Estructura del tejido muscular

esquelético.

Configuración de la célula muscular.

Estructura molecular del sarcómero.

Unión neuromuscular y sinapsis

neuromuscular.

Fenómeno de excitación –

Nunca consideres el

estudio como una

obligación, sino

como una

oportunidad para

penetrar en el bello

y maravilloso mundo

del saber.

Nucleus

Muscle fiber

(cell)

Striations

Skeletal muscle

Depósitos

EnergéticosCorrientes

Iónicas

AMP/ATP [Ca2+]i

Switch Metabólico [Utilización de Sustratos

Energéticos]

Expresión Génica [Adaptación Estructurales y

Funcionales]

Contracción Muscular

Vaina de

mielina

Fibra Muscular

La unión neuromuscular

consiste en la sinapsis

entre el botón terminal

del axon y la placa

motora del sarcolema de

la fibra muscular.

Arbolización Terminal

Placa motora

Terminaci

ón

Axonal

Vesícula

s

Sináptic

as

Espaci

o

Sinapti

coMembrana

Postsinápt

ica

Receptores

Nicotínicos

Membrana

Presinapti

ca

Postsynaptic

cell

Synaptic

vesicle

Action

potential

Axon

terminal

An action potential depolarizes

the axon terminal.1

1

Voltage-gated

Ca2+ channel

Postsynaptic

cell

Ca2+

Ca2+

Synaptic

vesicle

Action

potential

Axon

terminal

An action potential depolarizes

the axon terminal.

The depolarization opens voltage-

gated Ca2+ channels and Ca2+

enters the cell.

1

2

1

2

Voltage-gated

Ca2+ channel

Postsynaptic

cell

Ca2+

Ca2+

Docking

protein

Synaptic

vesicle

Action

potential

Axon

terminal

An action potential depolarizes

the axon terminal.

The depolarization opens voltage-

gated Ca2+ channels and Ca2+

enters the cell.

Calcium entry triggers exocytosis

of synaptic vesicle contents.

1

2

3

1

2

3

Voltage-gated

Ca2+ channel

Postsynaptic

cell

Ca2+

Ca2+

Docking

protein

Synaptic

vesicle

Action

potential

Axon

terminal

Receptor

An action potential depolarizes

the axon terminal.

The depolarization opens voltage-

gated Ca2+ channels and Ca2+

enters the cell.

Calcium entry triggers exocytosis

of synaptic vesicle contents.

Neurotransmitter diffuses across

the synaptic cleft and binds with

receptors on the postsynaptic cell.

4

1

2

3

4

1

2

3

Voltage-gated

Ca2+ channel

Postsynaptic

cell

Ca2+

Ca2+

Docking

protein

Synaptic

vesicle

Action

potential

Axon

terminal

Receptor

An action potential depolarizes

the axon terminal.

The depolarization opens voltage-

gated Ca2+ channels and Ca2+

enters the cell.

Calcium entry triggers exocytosis

of synaptic vesicle contents.

Neurotransmitter diffuses across

the synaptic cleft and binds with

receptors on the postsynaptic cell.

Cell

response

Neurotransmitter binding initiates

a response in the postsynaptic

cell.

4

5

1

2

3

4

5

1

2

3

Skeletal muscle

fiber

AChE

Action potential

ACh Acetyl + choline

Nicotinicreceptor

Motor endplate

Somatic motorneuron

Axon terminal

Voltage-gatedCa2+ channel Ca2+

Ca2+

Figure 11-13b

Skeletal muscle

Muscle fascicle:

bundle of fibers

Muscle fiber

Connective tissueConnective tissue

Tendon

Nerve and

blood vessels

Nucleus

II aI

II b

• Fibras I // oscuras // mioglobina y enzimas oxidativas //

• Fibras II // claras // enzimas glicolíticas //

–II a // enzimas glicolíticas y oxidativas //

–II b // enzimas glicolíticas //

FT 1

FT 2 b

FT 2 a

Mitochondria

Myofibril

Thick

filament

Thin

filament

T-tubules

Sarcoplasmic

reticulum

Sarcolemma

Nucleus

Sarcolemma

Thin filament

Thick filament

Triad Terminal

cisterna

T-tubule brings action

potentials into interior

of muscle fiber.

Sarcoplasmic reticulum

stores Ca2+.

Myofibril

(c) A band

Z disk

I bandM line

H zone

Z disk

Sarcomere

SarcomereA band

(a)

I band H zone I band

Z diskZ diskM line

Thick

filament

Thin

filament

Z disk Z disk

Titin

M line

Z disk

M line

Z disk

MyosinTitin provides

elasticity and

stabilizes myosin.

ActinNebulin helps

align actin.

Myosin tail

Myosin heads

Myosin molecule

(e)

Thick filaments

Hinge

region

M line

Thin filaments

Tropomyosin

Troponin

Actin chain

G-actin molecule

(f)Titin

Nebulin

Skeletal muscle

fiber

AChE

Action potential

ACh Acetyl + choline

Nicotinicreceptor

Motor endplate

Somatic motorneuron

Axon terminal

Voltage-gatedCa2+ channel Ca2+

Ca2+

Muscle fiber

Motor end plate

AChAxon terminal of

somatic motor neuron

Sarcoplasmic reticulum

Actin

Troponin

Tropomyosin

Myosin

head

Z disk

Myosin thick filament

M line

T-tubule

DHP

receptor

Ca2+

Somatic motor neuron

releases ACh at neuro-

muscular junction.

