Ascending Sensory Pathways I + II Flashcards
What is Somaesthetic pathways?
Involves perception of bodily senses – pain,
temperature, touch and position
What is Proprioception? What structures are invovled?
the positon of where you are in space
Involves the DCP
Golgi tendons or muscle spindles in the muscles that detect the positon of the muscles and what they are doing without you having to see
What does Somaesthetic pathways carry?
Carry information of different types or modalities from:
Skin, mucus membranes, joints and muscles to the brain
What detects each modality involved in Somaesthetic pathways?
Each modality is detected by specific sensory receptors/specialised nerve endings
What are the two Somaesthetic pathways?
Spinothalamic Pathway
Dorsal column pathway
Which somaesthetic modality is essential for survival?
Somaesthetic pathways
Which somaesthetic modality increases detail?
dorsal column pathway
What type of reception modality does Spinothalamic Pathway
- Pain, temperature, some touch and pressure
What type of reception modality does Dorsal Column Pathway carry?
Discriminative touch: 2-point discrimination and vibration
Proprioception
What type of fibers are involved in Spinothalamic Pathway? Is the conduction fast or slow?
Carried via thin, poorly mylinated or
unmylinated fibres
Conduction relatively slow
What type of fibers are involved in Dorsal column pathway? Is the conduction fast or slow?
Carried via large diameter, heavily mylinated fibres
Fast conduction
How many neurones are invovled in the general sensory pathway?
3
When talking about sensory sensation of the body where specifically in the thalamus is the neurone going to?
VPL of the thalamus
What part of the brain is involved in general sensation?
Post central gyrus
What is the role of each of the 3 neurones in the general sensory pathway?
1st neurone: Is a Pseudounipolar that synpase on the same side of the spinal cord that is entered in.
2nd neurone: Axon crosses midline –> Ascends to ventral posterior thalamus
3rd neurone: Axon projects to post central
Gyrus (parietal lobe)
What is a Pseudounipolar?
. A neuron with a single stalk, that splits to give of two process –> one branch runs to he periphery and the other to the spinal cord.
What is a dorsal root ganglion?
Collection of cell bodies of the dorsal root neurones.
Specifically Pseudounipolar
Afferent nerves as they carry information towards the brain
How many neurones does the general sensory pathway compromise and where do these neuroens reside and move?
1)Comprise 3 neurons: first order, second order and third order
2)Cell bodies of 1st order neurons reside in dorsal root ganglia (PNS)
3)Cell bodies of 2nd order neurons reside in CNS ipsilateral grey matter
4)Axons of 2nd order neurons cross midline and ascend to thalamus
5)Cell bodies of 3rd order neurons reside in thalamus and axons project to somato-
sensory cortex
.
What is the blood supply of the medial surface of the post central gyrus?
anterior cerebral artery
What is the blood supply of the lateral surface of the post central gyrus?
Medial cerebral artery
How can imput from the 1st to 2nd and then 3rd neuroens be modified?
It is not simple relay. Can be modified by other inputs: eg. Convergence/divergence or descending pathways.
Can make the message more widespread or specific
Describe the crossing over of the Spinothalamic
tract and Dorsal column.
The spinothalamic tract crossess over the midline as soon as it enters the spinal tract
The dorsal column does not cross the midline at the level it enters the cord. It will ascend right up to the medulla then it will cross over
Describe the route of the Spinothalamic
tract?
1) 1st neurone originates from the DRG and ascends towards the spinal cord
2) The 1st neurone fibre ascends 1-2 segments then
contacts 2 neurone in dorsal grey horn
3) The 2nd neurone crosses midline in ventral white commisure
4) Then the 2 neurone fibres ascend in Spinothalamic tract to thalamus
What is the position where the 2nd neurone in spinothalamic tract crosses over the midline?
anterior ventral to the ventral white commissure
Close association between VWC and central canal
What structures in the CNS are somatotopically tract?
Medulla, thalamus and spinal cord
Once the spinothalamic tract has passed the medula what does it become?
Spinal lemniscus
What part of the medulla does the spinothalamic tract go to?
Lateral lemniscus
What is the route of the dosral column pathway at the level of the spinal cord?
1) the 1st neurone is at the dorsal root ganglion and then goes into the same side of the spinal cord
2) Synapse and the second neurone ascend in one of
ipsilateral dorsal columns
There is no crossing over
What is the distribution of the gracile and cuneate fasciles?
