Muscle and nervous tissue

Why this matters

Every injection you give works on a nerve, and every extraction stretches or tears one. The muscle you palpate for tenderness, the muscle a colleague injects with botulinum toxin, and the muscle that can go rigid at anaesthetic induction and stop a paediatric dental list are all masticatory. The two commonest permanent injuries in dentistry — to the lingual and inferior alveolar nerves — are decided by histology: how many fascicles the nerve carried, whether its perineurium was breached, and whether the axon was lost or only its myelin. This lesson is the tissue-level reason for all of that.

The big picture

Two excitable tissues in one lesson. Muscle solves one problem three ways — how to get calcium to the contractile machinery, and what the calcium then switches on — and the three answers are what you see on a slide. Nerve solves a different problem: carry a signal a long way without losing it, and rebuild the wire when it breaks.

The 15 cards in this lesson

1. 01Nuclei name the muscle by WHERE they sit, not by how many there are
2. 02The optimal sarcomere length you were taught is a frog's
3. 03A fibre type is a statement about a method, not about a fibre
4. 04Masticatory muscle is not limb muscle with a different name
5. 05The intercalated disc is not three junctions in a row — most of it is a hybrid
6. 06Smooth muscle is switched on at the thick filament, not the thin
7. 07Seven questions separate the three muscle tissues
8. 08Clinical alert — in the lesson
9. 09One axon, many fibres — but every fibre has exactly one junction
10. 10One set of sensory neurons in your head keeps its cell bodies inside the brain
11. 11Glia are not packing material — four types in the CNS, two you must know in the PNS
12. 12Of the three sheaths, only the perineurium is a barrier
13. 13Fibre diameter sets conduction velocity, and that is why anaesthesia arrives in an order
14. 14Unmyelinated does not mean unensheathed — and the lingual nerve's problem is fascicle count
15. 15Clinical alert — in the lesson

You have got it when

You can now: (1) separate skeletal, cardiac and smooth muscle on nuclei, striation and branching, and say why striation alone cannot separate skeletal from cardiac; (2) explain with denominators why masticatory muscle is not limb muscle renamed; (3) name the three sheaths of a peripheral nerve and say which one is the barrier; (4) separate neurapraxia, axonotmesis and neurotmesis, and say which nerve findings need…