Cellular Components of the Nervous System

Question 1

Neurites

Answer 1

Dendrites

Axon

Question 2

Dendritic Spines

Answer 2

□ Cover dendrites, greatly increase receiving surface area of dendrite
□ Highly plastic- can change shape/ numbers rapidly in response to different stimulation patterns
□ New/more stable synapses formed (associations)
LTP can increase size of head of dendritic spine, allows for more receptors to form

Question 3

Soma

Answer 3

○ Produces energy via metabolism
Synthesizes macromolecules used by cell to maintain structure and execute functions

Diagram

Question 4

Axoplasmic Transport:

Answer 4

• Transports enzymes and neurotransmitters from soma to synaptic terminal
Precursors for neurotransmitters are produced in the soma, travels to synaptic terminal for further processing by synthesizing enzymes (also produced in the soma)

Question 5

Anterograde transport

Answer 5

§ Movement from cell body to synaptic terminal
§ Cytoskeletal proteins
§ Vesicles containing
□ Growth proteins
□ Mitochondria
Proteins/enzymes needed for neurotransmitter synthesis and secretion

Question 6

Retrograde transport

Answer 6

§ Movement from synaptic terminal to cell body
§ Vesicle membrane material, excess or degenerated axon proteins
§ Nerve growth factor (NGF)
□ Important for growth and survival of cell
□ Maintains connections
Influences ongoing gene expression

Question 7

Fast Axoplasmic Transport:

Answer 7

• 200-400mm/day
• Highly dependent on ATP and oxygen
• Molecules that are needed right away
○ Enzymes used in neurotransmitter synthesis
○ Newly synthesized synaptic vesicles from the Golgi containing precursors of neurotransmitters
○ Structural proteins
○ Mitochondria
• Anterograde transport facilitated by kinesin
Retrograde transport facilitated by dynein

Diagram

Question 8

Slow Axoplasmic Transport:

Answer 8

• 1-10mm/day
• Less urgently needed molecules
○ Replacement of proteins used for energy and growth
○ Movement of organelles and receptors from one region of the cell to another
Used by 75-80% of all materials carried in axons

Question 9

Facilitated Diffusion and Active Transport:

Answer 9

• Movement against the concentration gradient (in some cases)
• Initiated by binding of the substrate to the transporter protein
Rate of transport determined by the density of transporters

Question 10

Ligand Gated Ion Channel:

Answer 10

• Opens in response to stimulation
• Ligand gated
Channel opens in response to a ligand binding, when no ligand has bound, channel remains closed

Diagram

Question 11

Voltage Gate Ion Channel

Answer 11

○ Channel opens in response to a change in membrane potential
i.e.. Sodium and potassium channels in response to action potentials

Diagram

Question 12

Uniporter channel

Answer 12

Transports a single, larger molecule across the membrane in one direction

Diagram

Question 13

Antiporter Channel

Answer 13

○ Transports an ion through membrane, creates gradient, allows a larger molecules to move through the membrane
○ Doesn’t use ATP, energy generated through the co transport of molecules
Many vesicles have transmembrane proteins, many of which are antiporters

Diagram

Question 14

Symporter

Answer 14

Similar to the antiporter, but both molecules move in the same direction

Diagram

Question 15

Sodium-Potassium pump

Answer 15

○ Active co-transport mechanism
○ Uses energy provided by the mitochondria (ATP)
Pumps 3 Na+ out, 2 K+ ions in

Diagram

Question 16

Kinetics of Transport:

Answer 16

• Affinity- interaction of a substrate with the carrier that transports it across the membrane
○ Expressed by the Michaelis-Menten constant (Km)
§ Km- concentration of a substrate that yields half of the maximum velocity (Vmax) of membrane transport of a substrate for a given amount of the transporter protein
Higher Km- need more substrate, low affinity

Diagram

Question 17

Synaptic Terminal

Answer 17

Synaptic terminal contains lots of mitochondria, lots of golgi, high amounts of recycling occurs here

Question 18

Axodendritic synapse

Answer 18

Axon of pre synaptic neuron connects with dendrite of post synaptic neuron

Question 19

Axosomatic synapse

Answer 19

Axon of pre synaptic neuron connects with soma of post synaptic neuron

Question 20

Axoaxonic synpase

Answer 20

○ Axon of one neuron connects with axon of a second neuron, which connects with the soma of a third neuron
○ Demonstrates pre-synaptic inhibition/facilitation
§ If neuron 1 inhibits neuron 2, then neuron 3 will also be inhibited
If neuron 1 stimulates neuron 2, then neuron 3 will also be stimulated

Diagram

Question 21

Criteria of Traditional Neurotransmitters:

Answer 21

• Presynaptic terminal contains stored neurotransmitter
○ Endocannabinoids don’t store neurotransmitter (lipid soluble, would diffuse out)
• Applying the neurotransmitter to a synapse should mimic the effects caused by stimulation of the pre synaptic terminal
○ Stimulating pre synaptic terminal should cause release of neurotransmitter, squirting neurotransmitter on the post synaptic terminal should have the same effect
• Substance should bind to receptors on the post synaptic cell
○ Endocannabinoids act as retrograde messengers, move from post synaptic to pre synaptic neuron
• Application of an antagonist drug that blocks the receptors should inhibit both the action of the applied substance and the effect of stimulating the pre-synaptic neuron
• Mechanism must exist for the synthesis of the neurotransmitter (precursor and appropriate enzymes should be in the pre-synaptic terminal)
• Mechanism must exist for inactivating the transmitter
○ i.e. catabolic enzyme to degrade the transmitter (Ach)
i.e. Active re-uptake system in the pre-synaptic terminal (glycine) or in adjacent glial cells (glutamate)

Question 22

Neuromodulators:

Answer 22

• Released from neurons, glial cells, or other secretory cells that alter neurotransmitter function (enhance, reduce, prolong), synthesis, release, receptor interactions, reuptake, and metabolism
i.e. glucocorticoids influence the synthesis of norepinephrine by controlling its synthesizing enzyme

Question 23

Coexistence/Colocalization:

Answer 23

• One axon can release several neurotransmitters, which can often occupy the same vesicles
○ i.e. Molecule that synthesizes Ach also synthesizes galanin, which inhibits Ach

Vertebrates and invertebrates share many of the same neurotransmitters

Question 24

Neurotransmitter Synthesis:

Answer 24

• Small, water soluble molecules that are ionized at physiological pH, thus reducing their tendency to diffuse through the blood brain barrier
• Synthesized from dietary precursors, and transformed into active compounds by a series of biochemical reactions that can take place either in the cell body or nerve terminals
• 4 types of neurotransmitters
○ Amino acids
○ Monoamines
○ Acetylcholine (quaternary amine- nitrogen and 4 methyl groups)
○ Neuropeptides
§ Derived from protein precursors synthesized in the soma
Packaged into vesicles by the golgi and then transported to the nerve terminal for release (slow process)

Question 25

Release of Neurotransmitters:

Answer 25

• Voltage gated ion channel opens due to change in membrane potential from action potential
Calcium enters, promotes docking of synaptic vesicles via snare proteins to the presynaptic terminals, allows for exocytosis

Diagram

Question 26

Botulinum Toxin:

Answer 26

• Blocks release of Ach, which acts on nicotinic receptors at neuromuscular junctions, results in muscle paralysis
• Destroys snare proteins, which prevents docking and ultimately exocytosis from occurring
If this occurs in the respiratory tract, can result in death