Cambell Biology in Focus Chapter 37 practice test 2
What is a neuron?
are nerve cells that transfer information within the body. They use two types of signals to communicate: electrical signals (long-distance) and chemical signals (short-distance)
Neurons can be placed into three groups, based on their location and function.
Neurons systems process information in three stages:
a. Sensory input
c. Motor output
What is the function of the Sensory input?
Transmit information from a sense receptor to the brain or spinal cord
What is the function of Integration?
Integrate information within brain or spinal cord; connect sensory and motor neurons; located entirely within the CNS
What is the function of the Motor output?
Transmit information from the brain or spinal cord to a muscle or gland; Cause muscle contraction or gland secretion
Which division of the nervous system include the brain and spinal cord?
The central nervous system (CNS) where integration takes place; this includes the brain and a nerve cord
What is shown in the box above?
What do the red spheres represent?
What is indicated by the red arrows in the main figure?
Pathway of stimulus
What are glial cells?
cells that nourish or insulate most neurons
In this section you will need to recall information about the structure and function of the plasma membrane. Ions are not able to diffuse freely through the membrane because they are charged and so must pass through protein channels specific for each ion.
All cells have a membrane potential across their plasma membrane. What is the typical resting potential of a neuron?
is the membrane potential of a neuron not sending signals.
The basis of the membrane potential.
How are the concentration gradients of NA+ and K+ maintained in the membrane potential?
through the gated ions channels in the neurons that open or close in response to stimuli
As you see in the figure above, in a resting neuron, the outside of the membrane is positively charged relative to the inside of the membrane. If positively charged ions flow out, the difference in charge between the two sides of the membrane becomes greater. What is the increase in the magnitude of the membrane potential called?
When a stimuli is applied, ion channels will open. If positively charged ions flow in, the membrane is said to depolarize. If depolarization causes the membrane potential to drop to a critical value, a wave of depolarization will follow. What is this critical value called?
What is the wave of depolarization called?
a nerve impulse
Just like toppling dominoes in a row, either the threshold of depolarization will be reached and an action potential will be generated, or the threshold will not be reached and no wave will occur. What is this response to stimulus called?
An action potential
What are the two types of glial cells that produce myelin sheaths?
oligodendrocytes in the CNS; and Schwann cells in the PNS
How does a myelin sheath speed impulse transmission?
Action potentials are formed only at nodes of Ranvier. In the case of a myelinated neurone, the ions can only move in and out of the cytoplasm at the nodes of Ranvier. Because of this, the action potential will 'jump' from one node to the next, a process called saltatory conduction, and so will travel much faster than in an unmyelinated neurone.
In the disease multiple sclerosis, the myelin sheaths harden and deteriorate. How would this affect nervous system function?
will cause poor conduction and eventually conduction interruption at electrical synapses, the electrical current flows from one neuron to another.
When the wave of depolarization arrives at the synaptic terminal, calcium ion channels open. What occurs to the synaptic vesicles as the Ca2+ level increases?
The elevated CA2+ concentration in the terminal causes synaptic vesicles to fuse with the presynaptic membrane.
What is contained within the synaptic vesicles?
Six steps explaining how an action potential is transmitted from one cell to another across a synapse:
Step 1. presynaptic membrane
when an action potential depolarizes the plasma membrane of the synoptic terminal
Step 2. calcium ion channel
open voltage-gated calcium channels in the membrane, triggering an influx of CA2+
Step 3. synaptic vesicle
the elevated CA2+ concentration in the terminal causes synaptic vesicles to fuse with the presynaptic membrane
Step 4. presynaptic membrane
then the vesicles can release neurotransmitter into the synaptic cleft
Step 5. postsynaptic membrane
the neurotransmitter binds to the receptor portion of the ligand-gated ion channels in the postsynaptic membrane, opening the channels in the synapses, both NA+ and K+ can diffuse through channels
Step 6. Neurotransmitter
the neurotransmitter is released from the receptors, and the channels close. Synaptic transmission ends when the neurotransmitter diffuses out of the synaptic cleft, is taken up by the synaptic terminal or by another cell, or is degraded by an enzyme.
There are many different types of neurotransmitters. Each neuron secretes only one type of neurotransmitter. Some neurotransmitters hyperpolarize the postsynaptic membrane. Are these excitatory or inhibitory neurotransmitters.
they are inhibitory postsynaptic potentials (IPSPs) (hyperpolarizations that move the membrane potential farther from threshold)
Define and explain summation.
In spatial summation, EPSPs produced nearly simultaneously by different synapses on the same postsynaptic neuron add together
A single postsynaptic neuron can be affected by neurotransmitter molecules released by many
other neurons, some releasing excitatory and some releasing inhibitory neurotransmitters. What
will determine whether an action potential is generated in the postsynaptic neuron?
The combination of EPSPs through spatial and temporal summation can trigger an action potential
There is one neurotransmitter that is the most common neurotransmitter in both vertebrates and invertebrates, and it is released by the neurons that synapse with muscle cells at the neuromuscular junction. What is this very important neurotransmitter?