Podcast
Questions and Answers
What type of signals do ascending tracts carry and which direction do they travel?
What type of signals do ascending tracts carry and which direction do they travel?
sensory signals up the spinal cord
How many neurons are there in an ascending tract?
How many neurons are there in an ascending tract?
three
What is the name of the first neuron and what does it do?
What is the name of the first neuron and what does it do?
first order neuron; detects a stimulus and transmits a signal to the spinal cord or brainstem
What is the name of the second neuron and what does it do?
What is the name of the second neuron and what does it do?
What is the name of the third neuron and what does it do?
What is the name of the third neuron and what does it do?
What are the axons of these neurons called?
What are the axons of these neurons called?
What prefix normally is with the tract and what root follows it?
What prefix normally is with the tract and what root follows it?
What type of signals does gracile fasciculus carry?
What type of signals does gracile fasciculus carry?
What is the gracile fasciculus joined with and by what?
What is the gracile fasciculus joined with and by what?
What does gracile fasciculus consist of?
What does gracile fasciculus consist of?
Where does the gracile fasciculus end?
Where does the gracile fasciculus end?
What is proprioception?
What is proprioception?
What is discriminative touch?
What is discriminative touch?
What type of signal does cuneate fasciculus carry?
What type of signal does cuneate fasciculus carry?
What joins the cuneate fasciculus and where?
What joins the cuneate fasciculus and where?
Where does the cuneate fasciculus end?
Where does the cuneate fasciculus end?
In the medulla, what happens between the gracile fasciculus and the cuneate fasciculus?
In the medulla, what happens between the gracile fasciculus and the cuneate fasciculus?
What is the medial lemniscus?
What is the medial lemniscus?
Where do third order fibers go in the cuneate fasciculus?
Where do third order fibers go in the cuneate fasciculus?
What happens to the signal because of the decussation of the gracile fasciculus and the cuneate fasciculus?
What happens to the signal because of the decussation of the gracile fasciculus and the cuneate fasciculus?
What type of signal does the spinothalamic tract carry?
What type of signal does the spinothalamic tract carry?
Where do the first order neurons end in the spinothalamic tract?
Where do the first order neurons end in the spinothalamic tract?
What happens after the first order neuron ends in the spinothalamic tract?
What happens after the first order neuron ends in the spinothalamic tract?
What does the third order neuron do in the spinothalamic tract?
What does the third order neuron do in the spinothalamic tract?
Why do the sensory signals arrive in the cerebral hemisphere contralateral to their origin?
Why do the sensory signals arrive in the cerebral hemisphere contralateral to their origin?
What type of signals does the spinoreticular tract carry?
What type of signals does the spinoreticular tract carry?
Where do the first order neurons enter in the spinoreticular tract?
Where do the first order neurons enter in the spinoreticular tract?
What happens with the second order neuron in the spinoreticular tract?
What happens with the second order neuron in the spinoreticular tract?
What is the reticular formation?
What is the reticular formation?
What happens with the third order neurons in the spinoreticular tract?
What happens with the third order neurons in the spinoreticular tract?
What do the fourth order neurons do in the spinoreticular tract?
What do the fourth order neurons do in the spinoreticular tract?
Study Notes
Ascending Tracts Overview
- Ascending tracts carry sensory signals upward through the spinal cord.
- They consist of three neurons: first order, second order, and third order.
Neuron Types and Functions
- First Order Neuron: Detects stimuli, transmits signals to the spinal cord or brainstem.
- Second Order Neuron: Projects to the thalamus, continuing the signal relay.
- Third Order Neuron: Carries the signal from the thalamus to the cerebral cortex.
- Collectively, the axons of these neurons are referred to as neuron fibers.
Terminology
- Ascending tracts typically begin with the prefix "spino," indicating the tract’s origin in the spinal cord and its destination within the brain.
Gracile Fasciculus
- Carries signals related to vibration, visceral pain, deep and discriminative touch, and proprioception from the mid-thoracic and lower body.
- Forms connections with the cuneate fasciculus at the T6 level.
- Composed of first order neuron fibers extending to the gracile nucleus in the medulla oblongata.
Proprioception and Discriminative Touch
- Proprioception: The awareness of body position and movement without visual cues.
- Discriminative Touch: The ability to precisely locate touch stimuli on the body.
Cuneate Fasciculus
- Transmits sensory signals from the upper limbs and chest to the brain.
- Joins the gracile fasciculus at the T6 level and ends in the cuneate nucleus in the medulla oblongata.
- In the medulla, both fasciculi decussate and form the medial lemniscus, which continues to the thalamus.
Medial Lemniscus
- A nerve fiber tract transporting sensory information from the medulla to the thalamus.
Spinothalamic Tract
- Carries pain, temperature, pressure, tickle, itch, and light/crude touch sensations.
- First order neurons terminate in the posterior horn of the spinal cord.
- The second order neuron synapses, decussates, and forms the contralateral ascending pathway to the thalamus.
- Third order neurons extend from the thalamus to the cerebral cortex, conveying sensations to the opposite hemisphere due to decussation.
Spinoreticular Tract
- Transmits pain signals resulting from tissue injury.
- First order neurons enter the posterior horn; immediately synapse with second order neurons which decussate and ascend, terminating in the reticular formation.
- The reticular formation is a network of gray matter essential for arousal and consciousness.
- Third order neurons travel from the pons to the thalamus, and fourth order neurons complete the path to the cerebral cortex.
Summary of Neuronal Pathways
- Decussation in both the spinothalamic and spinoreticular tracts ensures that sensory signals reach the cerebral hemisphere opposite their point of origin.
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Test your knowledge on ascending tracts with these flashcards. This quiz covers essential concepts such as signal direction, the number of neurons, and the functions of the first-order neuron. Perfect for students studying neuroanatomy and physiology.
