Exam 4, Chapter 12: The Spinal Cord Flashcards
dorsal root ganglia are?
Sensory neurons
Surrounding the Neural tube,
Interneurons (assosiciation neurons), which receive sensory input from sensory neurons come from?
dorsal cells
Surrounding the Neural tube,
Motor neurons from?
ventral cells!
enclosed within the vertebral column from the foramen magnum to L1 / L2
Spinal Cord Gross Anatomy
afferent fibers (sensory)
Spinal Cord Gross Anatomy
Ascending fibers
efferent fibers (motor)
Spinal Cord Gross Anatomy
Descending fibers
protected by bone, meninges, and CSF
Spinal Cord Gross Anatomy
space between the vertebrae and the dural sheath (dura mater) which isfilled with fat and a network of veins
Spinal Cord Gross Anatomy
Epidural Space
Epidural anesthesia is delivered into this space via flexible cannula
Spinal Cord Gross Anatomy
Epidural space
terminal portion of the spinal cord
Spinal Cord Gross Anatomy
Conus medullaris
End of cord narrows to a cone shape between L1 and L2
Spinal Cord Gross Anatomy
Conus Medullaris
fibrous extension of the pia mater; anchors the spinal cord to the coccyx
Spinal Cord Gross Anatomy
Filum terminale
delicate shelves of pia mater; attach the spinal cord to the vertebrae
Spinal Cord Gross Anatomy
Denticulate ligaments
31 pairs attach to the cord by paired roots
Spinal Cord Gross Anatomy
Spinal nerves
8 cervical pair; 12 thoracic pair; 5 lumbar pair; 5 sacral pair; 1 coccygeal
Spinal Cord Gross Anatomy
Spinal Nerves
sites where nerves serving the upper and lower limbs emerge, so large ventral horns and multiple nerve roots leaving the cord in these regions
Spinal Cord Gross Anatomy
Cervical and Lumbar Enlargements
collection of nerve roots at the inferior end (below L2)
Spinal Cord Gross Anatomy Cauda equina (horse tail)
- Dura mater (single layer only; no periosteal attachment)
- Arachnoid mater with CSF in subarachnoid space
- Pia mater
Spinal Cord Gross Anatomy
Meninges
also circulates in the central canal which continues superiorly into the medulla oblongata
Spinal Cord Gross Anatomy
CSF
separates ventral funiculi (white matter tract regions)
Cross-Sectional Anatomy of Spinal Cord
Ventral median fissure
divides dorsal funiculi (white matter tract regions)
Cross-Sectional Anatomy of Spinal Cord
Dorsal median sulcus
consists of soma, unmyelinated processes and neuroglia
Cross-Sectional Anatomy of Spinal Cord
Gray Matter Columns
Gray Matter
connects R / L masses of gray matter; encloses central canal
Cross-Sectional Anatomy of Spinal Cord
Gray Matter Columns
Gray Commissure
Interneurons (Therefore, a sensory synapse will occur here)
Cross-Sectional Anatomy of Spinal Cord
Gray Matter Columns
Dorsal Horns
Somatic (voluntary) motor neurons & some interneurons
Cross-Sectional Anatomy of Spinal Cord
Gray Matter Columns
Ventral Horns
Contain sympathetic motor fibers; this column is present in T1-L2 only
Cross-Sectional Anatomy of Spinal Cord
Gray Matter Columns
Lateral Horns
dorsal root ganglion (sensory nerve cell bodies) lead to dorsal roots which
expand into rootlets before entering the spinal cord
Cross-Sectional Anatomy of Spinal Cord
Spinal Roots
Dorsal half
May synapse at a dorsal horn interneuron or continue via axons in the white matter
columns towards the brain
Cross-Sectional Anatomy of Spinal Cord
Spinal Roots
Dorsal Half
motor rootlets join to form motor roots
Cross-Sectional Anatomy of Spinal Cord
Spinal Roots
Ventral half
fuse laterally to form short spinal nerves
Cross-Sectional Anatomy of Spinal Cord
Spinal Roots
Dorsal and ventral roots
Body representation in four zones (maintain spatial relationships)
Cross-Sectional Anatomy of Spinal Cord
Spinal Roots
Gray matter Somatotopy
visceral sensory (VS), visceral motor (VM)
Cross-Sectional Anatomy of Spinal Cord
Visceral representation on the internal aspect
Gray matter Somatotopy
Somatic representation on the external aspect
Cross-Sectional Anatomy of Spinal Cord
Gray matter Somatotopy
somatic sensory (SS), somatic motor (SM)
ascending, descending, and transversely
Cross-Sectional Anatomy of Spinal Cord
White Matter Columns
Three Directions of Fiber movement
dorsal, ventral, lateral (T1-L2 only)
Cross-Sectional Anatomy of Spinal Cord
White Matter Columns
are Divided into three columns (funiculi)
Each white matter column contains several fiber tracts
- Fiber tract names reveal their origin and destination
- Fiber tracts are composed of bundled axons with similar sensory functions
Cross-Sectional Anatomy of Spinal Cord
White Matter Columns
All pathways decussate at some point
- Most consist of two or three neurons (relays)
- Most maintain somatotopy (organizational mapping)
- Pathways are paired (one on each side of the spinal cord or brain)
Neuron Pathways: Sensory (Afferent-Ascending)
General Features
(of two or more things) cross or intersect each other to form an X.
