Spinal Cord (CNS) Flashcards by Sarah L

What is the spinal cord?

terminal cord-like part of CNS located in vertebral canal

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How long is the spinal cord?

43-45 cm (occupies 2/3 of vertebral canal)

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Where does the spinal cord start and end?

start: medulla oblongata (at level of foramen magnum)
end: level of LI-LII intervertebral disc

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Where does the spinal cord end in infants?

as low as level of LIII

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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

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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

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External Features of the Spinal Cord

What does the cervical enlargement give rise to?

nerves innervating the upper limbs

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External Features of the Spinal Cord

What does the lumbar (lumbosacral) enlargement give rise to?

nerves innervating the lower limbs

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External Features of the Spinal Cord

How does the conus medullaris form?

spinal cord tapers down inferior to lumbar enlargement

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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

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External Features of the Spinal Cord

What emerges from the ventral (anterior) median fissure?

on either side, ventral (motor) rootlets of the spinal nerves

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External Features of the Spinal Cord

What emerges from the dorsal (posterior) median sulcus?

on either side, dorsal (sensory) rootlets of the spinal nerves

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External Features of the Spinal Cord

What do ventral rootlets join to form

ventral (motor) root of the spinal nerves

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External Features of the Spinal Cord

What do dorsal rootlets join to form?

dorsal (sensory) root of spinal nerves

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External Features of the Spinal Cord

What is each dorsal root of the spinal nerve associated with?

dorsal root ganglion

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External Features of the Spinal Cord

What does the dorsal root ganglion house?

cell bodies of the sensory neurons

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External Features of the Spinal Cord

What is each spinal nerve formed by?

union of ventral and dorsal roots

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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

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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)

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Internal Features of the Spinal Cord

Describe the gray matter of the spinal cord.

H-shaped, with ventral (anterior) horn and dorsal (posterior) horn

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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

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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)

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Internal Features of the Spinal Cord

What do the lateral horns of T1 to L2 carry?

cell bodies of sympathetic neurons

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Internal Features of the Spinal Cord

What do the lateral horns of S2 to S4 carry?

cell bodies of parasympathetic neurons

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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

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Spinal Cord (CNS) Flashcards

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