Chapter 10&11

Muscular

Tissue

• Like nervous tissue, muscles are excitable or "irritable”– they have the ability to respond to a stimulus

• Unlike nerves, however, muscles are also:

– Contractible (they can shorten

in length)

– Extensible (they can extend or

stretch)

– Elastic (they can return to their

original shape)

Functions of Muscular Tissue

Location Function Appearance Control

Skeletal

skeleton

movement,

heat,

posture

striated, multi-

nucleated

(eccentric), fibers

parallel

voluntary

Cardiac

heartpump blood

continuously

striated, one

central nucleus

involunta

ry

Visceral

(smooth

muscle)

G.I. tract,

uterus, eye,

blood

vessels

Peristalsis,

blood

pressure,

pupil size,

erects hairs

no striations,

one central

nucleus

involunta

ry

Three Types of Muscular Tissue

• Muscle makes up a large percentage of the body’s weight

• Their main functions are to:

– Create motion – muscles work with nerves, bones, and

joints to produce body movements

– Stabilize body positions and maintain posture

– Store substances within the body using sphincters

– Move substances by peristaltic contractions

– Generate heat through thermogenesis

Functions of Muscular Tissue

(b) Cardiac muscle (c) Visceral smooth muscle

(a) Skeletal muscle

Three Types of Muscular Tissue

Location Function Appearance Control

Skeletal

skeleton

movement,

heat,

posture

striated, multi-

nucleated

(eccentric), fibers

parallel

voluntar

y

Cardiac

heartpump blood

continuously

striated, one

central nucleus

involunta

ry

Visceral

(smooth

muscle)

G.I. tract,

uterus, eye,

blood

vessels

Peristalsis,

blood

pressure,

pupil size,

erects hairs

no striations,

one central

nucleus

involunta

ry

Skeletal Muscle

Skeletal Muscle

Skeletal muscle fibers are very long “cells” -

next to neurons (which can be over a meter

long),

perhaps the longest in the body

The Sartorious muscle contains

single fibers that are at least

30 cm long

A single skeletal muscle fiber

Skeletal Muscle

Sarcolemma

Motor neuron

The terminal processes of a

motor neuron in close proximity

to the sarcolemma of a skeletal

muscle fiber

Skeletal Muscle

• In groups of muscles the

epimysium continues to

become thicker, forming

fascia which covers many

muscles

• This graphic shows the

fascia lata enveloping the

entire group of quadriceps

and hamstring muscles in

the thing

Organization of Muscle Tissue


Organization of a single muscle

belly

Epimysium

Perimysium

Organization of a fasciculus


Organization of a muscle fiber


A muscle, a fasciculus, and a fiber all visualized


• An aponeurosis is

essentially a thick

fascia that connects two

muscle bellies. This

epicranial aponeurosis

connects the muscle

bellies of the occipitalis

and the frontalis to form

“one” muscle: The

occipitofrontalis

Epicranial aponeurosis

Frontal belly of the occipitofrontalis m.


Veins, arteries, and nerves are located in the

deep fascia between muscles of the thigh.


You should learn the names of the internal

structures of the muscle fiber

Sarcolemma

Sarcoplasm

T-tubules

Triad (with

terminal cisterns

Sarcoplasmic reticulum

Sarcomere

Myofibril

The Skeletal Muscle Fiber


Increasing the level of magnification, the

myofibrils are seen to be composed

of filaments

Thick filaments

Thin filaments

A scanning electron micrograph of a

sarcomere

• The basic functional unit of skeletal muscle fibers

is the sarcomere: An arrangement of thick and thin

filaments sandwiched between two Z discs


The “Z line” is really a Z disc when considered in

3 dimensions. A sarcomere extends from Z disc

to Z disc.

• Muscle contraction occurs in the sarcomeres


• Myofibrils are built from three groups of proteins

– Contractile proteins generate force during contraction

– Regulatory proteins help switch the contraction process

on and off

– Structural proteins keep the thick and thin filaments in

proper alignment and link the myofibrils to the

sarcolemma and extracellular matrix

Muscle Proteins

• The thin filaments are comprised mostly of the structural protein actin, and the thick filaments are comprised mostly of the structural protein myosin

• However, in both types of filaments, there are also other structural and regulatory proteins

Muscle Proteins

• In the thin filaments actin proteins are strung

together like a bead of pearls

• In the thick filaments myosin proteins look

like golf clubs bound together

Muscle Proteins

In this first graphic, the myosin binding sites on

the actin proteins are readily visible.

