Chapter 2, Structure and Function of the Nervous System Flashcards
1
Q
Neuron structure includes:
A
- Dendrites: receiving
- Cell body: collecting / summing
- Axon: sending
2
Q
Convergence
A
Each neuron
receives/integrates information from
many cells
3
Q
Divergence
A
Information may be
transmitted to a few or thousands of
other neurons
4
Q
Dendrites
A
- Dendrites are covered in spines
- Dendrites and spines are constantly modified and can change rapidly
5
Q
Soma
A
- The soma, or cell body, performs most metabolic functions
- Many proteins and neurotransmitters are created in the soma
and then must be transported
6
Q
Axon
A
- The myelin sheath protects the axon and increases speed of conduction along the axon
- Schwann cells in PNS
Oligodendroglia in CNS - Nodes of Ranvier are breaks in the myelin sheath; sites where APs are regenerated
7
Q
Resting Potential
A
- The resting potential of the cell is caused by the distribution of ions inside and outside the neuron
8
Q
Local Potentials
A
- Local potentials, or graded potentials, are small, transient changes in membrane potential
- Depolarization (Na+ flows in)
- Hyperpolarization (Cl-flows in)
- Summation (integration) is possible
- Integration of EPSPs and IPSPs at the axon hillock
- When summation reaches threshold (-50mV), an AP is triggered
9
Q
Action Potenial Phases
A
- A basic AP has the following phases:
- Rising phase, overshoot, falling phase, undershoot
10
Q
Action Potential
A
- The AP has an absolute refractory period because of the inactivation of voltage-gated Na+ channels
- Some drugs alter action potential conductance by blocking the voltage-gated Na+ channels.
- What would these drugs be used for?
- Other drugs alter the action potential by binding to closed Na+ channels
- What would these drugs be used for?
11
Q
Novocain
A
- Novocain inhibits the voltage-gated Na+ channels, which prevents APs from being generated
- Used in dental work to prevent pain
12
Q
Examples of natural toxins that can be used experimentally to alter the Na+ channels
A
- Pufferfish tetrodotoxin (TTX) – clogs Na+-permeable pore
- Red tide saxitoxin – blocks Na+ channels
13
Q
Characteristics of Local Potentials
A
- Graded
- Decremental
- Spatial and temporal summation
- Produced by opening ligand-gated channels
- Depolarization or hyperpolarization
14
Q
Characteristics of Action Potentials
A
- All-or-none
- Nondecremental
- Intensity of stimulus coded by rate of firing
- Produced by the opening of voltage-gated channels
- Depolarization
15
Q
Types of Synaptic Connections
A
- The most common is axodendritic, but many types of synaptic connections are possible
1. Axodendritic
2. Axosomatic
3. Axoaxonic - Small axons may only have one
active zone - Larger synapses have more active
zones - One axon terminal may contact
multiple postsynaptic cells
16
Q
Structure of Synapses
A
- Presynaptic cell: Synaptic vesicles
- Synaptic cleft
- Postsynaptic cell: Dendritic spine, Postsynaptic density: Area of the dendritic membrane facing the synaptic cleft with many neurotransmitter receptors.
17
Q
Criteria for a chemical to be considered a neurotransmitter:
A
- Presynaptic cell contains the chemical plus a mechanism to make it.
- A mechanism for inactivating the chemical should also be present.
- Chemical is released from the axon terminal when a neuron is stimulated.
- Receptors for the chemical are present in the postsynaptic cells.
- Direct application of chemicals or agonists has the same effect on postsynaptic cells as stimulating the presynaptic neuron.
* Applying an antagonist that blocks the receptors inhibits both the chemical’s action and the effect of stimulating the presynaptic neuron.
