L3 Central Somatosensory Pathways & Thalamus Flashcards
Sensory information about internal & external environment is carried to CNS in __________ nerve fibres running in cranial & spinal nerves
Sensory information about internal & external environment is carried to CNS in afferent nerve fibres running in cranial & spinal nerves
Sensory information carried in Cranial nerves (5)
Special Senses
- Olfaction
- Vision
- Taste
- Hearing
- Balance
How are Somatic Senses carried from the trunk/limbs and from the head?
Peripheral information carried from trunk/limbs in spinal nerves, from the head predominantly in one cranial nerve (trigeminal, V)
Modalities of the Somatosensory System? (4)
- Touch (discriminative (Fine), non-discriminative (Crude))
- Temperature
- Proprioception (body position: proprioceptors embedded in muscle fibers sense contraction of muscles => relays to cerebellum coordinating movement)
- Nociception (potentially injurious (‘noxious’) stimuli)
Somatosensory System reacts to diverse stimuli through receptors, causing impulses to flow via ____________nerves, through _________ in the spinal cord, and into the brain for processing
Somatosensory System reacts to diverse stimuli through receptors, causing impulses to flow via sensory (afferent) nerves, through tracts in the spinal cord, and into the brain for processing
What is carried along with discriminative (fine) touch afferents?
Vibration sense & conscious proprioception
What is carried along with pain/temperature afferents?
Non-discriminative (Course) touch & pressure
General principal of CNS organisation: pathways conveying sensory information to a conscious level as well as descending motor pathways _____________ from one side of CNS to other
General principal of CNS organisation: pathways conveying sensory information to a conscious level as well as descending motor pathways “cross over” ( decussate ) from one side of CNS to other
First Order (Primary) Neuron sends axon into ______ or _______; cell body lies in a ______
First Order (Primary) Neuron sends axon into cord or brainstem; cell body lies in a ganglion
Second order (secondary) neuron is located in _______ and its axon projects to ___________ (_________lateral)
Second order (secondary) neuron is located in CNS and its axon projects to the thalamus (Contralateral)
Third order (tertiary) neurone’s cell body is located in a specific __________ nucleus; axon projects to a specific area of _______lateral cerebral cortex (_______________________)
Third order (tertiary) neurone’s cell body is located in a specific thalamic nucleus ; axon projects to a specific area of ipsilateral cerebral cortex (primary somatosensory cortex)
Small vs. Large Mylenated First Order Neurons
Right & left Thalami control the flow of sensory information to the cortex and are across midline by the ________________ forming the lateral walls of the _________
Right & left Thalami control flow of sensory information to the cortex and are joined across midline by the Interthalamic Adhesion forming the lateral walls of the Third Ventricle
The Thalamus is the largest part of the ____________ (between brainstem/ cerebral hemispheres)
The Thalamus is the largest part of the Diencephalon (between brainstem/ cerebral hemispheres)
Organisation of Spinal Cord White Matter?
Pathway of Dorsal Columns
- First Order fibers enter the cord and ascend _________ in the _________________ (Lower limb/trunk) and __________________ (Upper Limb/trunk) to the __________________and synapse (Nucleus __________ or ___________)
- Second Order axons decussate in ____________________ and ascend as ______________ ________________ (aka. Trigemnial Lemnuscus) to the Thalamus
- Third Order neurons project from the Thalamus to the ____________________ “Somatotopically”
Pathway of Dorsal Columns
- First Order fibers enter the cord and ascend Ipsilaterally in the GRACILE FASCICULUS (Lower limb/trunk) and CUNEATE FASCICULUS (Upper Limb/trunk) to the MEDULLA OBLONGATA and synapse (NUCLEUS GRACILIS or CUNEATUS)
- Second Order axons decussate in MEDULLA and ascend as Contralateral Medial Lemnisus (aka. Trigemnial Lemnuscus) to the THALAMUS
- Third Order neurons project from the Thalamus to the POSTCENTRAL GYRUS “Somatotopically”
What effect do lesions of the Doral Columns have?
What is the common sign of this?
What Can cause these lesions? (4)
Lesions result in loss of fine tactile sensation and interference with proprioception e.g. Sensory Ataxia (ataxia = loss of coordination
Rommberg’s Sign
Causes:
- Vit B12 Deficiecny
- Multiple Sceleroris
- Diseases of Peripheral Nerves
- Tertiary Syphillis
Identify these parts of the Dorsal Column
Two types of Pain Localization/Temperature Fibers? What pathway are they carried on?
Carried on Spinothalamic Pathway
Arrangement of Dorsal Columns vs. Spinothalamic Tracts?
General Rules for the effect of Spinothalamic Pathways lesions?
- Pain Localization/Temperature: cross immediately => Lesion leads to Contralateral loss of pain/temperature a few segments below
- Proprioceptive/Fine Touch: ascend ipsilaterally, cross in MEDULA => Lesion leads to Ipsilateral loss of tactile and limb position sense at lesion level and below
- Lesions of SPINAL CORD and LOWER BRAINSTEM can damage one pathway preferentially and spare the other
- Lesions of HIGHER BRAINSTEM or CEREBRAL HEMISPHERE lead to loss of all sensation on Contralateral side
