LECTURE 4 Flashcards
Parts of Neuron
- Cell body
- Dendrites
- Axon
- Myelin Sheath
- Terminal buttons
Electrochemical signals
Nerves communicate via this
Electric signal
Action potential sends electrical charge traveling down the axon
Chemical signal
Neurotransmitter chemicals released from one neuron to next neuron at synapse
Neuron
A cell in the nervous system whose function it is to receive and transmit information.
Major parts of a neuron
- Cell body or soma: contains the nucleus of the cell and keeps the cell alive
- Dendrite: A branching treelike fiber which collects information from other cells and sends the information to the soma
- Axon: A long, segmented fiber, which transmits information away from the cell body toward other neurons or to the muscles and glands
Draw a neuron
Refer to figure
Myelin sheath
The layer of fatty tissue surrounding the axon
of a neuron that both acts as an insulator and allows faster transmission of the electrical signal.
Terminal button
The tip of the axon branches (axon branches out towards the end)
How does the nervous system operate?
The nervous system operates using an electrochemical process. An electrical charge moves through the neuron itself and chemicals are used to transmit information between neurons. Within the neuron, when a signal is
received by the dendrites, is it transmitted to the soma in the form of an electrical signal, and, if the signal is strong enough, it may then be passed on to the axon and then to the terminal buttons. If the signal reaches the terminal buttons, they are signaled to emit chemicals known as neurotransmitters, which communicate with other neurons across the spaces between the cells, known as synapses.
Resting potential
A state in which the interior of the neuron contains
a greater number of negatively charged ions than does the area outside the cell
Action potential.
Change in electrical charge that occurs in a neuron when a nerve impulse is transmitted
Process of neuron receiving and transmitting signal
The electrical signal moves through the neuron as a result of changes in the electrical charge of the axon. Normally, the axon remains in the resting potential, a state in which the interior of the neuron contains a greater number of negatively charged ions than does the area outside the cell. When the segment of the axon that is closest to the cell body is stimulated by an electrical signal from the dendrites, and if this electrical signal is strong enough that it passes a certain level or threshold, the cell membrane in this first segment opens its gates, allowing positively charged sodium ions that were previously kept out to enter. This change in electrical charge that occurs in a neuron when a nerve impulse is transmitted is known as the action potential. Once the action potential occurs, the number of positive ions exceeds the number of negative ions in this segment, and the segment temporarily becomes positively charged. the axon is segmented by a series of breaks between the sausage-like segments of the myelin sheath. Each of these gaps is a node of Ranvier. The electrical charge moves down the axon from segment to segment, in a set of small jumps, moving from node to node. When the action potential occurs in the first segment of the axon, it quickly creates a similar change in the next segment, which then stimulates the next segment, and so forth as the positive electrical impulse continues all the way down to the end of the axon. As each new segment becomes positive, the membrane in the prior segment closes up again, and the segment returns to its negative resting potential. In this way the action potential is transmitted along the axon, toward the terminal buttons.
Node of Ranvier.
The axon is segmented by a series of breaks between the segments of the myelin sheath
What manner does the action potential operate in
All-or-nothing. The neuron either fires completely, such that the action potential moves all the way down the axon, or it does not fire at all. Thus neurons can provide more energy to the neurons down the line by firing faster but not by firing more strongly.
Refractory period
The neuron is prevented from repeated firing
by the presence of a brief time after the firing of the axon in which the axon cannot fire again because the neuron has not yet returned to its resting potential.
How do nerve impulses travel
Electrical charges - within the nerve cell
Chemical transmissions - between the nerve cells
Synapses
Junction areas where the terminal buttons at the end of the axon of one neuron nearly, but don’t quite, touch the dendrites of another. The synapses provide a remarkable function because they allow each axon to communicate with many dendrites in neighboring cells.
Neurotransmitter
A chemical that relays signals across the synapses between neurons. When the electrical impulse from the action potential reaches the end of the axon, it signals the terminal buttons to release neurotransmitters into the synapse. Neurotransmitters travel across the synaptic space between the terminal button of one neuron and the dendrites of other neurons, where they bind to the dendrites in the neighboring neurons. Furthermore, different terminal buttons release different neurotransmitters, and different dendrites are particularly sensitive to different neurotransmitters. The dendrites will admit the neurotransmitters only if they are the right shape to fit in the receptor sites on the receiving neuron. For this reason, the receptor sites and neurotransmitters are often compared to a lock and key
Diagram of neurotransmitter being released
MEMORIZE FROM ARTICLE
The effect of neurotransmitters upon contact
When neurotransmitters are accepted by the receptors on the receiving neurons their effect may be either
excitatory (i.e., they make the cell more likely to fire) or inhibitory (i.e., they make the cell less likely to fire). Furthermore, if the receiving neuron is able to accept more than one neurotransmitter, then it will be influenced by the excitatory and inhibitory processes of each. If the excitatory effects of the neurotransmitters are greater than the inhibitory influences of the neurotransmitters, the neuron moves closer to its firing threshold, and if it reaches the threshold, the action potential and the process of transferring information through the neuron begins.
What happens to neurotransmitters rejected by receptor sites?
Neurotransmitters that are not accepted by the receptor sites must be removed from the synapse in
order for the next potential stimulation of the neuron to happen. This process occurs in part through the
breaking down of the neurotransmitters by enzymes, and in part through re-uptake.
Re-uptake
A process in which neurotransmitters that are in the synapse are reabsorbed into the transmitting terminal buttons, ready to again be released after the neuron fires.
Effect of neurotransmitters on the body
Have a wide and profound effect on emotion, cognition, and behavior. Neurotransmitters regulate our appetite, our memory, our emotions, as well as our muscle action and movement.
Agonist
A drug that has chemical properties similar to a particular neurotransmitter and thus mimics the effects of the neurotransmitter. When an agonist is ingested, it binds to the receptor sites in the dendrites to excite the neuron, acting as if more of the neurotransmitter had been present.
Example of an agonist
As an example, cocaine is an agonist for the neurotransmitter dopamine. Because dopamine produces feelings of pleasure when it is released by neurons, cocaine creates similar feelings when it is ingested.
Antagonist
A drug that reduces or stops the normal
effects of a neurotransmitter. When an antagonist is ingested, it binds to the receptor sites in the dendrite, thereby blocking the neurotransmitter.
