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Neurotransmitters
Properties of neurotransmitters:
1) synthesized in the presynaptic neuron2) 2) Localized to vesicles in the presynaptic neuron
3) Released from the presynaptic neuron underphysiological conditions
4) Rabidly removed from the synaptic cleft by uptake or degradation
5) Presence of receptor on the post-synaptic neuron.6) Binding to the receptor elicits a biological response
Neurotransmitter
Neurotransmitters are endogenous chemicals which relay, amplify, and modulate signals between a neuron and another cell.[1] Neurotransmitters are packaged into synaptic vesicles that cluster beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to receptors in the membrane on the postsynaptic side of the synapse. Release of neurotransmitters usually follows arrival of an action potential at the synapse, but may follow graded electrical potentials. Low level "baseline" release also occurs without electrical stimulation.
DiscoveryIn the early 20th century, scientists assumed that synaptic communication was electrical. However, through the careful histological examinations of Ramón y Cajal (1852-1934), a 20 to 40 nm gap between neurons, known today as the synaptic cleft, was discovered and cast doubt on the possibility of electrical transmission. In 1921, German pharmacologist Otto Loewi (1873-1961) confirmed the notion that neurons communicate by releasing chemicals. Furthermore, Otto Loewi is accredited with discovering acetylcholine—the first known neurotransmitter. [2]
Neurotransmitters found in the nervous system
EXCITATORY
Acetylcholine
Aspartate
Dopamine
Histamine
Norepinephrine
Epinephrine
Glutamate
Serotonin
INHIBITORY
GABA
Glycine
Glutamate
GABA (γ-aminobutyric acid)
AMINO ACID transmitters
What kinds of neurotransmitters are there?
Other Neurotransmitters:
Neurotransmitter Derived from
Enzyme
Histamine Histidine Histidine decarboxylase
GABA(γ-Amino butyrate)
Glutamate Glutamate decarboxylase
Nitric Oxide Arginine Nitric Oxide Synthase
Neurotransmitter Molecule
Derived FromSite of Synthesis
Acetylcholine Choline CNS, parasympathetic nerves
Serotonin5-Hydroxytryptamine (5-HT)
TryptophanCNS, chromaffin cells of the gut, enteric cells
GABA Glutamate CNS
Histamine Histidine hypothalamus
Epinephrine synthesis pathway
Tyrosine adrenal medulla, some CNS cells
Norpinephrine synthesis pathway
Tyrosine CNS, sympathetic nerves
Dopamine synthesis pathway
Tyrosine CNS
Nitric oxide, NO Arginine CNS, gastrointestinal tract
Buffers
• Buffer Solutions resist a change in pH
• Buffers contain relatively large concentrations of either– An acid, HA and its conjugate base A-
– A base, B, and its conjugate acid (BH+)
Buffers
Buffers
NH3 to react with H+
• When H+ is added, it reacts essentially to completion with the weak base presentH+ + A- HA or
H+ + B BH+
• When OH- is added, it reacts essentially to completion with the weak acid presentOH- + HA H2O + A-
OH- + BH+ H2O + B
• pH = pKa + log (base/acid)
• Want pH pKa 1• pH determined by
Ka of acid and ratio of acid/conjugate base
or
Kb of base and ratio base/conjugate acid
Formic Acid Ka
1.8 X 10-4
pKa
3.74
Barbituric Acid 9.8 X 10-5 4.01
Butanoic Acid 1.52 X 10-5 4.82
Buffer Table
• Choose a pKa near the desired pH
• pH = pKa + log (base/acid)
• 4.0 = 3.74 + log (base/acid)• 0.26 = log (base/acid)• 10.26 = 1.8 = (Na formate / formic
acid)
Buffer Choice
• Ammonia pKb = 4.74 pKa = 14.00 – 4.74 = 9.26
NH3 / NH4Cl used to buffer around pH 9.26
Biological Uses
In biological systems (saliva, stomach, and blood) it is essential thatthe pH stays ‘constant’ in order for any processes to work properly.e.g. If the pH of blood varies by 0.5 it can lead to unconsciousness and
coma
Most enzymes work best at particular pH values.
Other Uses Many household and cosmetic products need to control their pH values.
Shampoo Buffer solutions counteract the alkalinity of the soap and prevent irritation
Baby lotion Buffer solutions maintain a pH of about 6 to prevent bacteria multiplying
Others Washing powder, eye drops, fizzy lemonade
THANK YOU
BY:DEEPIKA TRIPATHI