Spinal Cord And Spinal Nerves Flashcards
What does the spinal cord do
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
Location and structure of spinal cord
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
Why is spinal cord shorter than vertebral canal
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
What is the conus medullaris
Where the spinal cord ends and forms a tapered structure
Corresponds to the sacral spinal cord
What are intervertebral foramina
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
What is the cauda equina
Long bundle of nerves inferior to the conus medullaris
As vertebral column grows the nerves grow with it and result in the cauda equina
What is the filum terminale
Thin strand of pita mater within the cauda equina that helps to anchor the conus medullaris to the coccyx
Spinal dura mater
At each intervertebral foramen the spinal dura mater extends between vertebrae and surrounds the spinal nerves
Dimensions of spinal cord
Diameter of ~ 2cm and its length ranges between 41-45cm
Cervical and lumbar enlargements
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
What emerges from grey matter
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
What is the central canal
In the central region of spinal cord
It’s a continuation of the 4th ventricle of the brain and contains cerebrospinal fluid CSF
Posterior and anterior regions of spinal cord
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
Basal plate and alar plate
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
Grey matter
Symmetrical appearance resembling a butterfly
Subdivided into regions that are referred to as horns
Dorsal horn
Lateral horn
Ventral horn
Dorsal horn
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
Lateral horn
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
Ventral horn
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
What forms the spinal nerve
The dorsal and ventral nerve roots
Spinal nerves contain both afferent and efferent fibres and signals
How are the neurones of the spinal cord organised
Into functional groups called nuclei representing their respective functions
Somatic sensory, visceral sensory, somatic motor, autonomic motor
White matter
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
Ascending tracts of spinal cord
Carry sensory information up to brain
Descending tracts of spinal cord
Carry motor commands from the brain
What are spinal/segmental nerves
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
How many spinal nerves is there
31 spinal nerves
Named according to the level of the spinal cord at which each one emerges
What is a neuronal or neural segment
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)
Spinal vertebral levels
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
Spinal nerves numbers
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
What are nerve plexus
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
Vertebrae numbers
7 cervical vertebrae
12 thoracic
5 lumbar
5 sacral
Coccyx- 3/4 fused
33 vertebrae total
Spinal nerve branches
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
Dermatomes
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
What is a myotome
A group of muscles which are innervated by a single spinal nerve which has derived from the same embryological segment
What is a Dermatome
An area of skin which is innervated by the dorsal root of a single spinal nerve
What is the part of spinal/segmental nerve that participates in formation of nerve plexuses
Anterior rami
What is a nerve plexus
Composed of afferent and efferent fibres that arise from the merging anterior rami of spinal nerves and blood vessels
Spinal neural levels that are comprised showing a unilateral loss of biceps jerk reflex
C5/C6
