changing your heart rate

unit 3 week 8 lesson 4

what paces the heart, preventing bmp of 100

sa node cells recieve input form both sympathetic and parasympathetic system. the parasympathetic is the one that keeps ur heart rate below 100 bpm when ur just resting

how does the parasympathetic communicate with the cells of the heart

thru neurotransmitters (aCh). ach will bind to the muscarinic receptors on the cells of the sa node to slow heart rate down below 100 bpm

how is heart rate slowed when ach binds to receptors

• want to slow down pacemaker down/decrease slope of pacemaker potential

• that way an ap wont occur as quickly, slowing the heart rate down

• when ach binds to the receptors, it wil decrease sodium permeability and slows down the movement of ca into sa node and allow potassium to leak out (increase permeability of k)

• since less sodium comes in, longer it takes the cell to become positive

what causes the hr to go above 100 bpm

• activate our sympathetic nervous system and it talks to the sa node

• norepinephrine is released form axon terminal of sympathetic nervous system neurons to bind to adrenergic receptors

• threshold is reached faster, causing ap to occur earlier

• binding of the receptor activates the cell to increase leakage of sodium coming in, increases ca coming in as well

what does the ans also innervate

the av node to properly slow down or speed up ap there and maintain a coordinated heart contraction

sympathetic nervous system also triggers release of what

hormone—epinephrine from adrendal gland.

this hormone also acts on cells of the sa node by binding to the adrenergic receptors, and therefore, both norepinephrine and epinephrine can speed up heart rate.