Week 2 - Michaels Flashcards
What does the term “somatotopic” mean?
Greek: body + place
- Contiguous map of the body surface can be found throughout all levels of the somatosensory system
- Ex: Topographic arrangement of the somatosensory cortex is often shown as the “Homunculus”
What is meant by the term “convergence”?
The small area where second order neuron receptive fields overlap.
-by stimulating a small area of skin in a particular area, it is possible to activate multiple second order neurons
Describe the major pathway by which information from the body about fine touch, vibration, and limb position reaches consciousness.
Dorsal Column/Medial Lemniscal Pathway:
- mechanoreceptors from the skin –> DRG
- DRG processes bifurcate –> dorsal horn
- dorsal horn –> enter fasciculus gracillus/cuneatus
- ascend spinal cord –> nucleus gracilis/cuneatus in caudal medulla
- 1° synapse –> 2°
- 2° cross midline –> medial lemniscus
- 2° ascend to synapse in ventrobasal complex (VPM/VPL) of the thalamus –> 3°
- 3° synapses on the posterior bank of the central sulcus (Primary Somatosensory Areas SI/SII and primary motor cortex)
What is the origin and termination of primary order neuron in the Dorsal Column/Lemniscal Pathway (fine touch, vibration, and position sense)?
- Origin:
- Peripheral process has mechanorecptors in the skin
- Cell body in DRG
- Central process enters dorsal horn on ipsilateral side –> Lamina V/Ventral horn/Dorsal column
- Termination:
- Central process terminates on 2° neuron in nuclei gracillus/cuneatus in caudal medulla
What is the origin and termination of secondary order neuron in the Dorsal Column/Lemniscal Pathway (fine touch, vibration, and position sense)?
- Origin:
- Cell body in dorsal column nuclei in the medulla
- Terminate:
- Axons cross midline in medial lemniscus and ascend to synapse on ventrobasal complex of the thalamus (VPL/VPM)
What is the origin and termination of tertiary order neuron in the Dorsal Column/Lemniscal Pathway (fine touch, vibration, and position sense)?
- Origin:
- Cell body in ventrobasal complex of thalamus (VPM/VPL)
- Terminate:
- Axon projects to Primary Somatosensory Area (SI), primary motor cortex, Secondary Somatosensory Area (SII), and association somatosensory cortical areas (parietal cortex)
Describe the major pathway by which information from the body about pain and temperature reaches consciousness.
Spinothalamic Tract: Pain and temperature pathway:
- 1° Nociceptive & Thermoreceptive afferent fibers enter Lissaur’s tract (ascend/descend)
- 1° form synapses in the substantia gelatinosa of the spinal cord –> 2° neurons
- 2° neurons cross midline in the anterior white commissure –> ascend in the anterolateral (ventrolateral) funiculus as the spinothalamic tract
- Collateral branches –> reticular formation/central gray to alert the body –> central lateral nucleus of the thalamus
- 2° synapses –> 3° neurons in VPL thalamus
- 3° project to ipsilateral primary somatosensory cortex (parietal lobe)
What is the origin and termination of primary order neuron in the Spinothalamic Tract (pain and temperature)?
- Origin:
- Peripheral process of nociceptive/thermoreceptive fibers in tissue
- Cell body in DRG
- Terminate:
- Central process passes through Lissaur’s tract (asend/descend) before synapsing in substantia gelatinosa
What is the origin and termination of secondary order neuron in the Spinothalamic Tract (pain and temperature)?
- Origin:
- Cell body in substantia gelatinosa
- Terminates:
- VPL (ventral posterolateral) thalamus
- collateral branches –> reticular formation/central gray –> central lateral nucleus of thalamus
What is the origin and termination of tertiary order neuron in the Spinothalamic Tract (pain and temperature)?
- Origin:
- Cell bodies in VPL (ventroposterolateral) thalamus
- Terminate:
- ipsilateral primary somatosensory cortex (parietal lobe)
Why is the synapse between the first and second order nociceptive neurons especially important?
- Intenxe noxious stimuli can cause the release of glutamate and Substance P (a neuropeptide) that can lead to changes in second order neuron
- e.g. upregulation of receptors with increase sensitivity to pain sensation
What is the hallmark of a brainstem lesion?
Cranial nerve signs on one side, coupled with long tract signs on the opposite side.
What are the two cranial nerves that attach at the forebrain?
Telencephalon: CN I - Olfactory (sensory)
Diencephalon: CN II - Optic (Sensory)
What are the two cranial nerves that attach at the midbrain?
CN III - Oculomotor (Motor)
CN IV - Trochlear (Motor)
What are the four cranial nerves that attach at the Pons?
- CN V - Trigeminal (Both)
- CN VI - Abducens (Motor)
- CN VII - Facial (Both)
- CN VIII - Vestibulo-cochlear (Sensory)
What are the three cranial nerves that attach at the medulla?
CN IX - Glosso-pharyngeal (Both)
CN X - Vagus (Both)
CN XII - Hypoglossal (Motor)
What is the one lonely cranial nerve that attaches at the cervical level of the spinal cord?
CN XI Spinal Accessory (Motor)
What is the mnemonic for the function of I-XII cranial nerves?
