Physiology II -- Unit 6 (EEG, Sleep, CSF, BBB, & Neural Plasticity)

What is an EEG?

electroencephalogram - measures electrical impulses in the brain (as waves)

-- from millions of neurons firing synchronously

What can EEG be used to diagnose/observe? (3)

1) Evaluation/diagnosis of epilepsy (rapid spiked waves)

2) Sleep Disorder

3) Understand overall activity of brain (coma, drug overdose/intoxication, brain damage)

Which of the 4 typical patterns of brain activity is typically seen in a calm, resting, and awake state? What kind of frequency and voltage is seen?

Alpha

-- Low frequency

-- Low voltage

Which of the 4 typical patterns of brain activity is typically seen in an adult activating the frontal and parietal lobes during planning/processing? What kind of frequency and voltage is seen?

Beta

-- HIGH frequency

-- Low Voltage

Which of the 4 typical patterns of brain activity is frequently seen in children or during emotional distress? What kind of frequency and voltage is seen?

Theta

-- Low frequency

-- HIGH voltage

(not particularly common)

Which of the 4 typical patterns of brain activity is seen during deep, slow-wave sleep? What kind of frequency and voltage is seen?

Delta

-- VERY low frequency

-- VERY HIGH voltage

What is the state of unconsciousness that a person can be aroused from?

Sleep

What is the state of unconsciousness that the person cannot be aroused from?

Coma

What are the two types of sleep which are differentiated by brain waves and activity?

1) REM: rapid eye movement

2) Slow-wave sleep

Which type of sleep is characterized by bouts of increased brain activity (B waves), occurring about every 90 mins and lasting 5-30 minutes? What percent of sleeping time does this make up?

REM: Rapid Eye Movement Sleep

(25% of sleep)

Which type of sleep is characterized as a restful sleep, lasting long (about 1hr) and making up the larger % of sleeping time?

Slow-Wave Sleep

Which type of sleep is associated with dreams and increased activity (heart rate, respiratory rate, and metabolic rate)?

REM

Which type of sleep is exceedingly restful and is associated with decreased activity in BP, respiratory rate, and metabolic rate?

Slow-Wave sleep

What is REM atonia?

Temporary paralysis

(due to motor neuron hyperpolarization)

Is REM or Slow-Wave more difficult to wake from?

REM sleep difficult to wake from

What are the three theories as to why we fall asleep?

1) Active inhibitory process

2) Lower reticular areas (Raphe Nuclei)

3) Inhibit activating centers

What is released by pineal gland after (indirect) stimulation by suprachiasmatic nucleus of hypothalamus in the light-dark cycle?

Melatonin

When the retina is exposed to light, what pathway occurs? (2)

1) Suprachiasmatic Nucleus (SCN) inhibits paraventricular nucleus (PVN) via GABA

2) No melatonin (no sleep)

When the reitna is not exposed to light (dark), what pathway occurs? (4)

1) Suprachiasmatic nucleus (SCN) activates Paraventricular Nucelus (PVN) via GLutamate

2) activates Superior Cervical Ganglion (SSG)

3) activates Pineal gland

4) Melatonin (sleep)

When is there peak secretion of Melatonin? At what age does this reduce by 60%? Reduce another 20%?

occurs in children prior to puberty

-- 60% --> after age 25-40

-- 20% --> after age 90

What is a potent inhibitor of the pineal gland activity?

Blue light

What half of the reticular activating system is stimulatory (activating) and which is inhibitory?

Superior portions are activating

Inferior portions are inhibitory (Raphe Nuclei --> Serotonin)

If the brainstem was sectioned at a mid-pontine level, what would occur?

Permanent state of wakefulness

(animals have been seen to die form exhaustion)

What does the Raphe nuclei release? Where does its fibers connect?

Serotonin

-- fibers connect to thalamus, hypothalamus, limbic system, cerebral cortex

If the formation of serotonin is blocked, what happens? What happens if the Raphe nucleus is stimulated?

Blocked 5HT: Cannot sleep

Raphe Nuc Stimulated: Fall asleep quickly

What 3 things is long term sleep deprivation associated with?

1) Poor cognition

2) Poor physical performance

3) Poor overall health

What are the 5 theories as to why sleep is necessary?

1) Neural maturation

2) Facilitation of learning/memory

3) Cognition

4) Clearance of metabolic waste (B-amyloid)

5) Conservation of energy

What is a sleep disorder characterized by pauses in breathing or insufficient breathing, interrupting the sleep cycle and resulting in fatigue?

