Exam 2 Deck 2 Flashcards
Where are the vestibular nuclei locarted?
Caudal pons and medulla
Which thalamic nucleus do neurons from the vestibular system that are responsible for the conscious perception of head orientation in space project to?
Ventral Posterior (VP) nucleus
This in turn projects to the parietal lobe, immediately posterior to the face area in the primary somatosensory cortex
Which nerves are involved in the afferent limb of the vestibulo-ocular reflex (VOR)?
CN VIII (Vestibular nerve from vestibulocochlear) to the medial vestibular nucleus (ipsilateral)
Which nerves are involved in the efferent limb of the vestibulo-ocular reflex (VOR)?
CN III, CN VI and the MLF (oculomotor, abducens, medial longintudinal fasciculus)
From vestibular to abducens nucleus. Then goes via MLF to ocolomotor to medial rectus, and to contralateral lateral rectus
Which horizontal canals are activated with head rotation to the right?
Right horizontal
Left is inhibited
What are some cerebellum-dependent characteristics of the vestibulo-ocular reflex?
Has gain
Is plastic
These features are dependent on the cerebellum
How does caloric testing test the horizontal canals?
Nystagmus from reflex
Cold water = nystagmus towards opposite ear
Warm water = nystagmus towards water-injected ear
(COWS)
What is the lateral vestibulospinal tract?
Descending motor tract from the vestibular nuclei that is critical for balance and postural control.
Influences motor neurons throughotu the length of the spinal cord (body)
What is the medial vestibulospinal tract?
Descending motor tract from teh vestibular nucleus that helps maintain the stability of the head on the necka s teh body moves
Critical in maintaining balance and postural control
What is the course of the lateral vestibulospinal tract?
Lateral vestibular nucleus goes to all levels of ipsilateral spinal cord
Receives input from cerebellum
Activates antigravity muscles
What is the course of the medial vestibulo-spinal tract?
From medial vestibular nucleus goes bilaterally through MLF to cervical and upper thoracic spinal cord
Activates neck muscles to counteract gravity
What is important about the vestibulocerebellar connections?
THE VESTIBULAR NERVE PROJECTS DIRECTLY TO THE CEREBELLUM
All five functional pathways of the vestibular system are under cerebellar control!!
How does the vestibulo-autonomic reflex work?
Vestibular nuclei receive primary vestibular input and send projections to the brainstem presympathetic control centers
Here, they converge with the baroreflex
Dysfunction here can cause orthostatic hypotension
How does orthostatic hypotension occur?
Dysfunction in the pathway of vestibulo-sympathetic reflex (vestibulo-autonomic)
There is convergence at the point of the presympathetic control centers in the brainstem of vestibular and baroreflex pathways
What is the origin of conductive hearing loss?
Outer ear, middle ear
What is the origin of sensory neural hearing loss?
inner ear, CNS
What are findings in conductive hearing loss?
Air conduction thresholds depressed, bonec onduction thresholds are normal (Air-bone gap)
What are findings in sensoryneural hearing loss?
Air and bone conduction are equal. Bilateral
What can cause conductive hearing loss?
Ear wax, fluid, eustachian tube swelling, tympanic perforation, cholesteatoma (mass), otosclerosis (fixation of stapes), fusion of bones, congenital, traumatic
What can cause sensory neural hearing loss?
Aging - high frequencies first, speech discrimination preserved
Genetic
Noise
Acoustic neuroma
Meniere’s disease
Toxins, virus
Trauma
How do you treat conductive hearing loss?
Drainage, surgery
How do you treat sensory neural hearing loss?
Surgery, radiation, hearing aid, cochlear implant
How does conductive hearing loss present with tunig fork tests?
Sound is perceived louder in the defective ear
How does sensorineural hearing loss present with a tuning fork test?
Sound is perceived as louder in normal ear (damaged ear hears less)
What is Rinne?
Comparing bone conduction to air conduction
Place tuning fork on mastoid then outside ear
Air should be heard longer/louder than bone (also true in sensorineural loss)
If air heard less than bone - conductive loss
What is vertigo?
Vestibular system disease that causes hallucination (false sense) of motion
What is imbalance?
Sensory disturbance in vestibular, visual, and/or proprioceptive systems. Can also be cerebellar, motor, etc
What is disequilibrium?
Patient feels like things are off balance, drunk
Can be caused by degenerative disorders, brainstem, multisensory, psychogenic
What is lightheadedness?
Patient feels like he/she will faint
Usually cardiovascular or metabolic
What is acute unilateral vestibular loss?
Sudden onset of vertigo, nausea, vomiting, nystagmus
Positive romberg, past pointing
Ataxic gait, veering towards sesion
Can be casued by virus, trauma, post surgery, infarction
What is Meniere’s syndrome?
Episodic vertigo
Spontaneous, unpredictable
History is crucial
lasts for hours
can be perfectly well between episodes
Audiogram is important - unilateral hearing loss
Treat with diuretics, vasodilators, ototoxic drugs on purpose, vestibular suppresants
What is benign positional paroxysmal vertigo (BPPV)?
Positional vertigo that lasts for seconds
Caused by canalithiasis (dislodged otoconia that float free in endolymph)
Cured by particle repositioning or surgical ablation
Excellent prognosis with relapses
Diagnose with Dix-Hallpike
What is the Dix-Hallpike maneuver?
Diagnostic teset for benign positional paroxysmal vertigo (BPPV)
What is bilateral vestibular loss?
presents with ataxia, oscillopsia (perception of oscillating vision)
Not true vertigo
Age related, can be caused by head trauma
Can be caused by drug toxicity or by infection, inflammation or autoimmune causes
Treat with rehab
Poor course
What are causes of central vertigo?
CNS Tumors, stroke, migraines, MS
What is central vertigo?
Severe imbalance/ataxia
Rarely presents with hearing loss or tinnitus
Can have diploplia, dysarthria and other non-auditory symptoms
What is peripheral vertigo?
Ataxia and imbalance that veers towards lesion
Nausea, vomiting, hearing loss, tinnitus, fullness in ear, and pain can be present
What causes peripheral vertigo?
Inner ear problems (Semicircular canal issues, otolith issues)
Vestibular nerve problems (BPPV, Meniere’s labyrinthitis)
What is the piriform cortex?
Amygdala, Uncus, and Parahippocampal gyrus
What is the role of the thalamus in olfaction?
Sensory information does not pass directly to it!
First goes to piriform complex, which sends it to various locations, including the thalamus, secondarily
Sends to Dorsal Medial Nucleus of Thalamus
What are funcitons of the olfactory system?
Detection and identification of odorants
Intake regulation
Detection adn avoidance of hazards
Role in sexual behavior
What are som eunique features of the olfactory system?
Cell bodies of primary afferents are contained directly in the olfactory epithelium (no ganglia)
Primary afferent neurons undergo continuous turnover (replaced constantly by basal stem cells)
Axons of primary afferents enter the cortex directly (no thalamic relay)
Pathway is entirely ipsilateral
What is special about olfactory epithelium?
