2. Syllabus
• Physiological properties of smooth muscle,
• automaticity of smooth muscle,
• impulse propagation within smooth muscle;
• correlation between excitation and contraction;
• irritants of smooth muscle;
• Contractile activity of smooth muscle;
• Physiologic properties of muscles in pediatric age;
• Changes in muscular tissue in aging process
4. Anatomy of smooth muscle fibres
Physical dimentions
• Diameter 1-5 micrometer
• 20-500 mcm in length
• To compare : skeletal muscle fibres 30 X diameter and 100s X length
Organization in bundles
Response to different stimuli
Characteristic in innervation
Function
5.
6. Multy-Unit smooth muscle
• Descrete, separate smooth muscle fibres
• Each fibre operates independently
• Each fibre is innervated by a singe nerve ending
• Each fibre is covered by a thin layer of the basement membrane like
substance mixture of collagen and glycoprotein to insulate this fibre
from the others
• Each fibre contracts independently of others
• Examples: ciliary muscles of the eye, iris muscles, piloerector muscle
7. Unitary smooth muscle
• Syncytial (visceral) smooth muscle
• Hundreds or thousands of muscle fibres contract together as a single
unit
• Fibres are arranged in sheets or in bundles
• There cell membranes are adherent to each other
• Cell membranes are connected with gap junctions through which ions
can flow, therefore these fibres contract together easily
• Name justification
9. Differences in Contractile mechanism
• Physical Organization
• excitation-contraction coupling
• Control of the contractile processes by Ca ions
• Duration of contraction
• Amount of energy required for contraction
10. Physical bases for smooth muscle contraction
• No striated arrangement of actin and myosin
• Instead of the Z disc Dense bodies
• Dense bodies are attached to the cell membrane or are dispersed
inside the cell
• Dense bodies of adjacent cells are bonded together by intercellular
protein bridges
• Actin filaments radiate from the dense bodies
• Among actin filaments are twice as thick and 5-10 times few myosin
filaments
• “Sidepollar” cross-bridges
19. changes in muscular tissue in aging process
• The age-related loss of muscle function is known as Sarcopenia[1],
derived from the Greek words for flesh (sarcos) and loss (penia) and
its definition includes loss of muscle strength and power, as well as
reduced function[2]. It occurs with increasing age, and is a major
component in the development of frailty.
• The loss of muscle mass during the aging process is important
clinically as it reduces strength and exercise capacity, both which are
needed to perform activities of daily living. The video below gives a
good summary of the changes and effects on performance and
health.
20. • Sarcopenia is not a disease but rather refers specifically to the universal,
involuntary decline in lean body mass that occurs with age, primarily due to the
loss of skeletal muscle. Systematic review and meta-analyses among Japanese
community-dwelling older adults suggest the prevalence of sarcopenia
(9.9% overall: 9.8% among men, and 10.1% among women), providing valuable
information in addressing sarcopenia prevention in the older community[4]. A
narrative review published in International Journal of Molecular Sciences (2020)
provides new evidence regarding the mechanisms, evaluation and detection
methods, and spinal sarcopenia treatment modalities[5].
• Sarcopenia has important consequences.
• The loss of lean body mass reduces function, and loss of approximately 40% of
lean body mass is fatal[6].
• It has been attributed to a reduction of muscle size as well as a reduction in
satellite cells (a stem cell that lies adjacent to a skeletal muscle filished omber
and plays a role in muscle growth, repair, and regeneration[7]), mitochondrial
numbers, and elasticity.
• Sarcopenia is seen in increasing numbers with advancing age but is not universal.
21. • Reduction in lower limb muscle cross-sectional area have been
observed to begin in early adulthood and accelerate beyond 50 years
of age.This reduction in muscle cross-sectional area associated with
decreases in contractile structures accompanied by increases in non
contractile structures such as fat and connective tissue.[11] A cross-
sectional study[12] suggested that the older inpatient showed an
increase in the intramuscular quadricep muscle adipose tissue approx
1.7 times that of the healthy older individuals. Also, the study
observed increased intramuscular adipose tissue with older inpatients
who were unable to walk independently as compared to older
inpatients who were able to walk freely.
22. • The total number of muscle fibers is significantly reduced with age,
beginning at about 25 years and progressing at an accelerated rate
thereafter The decline in muscle cross-sectional area is most likely
due to decreases in total fiber number, especially type II fast-twitch
glycolytic fibers. This results in reduced muscle power.[11] A study
examining 1-year changes in the physical functioning of older people
using the ICF framework showed a significant decrease in muscle
strength (both hip abductors and knee extensors) walking capacity,
speed, mobility, sit-to-stand performance, upper extremity function,
and balance performance at the end of 1 year[13]..
23. 1.Changes in Muscle Fiber Size
• Elderly individuals often fall because of poor muscle strength and reduced balancing
ability related to muscle aging. Types IIA and IIB muscle fibers decrease with age in the area
percentage, fiber number percentage, and mean fiber area, whereas Type I fibers increase
in area and number but not in size. Morphologically, Type II fibers appeared smaller and
flatter. Investigations suggest deterioration in muscle quality and balancing coordination in
elderly patients. A research done provided data to help determine treatments for reversing
muscle fiber changes and reducing the number of falls and related fractures in
patients.[14]The reduction in number of muscle fibers contributes more to the decrease of
whole muscle cross-sectional area than does the reduction in area of individual fibers. The
individual fast-twitch type II fibers decrease in cross-sectional area suggest that the relative
contribution of fast-twitch type II fibers to force generation is less in the older adult.
2. Motor Unit Number and Size
• The majority of the literature indicates that muscle fiber loss is due to a loss in motor
neurons. There is consistent denervation and reinervation of the muscle fiber throughout
one’s lifespan, but in the aged, denervation appears to outpace reinveration. Data indicate
that a 60-year-old has approximately 25-50% fewer motor neurons than a 20-year-old, with
the greatest losses in distal fast twitch motor neurons With the loss of the motor neuron,
the denervated fast twitch muscle fibers that were attached to it are either permanently
denervated and undergo apoptosis, or are reinverated with a different motor neuron most
likely that of a slow-twitch neuron, potentially making the fiber take on slow twitch
characteristics[15]
24. Physiologic properties of muscles in pediatric
age (http://www.pmmonline.org/page.aspx?id=134)
• Normal variants refer to normal development of the musculoskeletal
system, in particular the lower limbs. It is important to know about
them as they are a common cause for concern for parents and a
frequent reason for consultation.
• Normal variants include leg alignment issues, flat feet, knock-knees,
bow-legs, out-toeing, in-toeing or toe-walking.
• It is important to understand normal gait and motor milestones and
know about normal lower limb development in order to appreciate
when observations may be considered abnormal, what conditions to
consider and when to refer for a specialist opinion.
