Chapter 12: Nervous Tissue (Part 2) Flashcards
refractory period (2)
- the period of resistance to stimulation when an action potential can not be fired again
- only refers to a small patch of the neurons membrane
What are the 2 phases of the refractory period?
absolute & relative
absolute refractory period (2)
- no stimulate of any strength will trigger an action potential
- Na gates are open
relative refractory period (2)
- only especially strong stimulus will trigger an action potential
- K gates are open
For communication, the nerve signal must ______
travel to the end of the axon
Which fibers have voltage regulated ion gates along its entire length?
unmyelinated fibers
saltatory conduction in PNS
in myelinated fibers the signal seems to jump from node to node
What part of the myelinated fiber contains voltage gated ion channels?
Node of Ranvier
When a nerve signal reaches the end of the axon what happens?
triggers the release of neurotransmitters via exocytosis
Neurotransmitters stimulate what?
dendrites or directly onto a soma that triggers a local potential to the axon hillock
axodendritic synapse
presynaptic neuron synapse with a dendrite
axosomatic synapse
presynaptic neuron synapse with a soma
axoaxonic synapse
presynaptic neuron synapse with an axon of postsynaptic neuron
Where does typical synapse occur?
dendrites
What type of junctions are in electrical synapse?advantages & disadvantages?
gap junctions that join adjacent cells
advantages: quick transmission no delay for release & binding
disadvantages: cannot integrate info & make decisions
Why is it possible to integrate info?
because of the transfer of electrical to chemical signals
What are the 4 categories of neurotransmitters?
- acetylcholine
- amino acid neurotransmitters
- monoamines
- neuropeptides
Characteristics of neuropeptides? (5)
- chains of 2 to 40 amino acids
- act at lower concentrations
- longer lasting effects
- some function as hormones or neuromodulators
- stored in secretory granules
T/F Do neurotransmitters have the same effect everywhere in the body
FALSE
What are the actions of neurotransmitters? (4)
- excitatory
- inhibitory
- open ligand-regulated ion gates
- depend on receptor of post synaptic cell
3 Kinds of synapse
- excitatory cholinergic
- inhibitory GABA-ergic
- excitatory adrenergic
excitatory cholinergic synapse
employs ACh as its neurotransmitter (excites some postsynaptic cells & inhibits others)
inhibitory GABA-ergic synapse (3)
- employs gamma-aminobutyric acid as its neurotransmitter
- receptors are chloride channels
- postsynaptic neurons are inhibited
excitatory adrenergic synapse
- employs norepinephrine as its neurotransmitter
- act through second messenger system
- receptor is not an ion gate, but a transmembrane protein associated with a G protein
- slower to respond
What advantage does excitatory adrenergic synapse have over other synapses?
enzyme amplification:single molecule of NE can produce vast #s of product molecules in the cell
neuromodulators
hormones, neuropeptides, and other messengers that modify synaptic transmission
How do neuromodulators modify synaptic transmission? (2)
- stimulate neuron to install more receptors in the postsynaptic membrane adjusting its sensitivity to the neurotransmitter
- alter the rate of the neurotransmitter synthesis
enkephalins
a neuromodulator family the inhibit spinal interneurons from transmitting pain signals to the brain
nitric oxide
a neuromodulator (simple) gas released by postsynaptic neurons in some areas of the brain concerned with learning & memory
The ____ synapse in a neural pathway, the _____ it takes for info to get from its ____ to its destination
more; longer; origin
Why do we have synapses? (3)
- to process info & make decisions
- chemical synapses are the decision making devices
- more synapse the greater the decision capabilities
What is neural integration based on?
the postsynaptic potentials produced by neurotransmitters
excitatory postsynaptic potential? examples?
EPSP
any voltage change in the direction of threshold that makes a neuron more likely to fire
-ex. glutamate & aspartate
inhibitory postsynaptic potential?examples?
IPSP
any voltage change away from threshold that makes a neuron less like to fire
-ex. glycine & GABA
Which neurotransmitters can be excitatory or inhibitory?
ACh & norepinephrine
summation
the process of adding up postsynaptic potentials & responding to their net effects that occurs in the trigger zone
temporal summation
- occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
- 1 neuron
spatial summation
occurs when EPSPs from several different synapses add up to threshold at an axon hillock
-multiple neurons
facilitation
a process in which one neuron enhances the effect of another one
neural coding
the way in which the nervous system converts info to a meaningful pattern of action potentials
What does qualitative information depend on?
which neuron fires (labeled line code)
What does quantitative information depend on?
information about the intensity of a stimulus is encoded in 2 ways (different neurons have dif thresholds of excitation; more strongly a neuron is stimulated, the more frequently it fires)
neural pools
neurons function in large groups
diverging circuit
one nerve fiber branches & synapses with several postsynaptic cells
converging circuit
input from many dif nerve fibers can be funneled to one neuron (opposite of diverging)
reverberating circuit
neurons stimulate each other in linear sequence but one cell restimulates the first cell to start the process all over
parallel after discharge circuit
input neuron diverges to stimulate several chains of neurons
memory trace (engram)
physical basis of memory is a pathway through the brain
synaptic plasticity
the ability of synapses to change
synaptic potential
the process of making transmission easier
What are the 3 types of memory?
immediate
short
long
immediate memory (3)
- the ability to hold something in your thoughts for just a few seconds
- essential for reading
- our memory “echoes” in our minds for a few seconds (reverberating circuit)
short term memory (3)
- lasts from a few seconds to several hours
- quickly forgotten if distracted
- reverberating circuits
What causes memory to last longer?
facilitation
tetanic stimulation
rapid arrival of repetitive signals at a synapse (accumulation of Ca2+)
posttetanic potentiation
to jog a memory (Ca2+ level in synaptic knob stays elevated)
types of long term memory (2)
declarative
procedural
declarative long term memory
retention of events that you can put into words
procedural long term memory
retention of motor skills
alzheimer disease
deficency in ACh and nerve growth factors
parkinson disease
- progressive loss of motor function beginning in 50s or 60s- NO RECOVERY
- degeneration of dopamine releasing neurons
- involuntary muscle contractions