Gracile fascicle runs the whole length of the spinal cord –> information from the legs and lower part of the body
Cuneate fascicle runs above T6 only –> information from the upper body
What within the gracile and cuenate tubercles?
Gracile and Cuneate nucleus respectively where 1st neurone synpases
What type of sensation is involved in dorsal column pathway?
discriminative touch and
proprioception (plus some simple touch and pressure)
What type of sensation is involved in Spinothalamic pathway?
Pain, temperature, touch and pressure
At what point does the 1st neurone synapse with the second neurone in the dorsal column pathway?
At the closed medulla. At the gracile and/or cuneate fascicles
What occurs at the closed medulla in the dorsal column pathway?
1˚ sensory neurons contact 2 neurone fibres which
cross midline and enter medial lemniscus
What part of the medulla does the neurones of the dorsal column pathway run through?
Medial lemniscus
What is a lemniscus?
A collection of fibers
What is the name of the position where the 2nd neurones in dorsal column pathway cross the midline?
internal arcuate fibers –> going towards a specific part of the medial lemniscus
Medial lemniscus is somatotopically organized
What happens once the 2nd neurone reaches the medial lemniscus in the dorsal column pathway?
The secondary neurones project towards the VPL thalamus where they synapse.
The 3rd neurones are projected towards the somatosensory cortex
What direction does the fibers in the spinothalamic pathway travel in the spinal cord
Travel contralaterally in the cord
What direction does the fibers in the dorsal column pathway?
Travel ipsilaterally in the cord
What level does the fibers cross in the Spinothalamic pathway and DCP?
STP–> cross at level of spinal cord entry
DCP–> cross at level of closed medulla
What are the 3 branches of the trigeminal nerve?
V1 –> Opthalmic
V2 –> Maxillary
V3 –> Mandibular
What foramen do each of the trigeminal nerves pass?
V1 –> SOF
V2 –> foramen Rotundum
V3 –> forame ovale
What supplies the sensory information to the upper and lower teeth?
V2 supplies the upper teeth ( maxillary teeth) via the superior alveolar nerve.
V3 –> Supplies the mandibular teeth via the lower alveolar nerve
What cranial nerve does the herpes zoster virus infect?
It infects the sensory roots of trigeminal nerve .
Once the chicken pox has passed where does it reside?
The virus resides in the sensory roots of specific spinal nerves.
What does reactivation of the herpes zoster virus cause?
Reactivation causes shingles but the virus is restricted to a specific segmental spinal nerve, the vesicles blister and are distrubuted only in the dermatome of the affected spinal nerve
What are the somaethetic modalitis that are essenital to survival?
Pain, temperature, some touch and pressure
What are the somaethetic modalitis that increase detail?
Discriminative touch: 2-point discrimination and vibration
Proprioception
How many neurones are there in a neurone chain from receptor to sensroy cortex?
3
First order neurons
From PNS to CNS. Cell bodies in peripheral ganglia.
Second order neurons
Axons cross midline. Extend to thalamus
Third order neurons
Extend from thalamus to post-central gyrus
Where a cranial nerve nuclei located?
Within the brain stem
What do sensory and motor cranial nerve nuclei give rise to?
Sensory: receive information from fibres entering brainstem in cranial nerves
Motor: give rise to motor fibres that leave the brainstem in cranial nerves
What is equivelant to the dorsal grey horn of the spinal cord in the brain stem?
Sensory cranial nerve nuclei
Do the cranial nerves like the spinal nerves have the same cranial nerve nuclei?
No they don’t. The cranial nerve supplies different things so have specific sensory and motor cranial nerve nuclei.
General sensation from the head/face is carried in which 4 cranial nerves?
Trigeminal 5
Facial nerve 7
Glossopharyngeal 9
Vagus 10
The trigeminal nerve is a major carrier of general sensory from what areas of the head?
Major carrier of sensation from the face, nose, scalp and dura.
The facial nerve is a major carrier of general sensory from what areas of the head?
External ear
The glossopharyngeal nerve is a major carrier of general sensory from what areas of the head?
Posterior 1/3rd of tongue
Pharynx
Middle ear
The vagus nerve is a major carrier of general sensory from what areas of the head?
