Anatomy of spinal cord & function of spinal nerve

Question 1

Describe the general structure of the spinal cord. How does it vary in children vs adults?

Answer 1

The spinal cord starts at the base of the skull

In adults, the spinal cord terminates at L1- called conus medullaris
- below this is cauda equina.

In children, the spinal cord terminals L3 (lower)
- Because the spinal cord grows faster than the vertebral column
- As we grow taller, the terminal point of the spinal cord moves higher

The end area of the spinal cord is called the cauda equina
- Consists of the nerve roots of the lower portion of the spinal cord

NOTE: view diagram on notes

Question 2

Describe the internal structure of the spinal cord

Answer 2

The spinal cord is incompletely divided into 2 symmetrical halves by a dorsal median sulcus & a ventral median fissure.

In the centre of the cord is the small central canal , which is continuous rostrally with the cerebral ventricular system.

Surrounding central canal is spinal grey matter- consisting of nerve cell bodies, their dendrites & synaptic contacts.

The outer part of the cord consists of white matter- contains ascending & descending nerve fibres.
- Some of these join neighbouring cord segments for the integration of their functions, while others run between the cord & brain.

Many of the fibres that share a common origin, course & termination are grouped together in fascicles, forming the long tracts of the spinal cord.

Question 3

What does spinal cord look like under MRI?

Answer 3

View image on notes- very important!

Question 4

What parts (width) of the spinal cord innervates which areas of the body?

Answer 4

The cervical enlargement consists of cord segments C4–T1
- provides innervation for upper limb via brachial plexus

The lumbar enlargement is made up of segments L1–S3
- associated w/ innervation of lower limb via lumbosacral plexus.

NOTE: view diagram on notes

Question 5

What are the meningal layers of spinal cord?

Answer 5

Membranes that surround spinal cord & protect it

3 meningeal coverings: the pia mater, arachnoid mater & dura mater

Pia mater:
- innermost covering
- cannot be seen under microscope
- delicate, vascular membrane
- very closely applied to the surface of cord & nerve roots.
- forms tiny ligaments called the denticulate ligaments- suspend the spinal cord within the dural sac.

Arachnoid materL
- lies between the pia & dura
- translucent membrane that invests the cord like a loose-fitting bag.
- Between the pia & arachnoid lies the subarachnoid space- contains cerebrospinal fluid, which is produced in the cerebral ventricular system- usually pushes arachnoid mater against the dura mater, separating it from the pia mater

Dura mater:
- tough, fibrous membrane
- envelops the cord loosely
-separated from arachnoid by a theoretical plane- subdural space
- separated from bony wall of the vertebral canal by the epidural space .

Question 6

What is the cauda equina?

Answer 6

The collection of nerves at the end of the spinal cord
- Contains nerve roots from L2 to Co1 (coccygeal).

NOTE: view diagram on notes! + learn dermatomes

Question 7

Where would you take samples of cerebra-spinal fluid?

Answer 7

Sample taken below level of L3-
-there is greater range of flexion, so larger spaces between vertebra= means easier to pass between them & pierce dura mater.

Spinal cord stops at L1- called conus medullaris- below this is cauda equina.
- If needle enters level of spinal cord= can cause damage.

In children, done below L3

Question 8

How many spinal nerves are there?

Answer 8

The spinal cord gives branches at each vertebral level

Spinal nerve come in pairs (total of 31 pairs):
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal

2 enlargements:
- Cervical enlargement (c4-t1) which forms the brachial plexus
- Lumbar enlargement (l1-s3) which forms lumbosacral plexus & cauda equina

NOTE: view diagram on notes!

Question 9

Describe the structure of a spinal nerve root

Answer 9

Primary afferent neurons carrying sensory information enter via dorsal root
- Cell bodies of primary afferent neurons are found in dorsal root ganglion
- afferent neruons= deliver sensory info from skin

Primary efferent neurons carrying motor information leave via ventral root
- Cell bodies of these neurons are found in the grey matter of the anterior (ventral) horn.
- efferent neurons= control skeletal muscles= motor supply

The dorsal & ventral roots come together to form the spinal nerve.

