Cardiac and Smooth Muscle

Question 1

Cardiac muscle appearance

Answer 1

Striated, packed and regular arrangement, more branched than skeletal muscle

Question 2

Smooth muscle apperance

Answer 2

Non-striated, actin and myosin not arranged in sarcomeres

Question 3

Cardiac muscle structure

Answer 3

1. Sarcomeres lining up
2. intercollated discs with points of adhesion at junctions between muscle cells
3. Gap junction -> electrically coupling cells

Question 4

Contractile activity of cardiac muscle cells

Answer 4

Myogenic -> own pacemaker cells -> intrinsic pattern of activity controlled by SAN, AVN and outside influence
-> nerve fibres from autonomic ganglia

Question 5

Cardiac a.p. in general

Answer 5

lasts longer, slow depolarisation in SAN -> opposes K_ current

Question 6

When comparing a.p. and contraction of cardiac muscle cells

Answer 6

1. a.p. + contraction overlaps but there’s still a lag phase

2. Step wise increase in cytosolic conc., rest period built into a.p.

Question 7

Chronotropic regulation

Answer 7

Regulation of heart rate - usually by pacemaker activity through autonomic nerves

Question 8

Types of smooth muscle

Answer 8

1. Single-unit smooth muscle : mainly myogenic in origin + behaves as a syncytium
2. Multi-unit : largely initiated by autonomic nerve fibres -> neurogenic in origin except in erecto pilli on skin

Question 9

Smooth muscle structure

Answer 9

1. Loose matrix
2. Dense patterns = adhesion points
3. Contracts over long and unusual patterns -> no regular sarcomeres
4. gap junctions

Question 10

Smooth muscle contraction

Answer 10

1. Greater degree of shortening
2. Greater speed in relaxed state
3. No troponin -> calmodium activates myosin light chain kinase -> phosphorylated myosin
4. Longer period of tension in smooth muscle

Question 11

Smooth muscle contraction is modulated by

Answer 11

Autonomic nerves by local chemical factors and by circulating hormones