Neuro Flashcards
- Describe the laminae and their contents
- Laminae I – VI: SENSORY
- Lamina VII: AUTONOMIC
- Laminae VIII & IX: MOTOR
- Lamina X: Gray commissure, contains small neurons and glia.
Neuronal Architecture – Laminae (Sensory)
- Lamina I
- pain neurons tend to be small and non-myelinated
- thus they are exhausted when they reach the spinal cord
- lamina I contains the posteromarginal nucleus, which receives pain and temperature inputs
- first order neurons begin to synapse and partially form the spinothalamic tract
- Lamina II – Substantia Gelatinosa:
- Extends the entire length of the spinal cord, contains small neurons that send excitatory and inhibitory synapses onto the STT ^[spinothalamic] primary cells (gating effect on sensory transmission).
- Rostrally, it continues into the spinal nucleus of V.
- Afferents: small-diameter sensory fibres carrying pain & temperature, larger mechanoreceptor nerves
- Small inhibitory interneurons in the lamina filter and modulate incoming sensory information
- Efferents: contralateral STT (together with cells from Laminae I, IV & V)
- Contains small neurons that send excitatory and inhibitory synapses onto the STT primary cells (gating effect on sensory transmission).
- Contains high concentration of Substance P (neuropeptide, plays a role in pathways modulating pain sensibility) and enkephalinergic internuncials (opioid inhibiting pain transmission)
- Laminae III & IV (V) – Nucleus Proprius ^[aka trigeminal nucleus which is responsible for pain and temperature]:
- Extends the entire length of the spinal cord
- afferent: large sensory fibres carrying PRIMARILY position & light touch, - project to dorsal column nuclei. ^[no efferents?]
- which project to dorsal column nuclei
- afferent: small diameter sensory fibres carrying noxious stimuli (pain and temperature) and interneurons from lamina II
- project to contralateral spinothalamic tract
Neuronal architecture - Laminae (Sensory)
- Lamina VI
- small interneurons
- afferent from muscle spindles (proprioception)
- efferents to motor neurons in laminae VIII and IX
- play a role in spinal reflex arc
- send information to brain via spinocerebellar pathways
Neuronal Architecture – Laminae (Visceral)
- Lamina VII:
- large heterogenous zone: autonomic nervous system and unconscious activity
- size varies through the length of the spinal cord
- afferents from viscera
- efferents: motor information to viscera
- gives rice to cells involved in autonomic system
- Includes
- Dorsal Nucleus (Clarke’s nucl; Posterior Thoracic Nucl) for unconscious proprioception
- extends from C8- L2/3
- major relay station for unconscious proprioception
- afferents: sensory nerves from muscle spindles and tendon organs
- efferent/projection: posterior spinocerebellar tract
- Intermediomedial nucleus
- at all spinal cord levels
- afferents: sensory information from viscera
- efferents to lateral horn
- Intermediolateral Nucleus
- extends T1-L2
- preganglionic sympathetic neurons.
- Sacral autonomic nuclei
- extend S2-4
- preganglionic parasympathetic neurons
##### Neuronal Architecture – Laminae (Motor)
- Motor Neuron Columns:
- α motor neurons: Large multipolar cells innervate extrafusal muscle fibres of skeletal muscles
- γ motor neurons: Small multipolar cells innervate intrafusal muscle fibres of neuromuscular spindles
- Medial (VIII): LMNs to axial and proximal appendicular musculature
- Lateral (IX): LMNs to distal appendicular musculature. Present in cervical and lumbosacral segments
- Shorter distinct columns:
- C1-6: spinal accessory nucleus
- C3-5: phrenic motor nucleus
- S1-3: Onuf’s nucleus (striated mm control of defecation and micturition, pudendal n.)
Neuronal architecture - Lamina X(visceral)
- grey commissure
- surrounds the central canal
- site of decussation of commissural fibres
![[Pasted image 20240221105714.png]]
- Describe the course of the conscious ascending tracts
The tracts associated with conscious sensation are:
- DCML
- spinothalamic tract/spinal lemniscus
Unconscious sensation:
- dorsal spinocerebellar
- cuneocerebellar
- ventral and rostral spinocerebellar
-
Spinothalamic Tract: Originates from C / A∂-type fibres in the lateral part of the dorsal root. Carries information about pain and temperature(lateral), and crude touch and pressure, to the thalamus (anterior). There is a high degree of somatic organisation, allowing for discrimination of location and intensity of pain
- (1) Nerve fibres entering the dorsal horn
- (2) either enter Lissauer’s Tract (LT) and ascend or descend one or two levels.
- (3) then enter the dorsal horn, terminate in laminae I, II, III, IV, where they synapse. Most in Substantia gelatinosa
- (4) After synapsing, 2°fibres cross the midline, ventral to the intermediate grey, then traverse the anterior horn to reach the antero-lateral funiculus.
- (5) They turn and ascend to thalamus (VPL) and the somatosensory cortex
Characterised by a sharp stabbing pain.
Note:
- Fibres that enter caudally are displaced laterally by more rostral fibres.
- Collaterals of these fibres enter the reticular formation in the lower brainstem.
