WEEK 3: Nervous System - OBJECTIVES
Explain the roles of glial cells in the nervous system.
Glial cells assist neurons, providing nutrition and insulation. It is speculated that glial cells may have other roles as well, but this is an area of active research.
What is a major role of glial cells in the nervous system?
Glial cells provide nourishment to neurons.
What is the relationship between the PNS and the CNS?
The PNS receives commands from the CNS, and the CNS receives information about the external environment from the PNS.
Explain the levels of organization of the peripheral nervous system.
The PNS sends motor and sensory signals between the body and the central nervous system. The peripheral nervous system contains both afferent (incoming) or sensory neurons and efferent (outgoing) or motor neurons. The types of motor neurons can be further broken down into the somatic nervous system that controls the muscles of the body and the autonomic nervous system that controls organ function and maintains homeostasis. The autonomic nervous system can be broken down further into the parasympathetic nervous system, the sympathetic nervous system, and the enteric nervous system. The parasympathetic and sympathetic nervous systems often have opposite effects on target organs. The enteric system regulates the digestive system.
In which of the following should the rate of action potential conduction be the fastest?
a myelinated, large-diameter nerve
Which ligand binds to a ligand-gated ion channel on a postsynaptic neuron?
a neurotransmitter
Which of the following is an example of a glial cell that develops in the CNS?
astrocyte
Which nervous system structure propagates the action potential that allows information to be sent to another cell?
axon
What types of nerves does the peripheral nervous system contain?
both afferent and efferent nerves
Which neuron structure receives signals directly from other neurons?
dendrite
The membrane potential in a cell changes from -70 mV to -55 mV. What change has taken place in the cell?
depolarization
A deer is startled by a predator and runs away. Activation of which part of the peripheral nervous system leads to the increased heart rate that would be seen in the deer?
sympathetic
The autonomic division of the PNS is divided into which systems?
sympathetic, parasympathetic and enteric systems
The efferent part of the autonomic nervous system in the PNS is divided into which parts?
sympathetic, parasympathetic and enteric systems
The junction between a neuron and another neuron or other target cell is called a...
synapse.
If the membrane potential of a neural cell reaches its threshold point, which event is most likely to occur next?
the generation of an action potential
What are the three main regions from which the vertebrate brain originates?
the hindbrain, midbrain, and forebrain
How does the arrival of an action potential at the distal end of a neuron lead to the release of neurotransmitters?
through the movement of calcium ions into the cell interior
How does the arrival of an action potential at the synaptic terminal lead to the release of neurotransmitters?
through the movement of calcium ions into the presynaptic cell interior
What is NOT a feature of an electrical synapse?
use of neurotransmitters to carry information
Summarize neurotransmitter diversity.
A wide diversity and large number of neurotransmitters exist. They are generally grouped into one of five categories: acetylcholine, small amino acids, monoamines, neuropeptides, and inorganic gases. The types of neurotransmitters are associated with different types of cells and functions.
Which of the following statements is true about an action potential?
An action potential is generated after a threshold membrane potential is reached.
Which of the following is true about gray matter and white matter?
Gray matter is composed of unmyelinated axons dendrites and cell bodies, while the white matter is made of bundles of myelinated axons.
Summarize the role of ions in neuron membrane potentials.
Ions move into and out of cells through channel proteins in the cell membrane. Gated ion channels open or close in response to stimuli such as heat, pressure, light, chemicals, or a change in the membrane potential. Membranes also transport ions actively into and out of cells by means of ion pumps, which operate using energy supplied by the hydrolysis of ATP. In hyperpolarization, the inside of the cell becomes more negatively charged; a common method of hyperpolarization involves the efflux of potassium ions via K+ ion channels. Conversely, depolarization is the decrease in the negative charge inside the cell, and one common way this happens is by the influx of sodium ions into a cell. These changes produce a graded potential, so named because the amplitude of the potential is determined by the strength of the stimulus. Graded potentials are localized and of short term.
What happens at the peak membrane potential during an action potential?
Many sodium ion channels are closed and many potassium ion channels begin to open.
Describe the electrical potential across a neuron membrane.
Membrane potential is a measure of the electrical potential resulting from the unequal distribution of ions on the inside and outside of a cell membrane. For a cell at rest, that membrane potential is known as resting potential. The resting potential of neurons ranges from about -60 mV to about -80 mV. Membrane potentials can be measured by inserting microelectrodes into the interior of a cell and the extracellular environment. The difference in the readings from those two microelectrodes is the membrane potential.
Why does the presence of a myelin sheath increase the speed at which a nerve impulse travels?
Myelin insulates the axons, allowing nerve impulses to jump from one node of Ranvier to another node of Ranvier.
Chloride ions flow through a ligand-gated ion channel on a postsynaptic neuron. Which statement accurately describes the result of this situation?
Negatively charged ions will cause hyperpolarization, and an inhibitory postsynaptic potential (IPSP) will result.
Summarize the role of synaptic communication.
Neural messages travel from an axon to other cells in one of two ways: electrically or chemically. At electrical synapses, messages flow directly from one neuron to the postsynaptic cell through gap junction channels. At chemical synapses, a neurotransmitter released by the presynaptic neuron diffuses across the synaptic cleft and binds to receptor molecules in the membrane of the postsynaptic cell.
