Nervous System, Synapses, and Neurotransmitters (Unit 1) Flashcards
main divisions of nervous system
- Sensory
- Integrative
- Motor
Sensory Division of nervous system
tactile, visual, auditory, olfactory
perceiving sensation from the environment
Integrative Division
process information, creation of memory
Motor Division
respond to and move about in our environment
Neurons
The basic functional unit of the central nervous system
3 major anatomical/structural components of nervous system
- Soma
- Axon
- Dendrite
Soma
the main body of the neuron
Axon
extends from soma to synaptic terminal –> the effector part of neuron (the output side)
Dendrite
projections from soma; the sensory portion of neuron (the input side where information is received)
how many neurons in CNS?
over 100 billion
how many synaptic connections from input fibers on neuron?
anywhere from hundreds to as much as 200,000
Structure of a large neuron in the brain showing its important functional parts.
insert pic
Somatosensory axis of the NS function
Transmits sensory info from receptors of body surface and some deep structures through peripheral nerves to various sensory processing locations in the CNS
Skeletal motor nerve axis of the NS function
Motor functions include stimulation of
- Contraction of skeletal muscle
- Contraction of smooth muscle in organs
- Secretions of active chemical substances by both exocrine and endocrine glands
Major Types of Synapses (2)
chemical and electrical
Synapse
Junction point from one neuron to the next
Synapse Role in Info Processing
Play a role in info processing by performing selective action depending on input and modulation
Synapse determines the _____ nervous signals will spread throughout the NS
direction
most synapses in human are _____
chemical synapses
chemical synapse: mechanism
presynaptic neuron secretes neurotransmitter that acts on receptor proteins in the membrane of the next neuron
affects chemical synapse can have on the succeeding neuron (3)
- excite neuron
- inhibit neuron
- modify neuron
electrical synapse: mechanism
pre and post neurons are physically connected via gap junctions. Gap junctions allow free movement of ions, so action potentials are directly communicated from the interior of one neuron to the interior of the next neuron
Transmission direction of signals is through electrical synapse
bidirectional – allows coordination of activities of large groups/networks of interconnected neurons
Chemical synapses always communicate info in
ONE DIRECTION —allows for signals to be directed toward specific goals
_____ (#) presynaptic terminals about surface of dendrites (80-95%) and soma (5-20%) of motor neuron
10,000-200,000
% of presynaptic terminals about surface of dendrites vs. soma
80-95% and 5-20%
Neurons in different locations vary in (4 characteristics)
- Size of soma
- Length, size, # of dendrites
- Length, size of axon
- # of presynaptic terminals
Neurotransmitter binding to GPCR can induce( 4)
- Opening specific ion channels in postsynaptic membrane —ion channel effects through this mech stay open longer than those activated directly
- Activation of cAMP or cGMP
- Activation of 1 or more intracellular enzymes
- Activation of gene transcription
GPCR
G-protein coupled receptor
NTs that cause opening of cation channels in postsynaptic membrane = (excitatory vs. inhibitory)
excitatory
NTs that cause opening of anion channels in postsynaptic membrane = (excitatory vs. inhibitory)
inhibitory
G protein complex consists of:
guanosine diphosphate (GDP)
alpha (α) component that is the activator portion of the G protein
beta (β) and gamma (γ) components that are attached to the alpha component
G protein complex is found:
in the cytosol
G protein complex bound to GDP = active vs. inactive.
inactive
how does the nervous system get long-acting responses/changes in postsynaptic neurons?
activation of cell signaling 2nd messenger pathways
Mechanisms of excitation of postsynaptic neurons
Opening of Na+ channels
Decreased Cl- or K+ conductance
Changes in internal metabolism or gene expression
Mechanisms of inhibition of postsynaptic neurons
Opening of Cl- channels
Increased K+ conductance
Activation of receptor enzymes that cell metabolic fxn or gene expression
Concentration Differences of Ions across the Neuronal Somal Membrane.
sodium and chloride high in extracellular fluid, potassium high in intercellular fluid
why is there a low concentration of chloride in neurons?
negative voltage 9-65 mV) repels the negatively charged chloride ions, forcing them outward through channels until the concentration is much less inside the membrane than outside.
resting membrane potential of spinal motor neuron soma
-65 mV
diffusion potential for chloride with respect to neuron cell
-70 mV
Vm in neurons in the CNS is (less/more) negative than large peripheral neurons
less
importance of neuron have a less negative membrane potential
allows both positive and negative control of the degree of excitability of the neuron
EPSP
Excitatory postsynaptic potentials
Excitatory postsynaptic potential process
- Stimulation of the postsynaptic neuron with
excitatory NTs causing increased Na
permeability - Na influx raises the membrane potential to a less
negative (more positive) potential → EPSP (requires stimulation of multiple presynaptic terminals, not just one!) - If EPSP rises high enough to exceed threshold,
an AP will occur
In EPSP, where does the AP occur?
APs are not initiated immediately adjacent to
the synapse, but at the initial segment of the axon
IPSP
Inhibitory postsynaptic potentials
Neuron in an excited state
less negative intraneuronal potential (−45 millivolts) caused by sodium influx
Neuron in an inhibited state
more negative intraneuronal membrane potential (−70 millivolts) caused by potassium ion efflux, chloride ion influx, or both.
IPSP process
Increased conductance of Cl- or K+ =
hyperpolarization of the membrane potential –>decrease in membrane potential to a more negative value – makes it harder to get to the action potential threshold
spatial summation
the effect of summing simultaneous postsynaptic potentials by activating multiple terminals on widely spaced areas of the neuronal membrane
temporal summation
when successive discharges from a single presynaptic terminal occur rapidly enough such that they add to one another in summation
decremental conduction
the decrease in membrane potential as it spreads electrotonically along dendrites toward the soma
synapses that lie (near/far away from) the soma have far more effect in causing neuron excitation or inhibition that do those that lie (near/far) from the soma
near; far
do thresholds of neurons vary?
tresholds are different for different populations of neurons
when excitatory state rises above threshold for action potential, a neuron will:
fire repeatedly as long as it stays above the threshold
trend for firing rate of neurons
increases as excitatory state increases (arbitrary units) but then eventually plateaus at the max firing rate (has to due with the refractory period of the ion channels)
