ANA 303 Spinal Cord Flashcards
The spinal cord is located________and extends from _______ to __________?
Where does it occupy?
The spinal cord is located within the vertebral canal and extends from the foramen magnum
(medullary spinal junction) to the first or second lumbar vertebra.
It occupies the upper two thirds of the vertebral
column. The rest of the cord is occupied by cauda equina
The conical-shaped caudal end of the spinal
cord, known as the_____________
conus medullaris
What is the filum terminale internum?
A thin filament enclosed in pia and consisting of glial cells, ependymal cells, and astrocytes emerges from the conus medullaris. This filament is called the filum terminale internum.
What is the filum terminale externum?
At this level, a caudal thin extension
of the spinal dura, called the coccygeal ligament (filum terminale externum) surrounds the filum terminale.
What anchors the spinal cord?
Filum terminale
Why is it that in an adult, the spinal cord occupies only the upper two-thirds of the vertebral column?
The spinal cord occupies the whole length of the vertebral canal up to the third month of fetal life. Then it lengthens at a slower rate than the vertebral column
What is the cauda equina?
The lumbosacral nerve roots surround the filum terminale and form a cluster that resembles the tail of a horse and that is called the cauda equina
What is the lumbar cistern?
The subarachnoid space is the widest from the caudal end, L1. of the spinal cord to S2 and contains no CNS structures except the filum terminale and the nerve roots of cauda equina. This space is known as the lumbar cistern
Clinical significance of lumbar cistern
Because of this anatomic feature, this space is most suitable for the withdrawal of cerebrospinal fluid (CSF) by lumbar puncture. The site for performing a lumbar puncture changes with age in childhood. For example, in children, the caudal end of the spinal
cord is usually located at the third lumbar vertebra (L3); therefore, the needle for lumbar puncture is inserted at the L4–L5 level
How many segments does the spinal cord have?
31
How many pairs of nerves does the spinal cord have? How many does each segment have?
31 pairs
Cervical 8 pairs
Thoracic 12 pairs
Lumbar 5 pairs
Sacral 5 pairs
Caudal 1 pairs
At each level, the spinal nerves exit through the ____________
intervertebral foramina
Each spinal nerve consists of a______________
dorsal root (containing afferent fibers) and a ventral root (containing efferent fibers).
Function of the dorsal root ganglion
The spinal ganglion (dorsal root ganglion) is located within the intervertebral foramen and contains the neurons that give rise to afferent fibres entering dorsal horn of the spinal cord.
The dorsal and ventral roots are joined distal to the spinal ganglion and form the___________
common spinal nerve
Describe the cervical enlargement
The nerve roots emerging from this enlargement form the brachial plexus and innervate the upper extremities.
Describe the lumbar enlargement
The lumbar plexus (comprising the nerve roots from L1–L4) and sacral plexus ( consisting of nerve roots from L4–S2) emerge from the lumbar enlargement. The lumbar
plexus innervates the lower extremities.
The sacral spinal nerves contain and innervate____________
The sacral spinal nerves emerging from the conus medullaris contain parasympathetic fibres and motor fibres innervating the bladder
and its sphincters, respectively.
Describe the internal structure of the spinal cord with reference to the matter
The inner core of the spinal cord is formed by grey matter, and it is surrounded by white matter at the periphery consisting of ascending and descending bundles of myelinated and unmyelinated axons that are called tracts or fasciculi.
A tiny central canal filled with CSF at its center.
Surrounding the canal is a single layer of cells, the ependymal layer.
What is a funiculus?
A bundle containing one or more tracts or fasciculi is called a funiculus
What are the 3 funiculi?
In each half of the spinal cord, there are
three funiculi: (1) the dorsal (posterior) funiculus, which is located between the dorsal horn and a midline structure called the dorsal (posterior) median septum;
(2) the lateral funiculus, which is located between the sites where the dorsal roots enter and ventral roots exit from the spinal cord; and
(3) the ventral (anterior) funiculus, which is located between the anterior (ventral) median fissure and the site where the ventral roots exit
The anterior white commissure,
consisting of____________and located___________
decussating axons of nerve cells, is located
ventral to the gray commissure
The two sides of the gray matter are connected by a band of gray matter called the _____________
gray commissure (lamina X).
Where is the central canal located
in the grey commissure
The general senses are classified as follows:
- Exteroception: Sensations perceived by the body, arising from the external world and including touch, pressure, vibration, pain, thermal sensation, itch, tickle, etc.
- Proprioception: Sensations perceived by the body, generated by the own tissues and include perception of posture, joint position and movement, muscle contraction and stretch.
- Interoception: Sensations perceived by the body, arising from the internal world and including sensations
The ascending pathways are generally functional in
Fine/discriminitive touch
Proprioception (kinaesthesia)
Vibration
What are the ascending tracts of the spinal cord in the posterior/ dorsal column (medial leminiscus) ? What are their functions?
