1. Physiology of the Muscular System Chapter 11
Anatomy & Physiology

2. Functions
Movement
Heat production
Posture

3. Typical cells Muscle cell=fiber Plasma membrane Sarcolemma Cytoplasm
Sarcoplasm
Endoplasmic reticulum
Sarcoplasmic reticulum (SR)
Many mitochondria
Multiple nuclei

4. Muscle cell structures not found in other cells
Myofibrils: bundles of very fine fibers
Thick and thin myofilaments: very fine fibers that make up myofibrils
Sarcomere: segment of myofibril between two Z lines; contractile unit
T tubules: run transversely across sarcoplasm at right angle to long axis of the cell; transmit electrical impulses thru cell

6. Myofilaments
4 protein molecules that make up myofilaments: Myosin, actin, tropomyosin, troponin
Thin filaments: actin, tropomyosin, troponin
Thick filaments: mostly myosin

8. Contraction Motor neuron: nerve cell that stimulates muscle cells
Neuromuscular junction: motor neuron connects to sarcolemma
This connection is a synapse in which there is a narrow gap across which the neurotransmitter, acetylcholine, is released

9. Neuromuscular Junction

10. Mechanism of contraction
Motor neuron  acetylcholine binds to receptors on sarcolemma  impulse travels along sarcolemma thru T tubules to SR  Ca released from SR binds to troponin exposing actin molecules in thin filaments  myosin in thick filaments bind to actin and pull thin filaments to center of sarcomere

12. Mechanism of Relaxation
Ca pumped back into SR  shuts down the contraction  troponin can again block actin’s active site

13. Energy for Muscle Contractions
ATP: adenosine triphosphate
CP: creatine phosphate

14. Glucose & Oxygen Glucose stored in form of glycogen in muscle
Excess oxygen molecules in sarcoplasm bound to myoglobin

15. Anaerobic respiration
Allows body to avoid use of oxygen in short term
Produces lactic acid
Accumulation of lactic acid in muscles causes burning sensation

16. Motor unit One motor neuron plus the muscle fibers it attaches to
The fewer the number of fibers supplied by one motor neuron the more precise the movements that can be produced.

17. Myography
Force from the contraction of a muscle is recorded as a line that rises & falls as muscle contracts & relaxes
For a muscle to contract, an electrical stimulus of enough intensity (threshold stimulus) is applied to muscle

18. Twitch contraction Quick jerk of muscle
M. doesn’t contract at moment of stimulus
3 phases:
Latent period
Contraction phase
Relaxation phase

19. Treppe: Staircase Phenomenon
Gradual step like increase in strength of contractions that can be observed in a series of twitch contractions

20. Tetanus
If a series of stimuli come in a rapid enough succession, muscle doesn’t have time to relax completely
Smooth, sustained contractions

21. Tonic contraction (or muscle tone)
Continual partial contraction in a muscle
Important for maintaining posture
Flaccid: less tone than normal
Spastic: more tone than normal

22. Isotonic contraction “equal tension”
Tone or tension within a muscle remains the same, length of muscle changes
The muscle shortens

23. Isometric contraction “same length”
Muscle length remains the same while muscle tension increases
The muscle is unable to shorten

24. Cardiac muscle Striated involuntary
Cardiac m. fibers form strong electrically coupled junctions: intercalated discs
Branching of individual fibers
T tubules are larger than skeletal muscle

25. Smooth muscle Single nuclei, no T tubules
Calcium for contraction comes from outside the cell
2 types: visceral & multiunit
Visceral: found in digestive, urinary, reproductive tracts in hollow organs
Multiunit: found in vessels, arrector pili