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