Spinal nerve divides into 2 branches - small posterior branch, dorsal ramus & large anterior branch, ventral ramus.
- Dorsal ramus -Supplies muscles & skin of the back region
- Ventral ramus Supplies muscles & skin of the front of the body & also limbs

Nerves leaves the vertebral column via the intervertebral foramen below their corresponding vertebra
- Except in the cervical region & sacrum
- C1-C7 exits above the corresponding vertebra
- 8th pair of cervical nerves leave inferior to C7
- The sacrum is fused, therefore nerves leave via sacral foramina, not intervertebral foramina

NOTE: view structure of spinal nerve root on notes!

Question 10

What is the role of the branches after the spinal nerve splits? What about the ramus branches?

Answer 10

1. Anterior (ventral)
   - Larger
   - Innervates most regions of the body, except head which is almost exclusively innervated by the 12 cranial nerves
   - Forms the cervical, brachial, lumbar & sacral plexuses & the sympathetic ganglia &prevertebral plexuses
   - Nerve cell bodies located in the dorsal root ganglia
2. Posterior (dorsal)
   - Smaller
   - Contains sensory afferent neurons
   - Cell bodies are located in the dorsal root ganglion of the dorsal ramus

NOTE: ventral root is always anterior and dorsal root always posterior- Hence why they innervate posterior and anterior muscles of the body

Question 11

Define myotomes. Defime dermatomes.

Answer 11

Dermatome = an area of skin innervated by a single spinal nerve root

Myotome = group of muscles/ part of muscles that is innervated by a single nerve root

Question 12

How many vertebrae do we have? How are they grouped?

Answer 12

33 vertebrae

Grouped into 5 regions:
- 7 cervical vertebrae
- 12 thoracic
- 5 lumbar
- 5 sacral vertebrae that are fused to form the sacrum
- 4 coccygeal vertebrae

NOTE: view image on notes!

Question 13

Describe the shape of the spine? Why is it like this?

Answer 13

Chest & sacrum- spine curves forwards creating thoracic & sacral kyphoses (sg. kyphosis).

Neck & lower back - spine curves back forming cervical
& lumbar lordosis (sg. lordosis).

Shape helps us:
- Keep upright posture
- Distribute forces travelling throught the spine.

Question 14

Describe the shape of the spine in babies & young children.

Answer 14

Newborn- whole spine is kyphotic- as we’ve spent 9 months curled up.

3-4 months- cervical lordosis forms = allows weight of the head to be supported by spine, so baby can start holding head up independently.

6-9 months- thoracic kyphosis

1 year- lumbar lordosis starts to form
- baby can support their own body weight over their hips = start walking.

NOTE: view image on notes

Question 15

Name and describe the bony landmarks of the thoracic vertebrae.

Answer 15

Vertebral body - weight-bearing portion of the bones. - provides attachment for the discs that sit between the vertebrae.

Lamina- an arch of bone connected to the vertebrae by pedicles.

Vertebral canal - protects spinal cord.

Transverse processes- there are 2, one on either side.

Spinous processes - along w/ transverse processes, provides attachments for the muscles of the back.

NOTE: view anatomical image of it on notes- very important!

Question 16

Name and describe the bony landmarks of the cervical vertebrae.

Answer 16

Foramen transversarium - 2 small holes in their transverse processes
- provide a safe route for the vertebral artery to travel along the neck.

Bifid spinous process - a split in the spinous process.

+ features mentioned for thoracic vertebrae

NOTE: view anatomical image of it on notes- very important!

Question 17

Name and describe the bony landmarks of the lumbar vertebrae.

Answer 17

Most robust vertebrae because carry the greatest load.

