Reticular formation Flashcards
what is the organisation of the brainstem split into
dorsal part
middle part
ventral part
what does the dorsal part have in it
cranial nerve nuclei and sensory reflex centers
what does the middle part have in it
• Middle part (tegmentum) - ascending pathway and RETICULAR FORMATION (with integrating nuclei); descending sympathetic axons travel with reticulospinal tracts
what does the ventral part have in it
descending motor pathways e.g., corticospinal & corticobulbar tracts; rubrospinal, reticulospinal and vestibulospinal tracts arising in brainstem
what is the reticular formation
- It is a network of cells that run through the brainstem, medulla pons and midbrain
- it performs numerous integrative and modulatory functions.
what does the reticular formation of the brainstem do
- it is the core of the brainstem
- it controls basic functions and autonomic functions
what does the reticular formation consist of
- It consists of scattered clusters of neurons amidst ascending and descending axons of the tegmentum.
- Usually these clusters cannot be easily recognized as distinct nuclei.
describe the organisation of the reticular formation
- Lateral sensory inputs – sensory and other inputs from ascending and descending systems
- Motor – outputs – efferent output to midbrain, cerebellum, hypothalamus, thalamus and spinal cord
- Midline (modulatory- Raphe nuclei – 5HT – faciliatory or inhibitor pain, filtering inputs
what are the 4 principle functions of the reticular formation
- Arousal responses
- Autonomic nervous system control
- Control of muscle tone and reflexes
- Pain modulation
describe some other functions of the reticular formation
- Somatic reflex regulation – gain facilitation, for example how much tone the muscle has, it gives activity to particular muscle groups over other ones.
- Visceral regulation via control of autonomic functions – respiratory, cardiovascular, bladder control
- Maintenance of consciousness, sleep and arousal
- Sensory filtering and modulation
what are some examples of how somatic reflex regulation happens
- Premotor control, allows eye movements and coordinate movements, reflexes that involve both autonomic and somatic effects,
- there are somatic regulation of postural reflexes as well- extrapyramidal motor control
what do the reticulopsinal projects do
- Reticulospinal projects controlling postural adjustments and segmental control of motor reflexes that span the length of the brainstem
what does the caudal pontine and medullary reticular formation do
- Caudal pontine and medullary reticular formation – premotor coordination of lower somatic and visceral motor neuronal pools and raphe descending control
what does the mesencephalic and rostral pontine reticular formation do
- Mesencephalic and rostral pontine reticular formation – includes the conscious state
what is the role of the reticulospinal tract
- In the somatic nervous system it has a feedforwards and anticipated postural stability
- For example when you think to move you have to adjust other musculature, this is mediated by the reticulospinal output pathway
what pathway regulates postural adjustment
- The indirect extrapyramidal motor pathway that regulates postural adjustment
- If there is posture instability it goes up the pathway as negative feedback
wha are the reticular formation centres involved in control coordinating eye movements
paramedian pontine reticular formation (PPRF) and mesencephalic (vertical) gaze centres
- Following frontal eye field excitation the paramedian pontine reticular formation generates horizontal eye movements
what does lesions to the MLF do
. Lesions to the medial longitudinal fasciculus disrupt CNIII connectivity and function
what is the nucleus of solitary tract
The nucleus of the solitary tract is the main visceral sensory processing site
what does the nucleus of solitary tract do
– involved in taste, and inform about blood pressure and oxygen concentrations in the blood
how does the reticular formation control respiratory control
- The NTS is the sensory processing centre where inputs come about need for oxygen and breathing, this is the dorsal respiratory group
- The dorsal respiratory group is connected to the ventral respiratory group
- The ventral respiratory group has the nucleus ambiguous in it which surrounds the reticular formation
- The medullary pacecentre include the pre botzinger complex which mediates inrpsiationa nd exrpaition and generate the breathing rhythm
what happens if you get an lesion to the NTS (nucleus of solitary tract )
- get Cheyenne stokes respiration
what nucleus is in control of the dorsal respiratory group
nucleus of solitary tract
what nucleus is in control of the ventral respiratory group
nucleus ambiguous
what does the pontine reticular formation do
- Controls the ventral and dorsal medullary centres
- It fine tunes it
- Allows us to breath as we talk and do exercise, and sleep
- contains The pneumotactic and the apneustic centre c
what does the pneumotactic centre do
- The pneumotactic centre limits inspiration and facilitates expiration, it stops excessive breathing
what does the apenustic centre do
- The apneustic centre prolongs inspiration and reduces expiration
where does input come from to the NTS
- They arise from vagal lung mechoreceptor afferents
- CNIX arterial chemoreceptor (blood PO2) afferents
- Input also comes from chemoreceptors in the floor of the 4th ventricle that monitor pH of the CSF
what happens to breathing if there is a lesion below the medulla
Lesions below the medulla it is impcompatible with life and you cannot breath and vnetilaton stops
what happens if there is a lesion between pneumotaxic centres and apeneustic centre
Apneustic breathing
- with deep and prolonged inspiration followed by short, insufficient expiration
what does the NTS do in to terms of the cardiovascular system
- Mechanosensory baroreceptor input on blood pressure as well as chemosensory input on blood PO2 travels to the brainstem NTS in CN X and IX respectively
- The NTS relays this information to the hypothalamus and brainstem reticular nuclei.
