epliepsy case Flashcards
what is the normal physiology of sleep
Our bodies all require long periods of sleep in order to restore and rejuvenate, to grow muscle, repair tissue, and synthesize hormones. Memory is formed, and the brain is able to react to events of the previous day(s).
what is meant by entrainment
Entrainment is the process by which an environmental rhythm, such as the light-dark cycle, regulates the period and phase relationship of a self-sustained oscillator.
what is meant by circaidan (slave) oscillator
can drive a rhythmic output but requires other oscillators (known as pacemakers) for its entrainment and/or function. A slave oscillator can therefore be self-sustained but cannot operate properly independently of other oscillators.
what is meant by A zeitgeber
is any external or environmental cue that entrains, or synchronizes, an organism’s biological rhythms to the Earth’s 24-hour light-dark cycle and 12-month cycle. Regular meal times and light are zeitgebers.
describe the circadian rhythm
2am - deepest sleep 4-5am - lowest body temp 6-7am - sharp rise in BP 7-8am - secretion of melatonin stops 9am - high level of testosterone secretion (in males) 10am - high alertness 2-4pm - optimal coordination & reaction time 6-7pm - highest BP and body temp 9pm - melatonin secretion starts
what disturbs the circadian rhythm
The circadian rhythm is disturbed by exposure to 450-500nm light at night or lack of light exposure in the morning.
what regulates the body clock
Many areas of the body are involved in regulating the body’s clock. The primary mechanisms involve the timing of food consumption and the natural light-dark cycle. The following have roles in maintaining the circadian rhythms: cardiovascular tissue, liver, kidney, pancreas, gut, muscle and fat tissue.
what is the Suprachiasmatic nucleus (SCN)
The SCN is the small area above the optic chiasm in the anteroventral region of the hypothalamus. It is the master body clock and regulates other circadian rhythms; it is a circadian pacemaker. The master clock in the SCN is composed bilaterally paired nuclei which contain 8,000–10,000 clock cells packed closely together. The SCN receives light information via the retino-hypothalamic tract (RHT).
what is meant by the entrained SCN and what doe it do?
The entrained SCN coordinates the timing of slave oscillators in other areas of the brain (e.g. cortex) and peripheral organs (heart, liver), regulating brain homeostasis, peripheral metabolism (glucose homeostasis), vascular & peripheral regulation, and peripheral inflammation. The SCN also regulates amyloid plaque breakdown/ removal.
what is the role of melatonin
Entrainment is mediated by melatonin, a naturally occurring hormone which induces sleep. It is released in response to low levels of light.
how does melatonin induce sleep
Light is detected by the photoreceptors of the retina, including the rods and cones as well as photosensitive retinal ganglion cells (pRGCs), expressing the photopigment melanopsin. A signal is output to the SCN via the retino-hypothalamic tract (RHT), where it entrains an intracellular clock mechanism consisting of positive (BMAL1 and CLOCK) and negative (PER1/2 and CRY1/2) elements. The SCN projects excitatory information to the paraventricular nucleus (PVN). Long axons send nerve pulse to the preganglianic sympathetic neurons in the spinal cord. This modulates the activity of the superior cervical ganglia, projecting to the pineal gland and regulating melatonin secretion. The CLOCK genes operate on a negative feedback system; the under-lying principle of circadian clocks is successive gene activation in the form of a cycle: the initial activation of a gene is regulated by the last one in the sequence, making up an auto-regulatory feedback loop for which one cycle takes about 24-hours.
what is meant by wakefulness
The neurotransmitters involved in maintaining wakefulness include acetylcholine, norepinephrine, serotonin, and histamine
The brain is kept ‘awake’ by the activity of the Ascending Reticular Formation. The ascending reticular formation projects to the thalamus and cerebral cortex. It exerts some control over which sensory signals reach the cerebrum and come to our conscious attention. For example, if a loud sound is heard during sleep, the signal is received as an auditory impulse. Reticular formation radiates to the cerebral cortex, resulting in waking. Lesions to this brain area leads to constant sleep.
how are arousal signals stimulated
Cholinergic (ACh) cell groups in the upper pons – pedunculopontine (PPT) and laterodorsal tegmental nuclei (LDT) – and project through the thalamus and facilitate thalamocortical transmission of arousal signals.
what is involved in the second pathway of arousal signals
A second pathway involves the hypothalamus and cortical centres. It facilitates processing of thalamocortical inputs from midbrain centres.
