Lecture 10: Dermatomes, Myotomes, Plexi Flashcards
The paraxial mesoderm differentiates into the head and somites
What 3 primary things does the somite differentiate into?
Sclerotome (cartilage)
Myotome (skeletal muscle)
Dermatome (dermis, skeletal muscle)
____________________________
Also differentiates into:
Syndetome (tendons)
Endothelial cells (dorsal aorta)
Cells of the myotome will migrate to form the ______ and ________
Epimere
Hypomere
Posterior migrators populate the epimere and form _____ muscles
Epaxial
Anterior migrators populate the hypomere, forming the _____ muscles
Hypaxial
_______ cells condense aound the notochord to form the vertebrae
Sclerotome
The notochord contributes to the ________ _______ of the intervertebral disc
Nucleus pulposus
Somitic innervation occurs as branches of neural tissue migrate toward their corresponding muscles. Where does this neural tissue branch from?
Neural tube
Do epaxial or hypaxial have long processes for their developing innervation?
Hypaxial. Epaxial lie closer to nerve contacts
________ is the area of skin supplied with afferent nerve fibers by a single posterior spinal root
Dermatome
There are cranionuchal dermatomes, but other than that the face is one of the exceptions to dermatome innervation. Why is this?
The face is primarily controlled by cranial nerves
Anterior rootlets of the spinal cord refer to the ventral side, and provide ______ innervation
(Motor vs. sensory)
Motor
Posterior rootlets of the spinal cord refer to the dorsal region, and provide ______ innervation
(Motor vs. sensory)
Sensory
Afferent spinal nerves conduct what type of info?
Sensory
Efferent spinal nerves conduct what type of info?
Motor
A _________ is a unilateral area of skin innervated by the sensory fibers of a single spinal nerve
Dermatome
A ________ is a unilateral muscle mass receiving innervation from fibers conveyed by a single spinal nerve
Myotome
Posterior and anterior roots of the spinal cord unite to form _____ ______, which then split into posterior and anterior _____
Spinal nerves
Rami
________ ramus supplies the deep muscles of the skin of the back (epaxial)
Posterior ramus
_______ ramus supplies anterior and lateral musculature/dermis of trunk/limbs (hypaxial)
Anterior
What rami form the cervical plexus?
Anterior rami of C1-C4
What does the cervica plexus innervate?
Anterior neck muscles
Skin of neck, head, and shoulders
What are the following branches of the brachial plexus based on this anterior rami distribution:
C5-C7
C6-T1
C8-T1
C5-C7 = Musculocutaneous n.
C6-T1 = Median n.
C8-T1 = Ulnar n.
What are the following branches of the brachial plexus based on this anterior rami distribution
C5-T1
C8-T2
CA-T1
C5-T1 = Radial n.
C8-T2 = Medial brachial cutaneous n.
CA-T1 = Medial antebrachial cutaneous n.
What are the 5 branches of the lumbosacral plexus to the lower extremity?
Femoral n. Obturator n. Sciatic n. (Branches into tibial and common fibular nn.) Lateral femoral cutaneous n. Posterior femoral cutaneous n.
When looking at anterior-posterior innervation patterns, which ramus will appear larger, the anterior or posterior?
Anterior
When looking at anterior-posterior innervation patterns, why does the anterior ramus appear larger?
Because it supplies the lateral and ventral body wall and dermis (recall from hypomere-hypaxial muscles)
The posterior is shorter and smaller because it is specifically innervating dorsal musculature and skin (epimere –> epaxial)
Anterior rami of spinal nerves tend to follow what anatomical structures?
Ribs
What is the difference between segmental and plexus innervation?
Segmental innervation (such as with skin of the trunk) consists of separate spinal nerves travelling to their destination in a distinct linear pattern. Each individual spinal nerve contacts multiple dermatomes but they each have their own individual primary area of contact.
With plexus innervation (such as with skin of limbs), spinal nerves combine into one peripheral nerve through plexus formation. The nerves then emerge from the plexus as separate nerves again prior to supplying their distribution area.
How many nerves must be damaged in order to have an area of the body affected?
At least 2, due to overlapping
What embryological process leads to the “twisting” or “barbar-pole” pattern of innervation seen on adult nerve maps?
Limb rotation
Nerve plexuses like the brachial plexus and lumbosacral plexus have somatic sensory and somatic motor function.
There are also autonomic nerve plexuses, what type of information is transmitted in these?
Visceral sensory
Visceral motor
What are some examples of autonomic nerve plexuses?
Thoracic autonomic plexuses
Abdominal aorta autonomic plexuses
Mesenteric plexus
What are the terms for the divisions of the brachial plexus from roots to terminal branches?
Roots (5) Trunks (3) Anterior (3) and posterior (3) divisions Cords (3) Terminal branches
Lesions in the spinal cord result in varying degrees of severity based on the level of damage. What area of the spinal cord could be damaged with the least severe anatomical effects?
Conus medullaris or cauda equina
[the higher the level of damage, the more spinal cord mass you have separated from the brain = more severe damage]
