| Date | November 2009 | Marks available | 3 | Reference code | 09N.3.HL.TZ0.5 |
| Level | Higher level | Paper | Paper 3 | Time zone | TZ0 |
| Command term | Explain | Question number | 5 | Adapted from | N/A |
Question
Explain the role of the neurons used in the pain withdrawal reflex.
State one effect of tetrahydrocannabinol (THC) on brain function.
Markscheme
sensory neurons receive information from receptors;
transmit nervous impulses to the central nervous system;
relay neurons in the central nervous system transmit the information from sensory neurons to motor neurons;
motor neurons send impulse to effector;
inhibition of nervous impulses / binding to cannabinoid receptors / blocking of release of excitatory neurotransmitter
Examiners report
The majority of candidates used correct terminology in describing the transmission of a nervous impulse involved in a withdrawal reflex.
Many wrote that tetrahydrocannabinol (THC) had an inhibitory effect at the level of receptors; this was largely well answered.
