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BIOL1046 Human Biology II > Unit 4B: Muscle Classification, Naming and Attachments > Flashcards

Unit 4B: Muscle Classification, Naming and Attachments Flashcards

1
Q

A motor unit is…

A

a motor neuron and all the muscle fibers it controls

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2
Q

Motor Units

A
  • Axons of motor neurons from spinal cord (or brain) innervate numerous muscle fibers
  • The number of fibers a neuron inervates varies
  • Small motor units have less than five muscle fibers (allow for percise control of force output)
  • Large motor units have thousands of muscle fibers (allow for production of large amount of force - but not percise control)
  • Fibers of a motor unit are dispersed throughout the muscle (not just in one clustered compartment)
  • Number of motor units used is called “recruitment”
  • Recruitment determines extend of muscle contraction
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3
Q

Effects of Aging

Loss of muscle mass with age

A
  • Slow loss begins in person’s mid-30s due to decrease in activity
  • Decreased size, power, and endurance of skeletal muscle
  • Loss in fiber number and diameter (decrease in myofibrils)
  • Decreased oxygen storage capacity
  • Decreased circulatory supply to muscles with exercise
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4
Q

Effects of Aging

Reduced capacity to recover from injury

A
  • Decreased number of satellite cells
  • Fibrosis: muscle mass often replaced by dense regular connective tissue
  • Decreased flexibility
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5
Q

Effects of Anabolic Steroids

Effects of Large Doses

A
  • Increased rick of cardiovascular disease (hypertension, heart attack, stroke)
  • Kidney damage
  • Liver tumors
  • Acne
  • Aggressive behaviour (“roid rage”) and personality aberration
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6
Q

Effects of Anabolic Steroids

Side Effects in Males

A
  • Testicular strophy (shrinkage)
  • Reduced sperm count
  • Gynecomastia (breast development)
  • Sterility
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7
Q

Effect of Anabolic Steroids

Side Effects in Females

A
  • Menstural irregularities
  • Growth of facial hair
  • Atrophy of uterus and mammary glands
  • Sterility
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8
Q

Effects on Anabolic Steroids

Anabolic Steroids

A
  • Synthetic substances that mimic the actions of testosterone
  • Have some medical uses - treatment of delayed puberty, musle wasting due to HIV infection and impotence
  • Used by some athletes as performance enhancers becasue they stimulate increased muscle protein production, but this requires large doses
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9
Q

Effects of Anabolic Steriods

Anabolism

A
  • Building up of larger molecules from smaller ones, therefore can build muscle proteins
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10
Q

Effects of Exercise on Skeletal Muscle

Changes in muscle from a sustained exercise program

A
  • Endurance exercise leads to better ATP production (more mitochondria)
  • Resistacne exercise leads to hypertrophy
  • Muscle increases in size due to increases in synthesis of contractile proteins
  • Muscle also increases glycogen reserves and mitochondria
  • Limited amount of hyperplasia - increase in number of fibers
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11
Q

Effects of Exercise On Skeletal Muscle

Changes in muscle from lack of exercise

A
  • Atrophy: decrease in size due to lack of use (e.g. someone wearing a cast)
  • Initially reversible, but becomes permanent if extreme
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12
Q

Development of Skeletal Muscle

A
  1. Myoblasts (muscle building stem cells) form from mesoderm
  2. Myoblasts fuse to form muscle fibres - each keeps is nucleus, so muscle fibres become multinucleate
  3. Myofibrils form along the length of the muscle fibre
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13
Q

Development of Skeletal Muscle

Satellite Cells

A
  • Some of the myoblasts do not differentiate - they remain stem cells witin the muscle tissue
  • Once the muscle has formed, these stem cells are called satellite cells
  • Assist with repair of muscle tissue throughout life
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14
Q

Clininal Application

Intramuscular Injections

A
  • One route of medication administration
  • May be inserted into muscle with a syringe and need
  • Medication enters cardiovascular system through muscle’s blood vessels
  • Allows large amount of medication given at once
  • Ensures slower and more uniform delivery that orally or intravenously
  • e.g. vaccines, some contraceptive medications, some antibiotics
  • Common sites: deltoid, gluteal muscles, quadricepts femoris (usually larger muscles)
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15
Q

Muscle Attachments

Proximal/Distal Attachments

A
  • Proximal attachments of biceps brachii are on scapule
  • Distal attachment of biceps brachii is on radius
  • Contraction pulls radius toward scapula, flexing the elbow
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16
Q

Motor Units

How do motor units work?