-
Dorsal Column / Medial Lemniscus Pathway: Originates from large diameter, heavily myelinated A-type fibres (Aβ) in the medial part of the dorsal root. Carries conscious information about discriminative touch, 2-point discrimination, vibration, and conscious proprioception to the thalamus.
- (1) Large myelinated fibres enter medial to LT, turn rostrally and ascend in the posterior funiculus. Fibres from the lower limb form the gracile fasciculus, while fibres from the upper limb form the cuneate fasciculus.
- (2) Fibres from the lower limb synapse in the gracile nucleus; fibres from the upper limb synapse in cuneate nucleus in the closed medulla.
- (3) Secondary fibres take an arcuate course, cross the midline at the sensory decussation to form the medial lemniscus then again turn rostrally.
- (4) They turn and ascend to thalamus (VPL) and the sensory cortex
The next tracts carry unconscious sensory information to the cerebellum:
-
Dorsal Spino-cerebellar Tract: Carries unconscious proprioceptive information, concerning muscle force and stretch, from lower limb muscles and tendons to the cerebellum.
- (1) Information coded by Golgi tendon organs (strain) and muscle spindles (stretch) in lower limb muscles is carried in large diameter fibres (Aα) that pass through the dorsal horn and synapse on cells in Rexed’s lamina VII, Nucleus dorsalis / Clarke’s nucleus (C8-L2/3).
- (2) Secondary fibres enter the lateral funiculus, near the dorsal root, and turn rostrally, forming the Dorsal Spino-cerebellar Tract.
- (3) In the upper medulla, this tract enters the inferior cerebellar peduncle. and fibres terminate in the ipsilateral cerebellar cortex.
-
Cuneo-cerebellar Tract: Carries information from upper limb muscles and tendons about muscle force and stretch to the cerebellum. Upper limb equivalent of dorsal spino-cerebellar tract.
- (1) Information coded by Golgi tendon organs (strain) and muscle spindles (stretch) is carried in fibres that enter the dorsal horn then turn rostrally.
- (2) 1° fibres synapse in the Accessory cuneate nucleus, in the medulla (the Clarke’s column equivalent for the upper limb).
- (3) 2° fibres enter the inferior cerebellar peduncle, along with the Dorsal Spino-cerebellar fibres to terminate in the ipsilateral cerebellar cortex.
-
Ventral Spino-cerebellar Tract: Carries predominantly force information from lower limb muscles, to the ipsilateral cerebellum.
- (1) Information from Golgi tendon organs (strain) in the lower limb muscles is carried in fibres that enter the dorsal horn and synapse in the base of the dorsal horn (Rexed lamina VI).
- (2) 2°fibres cross the midline, enter the ventral part of the lateral funiculus, then turn rostrally in the Ventral spino- cerebellar tract.
- (3) In the pons/midbrain, these fibres enter the Superior Cerebellar Peduncle, then re-cross the midline to terminate in the ipsilateral cerebellar cortex
-
Rostral spino-cerebellar tract
Carries predominantly force information from upper limb muscles, to the ipsilateral cerebellum.
- (1): Information from Golgi tendon organs (strain) in the upper limb muscles is carried in fibres that enter the dorsal horn and synapse in the base of the dorsal horn (Rexed lamina VI).
- (2): 2°fibres ascend ipsilaterally
- (3):In the brainstem, fibres enter the cerebellum through the Inferior Cerebellar Peduncle
Other ascending pathways with role in pain sensation
Medial pain system: crude, not well-localised pain.
Medial tracts are usually more primitive.
Note also that tracts that go to the cerebellum do not decussate.
- spinoreticular
- old, multi-synaptic tract
- originates from dorsal horn neurons
- ipsilateral ascending fibres terminating in the reticular formation
- projects to intralaminar nuclei of thalamus
- important role in sensation of deep, burning chronic pain
- spinotectal
- originates from dorsal horn
- ascends contralaterally to superior colliculus & periaqueductal gray
- role in regulating pain
- Lissauer’s tract: a ‘bridge’
- Describe the course of the unconscious ascending tracts
The next tracts carry unconscious sensory information to the cerebellum:
-
Dorsal Spino-cerebellar Tract: Carries unconscious proprioceptive information, concerning muscle force and stretch, from lower limb muscles and tendons to the cerebellum.
- (1) Information coded by Golgi tendon organs (strain) and muscle spindles (stretch) in lower limb muscles is carried in large diameter fibres (Aα) that pass through the dorsal horn and synapse on cells in Rexed’s lamina VII, Nucleus dorsalis / Clarke’s nucleus (C8-L2/3).
- (2) Secondary fibres enter the lateral funiculus, near the dorsal root, and turn rostrally, forming the Dorsal Spino-cerebellar Tract.
- (3) In the upper medulla, this tract enters the inferior cerebellar peduncle. and fibres terminate in the ipsilateral cerebellar cortex.
-
Cuneo-cerebellar Tract: Carries information from upper limb muscles and tendons about muscle force and stretch to the cerebellum. Upper limb equivalent of dorsal spino-cerebellar tract.
- (1) Information coded by Golgi tendon organs (strain) and muscle spindles (stretch) is carried in fibres that enter the dorsal horn then turn rostrally.
- (2) 1° fibres synapse in the Accessory cuneate nucleus, in the medulla (the Clarke’s column equivalent for the upper limb).