Contains cell bodies of primary afferents directly!
Has basal stem cells that turnover these primary receptor cells
What are bowman’s glands?
Cells in the olfactory epithelium that produce mucus
How does olfactory transduction occur?
Odorants are detected at the cilia of the olfactory receptor cells by GPCRs, which leads to an action potential which transduces the signal
GPCR!
How is odor discrimination acheived?
Humans have ~400 different odor receptor proteins, and generally speaking each individual olfactory neuron expresses only one type of receptor
They are segregated spatially, which helps for the processing of olfactory bulb information by patterning
What is special about the olfactory tract?
They run ipsilateral
What are olfactory glomeruli?
Location of first synapse of olfactory cells with mitral cells
What are mitral cells?
Cells in the olfactory bulb which will project to the cortex
Many olfactory receptor cells will synapse on a single mitral cell
How does olfaction in humans differ than in other animals?
Olfaction is not a strong sense in humans
Other animals have more olfactory receptor neurons and proteins, with expanded olfactory epithelium and a larger portion of the brain devoted to olfaction
What is anosmia?
Loss of smell
What is hyposmia?
Decreased sensitivity to odorants
What is specific anosmia?
Unable to perceive odor of a particular compound or class of compound
What is hyperosmia/olfactory hyperesthesia?
Increased olfactory acuity
What is olfactory agnosia?
Aware of a smell, but can’t recall name
What is parosmia/dysosmia?
Distortion in a smell experience
What is olfactory hallucination/phantosmia?
Perception of a smell when no odor is present
What is cacosmia?
Formation of repugnant/disagreeable olfactory auras
What can cause anosmia or hyposmia?
URI, sinus disease
Head trauma
Tumors
Aging, degenerative diseases
Toxins, medications (smoking, cocaine, chemo)
What can cause hallucinations, cacosmia, or parosmia?
Epilepsy
Psychiatric disorders
What can cause hyperosmia?
Migraine
Psychosis
Substance abuse
Conversion
What can cause specific anosmia?
Genetics/congenital causes
Which cranial nerves contribute to taste?
CN VII, IX, X
(Facial, Glossopharyngeal, Vagus)
Where are taste buds found?
Tongue, palate, epiglottis, esophagus
What are the 5 categories of tastants?
Salt
Sour
Sweet
Bitter
Umami
What is the basis for the differential taste perception of the tongue?
All tastes can be detected over the entire surface of teh tongue, but different regions have varying thresholds for each taste
Each tastant category responds to a distinct class of receptor molecules
The taste categories are maintained in the CNS representaitons
What is the structure of taste receptor cells?
Distinct apical and basal surfaces (taste receptors on apical surface)
Which tastant categories use GPCR receptors?
Sweet, bitter, umami
Which tastant categories use ligand-gated ion channel receptors?
Salt, sour
What innervates the anterior 2/3 of the tongue?
The facial nerve via the chorda tympani
What innervates the posterior 1/3 of the tongue?
The glossopharyngeal nerve
What innervates the taste function of the epiglottis and esophagus?
Vagus nerve (CN X)
What is the course of taste sensation?
From taste buds to their corresponding cranial nerve
Synapse at the solitary tract nucleus in the brainstem
Here, neurons are projected to the VPM of the thalamus via the central tegmental tract
Then, tertiary neurons project ot the primary gustatory cortex
Discriminative affects of taste and is ipsilateral
What comprises the primary gustatory cortex?
Anterior insula and frontal operculum
What is ageusia?
Complete loss of taste
What is hypogeusia?
Decreased taste sensitivity
What is parageusia/dysgeusia?
Unpleasant perception of taste when the substance would normally taste good. Distortion in the perception of taste
What is cacogeusia?
Perceptioan of an unpleasant taste sensation
What is gustatory hallucination?
Perception of taste when none is present
What can cause taste disturbance?
Aging
CN VII lesions
Medications/radiation
Viral medications
Trauma
Diabetes
Seizures
Psychiatric
What are heavy metals that cause neurologic damage?
Lead
Mercury
Arsenic
Thallium
Manganese
How does lead poisoning present?
Different in children and adults
Children - acute encephalopathy, behavioral and IQ deficits
Adults - abdomina pain and motor neuropathy (wrist drop)
Discoloration of upper gums
Treat with chelators
How does mercury poisoning present?
Peripheral neuropathy, seizures, encephalopathy
Mad hatter syndrome
Treat with chelators
How does arsenic poisoning present?
Encephalopathy, vomiting, rice water stools, garlic breath, renal failure, arrhythmias
Treat with dimercaprol
How does thallium poisoning present?
Hair loss (chronic), vomiting, diarrhea, paresthesia, cognitive impairment
How does manganese poisoning present?
Confusion and Parkinsons-like symptoms
Hyperreflexia is an important distinction
What is marasmus?
“Balanced starvation”
seen in 0-1 year olds that present with wasting, mental changes, growth retardation
What is kwashiorkor?
Protein starvation
Seen in 1-3 year olds that present wiht encephalopathy, muscle wasting
What are neurological complications of obesity?
Pickwickian syndrome - Cardiorespiratory distress
Sleep apnea
Can be fatal
What are neurological complications of diabetes?
Dementia
Increased stroke risk
Ischemic cranial nerve palsies
Peripheral neuropathies
Loss of limbs (vascular complications)
What is thiamine deficiency?
Vitamin B1 deficiency due to impaired intake (seen in alcoholics) or impaired absorption (gastric disorders)
Can cause peripheral neuropathy
Beriberi = peripheral neuritis, symmetrical wasting, no edema
Wernicke’s encephalopathy = ataxia, opthalmoplegia/gaze palsies/nystagmus, confusion
Korsakoff’s psychosis = irreversible with severe memory defecit, confabulation, apathy
What is wernicke’s encephalopathy?
Ataxia
Opthalmoplegia/gaze palsies/nystagmus
Confusion
Caused by medial thalamic nuclei, mamillary body, periaqueductal, or brain stem nuclei
Can lead to Korsakoff’s psychosis
What is korsakoff’s psychosis?
Irreversible dementia that can be a sequella of wernicke’s encephalopathy
Seen in alcoholics or in thiamine deficiencies
What is pyridoxine deficiency?
Vitamin B6 deficiency
Peripheral neuropathy, convulsions, irritability, somnolence
Intractable seizures in infants
Can be induced by isoniazid
What is folic acid deficiency?
Vitamin B9 deficiency
Neural tube defects that occur in weeks 3-4 of gestation
What is cobalamin deficiency?
Vitamin B12 deficiency
Subacute combined degeneration of posterolateral column
paresthesias, babinski, loss of vibration, position sense, positive romberg, progressive spastic and ataxic weakness, myelopathy….
What is vitamin E deficiency?
Progressive spinocerebellar syndrome and posterior column degeneration
Peripheral neuropathy and hemolytic anomia
What are reflexes?
Involuntary movement that are the building blocks of purposeful movements.
Mechanoreceptors (sensory) in the skeletal muscle send info to the spinal cord and descending motor information is modified accordingly)
How are rhythmic, complex movements achieved?
