Chapter 37: The Nervous System - Neurons, Synapses, & Signaling

Question 1

Function of the nervous system

Answer 1

Regulated performance!
How?
-Integrating incoming information with information that is already stored in memory
-Translating present and past information into action via effectors.

Question 2

Part of the nervous system

Answer 2

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)

Question 3

Synapses

Answer 3

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.

Question 4

Receptors on postsynaptic cells

Answer 4

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

Question 5

Drugs -
Cocaine - Blocks re-uptake of 1) _________
SSRI (antidepressants) - Blocks re-uptake of 2) __________
Valium - Enhances 3) ___________ inhibitory effect

Answer 5

1) Dopamine
2) Serotonin
3) GABA’s

Question 6

Once the Action Potential Reaches the synaptic knob…

Answer 6

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.

Question 7

Potentials

Answer 7

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.

Question 8

Action potential

Answer 8

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

Question 9

Speeding up the action potential

Answer 9

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.

Question 10

Puffer fish - Tetrodotoxin

Answer 10

Blocks voltage-gated Na+ channels, ultimately blocking nerve signals and muscle contractions.
- TTX binding site = alpha-subunit on transmembrane protein

Question 11

The nervous system and its cells

Answer 11

BILLIONS of cells may contact few or MANY other nerve cells.
Types:
1) Neuroglia
2) Neurons

Question 12

Neurons: The structural and functional units of the NS

Answer 12

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

Question 13

Neuroglia

Answer 13

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.

Question 14

Collection of axons traveling together in the CNS

Answer 14

Tract

Question 15

Collection of axons traveling together in the PNS

Answer 15

Nerve

Question 16

Collection of cell bodies in the CNS

Answer 16

A nucleus (not to be confused with a cells nucleus)

Question 17

Collection of cell bodies in the PNS

Answer 17

A ganglion

Question 18

Nerve

Answer 18

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.

Question 19

Transmission of nerve signals

Answer 19

Transmitted as ELECTRICAL and CHEMICAL!

• Signals along neuron = Electrical
• Signals between one neuron and another neuron (or effector cell) = Chemical

Question 20

The resting cell

Answer 20

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

Question 21

What keeps a neuron at its resting potential?

Answer 21

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)

Question 22

Movement in/out of the cell

Answer 22

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.

Question 23

Pumps of the neurons plasma membrane

Answer 23

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.

Question 24

Inside of the neuron

Answer 24

MORE :

• Large anions
• K+

LESS:

• Na+
• Cl-

Question 25

Outside of the neuron

Answer 25

MORE:

• Na+
• Cl-

LESS:

• Large anions
• K+

Question 26

Equilibrium potential

Answer 26

E^Na+ = +60 mV
E^K+ = -90 mV
**These are never reached!
E^Cl- = -70 mV

Question 27

Action potentials happen when membrane reaches its threshold, which is usually 1) _________, causing 2) _________ to rush in because 3) __________ open.

Answer 27

1) -55 mV
2) Na+
3) Voltage-gated sodium channels

Question 28

Action potential seize, thus depolarizing when it reaches 1) _______, and 2) ________ open

Answer 28

1) +30 mV

2) Voltage-gated potassium channels

Question 29

Action potential at the 1) __________ reaches much further than 2) _________.

Answer 29

1) Node of ranvier

2) Unmyelinated axons

Question 30

1) Neuroglia provide 1) ________, 2) ________, and 3) ___________.
a) astrocytes/microglia
* CNS (oligodendroglia)
* PNS ( schwann cells)

2) Neurons are the 4) _________ and 5) _______ unit

Answer 30

1) support
2) nutrients
3) insulation
4) structural
5) functional