The regulatory proteins troponin and

tropomyosin have been added to the bottom

graphic: The myosin binding sites have been

covered

Muscle Proteins

In this graphic the troponin-tropomyosin

complex has slid down into the “gutters” of the

actin molecule unblocking the myosin binding

site

The troponin-tropomyosin complex can slide

back and forth depending on the presence of

Ca2+

Myosin binding site exposed

Muscle Proteins

• Ca2+ binds to troponin which changes the shape of the

troponin-tropomyosin complex and uncovers the myosin

binding sites on actin

Muscle Proteins

• Besides contractile and regulatory proteins,

muscle contains about a dozen structural

proteins which contribute to the alignment,

stability, elasticity, and extensibility of

myofibrils

• Titan is the third most plentiful protein in

muscle, after actin and myosin - it extends

from the Z disc and accounts for much of the

elasticity of myofibrils

• Dystrophin is discussed later as it relates to

the disease of muscular dystrophy

Muscle Proteins

• With exposure of the myosin binding sites on actin (the thin

filaments)—in the presence of Ca2+ and ATP—the thick and

thin filaments “slide” on one another and the sarcomere is

shortened

The Sliding-Filament Mechanism

• The “sliding” of actin on myosin (thick filaments on thin

filaments) can be broken down into a 4 step process


• Step 1: ATP hydrolysis

• Step 2: Attachment

• Step 3: Power Stroke

• Step 4: Detachment

The brain

The motor neuron

Acetylcholine (ACh)

Acetylcholinesterase

enzyme

Ach receptors on the

motor endplate

Na+-K+ channels on the

sarcolemma

Na+ flow

K+ flow

Regenerate AP

The T-tubules

The SR

Ca2+ release

Troponin/

Tropomyosin

ATP

Myosin binding

Filaments slide

Muscles contract

Role Players in E-C

coupling

Excitation-Contraction Coupling

Excitation-Contraction Coupling• EC coupling involves putting it all together

– The thought process going on in the brain

– The AP arriving at the neuromuscular junction

– The regeneration of an AP on the muscle membrane

– Release of Ca2+ from the sarcoplasmic reticulum

– Sliding of thick on thin filaments in sarcomeres

– Generation of muscle tension (work)

• Excitation-Contraction coupling (EC coupling)

involves events at the junction between a motor

neuron and a skeletal muscle fiber

Neuromuscular Junction

• An enlarged view of the neuromuscular

junction– The presynaptic membrane is on the neuron while the postsynaptic

membrane is the motor end plate on the muscle cell. The two membranes

are separated by a space, or “cleft”


• Conscious thought (to move a muscle) results in activation of a motor neuron, and release of the neurotransmitter acetylcholine (AcCh) at the NM junction

• The enzyme

acetylcholinesterase

breaks down AcCh

after a short period

of time


• The plasma membrane on the “far side” of the NMJ belongs

to the muscle cell and is called the motor end plate

• The motor end plate is rich in chemical (ligand) - gated

sodium channels that respond to AcCh. Another way to say

this: The receptors for AcCh are on the ligand-gated sodium

channels on the motor end plate


• The chemical events at the NMJ transmit the electrical

events of a neuronal action potential into the electrical

events of a muscle action potential


Limited contact between actin and myosin

Compressed thick

filaments

Length-Tension Relationship• Sarcomere shortening produces tension within a

muscle

Sources of Muscle Energy• Stored ATP

– 3 seconds

• Energy transferred from stored creatine phosphate

– 12 seconds

• Aerobic ATP production

• Anaerobic glucose use

– 30-40 seconds

Sources of Muscle Energy

• In a state of homeostasis, muscle use of O2 and

nutrients is balanced by the production of manageable

levels of waste products like

– CO2

– Heat - 70-80% of the energy used by muscles is lost as

heat - muscle activity is important for maintaining body

temperature

– Lactic acid (anaerobic)

Skeletal Muscle Metabolism

• Oxygen Debt, or "Excess Post-Exercise Oxygen Consumption" (EPOC) is the amount of O2 repayment required after exercise in skeletal muscle to: – Replenish ATP stores– Replenish creatine phosphate and

myoglobin stores– Convert lactic acid back into pyruvate

so it can be used in the Krebs cycle to replenish ATP


Cardiac and Smooth Muscle Metabolism• In response to a single AP, cardiac muscle

contracts 10-15 times longer than skeletal muscle,

and must continue to do so, without rest, for the

life of the individual

• To meet this constant demand, cardiac muscle

generally uses the rich supply of O2 delivered by

the extensive coronary circulation to generate ATP

through aerobic respiration

Cardiac and Smooth Muscle Metabolism

• Like cardiac muscle, smooth muscle (in your deep

organs) is autorhythmic and is not under

voluntary control (your heart beats and your

stomach digests without you thinking about it).

