Neuroanatomy 5: Cerebellum Flashcards
Cerebellum functions:
1) Affects ipsilateral motor function
2) Balance and posture
3) Fine tuning of skilled motor functions via feedback: compares what cortex said to do w/ what joints/muscles really did and corrects
4) Initiation, termination, coordination, and timing of movements: allows you to start and stop w/o overshooting. Allows you to simultaneously perform multi joint tasks (bring arm over head: not first bend elbow, then shoulder etc.)
5) Planning of motor movements
6) Motor learning
How does the cerebellum exert motor influence?
1) Rubrospinal (skeletal muscle control, tone, posture)
2) Vestibulospinal (balance in response to head movements)
3) Reticulospinal tract (influences reflexes and voluntary and autonomic
4) connections to the cerebral cortex, which can then influence the corticospinal tracts
Cerebellum anatomy:
Lobes:
-Anterior & posterior: provide subconscious movements
-Floculonodular lobe: regulates equilibrium
Vermis: “worm-like” structure that separates the 2 hemispheres
Foli: gyri-like convulsions on the surface if the cerebellum
Internal anatomy of cerebllum:
white matter: arbor vitae
Gray matter (cortex)-peripherally arranged around arbor vitae
Deep nuclei of cerebellum:
Deep nuclei: Dentate, interposed (consists of emboliform & globose nuclei): both voluntary movements
Fastigial: balance
Peduncles:
superior, middle, and inferior (“highways” into and out of cerebellum)
SCP: mostly output
MCP & ICP: mostly input
Functional divisions of the cerebellum:
Vestibulocerebellum (cooresponds to floculo-nodular lobe)
1) functions:
-Balance
-Coordination of eye movements
2) Major Inputs:
-Vestibular fibers from vestibulocochlear nerve & vestibular nuclei
3) Major Outputs: (via fastigial nucleus)
-Vestibulospinal tract (motor balance)
-Reticulospinal tracts (motor influences)
-Medial longitudinal fasciculus: runs from vestibular nuclei to interconnect occulomotor, trochlear & abducens nuclei in brainstem (eye movements)
Common problem w/ lesion: Nystagmus
Archicerebellum: Greek archi= first, hence the oldest part of the cerebellum
Nystagmus:
Rapid involuntary movements of the eyes that may be:
1) side to side (horizontal nystagmus)
2) Up and down (vertical nystagmus)
3) Rotary
Spinocerebellum (corresponds to the majority of the vermis):
Functions:
-Adjusts movements as they are occuring
-Corrective feedback of fine-tune motor skills
Major Input:
-Spinocerebellar, cuneocerebellar tracts (proprioception from periphery)
-Corticopontocerebellar fibers (primary motor: copy from cortex)
Major outputs: (via interposed nuclei)
-Rubrospinal, corticospinal
-common problems w/ lesions: gait is affected: because of loss of motor coordination.
Paleo: greek palaios=old; hence, paleocerebellum, the earliest stage in the evolution of the cerebellum
Cerebrocerebellum (neocerebellum or pontocerebellum):
Functions:
-Planning movements
-Rapid alternating movements
-Fine dexterity (quickness)
-Initiation, termination, coordination & timing of movements
-Motor learning
Major inputs:
-Corticopontocerebellar (premotor & association areas)
-Olivocerebellar
Major outputs: (via Dentate nucleus)
-Corticospinal, rubrospinal
-Common lesions problems include dysmetris, dysdiadochokinesia, asynergia
Ataxia:
“without order” (motor coordination is lost): inability to coordinate muscle activity during voluntary movement; most often due to disorders of the cerebellum or the posterior columns of the spinal cord; may involve the limbs, head, or trunk. Syn: ataxy, incoordination
-Dysarythria: ataxia of laryngeal muscles. (jerky articulations, separation of syllables, changing sound intensities)
-Cerebellar nystagmus: ataxia of ocular muscles (tremors of eyeballs that usually occurs when patient attempts to fix eyes on an object off to the side.
-Truncal ataxia: inability to maintain an upright position (affects gait). (unstable, wide gait w/ irregular steps & lateral bending
Dysmetria:
“wrong distance” can’t judge distance-movements “overshoot” & then overcompensate.
-Patient can’t touch finger to nose, heel to shin-leads to intention tremor
Dysdiadochokinesia:
“without ability to make rapidly alternating movements”
-loss of ability to predict where a body part will be at a given time, leading to the next movement in a sequence starting too early or too late
-test by asking patient to rapidly turn palm up and down: results in jumbled movements.
Hypotonia:
low muscle tone
Asynergia:
Lack of coordination between muscles or other body parts which usually work together (postural abnormalities)
Asynergy:
lack of coordination among various muscle groups during the performance of complex movements, resulting in loss of skill & speed.
when severe, results in decomposition of movement, wherein complex motor acts are performed in a series of isolated movements: caysed by cerebellar disorders.
Syn: asynergia
Organization of the nervous system:
Cranial nerves locations:
Cranial nerves innervations:
All CN innervate the ipsilateral (same) side.