Neuron Pathways: Sensory (Afferent-Ascending)
decussate
The central processes of “first-order neurons” branch diffusely as they enter the spinal cord
and medulla
-conduct impulsees and proprioceptors
-most synapse with 2nd-order neurons (interneuron) in the spinal cord or medullary nuclei
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
conduct impulses from cutaneous receptors (discriminative touch, pressure, vibration , temperature, pain)
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Conduct impulses
First Order Neuron
(feedback on position of joints & relative movement of joints)
-other branches take part in “spinal cord reflexes”
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Proprioceptors
most branches synapse with these, aka “interneuron” in the spinal cord or medullary nuclei
(nuclei in medulla oblongata)
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Second-order neurons
“red nucleus”
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Medulla oblongata nuclei
Location of third order-(inter)neuron
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Axons extend to thalamus
Extension of Third Order Neuron Axons
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Primary Somatosensory Cortex
Subconscious Second Order Axons where?
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Cerebellum
no additional synapses
Three Ascending Pathways?
Which send impulses to contralateral somatosensory cortex via thalamus?
Which sends ipsilateral impulses to cerebellum and do not contribute to sensory perception?
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
1. Dorsal Column- Medial Lemniscal Pathway
2. Spinothalamic Pathway
3. Spinocerebellar Pathway
a. 1 and 2
b. 3
Three Ascending Pathways
-These pathways are responsible for discriminative touch and pressure, vibration
and conscious proprioception
-Many receptors in a small area (dense receptive field), so easy to localize the
source of sensation precisely
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Dorsal Column-Medial Lemniscal Pathway (Dorsal Tract Location)
Three Ascending Pathways
-First-order fibers travel into & ascend the spinal cord along the dorsal white
columns, synapsing at the corresponding nuclei in the medulla oblongata.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Dorsal Column-Medial Lemniscal Pathway (Dorsal Tract Location)
Three Ascending Pathways
-The second-order fibers decussate in the medulla and synapse in the thalamus.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Dorsal Column-Medial Lemniscal Pathway (Dorsal Tract Location)
Three Ascending Pathways
-Third-order fibers terminate in the somatosensory cortex.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Dorsal Column-Medial Lemniscal Pathway (Dorsal Tract Location)
Three Ascending Pathways
-These pathways are responsible for temperature, pain, coarse touch and pressure
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinothalamic Pathway
(Ventral and Lateral tract locations)
Three Ascending Pathways
-Fewer receptors, so aware of the sensation, but not as precisely localized
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinothalamic Pathway
(Ventral and Lateral tract locations)
Three Ascending Pathways
-First-order fibers synapse in the dorsal horn of the spinal cord.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinothalamic Pathway
(Ventral and Lateral tract locations)
Three Ascending Pathways
-Second-order fibers decussate at the same spinal cord level, ascend the
spinothalamic fiber tracts and synapse in the thalamus.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinothalamic Pathway
(Ventral and Lateral tract locations)
Three Ascending Pathways
-Third-order fibers terminate in the somatosensory cortex.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinothalamic Pathway
(Ventral and Lateral tract locations)
Third Ascending Pathway
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinocerebellar Pathway
Three Ascending Pathways
-These pathways are responsible for subconscious proprioception.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinocerebellar Pathway
Three Ascending Pathways
-The tracts terminate in the cerebellum and therefore do not contribute to sensory perception.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinocerebellar Pathway
Three Ascending Pathways
-First-order neurons synapse in the dorsal horn of the spinal cord.
