PSYC 273 Lecture Notes - Lecture 2: Axon Terminal, Neuroglia, Motor Neuron
Chapter 2 Notes
The nervous system/ all tissues are composed of cells.
• Neurons (Nerve Cells): the basic unit of the nervous system each composed of receptive
extensions called dendrites, an integrating cell body, a conducting axon, and a
transmitting axon terminal. Highly organized cells that convey information between each
other across tiny gaps.
o Like little computers that underlie the most complex and simple behaviors.
o Produce readily measurable electrical signals.
• Supporting Cells, Glial Cells (Glia): nonneuronal brain cells that provide structural,
nutritional, and other types of support to the brain.
o Information processing
• Santiago Ramón y Cajal: able to show that although neurons come very close together
they are not quite continuous with one another.
o Showed that neurons and other cells of the brain are structurally, metabolically,
and functionally independent.
o Neuron Doctrine: Information is transmitted from neuron to neuron across tiny
gaps: synapses
▪ Synapse: the cellular location at which information is transmitted from a
neuron to another cell.
The neuron has 4 principle divisions
• Input Zone: the part of a neuron that receives information from other
neurons or from specialized sensory structures. neurons receive
information from other neurons at cellular extensions called dendrites.
o Dendrites: an extension of the cell body that receives information
from other neurons. May be elaborately branched to accommodate
synapses from many other neurons. Comprise the input zone.
• Integration Zone: an extension of the cell body that receives information from other
neurons. in addition to receiving additional synaptic inputs, the cell body integrates the
information that had been received to determine whether or not to send a signal of its
own. Deciding to fire an action potential.
o Cell Body (Soma): the region of a neuron that Is defined by the presence of the
cell nucleus.
o Axon Hillock: the cone-shaped area on the cell body from which the axon
originates. Gathers and integrates incoming information from the synapses on the
dendrites and cell body and converts those inputs into electrical pulses.
• Conduction Zone: the part of a neuron- typically the axon- over which the action
potential is actively propagated
o Axon (Nerve Fiber): a single extension from the nerve cell that carries action
potentials from the cell body toward the axon terminals. Only a few micrometers
(interneurons) to a meter (motoneurons and sensory neurons) in length
• Output Zone: the part of the neuron at which the cell sends information to another cell.
Axon terminals transmit the neuron’s signals across synapses to other cells.
o Axon Terminals (Synaptic Bouton): the end of an axon or axon collateral which
forms a synapse with a neuron or other target cell. Transmit information that
travelled down the axon to other neurons at the synapses.
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• Different Forms of Neurons:
o Motoneurons: a neuron that transmits neural messages to muscles or glands.
Control movement.
▪ Long axons that contract muscles in response to commands from the brain.
o Sensory Neurons: a nerve cell that is directly affected by changes in the
environment such as color, light, and odor. Carry messages from the periphery
back to the spinal cord and brain.
▪ Receive information
o Interneurons: most of the neurons in the brain. A nerve cell that receives input
from and send output to other neurons. Communicates information from neurons
to other neurons.
▪ Often integrate sensory and motor activity.
• 3 General Shapes:
o Multipolar Neurons: a nerve cell that has many dendrites and a single axon.
Most common type.
o Bipolar Neurons: a nerve cell that has a single dendrite at one
end and a single axon at the other end. Especially common in
sensory systems.
o Unipolar Neurons: a nerve cell with a single branch that leaves
the cell body and then extends in two directions- one end in the
input zone and the other end is in the output zone. Transmit touch information
from the body into the spinal cord.
Information is received through synapses
• Dendrites reflect the complexity of the inputs received.
• Synapse: the gap between two neurons. information is transmitted from an axon terminal
of a presynaptic (located on the transmitting side of the synapse) axon terminals to the
postsynaptic (referring to the region of the synapse that receives and responds to
neurotransmitters) dendrites. Composed from:
o Presynaptic Membrane: the specialized membrane on the axon terminal of a
nerve cell that transmits information by releasing neurotransmitter.
▪ Presynaptic axon terminals contain many
• Synaptic Vesicles: a small, spherical structure that contains
molecules of neurotransmitter. Each synaptic vesicle contains
molecules of
o Neurotransmitter: the chemical released from the
presynaptic axon terminal serves as the basis of
communication between neurons. Building blocks for
information processing throughout the brain.
o Postsynaptic Membrane: the specialized membrane on the surface of a neuron
that receives information by responding to a neurotransmitter from a presynaptic
neuron.
▪ Synaptic vesicles fuse with presynaptic membrane releasing content into
synaptic cleft. Neurotransmitter interact with
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• Neurotransmitter Receptors: a specialized protein often
imbedded in the cell membrane that selectively senses and reacts to
molecules of a corresponding neurotransmitter or hormone.
▪ Molecules of neurotransmitter do not usually enter postsynaptic neuron
o Synaptic Cleft: the space between the presynaptic and postsynaptic neurons at a
synapse. Once action potential travels down axon to terminal buttons-> vesicles
migrate to the membrane of presynaptic axon terminals and merge causing a
release of neurotransmitters into synaptic cleft.
▪ Released neurotransmitter binds to receptors on the postsynaptic neuron.
• Receptors: proteins that bind to specific neurotransmitters (like
lock and key).
• Receptor binding usually results in receptor opening or closing
where A SPECIFIC ION is now able to enter/exit the cell,
changing the overall electrical charge of the membrane.
• The electrical change affects likelihood of triggering Action
Potential in postsynaptic cell. If so, new Action Potential
ultimately causes release of neurotransmitters in subsequent
neuron terminals. Postsynaptic neurons have the potential to be a
presynaptic neuron for another neuron down the line.
o What are the ways to alter communication????
▪ Alter the form or structure of dendrites.
▪ Change the amount of neurotransmitter released.
▪ Change the number of receptors on the postsynaptic neuron.
o Dendritic Spines: options for forming connections with other neurons. Increase
the surface area of dendrites allowing for more points of contact and therefore
more information to be transferred.
▪ Changes in dendritic spines underlie many brain changes, including
motivation, learning, and memory.
▪ The number you have is altered by experiences.
• Neuroplasticity: the ability of the nervous system to change in response to experience or
the environment.
The axon integrates and then transmits information
o Axon Hillock: the cone-shaped area on the cell body from which the axon
originates. Gathers and integrates incoming information from the synapses on the
dendrites and cell body and converts those inputs into electrical pulses.
o Electrical pulses race down the axon that the neuron innervates: to
provide neural input to.
o Axon Collaterals: a branch an axon.
o Axonal Transport: the transportation of materials from the neural cell
body toward the axon terminal and from the axon terminals back toward
the cell body.
Glial cells protect and assist neurons
o Glial cells: provide neurons with raw materials, chemical signals, and specialized
structural components. Types of Glial: (wrap around successive segments of
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Document Summary
The nervous system/ all tissues are composed of cells: neurons (nerve cells): the basic unit of the nervous system each composed of receptive extensions called dendrites, an integrating cell body, a conducting axon, and a transmitting axon terminal. May be elaborately branched to accommodate synapses from many other neurons. Deciding to fire an action potential: cell body (soma): the region of a neuron that is defined by the presence of the cell nucleus, axon hillock: the cone-shaped area on the cell body from which the axon originates. Only a few micrometers (interneurons) to a meter (motoneurons and sensory neurons) in length: output zone: the part of the neuron at which the cell sends information to another cell. Axon terminals transmit the neuron"s signals across synapses to other cells: axon terminals (synaptic bouton): the end of an axon or axon collateral which forms a synapse with a neuron or other target cell.
