Chapter 10 Muscle Tissue

-mysium

connective tissue

epi

peri

endo

continues with tendons

tendons

connect muscle to bone

sarcolemma

cell membrane of muscle cells

Sarcoplasm

cytoplasm of muscle cells

Sarcomere

functional unit composed of many myofibrils

A-band

Anisotropic band

bends polarized light

overlapping actin & myosin filaments

I-band

Isotropic band

does not bend polarized light

actin filaments only

Z-disc

ends of the sarcomere

titan

elastic protein attaches myosin to Z-disc

M-line

Center of the sarcomere

titan extends from z-disc to m-line

Myosin

Thick filament

anchored to the middle of the sarcomere

Actin

Thin filament

anchored to the ends of the sarcomere

Troponin

Ca²⁺ binding site

Ca²⁺ required for muscle contraction and stored in the sarcoplasmic reticulum

Tropomyosin

Blocks the myosin binding site on actin when muscle is relaxed

T-tubules

allow conduction of neural impulses to travel deep into muscle tissue

When stimulated by a motor neuron…

Calcium is released from sarcoplasmic reticulum

When calcium binds to troponin…

tropomyosin moves from the myosin binding site, leaving it exposed

If the ATP is present then the __________ is formed

cross-bridge

muscle contraction can occur

Troponins Types

1. Troponin C (TnC) - Ca²⁺ binding site

2. Troponin T (TnT) - Binds troponin to tropomyosin

3. Troponin I (TnI) - Binds troponin to actin

COVID-19 characterized by…

non-necrotic broken TnT

Broken TnI (men) up to 14 months after infection

Relaxed state

Not stimulated

Tropomyosin blocks the myosin binding site

Calcium not released

ATP is required for both…

contraction “power stroke” and relaxation

Rigor mortis

No ATP available shortly after death

Myosin head remains attached to actin

Innervation

supply with energy

Muscle At Rest

• No neural impulse

• No release of acetylcholine (Ach; neurotransmitter) from presynaptic neuron

• Skeletal muscle NOT stimulated to contract

Muscle Active

• Impulse travels down presynatic neuron

• Stimulates migration of vesicles with Ach

• Ach released into synaptic cleft

• Ach receptors in sarcolemma are stimulated

• Impule for contraction travels deep into muscle via T-Tubules and Calcium is released from sarcoplasmic reticulum

Proprioceptors

Sensory receptors that signal CNS with information about the muscle

Muscle spindles

Stretch receptors (length) within perimysium that contains a few muscle fibers (intrafusal fibers)

—involved in monosynaptic reflexes (patellar reflex)

—respond to stretch (changes in length)

Golgi Tendon Organs

Enclose sensory axons that penetrate into myotendinous junction and detects changes in tension

inhibits motor neuron action when tension is high

—respond to force, muscle tension

Skeletal Muscle between individuals are different in

number and size of motor neurons

mitochondrial density

capillary density

oxidative and glycolytic capacity

—all influence performance

Type 1 Fibers

• slow contraction time

• small motor neurons

• high resistance to fatigue

• used for aerobic activities

• hours of use

• low power produced

• high mitochondrial density

• high capillary density

• high oxidative capacity

• low glycolytic capacity

• triglycerides is major storage fuel

Type 2a Fibers

• moderately fast contraction time

• medium size of neurons

• fairly high resistance to fatigure

• used for long-term anaerobic activities

• less than 30 mins of use

• medium power produced

• high mitochondrial density

• intermediate capillary density

• high oxidative capacity

• high glycolytic capacity

• creatine phosphate and glycogen for storage fuel

Type 2b Fibers

• very fast contraction time

• very large motor neurons

• low resistance to fatigue

• used for short-term anaerobic activities

• less than 1 min of use

• very high power produced

• low mitochondrial density

• low capillary density

• low oxidative capacity

• high glycolytic capacity

• creatine phosphate, glycogen for storage fuel

Cardiac Muscle

• striated like skeletal muscle

• short 15-30 micrometers in diameter and 85-120 micrometers long

• branched

• mononucleated

• nucleus located in cell center

• thick perimysium surrounds bundles of muscle fibers

• thin endomysium and dense capillary network surrounds each muscle cell

• perimysium + endomysium =cardiac skeleton

• wall thickness between chambers varies

• reflects pulmonary vs systemic pumps

• mitochondria= 40% cell volume

• sarcoplasmic reticulum less organized

• T-tubulues aligned with Z-discs

  • well developed in ventricles (less in atrium)

intercalated discs with desmosomes form…

junctions between myocardial cells

GAP Junctions located…

laterally

Arrangement facilitates…

impulse conduction & simultaneous contraction

Ischemia Reperfusion

1. Loose Adhesion (rolling)

2. firm adhesion/aggregation

3. diapedesis

Smooth Muscle aka Visceral Muscle

• 5-10 micrometers in diameter

• 20 micrometers in length (small vessels) to 500 micrometers (pregnant uterus)

• autonomic control (involuntary)

• No T-Tubules

• GAP Junctions- many synchronous contraction

• contraction similar to skeletal muscle, but is not linear

• organized into two layers (longitudinal and circular)

• found in the walls of hollow organs (except the heart)

Caveoli

ion channels that regulate sarcoplasmic reticulum in smooth muscle

Calmodium (not troponin & tropomyosin)

associated with actin in smooth muscles

Satellite Cells

regenerative cells that are normally inactive

• skeletal= becomes active after injury

• cardiac= lacks satellite cells

• smooth= capable of active regeneration