The following areas of the brain, and neurotransmitters are involved:
• Locus coeruleus, LC / noradrenergic
• Raphe / serotonergic
• Tuberomammillary nucleus, TMN / histaminergic
• Ventral periaqueductal grey matter, vPAG / dopaminergic
• Basal forebrain BF / GABA and ACh
• Lateral hypothalamus, LH / orexin – aka hypocretin – and melanin concentrating hormone
During sleep, the ventrolateral preoptic (VLPO) nucleus of the hypothalamus sends descending GABAergic inhibitory signals to the midbrain’s arousal centres, turning them off.
list the steps during the sleep cycle
A complete cycle of sleep is 90-110 minutes and is divided into 5 stages.
•Stage 1 - Light sleep. Muscle activity slows with occasional twitching
•Stage 2 - Breathing and HR slows. Slight decrease in body temperature. ~50% of sleep is stage two
•Stage 3 - Deep sleep begins. Brain generates slow delta waves
Stage 4 - Very deep sleep. Rhythmic breathing with limited muscle activity. Delta waves are produced.
Stage 5 - Rapid eye movement (REM). Brainwaves speed up and dreaming occurs. There is an increase in HR and breathing is rapid and shallow. ~20% of sleep is REM sleep. The first sleep cycles have relatively short periods of REM and long periods of deep sleep but later in the night, REM periods lengthen, and deep sleep time decreases.
what does EEG measure
Electroencephalography (EEG) is the measurement of electrical activity produced by the brain (cerebral cortex). It can be recorded from electrodes placed on the scalp.
what does gamma waves measure during the sleep cycle
Gamma waves (40-100 Hz) are involved in higher processing tasks as well as cognitive functioning.
what does the alpha waves measure during the sleep cycle
Alpha waves (9-14 Hz) bridge the gap between our conscious thinking and subconscious mind, promoting deep relaxation.
what does the theta waves measure during the sleep cycle
Theta waves (4-8 Hz) are involved in daydreaming and stage 1 sleep.
what does the delta waves measure during the sleep cycle
Delta waves (0-4 Hz) are the slowest recorded brain waves in human beings.
They are associated with the deepest levels of relaxation and restorative, healing sleep. They have also been found to be involved in unconscious bodily functions such as regulating heart beat and digestion; blood pressure, respiratory rate and basal metabolism is reduced by 10-30%. Less delta waves are produced as humans age.
Delta waves are produced in stages 3 and 4 (slow-wave sleep). During slow-wave sleep, the same neurons that are active during the day become re-active. Slow-wave sleep is implicated in memory consolidation. Long-term potentiation occurs in the synapses that are activated and are strengthened. In the elderly, stage 3-4 sleep is less commonly experienced, and there is increased cycling between stages and waking.
describe how neuromodulators modulate neurone transmitters
Neuromodulates modulate neurotransmitters. When a neuron is active, it generates ATP.
ATP signalling can regulate both excitatory and inhibitory neurotransmission. ATP surges during the initial hours of sleep, displaying a significant positive correlation with the intensity of slow-wave activity in non-rapid eye movement (NREM) sleep.
Intracellularly, ATP is metabolized to ADP then to AMP, then to adenosine.
what does the adenosinergic regaulation predominately mediate?
The adenosinergic regulation of sleep is predominantly mediated either via A1 inhibitory receptors (A1Rs). This activates purinergic receptors on glial cells, causing the release of low-levels of cytokines, such as TNF- and IL-ß1, and glutamate. They activate their own receptors, and can activate the transcription factor, NF-kB. This causes increased expression (insertion) of inhibitory A1 receptors on the post-synaptic neuron, altering the sensitivity of neurons. Thus, adenosine regulates either the amount of sleep or sleep homeostasis in multiple ways depending on the brain area and receptor subtype.
how are sleep regulatory substances involved in the synaptic scaling
Sleep-regulatory substances are involved in synaptic scaling, which increases or decreases the efficiency of synaptic efficiency. Events or skills are remembered if they are novel or emotional, mediated by the brain itself. If the brain decides the event is not important, the synapse is depressed; if the brain decides something is worth remembering, synapses stay active (potentiated) or depressed.
what is narcolepsy
Narcolepsy is a rare sleep disorder (0.02-0.06) characterised by excessive daytime sleepiness. It is possibly an autoimmune disorder caused by hypocretin deficiency.