Chapter 13: Sympathetic Stimulation of Heart Rate

Sympathetic System on Heart

- increases heart rate
- increases stroke volume (strength of contraction)

Molecular Process to Increase Heart Rate

increases speed of nodes

1. norepinephrine or epinephrine binds to beta-1 adrenergic receptor

2. alpha unit of G stimulatory complex is activates and activates adenylate cyclase

3. ATP + cAMP --> protein kinase

4. protein kinase phosphorylates funny channel and T-type Ca++ channel. Because they are phosphorylated, channels stay open longer allowing Na+ entry (funny channel) and Ca++ entry (T-type Ca++ channel)

5. Na+ and Ca++ cause depolarization in the autorythmic cells

Molecular Process to Increase Contractality

increases speed of myocardium contractions

1. norepinephrine or epinephrine binds to beta-1 adrenergic receptor

2. alpha unit of G stimulatory complex is activates and activates adenylate cyclase

3. ATP + cAMP --> protein kinase

4. protein kinase phosphorylatesL-type calcium channel, Ca++ channel in SR, Ca++ ATPase enzyme and myosin heads

5. faster contraction rates occur

Phosphorylation of L-Type Calcium Channel

phosphorylation allows channel to stay open longer, allowing for more extracellular Ca++ entry into the cell

Phosphorylation of Ca++ Channel of SR

dumps out more Ca++ into cell than normal

Phosphorylation of Calcium ATPase Enzyme

- make the pump go faster, pumping Ca++ back into SR
- inducing quicker relaxation

Phosphorylation of Myosin Heads

- creates a faster crossbridge cycle
- ATP --> ADP faster
- faster contraction rate

Beta-1 Adrenergic Receptor

- receptor located on the heart that increases heart rate and force of contraction
- norepinephrine or epinephrine binds