Reticular Formation and Cerebellum Flashcards
Reticular Formation Location
Central core of the brainstem
Reticular Formation Function
Regulates posture some stereotypic motor behaviors internal environment pain regulation sleep/wake cycles emotional tone
What are the 3 longitudinal zones of the reticular formation from medial to lateral?
Raphe/Median
Medial/Paramedial
Lateral
Raphe zone
Adjacent to the sagittal plane of the reticular formation
Medial zone of Reticular formation
alongside the raphe
mix of large and small neurons
location of mostly ascending and descending projections
Lateral zone of Reticular formation
Most extensive RF zone
Prominent in rostral medulla and caudal pons
Primarily involved in cranial nerves reflexes and visceral functions
Connections of the reticular formation
Neurons have extensive, complex connections
May innervate multiple levels of the spinal cord, brainstem, thalamus
Some have bifurcating axons that ascend and descend
Sleep paralysis
Transient, conscious state of involuntary immobility
Caused bu hyper polarization of the spinal motor neurons originating in the cholinoceptive neurons in reticular formation
What are the tracts of the Reticular Formation?
Medial reticulospinal tract
Lateral reticulospinal tract
Medial reticulospinal tract
Starts in the pons
Ipsilateral
Descends near the MLF in the anterior funiculus
Lateral reticulospinal tract
Starts in the medulla
Descends bilaterally in lateral funiculus
Causes muscles to be flaccid during sleep
How does the Reticular formation effect movement?
Major alternative to corticospinal tract in regulating spinal motor neurons
Influences spinal motor neurons directly, so that only harmful/noxious stimuli evoke a reflex
Also contains basic neural machinery for some complex patterned movements (sectioning brainstem-diencephalon junction in cat)
What pattern generators are located in the Reticular Formation
Gaze centers Mastication Locomotion Heart Rate Respiration Swallowing, vomiting
Gaze Center location
Midbrain vertical gaze center
Pontine horizontal gaze center
Mastication pattern generator location
Supratrigeminal nucleus (in the pons)
Locomotion pattern generator location
Pons
Medulla Vital Center
Location of the pattern generator for: Heart Rate Respiration Swallowing Vomiting
Bruxism
Stereotyped movement disorder that causes tooth grinding or clenching
Seen more in younger individuals
Bruxism symptoms
Tooth grinding/clenching, leading to:
Sounds
Jaw muscle discomfort
Abnormal wear of tooth
Bruxism Mechanism
During sleep, muscles are in a state of atonia and Jaw muscles are co-contracted
Opening and closing muscles are contracted at the same time
What are the Bruxism cause theories.
Peripheral causes theory
Central causes theory
Peripheral causes theory
Malocclusion results in premature and one-sided contact
Jaw movements occur in an attempt to reach resting position
This theory is based on clinical observation an treatment experience
Central causes theory
Sleep-related dysfunction causes bruxism
Input to the supratrigeminal nucleus may be form basal ganglia, lateral hypothalamus, and central nucleus of the amygdala
What structure is key to the brain’s facilitation of pain suppression?
Reticular Formation
The Periaqueductal gray (PAG) is central to…
One well described pain suppression system
From where does the PAG receive pain fibers from?
Spinomesencephalic fibers
Where does the PAG send pain fibers to?
The raphe, and then they go on to the posterior horn of the spinal cord and spinal V nucleus
How do Opiates work?
They control pain by activating the PAG-raphe at multiple levels.
Where are opiate receptors abundant?
PAG
Raphe
Posterior horn of the spinal cord
How can the raphe inhibit pain to the STT?
Directly
Indirectly - by activating interneurons that inhibit STT
Directly inhibit pain afferents
What is the pathway for the Reticular Formation response to environmental conditions?
From the body to the RF, and then projects to the brainstem autonomic nuclei and spinal cord
What visceral functions are controlled at the pons and medulla level of the RF?
Inspiration
Expiration
Rhythm of breathing
What visceral functions are controlled at the medulla level of the RF?
Heart Rate
Blood Pressure
Where does the RF send projections to for Arousal and consciousness
Thalamic intralaminar nuclei, and then diffusely to the cortex
Where does the RF receive fibers from for arousal and consciousness?
Midbrain and pons level RF get input from multiple sensory modalities, such as pain and spinoreticular fibers
What neurochemicals have nuclei in the brainstem?
Norepinephrine
Dopamine
Serotonin
What neurochemicals have nuclei in the Hypothalamus?
