
10:1
Anatomy of neurons
oexternal neurons are comprised of nine parts
Cell membrane: a semipermeable membrane that allows chemicals to cross
Cell body: the metabolic center of the cell containing the nucleus (cell's DNA)
Dendrites: short processes emanating from the cell body that receive
information from synaptic contacts with other neurons
Axon: a single projection from the cell body that can be as long as one meter
Axon hillock: the junction between the cell body and axon which is critical for
the conveyance of electrical signals by the neuron
Myelin sheaths: these sheaths insulate the axon and assist in conduction of
electrical signals. They are formed by oligodendroglia in the CNS and Schwann cells in
the PNS
Nodes of Ranvier: small spaces between adjacent myelin sheaths that allow
salutatory conduction (faster transmission of electrical signal along the axon)
Buttons: branches endings of the axon that release chemical signals allowing the
neuron to communicate with other cells
Synapse: the point of communication between the neuron and other cells
oIn the cell body:
The cell body is filled with cytoplasm and contains many structures relevant to
the functioning of the cell
In the cell, the nucleus contains the DNA and the mitochondria are energy
producers
The ER (rough or smooth) aid in the synthesis of proteins and fats
Ribosomes synthesize proteins and are found on the rough ER
The Golgi complex packages molecules in vesicles for transport
Microtubules rapidly transport materials throughout the neurons
oAt the button:
Synaptic vesicles found in the button of the axon contain neurotransmitters
which are molecules that will released from the button and influence the activity of
other cells
Neuron cell membrane
oThe neuron cell membrane is composed of a lipid bilayer (two layers of fat molecules)
oWithin this membrane are protein molecules that are important in defining the cell
membrane's function
oThere are channel proteins which allow certain molecules to pass through the
membrane and there are signal proteins where specific molecules can bind resulting in the
transfer of a signal to inside the neuron
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Cells of the nervous system
oFour basic classes of neurons: (based upon the number of processes that emanate from
the cell body)
Unipolar: one process extends from cell body
Bipolar: two processes extend from cell body
Multipolar: more than two processes extending from cell body
Multipolar interneuron: short or no axon
oCell clusters: CNS = nuclei; PNS = ganglia
oGlial cells and satellite cells
These are the most common types of cells found in the nervous system
Glial cells are found in the CNS and satellite cells are found in the PNS
Both provide physical and functional support to neurons
These cells form the myelin sheath of axons
The smallest glial cells are microglia which are basically the 'garbage men' of the
nervous system
They response to injury or disease by increasing in number and
engulfing cellular debris
They are also responsible for triggering inflammatory responses
The largest glial cells are astroglia (star-shaped) which are found only in the CNS
and support and nourish neurons
Neuroanatomical Techniques and Directions:
These are techniques that have allows researchers to study the anatomy of the enrvous system.
Because neurons are so tightly packed with their axons and dendrites intricately woven together it
is very difficult to study the anatomy of the nervous system
The various ways by which neural tissue can be prepared allows researchers to study various
neuroanatomical structures, information that can be later combined to provide a comprehensive
representation of structure
oGolgi stain: silver chromate stain and stains ingle neurons entirely black. Enables the
researcher to view an entire neuron as a silhouette
oNissl stain: dyes that selectively bind to structures in the cell bodies of neurons
oElectron microscopy: use an electron-absorbing substance to coat an extremely thin
section of neural tissue allows extraordinary detail of cell structure to be visualized.
Scanning electron microscopy provides 3D micrographs
oTracing techniques: chemical tracing of neuronal pathways
Anterograde tracing follows a path from the cell body to a specific area
Retrograde tracing follows a path to the cell body
Directions in the vertebrate nervous system
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Document Summary
The nervous system is a system of cells, tissue and organs that regulate the body"s responses to internal and external stimuli. The vertebrate nervous system consists of the central nervous system (cns) and the peripheral. The cns is divided into two divisions: the brain (in the skull) and the spinal cord (in the spine) The pns is the part of the nervous system that is located outside of the spine and skull. The cns division of the nervous system is simple to define in comparison to the pns which is somewhat more complex. Like the cns, the pns is divided into two divisions: the somatic nervous system and the autonomic nervous system o. Both of these divisions are composed of afferent and efferent nerves. Afferent nerves carry sensory signals from the pns to the cns. Efferent nerves carry motor signals from the cns to the pns. The autonomic nervous system is responsible for regulating the internal environment.
