Question

1. Mrs. J is in a car accident and her right leg is pinned under the crushed dashboard of her car. She is very scared and although she is in pain her endogenous pain suppression system is keeping it manageable. She is finally extracted from her car by emergency services and although she is relieved to be free from her car, the pain from her leg intensifies. The emergency personnel start her on a morphine drip (an exogenous pain medication) and she is transported to the nearest hospital. Unfortunately, her leg is too damaged to save and has to be amputated. Even though the damaged leg is removed, Mrs. J still swears that it is there because she can feel the pain and tingling coming from her toes. (10 points total)

1. What is the name given to the primary sensory receptors that transduce pain? (1)

2. Where does this primary sensory neuron synapse? (Be specific) (1)

3. What pathway carries pain sensation to the cortex to be perceived? (1)

4. In addition to synapsing at the thalamus before being relayed to the cortex a collateral branch from this pathway is also sent to the reticular formation. What role does the reticular formation play in pain perception? (1)

5. Name and briefly explain the mechanisms associated with two different endogenous pain suppression mechanisms that could have been activated while Mrs. J was trapped in her car. (4)

6. What name can be given to the phenomenon that makes Mrs. J believe her limb is still there? (1)
7. Briefly describe how this occurs. (1)

Answer 1

A) Nociceptors

B) synapses form in its dorsal horn.

C) The spinothalamic tract consists of two adjacent pathways. In its lateral spinothalamic tract conveys pain. Lateral spinothalamic tract which is a part of the anterolateral system, is a bundle of afferent nerve fibers ascending through the white matter of the spinal cord, carrying sensory information to the brain. It carries pain, crude touch and temperature sensory information to the thalamus. It is composed primarily of fast conducting sparsely myelinated A delta fibers and slow conducting, unmyelinated C fibers. There are secondary neurons which have already synapsed with the primary sensory neurons of the peripheral system in the posterior horn of the spinal cord.

D) The reticular formation has projections to the thalamus and cerebral cortex that allow it to exert some control over which sensory signals reach the cerebrum and come to our conscious attention. It plays a central role in states of consciousness like alertness and sleep.

E) Ascending and descending pain suppressing mechanism.

F) Phantom sensation

G) Phantom limb mechanism during amputation, peripheral nerves are severed. This results in massive tissue and neuronal injury causing disruption of the normal pattern of afferent nerve input to the spinal cord.