Spinal Cord (CNS) Flashcards
What is the spinal cord?
terminal cord-like part of CNS located in vertebral canal
How long is the spinal cord?
43-45 cm (occupies 2/3 of vertebral canal)
Where does the spinal cord start and end?
start: medulla oblongata (at level of foramen magnum)
end: level of LI-LII intervertebral disc
Where does the spinal cord end in infants?
as low as level of LIII
Why is there a difference between the end of the spinal cord in adults and infants?
elongation of spinal cord stops at age 4-5, but growth of vertebral column continues
External Features of the Spinal Cord
What does the spinal cord look like when viewed externally?
cylinder with 2 enlargements in its cervical and lumbar regions
External Features of the Spinal Cord
What does the cervical enlargement give rise to?
nerves innervating the upper limbs
External Features of the Spinal Cord
What does the lumbar (lumbosacral) enlargement give rise to?
nerves innervating the lower limbs
External Features of the Spinal Cord
How does the conus medullaris form?
spinal cord tapers down inferior to lumbar enlargement
External Features of the Spinal Cord
What are the 2 main longitudinal grooves on the surface of the spinal cord?
ventral (anterior) median fissure
dorsal (posterior) median sulcus
External Features of the Spinal Cord
What emerges from the ventral (anterior) median fissure?
on either side, ventral (motor) rootlets of the spinal nerves
External Features of the Spinal Cord
What emerges from the dorsal (posterior) median sulcus?
on either side, dorsal (sensory) rootlets of the spinal nerves
External Features of the Spinal Cord
What do ventral rootlets join to form
ventral (motor) root of the spinal nerves
External Features of the Spinal Cord
What do dorsal rootlets join to form?
dorsal (sensory) root of spinal nerves
External Features of the Spinal Cord
What is each dorsal root of the spinal nerve associated with?
dorsal root ganglion
External Features of the Spinal Cord
What does the dorsal root ganglion house?
cell bodies of the sensory neurons
External Features of the Spinal Cord
What is each spinal nerve formed by?
union of ventral and dorsal roots
External Features of the Spinal Cord
What is the spinal cord segment?
section of spinal cord that gives rise to a pair of spinal nerve
External Features of the Spinal Cord
How many spinal cord segments are there? Name the types and how many there are.
31 spinal cord segments
- 8 cervical segments (C1-C8)
- 12 thoracic segments (T1-T12)
- 5 lumbar segments (L1-L5)
- 5 sacral segments (S1-S5)
- 1 coccygeal segment (Co)
Internal Features of the Spinal Cord
Describe the gray matter of the spinal cord.
H-shaped, with ventral (anterior) horn and dorsal (posterior) horn
Internal Features of the Spinal Cord
What is the gray commissure?
narrow strip that connect right and left halves of gray matter, and contains central canal
Internal Features of the Spinal Cord
What is the lateral horn?
a third horn between ventral and dorsal horns in some segments (T1 to L2, and S2 to S4)
Internal Features of the Spinal Cord
What do the lateral horns of T1 to L2 carry?
cell bodies of sympathetic neurons
Internal Features of the Spinal Cord
What do the lateral horns of S2 to S4 carry?
cell bodies of parasympathetic neurons
Internal Features of the Spinal Cord
What do ventral horns contain?
cell bodies of motor neurons
Internal Features of the Spinal Cord
What do the axons of motor neurons form?
motor (ventral) roots of spinal nerves
Internal Features of the Spinal Cord
What do dorsal horns contain?
cell bodies of sensory neurons
Internal Features of the Spinal Cord
What do the axons of sensory neurons form?
form dorsal root of spinal nerves - when neurons receive info from sensory neurons in dorsal root ganglia
**unsure of this question
Internal Features of the Spinal Cord
Where is the white matter and how is it organized?
surrounds gray matter
organized as ventral, lateral, and dorsal columns (funiculi) on each half of spinal cord
Internal Features of the Spinal Cord
What do the ventral, lateral, and dorsal columns of white matter contain?
