Lecture 4: Part 1 (the spinal cord) Flashcards
where is the spinal cord enlarged within the vertebral column and why
1) cervical enlargement: ↑ circumference to accomodate ↑ in motor and sensory nerves for upper limbs
2) lumbar enlargement: same for lower limbs
dorsal root ganglion
dorsal root ganglion: A cluster of nerve cell bodies that emerges from each level of the spinal cord dorsally (posteriorly). Contains the cell bodies of sensory (afferent) neurons that bring information from the peripherary to the spinal cord (on to the brain)
conus medullaris
Conus Medullaris: the tapered terminal end of the spinal cord between L1-L2
- After the cord terminates, the nerve roots descend within the spinal canal as individual rootlets, collectively known as the cauda equina.
- Extending from the conus, the pia mater surrounding the spinal cord projects downward to form a delivate strand called the filum terminale, which connects the conus medullaris to the back of the coccyx and acts to give longitudinal support to the cord
cauda equina
Cauda Equina:“horses tail”
- A bundle of spinal nerves (surrounded by dura) that arise from the conus medullaris at the distal end of the spinal cord (L1-L2)
- They run in the subarachnoid space, before exiting at their appropriate vertebral level
Posterior Longitudinal Ligament
Posterior Longitudinal Ligament:
- Attached to the posterior surface of vertebral bodies and intervertebral discs, running continuously from the C1 to the sacrum
- Forms the anterior surface of the spinal canal (it’s within the spinal canal)
- Narrows as it travels caudally
Laminectomy
Laminectomy: Surgical excision of one or more spinous processes and their supporting laminae, removing most of the vertebral arch by transecting pedicles
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What is it for?
- Stenotic (narrowing) of vertebral foramen in one or more lumbar vertebrae; Laminectomy relieves pressure on the spinal cord or nerve roots – commonly caused by a tumor, herniated IV disc, bony hypertrophy (excess growth)
-
Most often lumbar vertebrae, why?
- Vulnerable to IV disc bulging, causing compression of spinal nerve roots
epirdural space (green)
- first encountered after laminectomy
- contains fat and batson’s plexus
Batson’s Plexus
- what is it
- where it is
- what is the significance
Batson’s Plexus:
- a valveless venous plexus (system of veins) in the epidural space - goes all the way from pelvis to head/neck
- connect the internal vertebral venous plexi with the deep pelvic veins
- has both an anterior internal plexus and posterior internal plexus (together called epidural plexus)
- anterior internal plexus associated with the anterior longitudinal ligament (ALL)
- posterior internal plexus associated with the supraspinous ligaments
- a conduit for infection and metastasis of cancers from breast/prostate/bladder to head and neck
Dura Mater:
- what layer
- what 2 things does it form
Dura mater:
- Tough, outermost membrane
- Forms root sleeve (blends with epineurium, the outer CT covering of spinal nerves)
- Forms spinal dural sac (at S3 vertebral level)
Arachnoid mater
- what layer
- what space does it enclose? (and 2 ways it forms connections)
- important property
- Delicate, middle membrane
- Avascular
- Encloses CSF-filled subarachnoid space
- Held against dura by CSF pressure
- Arachnoid trabeculae connect arachnoid and pia
Arachnoid trabeculae
Arachnoid trabeculae connect arachnoid and pia in subarachnoid space (in brain and spinal cord)
Pia mater:
- what layer
- what does it contain
Pia Mater:
- Delicate, innermost membrane
- Adherent (shrink-wrap) to brain, spinal cord, and nerve roots
- Contains denticulate ligaments:
- Lateral extensions of pia
- Attach to arachnoid/dura
- Provide support for spinal cord
Denticulate ligaments
- what is it
- what does it attach to
- purpose
Denticulate ligaments
- Lateral extensions of pia
- Attach to arachnoid/dura
- Provide support for spinal cord
Overview of neuron composition:
A. The _____ (containing the nucleus), is part of the receptive surface of the neuron.
B. The _____, an extension of the cell body specializing in receiving input from other neurons.
C. The _____, is wrapped in myelin and conducts information via action potentials.
D. The _____, are the transmitting region of the neuron.
Overview of neuron composition:
A. The cell body/soma (containing the nucleus), is part of the receptive surface of the neuron.
B. The dendrite, an extension of the cell body specializing in receiving input from other neurons.
C. The axon, is wrapped in myelin and conducts information via action potentials.
D. The synaptic varicosities, are the transmitting region of the neuron (aka axon terminal)
Neuron location
- Collections of neuronal cell bodies INSIDE the CNS (brain & spinal cord) are called ______
- what type of function?
- Collections of neuronal cell bodies OUTSIDE the CNS that are located in the PNS (every else) are called _____
- what type of function?
Neuron location
- Collections of neuronal cell bodies INSIDE the CNS (brain & spinal cord) are called nuclei.
- Nuclei can be sensory OR motor in function.
- Collections of neuronal cell bodies OUTSIDE the CNS that are located in the PNS (every else) are called ganglia.
