Lecture 6 Flashcards
What are the three sensory tracts?
•Dorsal Columns-Medial Lemniscal Tract
•Spinothalamic (Anterolateral Tract)
•Spinocerebellar and Cuneocerebellar Tracts
What is the motor tract?
Corticospinal
What are the two pathways in the Dorsal Columns-Medial Lemniscal Tract?
•Gracile Tract
•Cuneate Tract
What does the Gracile Tract sense?
Discriminative touch and conscious proprioception for on the contralateral side for lower limbs
What does the Cuneate Tract sense?
Discriminative touch and conscious proprioception for on the contralateral side for upper limbs
What is the difference between the Gracile Tract and the Cuneate Tract?
Gracile tract senses lower limbs and the Cuneate tract senses upper limbs
How many neurons are in the Gracile Tract pathway?
Three
How many neurons are in the Cuneate Tract pathway?
Three
What pathway are the Gracile and Cuneate tracts both apart of?
The Dorsal Column-Medial Lemniscus pathway
Where do the Gracile and Cuneate tracts synapse?
At the medulla and the VPL nucleus of the thalamus
Do the gracile and cuneate tracts switch sides and if so where?
Yes they do when they synapse at the medulla
What is Conscious Proprioception?
The ability to sense the position of your body in space and to feel where your natural range of movement should take you
What are the steps in the Gracile pathway?
- Sensory information is sensed in lower limbs by the PNS and carried in the CNS by the Gracile Tract
- The Gracile Tract synapses at the medulla and switches sides
- Information is then carried up the Medial Lemniscus pathway to the VPL nucleus of the Thalamus
- It synapses at the thalamus and then information is carried to the corresponding section of the primary somatosensory cortex
What are the steps in the Cuneate pathway? (DCML)
- Sensory information is sensed in upper limbs by the PNS and carried in the CNS by the Cuneate Tract
- The Cuneate Tract synapses at the medulla and switches sides
- Information is then carried up the Medial Lemniscus pathway to the VPL nucleus of the Thalamus
- It synapses at the thalamus and then information is carried to the corresponding section of the primary somatosensory cortex
Where do the Gracile and Cuneate pathway synapse?
At the Medulla and the VPL nucleus of the thalamus
How many neurons are in the Gracile and Cuneate pathways?
Three neurons
Where do the Gracile and Cuneate pathways crossover?
At the first synapse at the medulla
What is the organization of neurons from the PNS in the Gracile and Cuneate tracts?
Neuron 1 - From PNS to Medulla
Neuron 2 - Medulla to VPL nucleus in the thalamus
Neuron 3 - VPL nucleus in the thalamus to corresponding area of primary somatosensory cortex
What side of the brain is something processed in the Dorsal Column-Medial Lemniscal Pathway sensed?
The contralateral side
What side of the brain is something processed in the Cuneate Pathway sensed?
The contralateral side
What side of the brain is something processed in the Gracile pathway sensed?
The contralateral side
Of the Gracile and Cuneate tract which one is more medial and which one is more lateral?
•Gracile is medial
•Cuneate is lateral
What would a lesion to any of the Dorsal Column-Medial Lemniscus pathways cause?
Contralateral inability to have conscious proprioception and discriminative touch
What would cause contralateral inability to have conscious proprioception and discriminative touch?
A lesion to any of the Dorsal Column-Medial Lemniscus pathway
What would a lesion to Cuneate pathways cause?
Contralateral inability to have conscious proprioception and discriminative touch in upper limbs
What would a lesion to Gracile pathways cause?
Contralateral inability to have conscious proprioception and discriminative touch in lower limbs
What would a lesion to the Spinothalamic-Anterolateral pathways cause?
Contralateral Analgesia
What would cause Contralateral Analgesia?
A lesion to the Spinothalamic-Anterolateral Pathway
What does the Spinothalamic-Anterolateral pathway sense?
Somatic Pain
How many neurons are in the Spinothalamic-Anterolateral pathway?
Three
What are the differences between the Spinothalamic and the Dorsal Column-Medial Lemniscal pathway?
The Dorsal Column-Medial Lemniscal synapses at the medulla while the Spinothalamic-Anterolateral synapses at the spinal cord.
The Dorsal Column-Medial Lemniscal switches sides at the Medulla while the Spinothalamic-Anterolateral switches sides as soon as it synapses and reaches the spinal cord.
What is the Pathway of the Spinothalamic-Anterolateral tract?
- Pain is sensed from the PNS and carried into the spinal cord
- It synapses in the spinal cord and switches sides onto the spinothalamic tract
- It is carried to the thalamus where it synapses at the VPL nucleus
- From the VPL nucleus it goes to the corresponding portion of the primary somatosensory cortex
Where does the Spinothalamic-Anterolateral tract synapse
It synapses when it reaches the spinal cord and the VPL nucleus of the thalamus
What is the order of neurons in the Spinothalamic-Anterolateral Tract
- PNS to spinal cord
- Spinal cord to VPL nucleus in thalamus
- VPL nucleus in the primary somatosensory cortex
Does the Spinothalamic-Anterolateral tract switch sides and if so where?