- (3) 2° fibres enter the inferior cerebellar peduncle, along with the Dorsal Spino-cerebellar fibres to terminate in the ipsilateral cerebellar cortex.
-
Ventral Spino-cerebellar Tract: Carries predominantly force information from lower limb muscles, to the ipsilateral cerebellum.
- (1) Information from Golgi tendon organs (strain) in the lower limb muscles is carried in fibres that enter the dorsal horn and synapse in the base of the dorsal horn (Rexed lamina VI).
- (2) 2°fibres cross the midline, enter the ventral part of the lateral funiculus, then turn rostrally in the Ventral spino- cerebellar tract.
- (3) In the pons/midbrain, these fibres enter the Superior Cerebellar Peduncle, then re-cross the midline to terminate in the ipsilateral cerebellar cortex
-
Rostral spino-cerebellar tract
Carries predominantly force information from upper limb muscles, to the ipsilateral cerebellum.
- (1): Information from Golgi tendon organs (strain) in the upper limb muscles is carried in fibres that enter the dorsal horn and synapse in the base of the dorsal horn (Rexed lamina VI).
- (2): 2°fibres ascend ipsilaterally
- (3):In the brainstem, fibres enter the cerebellum through the Inferior Cerebellar Peduncle
- Describe the course of the conscious descending tracts
The corticospinal tracts
- Corticospinal fibres originate from both frontal and parietal cortices
- Cells of origin are large triangular or pyramidal cells in layer V of neocortex
- ![[Pasted image 20240313124535.png]]
- where things can go wrong: hemiparesis and failure to abduct eye; ptosis/dilation/down and out; tongue deviation
- ![[Pasted image 20240313124545.png]]
- Originate from cells in M1, SMA, PMA, S1 and descend through the corona radiata, then the internal capsule (posterior limb, posterior portion – CBT occupies anterior portion)
- Enter cerebral peduncles ~ middle 3/5; leg is most lateral
- Pass through the pons, crossed by the pontocerebellar fibres
- Enter the pyramids on the ventral aspect of the medulla
- 80% axons cross in the pyramidal decussation to formthe lateral corticospinal tract. ~10% do not cross andremain in the lateral CST (not shown); another ~10% also remain on the ipsilateral side and form the ventral/anterior corticospinal tract, the majority of these cross before entering the ventral horn
- Glutamatergic fibres terminate at all levels of the spinal cord
- Provide input to lower motor neurons of ventral horn that innervate skeletal muscles, especially flexors. Some send collaterals to thalamus, reticular formation dorsal column nucl,(sensory modulation) and interneurons in spinal cord (motor modulation)
The corticobulbar fibres
The corticobulbar fibres originate from cells in the head and face regions of the motor areas (lateral regions).
It controls both sides bilaterally.
Exceptions include lower part of CN VII and CN XII.
They descend through the corona radiata, then the middle (around the genu) part of the internal capsule.
They enter the cerebral pedncles medial to the CST fibres.
They synapse bilaterally on the motor nuclei of cranial nerves, directly and via interneurons (exc parts of VII and XII) and reticular formation.
They are glutamatergic/excitatory fibres.
![[Pasted image 20240314110956.png]]
Extrapyramidal tracts
There are four main extrapyramidal tracts.
- rubrospinal: important for quality of life, responsible for skilled movements, mainly terminate at cervical levels
- reticulospinal both medial and lateral, essential for life (posture, balance and gaze): modifies reflex control of extensors
- tectospinal: head orientation to external stimuli, mainly terminates at cervical levels
- vestibulospinal, both medial and lateral: responsible for posture and balance, medial tract terminates at cervical levels
### Rubrospinal
- controls flexion in upper limb e.g. involuntary arm movement to keep balance
- irginates from cells in red nucleus in the upper midbrain (level of superior colliculus)
- fibres cross midline in midbrain
- red nucleus receives input from motor areas that are somatotopically organised – output from nucleus is also somatotopic = “corticorubrospinal” pathway
- while it receives input from cortex it is not ITSELF involved in conscious control
- discrete bundle of fibres in the lateral medulla, and in the lateral SC adjacent to the corticospinal tract
- fibres terminate mainly in cervical levels, and mianly innervate flexor groups
- fibres are glutamatergic
### Reticulospinal
- pontine or medial – stimulate limb extensors and inhibit flexors
- does NOT cross
- originate from large cells in PRF
- terminate at all levels of spinal cord (VII, VIII) on ipsilateral alpha and gamma motor neurons
- activates spinal reflexes of antigravity muscles: stimulate limb extensors helping to maintain posture (enhances anti-gravity spinal reflexes that hold the body upright)
- stabilises in anticipation of other movements
- contains enkephalin, substance P as well as glutamate
- medullary/lateral tract
- stimulates limb flexors and inhibits axial and limb extensor muscles
- arises from large cells in the medial medulla
- fibres terminate at all levels of the spinal cord (8,9) on alpha and gamma motor neurons
- inhibits antigravity/axial muscles from relfex control, stimulate limb flexors (inhibits spinal reflexes that hold the body upright e.g. axial and limb extensors)
Tectospinal
- coordinates head and eye movement i.e. involuntary adjustment of head position on visual stimuli
- originate from cells in deep layers of superior colliculus
- SC gets direct input from retina, VC, somatosensory and auditory systems
- inputs are mapped
- fibres cross midline and midbrain
- descend in contralateral central medulla, close to medial lemniscus
- terminate in contralateral intermediate grey (laminae 6,7) in the cervical layers of sc
- primary role in orientation reflexes of the head, especially towards auditory, visual and somatosensory stimuli
### Vestibulospinal
- playa role in maintaining erect position by activation anti-gravity muscles i.e. control extension in extremities
- originate from cells in lateral and medial vestibular nuclei of CN VIII
- these are relay cells that get input from cells in the vestibular ggl (in IAM) and cerebellum
- fibres from the **medial vestibular nucleus descend bilaterallyin te MLF to lower medulla (spinal accessory nucleus) and upper cervical SC to innervate muscles controlling head position and orientation reflexes
- fibres from the **lateral nucleus project to all levels of the ipsilateral SC
- these pathways mainly innervate extensor groups and help maintain posture and balance
- Describe the course of the unconscious descending tracts
Extrapyramidal tracts
There are four main extrapyramidal tracts.
