1. More About Cardiac and Smooth Muscle Tissue http://classconnection.s3.amazonaws.comhttp://learningtosavetheearth.com

2. 2 Much of the text material is from, “Principles of Anatomy and Physiology, 14th edition” by Gerald J. Tortora and Bryan Derrickson (2014). I don’t claim authorship. Other sources are noted when they are used. Mappings of the lecture slides to the 12th and 13th editions are provided in the supplements.

3. 3 Outline Cardiac muscle Smooth muscle

4. 4 Cardiac Muscle

5. 5 Cardiac Muscle Fibers http://www.ucl.ac.uk

6. 6 Structure The walls of the heart are mostly composed of cardiac muscle. Between the layers of cardiac muscle fibers are sheets of connective tissue that also contain blood vessels, nerves, and a conduction sys- tem. Cardiac muscle fibers have the same arrangement of thin and thick elements, and the same bands, zones, and Z discs as found in skel- etal muscle. Chapter 10, page 317 Figure 20.9

7. 7 Structure (continued) Chapter 10, page 318 Figure 4.2e Cardiac muscle fibers are attached end-to-end by transverse thicken- ings of the plasma membrane known as intercalated discs. The discs have desmosomes to strengthen the muscle tissue and hold the muscle fibers together during contractions. The fibers have gap junctions to enable the rapid conduction of action potentials in each heart chamber. Desmosome = a cell structure specialized for cell-to-cell adhesion. Gap junction = directly connects the cytoplasm of two cells, which allows various molecules and ions to pass freely between cells. (Both definitions from http://en.wikipedia.org)

8. 8 Cardiac Muscle Response Cardiac muscle contractions are much longer in duration than skel- etal muscle contractions. The longer time results from the prolonged delivery of Ca 2+ from the sarcoplasmic reticulum to the sarcoplasm. Chapter 10, page 318

9. 9 Cardiac Muscle Stimulation As we discussed, skeletal muscle contracts when stimulated by ACh triggered by neuronal action potentials from somatic motor neurons. In comparison, cardiac muscle tissue contracts when stimulated by the autorhythmic muscle fibers in the heart—typically about 75 times per minute at rest. The autonomic nervous system regulates changes in heart rate and other aspects of cardiac activity in response to stress, physical exer- cise, and other conditions. Chapter 10, page 318

10. 10 ATP Production The mitochondria in cardiac muscle fibers are larger and more numer- ous than in skeletal muscle. Aerobic cellular respiration is the principal source of ATP in cardiac muscle—heart muscle requires more oxygen than many other tissues. Cardiac muscle can also use the lactic acid from contractions of skeletal muscle to produce ATP. Chapter 10, page 318

11. 11 Smooth Muscle

12. 12 Smooth Muscle Fibers http://faculty.ksu.edu.sa

13. 13 Single-Unit Tissue One type of smooth muscle is single-unit or visceral smooth muscle tis- sue. Their fibers form tubular arrangements in the walls of small arteries and veins. They also form the walls of hollow organs including in the digestive tract, urinary tract, and uterus. Gap junctions enable muscle action potentials to spread rapidly to allow smooth muscle fibers to contract in unison. Chapter 10, page 318 Figure 10.16

14. 14 Multi-Unit Tissue Multi-unit tissue consists of individual fibers, each with its own motor neuron terminals and few (if any) gap junctions. The stimulation of a multi-unit fiber causes contraction of only that one fiber. Multi-unit smooth muscle tissues are found in: -Walls of the large arteries -Airways (respiratory bronchioles) to the lungs -Muscles that attach to hair follicles -Muscles of the iris of the eye for constriction and dilation of the pupils -Ciliary muscles of the lens of the eye for focusing visual images on the retina Chapter 10, page 318 Figure 10.16

15. 15 Smooth muscle contracts in response to the release of neurotrans- mitters (acetylcholine and norepinephrine) from motor neurons of the autonomic nervous system. Some smooth muscles can also contract in response to: -Stretching -Hormones -pH changes -Oxygen and carbon dioxide levels in the blood -Body temperature -Ion concentrations Smooth Muscle Stimulation Chapter 10, page 318

16. 16 Smooth Muscle Response The contractions of smooth muscle start more slowly and last longer than in skeletal muscle. Because there are fewer transverse tubules in smooth muscle, Ca 2+ takes longer to reach the central region of the muscle fiber to trigger a contraction. Ca 2+ also exits the sarcoplasm,more slowly, which delays relaxation. Chapter 10, page 318

17. 17 Smooth Muscle Response (continued) Smooth muscle can shorten and stretch to a greater extent than skele- tal muscle and cardiac muscle. Smooth muscle fibers, unlike skeletal muscle, can be stretched consid- erably and still maintain their contractility. An example is a full stomach after a large meal—the stomach wall has substantial smooth muscle. Chapter 10, page 318