Combination of involuntary movements (i.e. reflexes) to adjust and compensate coupled with voluntary movements (i.e. purposeful, learned behaviors that require cortical structures) taht initiate the broad movement
What are spinal cord ventral horn motor neurons?
Motor neurons with direct acess to muscles
Site of integration of all descending and reflex pathways
(LMN)
What are cranial motor neurons?
E.g. facial nucleus, motor nucleus of V
LMN of the cranial nerve system
What are brainstem centers?
Nuclei in the brainstem that give rise to descending tracts that are important for postural control (vestibulospinal and reticulospinal tracts)
Under the control of motor cortex and cerebellum
What are the motor cortices?
Primary motor cortex (M1)
Premotor area (PM)
Supplementary motor area (SMA)
What is M1?
Primary motor cortex
Contains a map of muscles and/or movements and is involved in the execution of the motor plan
What are the premotor and supplementary motor cortex involved in?
Planning upcoming movements based on sensory cues or internally generated plans
What are the pyramidal structures of the motor system?
Spinal cord ventral horn and cranial motor neurons
Brainstem centers
Motor cortex
What are the extrapyramidal motor system structures?
Cerebellum
Basal Ganglia
What is the motor function of the cerebellum?
Integrates movements into smooth sequence
May be a comparator between real and intended movement through sensory feedback
May be a motor learning center and in some cases initiator of movement
What is the motor function of basal ganglia?
Possibly involved in rapid adjustments of movements (e.g. when turning suddenly)
May initiate some movements
What are the two types of muscle fibers?
Extrafusal - force generating
Intrafusal - no direct role in force generation, but part of the spindle (adjust sensitivity)
What are extrafusal muscle fibers?
Force-generating muscle fibers
Fast fatigable - glycolysis; pale; strong, but fatigable
Fatigue-resistant/slow - oxidative metabolism; deep red; less strong, but can sustain action
What are intrafusal muscle fibers?
Control and adjust the sensitivity of the muscle spindle
What are alpha motor neurons (αMN)?
Extrafusal fibers
Fast/fatigable = large
Slow/Fatigue-resistant = small
What are gamma motor neurons (γMN)?
Intrafusal muscle fibers
What is a motor unit?
The basic contractile unit of skeletal muscle
One motor neuron and all of the muscle fibers it innervates
The ratio of motor neurons to muscle fibers can vary from 1:10 to 1: 2000
A single muscle is composed of many motor units
What is the size principle in motor neuron recruitment?
Muscle force is graded by CNS commands that excite increasing numbers of motor units
Large αMNs innervate large, powerful, fast-fatigable muscles and form large motor units
Small αMNs innervate small, weak, non-fatigable muscles and form small motor units
Small αMNs and γMNs are the first to respond to low-level afferents
The largest MNs are the last to be recruited and require strongest afferent stimulation to reach firing threshold
Which are the first muscle fibers to respond to low-level afferent inputs?
Small αMNs and γMNs
What is the general layout of motor tracts?
How do skeletal muscles monitor changes in muscle length and tension during movement?
Muscle spindles are stretch receptors that record length and rate of change of muscles - in parallel with extrafusal muscle fibers
Golgi Tendon Organs (GTO) record tension generated in myotendinous junction during contraction
What are muscle spindles?
Feedback mechanism that record muscle length and rate of change
Stretch receptors that are attached with the extrafusal muscle fibers surrounding them
Have two functional regions:
In the central region, which are non contractile, they receive innervation from Group Ia and II sensory afferents
At the polar ends, they are comprised of contractile intrafusal muscle fibers receive motor innervation from γMNs
What are two ways to trigger muscle spindles?
Stretch the muscle - will intrinsically activate the Group Ia and II sensory afferents in the central region
Stimulate the γMNs - will contract the polar ends, producing a stretch in the central region, which will activate the sensory afferents.
What is alpha-gamma-coactivation?
Phenomenon that occurs during normal contraction during which gamma motor neurons are activated during alpha motor neuron activation as to maintain sensory afferents of muscle length during muscle contraction
Muscle contraction is mediated by extrafusal fibers (alpha motor neurons)
This would produce slack in the muscle, and reduce the sensory afferent signal (by group Ia and II fibers, in the central region), which would result in a lack of information about the length of the muscle
Therefore, intrafusal fibers (gamma motor neurons) fire to “pick up the slack”, keeping a constant tension and maintaining the sensory feedback although the muscle is shortening overall
What are golgi tendon organs (GTOs)?
They record the tension generated at the myotendinous junction during contraction
Located at the junction
Composed of Group Ib sensory afferents, interdigitated with surrounding collagen fibers
Encode tension information, but do not generate enough force to create muscle
When muscle creates tension, the fibers are squeezed and stimulates firing
Group Ib fibers stimulate spinal cord interneurons which terminate active muscle contraction and promote opposing contractions
Firing frequencies of the Group Ib fibers are proportional to the degree of force exerted on the myotendinous junction
Increased force = increased GTO recruitment
How are Group Ib fibers activated?
They are in the golgi tendon organ
Activated by stretch in muscle which causes impingement of the fibers by collagen
What is a reflex?
A motor resopnse to a stimulus and does not normally require volition
Sensory stimulus produces impulses in afferent fibers that subsequently (monosynaptically - direct; or multisynaptically - indirect) activate a pool of motor neurons
Generally, reflex excitation is always accompanied by inhibition
What is a myotatic reflex?
A.k.a. Stretch reflex or deep tendon reflex
The things you see in clinic
Stabilizes posture by regulating joint angle
Afferents are made up of Group Ia and II sensory fibers wrapped around muscle spindles
In the spine, alpha motor neurons are activated for the same muscle, and some too for other muscles that are synergistic
Inhibitory interneurons inhibit alpha motor neurons in antagonists
These contract the agonists
What is a homonymous muscle?
Same muscle
What is a heteronymous muscle?
Muscle that is synergistic to a muscle in question (the homonymous muscle)
What are the intraspinal connections in a myotatic reflex?
Group Ia and II sensory afferents synapse on alpha motor neurons of homonymous and to a lesser degree heteronymous muscles
Also activate inhibitory interneurons (Ia inhibitory), which inhibits alpha motor neurons of antagonistic muscles
What is recurrent inhibition?
Recurrent axon collaterals feed back to excite inhibitory interneurons (Renshaw cells) which inhibit the alpha motor neurons that initiated the reflex
Self-terminating reflex
Feedback inhibits the alpha motor neuron that recruited it and stops the relaxation of the antagonist muscle by inhibiting the Ia interneurons
What are Renshaw cells?
Special inhibitory interneurons that stop the contraction of agonist muscles in a reflex by feeding back to the alpha motor neuron that activated it and by stopping the relaxation of antagonist muscles
What is hyporeflexia and what causes it?
Decreased briskness and strength of reflex response
Can be caused by any disease that impairs conduction of action potentials - neuropathies, compression syndromes, motor neuron disease, demyelination, trauma, etc.
What is areflexia and what can cause it?
