The neuron at rest has an electrical potential of -70 mv due to negatively charged proteins it contains that can't pass through the cell membrane. K+ flows freely through gated ion channels, but Na+ is kept out of the cell. Action potential: incoming electrical signals cause the cell membrane potential to reach its threshold, causing the Na+ gated channels to open, while K+ is prevented from leaving the cell, briefly. The cell rapidly becomes positively charged, +40 mv. K+ channels open and the potassium leaves the cell, resulting in the cell becoming more negatively charged than at resting potential, -90 mv. Cell is in refractory period and cannot fire again. The sodium potassium pump removes the Na+ ions from the cell, draws K+ back in, bringing cell back to resting potential. During action potential, the electrical signal is perpetuated down the axon. When it reaches the axon terminal, neurotransmitters are released into the synapse, possibly starting the next action potential. The circadian rhythm is a 24 hour cycle. Stage 1: this is the first stage of sleep. Theta waves represent the brain's activity. Body temperature, breathing and heart rate will all decrease.
Stage 2: this is the second stage of sleep and theta waves still represent the brain activity. Sleep spindles and k complexes occur.
Stage 3: this is the first stage of deep sleep and delta waves between 20-50%. It's hard to wake someone up in this state.
Stage 4: this is the next stage of deep sleep. Delta waves occur more than 50%. It's even harder to wake someone up while in this state.
Rem sleep: also called rapid eye movement sleep. (Occurs between stages 2 and 1) brain activity levels are at their highest, expressed with beta waves. It is when a person dreams. Heart rate, breathing, and body temperature change erratically.
(Through the night, the sleeper moves from stage 1, to stage 2, to stage 3, to stage 4, and then cycles up to stage 3, stage 2, and then into REM sleep, before cycling down to 2, 3, 4, 3, 2 REM, etc. with more and more time spent in REM sleep as the night progresses. ) Elsie