3.2—how the nervous system works: cells and neurotransmitters Flashcards
1
Q
3.2 Learning Objectives
A
- know the key terminology associated with nerve cells, hormones, and their functioning.
- understand how nerve cells communicate.
- understand the ways that drugs and other substances affect the brain.
- understand the roles that hormones play in our behaviour.
- apply your knowledge of neurotransmitters to form hypotheses about drug actions.
- analyze the claim that we are born with all the nerve cells we will ever have.
2
Q
3.2 Focus Questions
A
- which normal processes of nerve cells are disrupted by a substance like snake venom?
- what roles do chemicals play in normal nerve cell functioning?
3
Q
Neurons
A
- neurons: one of the major types of cells found in the nervous system, that are responsible for sending and receiving messages throughout the body.
- genes in the cell body synthesize proteins that form the chemicals and structures that allow the neuron to function.
- the activity of these genes can be influenced by the input coming from other cells, received by dendrites.
- at any given point in time, a neuron will receive input from several other (sometimes over 1000) other neurons.
- the impulses from other cells travel across the neuron to the base of the cell body, known as the axon hillock.
- if the axon hillock receives enough stimulation from other neurons, it initiates a chemical reaction that flows down the rest of the neuron.
- the activity travels from the axon hillock to the axon, until it reaches the end of the axon, known as the axon terminal, bulb-like extensions filled with vesicles containing neurotransmitters.
- the impulse travelling down the axon will stimulate the release of neurotransmitters, allowing neural communication to take place.
- sensory neurons: receive information from the bodily senses and bring it toward the brain.
- motor neurons: carry messages away from the brain and spinal cord toward muscles in order to control their flexion and extension. (figure 3.13)
- some cells have few or no dendrites, while some have very many branches; the physical structure of a neuron is related to the function it performs.
-
neurogenesis: the formation of new neurons.
- stem cells: a type of cell that doesn’t have a predestined function; the deciding factor seems to be the stem cell’s chemical environment.
- for a long time, scientists thought that nerves couldn’t regenerate, but recently they have observed neurogenesis in a number of brain regions, particularly in a region critical for learning and memory.
4
Q
Cell Body | Neurons
A
(soma) the part of a neuron that contains the nucleus that houses the cell’s genetic material. (figure 3.12)
5
Q
Dendrites | Neurons
A
small branches radiating from the cell body that receive messages from other cells and transmit those messages toward the rest of the cell.
6
Q
Axons | Neurons
A
transports information in the form of electrochemical reactions from the cell bod to the end of the neuron.
7
Q
Neurotransmitters | Neurons
A
the chemicals that function as messengers allowing neurons to communicate with each other.
8
Q
Glial Cells | Neurons
A
specialized cells of the nervous system that are involved in mounting immune responses in the brain, removing waste, and synchronizing the activity of the billions of neurons that constitute the nervous system.
9
Q
Myelin | Neurons
A
- myelin: a fatty sheath, formed by glial cells, that insulates axons from one another, resulting in increased speed and efficiency of neural communication.
- multiple sclerosis: a disease in which the immune system doesn’t recognize myelin and attacks it—a process that can devastate the structural functional integrity of the nervous system.
- when myelin breaks down, it impairs the ability of the affected neurons to transmit information along their axons.
- as a result, groups of brain structures that normally fire together to produce a behaviour can no longer work as a functional network.
10
Q
The Neuron’s Electrical System
A
- the network of cells that make up the neuron allows messages to be transmitted within the brain and the rest of the body; this activity involves the most important function a neuron can perform: to fire.
- neural activity is based on changes in the concentrations of charged atoms called ions.
- when a neuron is not transmitting information, the outside has a high concentration of positively charged ions (Na and K), while the interior has a high concentration of negatively charged ions (Cl).
- electrostatic gradient: the inside and outside of the cell have difference charges.
- concentration gradient: different types of ions are more densely packed on one side of the membrane than on the other.
- ion channels: small pores in a cell membrane.
- most substances have a tendency to move from areas of high concentration to areas of low concentration.
- if ion channels opened up in the neuron’s cell membrane, there would be a natural tendency for positively charged sodium ions to rush into the cell.
- when a neuron is stimulated, the surge of positive ions into the cell changes the potential of the neuron.
- if enough positively charged ions reach the axon hillock to push its charge past that cell’s firing threshold, the neuron will initiate an action potential.
- when an action potential occurs, the charge of that part of the axon changes from -70mV to +35mV (from negatively to positively charged). (figure 3.15)
- once an axon becomes depolarized, it forces open the ion channels ahead of it, causing the action potential to move down the length of the axon as positively charged ions rush into the ion channels.
- at each point of the axon, ion channels shut as soon as the action potential occurs; the K- ions that came into the cell are pumped back out.
-
hyperpolarized: the cell is more negative than its normal resting potential.
- when the K- leave the cell, it causes the neuron to become hyperpolarized, making the cell less likely to fire.
11
Q
Resting Potential | The Neuron’s Electrical System
A
approximately -70mV; the relatively stable state during which the cell is not transmitting messages.
12
Q
Action Potential | The Neuron’s Electrical System
A
a wave of electrical activity that originates at the base of the axon and rapidly travels down its length. (figure 3.14)
13
Q
Refractory Period | The Neuron’s Electrical System
A
the brief period (2-3 milliseconds) in which a neuron can’t fire.
14
Q
Synapses | The Neuron’s Electrical System
A
- synapses: the microscopically small spaces that separate individual nerve cells.
- presynaptic cell: the cell that releases chemicals (neurotransmitters) into the synapse.
- postsynaptic cell: the cell that contain receptors to receive the chemical input.
- the dendrites of the postsynaptic cell contain specialized receptors that are designed to hold specific molecules, including neurotransmitters.
- excitatory: when a neurotransmitter causes the neuron’s membrane potential to become less negative; it has increased the probability that an action potential will occur in a given period of time.
- inhibitory: when a neurotransmitter causes the membrane potential to become more negative; it decreases the likelihood of an action potential occurring.
15
Q
All-Or-None Principle | The Neuron’s Electrical System
A
- all-or-none principle: individual nerve cells fire at the same strength every time an action potential occurs.
- when stimulated, a given neuron always fires at the same intensity and speed.
- the strength of a sensation is determined by the rate at which nerve cells fire as well as by the number of nerve cells stimulated.
16
Q
Neurotransmitters
A
- each neurotransmitter has its own unique molecular shape; like a lock and key. (table 3.1)
- after neurotransmitters have bound to postsynaptic receptors of a neighbouring cell, they’re released back into the synaptic cleft.
- prolonged stimulation of the receptors makes it more difficult for the cell to return to its resting potential.
- if a neurotransmitter attaches onto a receptor for long periods of time, it decreases the number of times that the neurons could fire (i.e. making your brain less powerful).
18
Q
Reuptake | Neurotransmitters
A
a process whereby neurotransmitter molecules that have been released into the synapse are reabsorbed into the axon terminals of the presynaptic neuron. (figure 3.17)
27
Q
Antagonists
A
- antagonists: inhibit neurotransmitter activity by blocking receptors or preventing synthesis of a neurotransmitter. (figure 3.18)
- Botox, which is derived from nerve-paralyzing bacterium that cause botulism, blocks the action of acetylcholine by binding to its postsynaptic receptor sites.
- since Botox directly binds with acetylcholine receptors, it’s considered a direct antagonist.
- if a chemical reduces the influence of a neurotransmitter without physically blocking the receptor, it would be classified as an indirect antagonist.
