Sept 30 - Spinal Cord, Spinal Nerves and Plexuses

Question 1

Name the three meninges of the spinal cord

Answer 1

The dura mater
The arachnoid mater
The pia mater

Question 2

Describe the dura mater of the spinal cord

Answer 2

It’s the outermost layer that is tough and fibrous and continous with dura of brain (through the foramen magnum) and ends at 2nd sacral vertebre. Unlike the brain, there is an epidural space between the dura and the spinal canal. It contains C.T., fat and veins

Question 3

Describe the arachnoid mater of the spinal cord

Answer 3

Adherent to the dura. It is continuous with the arachnoid of the brain and ends at S2. The space between it and the pia is filled with CSF

Question 4

What is the space between L1-2 and S2 called?

Answer 4

It’s called the lumbar cistern. It’s often used to access CSF without damaging the spinal cord (diagnostics, administering anesthetic)

Question 5

Describe the pia mater of the spinal cord

Answer 5

It is the innermost layer that is adherent to the cord. It is continuous with the pia of the brain and ends with the dura at S2. It is thickened laterally as denticulate ligament (suspends cord with dural sac)

Question 6

What is different about the meninges in the spinal cord, compared to the brain? (Name three differences)

Answer 6

The spinal cord is contained within a sac of dura but the dura is NOT attached to the bone of vertebral canal.
There is a “real” epidural space between the bone and the dura filled with fat, connective tissue and blood vessels.
Also, small “denticulate ligaments” that attach the spinal cord to the dural sac

Question 7

Describe the location/enviromnent of the spinal cord

Answer 7

It is contained within a dura/arachnoid sac that extends from the foramen magnum down to the 2nd sacral vertebrae (S2). It is surrounded by CSF. The spinal cord ends as the conus medullaris between L1 and L2 vertebrae

Question 8

What is the cauda equina?

Answer 8

Lumbar, sacral and coccygeal nerve roots that extend to exit the dural sac at a lower level

Question 9

What is the filum terminale?

Answer 9

An extension of the pia that tethers the spinal cord to the end of the dural sac (anchor)

Question 10

There are 2 enlargements of the spinal cord. Where are they? What are they called?

Answer 10

The cervical enlargement and the lumbosacral enlargement. The cervical enlargement of the cord is found between C4 and T1 and it is the site of innervation of the arm. The lumbosacral enlargement is found between L2 and S3 and it is the site of innervation of the leg

Question 11

Describe the roots of the cervical enlargement of the spinal cord

Answer 11

They are short and horizontal

Question 12

Describe the roots of the lumbosacral enlargement of the spinal cord

Answer 12

They are long and vertical forming the cauda equina

Question 13

Describe the internal structure of the spinal cord

Answer 13

It consists of white matter (ascending and descending axons) surrounding the butterfly-shaped gray matter. The gray matter consists of a “dorsal horn” (sensory) and a “ventral horn” (motor)

Question 14

Describe the role of the dorsal horn of the gray matter of the spinal cord

Answer 14

It is sensory; it processes and relays sensory information to the brain. Sensory information (touch, temperature, pain, proprioception, etc.) enters the cord via the dorsal root, which contains afferent fibres

Question 15

Where are the cell bodies of sensory neurons found?

Answer 15

They are located in the dorsal root ganglion (DRG)

Question 16

Describe the role of the ventral horn of the gray matter of the spinal cord

Answer 16

It contains large motor neurons that project to muscle (via the ventral root); referred to as motor efferents. The motor neurons are innervated by descending fibres (from the brain) carried in white matter

Question 17

Describe the white matter of the spinal cord

Answer 17

It consists of nerve fibres, neuroglia and blood vessels (not neuronal cell bodies). It’s white because of the high fat content (myelin)

Question 18

Fibres arise from cell bodies located in: ? (name three places

Answer 18

Brain: descending axons from cerebrum and brainstem
Spinal cord: Ascending axons from gray matter of spinal cord (dorsal horn)
Periphery: Ascending axons from the dorsal root ganglion

Question 19

Comment on the arrangement of the axons in the spinal cord

Answer 19

The axons arranged in tracts/fasciculi that have a similar origin, termination and function (sensory/motor). Sensory information travels up the cord to the brain; sensory fibres are added to sensory pathways as the ascend, e.g., at the thoracic level, sensory fibres from the leg are ascending the cord, but sensory fibres from the arm have not yet entered the cord. Motor activity travels down the cord to the neurons in the gray matter of the cord

Question 20

Where do you have the maximum amount of white matter

Answer 20

At the very top of the spinal cord

Question 21

Describe the gray matter of the spinal cord

Answer 21

Butterfly- or H-shaped. It consists mainly of neuronal cell bodies and neuroglia. The dorsal horn receives sensory input via the dorsal root; it is the site of interneurons and projection neurons (project axons to the brain). The ventral horn has a motor function; it sends projections to skeletal muscles via the ventral root

Question 22

Describe the nerves and roots of the spinal cord

Answer 22

There are 31 pairs of spinal nerves that leave the cord to pass through the intervertebral foramen and exit as peripheral nerves. Each nerve is attached to the spinal cord by a ventral root and a dorsal root

Question 23

How are the spinal nerves named?

