Although type B fibers are thicker than type C fibers, they are myelinated, thus are blocked before the unmyelinated, thin C fiber. Techniques
Local anesthetics can block almost every nerve between the peripheral nerve endings and the central nervous system. The most peripheral technique is topical anesthesia to the skin or other body surface. Small and large peripheral nerves can be anesthetized individually (peripheral nerve block) or in anatomic nerve bundles (plexus anesthesia). Spinal anesthesia and epidural anesthesia merge into the central nervous system. Injection of LAs is often painful. A number of methods can be used to decrease this pain, including buffering of the solution with bicarbonate and warming.Clinical techniques include:

Surface anesthesia is the application of an LA spray, solution, or cream to the skin or a mucous membrane; the effect is short lasting and is limited to the area of contact. Infiltration anesthesia is infiltration of LA into the tissue to be anesthetized; surface and infiltration anesthesia are collectively topical anesthesia
Field block is subcutaneous injection of an LA in an area bordering on the field to be anesthetized. Peripheral nerve block is injection of LA in the vicinity of a peripheral nerve to anesthetize that nerves area of innervation. Plexus anesthesia  is injection of LA in the vicinity of a nerve plexus, often inside a tissue compartment that limits the diffusion of the drug away from the intended site of action. The anesthetic effect extends to the innervation areas of several or all nerves stemming from the plexus.
Side effects on the central nervous system and the heart may be severe and potentially fatal. However, toxicity usually occurs only at plasma levels which are rarely reached if proper anesthetic techniques are adhered to. High plasma levels might arise, for example, when doses intended for epidural or intrasupport tissue administration are accidentally delivered as intravascular injection. Emotional reactions
When patients are emotionally affected in the form of nervousness or fear, it can lead to vasovagal collapse. This is the anticipation of pain during administration that activates the parasympathetic nervous system while inhibiting the orthosympathetic nervous system. What results is a dilation of arteries in muscles which can lead to a reduction in circulating blood volume inducing a temporary shortness of blood flow to the brain. Notable symptoms include restlessness, visibly looking pale, perspiration and possible loss of consciousness. In severe cases, clonic cramps resembling an epileptic insult may occur.On the other hand, fear of administration can also result in accelerated, shallow breathing, or hyperventilation. The patient may feel a tingling sensation in hands and feet or a sense of light-headedness and increased chest pressure.Hence, it is crucial for the medical professional administrating the local anaesthesia, especially in the form of an injection, to ensure that the patient is in a comfortable setting and has any potential fears alleviated in order to avoid these possible complications. Central nervous system
Depending on local tissue concentrations of local anesthetics, excitatory or depressant effects on the central nervous system may occur.