Reticular formation week 7

Question 1

What two constructs can conciousness be divided into?

What defines a vegetative state?

Answer 1

• Consciousness can be divided into two constructs:

– Arousal

– Content

• Arousal without content defines the vegetative state

Question 2

define the following terms:

coma

stupor

obtundation

Answer 2

• Coma: a state in which no stimuli, internal or external, will arouse a patient to consciousness

– Internal: hunger, thirst

– External: light, noise, verbal commands, pain

in coma, there is failure of cortical activation

• Stupor: the patient is unresponsive unless stimulated
• Obtundation: the patient is often unresponsive but arouses spontaneously.

-lighter than a stupor

• These patients may look like they are sleeping, but the EEG shows that they are not asleep

Question 3

What is the source of EEGs?

What are the frequency ranges for the following waves on EEG?

α, β, Θ, Δ, Γ

Answer 3

• α = 8 – 13 Hz
• β = 14 – 30 Hz
• Θ = 4 – 7 Hz
• Δ < 4 Hz
• Γ > 30 Hz

Question 4

What is the EEG pattern for a normal waking adult (awake with eyes closed)?

What changes occur when the eyes open?

Answer 4

Normal waking adult: β in front, α in back

• Mostly symmetric
• α blocks with eye opening (thalamocortical connection)
• Eye movement artifacts

Question 5

What is the EEG pattern for a drowsy individual?

Answer 5

Drowsiness:

• Loss of α (8-13 Hz)
• Widespread θ (4-7 Hz)

Question 6

What is the EEG pattern during stage 2 sleep?

Answer 6

Sleep

• Stage 2: sleep spindles: faster bursts of activity

Question 7

What is the EEG pattern during slow wave sleep?

Answer 7

Slow wave sleep

• Δ predominates

Question 8

What is the EEG pattern during REM sleep?

Answer 8

– REM sleep

• Resembles waking rhythm with lots of eye movements

Note that in REM sleep, there is faster activity with no slow waves. Larger peaks in attached EEG resemble eye movements.

Question 9

Note the EEG patterns during different stages of sleep. Note that it is harder to awake people increasingly higher numbered stages of sleep (harder to awake someone in stage 4 sleep vs stage 1).

Stages 3 and 4 are together known as slow wave sleep.

Question 10

Compare and contrast the following aspects between non-REM and REM sleep:

EEG

muscle tone

arousal threshold

mental activity (dreams)

autonomic activity (parsympathetic, sympathetic)

pulse, respiration

Answer 10

Note that REM sleep is termed paradoxical because there is a lot of cortical activity while the person is sleep.

Note that motor activity is inhibited during REM sleep. If this does not occur, will have a sleep disorder during which one acts out their dreams.

Question 11

At most levels of the brainstem, the reticular formation can be divided into three longitudinal zones arranged in a medial-to-lateral sequence.

List the three zones of the reticular formation.

Answer 11

raphé nuclei

medial zone

lateral zone

Question 12

Where are the raphe nuclei located within the brainstem? What plane are they adjacent to? (coronal, transverse, sagittal, etc.)

Where is the medial zone located relative to the raphe nuclei? What is the function of the medial zone?

In what part of the brainstem is the lateral zone the most prominent? What is the function of the lateral zone?

Answer 12

The raphé nuclei (from the Greek word rhaphe, meaning “seam,” referring to the midline seam of the brainstem) are thin plates of cells in and immediately adjacent to the sagittal plane.

The medial zone, alongside the midline raphe nuclei, contains a mixture of large and small neurons and is the source of most of the long ascending and descending projections from the reticular formation.

• Some of the neurons in the medial zone of the rostral medullary reticular formation are so large that this area is referred to as the gigantocellular reticular nucleus.

The lateral zone, which is particularly prominent in the rostral medulla and caudal pons, is primarily concerned with cranial nerve reflexes and visceral functions.

Question 13

Note that the reticular cell in attached pic innervates nuclei of the thalamus, hypothalamus, periaqueductal gray, nucleus gracilis, anterior horn of the spinal cord…reticular system affects autonomic, motor, sensory functions.

see reverse

Answer 13

Question 14

What is the function of the locus ceruleus? What NT is located there?

Answer 14

Controls movments during sleep. Major source of norepinephrine

Question 15

State the NTs each nucleus releases and the importance of the nuclei in wakefullness and sleep.

preoptic area

lateral hypothalamus

tuberomammillary nucleus

raphe nuclei

locus ceruleus

midbrain reticular formation

Answer 15

Preoptic area: secretes GABA which is important for sleep. GABA agonists such as benzodiazepines and barbiturates have sedatory effects

Orexin: Important for wakefulness, less for sleep. also imporant for normal eating behavior. Lack of orexin: anorexia

histamine important for wakefulness, less important for sleep

midbrain reticular formation: important for sleep but also memory formation. is lost in Alzheimer’s. Cholinergic drugs help memory function in Alzheimer’s disease

Question 16

Interaction between what two parts of the brain is conciousness dependent upon?

What anatomic problems can cause unconciousness?

Answer 16

• Consciousness depends on the interaction of the reticular activating system and the cortex
• Thus, only a limited number of anatomic problems can cause unconsciousness:

– Dysfunction of the reticular system. Can think of the reticular system as a pacemaker for the cortex. If there is not firing of the reticular system–> unconciousness

– Dysfunction of both cerebral hemispheres. unilateral cerebral dysfunction will not lead to unconciousness!

– Disconnection of these systems

Question 17

In evaluation of a comatose patient, what is the physical exam focused on? (what exams are performed?)

Answer 17

• Physical examination focused on

– Pupillary responses

– Extraocular movements

• Spontaneous roving eye movements: slow random predominantly horizontal conjugate eye movements (though there may be a degree of exophoria) similar to those seen in deep sleep
• Cervico-ocular reflexes (if cervical spine is intact!)-testing vestibular system
• Vestibulo-ocular reflexes
• Vertical eye movements: if lesion is below 3rd nerve nucleus, patient will still have vertical eye movements