- rubrospinal: important for quality of life, responsible for skilled movements, mainly terminate at cervical levels
- reticulospinal both medial and lateral, essential for life (posture, balance and gaze): modifies reflex control of extensors
- tectospinal: head orientation to external stimuli, mainly terminates at cervical levels
- vestibulospinal, both medial and lateral: responsible for posture and balance, medial tract terminates at cervical levels
### Rubrospinal
- controls flexion in upper limb e.g. involuntary arm movement to keep balance
- irginates from cells in red nucleus in the upper midbrain (level of superior colliculus)
- fibres cross midline in midbrain
- red nucleus receives input from motor areas that are somatotopically organised – output from nucleus is also somatotopic = “corticorubrospinal” pathway
- while it receives input from cortex it is not ITSELF involved in conscious control
- discrete bundle of fibres in the lateral medulla, and in the lateral SC adjacent to the corticospinal tract
- fibres terminate mainly in cervical levels, and mianly innervate flexor groups
- fibres are glutamatergic
### Reticulospinal
- pontine or medial – stimulate limb extensors and inhibit flexors
- does NOT cross
- originate from large cells in PRF
- terminate at all levels of spinal cord (VII, VIII) on ipsilateral alpha and gamma motor neurons
- activates spinal reflexes of antigravity muscles: stimulate limb extensors helping to maintain posture (enhances anti-gravity spinal reflexes that hold the body upright)
- stabilises in anticipation of other movements
- contains enkephalin, substance P as well as glutamate
- medullary/lateral tract
- stimulates limb flexors and inhibits axial and limb extensor muscles
- arises from large cells in the medial medulla
- fibres terminate at all levels of the spinal cord (8,9) on alpha and gamma motor neurons
- inhibits antigravity/axial muscles from relfex control, stimulate limb flexors (inhibits spinal reflexes that hold the body upright e.g. axial and limb extensors)
Tectospinal
- coordinates head and eye movement i.e. involuntary adjustment of head position on visual stimuli
- originate from cells in deep layers of superior colliculus
- SC gets direct input from retina, VC, somatosensory and auditory systems
- inputs are mapped
- fibres cross midline and midbrain
- descend in contralateral central medulla, close to medial lemniscus
- terminate in contralateral intermediate grey (laminae 6,7) in the cervical layers of sc
- primary role in orientation reflexes of the head, especially towards auditory, visual and somatosensory stimuli
### Vestibulospinal
- playa role in maintaining erect position by activation anti-gravity muscles i.e. control extension in extremities
- originate from cells in lateral and medial vestibular nuclei of CN VIII
- these are relay cells that get input from cells in the vestibular ggl (in IAM) and cerebellum
- fibres from the **medial vestibular nucleus descend bilaterallyin te MLF to lower medulla (spinal accessory nucleus) and upper cervical SC to innervate muscles controlling head position and orientation reflexes
- fibres from the **lateral nucleus project to all levels of the ipsilateral SC
- these pathways mainly innervate extensor groups and help maintain posture and balance
- List the somatic motor cranial nerves: entry, exit, function, location in brainstem
Recall that 3, 4, 6 and 12 have pure somatic motor nuclei and sit medially.
