S12-1
Muscular System
PCB 3703 Human Physiology
Human Physiology
Muscular System
S12-2
Muscular System
PCB 3703 Human Physiology
Muscle Classification
Functionally
1. Voluntarily
2. Involuntarily
Structurally
1. Striated
2. Smooth
Combined
1. Visceral
2. Cardiac
3. Skeletal
S12-3
Muscular System
PCB 3703 Human Physiology
Sarcomere
Z ZZ
Z ZZ
I
AA
A (I)
S12-4
Muscular System
PCB 3703 Human Physiology
Categories of skeletal muscle actions
Categories Actions
Extensor Increases the angle at a joint
Flexor Decreases the angle at a joint
Abductor Moves limb away from midline of body
Adductor Moves limb toward midline of body
Levator Moves insertion upward
Depressor Moves insertion downward
Rotator Rotates a bone along its axis
Sphincter Constricts an opening
S12-5
Muscular System
PCB 3703 Human Physiology
Myofilaments
1. Myosin: 110Å thick; confined to the A-band. (Mole. wt. 500,000 deltons; 200 molecules/myofilament)
A. Tail- 800Å long, composed of a double helix
B. Head (cross bridges)-600Å terminating in a globular double structure. Contains binding sites for actin & ATP
S12-6
Muscular System
PCB 3703 Human Physiology
Myofilaments
2. Actin: 60A thick; runs from Z-line (disc) to just inside A-band. Mole wt. 60,000 deltons.
G-actin (globular units): contracted form
F-actin (fibrous polymers): relaxed form
Actin associated proteins
A. Tropomyosin
B. Troponin
S12-7
Muscular System
PCB 3703 Human Physiology
Mechanics of Muscle Contraction
1. An action potential is generated by a motor nerve.
2. This causes the release of acetylcholine from the axon terminals at the neuromuscular junctions.
3. This Ach causes an increase in membrane permeability at the motor-end plate, causing the production of an end-plate potential (EPP).
S12-8
Muscular System
PCB 3703 Human Physiology
Mechanics of Muscle Contraction
4. The EPP depolarizes the fiber membrane (sarcolemma) causing a muscle action potential which spreads over the entire surface of the fiber membrane.
5. This depolarizes the T-tubules, causing ionic conduction through their extracellular fluid, and the release of inositol triphosphate as a second messenger.
S12-9
Muscular System
PCB 3703 Human Physiology
Mechanics of Muscle Contraction
6. Ca++ is then released from the endoplasmic reticular fluid of the cisterns (lateral sacs) into the surrounding myofibril.
7. Ca++ binds to the actin associated protein troponin, allowing the attachment of actin to the myosin-ATP complex to form a strong ATPase.
8. The ATPase splits ATP, releasing the energy needed for the movement of the myosin cross bridges.
S12-10
Muscular System
PCB 3703 Human Physiology
Mechanics of Muscle Contraction
9. Energy from creatine phosphate replaces ADP on the myosin cross bridges, thereby breaking the A-M bond and allowing the cross bridges to relax.
10. The Ca++ are forced back into the walls of the longitudinal tubules by active transport.
11. This restores the inhibitory action of the troponin-tropomyosin complex.
AA II
ZZHH
S12-12
Muscular System
PCB 3703 Human Physiology
Selective Terms
1. Motor Unit: consists of all the muscle fibers innervated by terminals from a single axon. (Range from 23 - 2,000 fibers)
2. All or None Law: at or above threshold levels; the degree of contractile response of a single muscle fiber (or motor unit) is independent of stimulus strength
3. Tension: force exerted by a contracting muscle
4. Load: force exerted on a muscle by the weight of an object
5. Isotonic contraction (same tension): the tension developed by the contracting is greater than the load. Therefore, the muscle shortens.
S12-13
Muscular System
PCB 3703 Human Physiology
Selective Terms
6. Isometric contraction (same length): the strength of the load is greater than the tension of the muscle. Therefore, the muscle remains at the same length.
7. Muscle spindle apparatus: a series of small spindle shaped fibers within the muscle for detecting changes in the length (stretch) of the muscle.
8. Golgi tendon organ: tension receptors located in tendons, and activated by the pull of a contracting muscle
Cross Extensor reflex
FlexorReflex
Inhibitoryinterneuron
inhibited
excitedReciprocalinhibition
excited
Repetitiveafter discharge
(oscillatory circuit)
From stimulussource
VasodilationBlood vesselAntidromic
Reflex
Red lineRed flarewheel
Nomotor activity
Renshawcell
Impulse Responses of Skeletal Muscles
1) Twitch Contraction phase (0.04 sec)Relaxation phase (0.05 sec)Latent period (0.002 sec)
2) Summation a) wave (frequency)
Tetanus fatigue
b) Multiple motor unit (recruitment) intensity
12
3 45 1. Subthreshold
2. Threshold3. suprathreshold4. Maximal5. Supramaximal
Voltage
c) Treppe (staircase phenomenon)
2 stimuli/sec
S12-17
Muscular System
PCB 3703 Human Physiology
Lactic Acid in Cellular Respiration (Glycolysis)
(LDH: Lactic Acid Dehydrogenase)
Acetyl CoA
Glucose Pyruvate
Lactic Acid
LDH
2 NADH
O2
S12-18
Muscular System
PCB 3703 Human Physiology
Glycolysis [cont.]
Fate of Lactic Acid
1. Used by the heart for energy: it can convert lactic acid back to pyruvate.
2. Decarboxylation (buffering action): CO2 which ventilation
3. Converted back to pyruvate then to TCA
S12-19
Muscular System
PCB 3703 Human Physiology
Glycolysis [cont.]
Pain
1. Bradykinin: a peptide released from damaged tissue. It excites the pain nerve endings.
2. Ischemia: If the brachial artery is occluded & the muscles of the forearm exercised, pain will begin in 15 seconds. With no exercise it takes 4 minutes.
S12-20
Muscular System
PCB 3703 Human Physiology
Strength-Duration Curve (Excitability Curve)
Utilization time (nerve)
Chronaxie of nerve
Utilization time (muscle)
Chronaxie of muscle2.0
1.5
1.0
.5
0.1 0.2
0.3
Duration of stimulus (seconds)
Str
en
gth
of
sti
mu
lus
1.65 m 3.65 m2.25 m
0 60 80 100 120 140 160
Percentage rest length
0.5
1.0R
ela
tive t
en
sio
n
1.25m
1.65m
2.0m 2.25m
3.65m