Sensory Systems of the Brain L3 Flashcards by sita clark

What is a Root?

2x bundles of axons

connects each spinal nerve to a segment of the cord by a bundle of axons called rootlets

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What is the Posterior Dorsal Root?

Contain ONLY Sensory axons
These conduct nerve impulses form the Peripheral sensory Receptors located in the skin, muscles and organs –> to the CNS Central Nervous System

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What is the Anterior Ventral Root?

Contain Axons of ONLY Motor Neurons

There conduct nerve impulses from the Central Nervous System CNS –> to Effector Muscles/Glands/Organs/cells

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What is a horn?

the Gray matter on Each Side of the spinal cord is Subdivided into region calls Horns

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What is the Posterior Dorsal Gray Horn?

Contains 2x neurons:

Cells bodies and axons of inter-neurons
Axons of incoming sensory neurons

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What is the Anterior Ventral Gray Horn?

Contains Somatic Motor Nuclei

-clusters of cell bodies of somatic motor neurons that Proved impulses for the contraction of skeletal muscle

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What is the AWC?

Anterior White Commissure

-Connects the white matter on the Right and Left sides of the spinal cord

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What is located at the lower end of the spinal cord?

Sensory neurons which carry the sensation of the lower limbs/anus
First fibres to come in
– additional fibres add in later (arm neurons lie lateral to the sensory neurons already entered from lower parts of the body)

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Where do the nerve fibres from the level of the arm lie in the spinal cord?

Additional fibres from non lower/leg/anus parts of the body add in later
Arm neurons lie LATERAL to the sensory neurons which have already entered from lower parts of the body

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What happens if you look at the spinal cord from the Midline Out?

Lower nerve fibres closer to the midline –> Upper nerve fibres(arms etc) more lateral
Large numbers of nerve fibres from the upper(arm) and lower(legs) limbs

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What are the Gracile Fasiculus and Cuneate Fasiculus?

Gracile and Cuneate Fasiculus together are Fibre bundles which form the Posterior Dorsal Column
Top of the spinal cord
-is a bundle which continues up the spinal cord,
Arm and leg neuron fibres dominate pathway
-going up, More and more fibres are added, results in the Posterior dorsal Column getting Thicker (gets bigger further up the spinal cord)
Continuously represented/nuclei

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What is the central pathway of discriminative sensation?

Touch and pressure

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What is the receptor for discriminative sensation?

Encapsulated receptors

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What is the pathway of the first order neuron in the central pathway of discriminative sensation?

Primary root afferents in skin/muscles/organs. (cell bodies in dorsal root ganglion)
Posterior Dorsal Column of the spinal cord
Axon terminates at Gracile/cuneate nuclei located in the dorsal column of the medulla

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What is the Gracile Nuclei/Fasiculus?

Part of the dorsal column/nuclei

Receives impulses from the Lower body (leg)

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What is the Cuneate Nuclei/Fasiculus ?

Part of the dorsal column/nuclei

Receives impulses from the Upper body (arm)

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Is the gracile and cuneate nuclei/fasiculus a discontinuous or continuous nuclei?

continuous nuclei

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What is the pathway of the second order neuron in the central pathway of discriminative sensation?

Gracile/cuneate nuclei in the dorsal column of the medulla
- -Sensory decussation–
Medial Lemniscus of the brain stem
VP VentroPosterior Nuclei in the thalamus

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What is the decussation pathway of the first order neuron in the central pathway of discriminative sensation?

Fibres cross over from the Gracile/cuneate nuclei in the dorsal column of the medulla –> to the Medial Lemniscus
fibres cross over at this point, in the Medulla, via the INTERNAL ARCUATE FIBRES, to the opposite side of the spinal cord (enters the lemniscus)

What is the Medial Lemniscus?

Big bundle of fibres (Millions)
In the brainstem
Thin, ribbon like, Projection tract
Extends form the Medulla –> to the VP of the Thalamus
Fibres are groups together so the order of representation is maintained

What is the VP VentroPosterior Nuclei?

In the Thalamus
One of the highly specialised areas in the Thalamus
Highly specialised to receive Just sensory information from the skin
Processes, suppresses, modifies sensory information
Critical role
-Works closely with the cerebral Cortex
If a stoke present here = you wont survive

What is the pathway of the third order neuron in the central pathway of discriminative sensation?

VP ventroposterior Nuclei in the Thalamus
Internal Capsule
Third axon terminates in the 1 Primary Somatosensory Cortex

What is the internal capsule?