Oculomotor
Motor nucleus
Superior colliculus
Edinger Westphal
Superior colliculus
Ciliary (parasympathetic)
Ciliary & pupillary muscles
Trochlea
Motor nucleus
Inferior colliculus
Superior oblique muscle
Trigeminal
Motor nucleus
Superior colliculus - pons
Principal V
Pons
Semilunar (sensory)
Spinal V
Medulla - upper spinal cord
Semilunar (sensory)
Mesencephalic
Superior colliculus - upper pons
VERY SPECIAL! Sensory cell bodies within the CNS
Sensation (proprioception) of face
Abducens
Motor nucleus
Pons
Lateral rectus muscle
Facial
Motor nucleus
Lower pons
Super salivatory
Lower pons
Pterygopalatine & Submandibular (parasympathetic)
Solitary nucleus (taste)
Open & closed medulla
Geniculate (sensory)
(Spinal V)
Medulla - upper spinal cord
Geniculate (sensory)
Somatic sensation around the ear
Glossopharyngeal
Solitary nucleus (rostral)
Open & closed medulla
Inferior ganglionof IX (in jugular foramen)
Solitary nucleus (caudal)
Open & closed medulla
Inferior ganglionof IX (in jugular foramen)
Spinal V
Medulla - upper spinal cord
Superior ganglionof IX (in jugular foramen)
Nucleus ambiguus
Open & closed medulla
Inferior salivatory
Openmedulla
Otic (parasympathetic)
Parotid gland
Vagus
Dorsal motor nucleus of X
Open & closed medulla
Walls of viscera (parasympathetic)
Spinal V
Medulla - upper spinal cord
Superiorganglionof X (in jugular foramen)
Solitary nucleus
Open & closed medulla
Inferior ganglionof X (in jugular foramen)
Taste (epiglottis); pharynx, larynx, trachea, esophagus, thoracic and abdominal viscera (visceral afferent)
Accessory (cranial)
Nucleus ambiguus
Open & closed medulla
Intrinsic muscles of thelarynx; spinal = scm, trapezius
Hypoglossal
XII motor nucleus
Open & closed medulla
Muscles of the tongue except palatoglossus
- List general sensory cranial nerves and their features
see C Brock table
- Describe visceral/branchial motor cranial nerves and their features
- Describe special sensory cranial nerves and their features
CN1 Olfactory Sensory Special Sensory: smell cribiform plate (ethmoid
bone)
Rostral to brain stem –
lies under frontal lobe
CN2 Optic
Retina ganglia optic
nerve optic chiasm Optic
tract thalamus (lateral
geniculate nucleus)
occipital lobe
Sensory Special Sensory: Sight
(joining of retinal ganglion cells)
Optic canal (sphenoid bone) Rostral to brainstem –
connects to occipital
lobe via thalamus
CN8 Vestibulocochlear
Travels through internal
acoustic meatus
(temporal bone) before
splitting into trochlear
and cochlear nerves
Sensory Special Sensory: Hearing (cochlear) and balance (vestibular) Internal acoustic meatus Pons (lateral and
caudal aspect
- Label a diagram of dorsal brainstem
- Label a diagram of ventral brainstem
- Describe the sensory territory of V1/2/3
- Ophthalmic branch or V1 - sensations from the nasal cavity, skin of forehead, upper eyelid, eyebrow and nose
- Maxillary branch or V2 - sensations from lower eyelid, upper lips and gums, teeth of the maxilla, cheek, nose, palate, and pharynx
- Mandibular branch or V3 - sensations from teeth of the mandible, lower gums and lips, palate and tongue
Describe innervation of facial nerve branches
Nerve reaches the muscles of facial expressions, reaches the parotid gland and split into five branches:
- temporal
- zygomatic
- buccal
- mandibular
- cervical
Nerve reaches the muscles of facial expressions, reaches the parotid gland and split into five branches:
- temporal
- zygomatic
- buccal
- mandibular
- cervical
- frontalis
- orbicularis oculi - circular, around the eye responsible for closing the eye
- levator labii superioris - elevating the upper lib
- zygomaticus
- buccinator - innervated by CN VII (drooling, big buccinator)
- risorius - smiling muscle
- procerus
- corrugator supercilli
- nasalis
- orbicularis oris - surrounds the lips and close your mouth
- depressor anguli oris - depressing angle of the mouth
- platysma - covers the neck
- depressor labii inferioris
- What relationship does sympathetic innervation of eye have to trigeminal nerve
Note: the trigeminal nerve does NOT have autonomic fibres BUT does have hitchhiking sympathetic and parasympathetic fibres.
The nasociliary nerve (off ophthalmic) carries sympathetic fibres, picked up in the cavernous sinus and distributes them:
- long ciliary branches (V1) to dilator pupillae muscles
- via branches of the ciliary ganglion (of III - oculomotor nerve), short ciliary nerves ^[post-ganglionic]
- sympathetic fibres to levator palpebrae superioris travel in upper division of oculomotor nerve (III)
- note that sympathetic fibres do NOT synapse, just pass through
- e.g. superior cervical ganglion—> internal carotid artery
- Name and describe the roles of the trigeminal nuclei
Motor nucleus of V
- located at mid pons,at level of entry of the nerve
- as it is a branchiomotor nucleus, we find it laterally, close to the sensory nucl.
- innervates mm connected to the embryonic mandibular arch: mm of mastication, mylohyoid, digastric (ant belly) + tensor veli palatini, tensor tympani
- receive bilateral corticobulbar input from motor cortices (contralateral more strongly)
#### Supratrigeminal nucleus
- part of the reticular formation
- acts as pattern generator for mastication
- in conscious person it is constantly active
- in erect position activates jaw closing
- in horizontal position activates the lateral pterygoid to prevent asphyxia
- general anaesthesia inactivates the nucleus ^[hence intubation is required]
Mesencephalic nucleus
- only sensory nucleus in the brain that acts as a ganglion within the CNS (ie it is equivalent to a dorsal root ganglion of the spinal cord, or the trigeminal ganglion, where cell bodies are found)
- dendrites of the pseudo-unipolar sensory cells originate at muscle spindles of the jaw mm (as well as TMJ itself?) (via V3) and as mechanoreceptors from periodontal ligaments in teeth and gums (via V2 and V3).