Describe the structures and functions of neurons.
Neurons are specialized cells that transmit signals to different parts of the body. The main parts of a neuron include the cell body, the axon, and the dendrites. The neuron receives a signal at the dendrites. The signal is transmitted along the axon and eventually passes to another neuron.
Which of the following statements is true about sensory neurons and motor neurons?
Sensory neurons take in information and send it to the CNS, whereas motor neurons receive information from the CNS and transmit it to muscle.
What is the difference between a sensory neuron and a motor neuron?
Sensory neurons take in information and send it to the CNS.
Describe the main structures and functions of the vertebrate brain.
The brain has specific regions that can be generalized as having certain functions, although there is overlap in function for different areas. The brainstem is found on top of the spinal cord and is responsible for the physiological responses necessary for life, such as breathing and swallowing. The forebrain is larger in vertebrates than in any other type of animal. It regulates the entire nervous system in mammals. The limbic system is responsible for our emotions and physiological drives such as hunger and thirst. The cerebral cortex covers the large cerebral hemispheres of the brain. The cerebral cortex is involved in higher-order information processing. It is broken down into four lobes: the frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe, each with specialized functions.
Which statement accurately describes the concentration of potassium ions in a resting neuron?
The concentration of potassium ions is greater in the interior of the cell than in the extracellular medium.
Explain the mechanism of a synapse.
The transmission of a neural message from one neuron to other cells begins when an action potential causes voltage-gated calcium channels to open at axon terminals, allowing calcium to enter the terminals. These ions cause vesicles to fuse with the plasma membrane and release neurotransmitter molecules into the synaptic cleft. The neurotransmitter molecules can then diffuse across the synaptic cleft and bind to receptor proteins in the membrane of the postsynaptic cell, causing changes in the types and quantities of ions crossing the membrane.
Describe the main components of the vertebrate nervous system.
The vertebrate central nervous system (CNS) consists of a brain and spinal cord. The CNS processes and integrates signals from the peripheral nervous system. The peripheral nervous system (PNS) consists of spinal and cranial nerves, and their associated ganglia.
What best describes the permeability of ligand-gated ion channels in the membrane of a postsynaptic neuron?
They are permeable to a number of different ions.
Following the arrival of an action potential at the distal end of a neuron and movement of calcium ions from the extracellular fluid into the cell interior via voltage-gated calcium ion channels, how do neurotransmitters from a presynaptic neuron reach the synaptic cleft?
They are released into the cleft when the neurotransmitter vesicle fuses with the plasma membrane of the presynaptic neuron.
Describe the mechanism of an action potential.
Voltage-gated ion channels open or close when there is a change in the membrane potential. In an action potential, the rapid opening of voltage-gated sodium channels results in an inward sodium current that produces rapid depolarization of the cell membrane. Action potentials are all-or-nothing changes in membrane potential produced by these changes that travel along the surface of the neuronal membrane. The speed with which an action potential moves along a neuron depends on two factors: the cross-sectional area of the neuron and the presence or absence of an insulting myelin sheath. The larger the cross-sectional area of the neuron, the faster the action potential moves. The presence of the myelin sheath also greatly speeds up transmission of action potentials. In axons with an insulating myelin sheath separated by naked sections of axon (nodes of Ranvier), action potential travels by saltatory conduction, or by jumping from one node to the next node.
Describe the variation of post-synaptic activity
When the receptor protein includes an ion channel, the receptor is called an ionotropic receptor. When the receptor protein lacks an ion channel and instead affects ion channels indirectly through intracellular second messengers, the receptor is called a metabotropic receptor. Typically, when postsynaptic ion channels are opened, the resulting change in membrane potential is too small to bring the axon hillock to threshold; therefore, no action potential is produced in the postsynaptic cell. Individual membrane potentials may be summed, however, and may eventually produce a potential exceeding the threshold point, initiating an action potential. Summation can occur as the result of two or more impulses arriving at nearly the same time (temporal summation) or to the same location (spatial summation).
What part of the human brain is divided into four lobes?
cerebral cortex
Which of the following is the largest part of the human brain?
cerebrum
If the membrane potential of a neuron reaches its threshold potential, which event is most likely to occur next?
generation of an action potential
Which two neurotransmitters are associated with inhibitory responses?
glycine and GABA
Which of the following choices is associated with the parasympathetic nervous system?
heartbeat slows down
What is a primary function of the cerebral cortex?
higher-order information processing
Which of the following causes the refractory period during an action potential?
inactivation of sodium channels
A neurotransmitter that directly opens or closes an ion channel works on what type of receptor?
ionotropic
Which of the following organisms would likely have the least intricate nervous system? 1) flatworms 2) jellyfish 3) bivalves 4) insects 5) All of these organisms have equally complex nervous systems.
jellyfish
The ions found in the highest concentrations within a resting neuron and in the extracellular space around the neuron, respectively, are ___ and ___.
potassium ions, sodium ions
During the process of repolarization, ___ ions flood into the ___.
potassium, extracellular space
In multiple sclerosis the myelination around axons is damaged. This decreases the speed at which action potentials are conducted by interfering with which of the following processes?
saltatory conduction
The action of which of the following maintains the normal resting potential of a neuron?
sodium/potassium pumps
