Physiology
Basic Cellular
Parasympathetic preganglionic neurons run in which of the following cranial nerves:
Answer:
Parasympathetic preganglionic neurons originate in the brainstem from which they run in cranial nerves III, VII, IX and X and also from the second and third sacral segments of the spinal cord.Autonomic Nervous System
Physiology / Basic Cellular / Autonomic Nervous System
Last Updated: 30th August 2019
The autonomic nervous system mediates homeostatic reflexes, allows the integration and modulation of function by central mechanisms in the brain in response to external and internal stimuli, and provides the efferent arm for the involuntary control of most organs. It is divided into the sympathetic and the parasympathetic nervous systems which work in concert, but often antagonistically. Both contain preganglionic neurons originating in the central nervous system that synapse with non-myelinated postganglionic neurons in peripheral ganglia; postganglionic neurons innervate the target organ or tissue.
Preganglionic Neurons
Sympathetic preganglionic neurons originate in the lateral horn of segments T1 - L2 of the spinal cord and exit the cord via the ventral horn on their way to the paravertebral or prevertebral ganglia.
Parasympathetic preganglionic neurons originate in the brainstem from which they run in cranial nerves III, VII, IX and X and also from the second and third sacral segments of the spinal cord.
Both sympathetic and parasympathetic preganglionic neurons release acetylcholine into the synapse, which acts on cholinergic nicotinic receptors on the postganglionic fibre. The postganglionic neurotransmitters and receptors depend on the system and organ.
Postganglionic Neurons
Parasympathetic peripheral ganglia are generally found close to or within their target, whereas sympathetic peripheral ganglia are located largely in two sympathetic chains on either side of the vertebral column (paravertebral ganglia), or in diffuse prevertebral ganglia of the visceral plexuses of the abdomen and pelvis. An exception is the sympathetic innervation of the adrenal gland, where sympathetic preganglionic fibres directly innervate the adrenal medulla.
Sympathetic postganglionic neurons terminate in the effector organs where they release the catecholamine noradrenaline (norepinephrine), which acts on alpha and beta adrenergic receptors which are linked via G-proteins to cellular effector mechanisms. A few sympathetic neurons release acetylcholine at the effector (e.g. sweat glands) and are thus known as sympathetic cholinergic neurons.
Parasympathetic postganglionic neurons release acetylcholine, which acts on cholinergic muscarinic receptors.
Principle Effects
Autonomic Nervous System. (Image by Geo-Science-International 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 |