No spinal reflex
Caused by severe disease or injury
What is hyperreflexia?
Overly brisk reflexes or exaggerated reflexes
What is the inverse myotatic reflex?
Tension-feedback reflex that reduces over-contraction by providing inhibition derived from the Group Ib sensory afferents that innervate the GTOs
Afferent: Group Ib
Intraspinal: Inhibit homonymous alpha MNs and synergists, excite antagonistic alpha MNs
GTOs are recruited in greater numbers as muscle contracts, this activates the reflex and prevents over-contraction
How is purposeful movement achieved?
By coordination and modulation of reflexes by descending influences from higher brain centers
All reflexes (except myotatic) operate through interneurons
Ascending pathways provide ongoing sensory information that helps tweak and modulate spinal reflexes and motion
What is lower motor neuron syndrome?
Flaccid paralysis that can also have:
Weakness and hypotonia (decreased resistance to passive manipulation)
Areflexia
Muscle atrophy
Fasciculations and fibrillations if the progression is slow
What is spinal shock?
Phenomenon that occurs in the event of a spinal trauma (e.g. knife wound) where reflexes may be lost or suppressed in lower regions of the spine even though the cord may be intact.
Gradually and variably returns
What is the pyramidal tract?
Composed of descending cortical fibers which arise from many areas (sensory and motor) of the cerebral cortex.
Only a fraction of the axons will extend to the spinal cord (corticospinal tracts)
The rest terminate in the brainstem nuclei
What are corticospinal tracts?
Axons in the pyramidal tract which pass through the caudal medulla, crossing in teh pyramidal decussation and form the **lateral corticospinal tract. **
Few remain ipsilateral and form the anterior corticospinal tract which goes to cervical spine then crosses.
What are the lateral descending pathways?
Lateral and anterior corticospinal tracts
Rubrospinal tract
Target motor neuron pools which control distal muscles and are critical for fine motor control of digits
What is the role of lateral group descending tracts?
Distal muscles and fine motor control
What are the medial descending spinal tracts?
Tectospinal tract
Lateral Vestibulospinal tract
Medial Reticulospinal tract
Lateral Reticulospinal Tract
Mostly target motor neuron pools that control axial and proximal muscles and control body posture and reflex adjustments that are imposed by sensory cues (antigravity)
How are flexors/extensors and distal/proximal motor functions controlled and located in the spinal cord?
How is somatopy maintained in the descending cortical motor projections?
What is the rubrospinal tract?
Arises from neurons in the red nucleus
Descending spinal tract (lateral group)
Axons cross completely and descend in the spinal cord in the lateral funiculus just ventral to the lateral corticospinal tract (descends contralaterally)
Axons terminate on contralateral spinal interneurons and facilitate flexor motor neurons and inhibit extensor motor neurons
What is the tectospinal tract?
Arises from the superior colliculus (tectum)
Axons terminate on spinal interneurons
Facilitates neck rotation (postural reflexes of the head)
What are the reticulospinal tracts?
Axons originate from teh pontine reticular nuclei = Medial RST
Axons originate from medullary reticular nuclei = Lateral RST
Medial is uncrossed (ipsilateral)
Lateral is bilateral
Have opposite effects
Medial = Extensors of axial muscles
Lateral = Inhibitory effect of axial extensors
What is the medial reticulospinal tract?
Originates in pons reticular nuclei
Ipsilateral tract that terminates on ipsilateral gamma-motor neurons and interneurons
Helps maintain posture, facilitates axial extensors
What is the lateral reticulospinal tract?
Axons originate on medullary reticular nuclei
Bilateral tract
Synapse on interneurons
Exerts inhibitory effect on axial extensors; helps maintain posture
What is the vestibulospinal tract?
Lateral and medial components that arise from the medial and lateral vestibular nuclei in the pons
Lateral runs ipsilateral and synapses on lateral gamma-motor neurons and interneurons
Tonic excitation of axial extensors. Helps maintain posture
Anti-gravity
What is the fasciculus proprius?
Fiber tract adjacent to the central grey at all levels of the cord that does not send axons beyond spinal cord
Generally forms short interneuon connections that are bilateral in ascending and descending fashion that help coordinate and integrate motor activities at different spinal levels
What structures help maintain posture?
Brainstem VST (Vestibulospinal tracts), RST (Reticulospinal tracts), cerebral cortex, and cerebellum
What provides tonic excitation for the anti-gravity muscles required for posture?
Lateral VST and the medial RST
What is the inhibitory input that balances tonic excitation of the anti-gravity muscles?
Purkinje cells in the cerebellum inhibit lateral VST
Cerebral cortex provides stimulation to the lateral RST which inhibits extensor motor neurons
What is the decerebrate rigidity model?
Correlates to spasticity clinically
Brainstem-transected cats demonstrate excessive hypertonia of extensor anti-gravity musculature
Knocks out cortical input to Lateral RST. This results in unbalanced activity of gamma-motor neurons which maintains the hypertonic state via a persistent myotatic reflex
Can be alleviated by lesioning DRGs
What is hypertonia?
Increased resistance to passive limb manipulation
What is rigidity?
Damage to structures of the basal ganglia; hallmark of Parkinson’s disease
Symptoms include hypoactive myotatic reflexes
Hypertonia throughout extensors and flexors
Cog-wheel type resistance
What is the primary motor cortex?
M1 area 4
Focused with motor execution
Cells discharge immediately before movement.
Organized into humunculus
Organized into interconnected cortical columns
Strictly contralateral
Small cells - delicate movements
Large cells - ballistic movements
Caudal precentral gyrus into anterior bank of central sulcus
What are features common to all motor cortical areas?
Neurons become active prior to movement onset
They have a low threshold of excitability
They have a small layer IV of cortex (large layer V)
Have corticospinal and other connections
Have thalamic inputs (from VLp and VLa)
Which neurons in the motor cortex are most immediately related to aspects of motor execution?
M1
How are primary motor cortex neurons organized?
Into heavily interconnected columns of elementary movements which can be recruited in different repertoires according to the motor task required
Where are corticospinal neurons located in the motor cortex?
Layer V
What are characteristics of the large corticospinal neurons of the motor cortex?
Betz cells
Concerned with ballistic bidirectional movements
Show all or none firing
Not influenced by sensory feedback
10% of pyramidal tract axons
What are characteristics of small corticospinal neurons of the motor cortex?
Concerned with slow, accurate, controlled movements
Unidirectional movement
Tight somatosensory feedback control
Graded firing potential to force exerted
90%
Majority synapse to interneurons
Which motor cortex cells are responsible for large, ballistic movements?
Betz cells (Large cells) of the corticospinal neurons
What cells of the motor cortex are responsible for slow, accurate, delicate, directionally selective movements?
Small corticospinal neurons
What are characteristics of the premotor cortex and the supplementary motor area?
Instruct M1
Involved in motor preparation and planning
Discharge before M1
What side of the body do M1 neurons correspond to?
contralateral
What side of the body do premotor cortex neurons correspond to?
