1. Muscle physiology

2. Myology – the study of muscles
Muscles make up 40-50% of body’s mass

3. Types of muscle control
Voluntary – muscles under conscious control of Somatic Division of nervous system
Ex.; arms, legs
Involuntary – muscles you cannot control; under Autonomic Division of nervous system
Ex.; heart, muscles of digestive tract
Both – voluntary and involuntary
Ex.; breathing, eyelids

4. Three Types of muscle tissue
differ in microscopic anatomy, location & control by nervous & endocrine systems
1. skeletal muscle – attached to bone
Striated – alternating dark and light bands
Primary function - to produce movement
Voluntary control (some are involuntary, like the diaphragm and muscles of posture)

5. 2. cardiac muscle – found in the heart
Function - to pump blood through the heart and blood vessels
Striated
Involuntary control
Autorhythmicity – built in rhythm of the heart; can be affected by hormones and neurotransmitters (speed up or slow it down)
Intercalated disc – thickened areas where one muscle fiber connects to another

6. 3. smooth muscle – also called visceral
Found in the walls of internal organs and blood vessels
Nonstriated (smooth)
Involuntary control
Function by contracting and relaxing to move substances through the body
(ex.; food through the digestive tract, urine through urinary system)

7. Functions of muscle 1. movement
2. posture - result of sustained muscle contractions
3. heat production - when muscle contracts, it produces heat which is used to maintain normal body temp.
4. moves substances within the body (food, waste, blood)
5. regulates organ volume: sphincters (rings of smooth muscle) that close the outlets of hollow organs

8. Characteristics of skeletal muscle
1. excitability – ability to receive & respond to stimuli by producing electrical signals called muscle action potentials
Muscles respond to a stimulus from the nervous system
Stimuli could be autorhythmic or chemical
2. contractility – the ability to shorten or contract
Two types of muscle contraction:
A. Isometric contraction –muscle tension is increased, but no movement is produced
B. Isotonic contraction – muscle maintains the same tension, movement between two parts

9. 3. extensibility - the ability of a muscle to stretch without being damaged
Ex., stomach filling with food
4. elasticity – the ability of muscle to return to its original length and shape after contraction

10. Structure of skeletal muscle

11. Structure of skeletal muscle
Each muscle is a separate organ containing
- muscle cells called fibers
- connective tissue called fascia
- blood vessels
- nerves
musclefasciclefibermyofibrilfilament

12. Fascia – sheet of fibrous connective tissue that surrounds and protects muscles
Superficial fascia – separates muscle from skin
-stores adipose (fat) tissue, which stores triglycerides & provides insulation to guard against heat loss
Deep fascia – dense (three layers), irregular connective tissue that holds muscle with similar function together
-contains nerves, blood vessels, lymphatic vessels
- allows free movement of muscles
- protects & strengthens muscle

13. Three layers of deep fascia
1. Epimysium - outermost layer of connective tissue that covers the entire muscle
2. Perimysium – connective tissue that surrounds groups of or more muscle fibers
These fibers grouped into bundles are called fascicles
3. Endomysium – innermost layer of connective tissue around each muscle fiber
All three of these combine to form Tendons – connective tissue cords that attach muscle to periosteum of bone

14. Muscle fibers
Muscle fibers arise from myoblasts (stem cells) that fuse during embryonic development
Once fusion has occurred, fibers cannot undergo cell division…so we are born with a set number of fibers
A few myoblasts remain as satellite cells, which fuse with other fibers to repair damaged fibers
A typical muscle fiber is ~ 100mm in length

15. Structure of muscle fibers
Covered in sarcolemma – cell membrane
Contains multiple nuclei (fused myoblasts)
Contains sarcoplasm – cytoplasm
contains glycogen, which can be split into glucose that’s used in ATP synthesis
Contains myoglobin, which is the oxygen binding protein needed for ATP production in mitochondria
Fibers divide into myofibrils

