• How does the sensitivity for blockade by a LA compare regarding the following types of fibres:
  1. myelinated fibres with unmyelinated fibres

Unmyelinated fibres and smaller myelinated fibres are blocked more efficiently by local anaesthetics than larger myelinated fibres therefore these unmyelinated fibres are more sensitive to local anaesthetics block

1. 2. pressure/touch nerves with the dorsal nerves that transmit pain impulses?

Blocking A-type fibres influences proprioception, touch, pressure and motor fibres. However these fibres are blocked last by local anaesthetics and are therefore not as sensitive to local anaesthetics.

• Make a list of the effects of LA on other tissues.

CVS: Acts as a class 1 anti-arhythmic drug, slow upstroke of sodium dependant Action potentials and prolongation of QRS duration

Skeletal Muscle: weak blocking action of no clinical application

Cocaine : elevates mood and influences the catecholamine mediated neurotransmission

• What is the basis for the selection of a LA?

A  Local Anaesthetic is selected based on

• • the type of procedure
  • the type of tissue that the drug must act on
  • the duration of the numbing effect that is required in that tissue.

• Why are LA solutions sometimes saturated with CO₂?

CO₂ acts as a buffer which reduces the pain od the injection and assists in a faster onset of action for the drug by increasing the effective concentration of the non-ionized form.

• Which of the LA are typically used for surface anaesthesia?

Cocaine ,Benzocaine and Oxybuprocaine