Contralateral, mostly but some bilateral
What side of the body do supplementary motor area neurons correspond to?
Bilateral
What is the function of premotor cortex neurons?
Sensory guided movement planning (e.g. reaching for a target in extrapersonal space based on sensory cues that dictate the movement)
What is the function of supplementary motor area neurons?
Guide internally generated movement planning
Especially for movements involving bimanual coordination
Activate upon even thinking about a movement, not just before the actual movement
Which lesions can present with upper motor neuron damage?
Damage to the coritcal areas, internal capsule, or pyramidal tract
What are some signs/symptoms of UMN lesions?
Weakness
Spasticity (hypertonus of extensor muscles and flexors of forearm
Clasp-knife response to passive manipulation of limbs
Babinski sign
Atrophy of muscle
What are some signs/symptoms of LMN lesions?
Weakness
Areflexia
Flaccid paralysis
Pronounced muscular atrophy
What additional impairments do you see in M1 lesions (apart from UMN)
Permanent loss of fine motor control including loss of independent finger movements
What additional impairments do you see in PM cortex lesions (apart from UMN)?
Severe impairment in performing sensory-guided motor tasks
What additional deficits do you see in SMA lesions (apart from UMN)
Impairment in performing self-initiated motor tasks and especially in those that require bimanual coordination.
Leads to forced grasping (difficulty letting go of objects)
What are the components of a motor exam?
Observation and palpation - gait, inspection fo muscles for symmetry, loss of bulk, atrophy, and fasciculations
Tone and Power - 0 to 5 scale (3 is against gravity)
Reflexes - absent to hyperreactive scale (0 to 4, 2 is normal)
What is the distribution of weakness in upper motor neuron lesions?
Upper extremities: Flex stronger than extensors
Lower extremities: Exntensors stronger than flex
What is hemiplegic gait?
Arm is held in flexion with marked weakness of extensors of fingers, wrist, shoulder
Hand and fingers are tightly clenched.
Outward swinging of leg and reduced armswing
UMN
What is spastic gait?
Toe walking
Slow, stilff, walking with small steps
Hyperreflexia, clonus and positive babinski
UMN
What is frontal (magnetic) gait?
Seen in normal pressure hydrocephalus
Problems getting out of chair and finging center of gravity
Walk as if feet stuck to ground
hyperreflexia, plantar response, but minimal weakness
What is ALS?
Both UMN and LMN abnormalities
Bulbar palsy - dysarthria, dysphagia, impaired jaw-jerk, tongue fasciculations
pseudobulbar palsy - emotional swings
Preservation of extraocular muscles with no cognitive or sensory changes
Pelvic floor muscles/sphincters spared
MUST demonstrate disease above foramen magnum to differentiate from other disorders
Poor prognosis
What is primary lateral sclerosis?
Similar to ALS but only involves UMN
Abscence of cognitive, LMN or sensory involvement and nof family history
What is Guillain-Barre syndrome?
Acute autoimmune polyneuropathy
MS of the PNS
Often follows infection (campylobacter jejuni is common)
Facial weakness, difficulty breathing, pain
Lost reflexes with weakness
Medical emergency
What are common presentations in peripheral neuropathy?
Distal weakness - longest nerves first
Steppage gait - LMN leg weakness due to distal muscles
Foot drop - weak ankle dorsiflexion
Weakness, hyporeflexia
What organism is Guillain-Barre syndrome associated with?
Campylobacter jejuni
What is steppage gait?
LMN leg weakness where the patient slaps foot on the floor because they make a conscious effort to raise the foot as to not drag it.
What are some presentations of myopathies?
Proximal weakness with normal sensation, sphincter function and preservation of reflexes
Gower’s sign - hard to climb up
What is myotonia?
Disorder of muscle membrane (channeloopathy)
Slow relaxation of muscles after voluntary contraction
Improved upon warming of muscles
What is botulism?
Toxin from clostridium botulinum
Infants present with floppy baby
What causes floppy baby?
C. botulinum spores (botulism)
What is tick paralysis?
Caused by neurotoxin in tick salivary gland that may look like Guillain Barre
Ascenidng paralysis and respiratory fialure. Reflexes decreased
What is ciguatera toxin?
Caused by injesting certain fish
Toxin from a seaweed
Patients develop nausea, vomiting, weakness, muscular cramps, metallic taste, paralysis, coma, respiratory fialure
What is monoplegia?
Paralysis of one limb
What is diplegia?
paralysis of both upper or lower limbs
What is paraplegia?
paralysis of both lower limbs
What is hemiplegia?
Paralysis of upper limb, torso, and lower leg on one side of body
What is quadriplegia?
paralysis of all four limbs
What are basic findings in spinal cord disease?
UMN findings below the sign (hyperreflexia and Babinski)
Sensory and motor involvement that localizes to a spinal cord level
Bowel and bladder dysfunction
Recall, spinal cord ends at T12-L1
What can cause a compressive myelopathy?
Spondylolisthesis - dislacement of vertebrae
Tumor
Abscess
Disc prolapse
Spinal shock
What are the dermatome landmarks?
What is Syringobulbia?
Syrinx that affects the brainstem - results from congenital, tumor, or trauma
May affect cranial nerves and cause facial palsies
What do you see in complete spinal cord transections?
All ascending tracts from below and all descending tracts from above will be interrupted
Caused by tumor, MS, viruses, vascular, autoimmune, herniated disk
Paraplegia, quadriplegia
What is Brown-Sequard syndrome?
Ipsilateral UMN, mechanosensation deficits below the lesion
Contralateral pain/temp deficits below lesion
At lesion - ipsilateral LMN deficits, ipsilateral loss of all sensation
If lesion is above T1 = horners
Normal bladder/bowel
What is central cord syndrome?
Usually invovles cervical lesion (classic is cervical spondylosis with a hyperextension injury)
Damage ot anterior white commisure, spinothalamic tract
Bilateral pain and temp loss, preserved mechanosensation
Similar to syringomyelia or syringobulba
What is posterolateral column disease?
Subacute demyelination of dorsal columns, lateral corticospinal tract, spinocerebellar tract
UMN issues
Parestheisas of hands and feet
Positive romberg
Can be caused by B12 deficiency, Vit. E deficiency. Vacuolar myelopathy (AIDS, HTLV-1, tropical spastic paraparesis)
What is is Conus Medullaris Syndrome?
Sudden onset with bilateral presentation
L1, L2 level of cord
Causes minimal symmetric weakness
Causes symmetric saddle anesthesia, pain is not prominent
LMN bladder and bowel dysfunction develops early
What is Cauda Equina Syndrome?
Gradual onset, with asymmetric presentation
At the level of L4, L5, S1 nerve roots
Flaccid paralysis, hypotonia, areflexia
Asymmetric saddle amnesia with radicular pain - painful
Decreased rectal tone
LMN bladder/bowel issues develop late
What occurs in disc prolapse?
Spinal cord/nerve root compression - most common are C or L spine
Radiculopathy - sharp shooting pain
Numbness, weakness, bowel/bladdre disruption
What is spondylolisthesis?
