Muscular System PCB 3703 Human Physiology S12-1 Human Physiology Muscular System.

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Muscular System

PCB 3703 Human Physiology

Human Physiology

Muscular System

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Muscular System


Muscle Classification

Functionally

1. Voluntarily

2. Involuntarily

Structurally

1. Striated

2. Smooth

Combined

1. Visceral

2. Cardiac

3. Skeletal

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Muscular System


Sarcomere

Z ZZ

Z ZZ

I

AA

A (I)

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Muscular System


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

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Muscular System


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

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Muscular System


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

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Muscular System


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).

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Muscular System



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.

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Muscular System



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.

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Muscular System



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

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Muscular System


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.

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Muscular System


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

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Muscular System


Lactic Acid in Cellular Respiration (Glycolysis)

(LDH: Lactic Acid Dehydrogenase)

Acetyl CoA

Glucose Pyruvate

Lactic Acid

LDH

2 NADH

O2

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Muscular System


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

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Muscular System


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.

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Muscular System


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

Muscular System PCB 3703 Human Physiology S12-1 Human Physiology Muscular System.

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Transcript of Muscular System PCB 3703 Human Physiology S12-1 Human Physiology Muscular System.