B7.016 Spinal Cord and Long Pathways Flashcards
how are neurons organized?
functional pathways or systems
composed of multi-neuron chains
transmit info from one part of the nervous system to another
facilitated by synaptic transmission
afferent
toward CNS
efferent
away from CNS
ascending
information from lower to higher levels
descending
information from higher to lower levels
corticospinal pathway
voluntary motor
dorsal column / medial lemniscus
sensory touch
anterolateral / spinothalamic
pain
tract
bundle of axons in the CNS (also fasciculus, lemniscus)
name of the tract often tells source and termination of axons
decussate
cross from one side of the brain to the other
somatotropy
adjacent structures in the body are represented by adjacent neurons in the CNS; contributes to regional specialization
organization of the dorsal column
sacral region most medial
cervical region most lateral
organization of the ventral column
sacral region most lateral
CS
ALS
cervical region most medial
relative lengths of spinal cords and vertebral column
spinal cord is much shorter
stain for cell bodies of neurons
Nissl Stain
gray matter stains darker because cell bodies congregate there
dorsal
sensory
ventral
motor
nucleus
group of cell bodies within the CNS
substantia gelatinosa
area within dorsal horn with pain neuron synapses
contains many cell bodies, but very few axons (appears white with myelin staining)
white matter staining
stains dark when myelin stain is used
many axons run through the white matter
describe the structure of the corticospinal system
2 neuron pathway carrying information from the motor cortex to striated muscles
responsible for voluntary motor control
2 neurons in the corticospinal system
- cortical motoneuron = upper motoneuron
2. alpha motoneuron = lower motoneuron
upper motoneuron
in motor cortex (precentral gyrus)
axons terminate with monosynaptic connections on alpha motoneurons (within ventral horn of spinal cord)
lower motoneuron
in ventral horn of spinal cord
axon projects through ventral root to striated muscle
describe the decussation of the corticospinal pathways
pyramidal decussation
occurs at the cervicomedullary junction (caudal end of medulla)
give a brief overview of the course of the corticospinal pathway
- precentral gyrus (motor cortex)
- posterior limb of internal capsule
- pyramidal decussation @ caudal end of medulla
- lateral corticospinal tract
- synapse in anterior horn of level of LMN
- LMN leaves through anterior root and travels to target muscle
what happens when you damage neurons in the corticospinal pathway
loss of voluntary motor control of the body
-paralysis
UMN damage
spastic paralysis
tone present
LMN damage
flaccid paralysis
limp muscle
relationship between deficit and site of lesion in corticospinal
- rostral to the decussation = contralateral
- caudal to the decussation = ipsilateral
- in spinal cord = caudal to lesion
overview of somatosensory pathways
information from periphery enters the spinal cord and ascends to the cortex 2 pathways: 1. dorsal column / medial lemniscus -fine touch -proprioception -vibration 2. ALS/ spinothalamic -pain and temperature -crude touch
dorsal root divisions
medial division = large fibers, DC/ML
lateral division = small fibers, ALS
characterize the DC/ML system
sensory modalities: -vibration -proprioception -discriminative touch large diameter, myelinated fibers rapidly conducting high fidelity system
characterize the ALS/spinothalamic system
sensory modalities: -pain -temperature small diameter myelinated and unmyelinated fibers slowly conducting
discuss the structure of the DC/ML pathway
three neurons
ascending pathway
carries fine touch, proprioception, and vibration information to the somatosensory cortex (postcentral gyrus)
anatomy of the primary DC/ML pathways
cell body of primary neuron located in dorsal root ganglion (DRG)
peripheral (distal) process innervated skin, joint or muscle
central process terminates in the medulla in either the
-nucleus cuneatus (arm)
-nucleus gracilis (leg)
together, these are called the dorsal column nuclei
DRG axons form the dorsal columns in the spinal cord
-gracile fasiculus (medial, legs)
-cuneate fasiculus (lateral, arms)
where is the site of decussation in the DC/ML pathway
medulla
anatomy of the secondary DC/ML pathways
axons of neurons in the dorsal column nuclei decussate in the medulla and ascend to the thalamus (this bundle of axons is called the medial lemniscus)
anatomy of the tertiary DC/ML pathways
axons in the medial lemniscus synapse in the ventral posterolateral (VPL)nucleus in the thalamus
VPL neurons send their axons to synapse in the primary somatosensory cortex
nature of deficit when you damage the DC/ML pathway
loss of touch, vibration, proprioception from specific regions
relationship between deficit and site of lesion in DC/ML
- rostral to the decussation = contralateral
- caudal to the decussation = ipsilateral
- in spinal cord = ipsilateral body surface, involving dermatomes at and below the level of the lesion
discuss the structure of the ALS/ spinothalamic pathway
three neurons
ascending pathways
carries pain and temp info to the somatosensory cortex (postcentral gyrus)
anatomy of primary ALS/ spinothalamic pathway
cell body of primary neuron located in dorsal root ganglion (DRG)
peripheral (distal) process of the DRG neuron innervates skin
central (proximal) process of DRG enters the spinal cord, ascends a level or two, and then synapses in the dorsal horn of the spinal cord (substantia gelatinosa)
anatomy of secondary ALS/ spinothalamic pathway
axons of the dorsal horn neurons decussate in the anterior white commissure
ascend to the thalamus in the spinothalamic tract, also called anterolateral pathway
anatomy of tertiary ALS/ spinothalamic pathway
axons in the spinothalamic tract synapse in the ventral posterolateral (VPL) nucleus in the thalamus
VPL neurons send their axons to synapse in the primary somatosensory cortex
nature of deficit when you damage the ALS/ spinothalamic pathway
loss of pain and temperature sensation from specific regions of the body
relationship between deficit and site of lesion in ALS/ spinothalamic pathways
- rostral to the decussation = contralateral
- caudal to the decussation = ipsilateral
- in spinal cord = contralateral body surface, involving dermatomes at and below the level of the lesion
which spinal cord level has the most white matter
cervical/ thoracic
which spinal cord level has the most gray matter
sacral / lumbar
SNS pathways from the spinal cord
thoracolumbar
PNS pathways from the spinal cord
craniosacral
