L4-5: Spinal Cord, Typical Spinal Nerve & ANS

Question 1

Define filum terminale.

Answer 1

• inferior extension of pia mater that is part of the cauda equina, It extends inferiorly and runs through the sacral hiatus, pierces the dural sac, taking with it arachnoid and dura mater and anchors to the posterior coccyx.

Question 2

Draw cross section of spinal cord with spinal nerve. Draw pathway of general visceral efferent neurons.

Answer 2

Question 3

What are spinal roots formed by? Explain what each contain. From what is the spinal nerve formed?

Answer 3

• Dorsal rootlets from the spinal cord form the dorsal root, which contain sensory neuronal processes in a CT sheath. Lateral from this are collections of sensory cell bodies (nuclei) contained with in structures/enlargements known as the dorsal root ganglia. These are within the intervertebral foramen. - Ventral rootlets from the spinal cord form the ventral root, which contain motor neuronal processes in a CT sheath. - Both dorsal and ventral roots come together to form spinal nerve, which is a mixed nerve, containing both motor and sensory fibers.

Question 4

Define afferent/efferent neuron.

Answer 4

• Afferent neurons sends impulses towards the CNS. These are sensory neurons. - Efferent neurons sends impulses away from the CNS. These are motor neurons.

Question 5

What is contained within the subarachnoid space?

Answer 5

• CSF and spinal nerve rootlets.

Question 5

Draw cross section of spinal cord with spinal nerve. Draw pathway of general somatic efferent neurons.

Answer 5

Question 6

What neurons in the spinal cord are part of the ANS?

Answer 6

• General visceral efferents. Visceral motor division.

Question 6

Dermatomal pattern for visceral afferent neurons from: a.) head and neck b.) heart and lungs c.) upper extremity d.) GI system: esophagus to rectum e.) Liver and GB f.) Pancreas and spleen g.) Urinary system h.) Testes/Ovaries i.) Uterus and cervix j.) Prostate k.) Lower extremities

Answer 6

• a.) T1-4 - b) T1-7 - c.) T5-7 - d.) T2 (esophagus) – L2 (rectum) - e.) T6-9 - f.) T5-11 - g.) T10-L2 - h.) T10-T11 - i.) T10-L2 - j.) L1-2 - k.) T10-L2

Question 7

Draw cross section of spinal cord with spinal nerve. Draw pathway of general somatic afferent neurons.

Answer 7

Question 8

Describe characteristics of the parasympathetic division of the ANS. Include: function, NT involved, location of pre-synaptic and postsynaptic cell bodies, course of cell processes.

Answer 8

Parasympathetic division: think craniosacral - function: rest, digest, feed and assimilate - neurotransmitter: ACh - cell body locations: a.) pre-synaptic cell bodies are CNs III, VII, IX and X that have their cell bodies in gray matter of brainstem; also sacral segments 2-4 have their cell bodies in gray matter of spinal cord S2-S4 segments b.) post-synaptic cell bodies in target organ being innervated - course of cell processes: a.) pre-synaptic cell processes travel directly from cranium (as CNs) or from sacral spinal cord as pelvic splanchnic nerves directly onto target organs where they synapse with post-synaptic fibers embedded in the wall of their target organs b.) post-synaptic cell processes are embedded within the wall of their target organs

Question 8

Explain the difference between the paravertebral ganglia and the prevertebral ganglia.

Answer 8

• Paravertebral ganglia also known as the sympathetic chain ganglia for right and left chains on each side of the vertebral column. They are contain incoming fibers sympathetic pre-ganglionic fibers arising from the spinal cord and also some sympathetic post-ganglionic cell bodies with processes that exit and travel to target organs. - Prevertebral ganglia are plexuses that surrounds origins of the main branches of the abdominal aorta for which they are named. They contain incoming sympathetic pre-ganglionic fibers from the spinal cord and some sympathetic post-ganglionic cells bodies with processes that exit and synapse at their target organs.

Question 9

Discuss the CT coverings of peripheral nerves and blood supply.