It switches sides when it synapses at the spinal cord
Which tracts switch sides?
So far the Dorsal Column-Medial Lemniscus pathway switches at the medulla. The Spinothalamic-Anterolateral pathway switches at the spinal cord
Where does each tract synapse?
Dorsal Column-Medial Lemniscus synapses at the medulla and the VPL. The Spinothalamic-Anterolateral synapses at the Spinal cord and the VPL
What are the similarities between the Dorsal Column-Medial Lemniscus pathway and the Spinothalamic-Anterolateral pathway?
Both are made of three neurons
Both switch sides
Both synapse at the VPL nucleus
Both end at the primary somatosensory cortex
Where does the Spinothalamic-Anterolateral pathway synapse when it reaches the spinal cord?
The Substantia Gelatinosa (the second layer of the dorsal horn)
What is the Substantia Gelatinosa?
The second layer of the dorsal horn where the Spinothalamic-Anterolateral pathway synapses
What is the topography of the spinal cord for the Dorsal Column-Medial Lemniscus pathway?
The leg is more medial than the arm
What is the topography of the spinal cord for the Spinothalamic-Anterolateral pathway?
The leg is more lateral than the arm
What is the blood supply for the Dorsal Column-Medial Lemniscus pathway?
I think the posterior spinal artery*
What is the Corticospinal tract for?
Conscious movement
How many neurons in the Corticospinal pathway?
Two
What is the pathway of the corticospinal tract?
- Upper motor neuron comes from the primary motor cortex
- Crosses sides at the medulla (but does not synapse)
- Synapses a lower motor neuron (LMN) in the spinal cord
- LMN releases ACth onto muscle
Where does the Corticospinal Tract cross over?
The Medulla
Where does the Corticospinal tract synapse?
In the spinal cord at the LMN
What are the similarities between the Dorsal Column-Medial Lemniscus pathway and the Spinothalamic-Anterolateral pathway and the Corticospinal Tract?
Dorsal Column-Medial Lemniscus pathway and the Spinothalamic-Anterolateral pathway are both three neuron pathways and synapse at the VPL. All three pathways cross over.
What are the differences between the Spinothalamic and the Dorsal Column-Medial Lemniscal pathway and the Corticospinal tract?
The Dorsal Column-Medial Lemniscus pathway and the Spinothalamic-Anterolateral pathway are three neuron pathways and end at the primary somatosensory cortex. The Dorsal Column-Medial Lemniscus pathway synapses at the medulla and the VPL. The Spinothalamic-Anterolateral pathway synapses at the spinal cord and the VPL. The Corticospinal tract synapses at the spinal cord and is a two neuron pathway
Where do all three pathways synapse?
•Dorsal Column-Medial Lemniscus synapses at the medulla and the VPL
•The Spinothalamic-Anterolateral pathway synapses at the spinal cord and VPL
•The corticospinal cord synapses at the spinal cord
Where do all three pathways crossover?
•Dorsal Column-Medial Lemniscus crosses over at the medulla
•The Spinothalamic-Anterolateral pathway crosses over at the spinal cord
•The corticospinal cord crosses at the medulla
What is the difference in crossing over between the Dorsal Column-Medial Lemniscal, Spinothalamic, and corticospinal tract?
The spinothalamic tract crosses over immediately at the level of the spinal cord so it travels in a different part of the spinal cord than the other pathways
Which artery in a stroke would knock out the primary motor or the primary somatosensory cortex?
The middle cerebral artery
What would happen in the pathways if there was a stroke in the middle cerebral artery?
•Wouldn’t be able to move on the contralateral half of the body (hemiplegia)
•Loss of discriminative touch
•Inability to feel pain on the contralateral side of the body
•All in the upper limbs
What kind of lesion would cause:
•Wouldn’t be able to move on the contralateral half of the body (hemiplegia)
•Loss of discriminative touch
•Inability to feel pain on the contralateral side of the body
All in upper limbs
Blockage of the MCA to the primary motor cortex and the primary somatosensory cortex
What would happen in the pathways if there was a lesion in the ACA in terms of pathways?
What kind of lesion would cause:
•Wouldn’t be able to move on the contralateral half of the body (hemiplegia)
•Loss of discriminative touch
•Inability to feel pain on the contralateral side of the body
All in lower limbs
What kind of lesion would cause:
•Wouldn’t be able to move on the contralateral half of the body (hemiplegia)
•Loss of discriminative touch
•Inability to feel pain on the contralateral side of the body
All in lower limbs
A lesion in the ACA
What part of the Cortex does the ACA supply and what part of the cortex does the MCA supply?
MCA - Lateral
ACA - Medial
What would a brainstem lesion cause?