Anterior-posterior slippage of the vertebrae
What is tabes dorsalis?
From Tertiary syphylis in which nerves of dorsal columns degenerate
Loss of sense of position, vibration, discriminative touch
Locomotor ataxia
Positive Romberg
Argyll Robertson pupils
What is an epidural abscess?
Rare infection (staph) that causes spinal cord/root compression
Back pain, radiculopathy are common
Need surgery and antibiotics
What organism commonly causes epidural abscesses?
Staph aureus
Common in immunosuppressed patients
What are the three classifications of tumors of the spinal cord?
Extradural (epidural) = most
Intradural extramedullary (in meninges)
Intramedullary (inside cord)
What is the more common origin of spinal cord tumors?
Metastatic - breast, prostate
What can cause an anterior spinal cord injury?
Anterior spinal artery infarct
What is anterior cord syndrome?
Caused by vascular injury
Bilateral loss of motor control, pain temperature
Preserved mechanosensation
Below T8 is less common because of Artery of Adamkiewicz
What is the watershed area of vascular disease of the spinal cord?
Above T8 (upper thoracic)
Below T8 you have Artery of Adamkiewicz to supply blood
What brainstem lesions affect descending motor pathways?
Anterior (ventral)
What brainstem lesions affect ascending sensory pathways?
Posterior (dorsal)
What is the hallmark of a brainstem lesion?
Crossed signs!!!
Lesions to CN cause symptoms on one side of the face
Lesions to the ascending or descending pathways cause symptoms on the other side of the body
What is Weber syndrome?
Lesions of the midbrain that affect CN III and the corticospinal tract
Caused by PCA blockages
Presents with diploplia, down and out eye (ipsilateral), ptosis
Contralateral hemiplegia
Patient presents with double vision, with right eye that doesn’t abduct. Has left sided weakness and trouble walking. Where is the lesion/
Anterior Pons
Affects CN VI and corticospinal tract
Blockages of Basilar artery
What is Millard-Gubler syndrome?
Lesions of the pons that affect CN VI, VII (and sympathetics), and the corticospinal tract
Basilar arteries usually involved
Ipsilateral facial palsy, lack of abduction, decreased corneal reflex, tear secretion, contralateral hemiplegia
What is Wallenberg Syndrome?
Lateral medulla lesion (caused by vertebral artery, PICA)
Affects CN V, spinothalamic tract, Nucleus ambiguous (9-11), vestibular nucleus, descending sympathetics from hypothalamus
loss of pain in ipsilateral face, contralateral body
Hoarse voice, dysphagia, dysarthria, decreased gag
Nystagmus, nausea/vomiting, vertigo, gait ataxia
Horner syndrome
What is Jackson Syndrome?
Ventral, medial medulla lesions
Affect CN XII, corticospinal tract
Issues with anterior spinal artery
Present with dysarthria with lingual quality. Hemiatrophy of trongue. Contralateral hemiplegia
What is Locked-in Syndrome?
Bilateral lesion of anterior pons
Affects corticospinal and corticobulbar tracts, CN VI, MLF
Spares CN III
Caused by basilar artery stroke, central pontine myelinosis
Patients present quadriplegic, aphonic, no horizontal eye movement, but can blink
Are conscious!
What are lesions of the lateral medulla called?
Wallenberg Syndrome!!!
Caused by vertebral artery or PICA infarcts
Loss of pain in ipsilateral face, contralateral body
Hoarse voice, dysphagia, dysarthria, decreased gag
Nystagmus, nausea, vomiting, gait ataxia,
Horner’s
What is the function of the cerebellum?
Key structure for motor learning and coordination
What is the main symptom of cerebellar damage?
Ataxia - issues synthesizing smooth, well-timed and proportional movements
What are the cerebellar lobes?
Anterior, posterior, flocculonodular
What are the Identify the anterior lobe of the cerebellum.
Identify the posterior lobe of the cerebellum
Identify the flocculonodular lobe of the cerebellum
What is a folium?
Equivalent to a gyrus in the cerebellum
What is a cerebellar lobule?
A combination of multiple folia in the cerebellum
Identify the primary fissure of the cerebellum
Identify the postero-lateral fissure of the cerebellum.
Idnetify the horizontal fissure of the cerebellum
What connections pass through the inferior cerebellar peduncle?
Connections fromthe medulla and spinal cord to the cerebellum
What information passes through the middle cerebellar peduncle?
Connections from the pontine nuclei to the cerebellum
What information passes through the superior cerebellar peduncle?
Exiting efferents from the cerebellum (except vestibular), and afferent ventral spinocerebellar tract axons
Where is the fastigial nucleus found?
In the vermis
Where is the interposed nucleus found?
Between fastigial and dentate nucleus
Where is the dentate nucleus found?
Lateral cerebellum
Identify the fastigial nucleus
Identify the interposed nucleus
Identify the dentate nucleus
What is the spinocerebellum?
Vermis and intermediate hemisphere
Contains somatotopic representations of the head nad body and sends efferents to spinal motor nuclear tracts
Which part of the spinocerebellum receives axial body input and projects through medial descending motor systems?
Vermis
Which part of the spinocerebellum receives distal body inputs and projects through lateral descending systems?
Paravermis (intermediate hemisphere sections)
What are the lateral hemispheres of the cerebellum responsible for?
Cerebrocerebellum - receive input from cerebral cortex via the pontine nuclei and do not receive direct somatosensory input
What is the flocculonodular lobe of the cerebellum responsible for?
The vestibular cerebellum.
Connectivity breaks all the rules of the other cerebellar structures
What is the part of the cerebellum responsible for vestibular functions?
flocculonodular lobe
What are the four spinocerebellar tracts?
Dorsal spinocerebellar tract - lower boddy proprioception
Ventral spinocerebellar tract - lower boddy error signal
Cuneocerebellar tract - upper body proprioception
Rostra spinocerebellar tract - upper body error signal
Which spinocerebellar tracts are involved with proprioception?
Cuneocerebellar tract (upper body)
Dorsal spinocerebellar tract (lower body)
Which spinocerebellar tracts are involved with transmitting error signals?
Rostral spinocerebellar tract (upper body)
Ventral spinocerebellar tract (lower body)
Which spinocerebellar tracts go to the lower body?
Dorsal and ventral spinocerebellar tracts
dorsal = proprioception; ventral = error signal
Which spinocerebellar tracts go to the upper body?
Cuneocerebellar tract = proprioception
Rostral spinocerebellar tract = error signal
What is the dorsal spinocerebellar tract?
Ipsilateral lower body proprioceptive tract
Muscle spindle afferents carry proprioception from lower body climb up the fasciculus gracilus and terminate in Clarke’s nucleus. Project through ipsilateral dorsolateral funiculus and inferior cerebellar peduncle to the intermediate zone of cerebellum
What is the cuneocerebellar tracts?
Proprioceptive upper body spinocerebellar tract
Ipsilateral
Muscle spindle afferents carry proprioceptive info to external cuneate nucleus. These axons travel up with teh dorsal spinocerebellar tract and end in intermediate zone of cerebellar cortex
What is the ventral spinocerebellar tract?