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinocerebellar Pathway
Three Ascending Pathways
-Second-order fibers terminate in the “ipsilateral cerebellum.”
Neuron Pathways: Sensory (Afferent-Ascending)
Ascending Pathway Organization
Spinocerebellar Pathway
Descending Pathways
-Descending tracts deliver impulses from the brain to the spinal cord, and are divided into
two groups
Neuronal Pathways: Motor (Efferent/Descending)
General Feature
Descending Pathways
-(from the motor cortex) , decussate at MEDULLA. descend from the motor
cortex regions and do not synapse until reaching the correct spinal cord level
Neuronal Pathways: Motor (Efferent/Descending)
General Features
=Direct pathways = pyramidal tracts
Descending Pathways
-(all others from the cerebellum, basal
ganglia, etc.) descend from sub-cortical motor nuclei and are multi-synaptic, complex
and often influenced via reflex activity
Neuronal Pathways: Motor (Efferent/Descending)
General Features
=Indirect Pathway=extrapyramidal tracts
Descending Pathways
-Motor pathways involve two motor neurons (upper and lower)
Neuronal Pathways: Motor (Efferent/Descending)
General Features
Descending Pathways
-pyramidal cells of the motor cortex and the neurons of the subcortical motor nuclei
Neuronal Pathways: Motor (Efferent/Descending)
Upper Motor Neuron (UMN)
Descending Pathways
-ventral horn motor neurons which directly innervate the skeletal muscles
Neuronal Pathways: Motor (Efferent/Descending)
Lower Motor Neuron (LMN)
Descending Pathways
-The direct pathway regulates fast and fine (skilled) movements
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Descending Pathways
- UMN - Most fibers originate in the pyramidal neurons in the primary motor cortex and related motor cortices
- Lateral tracts decussate at medulla pyramids
- Ventral tracts decussat at spinal cord level
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Pathway Specific
Descending Pathways
- Impulses descend the corticospinal tracts (lateral and ventral)
- lateral decussate at medulla pyramid
- ventral tracts decussate at spinal cord level
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Pathway Specific
Descending Pathways
-impulses synapse in the
ventral horn (with an interneuron or directly to a LMN); innervate skeletal muscles
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Pathway Specific
Descending Pathways
-Lateral tracts (>80%) decussate at the medullary pyramids
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Pathway Specific
Descending Pathways
-parts innervate cranial nerve nuclei
Neuronal Pathways: Motor (Efferent/Descending)
Direct (Pyramidal System)
Pathway Specific
Descending Pathways
These motor pathways modulate pyramidal input, primarily affecting
- Axial muscles that maintain balance and posture (=postural tone)
- Muscles controlling coarse movements of the proximal limb joints
- Control of complex, multi-joint movements
- Head, neck and eye movement coordination
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
General Features
Descending Pathways
-UMN Fibers originate in the basal ganglia, substantia nigra, cerebellum, various brain stem
vestibular nuclei & some in the sensory cortex
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Descending Pathways Tracts primarily descend through the reticular formation (pons & medulla) UMN to LMN through Include: -Reticulospinal tract -Vestibulospinal -Rubrospinal -Tectospinal tracts
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Descending Pathways
- Reticular formation origin
- maintain balance via Posture
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Reticulospinal Tracts
Descending Pathways
- Vestibular nuclei origin
- maintain balance via posture
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Vestibulospinal tracts
Descending Pathways
- Red nucleus origin
- control of Flexor Muscles
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Rubrospinal tracts
Descending Pathways
- Superior colliculi origin
- mediates head & neck following eye movements
Neuronal Pathways: Motor (Efferent/Descending)