Fasciculus gracilis (tract of Goll)
Transmit signals from the lower limb (below T6)
Fasciculus cuneatus (tract of Burdach)
Transmit signals from the upper limb (above T6)
Both are responsible for:
Fine touch
Vibration
Proprioception
Fasciculus gracilis and cuneatus pass directly to the ipsilateral posterior white column and ascend without synapse till they reach the
brainstem.
They synapse on the nuclei gracilis and cuneatus in the medulla oblongata
What are the tracts under the anterolateral spinothalamic tracts? What are their functions?
Anterior spinothalamic tract: responsible for crude touch and pressure
Lateral spinothalamic tract: pain and temperature
They enter the spinal cord and travel for a segment or two in the posterolateral tract of
Lissauer then synapse in lamina I, Il and IV.
After synapse, fibers from the second-order neurons cross to the opposite side in the white
and grey commissures and travel rostrally.
The anterolateral system shows somatotopic
organization.
Sensation from lower parts of the body travel laterally while sensation from upper parts travel medially,
Second-order neurons synapse in the ventral
posterolateral and intralaminar thalamic nuclei,
Third-order neurons send axons that pass through internal capsule to the somatosensory cortex.
What are the tracts under the spinocerebellar pathways? What are their functions?
Divided into two tracts
DORSAL Spinocerebellar tract
This tract carries unconscious proprioception from individual muscles of the lower limb
up to the cerebellum
They Convey proprioception and deep pressure
from the muscles to the cerebellum,
The First-order neurons synapse on Clarke’s
column.
Fibers from the second-order neurons enter the
ipsilateral lateral white funiculus.
Fibers from the second-order neurons ascend join the inferior cerebellar peduncle and terminate in the cerebellar cortex.
Sensory fibers from sacral and lower lumbar travel rostrally until they meet and synapse on the Clarke’s column
VENTRAL Spinocerebellar tract
This tract carries unconscious proprioception from ** the lower limb as a whole** up to the cerebellum
Has the same function of the posterior spinocerebellar tract in addition to sensation from the skin.
Axons synapse on Clarke’s column and most of the second-order neurons decussate and ascend to enter the cerebellum via the superior cerebellar peduncle.
Which tracts carry conscious and which carry unconscious information?
Conscious:
Posterior column (fasciculus graciclis and cuneatus)
Anterolateral spinothalamic tracts (anterior and lateral)
Unconscious:
Spinocerebellar tracts (anterior and posterior)
What are the upper limb equivalents of the Spinocerebellar tracts (anterior and posterior)?
PST - cuneocerebellar tract
AST - rostralspinocerebellar tract
these carry proprioceptive info of the upper limb and neck to the cerebellum
The descending pathways are generally functional in
response to sensory information
The types of descending pathways
Pyramidal and extra-pyramidal tracts
Why are they called pyramidal tracts
they pass through the medullary pyramids
What are the pyramidal tracts? What are their functions?
Corticospinal tracts:
Lateral Corticospinal tracts
Anterior Corticospinal tracts
They convey voluntary skilled movements
What are the extra-pyramidal tracts? What are their functions?
Rubrospinal tract: facilitatory to flexors of the upper limb
Tectospinal tract: involved in the coordination of head and movement with vision
Medial reticulospinal tract (ponto): facilitates voluntary muscle contraction and an increase in muscle tone
Lateral reticulospinal tract (medullary): inhibits voluntary movement, reduces muscle tone and plays a role in automatic breathing
Vestibulospinal tract: helps control balance and posture
Average length of SpinaI Cord in males and females
Average length of SpinaI Cord is 45 cm in Adult Males and, 42-43 cm in Adult Females
Average Weight of Spinal cord
30-35 grams
Average Length of Vertebral column
70 cm
The spinal cord is enlarged at the cervical and lumbosacral parts to give the origin to the
brachial and lumbosacral plexuses, respectively.
What is the anterior median fissure and posterior middle sulcus
The anterior median fissure is a deep longitudinal fissure in the anterior surface.
The posterior median sulcus is a shallow sulcus in the posterior surface, It contains
the posterior median septum (pia mater).
What is the posterolateral and anterolateral sulcus?
The posterolateral sulcus is the entry site for the posterior root (sensory) fibers.
The anterolateral Sulcus is the exit site for the anterior root (motor) fibers.
What is the filum terminale?
Filum terminale is a prolongation of the pia mater from the apex of the conus medullaris to the posterior surface of the coccyx
Describe the formation of the lumbar cistern
The subarachnoid space at the level of the cauda equina enlarges to form the lumbar
cistern (site for lumbar puncture and spinal anesthesia).
The pia mater attaches to the
vertebral column laterally by the_____________
denticulate ligament
Describe the grey matter
(Grey commissure, Nuclei horns etc.)
