State the dermatomes and myotomes for each of the spinal nerves. (C1-S5)
State what spinal nerves partipate in deep tendon reflexes (DTRs).
attached is slide 11 of notes
Fibers/axons contained within white matter of spinal cord that connect adjacent segments of the cord.
Within the ventral horn of the spinal cord, where are neurons that innervate axial musculature vs neurons that innervate the extremities?
Within the ventral horn of the spinal cord, where are neurons that innervate flexors? Extensors? Why are they in these areas?
1. Medially located motor neurons in the ventral horn supply axial (trunk) musculature while laterally located motor neurons supply the limbs.
2. Within the lateral limb representation, flexor motor neurons are located dorsally (closer to the corticospinal pathway) and extensor motor neurons are located ventrally (closer to the vestibulospinal and reticulospinal pathways).
Describe the amount of gray matter in the cervical cord and the reason for it.
What two dorsal columns of white matter are evident in the spinal cord? What is their anatomical relationship to one another? What pathway are these dorsal columns a part of?
Cervical cord: The cervical cord possesses an expansion of gray matter associated with an increased amount of neurons for innervation of the upper limbs (both increased cells to receive inputs form the dorsal roots/sensory and more lower motor neurson). This is particularly evident in the motor area (i.e. the lateral expansion of the ventral horn) for innervation of upper limb musculature.
In addition, in the cervical cord, two dorsal columns of white matter are evident here, the fasiculus gracilis (more medial) and the fasiculus cuneatus (more lateral). These columns of white matter are formed by ascending axons of the dorsal column pathway. Do you remember what kind of info this pathway conveys?
Describe the amount of gray matter in the thoracic cord and the reason for it.
What is a distinct anatomical feature of the thoracic cord? Where is it located? What is contained in this region?
Thoracic cord: The thoracic cord possesses narrow ventral horns bc unlike the cervical and lumbar regions of the cord, the thoracic cord does not provide innervation to limb musculature and thus there are no lateral expansions of the ventral horn. The lower motor neurons here supply the trunk and intercostal musculature.
One distinct feature of the thoracic cord is the presence of an intermediolateral cell column, which is a small bump btwn the dorsal and ventral horns. This contains the cell bodies of preganglionic sympathetic neurons.
Describe the amount of gray and white matter in the lumbar cord and the reason for it.
Which of dorsal column pathways are present in the lumbar cord? Why is only one present in this region of the spinal cord?
Lumbar cord: The lumbar cord, like the cervical cord, possesses expansions of gray matter for innervation of lower limbs; however when compared to the cervical cord, there is considerably less white matter in cross section. This white matter consists of tracts of axons which convey sensory and motor information passing to and from the brain.
In the lumbar cord, only the fasiculus gracilis is present (LG: lumbar-gracilis) in the region of the dorsal columns as at this level of the cord, only sensory fibers coursing from the lower body are present.
Compare the amount of white and gray matter in the sacral cord to other parts of the spinal cord.
What parts of the body do motor neurons in the gray matter of the sacral cord innervate?
What type of neurons are present in the intermediolateral cell column in the sacral cord?
What descends lateral to the sacral cord?
Sacral cord: The sacral cord possesses comparatively little white or gray matter. The motor neurons in the gray matter here provide innervation to the foot and perineal musculature. Though not as obvious in the thoracic cord, there is an intermediolateral cell column in the sacral cord where parasympathetic preganglionic neurons supplying the bladder and other pelvic viscera are located.
In cross sections of the sacral cord, the cauda equina is evident as these nerve fibers descend alongside the cord itself.
What longitudinally oriented vessels supply the spinal cord? Where do these vessels originate?
How many of them are there?
Longitudinally oriented vessels: These vessels originate in the cranial cavity (vertebral arteries) and descend longitudinally along the length of the spinal cord: Anterior spinal artery (1) and the posterior spinal arteries (2)
How do segmental spinal arteries gain access to the spinal cord?
What are these arteries branches of?
What arteries re-feed the anterior spinal artery along its length?
Where is the watershed zone of the spinal cord located? What artery supplies an important source of support to the anterior spinal artery? Where does this vessel branch from?
What does compromise of this artery result in?
Segmental Spinal Arteries:
1)Feeder arteries that gain access to the spinal cord through the intervertebral foramina at each level
2)These arteries arise from the aorta or its branches along the length of the cord. Radicular branches refeed the anterior spinal artery along its length.
3)Clinical Note: Segmental feeders are sparse in the mid-thoracic region, creating a watershed zone in the thoracic cord. An important source of support to the anterior spinal artery is the Great Radicular Artery that originates from the aorta at the lower thoracic or lumbar level. Compromise of this vessel (tumors, aortic clamping) puts the thoracic cord at risk causing an anterior spinal artery syndrome.
Where are veins that drain the spinal cord found? What else is found in this area?
Longitudinal channels of veins drain into an extensive internal vertebral plexus of veins found in the epidural space. Unlike in the cranial cavity, the epidural space is an actual space around the spinal cord filled with the vertebral plexus of veins and fat.