Smooth Muscle

Question 1

How are cells different in Smooth muscle in comparison to Skeletal Muscle?

Answer 1

• Cells are smaller
• Single, centrally located nuclei
• Less developed Sarcoplasmic reticulum
• Contain Actin & Myosin, but
  
  • These myofilaments are:
    
    • Thinner
    • More randomly distributed
    • Not organized in “True” sarcomeres

Question 2

Smooth Muscle: Structure

Action & Myosin compared to Skeletal Muscle

Answer 2

• Fewer overall myofilaments
• Actin/Myosin ratio - 16:1
• Myofilaments not as well organized
• Have longer Actin filaments
• Do not attach to Z-lines
• Attach to the Sarcolemma or to Sarcoplasmic proteins called Dense Bodies
• Dense Bodies analogous to the z disc
• Not considered a “true” sarcomere

Question 3

“Smooth” muscles are involuntary

They are under the control of:

Answer 3

• Thalamus and hypothalamus
• Brainstem
• Spinal cord

Question 4

Smooth muscles can be found in:

Answer 4

• Viscera
• Glands
• Blood vessels
• others

Question 5

Impulses to Smooth Muscles are carried via the

Answer 5

Autonomic Nervous System

Question 6

How many neurotransmitters are used in the Autonomic Nervous System?

What are they?

Answer 6

2 Neurotransmitters

1. Acetylcholine
2. Norepinephrine

This is different from Skeletal Muscle

Question 7

Smooth Muscle structure is necessary for function..

In many structures with Smooth Muscle..

Answer 7

• The condition of being stretched is present
• Still must be able to generate tension
  
  • Bladder stretches 2-3x resting length
  • Uterus: Stretches 8x resting length

Question 8

Smooth Muscle:

Accomodation

Answer 8

• Property not seen in Skeletal muscle
• As smooth muscle cells stretch
  
  • the muscle fibers “relax” to Accomodate the increase in length
• Able to keep the tension steady

Question 9

Smooth Muscle Contraction

How is Smooth Muscle triggered?

Answer 9

• Triggered by impulses from the Nervous system (same as skeletal muscle)
• Stretching can trigger smooth muscle contraction

Question 10

Smooth Muscle Contraction:

Sliding Filament Theory:

uses…

Answer 10

• Interaction between Actin and Myosin
• Uses calcium and ATP

Both same as Skeletal Muscle

Question 11

Smooth Muscle Contraction

Smooth Muscle lacks..

Answer 11

Smooth Muscle lacks Troponin

Uses a different protein to bind calcium

Question 12

Smooth Muscle is slower to

__________ & _________, so

it is more resistant to _______

Answer 12

contract & relax

fatigue

Question 13

Smooth muscle can change length without losing tension

Answer 13

Accomodation

Question 14

2 Major Functional Categories

Answer 14

Found in the various organs/structures of the body

1. Unitary (visceral)
2. Multi-Unit

Question 15

Unitary

Answer 15

• Cells contact as a single unit
• Only some of the cells in the unit have direct contact with a neuron
  
  • motor neurons from the autonomic nervous system
• Have gap junctions
  
  • specialized connections between cells
  • allows nerve impulses to spread from cell to cell
  • without a direct neuronal connections to every cell
• All the cells in the unit work simutaneously
• Examples
  
  • Stomach, intestines, bladder
    *

Question 16

Unitary

Because cells contract as a single unit

This gives the ability to

Answer 16

• This ability of one cell to stimulate the next cell
• Gives some Smooth Muscle with Unitary structure and a feature called Rhymicity
• Smooth muscle cells with a Unitary structure and Rhythmicity
  
  • can produce a wave-like motion
  • termed Peristalsis

Question 17

Unitary

Peristalsis

Answer 17

• The alternation between contraction and relaxtion in the different layers of smooth muscle in an organ
• In a tubular structure (like the intestine)
  
  • Helps move the contents in the tubular structure in one direction
  • i.e. moving digesting food down the intestinal tract

Question 18

Multi-Unit

Answer 18

• Contains units similar to Skeletal muscle
  
  • units are variable in size
• All cells must be stimulated by individual nerve fibers
  
  • Each cell has direct contact with a neuron from the Autonomic Nervous System
• Units can work independently
• Very few gap functions, if any
  
  • Examples:
    
    • Walls of blood vessels
    • Iris