Histamine containing neurons
What neurochemicals have nuclei in the Telencephalon?
Acetylcholine
Where are Noradrenergic (Norepinephrine) neurons located?
Solitary nucleus (Medulla) Locus ceruleus (Rostral pons) Ventrolateral medulla (spinal cord)
What is the function of norepinephrine in the Solitary nucleus?
Help with memory enhancement
What is the function of norepinephrine in the Locus ceruleus?
Provides cortex vigilance and attention
It is highly active during attentive situations, moderatly active while awake, and low activity during sleep
What is the function of norepinephrine in the ventrolateral medulla?
Pain regulation
Clinical depression
Locus ceruleus neuron activity is reduced, leading to less norepinephrine
Why do Parkinson’s disease patients often suffer from clinical depression?
The locus ceruleus neurons are lost in Parkinson’s disease
What is the mechanism of some anti-depression medications?
Increase the firing rate of locus ceruleus neurons
Where are Dopaminergic (Dopamine) neurons located?
In the midbrain, more specifically:
Substantia nigra
Ventral segmental area
Dopamine neurons in the Substantia nigra pathway and function
Project to the Caudate and Putamen
Sends dopamine to the brain and is responsible for motor production
Pathway is less effective in Parkinson’s
What are the two tracts of Dopamine that come from the Ventral Tegmental area?
Mesocortical fibers
Mesolimbic fibers
Mesocortical fibers
Dopaminergic fibers from the Ventral Tegmental area with heavy projections to the frontal cortex
Organizes and initiates thinking and planning
Mesolimbic fibers
Dopaminergic fibers from the Ventral Tegmental area to the amygdala
Associates emotional reward or sense of well being
Fibers are also associated with Drug dependency
What is implicated in Schizophrenia?
Ventral Tegmental area
What are the 2 components of Schizophrenia?
Social Withdrawal
Hallucinations
Cause of Social Withdrawal in Schizophrenia
Low levels of dopamine in the prefrontal cortex
Cause of Hallucinations in Schizophrenia
High levels of dopamine in the limbic system
Where are serotonergic (Serotonin) neurons located?
At all brainstem levels in the Raphe - “Raphe nuclei”
What is the function of raphe nuclei?
They direct attention by inhibiting distracting stimuli
Pojections to the hypothalamus are responsible for day-night cycles
Where do raphe nuclei project to?
They are very extensive and profuse, especially to the sensory and limbic areas
What do low levels of serotonin lead to?
High carbohydrate consumption
Binge eating
Carbohydrate preference in obese women
What do high levels of serotonin lead to?
Compulsive behavior
Anorexia nervosa
What do drugs that increase the levels of serotonin treat?
Depression
Anxiety
Where are cholinergic (Acetylcholine) neurons located?
Basal nucleus (of Maynert) Dorsal Pontine tegmentum
What is area is effected in Alzheimers?
Basal nucleus (of Maynert)
What is one treatment of Alzheimers discussed in class?
Cholinesterase inhibitors, to slow the breakdown of Acetylcholine
What is the cortex of the cerebellum, and what is it made of?
Outer surface
Gray matter
What is the inside of the cerebellum made of?
White matter
Functions of the cerebellum
Regulate equilibrium
Controls muscle tone and posture
Provides motor coordination for voluntary movements
At what points can the cerebellum control voluntary movements
In the near future
During execution
How does the cerebellum control voluntary movement in the near future?
Plan actions in space and time
How does the cerebellum control voluntary movement during execution?
Monitor ongoing activity and adjust the output of the motor cortex
What are the main fissures of the Cerebellum?
Primary fissure
Posterolateral fissure
Primary fissure
Divides the body of the cerebellum into anterior and posterior lobes
Posterolateral fissure
Separates flocconodular lobe from the body of the cerebellum
What are the functional connections of the Cerebellum?
Vermis
Hemispheres
What is the Vermis of the Cerebellum?
In the midline of the cerebellum
What are the hemispheres of the Cerebellum and where are they located?
