Physiology
Basic Cellular
Neurotransmitter release from the presynaptic membrane is triggered by:
Answer:
The neurotransmitter is synthesised and stored in vesicles in the terminal bouton of the preganglionic neuron. The arrival of an action potential at the nerve ending causes opening of voltage-gated Ca2+ channels in the presynaptic membrane, and a subsequent influx of Ca2+, which causes the neurotransmitter-containing vesicle to fuse with the presynaptic membrane and release its contents into the synaptic cleft by the process of exocytosis.Neurochemical Synaptic Transmission
Physiology / Basic Cellular / Action Potential
Last Updated: 26th July 2024
Action potentials in incoming neurons are transmitted by the release of neurotransmitters that bind to receptors on the postganglionic neuron or effector tissue. Between neurons (e.g. in ganglia), this occurs within the synapse, where the axon terminates in a bouton separated from the target by a synaptic cleft.
The neurotransmitter is synthesised and stored in vesicles in the terminal bouton of the presynaptic neuron. The arrival of an action potential at the nerve ending causes opening of voltage-gated Ca2+ channels in the presynaptic membrane, and a subsequent influx of Ca2+, which causes the neurotransmitter-containing vesicle to fuse with the presynaptic membrane and release its contents into the synaptic cleft. The neurotransmitter then diffuses across the synaptic cleft to bind with receptors on the postsynaptic membrane of the dendrite and activate the response. Neurotransmitter release can be suppressed by feedback onto presynaptic inhibitory receptors.
After activation at the postsynaptic membrane, neurotransmitters must be removed from the synaptic cleft. In cholinergic synapses, cholinesterase rapidly breaks down acetylcholine into choline and acetate which are then recycled. In adrenergic synapses, most noradrenaline is taken up by the nerve ending and recycled. Excess noradrenaline and sympathomimetic amines such as tyramine are metabolised in the neuron by mitochondrial monoamine oxidase (MAO).
Noradrenaline and other catecholamines in the circulation are metabolised sequentially by catechol-O-methyltransferase (COMT) and MAO.
Neurochemical Synaptic Transmission. (Image by Unknown [CC BY-SA 4.0 , via Wikimedia Commons)
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