They Composed of neuronal cell bodies, dendrites, initial parts of axons, and glial cells.
Divided into dorsal (posterior) and ventral (anterior) horns (H shape in cross sections),
The grey commissure connects the anterior and posterior horns. It contains the central canal.
The dorsal horn receives sensory information while the ventral horn projects motor commands.
The small lateral grey horn lie in the thoracic and upper lumbar segments. It functions as sympathetic synapse area.
The posterior grey horn has four nerve groups: 1. Substantia gelatinosa group (lamina Il)
2 Nucleus proprius group (laminae Ill & IV)
3. Nucleus dorsal is group (Clarke’s column lamina Vll)
4. Visceral afferent nucleus
The substantia gelatinosa is located in the apex of the posterior grey horn throughout the spinal cord. It receives afferents conveying pain, touch, and temperature.
The nucleus proprius is located anterior to the substantia gelatinosa throughout the spinal cord. It receives afferents conveying proprioception, two-point discrimination, and vibration from the posterior column.
Clarke’s column is situated at the base of the posterior grey horn from the lower cervical to the middle lumbar segment.
It receives proprioceptive input (mainly muscle and tendon spindles).
The visceral afferent nucleus lies lateral to the Clarke’s column from the first thoracic to the third lumbar segment,
It receives visceral afferent information
Describe the white matter and the funiculi
The white matter of the spinal cord is divided into the following columns (funiculi):
- Anterior column (between the midline and the anterior nerve roots)
- Lateral column (between the anterior and posterior nerve roots)
- Posterior column (between the posterior nerve roots and the midline)
It contains nerve axons and neuroglia along with blood vessels.
Each column is divided into tracts (fasciculi). These tracts can be ascending, descending, or intersegmental.
The nomenclature of the tracts start with the origin and ends with the destination. For example spino____tract.
(spinothalamic tracts) for ascending tract.
Descending tracts are named ____spinal tract, For example: corticospinal tract.
Ascending tracts are also known as__________
somatosensory pathways or systems.
Describe the ascending tract
The ascending tracts refer to the neural pathways by which sensory information from the peripheral nerves is transmitted to the cerebral cortex.
The Ascending tracts conducts the impulses from the periphery to the Brain through the Spinal cord.
Each tract usually consists of three neurons
First-order neuron
Second-order neuron
Third-order neuron
Second-order neurons decussate at different levels.
Third-order neurons are usually found in the
thalamus
These neurons branch to give input to motor
neurons and the reticular formation.
Afferent axons of the first-order neurons have their cell bodies
in the dorsal root ganglia
What are the ascending tracts?
Dorsal Column System
Spinocerebellar System
Anterolateral (spinothalamic) System
Describe second order and third order neurons
Second-order neurons decussate
and ascend forming the medial
lemniscus to synapse in the
ventral posterolateral nucleus of
the thalamus.
The third-order neurons pass
through the internal capsule to
reach the somatosensory cortex.
Other ascending tracts
Spinotectal tract (visual reflexes),
Spinoreticular tract.
Spino -olivary tract
Visceral sensory tracts.
Spinal cord lesions
Lesion of a single posterior root will cause pain in the skin and muscles innervated by that root.
Lesion of a single anterior root will cause paralysis to any
muscle supplied exclusively by that root.
Damage to the anterolateral system will cause
contralateral loss of pain, temperature and crude touch below the level of the lesion.
Damage to the dorsal column causes ipsilateral
disruption of proprioception, pressure and vibration below the level of the lesion.
Herpes zoster
Herpes zoster is a viral infection that affects sensory neurons,
It is characterized by pain and inflammation with vesicles in the area of distribution of the affected nerve.
This infection usually occur in the elderly.
Tabes dorsalis
Tabes dorsalis (neurosyphilis) results from the selective destruction to the dorsal roots.
This disease affects many sensations and reflexes.
It also causes ataxia (impaired balance or coordination) and hypotonia (weak muscle tone).
Spinal shock
Spinal shock results from severe injury to the spinal cord,
All sensations, reflexes, and motor functions of the spinal cord below the level of the injury will be suppressed as a result.
It may last to 24 hours or may extend to 12 weeks
Syringomyelia
Syringomyelia is a developmental or acquired
abnormality in the central canal usually in the brainstem and cervical spinal cord,
It is characterized by cavitation and gliosis of the
central part of the affected segment.
The ascending pathway is sensory/motor
The descending pathway is sensory/motor
Which is true
The ascending pathway is sensory
The descending pathway is motor
Do neurons synapse in the gry or white matter?
grey matter
all sensory information enters the spinal cord via the
dorsal horn
all motor information leaves the spinal cord via the
ventral horn
pathways for pain receptors under the spinothalamic tracts
A delta
C fiber
