Lec #2

Question 1

2 types of synapses: ______ and _______

Answer 1

•  Chemical synapse = chemical communication via
secretion of neurotransmitters
•  Electrical synapse = electrical communication via gap
junctions

Question 2

influx of Ca++ through voltage-gated channels

triggers _______

Answer 2

influx of Ca++ through voltage-gated channels

triggers exocytosis

Question 3

In electrical synapse:
•  Channels called _______ in pre- and postsynaptic
membranes align to form a pore connecting the two
cells
•  Ionic current flows between cells: ____, _____,
and virtually _____ (fraction of a millisecond)
•  First recorded in the crayfish escape movement

Answer 3

In electrical synapse:
•  Channels called connexons in pre- and postsynaptic
membranes align to form a pore connecting the two
cells
•  Ionic current flows between cells: passive, bidirectional,
and virtually instantaneous (fraction of a millisecond)
•  First recorded in the crayfish escape movement

Question 4

Describe the process of chemical synapse at the action potential.

Answer 4

1.  Action potential arrives at presynaptic terminal
2.  Changes the presynaptic membrane potential opens
voltage-gated Ca++ channels
3.  Elevated intracellular Ca++ triggers exucytosis =
synaptic vesicles to fuse with the presynaptic
membrane and empty NTs into synaptic cleft
4.  Delay in transmission (unlike electrical synpases)
5.  NTs diffuse and bind receptors on the postsynaptic
membrane
6.  Channels in the postsynaptic membrane open (or
close) to alter membrane potential to increase (or
decrease) probability of firing an action potential
7.  Removal of NTs by glial uptake or enzymatic
degradation terminates NTs actions

Question 5

Two typical categories of neurotransmitters: _______ and _______

Answer 5

•  Neuropeptides
-  Large transmitter molecules = enkephalins
-  3-36 amino acids
•  Small molecule NTs
-  Much smaller
-  Individual amino acids = GABA and glutamate
-  Few amino acids = acetylcholine
-  Also includes the biogenic amines = dopamine,
norepinepherine, serotonin, histamine

Question 6

Some examples of small molecules NTs

Answer 6

Small molecule neurotransmitters :
•  Acetylcholine – nicotinic and muscarinic receptors
•  Glutamate – AMPA, NMDA and kainate receptors
•  GABA – GABA A, B and C receptors
•  Biogenic amines :
-  Catecholamines: dopamine, norepinephrine, epinephrine
-  Histamine and serotonin

Question 7

Some examples of neuropeptides NTs

Answer 7

Neuropeptide transmitters :
•  Most hormones
•  Substance p
•  Endorphins, enkephalins, dynorphins

Question 8

What are the 3 criteria for neurotransmitters

Answer 8

1.  Substance must be present within the presynaptic
neuron (enzymes, precursors, NT)
2.  Substance must be released in response to Ca++
dependent presynaptic depolarization
3.  Specific receptors for the substance must be present
on the postsynaptic cell

Question 9

Describe the differences in synthesis and transport between small molecules and neuropeptides.

Answer 9

Synthesis:
- in small molecules
= locally within presynaptic terminal; enzymes needed to produce NTs are synthesized in cell body.
= Enzymes transported by slow axonal transport
- in neuropeptides
= occurs in cell body

Packaging:
- in small molecules
= synthesized NTs loaded into small clear-core vesicles (40-60 nm) via transporters in the vesicular membrane.
- in neuropeptides
= enzymes and precursers loaded into large dense-core vesicles (90-250 nm) in cell body
•  Fast axonal transport (400 mm/day) along axon to terminals
•  During transport and at terminal propeptides modified into neuropeptides

Degradation:
- in small molecules
= unbound NTs broken down by enzymes in cleft and taken back up into presynaptic terminal for recycling

• in neuropeptides
  = unbound
  neuropeptides broken down by enzymes in cleft

Question 10

Receptor molecules

Answer 10

Receptor molecules are proteins embedded in the
membrane of postsynaptic cells and have an
extracellular binding site that detects the presence
of NTs in the synaptic cleft

Question 11

What are the two categories of receptor molecules

Answer 11

•  Ionotropic receptors = ligand-gated ion channels;
combine transmitter-binding and channel functions
into one entity (Greek tropos means to move in
response to a stimulus) - Rapid effects (1-2 millisec)
•  Metabotropic receptors = G protein-coupled
receptors; metabolic steps leading to indirect
actions on an ion channel - Slower effects (minutes)

Question 12

Most neurons receive inputs from? ___ excitatory ___ inhibitory synapses

Answer 12

•  Most neurons receive inputs from both excitatory and inhibitory synapses

Question 13

EPSP vs IPSP is determined by what ?

Answer 13

EPSP vs IPSP is determined by the type of channel that is
coupled to the receptor
•  Glutamate (+) = Na+/K+ flow inward to depolarize = excite
•  GABA (-) = Cl- flow inward to hyperpolarize = inhibit

Question 14

summation

Answer 14

Activation of multiple synapses around the same time

causes the EPSPs (or IPSP) to summate to depolarize (or hyperpolarize) the postsynaptic neuron

Question 15

Summarise the synaptic transmission.

Answer 15

•  Neurons communicate in neural 
circuits via synapses that carry info by 
action potentials 
•  Action potential triggers NT (small 
molecule NTs vs neuropeptides) 
release by opening presynaptic Ca++ 
channels 
•  NTs bind receptors on postsynaptic 
neuron to open or close ion channels 
(directly via ionotropic vs indirectly via 
metabotropic) 
•  EPSPs and IPSPs triggered and 
summate to either evoke or inhibit an 
action potential

Question 16

in spinal cord, what information does dorsal roots and ventral roots carry ? (and so dorsal and ventral horns)

Answer 16

•  Dorsal roots = afferents carry sensory info to cord
•  Ventral roots = efferents carry motor output to muscle
•  Dorsal horn = receives sensory info (topographical
innervation in layers)
•  Ventral horn = contains cell bodies of motor neurons

Question 17

3 major functions for brainstem:

Answer 17

•  1. Target or source for the cranial nerves that deal
with sensory and motor function in the head and
neck
•  2. Throughway for all ascending sensory tracts from
spinal cord, head and neck, descending motor
tracts from forebrain, and local pathways that link
eye movement centers
•  3. Involved in regulating level of consciousness via
primarily the reticular formation

Question 18

functions of cerebellum

Answer 18

•  Movement coordination; does not initiate 
movement 
•  Precision 
•  Timing 
•  Motor learning 
•  Motor memory