- these large,heavily myelinated fibres form the mesencephalic tract,which surrounds the nucleus
- axonal processes of some of these cells project directly to the Motor nucl V, most synapse in the supratrigeminal nucl before they reach Trigeminal Motor nucleus
ntine nucleus
otherwise known as principal nucleus.
It is located in the mid pons, at level of entry of the nerve, lateral to the motor n.
It is a homologue of the dorsal column nuclei - ie., relays
information about discriminative touch sensations from the face
and oronasal cavity.
Information is carried by fast-conducting, heavily myelinated fibres.
Where is the information projected to in the cortex?
Spinal trigeminal nucleus
The spinal trigeminal nucleus is a large nucleus extending from the caudal-pons to about C3 level of spinal cord.
It has smaller diameter fibres from V1,V2 andV3, turn caudally on entering the pons, forming
the spinal trigeminal tract on the lateral aspect of the nucleus.
The fibres only synapse once they reach the target level of the nucleus. Then they follow the spinothalamic tract up to the VPM of the thalamus.
Divided into 3 parts:
- pars/nucl oralis (medullary-pontine junction),
- pars/nucl interpolaris (open medulla),
- pars/nucl caudalis (closed medulla).
Oralis and Interpolaris are small, and receive afferents from the mouth
Caudalis is a homologue of substantia gelatinosa (Rexed II).
The nucleus processes information concerning pain and temperature from the territories of V1,V2
and V3. This nucleus blends into dorsal horn of the spinal cord and the lower tract
blends into Lissauer’s tract
There are three main afferents to the spinal nucleus:
- Trigeminal nociceptive fibres from cornea (V1), teeth (V2 & 3), temporomandibular joint (V3), dura mater of anterior and middle cranial fossae (V2 & 3)
- Facial (CNVII), Glossopharyngeal (CNIX) and Vagal (CNX) afferents from pharynx, larynx, pharyngotympanic tube, outer and middle ear (cell bodies in geniculate ggl, inf ggl of IX, or inf ggl of X)
- Cervical afferents from nociceptive fibres of posterior roots of C1-3 (note: C1 is usually absent) from dura mater of post cranial fossa, spinal dura, intervertebral joints and suboccipital mm
Note: taste fibres or chemoreceptors carried by these nerves (VII, IX, X) which hitchhike with the trigeminal nerve, synapsing in the solitary tract nucleus.
**Describe stroke syndromes
**
MCA- supploes motor cortex and sensory cortex (upper limb and face), temporal lobe (Wernicke), frontal lobe (Broca)
Symptoms of lesion:
- CL paralysis of upper limb and fae
- CL loss of sensation upper and lower limbs and face
- aphasia if in dominent hemisphere
- hemineglect is nondominant side
ACA
- motor and sensory cortices, lower limb
- CL paralysis and loss of sensation in lower limb; R ACA= anosmia; personality/attitude/memory= frotal lobe damage
ASA: supplies lateral CS tract, medial lemniscus and caudal medulla esp hypoglossal nerve nucleus, tectospinal tract.
LEsion: CL hemiparesis of U and L limbs, decreased CL proprioception and ipsilateral hypoglossal dysfunction – ie tongue deviates ipsilateral side. Note that stroke is most commonly bilateral. Pain and temperature intact because isSTT is lateral and supplied by VA
Note also this is @medial medulla syndrome@ caused by infarct of paramedian ASA branches and vertebral arteries.
PICA- lateral medulla, vestibular nuclei, lateral STT, spinal tg N, N ambiguus, sympathetic fibres and inferior cerebellar peduncle.
Lesion: vomiting, vertigo and nystagmus. Reduced pain and temperature sensation from ipsilateral face and contralateral body, dysphagia, hoarseness, reduced gag reflex, ipsilateral Horner, ataxia ipsilateral cerebellar signs. Dysmetria.
AICA: Latearl pons: CN nuclei- VIII, VII, spinal T g nucleus, cochlear nuclei, sympathetic fibres; middle and infeerior cerebellar peduncles. Vomiting, vertigo, nystagmus, paralysis of face– specific to aica aka latearl pontine syndrome- reduced lacrimation, salivation, taste 2/3, corneal reflex. Face reduced pain and temperature, ipsilateral hearing, Ipsilateral horner, ataxia, dysmetria.
PCA- occipital cortex esp visual cortex
CL hemianopia with macular sparing
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Basilar: @locked in sydnrome’
pons medulla lower midbrain, CST, CBT, ocular CN nuclei, paramedian pontine reticular formation.
Note also:
- Amaurosis Fugax: Transient monocular blindness due to retinal (Ophthalmic) artery occlusion. A red flag for oncoming stroke.
- Carotid “T” Occlusion: Face-Arm-Leg weakness/numbness on contralateral side, global aphasia if dominant side affected, visual sparing.
