muscle tissue embryological origin
mesoderm
muscle tissue types
skeletal
cardiac
smooth
skeletal muscle
- characteristics (2)
- type of contraction
- appearance
characteristics -striated -voluntary strong, quick discontinuous contraction appearance -long, cylindrical peripherally located nuclei -multinucleated with cross-striations
cardiac muscle
- type of contraction
- appearance
strong, quick continuous (involuntary) contractions appearance -cross-striations -branched -end-to-end contact = intercalated discs
smooth muscle
- type of contraction
- appearance
weak, slow (involuntary) contractions
appearance
-collections of fusiform cells (do not show cross-striations)
muscle tissue is encased by… (broad term)
connective tissue
connective tissue network around muscle
- function
- types
function
-important for transmission of contractile forces through the entire muscle
-necessary since individual fibers don’t extend entire length
types
-epimysium
-perimysium
-endomysium
epimysium
- type of CT
- location
dense irregular CT
surrounds entire muscle
perimysium
- type of CT
- location
thin septa of loose CT
separates and surrounds individual bundles of muscle fibers
endomysium
- type of CT
- location
- what is a unique function?
fine connective tissue
surrounds individual fibers, mostly basal lamina and reticular fibers
unique function
-carries capillaries along and through entire muscle
myotendinous junction
- composition
- inserts where?
collagen fibers of regular dense connective tissue
insert into endomysium
striated muscle components (4)
myoblasts
myotubes - primary, secondary
muscle - primary, mature
satellite cells
satellite cell function
allow for some regenerative capability
regenerative capability of the 3 types of muscle tissue
cardiac -none skeletal -few satellite cells (limited production of myoblasts) --development of muscle fiber --"repair" of muscle is thus by hypertrophy of remaining muscle fibrils smooth -highly mitotic
muscle spindle
- location
- arrangement
- attached to…
location
-within skeletal muscles
arranged in parallel with the muscle fibers
attached to
-CT coverings of perimysium and endomysium
what will change the length of the muscle spindle
any change in length of the CT covering during muscle contraction or stretch
spindle responds to…
-what structures allow this response
responds to changes in length of the muscle
structures that allow this
-sensory endings located within an encapsulated area
-small muscle fibers positioned at the ends of the receptor area
–allow for “resetting” of the sensitivity of the muscle spindle
muscle spindle receptors are designed to respond to either…
dynamic (phasic) stretch
static (tonic) stretch
muscle spindle endings that respond to dynamic stretch
- rate of adaptation
- activity length
- what do they encode?
rapidly adapting activity is short-lived encode -velocity of stretch -duration of change
muscle spindle endings that respond to static stretch
- rate of adaptation
- function
- duration of respose
slow-adapting receptors
purpose
-maintain signaling of a stretch that is maintained
respond over time (long response)
how is the sensitivity of muscle spindle receptors altered?
via selective control by gamma motor neurons
what is a gamma motor neuron?
small motor neuron specific to muscle fibers within the muscle spindle
golgi tendon organ (GTO)
- location
- receptors responsible for..
located within the tendinous attachment of a muscle to bone
responsible for encoding tension within the tendon
in terms of where the encoded information is coming from, what is the difference between muscle spindles and GTOs?
muscle spindles
-encode information at muscle level
GTO
-encode information at tendon level
GTOs
-functions
signal change in tension (resistance to the force of contraction)
capable of signaling a response to excess tension as a protective mechanism
when a PT taps the patellar tendon, what is happening and what structures are causing change?
-what is the reflex that occurs called?
what is happening
-short instantaneous stretch of quadriceps
muscle spindle is being stimulated
little change to GTO since little tension is created
reflex called
-deep tendon reflex (DTR)
what reflex is the DTR sometimes confused with (ie they’re not the same)
stretch reflex
-aka muscle stretch reflex/myotatic reflex
cardiac muscle characteristics (3)
striated
-similar to skeletal muscle
branched cells
-attached to adjacent cell by intercalated disc
single or double centrally located nuclei
intercalated disc
-composition and function of each part
zonula adherens
-anchoring of actin fibers, similar to z-line
macula adherens (desmosomes)
-anchor cardiac cells together
gap junctions
-on longitudinal plane of uneven intercalated discs
-give ionic continuity of side-to-side cells
t-tubule system
- presence compared to in skeletal muscle
- represented as…
present but not as regular as in skeletal muscle
represented as diads
-t-tubule and only one sarcoplasmic reticulum
smooth muscle
-characteristics (6)
fusiform cells
non-striated
no T-tubule system
contraction initiated by Ca2+ (different mechanism than striated muscle)
Ca2+ is bound by calmodulin
contraction can be regulated by changes in cAMP levels
fusiform cells (smooth muscle) characteristics
encased in basal lamina and reticular fibers
centrally located nucleus (single)
what is calmodulin
calcium binding protein that activates myosin in smooth muscle
an increase in cAMP levels results in…
phosphorylation of myosin
-muscle then contracts
what is present in the smooth muscle of organ systems that is not present in the smooth muscle of other areas
-what is the purpose
gap junctions
-muscles contract together, so they function as a unit (syncytium)
what is one reason (apart from synchronized contraction) for having gap junctions in smooth muscle?
there is little innervation in visceral smooth muscle such as the small intestine
gap junctions allow the nervous activation or message to be spread cell to cell
what is a location with rich innervation of smooth muscle?
iris of the eye (multi-unit smooth muscle)
