Ascending Tracts Flashcards

Questions and Answers

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?

three

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?

second order neuron; continues up to the thalamus Signup and view all the answers

What is the name of the third neuron and what does it do?

third order neuron; carries the signal to the sensory region of the cerebral cortex Signup and view all the answers

What are the axons of these neurons called?

the first, second, or third order neuron fibers Signup and view all the answers

What prefix normally is with the tract and what root follows it?

spino; a root that denotes the location of its fibers in the brain Signup and view all the answers

What type of signals does gracile fasciculus carry?

carries signals from the mid-thoracic and lower parts of the body (vibration, visceral pain, deep and discriminative touch, and proprioception) Signup and view all the answers

What is the gracile fasciculus joined with and by what?

the cuneate fasciculus; T6 Signup and view all the answers

What does gracile fasciculus consist of?

first order neuron fibers that travel up the spinal cord Signup and view all the answers

Where does the gracile fasciculus end?

the gracile nucleus in the medulla oblongata Signup and view all the answers

What is proprioception?

non-visual sense of the position and movements of the body Signup and view all the answers

What is discriminative touch?

touch whose location one can precisely identify Signup and view all the answers

What type of signal does cuneate fasciculus carry?

sensory signals originating from the upper limbs and chest Signup and view all the answers

What joins the cuneate fasciculus and where?

the gracile fasciculus; T6 Signup and view all the answers

Where does the cuneate fasciculus end?

the cuneate nucleus in the medulla oblongata Signup and view all the answers

In the medulla, what happens between the gracile fasciculus and the cuneate fasciculus?

decussate and form the medial lemniscus Signup and view all the answers

What is the medial lemniscus?

a tract of nerve fibers that leads the rest of the way up the brainstem to the thalamus Signup and view all the answers

Where do third order fibers go in the cuneate fasciculus?

they go from the thalamus to the cerebral cortex Signup and view all the answers

What happens to the signal because of the decussation of the gracile fasciculus and the cuneate fasciculus?

the signals go to the contralateral cerebral hemisphere of the origin Signup and view all the answers

What type of signal does the spinothalamic tract carry?

pain, temperature, pressure, tickle, itch, and light/crude touch Signup and view all the answers

Where do the first order neurons end in the spinothalamic tract?

the posterior horn of the spinal cord near the point of entry Signup and view all the answers

What happens after the first order neuron ends in the spinothalamic tract?

the second order neuron synapses, which decussate and form the contralateral ascending spinothalamic tract until the thalamus Signup and view all the answers

What does the third order neuron do in the spinothalamic tract?

continue from the thalamus to the cerebral cortex Signup and view all the answers

Why do the sensory signals arrive in the cerebral hemisphere contralateral to their origin?

because of decussation Signup and view all the answers

What type of signals does the spinoreticular tract carry?

pain resulting in tissue injury Signup and view all the answers

Where do the first order neurons enter in the spinoreticular tract?

the posterior horn Signup and view all the answers

What happens with the second order neuron in the spinoreticular tract?

the first order neuron immediately synapses with the second order neurons after they enter the posterior horn and they decussate to the opposite anterolateral system, ascend the cord, and end in the reticular formation Signup and view all the answers

What is the reticular formation?

a loosely organized core of gray matter Signup and view all the answers

What happens with the third order neurons in the spinoreticular tract?

continue from pons to the thalamus Signup and view all the answers

What do the fourth order neurons do in the spinoreticular tract?

complete the path from the thalamus to the cerebral cortex Signup and view all the answers

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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Description

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.