PSYC 100 Lecture Notes - Lecture 3: Myelin, Peripheral Nervous System, Axon Terminal
23 Nov 2017
School
Department
Course
Professor
BioPsych
Central nervous system
• brain and spinal cord
Peripheral nervous system
• remaining nerves
Anatomy of the Nervous System
Glial cells
• support cells find in nervous system
• digest dead neurons, provide physical and nutritional support to neurons, make up myelin
sheath
• more frequent than neurons
Neurons- cells that communicate with each other to relay information
• receive information
• integrate information
• transmit information
Types of Neurons
• motor neurons
o transmit messages to the muscles from the spinal cord
• sensory neurons
o receive information from outside the nervous system and relay information to the brain
by way of the spinal cord
o have special ending to their dendrites for receiving signals for different senses
• interneurons
o connect all neurons
▪ connect information received by other neurons together using small circuits of
interneurons
o majority of all neurons one
• specialized neurons
o some neurons on specialized to their location
▪ Purkinje cells- connect cerebellum to brain and rest of spinal cord, bushy
dendrite
▪ Pyramidal Cells- in cerebral cortex, triangle body with one long dendrite with
smaller ones coming off of it
▪ Bipolar Cells- found in the eye, single axon and single dendrite
Components of Neurons
• Soma (cell body)- largest component of the neuron.
o Contains cell nucleus and provides chemical support of cell
▪ Also contains a porous cell membrane
o Coordinates information processing and keeps the cell alive
▪ Protein synthesis
▪ Energy production
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▪ Metabolism
• Dendrites- receive information and relay it to cell body
o branch like parts of the neuron
• Axons- long thin fibers that transmit signals away from the cell body to other neurons, muscles
or glands
o Myelin sheath- insulating fatty material that encases the axon some neurons. Allows
signal to transmit faster (jumps node to node)
▪ Composed of glial cells
▪ Demyelination- eli sheath deteriorates ad sigal does’t trael as fast
through neuron. Leads to loss of feeling, partial blindness, lack of coordinated
movement and cognition
o Terminal buttons- small knobs at the end of the axon that secrete neurotransmitters
• Synapse- junction where neurons interact with one another
o Between axon and dendrites of neurons
Electrochemical Actions
Two stages of communication of neurons:
• Conduction: movement of electrical signal within neurons (dendrites to cell body and then along
axon)
• Transmission: movement of single from one neuron to another through the synapse
Resting potential
• Difference in electric charge between outside and inside of cell
o Arises from difference in ions inside and outside cell membrane
• Stable, negative charge in the inactive cell of about -70mv
Depolarization
• Process during which positively charged sodium (Na+) ions flow into the axon making it less
negatively charged creates an action potential
Action Potential- electric signal conducted along the length of the axon to a synapse
• rief hage i a euro’s eletrial harge
o Na+/K+ pump:
▪ K+ is free to move across the membrane through protein channels creating the
resting potential of -70mv inside the cell. Na+ is stuck outside of the cell
▪ Electric stimulation of the cell closes K+ channels and opens the Na+ channels so
Na+ can enter the cell. This increases the charge on the inside of the cell (+40mv)
-> triggers the action potential
• Only occurs once a threshold is reached (minimum electric imbalance required)
o Going above the threshold does not increase the intensity of the action potential, the
action potential is an all or none response (like a gun firing)
o Intensity of stimulus increasing though can increase the number of neurons firing and the
frequency at which they fire resulting in a more intense feeling
• neural impulse
o electric current that flows along the axon as a result of an action potential
• action potentials generate at different points along axon to guarantee that the full intensity of the
action potential is felt (domino effect)
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• Myelin sheath (clumped around axon with spaces or nodes in between) speeds action potential
being transmitted because it allows the signal to jump from node to node (called nodes of Ranvier)
Absolute Refractory Period
• minimum length of time after an action potential during which another action potential cannot
begin
• Cell reverses the change to the electrical imbalance- K+ is brought back in and Na+ is released
from the inside
Synaptic Transmission (between neurons)
• Parts involved:
o Terminal buttons- knobs that branch out from axon, contain vesicles of neurotransmitters
o Neurotransmitters- chemicals that transmit information across the synapse to receiving
euro’s dedrites
o Receptors- part of cell membrane that receive neurotransmitters and prevent or initiate
new electrical signal
o Presynaptic neuron- neuron sending the message
• Action potential travels length of axon to terminal button. Neurotransmitters are released, float
across synapse and then bind to receptor site on receiving neuron (also known as postsynaptic
neuron). The process continues across that neuron onto the next and so on
• Underlines thought, behaviour and emotion
• Neurotransmitters can be specific to different parts of the brain
• Neurotrasitters ad reeptors sites ork like lok ad ke sstes. Oe reeptor site ol
fits one neurotransmitter
• Excess Neurotransmitters in synapse removed by:
o Reuptake- asored ak ito presapti euro’s terial utto
o Enzyme deactivation- destroyed by enzymes
o Autoreceptors- neurotransmitter binds to this site on presynaptic neuron. The amount of
neurotransmitter is detected by the autoreceptor and then the release of it is stopped
• postsynaptic potential (PSP)
o voltage change at receptor site
• P“P’s are graded
o i.e., they increase or decrease the probability of a neural impulse in the receiving cell in
proportion to their size
Types of PSPs
• excitatory PSP
o increases the likelihood that the postsynaptic neuron will fire
o depolarizes membrane
• inhibitory PSP
o decreases the likelihood that the postsynaptic neuron will fire
o hyperpolarizes membrane
Types of Neurotransmitters- if eurotrasitters i the rai are ee slightl ialaed a perso’s
thoughts, feelings and behaviour will be affected
• Acetylcholine (ACh)- involved in many functions, including voluntary motor control
• Dopamine (DA)- regulates motor behaviour, motivation, please and emotional arousal
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