L6 - muscle cells

Question 1

does connective tissue separate smooth muscle cells?

Answer 1

yes

Question 2

what happens to the nucleus of contracted muscle cells

Answer 2

they become stretched out and can possible see indentations

Question 3

what is epimysium

Answer 3

sheath of fibrous elastic tissue surrounding a muscle

Question 4

describe features of skeletal muscle

Answer 4

striated
peripheral nuclei
multinucleated cells

Question 5

what surrounds myofibrils

Answer 5

sarcolemma

Question 6

how can t tubules be identified

Answer 6

they run transversely

invaginations of the sarcolemma that indentate into muscle cells

Question 7

function of T tubules

Answer 7

contain many voltage gated channels that carry on the depolarisation

Question 8

what is the sarcoplasmic reticulum

Answer 8

Ca2+ store that surrounds myofibrils

Question 9

describe smooth muscle structure

Answer 9

uninucleate
no striations
spindle shapes

Question 10

why does connective tissue surround smooth muscle cells

Answer 10

allow nerve tracts and blood vessels

Question 11

define phasic contractions and give an example

Answer 11

periodic contractions

eg oesophagus, SI only contracts when food enters

Question 12

define tonic contraction

Answer 12

constant contraction, relax to open

eg sphincters

Question 13

what are single unit smooth muscle cells

Answer 13

cells connected by gap junctions and contract as a single unit

Question 14

what are multi unit smooth muscle cells

Answer 14

cells are not electrically linked and can be stimulated individually

Question 15

describe appearance of cardiac muscle

Answer 15

uninucleate
striated
branched
contain intercalated disks

Question 16

what are intercalated disks?

Answer 16

desmosomes and gap junctions

Question 17

where are cardiac muscle cell nuclei located

Answer 17

centrally

Question 18

explain process of contraction in skeletal muscle

Answer 18

1. ACh binds to receptors on post S membrane allowing Na entry
2. membrane depolarises and this depolarisation travels down the T tubules
3. alters conformation of DHP receptor which is directly coupled to Ryr receptor
4. leads to Ca2+ release from sarcoplasmic reticulum
5. Ca2+ binds to troponin on actin
6. causes tropomyosin to move exposing myosin binding site
7. power stroke

Question 19

does each muscle fibre need to be innervated separately for contraction?

Answer 19

yes

Question 20

explain process of power stroke

Answer 20

1. myosin head bends, sliding actin filament along , ADP and Pi released
2. new ATP binding to myosin head breaks cross bridge

Question 21

explain arrangement of actin and myosin in smooth muscle

Answer 21

1. dense bodies (connected to sarcolemma) throughout cell anchor actin filaments (like Z line)
2. myosin is surrounded by actin

Question 22

what connects dense bodies in smooth muscle

Answer 22

Intermediate filaments

Question 23

explain mechanism of smooth muscle contraction

Answer 23

1. Ca2+ enters cytoplasm from ECF and SR
2. Ca2+ binds to calmodulin (CaM)
3. Ca-CaM activates myosin light chain kinase
4. MLCK phosphorylates myosin heads and increases myosin ATPase activity
5. ADP + Pi will now be bound to myosin (increased ATPase activity)
6. cross bridge to actin can form sliding actin along

Question 24

explain mechanism of smooth muscle relaxation

Answer 24

1. Ca2+ pumped out of cell / into SR
2. Ca2+ unbinds from CaM
3. MLCK activity drops
4. myosin ATPase activity drops
5. cross bridges dont form
6. relaxation

Question 25

explain mechanism of cardiac muscle contraction

Answer 25

1. auto rhythmic cells fire APs 2. depolarisation spreads through gap junctions 3. Ca2+ enters cell 4. leads to Ca2+ release from sarcoplasmic reticulum 5. Ca2+ binds to troponin on actin 6. causes tropomyosin to move exposing myosin binding site 7. power stroke

Question 26

how is Ca2+ removed for relaxation of cardiac muscle

Answer 26

1. Na / Ca2+ antiport

Question 27

what anchors myosin filaments to Z line in striated muscle

Answer 27

titin