*Wouldn’t be able to move on the contralateral half of the body (hemiplegia)
*Loss of discriminative touch
*Inability to feel pain on the contralateral side of the body
What would a lesion in the Medulla cause?
•Hemiplegia - Wouldn’t be able to move on the contralateral half of the body
•Analgesia - Inability to feel pain on the contralateral side of the body
•But you would still have discriminative touch
What would cause:
•Hemiplegia - Wouldn’t be able to move on the contralateral half of the body
•Analgesia - Inability to feel pain on the contralateral side of the body
•But you would still have discriminative touch
A lesion to the medulla
What would a spinal cord lesion cause?
a. Contralateral Analgesia
b. Ipsilateral hemiplegia, ataxia, loss of discriminative touch
Depending on the side that is affected
What would cause:
a. Contralateral Analgesia
b. Ipsilateral hemiplegia, ataxia, loss of discriminative touch
Depending on the side that is affected
A spinal cord lesion
What would a peripheral nerve lesion cause?
Ipsilateral hemiplegia, Ataxia, Loss of discriminative touch, Analgesia
What would cause: Ipsilateral hemiplegia, Ataxia, Loss of discriminative touch, Analgesia?
A peripheral nerve lesion
What does the spinocerebellar tract sense?
Unconscious proprioception - like when you close your eyes and know exactly where your body is in space
Lower limb and joint position
What pathway senses Unconscious proprioception - like when you close your eyes and know exactly where your body is in space
Lower limb and joint position?
The Spinocerebellar tract
What are the steps in the Spinocerebellar Tract?
A-alpha sensory neurons from muscle spindles, golgi tendons, organs
They synapse in the spinal cord at the Dorsal Nucleus of Clarke onto the Dorsal Spinocerebellar Tract
The Dorsal Spinocerebellar Tract goes through the inferior cerebellar peduncle and to the cerebellum
Where does the Spinocerebellar Tract switch sides?
trick question it doesn’t
What levels is the Dorsal Nucleus of Clarke in the Spinocerebellar tract found?
Only from C8 to L2
Since the spinocerebellar tract only has Clarke’s Nucleus from C8-L2 how are things from below L2 sensed?
They hitchhike along the Gracile Tract and then synapse at Clarkes nucleus
What does the Cuneocerebellar tract do?
Proprioception, upper limb and joint position
What are the steps in the Cuneocerebellar tract?
- Upper limbs send joint position and proprioception to sensory nerves
- Sensory nerves synapse in the spinal cord onto the accessory cuneate nucleus
- This continues as the Cuneocerebellar Tract into the cerebellum
What is the difference between the Spinocerebellar Tract and the Cuneocerebellar tract?
They both sense unconscious proprioception but the Spinocerebellar tract is for the lower limbs and the Cuneocerebellar tract is for the upper limbs
How many neurons are in there in the Spinocerebellar Tract and the Cuneocerebellar tract?
Two neuron pathways
Where do the Spinocerebellar Tract and the Cuneocerebellar tract synapse?
At the spinal cord
What are the two separate blood supplies of the spinal cord?
•Dorsal Columns from the posterior spinal arteries
•Anterior spinal arteries
In which pathway does the spinal cord topography have the leg medial?
The dorsal column-medial lemniscal pathway
What is Lissauer’s Tract?
This is where the dorsal roots come in at the spinal cord
What layer of the Spinal cord is the Substantia Gelatinosa?
Layers II/III
What are the steps in the Knee Jerk reflex?
- Hammer strike deforms patellar tendon to cause muscle to stretch
- Sensory nerve proprioception nerve (a-alpha) initiates action potentials and sends signal back to spinal cord (L2-L4)
- It synapses on the quadriceps lower motor neuron and causes muscle stretch
- It also synapses on the interneuron which goes to synapse on the opposing lower motor neuron causing it to relax
- Causing the knee jerk
What is an example of the Withdrawal Reflex?
The crossed extensor reflex
What are the steps in the Crossed Extensor Reflec?
1) The ipsilateral leg (the one which steps on the nail) the flexors in hamstrings contract and the extensors in the quadriceps relax to lift the leg from the ground
2) On the contralateral side the flexors in the hamstring relax and the extensors in the quadriceps contract to support the weight of the body
3)However at the same time signals travel up the spinal cord and cause contraction of the contralateral muscles of the hip and abdomen to shift the body’s center of gravity
What is the coordination of the Crossed Extensor Reflex mediated by?
The cerebellum and cerebral cortex
Where does Cranial Nerve I sit?
In the nose
What is Cranial Nerve I?
The olfactory nerve
What is the Cribriform plate?
The part of the skull that CN I enters
What is the Pathway of CN I?
Sensation from nose ➡️ Olfactory tract ➡️ Primary olfactory cortex deep to the uncus
What does the Olfactory nerve bypass?
The thalamus