Medial Hemisphere - adjacent to the vermis
Lateral Hemisphere - adjacent to the medial hemisphere
What are the 3 cerebellar peduncles
Attach the Cerebellum to the cortex
- Inferior Cerebellar Peduncle
- Middle Cerebellar Peduncle
- Superior Cerebellar Peduncle
Inferior Cerebellar Peduncle
Receives input from the spinal cord and brainstem
Monitors muscle and limb movement
Contains the Juxtarestiform body
Juxtarestiform body
Interconnects vestibular nuclei and cerebellum
Middle Cerebellar Peduncle
The largest peduncle
Lateral to the pons
Receives afferents from the contralateral basis points
Relays motor signals form the cortex
Superior Cerebellar Peduncle
Sends efferent fibers from the red nucleus to the thalamus
What are the cerebellar deep nuclei from medial to lateral?
Fastigal
Globose
Emboliform
Dentate
What cerebellar deep nuclei make up the Interposed nucleus?
Globose
Emboliform
What is likely the most ancient deep cerebellar nuclei
Fastigal
Which deep nuclei contributes the most fibers in the Superior Cerebellar Peduncle?
Dentate nucleus
What is the relay system of cerebellar circuitry?
1) Inputs arrive via the ICP or MCP, and they get projected to the cortex
2) Cortex deals with the signals
3) Cortex sends info the the deep nuclei
4) Deep nuclei send projections (via the SCP) to other parts of the brain
What are the layers of the Cerebellar cortex from Superficial to deep?
Molecular layer
Purkinje cell layer
Granule layer
Molecular Layer of Cerebellar Cortex
Contains Purkinje cell dendrites and granule neurons axons
Parking Cell Layer of Cerebellar Cortex
Contain the only axons that leave the cortex
Microzone
A group of Purkinje cells all having the same somatotopic receptive field
Contain ~1000 Purkinje cells arranged in a long, narrow strip oriented perpendicular to cortical folds
What are the three fibers of Basic Cortical Circuitry
Climbing Fibers
Mossy Fibers
Parallel Fibers
Climbing Fibers
Emerge from the Inferior Olivary Nuclei - emerge medially and ascend to the contralateral ICP and enter the cerebellum
They divide into 5-10 branches with each branch synapsing on a different Purkinje cell
They regulate Purkinje cell firing
Mossy Fiber
Input form brainstem (pons), vestibular system, and spinal cord
Provide a major cortical input
Parallel Fiber
Axon from a granule cell
How is the cortex and deep nuclei connected?
Mossy and climbing fibers send collaterals to deep nuclei before axons enter the cortex
Parking cell axons end in the deep nucleus
What are the longitudinal zones of the Cerebellum?
Vestibulocerebellum
Spinocerebellum
Pontocerebellum
Spinocerebellum Input
Spinal cord
Brainstem
Spinocerebellum cerebellar location
Paranormal area
Part of the vermis
Spinocerebellum Output
Red nucleus
VA/VL of the thalamus
Spinocerebellum Function
Coordination of trunk and limb movements
Vestibulocerebellum Input
Vestibular end organ
Vestibular nuclei
Vestibulocerebellum cerebellar location
Flocconodular lobe
Part of the vermis
Vestibulocerebellum Output
Fastigal nucleus
Vestibular nuclei
Vestibulocerebellum Function
Control eye movement
Balance
Pontocerebellum Input
Motor cortex
Basilar pons
Middle cerebellar peduncle
Pontocerebellum cerebellar location
Lateral cerebellar hemisphere
Pontocerebellum Output
Dentate nucleus
Red nucleus
VA/VL of thalamus
Pontocerebellum Function
Planning and timing of movement (especially of the upper extremities)
Coordination of speech
Lateral hemisphere function
Planning learned, skillful movements (those that become more precise and rapid with practice)
Lateral hemisphere injury
Involves arm and speech
- intention tremor
- dysdiadochokinesia (rapid, alternating movements)
- dysmetria (finger-to-nose test)
- dysarthria (scanning or explosive speech)
Medial hemisphere function
Adjusting limb movement
Vermis function
Postural adjustments
Vermis Injury
Leads to
- truncal ataxia
- disturbances in balance while seated or standing
- gait ataxia
Flocculus and vermis Function
Eye movements
Flocculus and vermis Injury
Leads to:
-Nystagmus (back and fourth eye movements)
Vermis input projects to
Fastigal nuclei
Medial hemisphere projects to:
Interposed nucleus (Globose and Embeliform)
Lateral hemisphere projects to:
Dentate nuclei
What is the principle output from the cerebellar nuclei?
Superior Cerebellar Peduncle
Cerebral hemisphere controls what side muscles?
Contralateral
Cerebral hemisphere influences what side limbs?
Ipsilateral
Cerebral hemisphere projects to what side of the thalamus?
Cotnralateral