Lower body error signal spinocerebellar tract
Contralateral ascent, re-cross in cerebellum
GTO afferents project to spinal interneurons. Cross in spinal cord and ascend in the ventrolateral funiculus
Travel through superior cerebellar peduncle and recross midline
Cerebellar projection is ipsilateral
What is the rostral spinocerebellar tract?
Upper body error signal tract
GTO to interneurons through inferior cerebellar peduncle to cerebellum
Which spinocerebellar tracts course through the inferior cerebellar peduncle?
Cuneocerebellar, dorsal spinocerebellar, rostral spinocerebellar
Ventral spinocerebellar courses through the superior cerebellar peduncle
Which spinocerebellar tract courses through the superior cerebellar peduncle?
Ventral spinocerebellar tract
Dorsal, cuneocerebellar, and rostral course through inferior peduncle
What are the inputs to the cerebellum?
Spinocerebellar tracts (4 of them)
Reticular formation
Vestibular nerve, nuclei
Pontine nuclei
Inferior olivary complex
What are the layers of the cerebellar cortex?
Molecular = closest to pia
Purkinje = middle
Granular = deepest
Which cells are the key to the cerebellar cortex?
Purkinje cells
Reside in the purkinje layer
GABAergic, inhibitory neurons
What cells reside in the molecular layer?
Purkinje cell apical dendritic trees (perpendicular to long axis)
Climing fiber axon terminals - which provide direct, convergent input to purkinje cells
Stellate cells = inhibitory interneurons to Purkinje dendrites
Basket cells = inhibitory interneurons to Purkinje cell bodies
Excitatory parallel fibers (course parallel to long axis)
What are the climbing fibers?
Synapse directly to Purkinje cells and arise from the Inferior Olivary Complex
Provide convergent excitation (one purkinje cell receives input from one climbing fiber; but each climbing fiber innervates only a few Purkinje cells; however, the climbing fibers make thousands of synapses on each Purkinje)
What are mossy fibers?
Provide input from all sources except inferior olivary complex
Provide indirect input to purkinje cells. Relayed via parallel fibers of granule cells located in glomeruli
These convey excitatory information to large number of Purkinje cells
What is a cerebellar glomerulus?
Located in granular layer
Comprised of mossy fiber axon terminal (excitatory; Golgi cell axon terminal (inhibitory) and several post-synaptic granule cell dendrites
Describe the inputs of cerebellar cortex
What are the outputs of the cerebellar cortex?
Purkinje cell is the only output
Project to cerebellar nuclei or to the vestibular cerebellum
How doe the cerebellum control pusture?
Flocculonodular lobe and vermis project to the vestibular nuclei of the brainstem (bilaterally) with no cerebellar relay. From here goes to reticulospinal and vestibulospinal tracts to the axial, neck muscles
Some vermis projections to the vestibular nuclei relay through the fastigial nucleus
How does the cerebellum control motor control?
Paravermis nuclei (interposed nuclei = globulose and emboliform nuclei) project through the superior cerebellar peduncle to the contralateral red nucleus (decussates)
Activate rubro-olivary tract (red nucleus to inf. olivary complex, to cerebellar peduncle and climbing fibers)
Activate rubrospinal tract (red nucleus to midbrain decussation to distal misculature)
How does the cerebellum control motor planning?
Lateral hemispheres of the cerebellum project to the dentate nuclei which send axons through superior cerebellar peduncle to the VLp in the thalamus (contralateral). These go to the cerebral cortex which send projections to the distal musculature through corticospinal tract
Dentate nuclei also project to red nucleus , which lets the red nucleus integrate info from paravermal intermediate zone and lateral hemispheres
Why are cerebellar deficits always ipsilateral to the lesion?
All outpus (except vestibular) course through the superior cerebellar peduncle. This decussates as it ascends and targets the red nucleus and cerebellar cortex through the thalamus. The resulting descending tracts also cross (back) to the muscles of the ipsilateral side of the lesion
What are cardinal features of cerebellar dysfunction?
Ataxia
Decomposition of movement
Dysarthria
Dysdiadochokinesea
Dysmetria
Hypotonia
Nystagmus
Scanning Speech
Tremor
What is ataxia?
Reeling, or wide-based gait
What is decomposition of movement?
Inability to correctly sequence fine coordinated acts
What is dysarthria?
Inability to articulate words correctly with slurring and inappropriate phrasing
What is dysdiadochokinesia?
Inability to perform rapid altering movements
What is dysmetria?
Inability to control range of movement (abnormal trajectories through space)
What is hypotonia?
Decreased muscle tone
What is scanning speech??
Slow enunciation with a tendency to hesitate at the beginning of a word or syllable
What is tremor?
Rhythmic, alternating, oscillatory movement of a limb as it approaches a target (intention tremor)
What are features of Vermis Syndromes?
Symptoms that affect the trunk
Wide-based gait and stance
Truncal titubations (staggering)
Arm and leg coordination are spared
Gait abnromalities not improved by visual orientation (indiscriminate falling)
Eye movement disturbances
Rotated postures of head
Test by tandem toe-heel walking; walking backwards; hop on each foot; romberg
What is the most common cause of midline (vermis) cerebellar syndromes?
Chronic alcohol use
What are symptoms of hemispheric cerebellar syndromes?
Appendicular ataxia - loss of coordination of limbs ipsilateral to lesion
Impaired rapid alternating movements
Gait abnormalities not improved by visual orientation - fall toward lesion
Dysdiadochokinesia, Dysarthria, Dysmetria
Tremors
Hypotonia
Test with rapidly alternating movements (finger to nose, heel-knee-shin), check and rebound, past pointing
What are common causes of cerebellar hemisphereic syndromes?
Metastasis, infarcts, abcesses
What are pancerebellar syndromes?
Combination of vermis and hemispheric syndromes
Can be caused by infectious processes, hypoglycemia, paraneoplastic disorders, drunkenness
What oculomotor dysfunctions are commonly seen in cerebellar disorders?
Nystagmus (gaze evoked, upbeat, rebound)
What is the Romberg Sign?
Close eyes and stand still
Patients will fall with both cerebellar and posterior column disease
With eyes open, patients with cerebellar disease will fall.
Posterior column defecits will present with eyes closed (falling out of shower)
What do cerebellar tremors present as?
Intention tremors
Occur during purposeful/directed movement (especially near end)
Usually slow frequency, coarse, and broad
What do non-cerebellar tremors present as?
Resting tremors, usually
Occur maximally at rest and decrease with activity
What structures are likely affected in a patient with a resting tremor that improves with motion?
Not cerebellum!
What structure is likely affected in a patient with a tremor that worsens with movement and is worse at the end of a movement towards an object?
Cerebellum!
What is a resting tremor?
Maximal at rest
Decreases with activity
Usually symptom of Parkinson’s
What is a postural tremor?
Maximal with limb in a fixed position against gravity
Gradual onset suggests physioloic or essential tremmor
Acute onset suggests toxic/metabolic disorder
What is an intention tremor?
