Module 3 - Somatosensory systems: major ascending pathways Flashcards
What is the caudal medulla?
The transition area between the spinal cord and the brainstem
What is the obex?
The obex (from the Latin for barrier) is the point in the human brain at which the fourth ventricle narrows to become the central canal of the spinal cord. The obex occurs in the caudal medulla. The decussation of sensory fibers happens at this point.
At every brainstem level rostral to obex, 3 general areas can be identified, what are they?
- Area posterior to ventricular space (tectum, inferior and superior medullary vela)
- Area anterior to ventricular space (tegmentum)
- Large structures “appended” to anterior surface of brainstem (crus cerebri, basal pons, pyramids)
What is in the tectum of the brainstem?
- superior colliculus
- inferior colliculus
What 4 structures are in the tegmentum of the brainstem?
- reticular formation nuclei
- cranial nerve nuclei and tracts
- ascending tracts from spinal cord
- descending tracts
What X structures are in the base of the brainstem?
- Crus cerebri
- Basal pons
- Pyramids
- Substantia nigra
- Cerebral peduncle
On this anterior image of the brainstem, identify the:
- thalamus
- midbrain
- pons
- medulla
On this anterior image of the brainstem, and specifically within the medulla, identify the:
- pyramids
- decussation of the pyramids
- anterior median fissure
On this anterior image of the brainstem, identify the anterolateral structures of:
- the Olives (bump produced by the large
inferior olivary nucleus) - Preolivary sulcus (rootlets of CNXII
emerge from this sulcus) - Postolivary sulcus
In this posterior image of the medulla, locate the:
- closed portion
- open portion
- obex
- Gracile tubercle
- Cuneate tubercle
- Posterointermediate sulcus
- Posterior median sulcus
Where is the fasciculus grascilis and what is it implicated in?
Ascending - fine touch and proprioception from ipsilateral lower limb
Where is the fasciculus cuneatus and what is it implicated in?
Ascending - fine touch and proprioception from ipsilateral upper limb
Where is the spinocerebellar tract and what is it implicated in?
Propriotception from limbs to cerebellum
Where is the lateral corticospinal tract and what is it implicated in?
Motor to ipsilateral ventral horn, mostly limb musculature
Where is the spinothalamic tract and what is it implicated in?
Pain and temperature from the contralateral side of the body
Where is the anterior corticospinal tract and what is it implicated in?
Motor to ipsi- and contra-lateral ventral horn mostly axial musclature
On this anterior image of the brainstem, where is the:
- basal pons
- cerebral peduncles (crus cerebri)
- interpeduncular fossa
The tectum, of roof of the midbrain, contains the inferior and superior colliculi. Can you locate them on this posterior image of the brainstem?
On this micrograph of the caudal medulla, can you locate the anterior spinocerebellar tract (it carries motor to ipsi- and contra-lateral ventral horns; mostly axial musclature)
On this micrograph of the medulla, can you locate the pyramids? What are they associated with?
The medullary pyramids are paired white matter structures of the brainstem’s medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts. The lower limit of the pyramids is marked when the fibers cross (decussate).
On this micrograph of the medulla, where are the nucleus gracilis located? What are they implicated in?
Fine touch and proprioception
On this micrograph of the medulla, where are the nucleus cuneatus located? What are they implicated in?
On this micrograph of the medulla, where is the fasciculus gracilis? What is it implicated in?
fiber bundle that carries tactile and proprioceptive information from the lower half of the body, the fasciculus gracilis is part of the posterior columns and terminates in the nucleus gracilis.
On this micrograph of the medulla (#4), where is the fasciculus cuneatus? What is it implicated in?
fiber bundle that carries tactile and proprioceptive information from the upper limbs and torso, the fasciculus cuneatus is part of the posterior columns and terminates in the nucleus cuneatus.
On this micrograph of the medulla (#4), where is the spinothalamic tract? What is it implicated in?
The spinothalamic tract is an ascending pathway of the spinal cord. Together with the medial lemnicus, it is one of the most important sensory pathways of the nervous system. It is responsible for the transmission of pain, temperature, and crude touch to the somatosensory region of the thalamus.
decussation
when fibers cross from one side of a structure to the other.
What is this micrograph showing?
Superior/rostral/open medulla
On this micrograph of the superior medulla (#5) where are the pyramids? What are they implicated in?
