The Spinal Cord: Chapter 4

The spinal cord is internally divided into 31 segments that give rise to 31 pairs of spinal nerves: ___ cervical, ____ thoracic, __ lumbar, ___ sacral, and ___ coccygeal spinal nerve. Each segment is divided into an inner gray matter containing neuron cell _____ (bodies or tracts?) and and outer covering of white matter (with tracts or cell bodies)? The ventral horn of gray contains _____ and ________ motoneurons (neural tube), the intermediate horn contains (pre or post ganglionic neurons)?

8 12 5 5 1 =31 pairs neuron cell bodies (ganglia) tracts (white matter, funciulus) alpha (1a extrafusal fibers) gamma (type II sets tone of intrafusal fibers) IML = pre-ganglioninc that go through the white rami (gray rami= post ganglionic) either to dorsal or ventral horn.

All lesions of the spinothalamic tract in the spinal cord, brain stem, or cortex produce "contralateral" loss of pain and temperature below the lesion (because it decussates so soon) Note that a central cord lesion at the spinal canal (syringomyelia) produces bilateral or ipsilatearl loss of pain and temperature at the level of the lesion.

Bilateral.

Motor Pathways: CST axons leave the cerebral hemispheres through the _________ limb of the internal capsule and descend medially through the midbrain, pons, and medulla.

CST posterior limb (lenticulostriate arteires of the MCA)

The primary (1) afferent neurons of this pathway have their cell bodies in the dorsal root ganglia (DRG)?

DCML and the anterolateral system.

Sensory pathways: Most sensory systems use 3 neurons to project sensory modalities to the cerebral cortex except for CST (2 neurons, UMN and LMN) The first neuron (primary afferent neuron) has its cell body in the _________ of the spinal nerve. The first order axon enters the spinal cord and either synapses in the spinal cord (_________ system) or the brain stem (_______). The 1st, 2nd or 3rd neuron will decussate and project to the thalamus? The _____ neuron then projects from the thalamus (VPM (face) or VPL (body) to the somatosensory cortex of the parietal lobe. (somatosensory cortex 3,2,1)

DRG (neural crest) PNS anterolateral DCML (cuneta and gracile nucleus) 1st synapses, but the 2nd decussates up to the thalamus 3rd

Motor Pathways: Between the UMN and LMN, which one is the "final common pathway"?

LMN= final common pathway

The anterolateral pathway carries "pain and temperature" sensations in the lateral STT and the Does the First order neuron enter the spinal cord and synpase first or decussate first? What nucleus does the STT first synapse with? and what rexed laimna is this?

The first neuron fibers enter the spinal cord and synapses "first" (1st) in the dorsal horn with the second neurons substantia gelantinosa (dorsal horn) rexed lamina II (rexed lamina IV (4) is the nucleous proprius (proprioception)

Where do the primary afferents 1 neurons first synapse?

They synapse with the second neuron in the same named nuclei in the lower medulla. gracile nucleus (medial) or cuneate nucleus (lateral)

What does the 1st order neuron do before they "synapse" with the substantia gelatinosa?

ascend or descend 1-2 segments.

A negative Romberg test indicates lesions of the sensory input to the _________?.

cerebellum

Lesions above the decussation (in the brain stem or cortex) produce contralateral or ipsi loss of joint position, vibration, and touch, whereas lesions "below" decussations (in the spinal cord) produce ipsilateral or contra deficits below the level of the lesion.

contralateral ipsilateral

Motor Pathways: • The corticospinal tract is involved in the voluntary contraction of skeletal muscle, especially in the _____ (distal or proximal) extremities. This pathway consists of 2 neurons, which are?

distal UMN and LMN

Where is "clarkes nucleus found? dorsal or ventral horn?

dorsal

A positive Romberg indicates damage to what CNS structure?

dorsal columns (loss of proprioception) sensory in nature.

DCML axons enter the spinal cord and ascend in the ________ columns of the white or gray matter as the fasciculus _______ (from lower limb, T6 and below)) or the fasciculus ________ (from upper limb) (T5 and above)

dorsal columns (not the dorsal horn) posterior funicului (white matter) T5 and above UL: cuneate fasiculus T6 and below LL: gracile fasiculus

This pathway conducts sensory information for touch, proprioception, vibration, and pressure?

epicritics (DCML) dorsal columns

The outer part of the spinal cord is the "white matter" containing ascending and descending axons that form tracts located within _____?.

funiculi (anterior posterior and lateral (cerebellum)

Axons of the second neuron decussate and "initially" form what fibers prior to the medial lemniscus? and ascend the midline of the brain stem in the "medial lemniscus" to reach the what nucleus of the thalamus for the contralateral body?

internal arcuate fibers (lower medulla) VPL (VPL nucleus)

Motor Pathways: Most of the upper motor neurons have their cell bodies in the primary motor cortex (area 4) laminae? and premotor cortex (are 6) of the _____ lobe.

internal granular layer = thalamocoritcal projections (internal granular layer laminae IV frontal lobe, internal pyrmidal layer (5)m

The spinothalamic tract ascends the lateral or medial aspect of the brain stem and synapses in the VPL nucleus of the thalamus where the third neuron projects to the cortex.

lateral

Motor Pathways: Lesions "above" the decussation (in the brain stem or cortex) produce contralateral or ipsilateral deficits, and lesions below the decussation (in the spinal cord) produce ipsilateral or contralateral findings

lesions above medulla decussation = contra below medulla pyramidal decussation = ipsi.

Motor Pathways: In the ________, 80-90% of these dorsally located ( CST ) fibers decussate at the pyramids and then descend in the spinal cord as the "lateral corticospinal" tract in the ________ funiculus of the white matter.

medulla, lateral

The third neuron then projects through the ________ limb of the internal capsule to the somatosensory cortex (3,1,2) of the DCML

posterior limb (so does the CST located dorsally and laterally).

Motor Pathways: These CST fibers enter the ventral or dorsal horn of gray at each cord segment and synapse upon the lower motor neurons. Axons of the lower neurons leave via the ventral or dorsal root of the spinal nerves and innervate the skeletal muscles.

ventral where they synpase onto LMN (UMN = spastic weakness) LMN = flaccid weakness ventral

The second neuron axons then decussate across the ____ ______ _______ and ascend the spinal cord and form the spinothalamic tract in the (lateral or medial) funiculus of the white matter?

ventral white commissure (syringomyelia) latearl funiculus (white mater)