A
  • Muscle is stimulated repeatedly
  • As voltage increase, more units are recruited to contract
  • Recruitment is also called multiple motor unti summation
  • It explains how muscles exhibit carying degrees of force - recruit few motor units to lift pencil vs. many to life a suitcase
  • Above a certain voltage, all units are recruited, and so maximum contraction occurs (regardless of hoe much higher voltage is)
  • Recruitment order based on size of motor units (small first, large last)
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17
Q

Putting it all Together:

Where is ATP used in muscle contraction/relaxation?

A
  1. Calcium pump (active transport) to keep calcium out of synaptic knob in stimulating neuron - when actional potential reaches synaptic knob, calcium enters and binds to vesicles to stimulate release of neurotransmitter
  2. Release of neurontransmitter from synaptic knob - released by exocytosis (active transport)
  3. Sodium-potassium pumps to maintain muscle membrane potential - active transport of Na+ and K+ aganist their concentration gradient
  4. Detaching myosin head from actin during contraction - ATP detaches head and then resets it to high eneergy rate
  5. Active transport of neurotransmitter components back into synaptic knob - after breakdown by acetylcholinesterase, acetic acid and choline, re-used to make more ACh
  6. Active transport of calcium back into sarcoplasmic reticulum - calcium pumps
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18
Q

Energy for Skeletal Muscle Contraction

Mitochondria and other structures associated with energy production

A
  • Muscle fibres have abundant mitochondria for aerobic ATP production
  • Myoglobin within cells allows storage of oxygen used for aerobic cellular respiration
  • Glycogen is stored for when feul is needed quickly
  • Creatine phosphate can quickly give up its phosphate group to help replenish ATP supply
19
Q

Energy for Skeletal Muscle Contraction

Muscle cells have only a little ATP in storage

A
  • Stored ATP is spent after about 5 seconds of intense exertion
  • Additional ATP rapidly produced via myokinase - phosphate transferred from one ADP to another to make ATP
20
Q

Energy for Skeletal Muscle Contraction

Three ways to generate additional ATP in skeletal muscle fiber:

A
  1. Creatine phosphate
  2. Glycolysis
  3. Aerobic cellular respiration
21
Q

Energy for Skeletal Muscle Contraction

Creatine Phosphate

A
  • Contains a high-energy bond between creatine and phosphate
  • Phosphate can be transferred to ADP to form ATP
  • 10-15 seconds of additional energy
22
Q

Energy for Skeletal Muscle Contraction

Glycolysis

A
  • Does not require oxygen
  • Occurs in sarcoplasm
  • Glucose (from muscle’s glycogen or through blood) is converted to two pyruvate molecules
  • 2 ATP released per glucose molecule
23
Q

Energy for Skeletal Muscle Contraction

Aerobic cellular respiration

A
  • Requires oxygen - if no oxygen present, pryruvate is converted to lactate (lactic acid), which is stored in the liver and muscles (this is what causes “stiffness after vigorous exercise)
  • Occurs in mitochondria
  • Pyruvate oxidized
  • Produces net 30 ATP per glucose molecule
  • Triglycerides can also be used as fuel to produce ATP
24
Q

Energy for Skeletal Muscle Contraction

Lactate formation and its fate

A
  • Lactate formation from pyruvate occurs under conditions of low oxygen avalibility
  • Pyruvate converted to lactate by lactate dehydogenase
  • Lactate can be used as fuel by skeletal muscle fiber or enter blood and taken up by cardiac muscle or liver
  • Lactic acid cycle - cycling of lactate to liver where it’s converted to glucose, and transport of glucose back to muscle (takes hours to days)
25
Q

Energy for Skeletal Muscle Contraction

Energy supply and varying intensity of exercise

A
  • For a 50 - metre sprint (less than 10 seconds) - ATP suppiled primary by phosphate transfer system
  • For a 400 - metre sprint (less than a minute) - ATP supplied primarily by glycolysis after first few seconds
  • For a 1500 - metre run (more than a minute) - ATP supplied primarily by aerobic processes after first minute
26
Q

Energy for Skeletal Muscle Contraction

Oxygen Debt

A
  • Amout of additonal oxygen needed after exercise to restore pre-exercise conditions
  • Additonal oxygen required to;
  • Replace oxygen on hemoglobin and myoglobin
  • Replenish glycogen
  • Replenish ATP and creatine phosphate
  • Convert lactic acid back to glucose
27
Q

Muscle Tone

A
  • Resting tension in a muscle
  • Generated by involuntary nervous stimulation of muscle
  • Some motor units stimulated randomly at any time
  • Chnage continuously so units not fatigued
  • Do not generate enough tension for movement
  • Decreases during deep sleep
28
Q

