Biomedical Engineering Reference
In-Depth Information
Table 2.3 Examples of neurotransmitters and their actions.
Neurotransmitter
Action
Structure
Excitatory, triggers muscle
contraction
Stimulates hormone secretion in CNS
O
Acetylcholine
N
+
d
n
4
t
3
n
g
|
0
O
Brain—regulation of motor behavior
Connected to motivation and
emotion
HO
Dopamine
HO
NH
2
Fast inhibitory effect at synapses in
the brain
O
GABA
H
2
N
OH
+
H
3
N
Fast excitatory effect at brain and
CNS synapses
O
Glutamate
O
-
-
O
O
Import mat with respect to
attentiveness, sleep, emotion
Released as a hormone into the blood
steam
OH
HO
NH
2
Norepinephrine
n
3
.
HO
N
Regulates appetite, sleep, mood,
behavior and muscle contraction
Serotonin
HO
NH
2
GABA, g-aminobutyric acid.
2.4.2 Action Potential and Electrical Conduction
An electrical potential difference exists across the membranes of most
biological cells including neurons.
18
By convention the value of the potential,
which varies between about
10 and
100 mV, is given a negative sign to
recognize that the interior of the cell is charged negatively with respect to the
exterior. This parameter is most often referred to as the 'resting' or 'steady state
membrane potential'. The cell membrane is permeable to Na
1
,K
1
and Cl
via
specific channels rather than simple pores. The chloride concentration in the
ECM is relatively high, resulting in diffusion into the cell, but the negatively
charged interior opposes this process by electrical repulsion with the end result
of an equilibrium situation. The reverse situation exists for the potassium
cation distribution. With respect to Na
1
both the electrical and concentration
gradients are in the same direction—inward. These are passive considerations,
but in reality active transport of both sodium and potassium cations across the
membrane is involved, which tends to keep the interior concentration of the
