Muscle microstructure and contraction

Question 1

smooth muscle is under —- control from the —— nervous system

Answer 1

involuntary

autonomic

Question 2

cardiac muscle can contract ——- but is under the influence of the —— nervous system and —— ——

Answer 2

autonomously
autonomic
circulating chemicals

Question 3

Skeletal muscles are under ——– control, usually attached to —– and —— to bring about ——-

Answer 3

voluntary (somatic nervous system)
bones
contract
movement

Question 4

bundles of muscle fibres (myofibres)

Answer 4

fasicles

Question 5

myofibres are made up of

Answer 5

myofibrils made up to myofilaments

Question 6

connective tissue surrounding muscles

Answer 6

epimysium

Question 7

connective tissue surrounding fasicles

Answer 7

perimysium

Question 8

connective tissue surrounding myofibres adjacent to sarcolemma

Answer 8

endomysium

Question 9

myofibres are covered by

Answer 9

sarcolemma (plasma membrane)

Question 10

cytoplasm in a myofibre is called, and —– / —— are present

Answer 10

sarcoplasm

mitochondria myoglobin

Question 11

function of t tubules

Answer 11

to carry impulse deep into center of myofibre, innervating all myofibrils

Question 12

dense protein - —– separate sarcomeres !!!!!!!!!!!!!!!!!

Answer 12

Z - discs

Question 13

Dark band

Answer 13

A band (thick - myosin)
overlap of myosin and actin

Question 14

Light band

Answer 14

I band ( thin - actin)

Question 15

myosin has - globular heads

single tail formed by — ——-

Answer 15

2

a-helices

Question 16

structure of actin
each molecule has a
filaments also contain

Answer 16

molecules twisted into helix
myosin binding site
troponin and tropomyosin

Question 17

during contraction

I / A / H band

Answer 17

I - shorter
A - same
H - shorter / disappeared

Question 18

middle of sarcomere is the

Answer 18

M - line

Question 19

Initiation of muscle contraction

Answer 19

action potential propagates across sarcolemma and into t-tubules
Dihydropyridine (DHP) senses ΔV / changes conformational shape
opens ryanodine receptor
Ca2+ released from sarcoplasmic reticulum into sarcoplasm surrounding filaments
Ca2+ binds to troponin
tropomyosin moves
exposing myosin binding site on actin
charged myosin head binds to actin
binding and discharge of ADP causes myosin head to pivot POWER STROKE
ATP binding unbinds myosin head from actin filament
*while action potentials continue Ca2+ continuously actively transported into SR and pumped out.

Question 20

motor unit

Answer 20

one motor nerve and all muscle fibres innervated by it

Question 21

motor nerves can innervate ——- myofibres.

Myofibres can be innervated by —– —- nerve

Answer 21

multiple (avg 600)

only one

Question 22

Slow motor unit, S type 1

Answer 22

smallest diameter cell body
small dendritic trees
thinnest axons
slowest conduction velocity

Question 23

Fast, fatigue resistant motor unit

FR type IIA

Answer 23

larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

Question 24

Fast, fatiguable motor unit

FF type IIB

Answer 24

larger diameter cell bodies
larger dendritic trees
thicker axons
faster conduction velocity

Question 25

Slow type 1 muscle fibre
Myoglobin content
Colour 
Aerobic capacity
Anaerobic capacity

Answer 25

High
thus Red
High
Low

Question 26

Fast fatigue resistant muscle fibre 
FR type IIA
Myoglobin content
Colour 
Aerobic capacity
Anaerobic capacity

Answer 26

High ish
thus pink
moderate
High ish

Question 27

Fast fatiguable muscle fibre
FF type IIB 
Myoglobin content
Colour 
Aerobic capacity
Anaerobic capacity

Answer 27

Low
thus white
low
High

Question 28

Regulation of muscle force

Answer 28

recruitment - smaller units recruited first, if more force required more units recruited
Rate coding - slower units fire at lower frequency, rate increases force increases

Question 29

Summation (rate coding)

Answer 29

units fire too fast to allow muscle to relax between arriving action potentials

Question 30

if a fast and slow twitch muscle are cross innervated

Answer 30

the slow one becomes faster
the faster becomes slower
the motor neurone has some effect on the properties of the muscle fibres it innervates

Question 31

Types of muscle contraction

Answer 31

isometric - hold / muscle stays same length whilst generating force
concentric - contraction
eccentric - controlled relaxation

Question 32

Skeletal muscle structure

Answer 32

Three main types of muscle: smooth, cardiac and skeletal
Skeletal muscle is composed of myofibres, myofibrils and myofilaments
Skeletal muscle is striped and component parts are arranged in sarcomeres
Actin and myosin are proteins involved in contraction.

Question 33

Muscle contraction

Answer 33

Ca2+ is released from sarcoplasmic reticulum
Ca2+ binding to troponin on actin causes change in tropomyosin revealing myosin binding site
crossbridges formed
POWERSTROKE causes contraction
ATP used for contraction and release

Question 34

Motor units

Answer 34

name for neuron and all muscle fibres
3 main types (slow, fast fatigue resistant and fast fatiguable)
contraction of motor unit causes contraction of all fibres of unit
sizes vary
muscles have varying proportions of types of unit
units have different properties
recruitment and coding mechanisms for controlling contraction (force)
neuron has effect on fibre type (neurotrophic factors)
different types of contraction by skeletal muscles

Question 35

Plasticity

Answer 35

motor units can change following training
typically type IIB to IIA
spinal cord injury and microgravity can cause shift from slow to fast
ageing causes loss of slow and fast, but predominantly fast