Answer 9

• Peripheral nerves are covered/protected by 3 CT layers: a.) Endoneurium: delicate CT sheath surrounding neurolemma cells and axons b.) Perineurium: dense CT that encloses fascicle (bundle) of peripheral nerve fibers providing effective barrier against penetration of the nerve fibers by foreign substances c.) Epineurium: thick CT that surrounds and encloses a bundle of fascicles, forming the outermost covering of the nerve. It includes fatty tissues, blood vessels and lymphatics. - Blood vessels that supply nerves are called vaso nervorum and are found within the epineurium layer (CT layer surrounding nerve fascicles).

Question 10

Describe the spinal cord. Identify regions, enlargements and terminations.

Answer 10

• Starts: foramen magnum - Ends: at L2 vertebral body. Terminal portion known as conus medullaris, rootlets that exit the remaining lumbar intervertebral formina are are contained with the lumbar cistern (subarachnoid space adjacent and inferior to L2 extending to ~ S2) are known as the cauda equina. Contained within the cauda equina is an extension of pia mater that continues inferiorly and penetrates the most inferior end of the dural sac, taking with it arachnoid and dura mater, passes through sacral hiatus and anchors to posterior coccyx. - Contains myelinated axons/dendrites in outer portion of spinal cord (white matter) and unmyelinated cells bodies in inner portion of spinal cord (grey matter) - Enlargement to cervical cord for upper limb innervation - Enlargement to lumbosacral cord for lower limb innervation

Question 10

Describe the anatomical structures/features found within a cross section of spinal cord. Provide anatomical directionality when describing components found within the spinal cord.

Answer 10

• Gray matter (inner): contains the dorsal horn (posterior horn) and carries sensory fibers and gives rise to dorsal rootlets, roots and DRG arise. Contains the ventral horn (anterior horn) and carries motor fibers and gives rise to ventral rootlets and roots. At levels T1-L2, it contains the lateral horn (aka intermediolateral cell columns) which are autonomic sympathetic fibers. - White matter (outer)

Question 11

What is gray matter? What is white matter?

Answer 11

• Gray matter are collections of cell bodies and unmyelinated axons and dendrites within the CNS - White matter are collections of axons/dendrites within the CNS

Question 12

Draw cross section of spinal cord and spinal nerve with various attachments and components necessary to receive and transmit signal. Do not include pathways.

Answer 12

Question 13

What happens to each spinal root as it travels laterally from the spinal cord?

Answer 13

• It gives rise to the dorsal and ventral primary rami, which are mixed nerves that distribute to the ventral and dorsal aspects of the body.

Question 14

What is the definition of a nerve?

Answer 14

• collection of cell processes, dendrites and axons, surrounded by CT coverings.

Question 14

What is the SCG, where is it located?

Answer 14

• The sympathetic chain ganglion is a collection of cell bodies and processes outside of the CNS that are autonomic. Pre-synaptic cell bodies that arise in the CNS synapse with post-sympathetic cell bodies in this structure or bypass it via splanchnic nerves to the prevertebral ganglia. Some Post-sympathetic cell bodies are found her and travel directly to their target organ.

Question 16

What are rootlets? Where are they located on the spinal cord? What are contained in each?

Answer 16

• Rootlets are neurons branching off of the spinal cord on the dorsal and ventral aspects. Dorsal rootlets contain sensory neurons, while ventral rootlets contain motor neuron. Rootlets from each aspect join together into a root.

Question 17

Which is larger, ventral or dorsal primary rami? Why?

Answer 17

• Ventral rami. Dorsal primary rami carry sensory / motor fibers to/from deep back muscles, synovial joints of vertebral column and overlying skin of back. Ventral rami run everything else, which is remaining areas of trunk, upper and lower limbs. They form nerve plexuses.

Question 17

What are the prevertebral ganglia, where are they located?

Answer 17

• These are collection of cell bodies and processes outside the CNS that are autonomic. They contain pre-synaptic cell processes that synpase onto their post-synaptic cell bodies. They contain post-synaptic cell bodies that depart this structure and travel to their target organ.

