BIO 012 Lecture Notes - Lecture 6: Lysosome, Ileum, Motor Neuron
19 Jun 2018
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Chapter 45
(section 45.1)
p. 925 What are the two main types of cells in the nervous system? What are action potentials and
which cells use them? What are the general structural features of a neuron and what is the
overall function of each structure? What is the difference between a pre-synaptic cell and a
post-synaptic cell? (you will need to what a synapse is as well)
Neurons and glia. Action potentials are info that is communicated from the presynaptic to the
postsynaptic cell. A neuron has a cell body – nucleus and organelles; dendrites that bring info
from other neurons to the cell body; an axon terminal – carries info to terminal and then from
dendrites to the cell body; and a synapse which is the space where the info is conveyed between
the two cells.
p. 926 What two types of synapses are there? What function do oligodendrocytes and Shwann cells
share? How are these glial cells different? What is the function of myelin? What is the blood
brain barrier and why is it important? What are 6 specific functions of an astrocyte?
Electrical and chemical synapses. Oligodendrocytes and Shwann cells both wrap the axons in
myelin. Oligodendrocytes do this in the CNS while the Schwann cells do it in the PNS. Myelin
helps the cells conduct action potentials more rapidly and protects the axons. The blood brain
barrier protects the brain from toxic chemicals in the blood. Six function of an astrocyte are:
nourishes neurons with glycogen, signals (releases neurotransmitters), reuptake of
neurotransmitters (keeps postsynaptic cell from over activating), repairs and regenerates
neurons, communicates changes in blood, and regulates potassium in the extra cellular brain.
p. 927 What is meant by a tripartite synapse? What are microglia?
The tripartite synapse is the idea that a synapse includes connections from astrocytes and not
just the pre- and postsynaptic neurons. Microglia act as macrophages and give the nervous
system immune defenses (CNS immunity)
(section 45. 4)
p. 940 What are the 3 functional categories of neurons in the neural network and what is the
function of each?
Sensory neurons (input – afferent) – carry sensory info into the nervous system. Motor neurons
(output – efferent) – carry commands out of the nervous system to muscles and glands.
Interneurons – integrate and store info and communicate between afferent neurons and
efferent neurons.
p. 940 What differences in the nervous system organization do we see between organisms that
require processing large amounts of complex information and organisms who do not need to
process complex information? What is the general organization of a vertebrate nervous
system? Track the path of a monosynaptic spinal reflex utilizing both motor and sensory
neurons (also understand efferent and afferent signals)
Organisms that process large amounts of info perform more functions that organisms that do
not. The general organization of a vertebrate nervous system is that most cells of the nervous
system are found in the CNS. Info is transmitted from sensory cells to the CNS and from the CNS
to effectors via neurons that extend or reside outside the brain and the spinal cord the PNS.
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The spinal cord conducts info in both directions between the brain and the peripheral neurons
of the body’s organs. Where there is only one synapse between the afferent and efferent
neurons is a monosynaptic reflex; but most spinal networks are more complex. Sensory input
that activates the motor neuron of one muscle must inhibit the antagonist muscle. Ex: one
muscle in the leg is a flexor and the other muscle is an extensor. Both cannot work at the same
time.
p. 942 What is a polysynaptic reflex arc and why is it important that such reflexes do not include
processing by the brain?
The act of withdrawal or movement that does not need to be processed in the brain is the
polysynaptic spinal reflex. A spinal reflex is the conversion of afferent to efferent information in
the spinal cord without participation of the brain. Five components to the polysynaptic reflex
arc are, the receptors, afferent neuron, interneuron, efferent neuron, and the effector. Before
the brain is aware of the pain, but synapses of the sensory neurons with other interneurons
stimulate and inhibit a variety of different motor neurons in the spinal cord.
p. 943 Beyond simply size, what is meant by the brain increasing in complexity as you move up
through vertebrate species (for example from shark, toalligator, to pig, to human)?
Animals that are more complex and move about in search of food and mates must process and
integrate large amounts of info. As the brain increases in complexity, different functions
become more necessary. Simple animals process info with a limited number of simple neural
networks that do little more than provide direct lines of communication from sensory cells to
effectors; there is little or no integration or processing of signals. The brainstem differs less
among the four species than does the cerebrum which is responsible for complex behavior and
learning.