- Vagal output originating in the dorsal motor nucleus of the vagus and n. ambiguus as well sympathetic n.s. outputs (via reticulospinal hypothalamo-spinal projections) mediate compensatory changes in cardiac function and peripheral vasculature in response to altered afferent input.
what does the reticulospinal tract input
Reticulospinal tract projects to the preganglionic autonomic neurones (both sympathetic and parasympathetic).
what happens if the reticulospinal tract is damaged
If the reticulospinal tract is damaged the autonomic output is lost leading to loss of blood pressure, temp regulation (sweating), bladder and bowel control
what is the main centre for noradrenaline
locous coerculeus
Dopamine
- what is the nucleus involved
- what does it do - what happens if there is a loss of movement
- what area is it in
- Substantia Nigra (SN)- nigrostriatal pathway
Control of movement- initiation/ switching
- Loss Parkinson’s disease
Organising behaviour; focusing & attention; reward & motivation
Ventral tegmental area (VTA)
- Mesolimbic and mesocortical pathways
what happens if there is a distribuance in dopamine
Schizophrenia; Addiction
noradrenaline
- what is the nucleus involved
- what does noradrenaline do
Locus coeruleus and other nuclei
Sympathetic NS control centre activated by the hypothalamus
- Descending fibres carried in reticulospinal tract activate preganglionic sympathetics
- Also activates the motor system so our reflexes are faster.
- Also inhibition of pain
- Ascending fibres to the forebrain activate a central sympathetic system behavioural alertness & arousal (esp. to stress/ stimuli evoking fear)
Sertonin
- what is the nucleus involved
- what does it do
- what do deficits produce
Raphe nuclei – midline nuclei
- Rostrally Inhibits basal forebrain cholinergic GABA cells to produce arousal; gate sensory input to cortex; effects on cognition, mood
- Caudally - modulates pain perception and facilitates muscle activity
- Numerous receptor types/ complex
Deficits produce OCD, depression, anxiety, aggression
what drugs target serotonin
Drugs that target 5HT receptors affect mood e.g. anti depressants, also anti-migraine, anxiolytics, hallucinogens, anti-psychotics
Acetycholine
- what is the nucleus involved
- what does it do
- Involved in Pedunculopontine & lateral dorsal tegmental nuclei of the brainstem
- Cortical arousal and sensory filtering through thalamic projection and movement
- Mediates activity of the thalamus
what is the sleep promoting system
- Anterior hypothalamus
- Ventrolateral preoptic (VLPO) area
- GABA/ galanin
- Inhibit wake promoting neurons
what does a lesion in the sleep promoting system cause
Insomnia (anterior hypothalamus
what is the ascending arousal (sleep waking system)
- increase firing in anticipation of waking and in arousal
- Brainstem reticular formation (RF)
- damage to can lead to coma
locus coeruleus (NA) and raphe n (5HT) Posterior hypothalamus - Tuberomammillary nucleus (TMN) of the hypothalamus – Histamine
what does a lesion to the posterior hypothalamus and ascending arousal system lead to
hyersommia
what does acetylcholine do in ascending arousal systems
ACh promotes forebrain activation in both waking and REM sleep (via thalamus + basal forebrain)