The medullary pyramids are paired white matter structures of the brainstem’s medulla oblongata that contain motor fibers of the corticospinal and corticobulbar tracts – known together as the pyramidal tracts.
On this micrograph of the superior medulla (#5) where are the inferior olivary nuclei? What are they implicated in?
coordinates signals from the spinal cord to the cerebellum to regulate motor coordination and learning.
On this micrograph of the superior medulla, where is the medial lemniscus? What is it implicated in?
Medial lemniscus: major ascending pathway for carrying tactile and proprioceptive information to the thalamus
On this micrograph of the superior medulla, where is the medial lemniscus? What is it implicated in?
On this micrograph of the caudal pons and cerebellum, where is the medial lemniscus? What is it implicated in?
major ascending pathway for carrying tactile and proprioceptive information to the thalamus.
On this micrograph of the caudal pons and cerebellum, where is the spinothalamic tract? What is it implicated in?
The spinothalamic tract is an ascending pathway of the spinal cord. Together with the medial lemnicus, it is one of the most important sensory pathways of the nervous system. It is responsible for the transmission of pain, temperature, and crude touch to the somatosensory region of the thalamus.
On this micrograph of the caudal pons and cerebellum, where are the corticospinal fibers?
What are the pontine nuclei? What are they implicated in?
Pontine nuclei receive visual, auditory, and somatosensory information from cortical and subcortical regions which is transmitted via mossy fiber axons to cortical granule cells, the most numerous cells in the cerebellum.
Ascending
On this micrograph of the rostral pons/caudal midbrain, where is the inferior colliculus? What is it implicated in?
The inferior colliculus is best known for its role in hearing. It is the largest nucleus of the auditory system in humans, and it is the point in the brainstem where all auditory pathways traveling through the brainstem converge
On this micrograph of the rostral pons/caudal midbrain, where is the medial lemniscus? What is it implicated in?
major pathway for carrying tactile and proprioceptive information to the thalamus. The medial lemniscus is formed in the medulla as fibers from the posterior column nuclei cross the midline.
ascending
On this micrograph of the rostral pons/caudal midbrain, where is the spinothalamic tract? What is it implicated in?
The spinothalamic tract is an ascending pathway of the spinal cord. Together with the medial lemnicus, it is one of the most important sensory pathways of the nervous system. It is responsible for the transmission of pain, temperature, and crude touch to the somatosensory region of the thalamus.
Ascending
On this micrograph of the rostral pons/caudal midbrain, where are the corticospinal fibers?
On this micrograph of the rostral pons/caudal midbrain, where is the cerebral aqueduct? What is it implicated in?
The cerebral aqueduct is a narrow 15 mm conduit that allows for cerebrospinal fluid (CSF) to flow between the third ventricle and the fourth ventricle.
On this micrograph of the superior/rostral midbrain, where is the superior colliculus? What is it implicated in?
Although the complete scope of functions that can be attributed to the superior colliculi has not been fully delineated, the superior colliculi are understood to be important to directing behavioral responses toward stimuli in the environment. In other words, the superior colliculus seems to be able to receive information from the environment and then use that information to initiate a behavioral response appropriate to the current environmental context.
Vision particularly
On this micrograph of the superior/rostral midbrain, where is the red nucleus? What is it implicated in?
This neural network is the part of the motor system involved in generating involuntary movements.
On this micrograph of the superior/rostral midbrain, where is the substantia nigra? What is it implicated in?
The substantia nigra (SN) is a midbrain dopaminergic nucleus which has a critical role in modulating motor movement and reward functions as part of the basal ganglia circuitry.
On this micrograph of the superior/rostral midbrain, where is the medial lemniscus? What is it implicated in?
major pathway for carrying tactile and proprioceptive information to the thalamus.
Ascending
On this micrograph of the superior/rostral midbrain, where is the spinothalamic tract? What is it implicated in?
The spinothalamic tract is an ascending pathway of the spinal cord. Together with the medial lemnicus, it is one of the most important sensory pathways of the nervous system. It is responsible for the transmission of pain, temperature, and crude touch to the somatosensory region of the thalamus.
Ascending
What is the medial lemniscus system implicated in?
Discriminative (fine) touch,
pressure, vibratory sense and conscious proprioception (joint position sense).