Sleep Apnea

What type of sleep apnea is the most common with collapsible airways of pharynx due to URTI, obesity, or teeth/jaw dysfunction?

Obstructive sleep apnea

What type of sleep apnea is due to imbalanced respiratory control centers in the medulla (nucleus of solitary tract) which normally receives sensory information from chemoreceptors, baroreceptors, and stretch receptors of lungs and relays the information to pneumotaxic and apneustic centers of pons/medulla? What does pneumotaxic vs apneustic centers do?

Central sleep apnea

Pneumotaxic = decrease inspiration activity

Apneustic = increase inspriation

What is the neurodegenerative disease characterized by the inability to regulate sleep/wake cycle ("blurred lines") due to degeneration of orexin releasing neurons from lateral hypothalamus

Narcolepsy

What are 5 key features of narcolepsy?

1) Daily sleepiness

2) Cataplexy (sudden muscle weakness)

3) Inability to move at start/end of sleep

4) Vivid hallucinations

5) Fragmented sleep

What type of epilepsy (seizures) involves small, localized affected areas? Which involves diffuse, bilateral affected areas?

Small/localized = Focal (partial)

Diffuse/bilateral = Generalized

What are the 3 features of Generalized seizures (Generalized Tonic-Clonic/Grand Mal seizure)

1) Loss of consciousness

2) affect all areas of brain

3) alternating tonic (tightness) and clonic (spasmodic convulsions)

What are 5 symptoms of tonic-clonic seizures?

1) Biting tongue

2) Possible cyanosis

3) Loss of control of bowel/bladder

4) Lasts 3-4 minutes

5) State of confusion after

The brain is supplied by 2 _______ arteries and 2 ________ arteries

2 Internal carotid arteries

2 vertebral arteries

The Circle of Willis is present at the ______ of the brain, and the named arteries branch and divide into what 3 things (in sequence)?

Base of the brain

Named arteries --> Pial arteries --> Penetrating arteries & arterioles --> Capillaries

How is blood flow regulated in the brain?

Cerebral blood flow determined primarily by tissue metabolism

-- increased metabolism = increased CO2 concentration = increased localized blood flow

Why does an increase in CO2 concentration increase localized blood flow?

CO2 + H2O = Carbonic acid

-- this increased H+ ions which then causes localized vasodilation

(ACIDS increase vasodilation)

T/F: Brain recieves more blood flow compared to other organs

TRUE

15% of cardiac output for only 2% of body weight

Cerebral blood flow is controlled by what innervation? Why?

Sympathetic innervation

What provides the sympathetic innervation to the cerebral arteries along with smaller arterioles?

Superior cervical ganglion

In the autoregulation of the brain, the cerebral blood flow is tightly controlled, even with fluctuating blood pressures, and keeps a steady flow of blood between ___________ mmHg?

60-140mmHg

The autoregulation of the brain is controlled by larger cerebral arteries to protect what?

Smaller vessels from rupture (hemorrhagic stroke)

What is the interruption of cerebral blood flow?

Stroke

When there is a blockage of cerebral blood flow, what kind of stroke is this known as? How about if there is a rupture/bleeding of cerebral blood flow?

Blockage = Ischemic stroke

Rupture/bleeding = Hemorrhagic stroke

Motor (UMN) and Sensory deficits possible with what condition?

Stroke

The cortex receives _____x as much blood flow than white matter? Why?

4x

-- far more activity in the cortex (gray area)

In 1880s, dyes were injected into venous circulation, and it stained all organs except the brain & spinal cord. When injected into CSF, it stained only the brain and spinal cord. What discovery was this?

The Blood Brain Barrier!

What are 3 exceptions to the BBB? Why?

1) Some areas of hypothalamus & pituitary --> water balance & neuroendocrine

2) Pineal gland --> melatonin release

3) Area postrema --> toxins stimulate vomiting; angiotensin II increases blood pressure

What is the function of the BBB? What clinical consequence does this have?

Protect brain from pathogens, toxins, immune factors, antibodies

-- makes treatment of many neurological conditions difficult via pharmacological means

The specialized capillary endothelial cells that form the BBB are different form the normal capillary endothelial cells elsewhere in the body for what 2 reasons?