tracts (bundles of myelinated nerve fibers) that travel along length of spinal cord
Internal Features of the Spinal Cord
What are the 2 main groups of tracts in the white matter?
ascending (sensory) tracts
descending (motor) tracts
Internal Features of the Spinal Cord
What do ascending (sensory) tracts do?
convey messages from periphery to upper centers of the nervous system
ie. dorsal (posterior) spinocerebrellar tract, dorsal column (medial lemniscus) tract, and lateral spinothalamic tract
Internal Features of the Spinal Cord
What do descending (motor) tracts do?
convey messages from upper centers of the nervous sytem to periphery
ie. lateral and ventral corticospinal tracts
Major Sensory Tracts (Pathways)
What do sensory tracts of the spinal cord do?
relay sensory info from sensory receptors to sensory areas of the brain
Major Sensory Tracts (Pathways)
What do sensory tracts consist of?
3 sets of neurons
exception: dorsal spinocerebellar tract
Major Sensory Tracts (Pathways)
Where is the first-order neuron?
dorsal root ganglion of spinal nerve
Major Sensory Tracts (Pathways)
What does the first-order neuron do?
conducts impulses from sensory receptors to spinal cord or medulla oblongata
Major Sensory Tracts (Pathways)
Where is the second-order neuron?
either in dorsal horn of spinal cord, or within medulla oblongata
Major Sensory Tracts (Pathways)
What does the second-order neuron do?
relays impulses to thalamus
Major Sensory Tracts (Pathways)
Where is the third-order neuron?
thalamus
Major Sensory Tracts (Pathways)
What does the third-order neuron do?
conveys impulses to general sensory area of parietal lobe of cerebral cortex
Major Sensory Tracts (Pathways) - Dorsal Spinocerebellar Tract
What does this tract do?
conducts impulses concerned with unconscious proprioception (sense of position), collected from joints and muscles of lower limb and trunk, to cerebral cortex
**unconscious proprioception from upper limb is conveyed to the cerebellum via a different tract
Major Sensory Tracts (Pathways) - Dorsal Spinocerebellar Tract
Where is the first-order neuron of this tract?
What does it synapse with?
in dorsal root ganglion of spinal nerve
synapses with second-order neuron that resides in dorsal horn of spinal cord
Major Sensory Tracts (Pathways) - Dorsal Spinocerebellar Tract
What do axons of second-order neurons form?
dorsaal spinocerebellar tract that travels in lateral column (funiculus) of the spinal cord
Major Sensory Tracts (Pathways) - Dorsal Spinocerebellar Tract
Where does this tract travel?
in lateral column (funiculus) of spinal cord
ascends through medulla oblongata, and ends to the ipsilateral cerebellar cortex after passing through inferior cerebellar peduncle
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
What does this tract do?
conducts nerve impulses for conscious proprioception, and discriminative (fine) touch
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
Where is conscious proprioception collected from?
joints and muscles
exception: temporomandibular joint
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
Where is discriminative (fine) touch collected from?
entire body
exception: most of head region
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
Where is the first-order neuron of this tract?
in dorsal root ganglion of spinal nerve
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
Where does the axon of the first-order neuron travel?
What does it synapse with
ascends in dorsal column of spinal cord
synapses with the second-order neuron in nucleus gracilis and nucleus cuneatus within medulla oblongata
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
Where does the axon of the second-order neuron travel?
What does it synapse with?
crosses midline and ascends through brainstem as the medial lemniscus
medial lemniscus synapses with third-order neuron in thalamus
Major Sensory Tracts (Pathways) - Dorsal Column (Medial Lemniscus) Tract
What does the axon of the third-order neuron do?
projects to sensory area of the cerebral cortex for conscious sensation
Major Sensory Tracts (Pathways) - Lateral Spinothalamic Tract
What does this tract do?
conveys impulses concerned with pain and temperature, collected form entire body (except head region)
Major Sensory Tracts (Pathways) - Lateral Spinothalamic Tract
Where is the first-order neuron of this tract?