The ascending medial lemniscus pathway carries discriminative touch, proprioception and vibration. Where does it dessucate?
medulla
The posterior column-medial lemniscus system travels up the spinal cord within the [blank]
Posterior column
An ascending sensory tract, fibers of the posterior column-medial lemniscus system transmit information about what 4 things?
- Discriminative touch
- presssure
- vibration
- proprioception
What supplies blood to the posterior column medial lemniscus system?
Posterior spinal arteries
What is the VPL of the thalamus?
Ventral posterolateral nucleus (VPL): nucleus of the thalamus that receives sensory input from the medial lemniscus and spinothalamic tract and projects to the somatosensory cortex.
Where does the medial lemniscus terminate?
In the VPL of the thalamus. From the thalamus, fibres project to and terminate in the primary somatosensory cortext
In the spinal cord, [blank] fibers (above [blank]) enter the fasciculus cuneatus (lateral) to ascend.
In the spinal cord, rostral fibers (above T6) enter the fasciculus cuneatus (lateral) to ascend.
In the spinal cord, [blank] fibers ([blank] T6) enter the fasciculus gracilis (medial) to ascend.
In the spinal cord, caudal fibers (below T6) enter the fasciculus gracilis (medial) to ascend.
Where do secondary neurons of the PCML pathway cross the midline? What do they cross the midline as?
In the caudal medulla
As arcuate fibers
What are the spinocerebellar tracts implicated in?
Unconscious proprioception (joint position sense) to the cerebellum
Note: Information about limb position sense carried in the dorsal column - medial
lemniscus system is considered “conscious” proprioception because it reaches
the cerebral cortex.
What is another name for the spinothalamic tract?
the anterolateral system
Is the spinothalamic tract ascending or descending?
ascending
What does the:
a) lateral
b) anterior
part of the spinothalamic tract do?
a) the lateral part carries pain and temperature
b) the anterior part carries crude touch and pressure
What supplies blood to the spinothalamic tract?
The anterior spinal artery
Paleospinothalamic and spinoreticulothalamic tracts - function?
These 2 tracts thought to have a role in the sensation of dull, aching,
poorly localized pain related to that mediated by C fibers. Also have a
role in affect and cortical arousal associated with pain.
Spinomesencephalic tract - function?
b. Involved in modulation of pain.
What are the three types of nociceptors?
- Adelta fibers
- C fibers
- Abeta fibers
What are the characteristics of Adelta fibers?
- fast and myelinated
- first to recognize and localize pain
- activated by mechanical and thermal stimulation
What are the characteristics of C fibers?
- Slow and unmyelinated
- Signals are diffuse and secondary
- Activated by chemical reaction referred to as the inflammatory soup
What are the characteristics of Abeta fibers?
- General sensory fibers
- involved in pain modulation
How do pain signals make their way to the spinal cord?
Via the spinal ganglion
The anterolateral system comprises all fibers carrying [blank] and [blank] from the spinal cord to the [blank] and [blank]
The anterolateral system comprises all fibers carrying pain and temperature from the spinal cord to the thalamus and brainstem
What are the 4 tracts of the anterolateral system?
- Spinothalamic tract (to the thalamus and then on to cortical structures)
- Spinohypothalamic tract (to the hypothalamus)
- Spinomesencephalic tract (to the midbrain - periaqueductual gray)
- Spinoreticular tract (to the brainstem reticular formation - locus ceruleus and Raphe nuclei)
Is there a single pain center in the brain?
No, there is a pain matrix which integrates cortical, subcortical, and brainstem systems in pain perceptions
Cortical regions involved in pain can ben divided into two systems, what are they?
- Lateral pain system
- Medial pain system
What is the lateral pain system and where is it located?
Localization of pain
Primary and secondary somatosensory cortices
What is the medial pain system and where is it located?
Affective-motivational component (i.e., suffering - “ouch”); emotion associated with actual and imagined pain
anterior cingulate cortex; insula; amygdala; hypothalamus
What are the three major mechanisms for pain modulation?
- gate control theory
- descending pathways
- endogenous opioid system
Almost all sensory pathways do what 3 things?
Almost all sensory pathways synapse, cross, and ascend to the thalamus
Which part of the thalamus is the principle sensory component of the diencephalon?
