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Lecture

PSYCH261 Lecture Notes - Myelin, Peripheral Nervous System, Axon Terminal


Department
Psychology
Course Code
PSYCH261
Professor
Deltcho Valtchanov

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STRUCTURES AND FUNCTIONS OF CELLS OF THE NERVOUS SYSTEM
Movement and behavior- primary function of the nervous system
Sensory neurons a neuron that detects changes in the external or internal environment and sends information
about these changes to the central nervous system
o Information in the form of light, sound waves, odors, tastes, or contact with object is gathered from the
environment by these specialized cells
Motor neuron movements accomplished by the contraction of muscles are controlled by these neurons
o Also controls the secretion of the gland
Interneuron A neuron located entirely within the central nervous system
Local interneurons form circuits with nearby neurons and analyze small pieces of information.
Relay interneurons connect circuits of local interneurons in one region of the brain with those in other regions
100 billion of neurons - estimated number of neurons in the brain
CENTRAL NERVOUS SYSTEM (CNS) consist of the parts that are encased by the bones of the skull and spinal column:
the brain and the spinal cord
PERIPHERAL NERVOUS SYSTEM (PNS) - consist of the nerves and most of the sensory organs
CELLS OF THE ENRVOUS SYSTEM
Neurons nerve cell; most important cells of the nervous system; the information processing and the information-
transmitting element of the nervous system.
o BASIC STRUCTURE OF NEURONS
Cell body or soma contains the nucleus and much of the machinery that provides for the life
processes of the cell
Dendrites grk: tree; Dendrites serve as an important recipient of these messages as the neurons
converse to each other
the messages that pass from neuron to neuron are transmitted across the synapse a
junction between the terminal buttons of an axon and a membrane of another neuron ;
the messages that pass from neuron to neuron are transmitted here
Axon - a long slender tube covered by a myelin sheath; it carries information from the cell body
to the terminal buttons
Action potential the basic message that is being carried by an axon
o A brief electrical/ chemical event that starts at the end of the axon next to the
cell body and travels toward the terminal buttons. *full strength action
potential
Multipolar neuron - a neuron with one axon and many dendrites attached to its soma
Bipolar neuron give rise to one axon and one dendritic tree, at opposite ends of the
soma.
o Bipolar neurons are sensory (i.e. the detect events occurring in the
environment and communicate it to the CNS)
Unipolar neuron one axon attached to its soma then the axon divides with one branch
receiving sensory info and the other sends info to the CNS
Terminal buttons secretes neurotransmitters (has an inhibitory or excitatory effect on another
neuron)
o INTERNAL STRUCTURE
Membrane a structure consisting principally of lipid molecules that defines the outer
boundaries of the cell and also constitutes many of the cell organelles, such as the Golgi apparatus
Nucleus round in structure and is enclosed by the nuclear membrane containing the nucleolus
and chromosome
Nucleolus produces ribosomes
Ribosome a cytoplasmic structure, made of protein, that serves as the site of production of
proteins translated from mRNA
Chromosome a strand of DNA, with associated proteins, found in the nucleus; carries genetic
info
DNA (deoxyribonucleic acid) a long complex macromolecule consisting of two interconnected
helical strands; along with associated proteins, strands of DNA constitute the chromosome
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SUPPORTING CELLS
o Glia neuroglia or nerve glue is most important supporting cells of the CNS
Glue the CNS together
Surround neurons and control their supply of nutrients and some of the chemicals they need to
exchange chemicals with the neurons
They insulate neurons to one another so that neural messages do not get scrambled
They destroy and remove the carcasses of neurons that are killed by disease
Types of Glial Cells:
Astrocytes star cell; provides physical support to neurons and cleans up debris within
the brain
o They help control the chemical composition of the fluid surrounding neurons
o Involved in providing nourishment to neurons
o Holds neurons in place the nerve glue
o Clean debris when cells in the CNS die
o Phagocytosis the process by which cells engulf and digest other cells or
debris caused by cellular degeneration
Oligodendrocytes a type of glial cell; provide support to axons and provide the myelin
sheath
o Myelin sheath a sheath that surrounds axons and insulates them ,
preventing messages from spreading between adjacent axons (80% lipid, 20%
protein)
o Node of Ranvier a naked portion of a myelinated axon between adjacent
oligodendroglia or Schwann cells.
Microglia the smallest of glial cells; act as phagocytes and protect the brain from
invading microorganisms
SCHWANN CELLS
- A cell in the peripheral nervous system that is wrapped around a myelinated axon, providing one segment of its
myelin sheath
THE BLOOD BRAIN BARRIER
- A semipermeable barrier between the blood and the brain produced by the cells in the walls of the brain’s capillaries
- It makes it easier to regulate the composition of the extracellular fluid (bec. If the composition of the extracellular
cells are changed slightly, the transmission of the messages will be disrupted)
- It also prevents chemicals (from the food we eat; that may cause disruption to cell messaging) from reaching the
brain
- Area postrema: a part of the brain that controls vomiting wherein the blood brain barrier is much weaker there,
permitting neurons in this region to detect the presence of poisons in the blood which initiates vomiting
COMMUNICATION WITHIN A NEURON
- Dendrites of the sensory neuron are stimulated by the hot object and releases neurotransmitter so sends msg to
terminal buttons in the spinal cord…..
-
Components of a simple Withdrawal Reflex
o Sensory Neuron Motor neuron - interneuron -it decides that something is
happening and the muscle decides to do an action (e.g. reflex from something
hot) Then the brain decides what to do
o Inhibition in the Withdrawal Reflex
Brain input prevents the withdrawal reflex by decreasing activity of
the motor neuron
It can inhibit pain and many others
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