Auditory canal
Larynx
Pharynx
Oesophagus
What common site do all the sensory fibres from the cranial nerves V, 7,9 and 10 run through?
All run within the trigeminal nucleus to the thalamus
What are the name of the 3 parts of the trigeminal nucleus and where in the brain stem are they situated?
Mesenphalic nucleus of trigeminal nerve –> found at the top of the pons bordering the mid brain
Prinicpal sensory nucleus of trigeminal nerve (chief) is found in the middle of the pons
Spinal tract and spinal nucleus of trigeminal nerve which is found in the brain stem/spinal tract
What part of the trigeminal nerve does cranial nerve 7,9 and 10 enter?
Cranial nerve 7 Enters the bottom part of the chief region.
Cranial nerve 9 and 10 enter the spinal tract and spinal neurone of trigeminal nerve region
What is the position of motor cranila nerve nuclei to the sensory of the trigeminal?
The motor nuclei of the trigeminal lies medially to the sensory nuclei
What part of the trigeminal nucleus recieves pain and temperature modality?
Caudal part of the spinal nucleus
What part of the trigeminal nucleus recieves simple touch and pressure modality?
Rostal part of the spinal nucleus
Explain the pain and temperature pathway?
The fiber is thin and slow
The 1st neurone cell bodies starts in the trigeminal ganglion
The fibres run caudually in spinal tract of trigeminal lateral to the nucleus
Synapse with the 2nd fiber in the spinal nucleus on the same side
Cross the midline and ascends in trigeminothalamic tracts towards the thalamus (VPM)
Are the descending fibers running towards the spinal trigeminal necleus in the brain stem superficial or deep?
They are superficial and therefore easily damaged
Are the trigeminothalamic tract deep or supefecial?
They are deep, they run adjacent to the cerebal aqueduct.
Explain the dscriminatory touch pathway?
Fat and Fast Fibres
1st neurone cell bodies found in trigeminal ganglion.
They do not descend but enter at the pontine chief nucleus.
Then synapse with the 2nd neurone at the chief nucleus
Cross the midline and ascend in the trigeminothalamic tract to the thalamus
What part of the trigeminal nerve recieve disciminatory touch sensation?
The pontine chief nucleus
Explain the touch and pressure pathway?
Thin and slow fibers
1st neurone cell bodies in the trigeminal ganglion
Fibres descend in spinal tract of trigeminal to the rostal part of the spinal nucleus.
Synapse with the 2nd neurone more rostarlly in the spinal nucleus
Cross the midline and ascends in trigeminothalamic tracts (VPM)
What type of lesion would damage ascending spinothalamic tract and descending spinal tract? From what side of the body would they be coming from at the level of the medulla oblongata?
A superior lesion.
The spinothalamic tract would be coming from the contralateral side –> so damage to that nerve would cause sensory loss of the contralateral side of the body
The descending spinal tract would be coming from the ipsilateral side so the same side of the face would be affected.
Where does discrimintive touch sensory pathway synapse in the trigeminal nerve?
At the pontine (chief) nucleus
Where does proprioception pathway synapse in the trigeminal nerve?
Mesencephalic nucleus
What is unique about the propriception pathway?
The 1st nucleus begins at the mesencephalic nucleus and not at a ganglion outside the brain stem
What is the propioception pathway? Both sensroy and motor.
Most of these axons travel in the mandibular divsion of trigeminal as it involves understanding the position of your jaw.
1st neurone in the mesencephalic nucleus
Synapse along the mesencephalic nucleus
Cross the midline and ascend to the thalamus in trigeminothalamic tract
Other fibers from the Mesencephalic necleus contact motor neuroens in trigeminal motor nucleus.
Motor fibers go to muscles of mastication
What are sensory pathways?
Somatotopic
Is synaptic transmissioon of 1st ,2nd to 3rd neurone in the sensory pathway simply relay?
No it is not it can be modified by other inputs such as descending pathways
How does convergence modification of synaptic transmission work?
Several inputs from a axon leads to the output of one neurone
How does divergence modification of synaptic transmission work?
Is when the input of one neurone leads to the output of several
Fibres travelling from the thalamus to the post central gyrus via what?
The posterior limb of the internal capsule
Aneurysm in what artery would cause damage to the spinothalamic tract and spinal tract of the trigeminal?
Aneurysm in the anterior inferior cerebellar artery
