Flashcards in Lecture 2: Ascending Sensory Pathways I Deck (16):
Which of the sensory modalities are essential to survival?
- Pain, temperature, some touch and pressure
- Carried via thin, poorly mylinated or
- Conduction relatively slow
- Run in the spinothalamic pathway
Which of the sensory modalities increase detail?
- Discriminative touch: 2-point discrimination and vibration
- Carried via large diameter, heavily mylinated fibres
- Fast conduction
- Run in the dorsal column pathway
How many neurons are in a general sensory pathway neuron chain?
What type of neuron is the spinothalamic tract primary neuron and where does its cell body lie?
Cell body in dorsal root ganglion
On which side does the primary neuron of the spinothalamic tract synapse?
On the same side it enters
What happens to the secondary neuron in the spinothalamic tract?
Crosses over to the contralateral side immediately and synapses in the vetroposterolateral nucleus of the thalamus.
What is a diverging circuit?
One (or more) neurons synapse onto a greater number of neurons.
What is a converging circuit?
More than one neurons synapses onto a smaller number of neurons.
Does the spinothalamic pathway cross over at the level it enters the cord?
Does the dorsal column pathway cross over at the level it enters the cord?
No - ascends on the ipsilateral side first then crosses over.
Where does the axon of the secondary neuron feeding the spinothalamic pathway cross over in the spinal cord?
At the ventral white commissure.
What is the spinothalamic tract called once it reaches the medulla?
The lateral lemniscus
Where does the spinothalamic pathway end?
The postcentral gyrus
What happens to primary neurons in the dorsal column pathway?
Ascend the cord on the ipsilateral side in the cuneate fascicle (above T6 only), below T6 it runs in the gracile fascicle. Up to the corresponding tubercles (containing nuclei).
What happens to the dorsal column pathway in the closed medulla?
Primary neurons synapse with secondary neurons in gracile/cuneate nuclei. Secondary axons cross the midline and ascend in the medial lemniscus to the thalamus.