18
Q
Major neurotransmitter classes
A
Classical neurotransmitters
* Amino acids
* Monoamines
* Acetylcholine (Ach) Purines
Nonclassical neurotransmitters
* Neuropeptides
* Lipids
* Gases
19
Q
Examples of Amino Acids
A
- Glutamate
- GABA
- Glycine
20
Q
Examples of Monoamines
A
- Dopamine (DA)
- Norepinephrine (NE)
- Serotonin (5-HT)
- Histamine (HA)
21
Q
Examples of Acetylcholine (Ach) Purines
A
- Adenosine triphosphate (ATP)
- Adenosine
22
Q
Examples of Neuropeptides
A
- Endorphins and enkephalins
- Corticotropin- releasing factor (CRF)
- Orexin/hypocretin
- Brain-derived neurotrophic factor (BDNF)
23
Q
Examples of Lipids
A
- Anandamide
- 2-Arachidonoylglycerol
24
Q
Examples of Gases
A
- nitric oxide (NO)
- Carbon monoxide (CO)
- Hydrogen sulfide (H2S) (small 2)
25
The steps of neurotransmission
1. Synthesis & storage
2. Release
3. Receptor Action
4. Inactivation
26
Neurotransmitter Synthesis
* Most neurotransmitters are made in the axon terminals; enzymes for their synthesis are transferred to the terminals.
* Neuropeptides are made from protein precursors. Precursors are shipped from the cell body to axon terminals in large vesicles. Replenishment is thus slower than for small molecules.
27
Neurotransmitter Storage
* An individual neuron can make one or several neurotransmitters
* Vesicles can hold one or more types of transmitters
28
Neurotransmitter Release
* Neurotransmitter release is regulated by:
* Rate of neuron firing;
* The probability that vesicles will undergo exocytosis;
* Autoreceptors, which are receptors for the same transmitter released by the neuron.
29
Neurotransmitter Inactivation
* Reuptake
* Diffusion
* Enzymatic degradation
* Re-uptake by glial cell (glutamate only)
30
How cocaine disrupts neurotransmission
* Cocaine blocks transporters for DA (as well as 5-HT and NE)
* DA cannot be inactivated and thus stays in the synapse
31
Lipid and Gaseous Transmitters
* Lipid and gaseous transmitters are not stored in nor released from synaptic vesicles
* Synthesized on demand by postsynaptic cell
* Act as retrograde messengers on the presynaptic cell, and also diffuse to other neurons
32
Neurotransmitter Receptors
* NT receptors are proteins located on cell membranes
* NTs bind to more than on type of receptor type
* The effect of receptor activation may be excitatory or inhibitory
* Drugs can be designed to affect specific receptor subtypes
33
Ionotropic Receptors
* Contain a pore that allow ions to pass through when open
* Opens pore in response to NT binding
* Fast to respond
* Effects are brief
* Made of 4-5 subunits with a pore (an ion channel) in the centre
* The pore matters
* Some receptors are Na+ channels à excitatory response
* Others are Cl- channels à inhibitory response
34
Metabotropic Receptors
* No pore
* Activates G protein in response to NT binding
* Relatively slow
* Effects can be long lasting
* More possibilities for what can happen
* Made of a single protein subunit with 7 transmembrane domains
* AKA G-protein coupled receptor
* Made of a single protein subunit
with 7 transmembrane domains
* AKA G-protein coupled receptor
* G proteins can
* Inhibit or activate ion channels
* Stimulate or inhibit effector enzymes in
the cell membrane that synthesize or
break down second messenger
molecules
Some second messengers:
* Cyclic adenosine monophosphate
(cAMP) – stimulates protein
kinase A (PKA)
* Cyclic guanosine monophosphate
(cGMP) – stimulates protein
kinase G
* Phosphoinositide – stimulates
protein kinase C (PKC)
* Ca2+ can act as a 2nd messenger
– stimulates calcium/calmodulin
kinase II (CaMKII)
35
Binding Sites
* All receptors have binding sites for neurotransmitters
* Many receptors have additional binding sites, called allosteric sites which modify (positively or negatively) the effects of an agonist
36
Synaptic Plasticity
* Functional and structural synaptic changes including change in strength, growth of new synapses, growth of axon terminals, dendrites, spines, etc.
Examples of plasticity:
* Plasticity in development (pruning is normal)
* Learning and memory
Many neurological disorders are associated with abnormal
spines
Synaptic change can result from sensory/environmental stimuli,
and from psychoactive drugs—especially with repeated
exposure
37
Hormones vs. Neurotransmitters
Endocrine communication is different than synaptic
transmission but... The same substance can act as both an NT
and a hormone
38
Cholinergic Projections
39
Noradrenergic Projections
40
Dopaminergic Projections
41
Serotonergic Projections