What does it synapse with?
in dorsal root ganglion of spinal nerve
synapses with second-order neuron in dorsal horn of spinal cord
Major Sensory Tracts (Pathways) - Lateral Spinothalamic Tract
Where does the axon of the second-order neuron travel?
crosses midline and ascends through lateral column of spinal cord as the lateral spinothalamic tract
Major Sensory Tracts (Pathways) - Lateral Spinothalamic Tract
What does the lateral spinothalamic tract synapse with?
third-order neuron in the thalamus
Major Sensory Tracts (Pathways) - Lateral Spinothalamic Tract
What does the third-order neuron do?
projects to sensory area of the cerebral cortex where the info is processed into conscious sensation
Major Sensory Tracts (Pathways) - Anterior Spinothalamic Tract
What is this tract?
ascending tract with similar neuronal design (origin, course and termination)
Major Sensory Tracts (Pathways) - Anterior Spinothalamic Tract
What does this tract do?
conveys impulses of non-discriminative (crude) touch
Major Motor Tracts (Pathways)
What do motor tracts do?
relay motor instruction either from motor areas of frontal lobe of cerebral cortex or some of the nuclei of the brainstem to the spinal cord
Major Motor Tracts (Pathways)
What are the 2 types?
pyramidal
extrapyramidal
Major Motor Tracts (Pathways)
What do pyramidal tracts do?
convey impulses for control of skeletal muscles of limbs and trunk
Major Motor Tracts (Pathways)
What tracts do pyramidal tracts include? (2)
lateral corticospinal tract
ventral corticospinal tract
Major Motor Tracts (Pathways)
What do extrapyramidal tracts do?
conduct signals that regulate body movements that are subconscious or postural in nature
Major Motor Tracts (Pathways)
What tracts do extrapyramidal tracts include? (4)
rubrospinal tract
tectospinal tract
vestibulospinal tract
reticulospinal tract
Major Motor Tracts (Pathways)
How many sets of neurons do both the pyramidal and extrapyramidal tracts consist of?
2
upper motor neurons (UMNs)
lower motor neurons (LMNs)
Major Motor Tracts (Pathways)
Where are the upper motor neurons (UMNs) of the pyramidal tracts?
in motor cortex of cerebral hemispheres
Major Motor Tracts (Pathways)
Where are the upper motor neurons (UMNs) of the extrapyramidal tracts?
within brainstem and cerebellar cortex
Major Motor Tracts (Pathways)
Where are the lower motor neurons (UMNs) of both the pyramidal and extrapyramidal tracts?
in anterior horn of spinal cord
Major Motor Tracts (Pathways)
How do the axons of LMNs exit the spinal cord?
What do they target?
exit as the ventral root of the spinal nerve
target skeletal muscles
Major Motor Tracts (Pathways)
Where are the UMNs of the corticospinal tract?
in motor cortex of cerebrum, and their axons descend through brainstem
Major Motor Tracts (Pathways)
What is the lateral corticospinal tract?
majority of UMN axons (in motor cortex) decussate at level of caudal medulla oblongata, and continue in lateral column of spinal cord as the lateral corticospinal tract
Major Motor Tracts (Pathways)
What do the axons of the UMNs of the lateral corticospinal tract synapse with?
LMNs of the ipsilateral ventral horn of the spinal cord
Major Motor Tracts (Pathways)
What do the rest of the axons of the corticospinal tract do?
continue to descend in ventral column of spinal cord, as the ventral corticospinal tract
which dcussate before synapsing with LMNs of the contralateral ventral horn of the spinal cord
Major Motor Tracts (Pathways)
What is the rubrospinal tract?
part of extrapyramidal pathways
UMNs reside in red nucleus of midbrain
their axons decussate at level of midbrain, and then descend through medulla oblongata and lateral column of spinal cord
axons synapse with LMNs of ipsilateral ventral horn of spinal cord