Question 18

What are splanchnic nerves?

Answer 18

• These convey visceral efferent (ANS) and afferent fibers to and from viscera of the body cavities.

Question 20

Describe the meninges of the spinal cord.

Answer 20

• consists of 3 layers: dura, arachnoid and pia mater - outer to inner (including spaces): a.) epidural space b.) dura mater c.) arachnoid mater (has projections known as arachnoid trabeculae that anchor it to the pia mater) d.) subarachnoid space (contains CSF and rootlets off of spinal cord) e.) pia mater: (denticulate ligaments are lateral extensions of pia that anchor into the dural sac boundary providing stability, filum terminale is inferior extension that pierces dural sac and anchors spinal cord to coccyx)

Question 21

Define denticulate ligaments.

Answer 21

• Denticulate ligaments are projections of pia mater that extend laterally, midway between anterior and posterior roots, from the spinal cord, and anchor to the dural sac boundary.

Question 22

What is important to know about posterolateral herniations of lumbar IV discs? Provide examples to show your understanding.

Answer 22

• These herniated discs impinge on the nerve that is at the next lower level and not that of the level where the herniation occurs. This is due to the arrangement of the cauda equina and also that the nerve of that level leaves the vertebral canal through the superior aspect of the intervertebral foramen. - L4-5 herniation impinges the L5 nerve. - L5 herniated disc (which is below the L5 vertebra) impinges on the S1 nerve.

Question 22

Describe characteristics of the sympathetic division of the ANS. Include: function, NT involved, location of pre-synaptic and postsynaptic cell bodies, course of cell processes.

Answer 22

Sympathetic division: think thoracolumbar - function: flight, fright or fight - neurotransmitter: norepinephrine - cell body locations: a.) pre-synaptic cell bodies in lateral horn (grey matter of spinal cord) between T1 and L2/3; b.) post-synaptic cell bodies in SCG or prevertebral ganglion - course of cell processes: a.) pre-synaptic cell processes enter spinal nerve via ventral root, enter SCG via white rami communicantes, synapse immediately in SCG (1) at level of entry OR ascend/descend (2) trunk to synapse OR pass through SCG (3) without synapsing in splanchnic nerves and synpase in the prevertebral ganglion. Fibers innervating head, neck, body wall, limbs and thoracic cavity will follow courses 1 or 2. Fibers innervating viscera within abdominopelvic cavity follow course 3. b.) post-synaptic cell processes arising in SCG travel through gray rami communicantes and enter spinal nerve branching to either the ventral or the dorsal primary rami – they travel with all 31 pairs of spinal nerves. These fibers stimulation vasomotion, pilomotion and sudomotion. Post-synaptic fibers that perform these function in head (including dilate iris) have their cell bodies in sup. cervical canglion and branch to form periarterial plexuses of nerves which following branches of carotid arteries. Post-sympathetic cell processes that innervate viscera can travel either directly from SCG to organ or from their cell bodies in prevertebral ganglion to their organ. In the last two cases, these are in splanchnic nerves.

Question 24

What are the plexuses/major nerves formed by the ventral primary rami (that is the spinal nerve plexuses)? From what levels of spinal nerve are they formed?

Answer 24

• Cervical plexus (C1-C5) - Brachial plexus (C5-T2) - Intercostal nerves (T1-T11) - Lumbar plexus (T12-L4) - Sacral plexus (L4-S5) - Coccygeal nerve (Co)

Question 25

Define synapse.

Answer 25

• functional communication between a series of neurons

Question 27

What is the lumbar cistern?

Answer 27

• It is the area of subarachnoid space within the dural sac from L2 to S2 containing CSF, the cauda equina, including filum terminale.

Question 28

What type of fibers (sensory or motor) do motor nerve branches from ventral rami contain? Cutaneous sensory nerve branches? Explain.

Answer 28

• Both are mixed nerves containing both sensory and motor fibers. Both contain ANS fibers.

Question 29

What is the DRG? Where is it?

