MSK - NMJ Physiology and Pharmacology

Question 1

Compare and contrast chemical and electrical synpases.

Answer 1

• Electrical synapses pass voltage changes directly from one cell to another across the low-resistance continuity that is provided by the connexon channels.
• Chemical synapses link two cells by the diffusion of a chemical transmitter across the large gap separating them

SEE TABLE ON SLIDE 4

Question 2

Describe electrical synapses.

Answer 2

• Directly link the cytoplasm of adjacent cells
• Formed by connexon channels of gap junctions that link the cytoplasm of two cells.
• Channels thus provide a low-resistance path for electrotonic current flow and allow voltage signals to flow with little attenuation and no delay between two or more coupled cells.
• Reciprocal gap junctions pass current between cells in both directions
• Rectifying gap junction allow current to pass in only one direction indicating the underlying junctional conductance is voltage dependant

Question 3

Describe chemical synapses.

Answer 3

• Use neurotransmitters to provide electrical continuity between adjacent cells
• Rectifying (one direction propagation of current)
• Considered a unidirectional pathway for signal propagation
• Modulated by bidirectional chemical communication between interacting cells (auto receptor, co transmission of neurotransmitter, neuromodulation molecules such as NO)

REFER TO DIAGRAM ON SLIDE 6

Question 4

Describe neurotransmitters.

Answer 4

• Can activate ionotropic (LGIC) or metabotropic receptors (GPCR)
• Some can activate both e.g ACh, glutamate, serotonin, GABA and glycine
• ACh activates skeletal muscle through nicotinic type 2 receptor and inhibits cardiac muscle through M2 muscarinic receptor

SEE DIAGRAM ON SLIDE 7