Sensory Systems of the Brain L3 Flashcards
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
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
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
What is a horn?
the Gray matter on Each Side of the spinal cord is Subdivided into region calls Horns
What is the Posterior Dorsal Gray Horn?
Contains 2x neurons:
- Cells bodies and axons of inter-neurons
- Axons of incoming sensory neurons
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
What is the AWC?
Anterior White Commissure
-Connects the white matter on the Right and Left sides of the spinal cord
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)
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
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
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
What is the central pathway of discriminative sensation?
Touch and pressure
What is the receptor for discriminative sensation?
Encapsulated receptors
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
What is the Gracile Nuclei/Fasiculus?
Part of the dorsal column/nuclei
Receives impulses from the Lower body (leg)
What is the Cuneate Nuclei/Fasiculus ?
Part of the dorsal column/nuclei
Receives impulses from the Upper body (arm)
Is the gracile and cuneate nuclei/fasiculus a discontinuous or continuous nuclei?
continuous nuclei
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
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?
- Starts at Primary Root afferents
- Dorsal root ganglion containing the cell bodies
- 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?
- Dorsal gray horn of the spinal cord
-Decussation at AWC Fissure - Lateral Spinothalamic Tract
Joins the Medial Lemniscus - 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?
- VP Ventroposterior nucleus in the Thalamus
- Internal capsule
- 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