Indirect (Extrapyramidal) System
Pathway Specific
Tectospinal tracts
Clinical Correlates
Loss of motor function
Paralysis
-severe damage to the ventral root or ventral horn cells
Flaccid Paralysis
-Lower motor neurons are damaged and impulses do not reach muscles
Flaccid Paralysis
-There is no voluntary or involuntary control of muscles
Flaccid Paralysis
-only upper motor neurons are damaged
Spastic Paralysis
-Spinal neurons remain intact and muscles are stimulated irregularly by reflex activity
Spastic Paralysis
-There is no voluntary control of muscles
Spastic Paralysis
-contralateral side of body affected
opposite side affected
Spastic Paralysis
hemiplegia
Clinical Correlate
-A complete transection of the spinal cord at any level results in total motor and sensory loss
in regions inferior to the cut
Spinal Cord Injury (SCI) and Transection
Clinical Correlate
-transection between T1 and L1 (affects trunk & lower extremities)
Spinal Cord Injury (SCI) and Transection
Paraplegia
Clinical Correlate
-transection in the cervical region (affects trunk & all extremities)
Spinal Cord Injury (SCI) and Transection
Quadriplegia
Clinical Correlate
-Damage to the ___ causes sensory loss inferior to the level of damage
Spinal Cord Injury (SCI) and Transection
dorsal columns
Clinical Correlate
-Damage to the ____ would cause a combination of motor & sensory
loss inferior to the level of damage
Spinal Cord Injury (SCI) and Transection
ventral or lateral columns
Clinical Correlates
classifications : ASIA A, B, C, D, E
A Worst
E Normal function
Spinal Cord Injury (SCI) and Transection
American spinal Injury Assocation classifications
Clinical Correlates
Destruction of the ___ by the poliovirus
Poliomyelitis
Ventral horn motor neurons
Clinical Correlates Early symptoms: -fever, -headache, -muscle pain and weakness, -loss of somatic reflexes
Poliomyelitis
Clinical Correlates
Advanced symptoms –
-paralysis & muscle atrophy;
-recent surge in post-polio syndrome
Poliomyelitis
Clinical Correlates
Vaccines are readily available and can prevent infection
Poliomyelitis
Clinical Correlates
- a.k.a. Lou Gehrig’s disease;
- modern face of ALS = Stephen Hawking
Amyotrophic Lateral Sclerosis (ALS)
Clinical Correlates
-Progressive destruction of ventral horn motor neurons and fibers of the pyramidal tract
Amyotrophic Lateral Sclerosis (ALS)
Clinical Correlates
-Symptoms – progressive loss of the ability to speak, swallow and breathe
Amyotrophic Lateral Sclerosis (ALS)
Clinical Correlates
-Linked to malfunctioning genes for glutamate transporter (= excess excitotoxic glutamate)
Amyotrophic Lateral Sclerosis (ALS)
Clinical Correlates
- Death typically occurs within five years;
- Drug which inhibits glutamate signaling promising
Amyotrophic Lateral Sclerosis (ALS)
Clincal Correlate
- Incomplete closure of neural tube (caudal vertebral arches);
- no laminae or spinous process
Spina Bifida
Clincal Correlate
Varying degrees of severity
Spina Bifida
Clincal Correlate
-Mild form: ; hair patch / birth mark /dimple only
Spina Bifida
-Spina bifida occulta (20% of population)
Clincal Correlate
-Most severe form: (out-pocketing of meninges, CSF & spinal cord)
Spina Bifida
Myelomeningocele
Clincal Correlate
Prenatal ___ essential for complete neural tube closure
Spina Bifida
folic acid
CNS is established during the ___ month of development
first
Gender-specific areas appear in response to ___ (or lack thereof, if a Y chromosome)
testosterone
Maternal exposure to
-Radiation, drugs (e.g., alcohol and opiates), or infection can harm the fetus’ developing CNS
-Smoking decreases oxygen in the blood, which leads to neuron death & fetal brain damage
-
duh
The ___ s is one of the last areas of the CNS to develop
hypothalamu
___ develops slowly over the first 11 weeks
Visual cortex
Growth and maturation of the nervous system occurs throughout childhood and reflects
___
progressive myelination
Normal aging brings some cognitive declines, but these are not significant in healthy individuals until they reach their 80s
fact
Excessive use of alcohol causes signs of senility unrelated to the aging process
truth