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Pontine stroke syndromes typically a result of occluded perforations
- Foville/dorsal pons: ipsilateral lateral gaze palsy and LMN facial palsy
- Rymond’s/ventral pons: ipsilateral lateral rectus palsy and contralateral hemiplegia
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- Weber’s Syndrome
- I/L ophthalmoplegia and ptosis, dilation of pupil, no light response, no accommodation, C/L paralysis of arm and leg (CNIII nuclei &/or nerve fibres, corticospinal fibres)
- Benedikt’s Syndrome
- C/L involuntary limb movements, C/L loss of sensation (red nucleus and ascending SCP fibres, spinal and medial lemnisci)
- Compare and contrast Rinne and Weber hearing tests and explain findings if hearing loss is conductive or sensorineural
hearing loss can be described as
- Conductive - outer or middle ear damage
- Sensorineural - inner ear or vestibulcochlear (CNVIII) nerve, or pathway damage.
To distinguish between these hearing losses, two simple auditory examinations may be conducted:
Weber test:
Tuning fork (512 Hz) is placed in the midline of the forehead. In normal hearing, the vibration should be heard equally, on both sides. In conductive hearing loss, stronger vibration is localised on the damaged side. This is explained by the loss of the masking effect of ‘background noise’, normally coming through the tympanic membrane, on the bone conduction. In sensorineural hearing loss, the stronger vibration is felt on the healthy side.
Rinne test:
Compares air and bone conduction. Tuning fork is placed in front of the external auditory canal, and then on the mastoid process. Patient is asked which sound appears louder. In normal hearing, and sensorineural hearing loss, the air conduction will be heard louder. In conductive hearing loss, the sound from the skull (mastoid process) will be heard louder.
For more precise detection of hearing loss, audiometry is performed.
- Interpret audiometry graph
Audiometry measures hearing acuity using a variety in sound intensity and pitch by identifying the hearing thresholds at different frequencies of sounds.
- Label sagittal/axial/coronal diagrams of brain
- Label the following sections of the brainstem – rostral and caudal midbrain, rostral and caudal pons, open and closed medulla. Predict the effect of lesions
See doc- labelled brainstem
- Label the basal ganglia, describe the circuitry and relate to hypokinetic disorders
Basal ganglia:
- Striatum: caudate, putamen, (n accumbens)
- Pallidum: globus pallidus – medial (internal) and lateral (external) segments (includes substantia nigra ‘pars reticulata’ which may be considered functionally continuous with GPi. It is only separated by internal capsule fibres)
- putamen plus globus pallidus makes lentiform mucleus
- Sub-Thalamic Nucleus
- Substantia Nigra pars compacta
- Sub-thalamic nucleus and substantia nigra are regulators of the basal ganglia
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Caudate
- Connected mainly to frontal and pre-frontal areas, and Posterior Parietal Cx.
- Influence on social/moral behaviours.
- More active during the acquisition of new motor skills and planning ahead during more complex motor intentions.
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Putamen
- Mainly connected to somatic cortical areas.
- Has a mapped representation of the body.
- More involved in cognitive loops
Striatum = caudate + putamen
- Complex structure, but one functional unit with connections to the cortex (1000s:1) .
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Cognitive Loop (Caudate):
- Planning ahead for motor intentions.
- Once learned → motor loop.
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Limbic Loop (N. Accumbens):
- Involves reward/motivational behaviours, memory, and motor expression relevant to emotions (smiling/gesturing).
- In Parkinson’s Disease (PD), there are problems with expressions.
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Oculomotor Loop (Caudate):
- In PD, there are problems with saccades.
-**
Motor loop (putamen)
- Scaling strength of muscle contractions
- in collaboration with SMA
- Putamen provides a reservoir of learned
programs
- Execution of motor programs involves decision/plan of what to do, integrating all cortical inputs to determine appropriate motor programs, with motor instructions sent to Motor Cx.
- decision or planning what to do occurs in frontal/parietal; temporal, insular and cingulate cortices —->
- basal ganglia integrates all cortical inputs to determine approporiate motor programs —>
- thalamic nuclei sends motor instuctions to motor cortex
- SMA and M1 execute motor programs
- enact action from M1
Cognitive Loop:
- e.g. for any learnt motor program
- Strong projection to caudate which becomes active during learning new motor skills – reinforcement learning.
- Thought to incorporate planning ahead during new motor tasks & action selection.
- Returns to prefrontal and premotor cortices via VA & MD nuclei of thalamus.
- When the new task is well practiced, the task comes under control of the motor loop.
Example loop:
- prefrontal and PPC
- Putamen, caudate and GP
- VA/MD thalamus
- SMA
Limbic Loop
- e.g., Memory, motivational behaviours, gesturing, facial expressions…
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Nucleus Accumbens
- Anterior end of putamen/caudate
- Connected to inferior prefrontal Cx (limbic system)
- Returns signals to Cx via MD nuclei of thalamus
- Limbic Cx determines appropriate emotional status for the environmental conditions
- Important in gesturing and expression of affect
- Rich in dopaminergic input may explain loss of affect / ‘mask-like’ appearance of PD patients.
Example loop:
- Limbic Cx
- N. Accumbens
- MD Thalamus
- Inf. Prefrontal Cx
Oculomotor Loop
- e.g., Fixation
- Substantia Nigra pars reticularis (SNr)
- Connected to the ‘frontal eye fields’ and parietal association cortex
- Returns to Cx via VA & MD nuclei of thalamus
- During fixation, SNr tonically inhibits cells in the superior colliculus (SC)
- When a deliberate saccade is about to be made, SNr activity stops, to disinhibit SC.