- Ganglia can be sensory OR motor in function.
Efferent Neurons
- are what type of neuron (motor or sensory)
- carry info from where to where
- 2 subtypes
Efferent neurons:
- motor neurons
- carry info away from the CNS towards peripheral effector tissue
- 2 major efferent systems: somatic (voluntary) and autonomic
- The cell bodies of preganglionic general visceral efferent neurons (autonomic motor neurons) are located ______ at _____ spinal levels.
- then extends it’s long axon through a _____, to eventually a _______
- The post-ganglionic neurons are located ______ in various _______
Autonomic Efferent (motor) Neurons:
- The cell bodies of preganglionic general visceral efferent neurons (autonomic motor neurons) are located in the lateral horns (aka intermediolateral column) in the spinal cord gray matter ONLY at T1-L2 and S2-S4 spinal levels.
- From the gray matter of the spinal cord, it extends it’s long axon through a ventral root, to eventually a spinal nerve
- The post-ganglionic neurons are located OUTSIDE the CNS in various visceral motor ganglia
multipolar neuron
Multipolar neurons = Efferent (motor) neurons
- the most common type of neuron
- located in the central nervous system (brain and spinal cord) and in autonomic ganglia.
- has multiple dendrites extending from the cell body and a single axon extending in the opposite direction.
pseudounipolar neuron
- where is the soma
- what branches where
- what types of neurons
Pseudounipolar neuron = Affarent (sensory) neuron
- soma is located in the dorsal root ganglion (not in the gray matter of the spinal cord)
- dorsal root ganglion = complex of soma outside of the CNS
- has a single axon that splits into one branch that runs to the peripheral tissues and a second branch that leads to the spinal cord.
Affarent neurons:
- carry information from _____ to _____
- the cell body is located outside _____ in the _____
- name this subtype of neuron
- 2 subtypes: _____ and _____
Affarent neurons: Sensory
- carry information from peripheral sensory receptors towards the CNS
- the cell body is located outside the CNS in the sensory dorsal root ganglion
- pseudounipolar neuron (soma located in the dorsal root ganglion, which is a complex of soma outside the CNS)
- 2 subtypes: voluntary (somatic) and autonomic (visceral)
Affarent vs. Efferent
- location of soma
- location of horns/roots/rootlets
Affarent (sensory) neurons
- soma is located outside of the CNS in dorsal root ganglion
- dorsal (posterior) horn -> rootlets -> root
Efferent (motor) neurons:
-
Soma of voluntary efferent:
- cell bodies of general somatic efferent neurons are located in the ventral horns of the spinal cord gray matter at all spinal levels
-
Soma of autonomic efferent:
- cell bodies of preganglionic general visceral efferent neurons (autonomic motor neurons) are in lateral horns in the spinal cord gray matter ONLY at T1-L2 and S2-S4 levels
- the post-ganglionic neurons are located outside of the CNS in various visceral motor ganglia
- ventral (anterior) horn -> rootlets -> root
Spinal (peripheral) Nerves:
- Exit the _____ through _____
- ______ total pairs (one on each side of the body) attached to the spinal cord
- # cervical, # thoracic, # lumbar, # sacral, # coccygeal
- what type (motor or sensory)
Spinal (peripheral) Nerves:
- Exit the vertebral column through intervertebral foramina
-
31 total pairs (one on each side of the body) attached to the spinal cord
- 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccygeal
- MIXED (sensory and motor)
- sensory neurons are associated with ______
- motor neurons are associated with ______
- sensory neurons are associated with dermatomes (affarent) (blue)
- we have sensory perceptors (perhaps due to pain) that we follow back into the system, arriving where the soma are in the dorsal root ganglia and then going onto the spinal cord
- motor neurons are associated with myotomes (efferent) (red)
- in spinal cord, we have efferents leaving the ventral root, coming out to do motor control of muscles
Somatic afferents of the thorax
- what do somatic and afferent mean
- clinical relevance
Somatic afferents of the thorax
- somatic = body wall
- afferent = sensory
-
Clinical Relevance (Herpes zoster infection): Reactivation of chicken pox viruses which reside dormant in the Dorsal root ganglion.
- Symptoms: Sharp burning pain follows a strip of dermatome supplied by the involved nerve. Sometimes accompanied by skin eruption.
Innervation of the body wall
- Sensory (afferent) is perceived by the_____ axons carried in _____
- Motor is carried by the _____ axons carried in the same _____
Innervation of the body wall (somatic neurons)
- Sensory (affarent) is perceived by the general somatic afferent axons carried in ventral/anterior primary rami and therefore are segmental!
- Motor is carried by the general somatic efferent axons carried in the same ventral/anterior primary rami and therefore are segmental!