Smooth Muscle Contraction

Smooth Muscle Cells

A
  • Have fusiform shape
  • Uninucleate
  • Smaller than skeletal muscle fibers
  • Thick and thin filaments are arranged in a “fishnet” pattern throughout the cell so the cells are “squeezed” instead of contracting to shorten the length in one direction
29
Q

Smooth Muscle Contraction

Smooth Muscle Contraction Characteristics

A

Long latent period
- Takes time to phosphate myosin head
- Slow ATPase activity
Long duration
- Slow calcium pumps
- Need for dephosphorylation of myosin head
- Latchbridge mechanism
Slowness fits its functional requirements
- Extended contractions low compared to skeletal muscle
- e.g. in walls of blood vessels
Fatigue-resistane
- Energy requirements low compared to skeletal muscle
- Can maintain contraction without ATP
Broad length-tension curve
- Has no Z discs, myosin heads present in center of thick filaments
- Can contract forcefully, even when already stretched - e.g. allows emptying bladder regardless of amount of urine

30
Q

Smooth Muscle Contraction

Control of Smooth Muscle

A

Autonomic (involuntary) nervous system secrete transmitters
- Muscle’s response depends on neurotransmitter present and muscle’s receptor for it
- e.g. smooth muscle of bronchioles contracts in response to ACh and relaxes in response to norepinephrine
Response to stretch
- Myogenic response is contraction in reaction to stretch
- Stress-relaxation response is relaxation after prolonged stretch
Other stimulating factors include:
- Various hormones
- Low pH
- Low oxygen
- High carbon dioxide
- Certain drugs
- Pacemaker cells

31
Q

Classification by Muscle Fibre Orientation

Circular Muscles

A

Concentrically arranged fascicles
- Create a sphincter
- Control material passage through an opening

32
Q

Classification by Muscle Fibre Orientation

Parallel Muscles

A

Fascicles run parallel to muscle’s long axis
- Sometimes have an expanded contral belly
- High endurance muscles

33
Q

Classifcation by Muscle Fibre Orientation

Convergent Muscles

A

Fascicles merge toward a common attachment site
- Can pull in varying directions, but not as hard as parallel muscles

34
Q

Classification by Muscle Fibre Orientation

Pennate Muscles

A

Fascicles organized as if part of a large feather
- Fibres pull at an ongle to the tendon
- Generate more tension but don’t pull their tendons as far as parallel muscles
Three subtypes:
- Unipennate - fascicles on same side of tendon
- Bipennate - fascicles on both sides of tendon; most common
- Multipennate - branches of tendon within muscle, and fascicles arranged around both sides of each tendon branch

35
Q

Classification by Muscle Action

Agonist

A
  • Prime mover; muscle that contracts to produce a movement
  • e.g. triceps brachii is agonist for forearm extension
36
Q

Classification by Muscle Action

Antagonist

A
  • Muscles whose contraction opposes that of the agonist - this allows for smooth movement of controlled speed
  • e.g. biceps brachii is antagonist for forearm extension
37
Q

Classification by Muscle Action

Synergist

A
  • Muscle that assists agonist by contributing tension or stabilizing point of origin (acting as fixators)
  • e.g. biceps brachii and brachialis musle work synergistically to flex elbow joint
38
Q

Naming Muscles

Action

A

Indicates muscle’s primary action
- e.g. flexor digitorum longus flexes digits

39
Q

Naming Muscles

Location

A

Specific body regions: indicates muscle location
- e.g. rectus femoris is near the femur

40
Q

Naming Muscles

Attachments

A

Muscle attachments: indicates origins and/or insertions
- e.g. sternocleidomastoid originates on the sternum and clavicle and inserts on the mastoid process of the temporal bone

41
Q

Naming Muscles

Direction of Fibres

A

Orientation of Muscle Fibres: indicates organization of muscle fascicles
- e.g. rectus abdominis is composed of fibres running in vertically straight (“rectus”) orientation

42
Q

Naming Muscles

Shape

A

Muscle shape
- e.g. deltoid is shaped like a triangular delta symbol
- e.g. abductor pollicis longus is a long muscle

43
Q

Naming Muscles

Size

A

Muscle size
- e.g. gluteus maximus is the largest of the buttocks muscles

44
Q

Naming Muscles

Number of Heads

A

Number of muscle heads at an attachment site: indicates number of muscle bellies or head each contains at the superior or proximal attachment site
- e.g. triceps brachii has three heads

BIOL1046 Human Biology II (14 decks)

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