Physiology
Basic Cellular
Regarding the neuromuscular junction, which of the following statements is CORRECT:
Answer:
The neuromuscular junction is found between the motor neurone and the motor end plate of a muscle fibre. Neurotransmitter release is triggered from the prejunctional membrane by an influx of calcium. Acetylcholine is released which acts on nicotinic receptors on the postjunctional membrane resulting in a postjunctional end plate potential.Neuromuscular Junction
Physiology / Basic Cellular / Skeletal Muscle Physiology
Last Updated: 29th July 2024
For skeletal muscle to contract, there must be neuronal activation to the muscle fibres themselves from either higher centres in the brain or via reflex pathways involving either the spinal cord or brainstem.
The neurons that innervate skeletal muscles are called alpha-motor neurons. Each motor axon splits into a number of branches that make contact with the motor end plate of individual muscle fibres at the neuromuscular junction (NMJ). The role of the NMJ is the one-to-one transmission of excitatory impulses from the alpha-motor neuron to the muscle fibres it innervates.
The motor neuron axon terminal has a large number of vesicles containing the neurotransmitter acetylcholine (ACh). When an action potential reaches the prejunctional membrane, the opening of voltage-gated Ca2+ channels increases the permeability to Ca2+ ions and the sudden Ca2+ influx causes the release of acetylcholine by exocytosis.
Acetylcholine diffuses across the synaptic cleft between the nerve and the muscle cells, and stimulates a large number of cholinergic nicotinic receptors on the post-junctional membrane. These receptors contain an integral ion channel, which opens and allows the influx of small cations, mainly Na+. This movement of positively charged ions generates an end plate potential (EPP) that is above threshold for triggering a self-propagating action potential in the muscle fibre.
Neuromuscular Junction. (Image by OpenStax [CC BY 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 |
