Question

A typical spinal cord has how many pairs of spinal nerves, and it ends at the level of what vertebrae?

After injuring her back, a 22-year old woman exhibits a positive Babinski reflex. What does this imply about her injury?

Describe a dermatome. ?

please type it

Answer 1

- Central nervous system consists of brain and spinal cord. Spinal cord typically has 31 pairs of spinal nerves. Out of these 31 pairs of spinal nerves, there are 8 pairs of cervical spinal nerves, 12 pairs of thoracic spinal nerves, 5 pairs of lumbar spinal nerves, 5 pairs of sacral spinal nerves and 1 pair of coccygeal spinal nerve.

- Spinal cord is about 45 cm in length and extends from upper border of atlas (C1) vertebra to lower border of L1 vertebra in adults. In newborns, spinal cord extends upto L3 vertebra.

- An extensor type of plantar reflex is known as positive plantar response or positive Babinski sign. During eliciting a plantar reflex, if the great toe extends upwards and backwards with the fanning out of other toes, it is known as positive Babinski reflex or extensor (upward) type of plantar reflex. It indicates upper motor neuron lesion due to damage to corticospinal tract as a result of brain or spinal cord injury. It can also be seen in infants as the central nervous system is still developing in them. In healthy adults, plantar reflex is usually of downward (flexion) type. Thus, the 22 years old woman after her back injury must have injured her corticospinal tract (upper motor neuron lesion) due to brain or spinal cord injury as a result of which she exhibits a positive Babinski reflex.

-Dermatome is a particular area on the skin surface which is supplied by afferent (dorsal) nerve fibers of spinal nerve. A spinal cord is a mixed nerve with both sensory (dorsal/afferent) root and motor (ventral/efferent) root. Dorsal or afferent root of spinal nerve transmits sensory information from periphery of the body to the interneuron in spinal cord for integration. Ventral or efferent root of spinal nerve transmits motor signals from spinal cord to the effector organ. Thus, that part on the skin surface which is supplied by the dorsal or afferent fiber of spinal nerve is called as dermatome. Referred pain is felt due to the sensory nerve fibers from a particular dermatome is at the same level as that of a general visceral afferent fibers bringing sensory information from a viscera. Example of referred pain:- in myocardial infarction, the general visceral afferent fibers from the heart are stimulated which comes at the same level as those sensory nerve fibers from the dermatome of shoulder, left arm or jaw hence when the the general visceral afferent fibers are stimulated during myocardial infarction, pain is also felt in the left arm, shoulder and jaw regions along with the chest pain.