EXCEPT: CN II
therefore, motor fibers will provide efferent innervation to the same side and sensory fibers will carry afferent information from the same side.
Nuclei of CN III-XI originate w/in brainstem & nerves exit off brainstem
EXCEPT: CN I and II which originate in specific locations
CN mapping:
Motor component of the CN:
UMN’s coming from cortex send mostly (not always) bilateral innervation to the nuclei of the CN (LMNs) which then project to the ipsilateral muscles (with one exception)
Cortex to Cranial nuclei in the brainstem: corticobulbar or corticonuclear (UMN)
CN nuclei to the muscles by LMNs
Exception for CN IV:
The trochlear nucleus sends innervation to the contralateral superior oblique muscle rather than the ipsilateral muscle.
Exception for CN VII:
the lower part of the facial motor nucleus that innervates the lower face muscles receives ONLY contralateral innervation from the cortex rather than bilateral
Exception for CN XII:
those neurons in the hypoglossal nucleus that innervate the genioglossus muscle receive contralateral innervation from the cortex rather than bilateral
Sensory components of the CNs:
1st neuron is in the sensory ganglion of the cranial nerve
2nd neuron in the ipsilateral (mainly)sensory nucleus of the CN nerve in the brainstem
3rd neuron in the thalamus (mainly contralateral) and terminates in the contralateral cortex
Exception for CN I:
The olfactory nerve (CN I):
1st neuron is in the olfactory epithelium & 2nd nerve is in the olfactory bulb that goes to the olfactory areas of the brain.
Exception for CN II:
optic nerve (CN II):
1st neuron is in the retina, and 2nd neuron is in the thalamus, & from there, it goes to the visual cortex
Olfactory nerve (CN I) pathway:
-Receptors originate in the superior parts of the nasal cavity in the mucosal lining
-Axons enter cranial cavity through the olfactory foramina in the cribriform plate of ethmoid
-Synapse in olfactory bulbs inferior to frontal lobe w/in anterior cranial fossa (bulbs sit between frontal lobe and cribriform plate)
-Signals travel into frontal cortex via olfactory bulb
Foramina: Olfactory foramina of Ethmoid
Function: special senses= smell
-Special visceral afferent (SVA)
How does the olfactory nerve get injured and what is the outcome?
1) nasal trauma
2) Fracture of ethmoid/cribriform plate (if fractur is suspected, do not intubate patient via nasal cavity)
3) tumor in anterior cranial fossa/frontal lobe
Outcome:
-Lack of smell “anosmia”
-CSF rhinorrhea: leakage of CSF from subarachnoid space due to trauma of the associated bones and meningeal layers (not seen with tumor)
Testing CNI: performed usually after head trauma
1) ask patient to identify commonly known odors such as vanilla, coffee, soap (with their eyes closed)
Optic nerve pathway (CN II):
-Receptors found in retina of the eyeball transmit signals via optic nerve to the optic chiasm & then optic tract
-Travels posteriorly to synapse in:
1) thalamus
2) Occipital lobe
Foramina: Optic canal of sphenoid
Function: Special senses=Vision
-Special somatic afferent (SSA)
Testing CN II: test each eye individually:
1) Visual acuity test (Snellen eye chart)
2) Pupillary light response (discussed in L21)
Muscles of the eyeball:
Extrinsic eye muscles and their innervations:
Oculomotor nerve (CN III) Pathway:
-Nerve begins at midbrain and travels anteriorly towards orbit
-Innervates several muscles of eyball after passing through superior orbital fissure
Foramina: Superior orbital fissure of sphenoid (posterior orbit)
Function: Nerve has 2 axon modalities:
-General somatic efferent (GSE): Voluntary motor to levator palpebrae superioris, & several extraocular eye muscles: superior rectus, medial rectus, inferior rectus, & inferior oblique muscle
-Genral Visceral Efferent (GVE): visceral motor (parasympathetic) innervation to sphincter pupillae for pupil constriction
(synapses in ciliary ganglion)
Common causes of injury to oculomotor nerve and patient presentation:
Causes:
-Diabetic neuropathy
-Aneurysm
-Cerebral trauma
-Increased intracranial pressure
-Cavernous sinus syndrome
Patient presentations:
-Ptosis: droopy upper eyelid
-mydriasis: permanent dilation of pupil
-Strabismus: lazy eye (eye position is doen and out, due unopposed action of superior oblique and abducens muscle
-Diplopia: double vision
Trochlear nerve (CN IV) pathway:
-Originates at midbrain, travels toward eyeball, exits superior orbital fissure
Foramina: superior orbital fissure (posterior orbit)
Function: Voluntary motor to superior oblique muscle= normally pulls the eye down and out
-General Somatic Efferent (GSE)
Abducens nerve (CN VI) pathway:
-Originates at pons, travels toward eyeball, exits superior orbital fissure
Foramina: Superior Orbital Fissure (posterior orbit)
Function: Voluntary motor to lateral rectus muscle=normally abduct the eye away from the midline
(General Somatic efferent (GSE))
Testing CN III, IV, and VI=test each eye individually
1) eye movement in “H” pattern, observe for differences
