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)
What is known as the Sensory Relay Station?
Thalamus
All sensory information to cerebral cortex synapses in the _________ before going to the cortex (_______ is a partial exception)
All sensory information to cerebral cortex synapses in the thalamus before going to the cortex (smell is a partial exception)
__________________ connects directly to the thalamus while other cranial nerves send fibres to the thalamus from lower (brainstem) nuclei
Cranial nerve II (optic) connects directly to the thalamus while other cranial nerves send fibres to the thalamus from lower (brainstem) nuclei
The projection from the thalamus to the cortex uses the ______________
The projection from the thalamus to the cortex uses the Internal Capsule
______ horns receive axons of sensory (afferent) neurons
Dorsal horns receive axons of sensory (afferent) neurons
______ horns send out the axons of motor (efferent) neurons
Ventral horns send out the axons of motor (efferent) neurons
Spinal nerve roots are functionally distinct :
- ____________ sensory
- _____________ motor
Spinal nerve roots are functionally distinct
- Posterior (dorsal) sensory
- Anterior (ventral) motor
Organisation of Spinal Cord White Matter?
Sensory modalities carried by the Dorsal Column Pathway? (3)
- Discriminative Touch
- Vibratory Sense
- CONSCIOUS Proprioception
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”
Primary Somatosensory area (receptive area for touch) of the cortex?
Postcentral Gyrus of the Parietal Lobe
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
Sensory modalities carried by the Spinothalamic Pathway? (4)
- Pain Localization
- Temperature
- Non-Discriminative Touch
- Pressure
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
Sensory modalities carried by the Spinocerebellar Pathways?
What is special about the way this is conveyed?
Unconscious Proprioception
- Do not project to the thalamus/cerebral cortex, and hence DOES NOT REACH CONSCIOUS AWARENESS
- Most proprioceptive information (tendons, muscles and joints) is transmitted directly to the cerebellum (Two-Neuron Pathway)
- Provides the cerebellum with minute-by-minute feedback on what the muscles are doing
Spinocerebellar pathways remain IPSILATERAL!
- Posterior tract does not cross
- Anterior tract ‘double-crosses’!
Spinocerebellar pathways IPSILATERAL or CONTRALATERAL
Consequences of Lesion?
Spinocerebellar pathways are IPSILATERAL?
- Posterior tract does not cross
- Anterior tract ‘double-crosses’!
Cerebellar Lesions => IPSILATERAL Malfunctioning
Cerebral Lesions => CONTRALATERAL Malfunctioning
What is Romberg’s Sign and what is it indicative of?
Romberg’s Sign: can maintain balance with the eyes open (Begins to totter when asked to close eyes)=> indicative of DORSAL COLUMN LESION
Dorsal Columns vs. Spinothalamic Tracts?
Pathways?
Sensory Information?
Dorsal columns: carry information related to proprioception, touch, and vibration sensations from skin and muscle to brain.
- Fasciculus Gracilis: lower extremities
- Fasciculus Cuneatus: upper extremities.
Spinothalamic tracts information related to pain, temperature, and crude touch from the skin/internal organs to brain.
- Lateral spinothalamic tract: pain and temperature
- Anterior spinothalamic tract: crude touch.
