L9/10- Smooth muscle

Question 1

shape of smooth muscle cells

Answer 1

spindle shaped

Question 2

nucleus in smooth muscle

Answer 2

single large central nucleus

Question 3

smooth muscle cells are not …… unlike skeletal and cardiac

Answer 3

striated- no sarcomeres

Question 4

contraction in smooth muscle relies on

Answer 4

actin-myosin interactions

Question 5

type of contraction

Answer 5

slower, but more sustained- requires less ATP

Question 6

how do smooth muscle cells aggregate

Answer 6

form sheets, bundles or layers

Question 7

have numerous

Answer 7

caveolae (smal cave-like invaginations

Question 8

similarities to striated muscle

Answer 8

• Contain actin and myosin contractile proteins o Anchored by a dense body (z-disc) o Calcium supplied by SR

Question 9

what sort of stimuli do smooth muscle respond to

Answer 9

• Nerve signals- autonomic nervous system - Hormones - Mechanical- distension - Drugs - Local concentration of blood gases

Question 10

smooth muscle distribution

Answer 10

Forms contractile walls of passageways or cavities - Vascular structures - Gut - Respiratory - Genitourinary system

Question 11

smooth muscle is completely

Answer 11

involuntary

Question 12

clinical disorders related to smooth muscle

Answer 12

• Primary hypertension - Dysmenorrhea- painful menstruation - Asthma - Abnormal gut mobility (IBS) - Incontinence

Question 13

too much contraction of smooth muscle

Answer 13

can lead to damage

Question 14

relaxed vs contracted smooth muscle

Answer 14

Question 15

smooth muscle innervation

Answer 15

Axons of the ANS do not form highly organised NMJs with smooth muscle. A series of NT-filled buneles called varicosities-form motor units.

Question 16

varicosities release

Answer 16

NT into the synaptic cleft

Question 17

how is smooth muscle excitation contraction coupling different to striated muscles

Answer 17

S.muscle does not contain troponin

Question 18

cross bridge formation is not regulated by the troponin-tropomyosin complex but instead by

Answer 18

calmodulin

Question 19

smooth muscle contraction is

Answer 19

calcium dependent

Question 20

outline smooth muscle exciation contraction coupling

Answer 20

1. Mechanical stimuli on the sarcolemma (distension) causes calcium channels to open and calcium to flood into the sarcoplasm
2. Calcium binds to calmodulin (like troponin C)
3. Calcium-calmodulin complex activates Myosin light chain kinase (MLCK) which adds phosphates to the myosin head
4. Myosin heads that haver phosphate added by MLCK can form cross- bridges between myosin heads and actin filaments initiating contraction
5. Smooth muscle relaxation occurs when MLC phosphorylation is reduced e.g. when calcium levels are reduced- this activates MLCP- myosin light chain phosphatase- which removes phosphate front he myosin head causing it to relax)

Question 21

skeletal muscle cells and muscle tearing

Answer 21

cannot divide but can regenerate by mitotic activity of satellite cells, so that hyperplasia follows muscle injury.

Question 22

satellite cells can

Answer 22

fuse with excisting msucle cells to increase mass (skeletal muscle hypertrophy)

Question 23

can adult cardiac muscle regenerate

Answer 23

no

Following damage, fibroblasts invade, divide and lay down scar tissue

Question 24

smooth muscle cells retain their ability to

Answer 24

mitose and can form new smooth msucle cells

Question 25

what is a good example of smooth mucle cell division

Answer 25

Particularly evident in the pregnant uterus where the muscle wall becomes thicker by hypertrophy (cell enlargement) and hyperplasia (mitosis) of individual cells