- Some (CN I - Sensory)
- Say (CN II - Sensory)
- Marry (CN III - Motor)
- Money (CN IV - Motor)
- But (CN V - Both)
- My (CN VI - Motor)
- Brother (CN VII - Both)
- Says (CN VIII - Sensory)
- Big (CN IX - Both)
- Brains (CN X - Both)
- Matter (CN XI - Motor)
- Most (CN XII - Motor)
How many pairs of spinal nerves are there?
31 pairs
What is the role of “reticular formation” in performing basic physiologic functions?
- “Packing material” that is key to survival
- Arousal, respiration, swallowing, HR, BP
What is the role of “pattern generators” in basic physiologic functions?
- An “autopilot” type of coordinated response
- Activated when a command comes down from motor cortex to a collection of brainstem neurons
- Neurons are wired together in a way such that pools of neurons are activated in the right order and timing to make something happen
What do cross-sections of the midbrain, pons, and brainstem look like or what are their unique features?
- Midbrain - Mickey Mouse
- Pons - potato
- Brainstem - monster
Where is the motor tigeminal nuclei located?
Dorsal mid pons
(medial to Main sensory nucleus)
How is the motor trigeminal nuclei organized?
- Receives central process of axons in Mesencephalic Trigeminal Nucleus
- Contains motor neurons of the trigeminal nerve.
- project to muscles of mastication & tensor tympani in middle ear
Where is the sensory trigeminal nuclei located?
“Main Sensory Nucleus”
Dorsal mid pons
(lateral to Trigeminal Motor Nucleus, inferior to superior cerebral peduncle)
How is the Main Sensory Nucleus organized?
- Major input to the nucleus is from mechanoreceptors
- Projects 2° neurons to the contralateral VPM of the thalamus by joining Ventral Trigeminothalamic Tract (VTT).
Where is the Spinal Trigeminal Nucleus located?
- A long nucleus extending all the way from the dorsal pons to the spinal cord
Inferior to Main Sensory Nucleus/Motor Nucleus
Medial to Spinal Trigeminal Tract
How is the Spinal Trigeminal Nucleus organized?
- Like face looking up the spinal cord to the cortex
- Superior part is mouth –> nose –>eyes –> forehead –> top of head –> back of head
How is touch, vibration, and position sense of the face processed?
- Mechanoreceptor of peripheral 1° axon picks of info –> sends to cell body in Trigeminal Ganglion
- Central process of 1° axon relays info to Main Sensory Nucleus in the pons –> synapses on 2° neuron
- 2° neuron projects to contralateral thalamus via Ventral Trigeminal Thalamic Tract –> enters VPM
How is pain & temperature information from the face processed?
- Mechanoreceptor of peripheral 1° axon picks of info –> sends to cell body in Trigeminal Ganglion
- Central process of 1° axon relays info to Main Sensory Nucleus in the pons –> synapses on 2° neuron that travels down through Spinal Trigeminal Tract
- 2° neuron projects to the lower part of the Spinal Trigeminal Nucleus –> crosses to contralateral side and projects to the contralateral thalamus
How do second order neurons project to the VPM of the thalamus?
via the Ventral Trigeminothalamic Tract (VTT)
How does sensory information of the intraoral cavity get processed?
- Mechanoreceptor of peripheral 1° axon picks of info –> sends to cell body in Trigeminal Ganglion
- Central process of 1° axon relays info to Main Sensory Nucleus in the pons –> synapses on 2° neuron
- 2° neuron projects to bilateral thalamus via Dorsal Trigeminal Thalamic Tract –> enters VPM
How is the VPM organized?
Medial –> Lateral
Taste –> Intraoral –> Face
What are the sensory functions of the facial nerve?
- Somatic sensory:
- afferent supply to ipsilateral part of outer ear, nasal cavity and soft palate
- Visceral (special) sensory:
- Ipsilateral afferent supply for tast to the anterior 2/3rds of the tongue
What are the motor functions of the facial nerve?
- Branchial motor
- Major role
- Efferent supply to ipsilateral muscles of facial expression & stapedius
- Visceral motor
- Preganglionic parasympathetics to lacrimal gland, submandibular gland, & sublingual gland
Where is the Motor Facial Nucleus in the brainstem?
Ventrolateral caudal pons
(near the intersection of the pons & medulla)
What is the course taken by the motor nerve fibers as they exit the Motor Nucleus of VII?
- Motor neurons originate in the Motor Nucleus of VII (caudal pons) –>
- project up and over abducens nucleus as the internal genu –>
- exit brainstem to innervate the ipsilateral side of the face
What is the role of the trigeminal and facial nerve in the corneal blink reflex?
- Sensory afferents travel in V1 to the trigeminal ganglion –> descend to Spinal Trigeminal Tract
- Output from the Spinal Trigeminal Nucleus is to both motor nuclei of the facial nerve (bilateral)
- Efferents from the Facial Motor Nuclei project to orbicularis oculi causing a bilateral blink!
What is the result of upper motor neuron damage?
- Unilateral corticobulbar damage (upper motor neuron damage on one side) causes weakness of the contralateral lower face ONLY
- spares the contralateral upper face
What is the result of lower motor neuron damage?
- Unilateral lower motor neuron damage causes weakness in the entire ipsilateral half of face
- due to facial nerve or nucleus damage
