FORM & FUNCTION (Synaptic Transmission)

Question 1

Sensory input: mechanosensitive channels example

Answer 1

-when patellar tendon is tapped with a reflex hammer, it causes the muscle to stetch
-stretching opens a population of mechanosensitive channels that allow positive ions to flow in and generate a RECEPTOR CURRENT

Question 2

Receptor potential magnitude correlates with:

Answer 2

-stimulus strength
-when receptor potential threshold, VG Na+ channels open=initiating an AP

Question 3

If receptor potential surpasses the threshold value:

Answer 3

-triggers multiple Aps
-higher receptor potential intensity leads to more FREQUENT APs

Question 4

AP frequency is limited by:

Answer 4

-duration of the absolute refractory period

Question 5

Synaptic transmission at neural junction:

Answer 5

-AP reaches end of presynaptic neuron
-VG Ca2+ channels open in response
-influx of Ca2+ ions causes synaptic vesicles to release NTs
-NTs bind to receptors on postsynaptic neuron
-binding opens ligand-gated ion channels, leading to influx of ions
-if induces a significant change in potential, a new AP can be initiated in the postsynaptic neuron

Question 6

NT vesicles moving and release of NTs:

Answer 6

1. Minor increase in Ca2+ promotes vesicles to move to Active Zone via actin
2. Several proteins participate in attaching vesicle to the active zone
3. Docking: complex of SNARE proteins docks vesicle to membrane
4. Fusion between vesicle and membrane requires an increase in Ca2+ in cytoplasm
5. Ca2+ binds with synaptotagmin and interacts with SNARE complex and cause fusion

Question 7

Proteins involved in NT vesicles release:

Answer 7

-synaptotagmin
-v-SNARES: on the vesicle surface
-t-SNARES: on membrane
*SNARE is a neurotoxin target

Question 8

Chemical synapses:

Answer 8

-AP causes opening of VG Ca2+ channels in pre-synaptic terminal
-quantal release of NT: each AP releases the same amount of NT into the synaptic cleft
-‘on signal’ for post-synaptic neuron is binding of NT to receptors
-‘off signal’ is some mechanism of removing the NT from the synaptic cleft

Question 9

Mechanisms of NTs removal:

Answer 9

1. Enzymatic breakdown of enzymes
2. Reuptake
3. Diffusion

Question 10

Enzymatic breakdown of enzymes:

Answer 10

-Ach is broken down into choline and acetic acid by AChE (Ach esterase) at the synaptic cleft
>AChE is on membrane of post-synaptic neuron

Question 11

Reuptake of NT:

Answer 11

-NT taken up by specific transporters on the presynaptic neuron (ex. serotonin, NE) or on astrocytes (ex. glutamate)

Question 12

Diffusion:

Answer 12

-occurs to a certain extent with all NTs
-only mechanism of removal of peptide NTs
-slow=long duration of action if this is only mechanism of removal

Question 13

Substance P:

Answer 13

-neuropeptide involved in pain
-can use it as a potential biomarker of pain assessment in dogs

Question 14

Response initiation on postsynaptic neuron:

Answer 14

-NTs influence cellular activated based on receptor type, altering MP directly or indirectly through a secondary messenger system

Question 15

Receptor diversity:

Answer 15

-a single NT can elicit varied responses by bind to different receptor subtypes

Question 16

Receptor types:

Answer 16

-ionotropic receptors (fast)
-metabotropic receptors (slow)

Question 17

Ionotropic receptors:

Answer 17

-fast
-directly coupled to ion channels, causing IMMEDIATE MP changes upon biding
Ex. Na and Cl

Question 18

Metabotropic receptors:

Answer 18

-influences ion channels INDIRECTLY through intracellular signaling pathways
-more steps=slower
Ex. GPCR

Question 19

PNS NTs:

Answer 19

-Ach: parasympathetic
-NE and E (sympathetic)

Question 20

CNS NTs:

Answer 20

-glutamate and aspartate (excitatory: cause depolarization)
-glycine and GABA (inhibitory: hyperpolarization)

Question 21

Ach receptors:

Answer 21

-nicotinic cholinergic receptor (ionotrop)ic): skeletal muscle
-muscarinic cholinergic receptor (metabotropic): autonomic NS

Question 22

E/NE receptors:

Answer 22

-metabotropic: autonomic NS
>alpha-adrenergic receptor
>beta-adrenergic receptor

Question 23

Regeneration in peripheral nerves:

Answer 23

1. Nerve fiber and its myeline sheath distal to the injury degenerates
2. Schwaan cells proliferate to form a column to guide axon regeneration (0.5-3mm/day)
3. Functional connections with muscles established after several months

Question 24

CNS vs. PNS synaptic types:

Answer 24

-CNS: complex (axodendritic, axosomatic and axoaxonic synapse)
-PNS: direct: simple synapses (NM or neuroglandular)

Question 25

CNS vs. PNS myelination:

Answer 25

-CNS: one oligodendrocyte insulates many axons
-PNS: one Schwann cell insulates one axon

Question 26

CNS vs PNS regeneration capacity:

Answer 26

-CNS: limited due to complex microenvironment
-PNS: possible when damage is moderate (Schwaan cells play a pivotal role in guiding and supporting axonal regrowth and target innervation)