16. myofibrils - contractile unit of skeletal muscle
- extend entire length of muscle fiber
- make muscles fiber look striated
- can increase or decrease in number
sarcoplasmic reticulum –encircles each myofibril
- in relaxed muscle fibers, it stores calcium
- release of calcium triggers muscle contraction
T-tubules - connect myofibrils to sarcolemma
- receive nerve impulses
- allows action potential to quickly spread thoughout the fiber

17. Muscle proteins Myofibrils - built from 3 different types of proteins
1. contractile proteins – generate force during contraction
Actin – thin filaments
Myosin – thick filaments; converts chemical energy of ATP into mechanical energy of motion
2. regulatory proteins - turn contraction on and off
Troponin
Tropomyosin
3. structural proteins - give myofibril extensibility and elasticity
Myofibrils divide into filaments

18. filaments Filaments - arranged in sarcomeres
Sarcomere -structural unit of myofibril
Thick filaments – contain myosin
Thin filaments – contain actin
-thick and thin filaments overlap each other, which shows up as striations
Z discs – separates one sarcomere from the next
M line - middle of sarcomere
A Band – dark middle part of sarcomere made up of thick filaments (myosin) and part of thin (actin)
I band – lighter area made up of thin filament only (actin)

19. THICK FILAMENT
Myosin – acts as a motor protein (push or pulls what’s attached to it to achieve movement
~300 molecules of myosin make up a single thick filament
THIN FILAMENT
Actin – individual actin molecules join to form an actin filament that’s twisted into a helix
Contain myosin-binding sites – where myosin heads can attach
Tropomyosin – covers the myosin binding sites on actin in relaxed muscles
Troponin – holds tropomyosin in place

20. Muscle contraction Sliding Filament Mechanism
thick and thin filaments slide past each other during contraction, shortening the muscle
- when contraction occurs, myosin binds to actin, pulling it towards the M line
- Sarcomere shortens – thick and thin DO NOT shorten…they slide past each other to overlap
- Sarcomere shortens, fiber shortens, muscle shortens (contracts)

21. Steps in Muscle contraction
1. stimulus received from nervous system
2. action potential spreads through T-tubules
3. sarcoplasmic reticulum releases calcium
4. calcium causes troponin to change shape
5. troponin pulls on tropomyosin uncovering myosin binding site on actin
6. myosin attaches to actin and pulls on it

22. 7. thick and thin filaments slide past each other
8. when action potential stops, calcium is pumped back into the sarcoplasmic reticulum
High calcium levels in sarcoplasm starts contraction
Low calcium levels in sarcoplasm ends contraction
*****ATP POWERS THE ENTIRE PROCESS*****

23. CLINICAL APPLICATION- RIGOR MORTIS
After death, calcium leaks out of sarcoplasmic reticulum
Myosin binds to actin
No ATP synthesis so muscles stay contracted
Begins ~3-4 hours after death, peaks at 12 hours and stops at 24 hours when tissues begin to breakdown

24. Nerve and blood supply within muscles
Motor neurons - nerves that stimulate muscles to contract
-requires a lot of energy (ATP) & produces lots of waste…so there are lots of capillaries in the endomysium
Motor unit – a motor neuron and the skeletal muscles it stimulates
Synapse – meeting place where a muscle and a nerve communicate with each other
Synaptic cleft – a small gap that exists between the neuron and the muscle fiber at the synapsis
Neurotransmitter – a chemical that allows nerves and muscles to communicate across that gap
Acetylcholine (ACH) – the neurotransmitter for skeletal muscle contraction

25. Neuromuscular junction
Neuromuscular junction – a synapse between a motor neuron and a skeletal muscle
Each motor neuron has an axon that divides into several axon terminals
At the end of each axon terminal are little sacs called synaptic vessicles that contain acetylcholine
The motor end plate is the region of sarcolemma adjacent to the synaptic vessicles. It contains acetylcholine receptors (30-40 million receptors/end plate)

26. Acetylcholinesterase – enzyme that breaks down acetylcholine
When acetylcholine binds to the receptor on the muscle, it causes sodium (Na+) to go into the muscle cell…contraction occurs
Acetylcholinesterase – enzyme that breaks down acetylcholine
with no acetylcholine, the action potential is ended.