Chapter 37: The Nervous System - Neurons, Synapses, & Signaling Flashcards
(30 cards)
Function of the nervous system
Regulated performance!
How?
-Integrating incoming information with information that is already stored in memory
-Translating present and past information into action via effectors.
Part of the nervous system
Central NS - Brain - Spinal cord Peripheral NS - All of the nervous tissue outside of the CNS
- Information from stimuli is received by receptors and is transmitted to effectors ( muscles = mechanical, glands = chemical)
Synapses
Junctions between neurons and a) other neurons and b) effector cells.
- Chemical signals occur at synaptic cleft ( ~20nm, VERY narrow = less space for signal to travel!)
PRESYNAPTIC Neuron - carries signal down axon, toward synaptic KNOB. Chemical signal (neurotransmitter) is released in synaptic CLEFT.
-Neurotransmitter diffuses across cleft to POSTSYNAPTIC cell, where it bind to receptors.
Receptors on postsynaptic cells
Chemical-gated, or ligand-gated, ion channel.
- neurotransmitter temporarily changes conformation of receptor, thus changing its permeability to specific ions.
- EPSP = Depolarize
- IPSP = Hyperpolarize
Neurotransmitters are “re-uptake-“en
Drugs -
Cocaine - Blocks re-uptake of 1) _________
SSRI (antidepressants) - Blocks re-uptake of 2) __________
Valium - Enhances 3) ___________ inhibitory effect
1) Dopamine
2) Serotonin
3) GABA’s
Once the Action Potential Reaches the synaptic knob…
Influx of Ca+ INTO the presynaptic neuron. This induces vesicular exocytosis and vesicles release neurotransmitter into cleft. Receptors are stimulated, neurotransmitter is re-absorbed, and re-stored in vesicles.
Potentials
Graded = depolarizes or hyperpolarizes.
- mediated by chemical-gated ion channels
- amplitude depends on the amount of the chemical binding to receptors
- polarization changes can either “add-up,” or “cancel out” (SUMMATION)
Action potential = Depolarization that reaches threshold
- mediated by voltage-gated ion channels, which open to either Na+ or K+.
- SUMMATION IS NOT A POSSIBILITY, this is all or nothing.
Action potential
Summation of graded potentials must reach the axon hillcock’s threshold of (-55mV/-50mV).
- Voltage gated Na+ channel OPEN
- Na+ moves IN down its gradient, peak = (+30mV)
- Before E^Na+ (+60 mV) is reached, channels CLOSE and K+ OPENS
- Voltage gated K+ channels now allow K+ to move down its chemical gradient, returning the inside of the cell back to it negative state.
- Before E^K+ (-90mV) is reached, channels close
Speeding up the action potential
Myelinated axons are “skipped” due to there conduction properties
- Saltatory conduction
* 1-2 m/sec = burning pain unmyelinated
* 5-6 m/sec = sharp pain myelinated
- “Skipping/jumping” speeds up conduction
People with MS (autoimmune disease) have CNS myelin sheath damage.
Puffer fish - Tetrodotoxin
Blocks voltage-gated Na+ channels, ultimately blocking nerve signals and muscle contractions.
- TTX binding site = alpha-subunit on transmembrane protein
The nervous system and its cells
BILLIONS of cells may contact few or MANY other nerve cells.
Types:
1) Neuroglia
2) Neurons
Neurons: The structural and functional units of the NS
1) Dendrites - carries signal toward soma
2) Cell body/Soma- houses nucleus
4) Axon hillcock - beginning of nerve impulse
5) Axon - carries signal from soma to synapse
6) Myelin sheath - insultes axon
7) Nodes of ranvier - un-myelinated axon (junctions between adjacent neurological cells are important in transmission of nerve signals!)
8) Terminal buttons
9) Synaptic knob
10) Synaptic cleft
Neuroglia
Oligodendroglia/Schwann cells
- Myelin is made of plasma membrane of neuralgial cells that are wrapped tightly. There are LESS PROTEINS than normal plasma membranes. This means that there are FEWER CHANNEL PROTEINS, making these regions good electrical insulators that speed up conduction.
Collection of axons traveling together in the CNS
Tract
Collection of axons traveling together in the PNS
Nerve
Collection of cell bodies in the CNS
A nucleus (not to be confused with a cells nucleus)
Collection of cell bodies in the PNS
A ganglion
Nerve
A collection of axons traveling together in the PNS
- Several nerve fibers surrounded by various layers of connective tissue.
- May contain thousands of efferent (outbound) and afferent (inbound) fibers.
Transmission of nerve signals
Transmitted as ELECTRICAL and CHEMICAL!
- Signals along neuron = Electrical
- Signals between one neuron and another neuron (or effector cell) = Chemical
The resting cell
The plasma membrane has an electrical difference (a.k.a voltage)
- Cytoplasm (intracellular) side = -70mV, meaning it is 70mV more negative than the extracellular side of the membrane.
- At rest, the neuron is said to be “polarized,” which is a fancy word for the neurons resting potential.
- This potential is a result of the combination of opposite charges attracting each other and pulling ions down their concentration gradients.
* ANION = (-) Negative
* CATION = (+) Positive
What keeps a neuron at its resting potential?
Ion pumps - these require _________ (hint: NRG!)
- For every 3 Na+ moved out, there are 2 K= moved in ( meaning there is a net of +1 Na+ being removed) - The membrane is 70X more permeable to K+ - There are fixed ANIONS inside the cell that are too large to be removed ( proteins, carbs, nucleic acids, which all contribute to the neurons - charge)
Movement in/out of the cell
K+ has a chemical gradient - This moves K+ OUT of the cell. This is because there is 25-30X MORE K+ on the cytoplasmic side.
K+ has an electrical gradient - This moves K+ INTO the cell. These forces result in little net movement.
Na+ has both a chemical and an electoral gradient. Both work to move Na+ INTO the cell because there is 10X more on the extracellular side.
Pumps of the neurons plasma membrane
Sodium-potassium pump
- This pump is a protein! As in, it is a string of amino acids
- Uses energy (remember ATP?) to move ions against their gradients.
Inside of the neuron
MORE :
- Large anions
- K+
LESS:
- Na+
- Cl-