Answer 23

They are named according to their association with the vertebral column; there are 8 pairs of cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal nerves

Question 24

What is particular about the naming of the cervical nerves?

Answer 24

The cervical nerves exit ABOVE the vertebrae, except number 8, which exits below the 7th cervical vertebrae. The remaining nerves exit below the vertebrae.

Question 25

Where are the cell bodies of the motor neurons?

Answer 25

They are found in the ventral horn of the spinal cord

Question 26

The brain receives sensory information from a number of sensory systems. Explain

Answer 26

Receptors convert stimuli into action potentials. These action potentials enter the CNS via the dorsal roots of the spinal nerves. These afferent signals may be used in reflexes or the signals may be relayed via the neurons in the spinal cord or brainstem to higher centres

Question 27

Name three different stimuli that the sensory system is capable of detecting

Answer 27

Mechanical stimuli (by mechanoreceptors), pain (by nociceptors) and temperature (by thermoreceptors)

Question 28

Name different types of mechanoreceptors

Answer 28

Neuromuscular spindles and golgi tendon organs

Question 29

What are the roles of neuromuscular spindles?

Answer 29

They are receptors for stretch, they respond to change in length (basis for stretch reflex, i.e., knee jerk)

Question 30

How are Golgi tendon organs stimulated? What is their role?

Answer 30

They are stimulated by tension in tendons (protection against damage from excessive stretch)

Question 31

Where are the cell bodies of sensory neurons in the PNS?

Answer 31

In the DRG. One process of the sensory cell projects from the spinal nerve into the periphery where it ends in a sensory receptor while another process projects to the CNS (spinal cord). Signal travels from the receptor to the CNS (i.e., afferent)

Question 32

Explain the production of efferent signals

Answer 32

Descending fibres from the cerebral cortex and brainstem active the motor neurons of the ventral horn of the spinal cord that innervate skeletal muscle to produce a voluntary (and reflexive) movement. Efferent signals can also exit the brain through cranial nerves

Question 33

Explain the travel of the dorsal and ventral roots from the spinal cord

Answer 33

Both roots pass through the intervertebral foramina to then join and form a spinal nerve (becomes a mixed nerve). They exit the foramen as a spinal nerve and divide into a dorsal ramus (smaller) and a ventral ramus (larger). They supply the myotomes and dermatomes that encircle the body

Question 34

What is a myotome?

Answer 34

The group of muscles that a single spinal nerve root innervates with motor fibres

Question 35

What is a dermatome?

Answer 35

The area of skin that is innervated by sensory fibres of a single spinal nerve root

Question 36

Where do the dorsal rami go?

Answer 36

They travel posteriorly around the vertebral column to innervate muscles and skin of the back

Question 37

Where do the ventral rami go?

Answer 37

They travel anteriorly to innervate muscles and skin of the anterolateral body wall and limbs. The ventral rami join together in a complex plexus of fibres in the cervical (brachial) and lumbar (sacral) regions

Question 38

What is a nerve plexus?

Answer 38

It is formed by ventral rami of spinal nerves. Nerve fibres pass from one to another peripheral nerve and it results in a mixture of nerve fibres (from more than one spinal nerve) all bundled together in one peripheral nerve

Question 39

Name four plexuses

Answer 39

Cervial, brachial, lumbar and sacral

Question 40

What is the cervical plexus made up of? What does it innervate?

Answer 40

C1-C4. Motor innervation of muscles of neck and diaphragm. Sensory innervation of neck, diaphragm and ajacent peritoenum

Question 41

What is the brachial plexus made up of? What does it innervate?

Answer 41

C5-T1. Motor and sensory innervation for shoulder and upper limb. It is the largest plexus

Question 42

What is the lumbar plexus made up of? What does it innervate?

Answer 42

T12-L4. Motor for hip muscles, quadriceps and sartorious muscles. Sensory innervation of the lower anterior abdomen, ventral thigh and knee

Question 43

What is the sacral plexus made up of? What does it innervate?

Answer 43

L4/L5-S3. Motor for pelvis, perineum and most muscles of the lower limb (not quadriceps or sartorious). Sensory for perineum and most of the lower limb

Question 44

What is the potential consequence of peripheral nerve damage?

Answer 44

Motor and/or sensory changes. Flaccid paralysis followed by muscle degeneration (motor). Loss of cuteaneous sensibility (pinprick test; sensory)