Spinal Cord And Spinal Nerves

Question 1

What does the spinal cord do

Answer 1

Transmits sensory information from the periphery of body to the brain and motor commands from brain to periphery
Designed to coordinate and execute reflexes independently from brain

Question 2

Location and structure of spinal cord

Answer 2

Spinal cord runs within the vertebral canal (neural canal) of the vertebral column
Whilst the vertebral column is built from segments of single vertebrae that are linked by intervertebral joints, the spinal cord presents as a single continuous block of neural tissue
Divided into 4 tissue blocks: cervical region, thoracic region, lumbar region, sacral region

Question 3

Why is spinal cord shorter than vertebral canal

Answer 3

Because spinal cord doesn’t grow in length significantly after first or second year of life however the vertebral column continues to grow in line with rest of skeleton
Therefore names of spinal cord regions and vertebral regions dont match up
The lumbar and sacral spinal cord segments are found between vertebral levels T9 and L2, spinal cord ends around L1-2 vertebral level

Question 4

What is the conus medullaris

Answer 4

Where the spinal cord ends and forms a tapered structure
Corresponds to the sacral spinal cord

Question 5

What are intervertebral foramina

Answer 5

Serves as a doorway between spinal canal and periphery
Lies between pedicles of neighbouring vertebrae at all levels in spine
The nerves that emerge from the spinal cord pass through them at the corresponding vertebral segments

Question 6

What is the cauda equina

Answer 6

Long bundle of nerves inferior to the conus medullaris
As vertebral column grows the nerves grow with it and result in the cauda equina

Question 7

What is the filum terminale

Answer 7

Thin strand of pita mater within the cauda equina that helps to anchor the conus medullaris to the coccyx

Question 8

Spinal dura mater

Answer 8

At each intervertebral foramen the spinal dura mater extends between vertebrae and surrounds the spinal nerves

Question 9

Dimensions of spinal cord

Answer 9

Diameter of ~ 2cm and its length ranges between 41-45cm

Question 10

Cervical and lumbar enlargements

Answer 10

Represent an increased number of neurons in the grey matter and axons in the white matter that serve the upper limbs and lower limbs respectively

Question 11

What emerges from grey matter

Answer 11

Spinal nerve rootlets
Axons coming from dorsal root ganglion enter the posterior side through the dorsal nerve root
The axons emerging from the anterior side do so through ventral nerve root
The posterior and anterior nerve roots fuse together to from the spinal nerves

Question 12

What is the central canal

Answer 12

In the central region of spinal cord
It’s a continuation of the 4th ventricle of the brain and contains cerebrospinal fluid CSF

Question 13

Posterior and anterior regions of spinal cord

Answer 13

Generally the posterior regions are responsible for transmitting sensory info to the CNS and the anterior regions are associated with motor functions
This comes from the initial development of the spinal cord which is divided into the basal plate and alar plate

Question 14

Basal plate and alar plate

Answer 14

The basal plate is closest to the ventral midline of the neural tube which will become the anterior face of the spinal cord and gives rise to motor neurones
The alar plate is on the dorsal side of the neural tube and gives rise to neurones that will receive sensory input from the periphery

Question 15

Grey matter

Answer 15

Symmetrical appearance resembling a butterfly
Subdivided into regions that are referred to as horns
Dorsal horn
Lateral horn
Ventral horn

Question 16

Dorsal horn

Answer 16

Responsible for sensory processing and contain the axons of the sensory neurones and the cell bodies of interneurons
The axons of sensory neurones are bundled into the posterior nerve root and are coming directly from dorsal root ganglion which contains cell bodies of sensory neurones

Question 17

Lateral horn

Answer 17

Found in the thoracic, upper lumbar and sacral regions is a central component of the autonomic nervous system and contains cell bodies of autonomic motor neurones which innervate cardiac, smooth muscle and glands

Question 18

Ventral horn

Answer 18

Contains cell bodies of somatic motor neurones that control skeletal muscles
The somatic motor neurones are largest neurones of body
The fibres that cause contraction of skeletal muscle are the axons of these neurones, which exit the spinal cord through ventral nerve root

Question 19

What forms the spinal nerve

Answer 19

The dorsal and ventral nerve roots
Spinal nerves contain both afferent and efferent fibres and signals