(a)

1

1

Muscle fiber

Motor end plate

AChAxon terminal of

somatic motor neuron

Sarcoplasmic reticulum

Actin

Troponin

Tropomyosin

Myosin

head

Z disk

Myosin thick filament

M line

T-tubule

DHP

receptor

Ca2+

Somatic motor neuron

releases ACh at neuro-

muscular junction.

Net entry of Na+ through ACh

receptor-channel initiates

a muscle action potential.

Na+

K+

(a)

potential

1 2

1

2 Action potential

(b)

Action potential in

t-tubule alters

conformation of

DHP receptor.

3

3

Ca2+

Ca2+

Ca2+

released

(b)

Action potential in

t-tubule alters

conformation of

DHP receptor.

DHP receptor opens Ca2+

release channels in

sarcoplasmic reticulum

and Ca2+ enters cytoplasm.

3 4

3

4

Ca2+

Ca2+

released

(b)

Action potential in

t-tubule alters

conformation of

DHP receptor.

DHP receptor opens Ca2+

release channels in

sarcoplasmic reticulum

and Ca2+ enters cytoplasm.

Ca2+ binds to troponin,

allowing strong actin-

myosin binding.

3 4 5

3

4

5

M line

Ca2+

Ca2+

released

Myosin thick filament

(b)

Action potential in

t-tubule alters

conformation of

DHP receptor.

DHP receptor opens Ca2+

release channels in

sarcoplasmic reticulum

and Ca2+ enters cytoplasm.

Ca2+ binds to troponin,

allowing strong actin-

myosin binding.

Myosin heads execute

power stroke.

3 4 5

6

3

4

5

6

M line

Ca2+

Distance actin moves

Ca2+

released

Myosin thick filament

(b)

Action potential in

t-tubule alters

conformation of

DHP receptor.

DHP receptor opens Ca2+

release channels in

sarcoplasmic reticulum

and Ca2+ enters cytoplasm.

Ca2+ binds to troponin,

allowing strong actin-

myosin binding.

Myosin heads execute

power stroke.

Actin filament slides

toward center of

sarcomere.

3 4 5

6 7

3

4

5

6

7

Pi

Pi

ADP

ADP

G-actin moves

Cytosolic Ca2+

Tropomyosin shifts,

exposing binding

site on G-actin

TNTN

Power stroke

TroponinG-actin

Tropomyosin

blocks binding

site on G-actin

Myosin head

(b)(a) Initiation of contractionRelaxed state

Ca2+ levels increase

in cytosol.Ca2+ binds to troponin.

Troponin-Ca2+ complex

pulls tropomyosin away

from G-actin binding site.

Myosin binds to actin and

completes power stroke.

Actin filament moves.

3

4

3 4

1 2

1

2

5

5

PiADP

TN

TroponinG-actin

Tropomyosin

blocks binding

site on G-actin

Myosin head

(a) Relaxed state

PiADP

G-actin moves

Cytosolic Ca2+

Tropomyosin shifts,

exposing binding

site on G-actin

TN

Power stroke

(b) Initiation of contraction

Ca2+ levels increase

in cytosol.Ca2+ binds to troponin.

Troponin-Ca2+ complex

pulls tropomyosin away

from G-actin binding site.

Myosin binds to actin and

completes power stroke.

Actin filament moves.

3

4

3 4

1 2

1

2

5

5

ADP

Cytosolic Ca2+

Ca2+ levels increase

in cytosol.1

1

ADP

Cytosolic Ca2+

TN

Ca2+ levels increase

in cytosol.

Ca2+ binds to

troponin.

1

2

1

2

ADP

Cytosolic Ca2+

Tropomyosin shifts,

exposing binding

site on G-actin

TN

Ca2+ levels increase

in cytosol.

Ca2+ binds to

troponin.

Troponin-Ca2+

complex pulls

tropomyosin

away from G-actin

binding site.

1

2

3

1

2

3

ADP

Cytosolic Ca2+

Tropomyosin shifts,

exposing binding

site on G-actin

TN

Power stroke

Ca2+ levels increase

in cytosol.

Ca2+ binds to

troponin.

Troponin-Ca2+

complex pulls

tropomyosin

away from G-actin

binding site.

Myosin binds

to actin and

completes power

stroke.

1

2

3

4

1

2

3

4

PiADP

G-actin moves

Cytosolic Ca2+

Tropomyosin shifts,

exposing binding

site on G-actin

TN

Power stroke

Ca2+ levels increase

in cytosol.

Ca2+ binds to

troponin.

Troponin-Ca2+

complex pulls

tropomyosin

away from G-actin

binding site.

Myosin binds

to actin and

completes power

stroke.

Actin filament

moves.

1

2

3

4

5

1

2

3

4

5