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Biology 201 Human Anatomy I

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Biology 201 Human Anatomy I Histology of Muscle – PowerPoint PPT presentation

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Title: Biology 201 Human Anatomy I


1
Biology 201Human Anatomy I
  • Histology of Muscle

2
Muscle Tissue 3 Types
Skeletal Muscle
Cardiac Muscle
Smooth Muscle
3
Skeletal Cardiac
Smooth Muscle Muscle
Muscle
Very long Unbranched Shorter Branched Short Unbranched Spindle-shaped
Hundreds per cell Peripheral One or two per cell Central One per cell Central
Yes Yes No
Myocytes Nuclei Striations
4
Muscle Special Terminology Prefixes Cell
Plasma membrane Endoplasmic reticulum
Cytoskeletal Filaments
5
Skeletal Muscle
Always voluntary. Each myocyte connected to and
controlled by an axon from a motor neuron.
Because of high metabolism, myocytes must be very
close to capillaries.
Myocytes are all oriented parallel to long axis
of muscle which is Parallel to direction
which muscle pulls when it contracts
lengthens
when it relaxes
6
Prominent Organelles in Myocytes -
Sarcolemma - Nuclei - Myofibrils (highly
organized bundles of myofilaments -
Transverse tubules (inward extensions of
sarcolemma) - Sarcoplasmic reticulum -
Mitochondria
Keep in mind Even though not prominent, all
other organelles also
present (vesicles,
ribosomes, lysosomes,
Golgi apparatus, etc.
7
Skeletal Muscle Anatomy
Each myocyte surrounded by, and firmly attached
to, layer of loose connective tissue called
8
Skeletal Muscle Anatomy
Myocytes grouped together into bundles called
each fascicle surrounded by, and
firmly attached to, layer of dense irregular
connective tissue called
9
Skeletal Muscle Anatomy
Entire muscle surrounded by, and firmly attached
to, layer of dense irregular connective tissue
called
10
Skeletal Muscle Anatomy
All three layers of connective tissue blend
together at each end of muscle. Thus force
transmitted from Myocytes Endomysium Perimysiu
m Epimysium Tendon, bone, etc.
11
Myocyte (muscle cell)
Myofibril
Thick thin myofilaments
12
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14
Thick and thin myofilaments forming part of a
myofibril
15
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17
Myocyte Contraction
Stimulus from motor neuron (nerve cell) Spread of
stimulus along sarcolemma and into myocyte
through transverse tubules Release of Ca from
sarcoplasmic reticulum into cytoplasm of
myocyte Binding of calcium to thin
myofilaments Formation of cross-bridges between
thin myofilaments and thick myofilaments
18
Myoneural junction or Neuromuscular junction
19
Stimulation of the myocyte begins when the neuron
releases a chemical neurotransmitter from its
synaptic vesicles into the synaptic cleft between
the neuron and the myocyte.
The neurotransmitter diffuses across the synaptic
cleft and binds onto receptors which are located
on the sarcolemma of the myocyte. This causes an
electrical change of the sarcolemma
20
When resting, the sarcolemma of the myocyte
is polarized. Sodium ions are concentrated on
its outer surface potassium ions are
concentrated on its inner surface. Large
negative ions (proteins, phosphate, sulfate, etc)
are also concentrated on the inner surface.
Sodium channels and potassium channels are
closed.
21
When molecules of the neurotransmitter bind onto
their receptors on the sarcolemma, sodium gates
(or "gated channels") open. For now, don't
worry about what causes this to happen. Sodium
ions, carrying their positive charges, flow into
the cell, making the inner surface of the
sarcolemma more positive. The sarcolemma has
begun to depolarize.
22
A few milliseconds later, potassium gates on
the sarcolemma open as the sodium
gates close. Potassium ions, with their positive
charges, flow out of the cell, again making the
outer surface of the sarcolemma more positive.
The plasma membrane has begun to repolarize.
23
This depolarization / repolarization spreads
along the sarcolemma in all directions away from
the myoneural junction
24
When the signal reaches the openings of
transverse tubules, these carry it deep into the
myocyte
25
As the signal travels along the transverse
tubules, it stimulates the sarcoplasmic reticulum
to release large amounts of calcium ions (Ca)
into the cytoplasm of the myocyte
26
This calcium binds onto troponin of the thin
myofilament which moves
the tropomyosin
to expose active sites on actin Myosin head
groups can now bind to the actin, forming cross
bridges, after which they flex to move the thin
filament
27
These cross-bridges form between myosin molecules
of the thick filaments and actin molecules of the
thin filaments where these overlap in the A-band
28
As long as calcium ions bind to troponin of thin
myofilament, Cross-bridges will continue to
form between thin and thick myofilaments,
so Myocyte will remain contracted
Therefore To make myocyte relax (no
crossbridges form), calcium ions must be removed
from thin myofilaments
But Calcium ions will bind onto thin
myofilaments anytime it is available in cytoplasm
of the myocyte
29
So Relaxation occurs when calcium ions are
removed from the cytoplasm. by being pumped
into the sarcoplasmic reticulum (thus out of the
cytoplasm), where it is not available to bind to
troponin.
Sarcoplasmic reticulum takes up calcium ions only
if no electrical signals are travelling down
transverse tubules which Happens only if the
sarcolemma is not being stimulated by a motor
neuron
30
Quick
Summary Contraction
Relaxation
Motor neuron stimulates sarcolemma of
myocyte Stimulus spreads along sarcolemma into
myocyte through transverse tubules This causes
release of Ca from sarcoplasmic reticulum into
cytoplasm of myocyte Calcium binds to thin
myofilaments Cross-bridges can now form between
thin myofilaments and thick myofilaments
Motor neuron stops stimulating sarcolemma Sarcolem
ma stays polarized Sarcoplasmic reticulum pumps
calcium back into its lumen, removing it from the
cytoplasm Thin myofilaments change shape
Cross-bridges break between thin and thick
myofilaments
31
One motor neuron All myocytes
it innervates
32
Skeletal Muscle
1. Myocytes and muscles always pull (exert force
by contraction), they never push. They
usually, although not always, pull on bone
through a tendon.
2. If a sarcomere shortens, it always does so
completely "All-or-none"
3. All of the sarcomeres in the entire myocyte
shorten at the same time. "All-or-none"
But 4. All of the myocytes in a muscle
don't always contract at the same time.
No "all-or-none"
33
Skeletal Muscle
The total force produced by a myocyte is equal to
the sum of the forces produced by individual
sarcomeres. Thus More sarcomeres more force
The total force produced by a muscle is equal to
the sum of the forces produced by individual
sarcomeres. Thus More myocytes more force
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