Example loop
- frontal eye fields and PC to caudate and SNr (inhibits SC)
- VA/MD thalamus
- frontal eye fields
- frontal eye fields and PC directly to SC
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Direct: Go!
- Direct pathway feeds information to the thalamus via striatum and GPi
- Results in an increase in muscle activity
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Indirect: Stop!
- Indirect pathway includes a ‘side loop’ from GPe > STN > GPi
- Net effect is suppression of muscle activity
- This pathway dominates during inactivity
Parkinson’s Disease: Effect of DA Loss
- Dopaminergic cells in the SNc are lost; striatum neurons eventually die, leading to disengagement of the direct pathway and default prevalence of the indirect pathway.
- Increased excitation and decreased inhibition of GPi result in enhanced inhibition of the thalamus, leading to hypokinesia i.e. difficulty starting motor program.
- Symptoms include tremor, rigidity, poor facial expression, and saccades.
- tremor and rigidity of both flexors and extensors not explained by hypokinesia
![[Pasted image 20240314140120.png]]
Huntington’s Chorea
- Uncontrolled, abrupt, and jerky movements of distal muscles due to a chromosome 4 defect causing GABAergic cell death in the striatum.
- Early D2 MSNs and later D1 MSNs are affected, applying harder brakes to STN and reducing basal inhibition on the thalamus, leading to execution of otherwise suppressed motor behaviors.
- Results in dementia due to retrograde loss of cortical neurons as striatal targets die.
![[Pasted image 20240314140134.png]]
Movement Disorders
- Athetosis: Slow, involuntary convoluted writhing movements; symmetry maintenance is difficult.
- Chorea: Quick, involuntary “dance-like” movements, not repetitive or rhythmic.
- Hyperkinesia: Chorea and Huntington’s disease are examples.
- Ballism: A form of hyperkinesis.
- Describe the contents and location of the cavernous sinus, and describe the expected clinical signs and symptoms of cavernous sinus thrombosis
Contents of the cavernous sinus:
- trigeminal ganglion
- V1, V2; III, IV, VI
- internal carotid artery
- sympathetic nerves
Cavernous sinus syndrome is characterized by ophthalmoplegia and sensory deficits over the head due to combined deficits of the three cranial nerves (third, fourth, and sixth) responsible for eye movements and pupil function, and at least one branch of the trigeminal nerve.
may cause isolated or combined ophthalmoplegia, painful ophthalmoplegia, anesthesia in CNIII, unitemporal or bitemporal visual field defects, acromegaly, and galactorrhea
- A lesion in spinocerebellum would cause what signs? A lesion in cerebro? A lesion in…?
- spinocerebellum:
Ataxic Gait; Uncoordinated, Clumsy Movements of the Limbs; Stagger to Side of Lesion.
- cerebrocerebellum:
- Hypotonia & Intention Tremor- ipsilateral to cerebellar lesion
- Dysmetria - Overshooting Targets: a failure to provide cerebral cortex with information necessary to plan and execute the movement accurately
- Dysdiadochokinesia - Loss of Rhythmic Control, especially with alternate limb patterns
- Loss of Timing and Control of Speech
- vestibulocerebel:
- Ataxic Stance (Swaying – Like a Toddler)
- Nystagmus (Lateral, Fast-Slow Eye Movements)
- Which two CNs are responsible for the light reflex arc. Describe the arc. Describe how to test it
The pupillary response or pupil reflex constricts the pupil in response to light ^[https://www.ncbi.nlm.nih.gov/books/NBK537180/].
The afferent segment of the pupillary response are the ganglion cells that form the optic nerve. They project from the retina to the midbrain. travels to the pretectal olivary nuclei. It decussates in the nasal retina but not in the temporal retina.
The interneuron segment of the pupillary response are the cells of the pretectal nucleus. They project bilaterally to the parasympathetic nuclei of CNIII, known as Edinger-Westphal nuclei (preganglionic parasympathetic nuclei in the midbrain.)
The efferent segment runs from the Edinger- Westphal nuclei to the pupillary constrictor muscle to constrict the pupil, via the ciliary ganglion, which sends postganglionic axons to directly innervate the iris sphincter muscles ^[https://www.ncbi.nlm.nih.gov/books/NBK537180/].
First order pre ganglionic parasympathetic fibres exit the mifbrain in the oculomotor nerve, without crossing, synapsing in ciliary ganglion.
Second order post ganglionic neurons send axons from the ciliary ganglion to the sphincter pupillae via short ciliary branches.
The direct response is constriction of pupil in the ipsilateral eye; the consensual response is constriction of pupil in the contralateral eye.
It is tested by shining a light into one pupil and looking for a response in the other pupil (which constricts as well).
The swinging lamp sign: move light to the contralateral pupil; the ipsilateral pupil will then dilate after light has moved away from it (this is called an afferent pupillary defect) ^[https://www.derangedphysiology.com/files/cranial%20nerve%20exam.pdf]
The pupillary reflex exam is considered part of a neurological exam.