Reticular formation

Question 1

what is the organisation of the brainstem split into

Answer 1

dorsal part
middle part
ventral part

Question 2

what does the dorsal part have in it

Answer 2

cranial nerve nuclei and sensory reflex centers

Question 3

what does the middle part have in it

Answer 3

• Middle part (tegmentum) - ascending pathway and RETICULAR FORMATION (with integrating nuclei); descending sympathetic axons travel with reticulospinal tracts

Question 4

what does the ventral part have in it

Answer 4

descending motor pathways e.g., corticospinal & corticobulbar tracts; rubrospinal, reticulospinal and vestibulospinal tracts arising in brainstem

Question 5

what is the reticular formation

Answer 5

• It is a network of cells that run through the brainstem, medulla pons and midbrain
• it performs numerous integrative and modulatory functions.

Question 6

what does the reticular formation of the brainstem do

Answer 6

• it is the core of the brainstem

- it controls basic functions and autonomic functions

Question 7

what does the reticular formation consist of

Answer 7

• 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.

Question 8

describe the organisation of the reticular formation

Answer 8

• 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

Question 9

what are the 4 principle functions of the reticular formation

Answer 9

1. Arousal responses
2. Autonomic nervous system control
3. Control of muscle tone and reflexes
4. Pain modulation

Question 10

describe some other functions of the reticular formation

Answer 10

• 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

Question 11

what are some examples of how somatic reflex regulation happens

Answer 11

• 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

Question 12

what do the reticulopsinal projects do

Answer 12

• Reticulospinal projects controlling postural adjustments and segmental control of motor reflexes that span the length of the brainstem

Question 13

what does the caudal pontine and medullary reticular formation do

Answer 13

• Caudal pontine and medullary reticular formation – premotor coordination of lower somatic and visceral motor neuronal pools and raphe descending control

Question 14

what does the mesencephalic and rostral pontine reticular formation do

Answer 14

• Mesencephalic and rostral pontine reticular formation – includes the conscious state

Question 15

what is the role of the reticulospinal tract

Answer 15

• 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

Question 16

what pathway regulates postural adjustment

Answer 16

• The indirect extrapyramidal motor pathway that regulates postural adjustment
• If there is posture instability it goes up the pathway as negative feedback

Question 17

wha are the reticular formation centres involved in control coordinating eye movements

Answer 17

paramedian pontine reticular formation (PPRF) and mesencephalic (vertical) gaze centres
- Following frontal eye field excitation the paramedian pontine reticular formation generates horizontal eye movements

Question 18

what does lesions to the MLF do

Answer 18

. Lesions to the medial longitudinal fasciculus disrupt CNIII connectivity and function

Question 19

what is the nucleus of solitary tract

Answer 19

The nucleus of the solitary tract is the main visceral sensory processing site

Question 20

what does the nucleus of solitary tract do

Answer 20

– involved in taste, and inform about blood pressure and oxygen concentrations in the blood

Question 21

how does the reticular formation control respiratory control

Answer 21

• 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

Question 22

what happens if you get an lesion to the NTS (nucleus of solitary tract )

Answer 22

• get Cheyenne stokes respiration

Question 23

what nucleus is in control of the dorsal respiratory group

Answer 23

nucleus of solitary tract

Question 24

what nucleus is in control of the ventral respiratory group

Answer 24

nucleus ambiguous

Question 25

what does the pontine reticular formation do

Answer 25

- 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

Question 26

what does the pneumotactic centre do

Answer 26

- The pneumotactic centre limits inspiration and facilitates expiration, it stops excessive breathing

Question 27

what does the apenustic centre do

Answer 27

- The apneustic centre prolongs inspiration and reduces expiration

Question 28

where does input come from to the NTS

Answer 28

- 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

Question 29

what happens to breathing if there is a lesion below the medulla

Answer 29

Lesions below the medulla it is impcompatible with life and you cannot breath and vnetilaton stops

Question 30

what happens if there is a lesion between pneumotaxic centres and apeneustic centre

Answer 30

Apneustic breathing | - with deep and prolonged inspiration followed by short, insufficient expiration

Question 31

what does the NTS do in to terms of the cardiovascular system

Answer 31

- 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.

Question 32

what does the reticulospinal tract input

Answer 32

Reticulospinal tract projects to the preganglionic autonomic neurones (both sympathetic and parasympathetic).

Question 33

what happens if the reticulospinal tract is damaged

Answer 33

If the reticulospinal tract is damaged the autonomic output is lost leading to loss of blood pressure, temp regulation (sweating), bladder and bowel control

Question 34

what is the main centre for noradrenaline

Answer 34

locous coerculeus

Question 35

Dopamine - what is the nucleus involved - what does it do - what happens if there is a loss of movement - what area is it in

Answer 35

- 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

Question 36

what happens if there is a distribuance in dopamine

Answer 36

Schizophrenia; Addiction

Question 37

noradrenaline - what is the nucleus involved - what does noradrenaline do

Answer 37

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)

Question 38

Sertonin - what is the nucleus involved - what does it do - what do deficits produce

Answer 38

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

Question 39

what drugs target serotonin

Answer 39

Drugs that target 5HT receptors affect mood e.g. anti depressants, also anti-migraine, anxiolytics, hallucinogens, anti-psychotics

Question 40

Acetycholine - what is the nucleus involved - what does it do

Answer 40

- 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

Question 41

what is the sleep promoting system

Answer 41

- Anterior hypothalamus - Ventrolateral preoptic (VLPO) area - GABA/ galanin - Inhibit wake promoting neurons

Question 42

what does a lesion in the sleep promoting system cause

Answer 42

Insomnia (anterior hypothalamus

Question 43

what is the ascending arousal (sleep waking system)

Answer 43

- 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

Question 44

what does a lesion to the posterior hypothalamus and ascending arousal system lead to

Answer 44

hyersommia

Question 45

what does acetylcholine do in ascending arousal systems

Answer 45

ACh promotes forebrain activation in both waking and REM sleep (via thalamus + basal forebrain)