North and south motor way

where all the nerve fibre from VPThalamus –> Cerebral cortex Pass Through

Where is the termination placement of the discriminative sensation’s third order neuron?

in the 1 Primary Somatosensory cortex
Termination placement is according to which body part the sensory Input is coming From
-as the 1 primary somatosensory cortex/post-central gyrus is somatotopical

What does the primary somatosensory cortex have?

a conscious appreciation for sensation | -where you appreciate sensory feeling

What is special about the cerebral cortex?

cerebral cortex is the most highly organised part of the CNS | you MUST pass through the Thalamus in order to access the Cerebral cortex

What would occur to discriminative sensation if there was a lesion in the spinal cord?

Lesion in Left of Spinal cord Loss of Discriminative sensation (touch and pressure) in the SAME Left side of the body -as decussation occurs at the gracile/cuneate nuclei of the medulla (hasn't occurred)

What would occur to discriminative sensation if there was a lesion in the brain/brainstem?

Lesion in the Left of the Brainstem/ Brain Loss of discriminative sensation (touch and pressure) in the OPPOSITE Right side of the body - as decussation occurs prior to the brain/brainstem (has occurred)

What would occur to non-discriminative sensation if there was a lesion in the spinal cord?

Lesion in Left of Spinal cord Loss of Non-Discriminative sensation (pain and temperature) in the OPPOSITE Right side of the body -as decussation occurs at the AWC Anterior White Commissure in the Spinal Cord (has occurred)

What would occur to non-discriminative sensation if there was a lesion in the brain/brainstem?

Lesion in the Left of the Brainstem/ Brain Los of Non-discriminative sensation (pain and temperature) in the OPPOSITE Right side of the body -as -as decussation occurs at the AWC Anterior White Commissure in the Spinal Cord (has occurred) Prior to the brain stem

What is the sensory loss due to a lesion in the Spinal Cord like?

Dissociative Loss - as discriminative and non-discriminative pathways decussate at different levels of the spinal cord - discriminative -sensory loss on same side of the body - non-discriminative - sensory loss on the opposite side of the body

What is the sensory loss due to a lesion in the Brain/Brainstem like?

Associative Loss - as discriminate and discriminative pathways have both decussated by the time of the spinal cord Both loss of sensations are on the opposite side of the body

Which somatosensory pathway contains more fibres?

Discrimintive Sensations

Which somatosensory pathway contains Less fibres?

Non-discriminative Sensations

What are the sensations of the non-discriminiative somatosensory pathway?

pain and temperature sensations

What is the pathway of the first order neuron in the central pathway of non-discriminative sensation?

1. Starts at Primary Root afferents 2. Dorsal root ganglion containing the cell bodies 3. Terminates in the Most dorsal region of the Dorsal Gray horn, terminating in the spinal cord at the same level it entered

What is the pathway of the second order neuron in the central pathway of non-discriminative sensation?

3. Dorsal gray horn of the spinal cord -Decussation at AWC Fissure 4. Lateral Spinothalamic Tract Joins the Medial Lemniscus 5. VP VentroPosterior Nuclei in the Thalamus

Where is the decussation in the central pathway of non-discriminative sensation?

From the dorsal gray horn of the spinal cord, the decussation occurs at the AWC Anterior White Commissure Fissure - the group of fibres cross over to join the Lateral Spinothlamic Tract - the fibres go up and join the encapsulated discriminative neurons in the Medial Lemniscus

What is the Lateral Spinothalamic Tract?

millions of fibres Lateral to the medulla Runs from the Spine up to the Thalamus Close to the lateral side of the medial lemniscus, eventually joins and mixes with he discriminative neurons in the medial lemniscus Organisation= First to arrive =leg. Last to arrive =neck

What does Commissure mean?

"crossing"

What is the pathway of the third order neuron in the central pathway of non-discriminative sensation?

5. VP Ventroposterior nucleus in the Thalamus 6. Internal capsule 7. 1 Primary Somatosensory Cortex (Termination placement accordingly)

Where is the termination placement of the non-discriminative sensation's third order neuron?

1 Primary Somatosensory Cortex The Non-discriminative 3rd order neuron's termination placement is according to which body part the non-discriminative Sensory INput is coming FROM -(as 1 Primary Somatosensory cortex/Post-central gyrus is somatotopically organised)

What is the organisation of the Lateral Spinothalamic Tract?

First fibres into LST = from Leg | Last fibres into LST = from neck

What is in the area between the Dorsal and Ventral Gray horn?

Mixture of Sensory and Motor (small LMNs) which innervate the muscle of the gut

What is the most highly organised part of the brain?

cerebral cortex | must pass through the thalamus to access it

What occurs at each synapse?

Information can be suppressed or highlighted

What sensory modification occurs originating from the cortex?

coming down from the cortex there are fibres which come down to modify the information which reaches the sensory cortex e.g. when you're having a kiss, you're not worrying about your foot Attends to the information/sensory area interested in -Modifies information at each level -Pay attention -Sensory modification/Modulation to selectively pick out what you want to hear