The ventral posterior part
What are the three main types of somatosensory information?
- discriminative touch
- pain and temperature (also dsicriminative, but relies on free nerve endings)
- . proprioception
What is discriminative touch?
Mediates mechanical perception of pressure, vibration and texture, and relies on receptor organs in the skin
What is proprioception?
Mediates limb, muscle and joint position/force/ And similar to cutaneous receptors, has both rapid- and slow-acting components
Most sensory information ultimately projects where?
To the primary sensory cortex, which occupies the post-central gyrus and extends onto the medial surface
When referring to somatosensory systems, does the cerebral cortex operate on a contra- or ipsilateral basis?
contralateral
Although somatosensory information to the cortex is contralateral, proprioceptive information to the cerebellum is [blank]
ipsilateral
By what mechanism do third order sensory neurons project to the cortex?
internal capsule
How many types of neurons are there in the sensory pathways?
first order, second order, third order
Touch, vibration and proprioception employ the dorsal column medial lemniscal system; what is the pathway of this system?
- Enters the spinal cord through spinal ganglion
- Synapses are first made at the level of the medulla
- Second order neurons then synapse at the thalamus
- Then through internal capsule to the primary somatosensory cortex
Pain and temperature employ the spinothalamic anterolateral system; what is the pathway of this system?
- Incoming afferents containing pain or temperature information will climb up or down within the lissauer tract
- Synapse in the spinal cord
- Second order neurons then cross over through the anterolateral spinal cord grey matter and ascend through the medulla, pons and midbrain
- Second order synapses occur within the thalamus
- Pain information ascends through the internal capsule to the primary somatosensory cortex
Where does the trigeminothalamic tract terminate?
In the thalamus (VPM)
From where does the trigeminal nerve emerge?
The mid-pons
What are the cranial fossae?
The bones of the brain case surround and protect the brain, which occupies the cranial cavity. The base of the brain case, which forms the floor of cranial cavity, is subdivided into the shallow anterior cranial fossa, the middle cranial fossa, and the deep posterior cranial fossa.
In which cranial fossa do the sensory ganglion of the trigeminal nerve (CN V) sit?
The middle cranial fossa
What are the 3 branches of the trigeminal nerve (CN V)?
- Ophthalmic
- Maxillary
- Mandibular
The trigeminal nerve (CN V) divides into 3 branches (ophthalmic, maxillary and mandibular), where does the opthalmic branch exit the skull?
Through the superior orbital fissure
The trigeminal nerve (CN V) divides into 3 branches (ophthalmic, maxillary and mandibular), where does the maxillary branch exit the skull?
Through the foramen rotundum
The trigeminal nerve (CN V) divides into 3 branches (ophthalmic, maxillary and mandibular), where does the mandibular branch exit the skull?
Through the foramen ovale
What is the function of the trigeminal nerve (CN V)?
The trigeminal nerve is the main sensory nerve for the head. It carries pain and temperature as well as discriminative touch, vibration and proprioception in all three divisions (opthalmic, maxillary, and mandibular)
It also carries motor to the muscles of mastication. This motor component is only located in the mandibular division.
The spinal trigeminal tract and nucleus carry what information? From where to where do they extend?
Pain and temperature
Extends from medulla to pons
On this micrograph of the caudal medulla, where is the spinal trigeminal:
1) tract
2) nucleus
nucleus in light green
tract in dark green
On this micrograph of the caudal medulla, where is the spinal trigeminal:
1) tract
2) nucleus
tract = dark green
nucleus = light green
The Chief Sensory Nucleus of V carries what information? It is located in the mid pons, where exactly?
The Motor Nucleus of V carries what information? It is located in the mid pons, where exactly?
Motor information to muscles of mastication
The Mesecephalic nucleus of V carries what information? It is located in the caudal midbrain, where exactly?
The trigeminal nerve hase 4 main nuclei associated with it. What are they?
- Chief sensory nucleus,
- Mesencephalic nucleus
- motor nucleus
- spinal nucleus of V
Where do the fibers of the fasciculus gracilis and cuneatus cross the midline? And through what?
At the medulla, at the internal arcuate fibers
What do the internal arcuate fibers become?
Medial lemniscus (part of the dorsal column medial lemniscus system) - ascending from the medulla as a midline structure