HINT: all named “nerves” are ventral primary rami (two exceptions in HN greater occipital and suboccipital nerves which are dorsal/posterior primary rami)
Somatic Body Wall:
- all named “nerves” are ______
- two exceptions in _____ and _____ which are _____
Somatic Body Wall
- All named “nerves” are ventral primary rami
- example: long thoracic nerve (brachial plexus - ventral primary rami of spinal nerves C5-C7) and phrenic nerve (ventral primary rami of spinal nerves C3-C5 - cervical plexus)
- two exceptions in head and neck - greater occipital and suboccipital nerves which are dorsal/posterior primary rami
Somatic Affarents (Sensory) of the Thorax
Two of the ventral primary rami from specific spinal cord levels are given new names:
- _______ (name and nerves)
- _______ (name and nerves)
Somatic Affarents (Sensory) of the Thorax
Some of the ventral primary rami from specific spinal cord levels are given a new name:
- Thoracoabdominal nerves (resemble intercostals nerves) – anterior primary rami of inferior six thoracic nerves (T7-T11)
- Subcostal nerve – anterior primary ramus of T12 spinal nerve
Herpes zoster:
- The virus that causes shingles and chicken pox, which “hides” in _____
- If the virus becomes active, it will appear in the region supplied by the _____ in this _____
- Thus, pain, redness, and swelling appears in the ______ supplied by the involved ______
Herpes zoster
- The virus that causes shingles and chicken pox, “hides” in spinal ganglion.
- If the virus becomes active, it will appear in the region supplied by the nerve cells in this spinal ganglion.
- Thus, pain, redness, and swelling appears in the dermatome supplied by the involved nerve.
Spinal Nerve (e.g. reflex arc)
- Pathway of afferent in back
- Pathway of efferent in back
- Pathway of afferent everywhere else
- Pathway of efferent everywhere else
Spinal Nerve (e.g. reflex arc)
-
Pathway of afferent in back: Sensory = Pink (e.g. you were stabbed in the back)
- you would feel pain coming in through a dorsal ramus -> spinal nerve -> to the soma in the dorsal root ganglion -> into the spinal cord dorsal root (in posterior horn gray matter)
-
Pathway of efferent in back: Motor = Green (e.g. how you would react to pain of being stabbed in the back)
- motor (to move away from knife) would come out of the ventral horn -> ventral root -> dorsal root ganglion -> spinal nerve -> travel out through the dorsal ramus to contract your back muscle
-
Pathway of afferent everywhere else: Sensory = Blue (e.g. you burn your finger)
- would feel that pain via sensory neurons that travel through ventral ramus -> spinal nerve -> dorsal root -> dorsal horn
-
Pathway of efferent everywhere else: Motor = Yellow (to move hand off hot pan)
- ventral horn -> ventral root -> spinal nerve -> ventral ramus -> hand muscles (anywhere but midline of the back)
Roots carry _____ modality
- dorsal root carries _____
- ventral root carries _____
Roots carry only one modality
- dorsal root carries sensory (afferent)
- ventral root carries motor (efferent)
Spinal nerves carry _____ modality/modalities
- location of spinal nerves: ________
Spinal nerves carry mixed modalities (motor and sensory)
- location of spinal nerves: intervertebral foramen
Rami carry _____ modality/modalities
- dorsal ramus carries
- ventral ramus carries
Rami carry mixed (motor and sensory) modalities
- dorsal ramus carries: skin along the midline of back and intrinsic back muscles
- ventral ramus carries: everywhere else
The spinal cord grows ______ than the bony vertebral column; thus ‘shifting’ the cord to _____ & tapering to an end between _____ and _____ spinal levels
- shape of spinal cord as a fetus and how it changes
- what is the significance of this?
The spinal cord grows slower than the bony vertebral column; thus ‘shifting’ the cord to a higher level & tapering to an end between L1 and L2 spinal levels
- in fetus: you have a full C shaped curvature (completely kyphotic) but as we grow, the spinal cord shifts to a higher level, so the end of the spinal cord resides at the bony level L1-L2, but the soft structure itself (nerves) corresponds to the sacral region nerves
- clinincal significance: therefore, if you are concerned about a trauma break to the thoracic region, the actual nerve damage may be in the lower thoracic or lumbar region (example: if trauma to location of green arrow in picture)
where does the spinal cord end at the bony level?
- how does this relate to the conus medullaris?
- how does this relate to the cauda equina?
- how does this relate to the filum terminale?
where does the spinal cord end at the bony level? L1-L2
- how does this relate to the conus medullaris?
- this is the location of the conus medullaris = the tapered, lower end of the spinal cord
- how does this relate to the cauda equina?
- the cauda equina are the nerve roots extending below conus medullaris
- these are the ventral rami (nerves) predesined to be S1, S2, S3, S4….. that have “jump ship” at the conus medullaris to exit to their predestined intervetebral foramina
- located within the subarachnoid space (lumbar cistern) below the level of the conus medullaris (submerged in CSF)
- looks like a horse’s tail
- the cauda equina are the nerve roots extending below conus medullaris
- how does this relate to the filum terminale?
- filum terminale are thin fibrous meninges at end of conus medullaris that extend to attach it to the sacrum and coccyx