1) Continuous tight junctions (maintained by astrocytes)

2) No transendothelial pathways

Which types of molecules readily diffuse in the BBB? Which types are blocked form diffusion and must be transported?

Diffuse = Hydrophobic (uncharged) --> Lipids, O2, CO2, alcohol, anesthetics

Blocked = Hydrophilic (charged)

T/F: Glucose, Amino Acids, and H20 all need transport proteins to move in/out of brain.

FALSE

Glucose & AA NEED transport proteins

H2O freely moves into and out of brain

What are 4 diseases that can break down the BBB?

1) MS

2) Strokes

3) Tumors

4) Encephalitis

Our brains are _____ fluid by weight, with majority of the fluid being _____. 1/2 L of this fluid is made per day by what?

80% fluid by weight

Fluid = CSF

CSF formed by Choroid Plexus

What are the 2 functions of the CSF?

1) Protection -- brain floats in CSF & it minimizes movement of brain w/in cranium

2) Lymphatic function -- carry proteins & metabolic waste from brain tissue

T/F: There is no true lymphatics in brain tissue

TRUE

-- this is why CSF has lymphatic function

CSF moves through perivascular spaces & into large cerebral veins via what?

Arachnoid granulations

Obstructions (ex: tumors) can obstruct normal flow of CSF, and instead of being returned to venous circulation, CSF builds up in the ventricles or subarachnoid space, causing what pathology?

Hydrocephalus

While awake, the brain accounts for approximately ________ of the body's total metabolism. Why?

15-25%

-- neurons are EXTREMELY active

-- 7.5x the metabolism of an average cell

Why is oxygen required to be delivered constantly in the brain for brain metabolism? Lack of oxygen can result in what within 5-10 seconds?

Neurons CANNOT undergo anaerobic metabolism, so has special requirement of oxygen

-- Unconsciousness w/ lack of O2

What type of imaging can detect increased signals in localized brain regions due to arteriole dilation and increased local blood flow to areas consuming more oxygen (aka increased metabolic activity)?

Functional Magnetic Resonance Imaging (fMRI)

What type of imaging can measure metabolic rates through a radioactive glucose injection, and is useful in detecting brain activity, location of an infarction (decreased activity), or location & therapy responsiveness in tumors (increased activity)?

PET scans

In nervous system damage, what part of the neuron are most injuries involving? Does the PNS or CNS regenerate better?

Most injuries to axons

(postsynaptic neuron can atrophy & die)

-- PNS regeneration better

Which of the two steps of the PNS response to damage (transected PNS axon) occurs after 1-2 weeks post injury, due to removal of cut/damaged segment & myelin?

Wallerian degeneration completion

Which of the two steps of the PNS response to damage (transected PNS axon) is when there is inhibition of synapse related action and activation of growth of cytoskeletal components?

Schwann cells proliferating and releasing trophic factor

What type of cells restrict repair? How do these cells restrict the repair process?

Glial cells

-- Wallerian degeneration occurs but no trophic factor released and no connections reestablished

T/F: CNS neurons are totally incapable of regenerating.

FALSE

- NOT totally incapable of regenerating

What is the phenomenon called when damage can stimulate remodeling of neural pathways?

Neural plasticity

--> CNS is very plastic

When is neural plasticity greatest?

In developing brain

In the brain, early development is crucial, and only a general layout of nervous system is pre-determined, whereas later stages of development are when what occurs?

Neuronal connections are made and matched to environment, based on our world and set of experiences (sensory, association, motor)

What is the positive side to neuroplasticity? What is the negative?

Good: allows maturation of nervous system in environment it will live in

Bad: once connections made and maturation occur, limited ability to repair after and injury or disease

T/F: Once connections are made, there is a more limited amount of plasticity

TRUE

What is vital about our continual ability to adjust synaptic strength?

Learning & memory processes

Existing survival plasticity relies on what two things?

1) Nerve Growth factor

2) Neurons die without

Neurons are overproduced in early development, and only select neurons survive. Why?

Need appropriate interaction & neurotrophic factors

T/F: Axons that survive during development are shown to become much simpler with a more streamline, concise path.

FALSE

- become more complex with sprouting dendrites and axonal branches

What periods of development are when structural changes are made, and differ depending on location in nervous system?

Critical periods of development

Do primary areas mature/close their critical periods first or association areas?

Primary areas mature 1st (motor, somatosensory, visual)

Association areas mature last (ex: prefrontal cortex matures at 25ish)