Answer 29

• Dorsal root ganglia are collection of sensory cell bodies outside the CNS. They receive sensory information from the periphery and transmit that back into the CNS. - It is found off the dorsal root before the ventral and dorsal root form the spinal nerve and lies within the intervertebral foramina.

Question 30

What are the divisions of the ANS? From what locations in the spinal cord do these divisions arise?

Answer 30

• Sympathetic: thoracolumbar - Parasympathetic: craniosacral

Question 31

What are the neurons contained within typical spinal nerves? What is the function of each type?

Answer 31

• General somatic afferents: transmit pain, temp, touch, pressure and proprioception to spinal cord - General somatic efferents: transmits impulses to skeletal muscle from spinal cord - General visceral afferents: transmits reflex pain from viscera, glands, mucous membranes and blood vessels to spinal cord - General visceral efferents: transmits impulses to smooth muscle and glandular tissue from spinal cord

Question 32

What are the horns within the spinal cord? Are they found within the gray matter or white matter?

Answer 32

• Found within gray matter are the ventral horn, dorsal horn and lateral horn (only T1-L2). - Ventral horn contains motor fibers and gives rise to ventral rootlets and root. - Dorsal horn contains sensory fibers and gives rise to dorsal rootlets, root and DRG. - Lateral horn (T1-L2) contains autonomic sympathetic fibers.

Question 34

What are dermatomes? What are myotomes?

Answer 34

• Dermatomes are sensory nerve distributions - Myotomes are motor nerve distributions

Question 36

Define somatic and visceral/splanchnic neurons.

Answer 36

• Somatic pertains to the body, typically the body wall - Splanchnic pertains to the gut, viscera

Question 37

At what vertebral level is an LP/spinal tap performed? What space is being accessed?

Answer 37

• LPs are typically done by inserting needle between spinal processes of L3 and L4, can be between L4 and L5. One is accessing CSF contained in the subarachnoid space.

Question 38

How many spinal nerves are there? What is the breakdown for each region of the spine? How are they numbered? Provide examples.

Answer 38

• 31 pairs - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal - Cervical high, thoracic lumbar sacral coccygeal low, C8 under C7. C1-7 come out above their respective vertebral number, C8 is under vertebra C7, every other spinal nerve comes out below their vertebral number. - L2 spinal nerve comes out below L2; C2 comes out above C2; etc.

Question 39

Draw cross section of spinal cord with spinal nerve. Draw pathway of general visceral afferent neurons.

Answer 39

Question 41

Which form plexuses, the ventral or dorsal primary rami?

Answer 41

• Ventral primary rami form

Question 42

What are the gray and white rami communicantes? What fibers do each contain and at what spinal cord levels are each found?

Answer 42

• They connect the sympathetic chain ganglia to the spinal nerves. White rami contain myelinated presynaptic axons (that originate in lateral horn of spinal cord and travel via ventral root into SCG) and are found at T1-L2 levels (same as SCG itself). - Gray rami contain unmyelinated postsynaptic axons that have their cell bodies in the SCG and are travelling via the gray rami into the spinal nerves or out into splanchnic nerves.

Question 43

What is the definition of ganglion?

Answer 43

• collection of cell bodies outside the CNS

Question 44

Where do visceral afferent neurons course within the body?

Answer 44

• They travel with the sympathetic division of the ANS in a dermatomal pattern within splanchnic nerves.

Question 45

What spaces normally exist within, underlying and overlying the meninges of the spinal cord? What spaces are abnormal?

Answer 45

• Normal: Epidural space, subarachnoid space - Abnormal: subdural space

Question 46

What fibers: sensory or motor, are contained within the: a.) Dorsal root? b.) Ventral root? c.) Spinal nerve? d.) Ventral primary rami e.) Dorsal primary rami

Answer 46

• a.) sensory - b.) motor - c.) mixed - d.) mixed - e.) mixed

Question 47

What cranial nerves contain autonomic fibers? Are these exclusively autonomic?

Answer 47

• CN III, VII, IX and X contain parasympathetic fibers
• Not exclusively autonomic, contain other efferent/afferent somatic and visceral fibers