A and P chap 15- Sensory pathways

what are the three general considerations of sensory pathways?

1. decussation- most pathways cross from one side of CNS to the other at some point

2. relay- most pathways have 2 or more neurons relaying the signal from the PNS to the CNS

3. symmetry- all pathways are paired symmetrically. One member of each pair is on separate sides of the spinal cord.

Describe the BASIC PLAN for a sensory pathway.

stimulus applied → detected by the receptor → first order neuron (cell body of this sensory neuron is in the dorsal root ganglia) → second order neuron (interneuron in the spinal cord of brain → CROSSES to third order neuron in Thalamus → cerebral cortex ( neuron in the primary sensory area - post central gyrus) → conscious perception of stimulus

Is all sensory ascending or descending?

ASCENDING

what side of the spinal cord carries sensory info?

POSTERIOR/ DORSAL

What kind of sensations does the posterior column pathway carry?

• highly localized touch, pressure, vibration, and proprioception

Describe directions of sensations of posterior column pathway

• 1st order neuron- ascends through posterior column and synapse in MEDULLA OBLONGATA

• 2nd order neuron - ascends through medulla, crosses, synapse to thalamas

• 3rd order neuron- travels to post-cental gyrus

what type of sensations do the anterior spinothalamic pathways carry?

• poorly localized touch and pressure

Describe directions of sensations of anterior spinothalamic pathway

• 1st order neuron- synapse within posterior gray horn (spinal cord)

• 2nd order neuron- crosses over and ascends through anterior column to synapse to thalamus

• 3rd order neuron- travels to post-central gyrus

what kind of sensations does the lateral spinothalamic pathway carry?

poorly localized sensation of pain and temp

Describe the directions of sensations in the lateral spinothalamic pathway

• 1st order neuron- synapse within posterior gray horn (spinal cord)

• 2nd order neuron- crosses over and ascends through the lateral column to synapse to the thalamus

• 3rd order neuron- travels to post-central gyrus

How many neurons are involved in the posterior column, anterior spinothalamic pathway, and lateral spinothalamic pathway?

3 neurons

How many neurons are in the corticospinal pathway?

2 neurons

characteristics of corticospinal pathway

• motor

• descending

• 2 neurons

• Upper motor neuron - primary motor cortex

• lower motor neuron- cranial or spinal nerves

what afferent neuron carries the sensation to the CNS?

• 1st order neuron

Motor neurons whose cell bodies reside in the spinal cord are: LMN or UMN?

upper motor neurons

If someone is unable to move their lower limbs, what type of tract is damaged? (descending or ascending)

• descending