Transverse & spinous processes are particularly prominant because the lumbar vertebrae need powerful muscles to move them.

+ features mentioned for thoracic vertebrae

NOTE: view anatomical image of it on notes- very important!

Question 18

Give examples of atypicalical vertebrae and how they’re different.

Answer 18

C7 - shares some features w/ thoracic vertebrae.
T12 - has a mix of thoracic & lumbar features.

C1 - atlas
- Missing spinous process & vertebral body.
- Instead has a much larger vertebral canal.

C2 - axis
- Dens or odontoid peg - upward pointing projection.
- It is where the vertebral body of C1 has ended up (fused to the vertebrae below it).

NOTE: view images on notes- very important!

Question 19

Name the movements of the spine

Answer 19

• Flexion - forwards
• Extension - backwards
• Lateral flexion - either side
• Rotation

Question 20

Where are facet joints found and what is their function?

Answer 20

These are bony projections which form joints w/ the articular facets of the vertebrae above & below.

Allow for flexion, extension, lateral flexion &rotation of spine
- Lumbar facet joints = mainly flexion & extension.
- Thoracic facet joints = mainly lateral flexion

Also create space - intervertebral foramen- the path for spinal nerves to leave the vertebral canal & enter the body.

NOTE: view images on notes- very important!

Question 21

Where is the atlanto-occipital joint and what movements does it allow?

Answer 21

Joint between Occipital bone & C1 (atlantis).

Allows head to rock backwards and forwards.
- Helps w/ flexion & extension.

Note: view image on notes!

Question 22

Where is the atlanto-axial joint and what movements does it allow?

Answer 22

Joint btw C1 & C2 - the odontoid peg of C2 pushes up into C1.
- transverse ligament passes behind peg- secures the 2 bones & allows bones to rotate.

Called the atlanto-axial joint.

Note: view image on notes!

Question 23

Name the muscles of the back (large + small), their location and their movements.

Answer 23

Erector spinae group- transverse length of back:
- Iliocostalis - from ilium to ribs- found laterally
- Longissimus- from sacrum to head- longest- found in middle
- Spinalis - very small & most medial.

All 3 muscles found on either side of spine

Movements:
- Extend our spine so we can stand upright
- Lateral flexion.

Greater ROM (flexion)= more strain on vertebra & discs in-between them= More common to have prolapsed disc in lumbar region]

NOTE: NOTE: Sometimes people refer to these muscles more specifically by adding these prefixes on the end e.g. iliocostalis thoracis.

Smaller muscles:

Split into 3 groups:
1. rotators
- from transverse process to spinous process then from spinous process to other transverse process
2. semispinalis
- semispinalis cervicis & semispinalis thoracis
- from transverse process of 1 vertebrae to spinous process of another
3. multifidus
- same as above but span fewer vertebrae (so shorter)

Function:
- rotate spine
- help maintain posture

NOTE: view images on notes- very important!
https://www.notion.so/PBL-week-13-13e7f545d1e747c09b35b782ab1516ce

Question 24

Name the ligaments in the spine. What is their function?

Answer 24

NOTE: The function of the ligaments is to limit movement.

Anterior longitudinal ligament (blue)
- runs full length of vertebral column
- Thick & prevents hyperextension of vertebral column.

Posterior longitudinal ligament (red)
- runs full length of vertebral column
- Thinner & prevents hyperflexion.

Ligamental flavum (purple)-
- extends between lamina of adjacent vertebra.

Interspinous ligament (green)
-join the spinous process of adjacent vertebrae
-attaches between processes.

Supraspinous ligament (orange)
- join the spinous process of adjacent vertebrae
- Variable- In cervical region, its replaced by ligament called ligamentum nuchae (more elastic- allows greater movement) & around L4/S1 its replaced by criss- crossed fibers of erector spinae muscles (greater ROM)

NOTE: view image on notes- very important