Thorax and Abdomen

Question 1

How many intercostal nerves are there?

What does the vagus nerve do?

Answer 1

Note the spinal nerves emerging from the vertebral column and running with the ribs. These are the intercostal nerves. There are 11 intercostal nerves, plus one subcostal nerve that runs under rib 12.

On the specimens, identify the vagus nerve (cranial nerve X) which provides parasympathetic innervation to the thorax and abdomen and the phrenic nerve (C3,4,5) which supplies the diaphragm and is therefore important for breathing. The vagus nerve is one of 12 pairs of cranial nerves which arise from the base of the brain. You have encountered these structures in previous sessions.

Question 2

• x the cervical and lumbar enlargements,
• x the conus medullaris
• x the cauda equina,
• x the filum terminale,

Answer 2

which innervate the limbs

where the spinal cord ends at a tapering point

composed of many dull, yellow-coloured roots

, a single white fibrous cord

Question 3

Where does the spinal cord end?

Answer 3

L2

Question 4

What is the spinal cord enclosed in?

Answer 4

The spinal cord is enclosed within a tough fibrous dural sac. The spinal dura is continuous with the cranial dura at the foramen magnum. The dural sac is lined by arachnoid, a transparent membrane that may be more difficult to identify. The space between the arachnoid mater and spinal cord is the subarachnoid space. It is filled with cerebrospinal fluid (CSF). The spinal cord itself is invested by pia mater, a delicate vascular membrane that closely adheres to the surface of the cord. The pia is difficult to identify with the naked eye, except where it forms the serrated denticulate ligament (Latin: dent, tooth) on either side of the spinal cord, between the dorsal and ventral roots. Try to identify the denticulate ligament on each side of the cord. Note that inflammation of the meninges (meningitis) can be a life-threatening condition