Question 20

How are the neurones of the spinal cord organised

Answer 20

Into functional groups called nuclei representing their respective functions
Somatic sensory, visceral sensory, somatic motor, autonomic motor

Question 21

White matter

Answer 21

Separated into columns
Between the two dorsal horns of grey matter are the posterior columns which are composed of axons of the ascending tracts
Between the two anterior horns and bounded by the axons of motor neurons emerging from that grey matter area are the anterior columns
The lateral columns are between the posterior horn and axons of anterior horn neurons
The anterior and lateral columns are composed of many groups of axons of both ascending and descending tracts

Question 22

Ascending tracts of spinal cord

Answer 22

Carry sensory information up to brain

Question 23

Descending tracts of spinal cord

Answer 23

Carry motor commands from the brain

Question 24

What are spinal/segmental nerves

Answer 24

The nerves that emerge from the spinal cord
Each segment of the spinal cord issues a pair of bilaterally symmetrical spinal nerves that gradually course away from spinal cord and as they do so the various components that make up the nerve unravel in a systematic and predictable manner

Question 25

How many spinal nerves is there

Answer 25

31 spinal nerves
Named according to the level of the spinal cord at which each one emerges

Question 26

What is a neuronal or neural segment

Answer 26

Each of the spinal nerves carry signals that are then processed for reflexes, central or peripheral transmission by a defined segment of spinal cord- known as neuronal or neural segment
The corresponding nerve to this segment is known as a spinal segmental nerve
In neurological terms a given spinal neuronal segment is known as a ‘spinal neural level’
C (cervical), T (thoracic), L (lumbar), S (sacral)

Question 27

Spinal vertebral levels

Answer 27

Denote the level of each vertebra of the spinal column
Different from spinal neural levels
Vertebral levels of cervical spine are C1 to C7 but the neural elements of the cervical spinal neural levels are C1 to C8

Question 28

Spinal nerves numbers

Answer 28

8 pairs cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral nerves
One pair of coccygeal nerves
The nerves are numbered from superior to inferior position, each emerges from the vertebral column through the intervertebral foramen at its level

Question 29

What are nerve plexus

Answer 29

Some Spinal nerves come together to form a bundle of intersecting nerves
Occurs at 4 places along length of vertebral column
4 main nerve plexus in body:
Cervical plexus-supplies nerves to posterior head and neck as well to the diaphragm
Brachial plexus- supplies nerves to arm
Lumbar plexus- supplies nerves to anterior leg
Sacral plexus- supplies nerves to posterior leg

Question 30

Vertebrae numbers

Answer 30

7 cervical vertebrae
12 thoracic
5 lumbar
5 sacral
Coccyx- 3/4 fused
33 vertebrae total

Question 31

Spinal nerve branches

Answer 31

After exiting the intervertebral foramen each spinal nerve splits into 3 branches called rami
On the posterior side the dorsal ramus is a short nerve that innervates deep muscle and skin of back
On anterior side the ventral ramus splits into multiple branches that may form nerve plexuses, innervates anterior and lateral portions of trunk, upper and lower limbs
Spinal nerves are also associated with other branches called rami communicantes which connect spinal nerve to autonomic ganglia
Meningeal rami- supply sensory and vasomotor innervation to spinal meninges and vertebral column

Question 32

Dermatomes

Answer 32

The spinal nerves which contain sensory fibres with endings in the skin connect with the skin in a topographically organised manner illustrated as dermatomes
E.g. the fibres of C8 innervate the medial surface of forearm and extend out to fingers
All spinal nerves except C1 innervate a region on skin
Dermatomes important in clinical setting as they can help identify potential damage to spinal nerves
And are also associated with visceral pain as the spinal nerves innervated regions of skin also innervate internal organs

Question 33

What is a myotome

Answer 33

A group of muscles which are innervated by a single spinal nerve which has derived from the same embryological segment

Question 34

What is a Dermatome

Answer 34

An area of skin which is innervated by the dorsal root of a single spinal nerve

Question 35

What is the part of spinal/segmental nerve that participates in formation of nerve plexuses

Answer 35

Anterior rami

Question 36

What is a nerve plexus

Answer 36

Composed of afferent and efferent fibres that arise from the merging anterior rami of spinal nerves and blood vessels

Question 37

Spinal neural levels that are comprised showing a unilateral loss of biceps jerk reflex

Answer 37

C5/C6