Maximal during movement toward a target (finger to nose)
Suggests cerebellar disorder but may be due to somethign else (MS, Wilson’s)
What is asterixis?
Flapping “tremor” in wrist due to liver failure (think metabolic)
Caused by interruptions of contraction in wrist extensors
What is a pill-rolling tremor indicative of?
Parkinsons!
What do dysfunctions of the basal ganglia present as?
Motor behavior and reward seeking deficits
Tremor, rigidity, dyskinesias, loss of postural reflexes, chorea, ballismus, dystonia, addiction
Parkinson’s, Huntingtons, Tourette’s, hemibalismus are diseases
What are the components of the basal ganglia system?
Striatum (dorsal = caudate nucleus + putamen; ventral = nucleus accumbens septi)
Pallidum (external, internal, ventral)
Substantia nigra (compacta, reticulata)
Ventral tegmental area
Subthalamic nucleus
What are the major inputs to the basal ganglia system?
Cerebral cortex (huge) - glutamatergic
Thalamus - glutamatergic
Midbrain - dopaminergic
Raphe nuclei - serotinergic
Locus ceruleus - noerepinephrine
How is cerebral cortical input to the basal ganglia organized?
Topographically
from all areas, but especially the frontal lobe
Where does thalamic input to the basal ganglia originate from?
Ventral group (VA/VM; VLa)
Inrtralaminar nuclei (CM)
Medial Dorsal Nucleus (MD)
What are the main efferent cells of the striatum?
Medium Spiny Neurons (GABA-ergic)
What are the two subtypes of the medium spiny neurons of the striatum?
Substance-P colocalizing neurons with D1 receptors (excitatory)
Enkephalin colocalizing neurons with D2 receptors (inhibitory)
Project to Globus Pallidus and Substantia Nigra
What are the components of the striatum?
Dorsal = caudate and putamen
Ventral = nucleus accumbens septi, olfactory tubercule
What is the dorsal striatum?
Putamen and caudate nucleus
What is the ventral striatum?
Nucleus accumbens and olfactory tubercule
What is the subthalamic nucleus?
STN - pod-shaped, located rostral and lateral to substantia nigra
Output is excitatory (Glutamatergic)
What is the globus pallidus?
Located lateral to the interanl capsule and medial to the putamen
3 parts: External, internal, ventral
External (GPe) and inner (GPi) are dorsal pallidum; ventral pallidum (VP) is ventral to anterior commissure
All are GABAergic
What is the substantia nigra?
Two parts (pars reticulata (SNpr), and pars compacta (SNpc))
SNpr is caudomedial extension of GPi = both are GABAergic
SNpc is midbrain dopaminergic cell group that provides input to striatal MSN
Which are the major output centers of the basal ganglia?
GPi, SNpr and VP
Which basal ganglia output center contorls head and neck motor control?
SNpr
Which basal ganglia output center controls motor body function?
GPi
How does output to the pyramidal system occur from the basal ganglia?
GPi/SNpr axons travel to thalamus via ansa lenticularis and lenticular fasciculus
What are the important functions of the ansa lenticularis and lenticular fasciculus?
Tracts of output from the GPi/SNpr axons to the thalamus
What are the pathologic hallmark of parkinson’s disease?
Lewy bodies
What is a lewy body?
Pathologic hallmark for Parkinson’s Disease
Eosinophilic inclusion in neuron made of alpha synuclein and ubiquitin
Classically in Substantia Nigra, but also found elsewhere
How is Parkinson’s diagnosed?
Clinically
Cardinal signs:
Bradykinesia, rigidity, tremor, postural instability
What is the characteristic parkinson’s tremor?
3Hz, 3-5Hz, pill rolling
How is Parkinson’s treated?
Symptomatically - no cure
Levodopa (precursor to dopamine that crosses BBB)
MAOI -B inhibitors - increases dopamine levels
COMT inhibitors - keep plasma levodopa levels high
Amantadine - antiviral agent that keeps endogenous dopamine levels high
Anticholinergics
Deep brain Stimulation
What is Lewy Body Dementia?
Parkinsonism, dementia, fluctuations in arousal and attention, myoclonus, visual hallucinations
What is progressive supranuclear palsy (PSP)?
Symmetric Parkinsonism
Early postural instability with falls
Typically onset after 70 years old, and no response to levodopa
What is Cortical basal ganglionic degeneration?
Rare condition with onset in 60s or 70s with rapid course
Asymmetric, atremulous parkinsonism
Cortical involvement with issues writing, aphasia
no response to levodopa
What is multiple system atrophy?
Onset in 40s-60s and can mimic Parkinson’s
parkinsonian, cerebellar, or autonomic
early autonomic dysfunction (orthostatic, incontinence)
symmetrical parkinsonism, with rapid progression
What is Wilson’s Disease?
Movement disorders that present at 10-25 years old with liver disease
(liver + neuro/psych = wilsons)
Can lead to renal failure, retardation
Dysarthria, dystonia, tremor, parkinsonism, Kaiser Fleischer rings (copper in cornea),
Autosomal recessive caused by mutations in copper transporter ATPase. Causes copper accumulation
If under 50 with parkinsonism = test for Wilsons!
Treat with chelators!!!!
What is Huntington’s Disease?
Chorea - starts as clumsiness/fidgetiness progresses to full chorea
Dysarthria, dysphagia, motor impersistence
Parkinsonism
Depression, psychosis, dementia
Slowed saccades
Atrophy of the striatum - particularly caudate
Initially degenerates indirect pathway, eventually both
Treat with Dopa antagonists and Dopa depleting agents
Autosomal dominant - CAG repeats in huntingtin gene (Chr 4 >38 repeats
What is chorea?
Involuntary continual irregualr and unsustained movements
Not predicatable or suppresable
Motor impersistence, mild hypotonia
In Huntingtons, side effect of L-Dopa, antipsychotics
What are tics?
Unvoluntary production of movements, sounds
Premonition sensation, suppressible, suggestible, stereotyped
Childhood onset, co-occurs with OCD, ADHD (Tourette’s)
What are tremors?
Involuntary rhythmic oscillations, usually 3-12 Hz
Essentail tremor = head, hands voice (6Hz)
Cerebellar dysfunction = 3 Hz
Parkinsonism = 3Hz
Alcohol improves essential tremor
Treat with DBS, botulinum, anticonvulsants
What is dystonia?
Slow, twisting, repetitive movements that produce abnormal postures
Task specific, persist over time, spread
Sensory tricks can aleviate
Dopamine, ACh dysfunction in basal ganglia
What happens in hypokinesis?
Indirect pathway dominates over direct pathway - net inhibition of thalamus - decreased cortical output - decreased quality of movement
Parkinsons = loss of Dopaminergic SNpc neurons
What happens in hyperkinesis?
Direct pathwya predominates over indirect pathway with net disinhibition of the thalamus - increased cortical signals - increased movement
Huntingtons - death of neurons that initiate indirect pathway; D1 Substance P MSNs are spared, but lost over time