(section 45.2)
p. 927 What is the function of a sodium-potassium pump? (also see p 928) What is membrane
potential and how is this potential maintained?
The sodium potassium pump actively expels sodium ions out the cell and brings potassium ions
into the cell. The membrane potential is the difference in charge created across the membrane
where there is more positive outside than inside when it is measured.
p. 927 What is the resting potential?
The resting potential is the difference in charge across the membrane when the cell isn’t doing
its main activity. In neurons, this is called the steady state membrane potential.
p. 928 How does the resting potential provide the necessary force to cause action potentials? What
is voltage and how is this accomplished in cells? What are two forces that determine how ions
move across a membrane?
With the resting potential, the ions are unequally distributed on the inside and outside of cells,
and the cell membranes are selectively permeable to different ions. The membrane is highly
permeable to potassium ions and has a high concentration of them inside the cell and less
outside (leaky K+ channels and pull back in). Voltage is a force that causes electrically charged
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particles to move between 2 points. Two forces are the concentration gradient and the charge
gradient.
p. 930 Name the three types of gated ion channels and what affects the opening and closing of each?
Mechanical gates are affected by mechanical movement or stimulus of the membrane that
causes it to open; chemical gates are triggered by the presence of absence of a specific
molecule; voltage gates are affected by a change in voltage across the plasma membrane.
p. 931 What is the difference between depolarization and hyperpolarization?
Depolarization is where there is a decrease in the charge difference across the membrane due
to positive charges moving into the cell and the outside becoming more negative. Ex: sodium
ions into the cell. Hyperpolarization is where there is an increase in the charge difference across
the membrane due to positive charges moving outside the cell, and the inside becoming more
negative. Ex: potassium ions leaving the cell
p. 932 What characterizes a graded potential and how does this differ from an action potential? How
do graded potentials cause a threshold to be reached?
A graded potential is just many small depolarizations (such as sodium coming into the cell).
Graded potentials are chemical and mechanical gates while action potentials are voltage gates.
Many graded potentials add up through summation and help the cell reach the threshold and
the action potential is initiated.
p. 933 What happens at the threshold to create a full action potential? How does a membrane return
to resting after depolarization? What is after-hyperpolarization, or undershoot, and why is it
important?
At the threshold enough depolarizations have built up for the action potential to be initiated
and the process then restarts. After depolarization (where sodium comes into the cell),
potassium begins to leave the cell in repolarization and the cell becomes more negative. Then
there is hyperpolarization where the cell charge goes past resting potential and potassium
continues to leave the cell. This cause the cell charge to undershoot repolarization. The cell
realizes this and begins to pull potassium back in during the after-hyperpolarization phase.
Therefore it returns to the resting potential and the process can restart.
p. 934 What is meant by “all or none” response? How does positive feedback work in action
potential depolarization (we didn’t specifically talk about this in class, but you should be able
to put think this through and put this together from reading)?
All or none describes the action potential, there are no little or big action potentials. It is either
that it comes or it doesn’t. Positive feedback works in action potential depolarization because it
magnifies the effect when sodium is brought into the cell. More sodium coming in triggers even
more to come in and it diffuses and the action potential will continue down the axon.
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Document Summary
What is the difference between a pre-synaptic cell and a post-synaptic cell? (you will need to what a synapse is as well) Action potentials are info that is communicated from the presynaptic to the postsynaptic cell. Oligodendrocytes and shwann cells both wrap the axons in myelin. Oligodendrocytes do this in the cns while the schwann cells do it in the pns. Myelin helps the cells conduct action potentials more rapidly and protects the axons. The blood brain barrier protects the brain from toxic chemicals in the blood. The tripartite synapse is the idea that a synapse includes connections from astrocytes and not just the pre- and postsynaptic neurons. Microglia act as macrophages and give the nervous system immune defenses (cns immunity) (section 45. Sensory neurons (input afferent) carry sensory info into the nervous system. Motor neurons (output efferent) carry commands out of the nervous system to muscles and glands.