• Unlike cardiac (and skeletal muscle) however,

smooth muscle has a low capacity for generating

ATP and does so only through anaerobic

respiration (glycolysis)

• Motor Unit is composed of a motor neuron plus all of the

muscle cells it innervates

• High precision

– Fewer muscle fibers per neuron

– Laryngeal and extraocular muscles (2-20)

• Low precision

– Many muscle fibers per neuron

– Thigh muscles (2,000-3,000)

The Motor Unit

Florescent dye is used to show the terminal

processes of a single neuron which terminate on a

few muscle fibers

The Motor Unit

• All-or-none principle of muscle contraction

– When an individual muscle fiber is stimulated to

depolarization, and an action potential is

propagated along its sarcolemma, it must contract

to it’s full force—it can’t partially contract

– Also, when a single motor unit is recruited to

contract, all the muscle fibers in that motor unit

must all contract at the same time

The Motor Unit

• A twitch is recorded when a stimulus that results in

contraction (force) of a single muscle fiber is

measured over a very brief millisecond time frame

Tension in a Muscle

• Applying increased numbers of action potentials to a muscle

fiber (or a fascicle, a muscle, or a muscle group) results in

fusion of contractions (tetanus) and the performance of

useful work

Tension in a Muscle

• Two motor units, one in green, the other in purple,

demonstrate the concept of progressive activation of a

muscle known as recruitment

– Recruitment allows a muscle to accomplish increasing

gradations of contractile strength

Tension in a Muscle

Muscle Contraction• Isotonic contractions results in movement

– Concentric isotonic is a type of muscle contraction in which

the muscle shorten while generating force

– Eccentric isotonic is a contraction in which muscle tension is

less than the resistance (the muscle lengthens)

• Isometric contractions results in no movement

– Muscle force and resistance are equal

– Supporting objects in a fixed position and posture

Muscle Contraction

• Skeletal muscle fibers are not all alike in appearance or

function. By appearance:

– Red muscle fibers (the dark meat in chicken legs) have a

high myoglobin content, more mitochondria, more energy

stores, and a greater blood supply

– White muscle fibers (the white meat in chicken breasts)

have less myoglobin, mitochondria, and blood supply

Skeletal Muscle Fiber Types

• Slow oxidative fibers (SO) are small, appear dark red, are

the least powerful type. They are very fatigue resistant

– Used for endurance like running a marathon

• Fast oxidative-glycolytic fibers (FOG) are intermediate in

size, appear dark red, and are moderately resistant to

fatigue. Used for walking

• Fast glycolytic fibers (FG) are large, white, and powerful

– Suited to intense anaerobic activity of short duration


Smooth Muscle

• Cells are not striated• Fibers smaller than those in skeletal

muscle• Spindle-shaped; single, central

nucleus• More actin than myosin• No sarcomeres

– Not arranged as symmetrically as in skeletal muscle, thus NO striations.

• Dense bodies instead of Z disks – Have non contractile

intermediate filaments

Smooth Muscle• Grouped into sheets in walls of hollow organs

• Longitudinal layer – muscle fibers run parallel to organ’s long axis

• Circular layer – muscle fibers run around circumference of the organ

• Both layers participate in peristalsis

Smooth Muscle

• Visceral or unitary smooth muscle– Only a few muscle fibers innervated in each group– Impulse spreads through gap junctions

• Multiunit: – Cells or groups of cells act as independent units– Arrector pili of skin and iris of eye

Cardiac Muscle• Found only in heart where it forms a thick layer called

the myocardium• Striated fibers that branch• Each cell usually has one centrally-located nucleus• Fibers joined by intercalated disks

– IDs are composites of desmosomes and gap junctions– Allow excitation in one fiber to spread quickly to adjoining fibers

• Under control of the ANS (involuntary) and endocrine system (hormones)

• Some cells are autorhythmic– Fibers spontaneously contract (aka Pacemaker cells)

Cardiac Muscle Tissue

Disorders of Muscle Tissue

• Muscular dystrophy – a group of inherited muscle destroying disease– Affected muscles enlarge with fat and

connective tissue – Muscles degenerate

• Types of muscular dystrophy– Duchenne muscular dystrophy – Myotonic dystrophy

Disorders of Muscle Tissue

• Myofascial pain syndrome – pain is caused by tightened bands of muscle fibers

• Fibromyalgia – a mysterious chronic-pain syndrome– Affects mostly women– Symptoms – fatigue, sleep abnormalities,

severe musculoskeletal pain, and headache

Developmental Aspects: Regeneration

• Cardiac and skeletal muscle become amitotic, but can lengthen and thicken

• Myoblast-like satellite cells show very limited regenerative ability

• Cardiac cells lack satellite cells• Smooth muscle has good regenerative ability• Women’s skeletal muscle makes up 36% of their

body mass• Men’s skeletal muscle makes up 42% of their body

mass

Developmental Aspects: Male and Female

• These differences are due primarily to the male sex hormone testosterone

• With more muscle mass, men are generally stronger than women

• Body strength per unit muscle mass, however, is the same in both sexes

Developmental Aspects: Age Related

• With age, connective tissue increases and muscle fibers decrease

• Muscles become stringier and more sinewy• By age 80, 50% of muscle mass is lost

(sarcopenia)• Decreased density of capillaries in muscle• Reduced stamina• Increased recovery time• Regular exercise reverses sarcopenia

• Exercise-induced muscle damage– After intense exercise electron micrographs

reveal considerable muscle damage including torn sarcolemmas and disrupted Z-discs

– Blood levels of proteins normally confined only to muscle (including myoglobin and the enzyme creatine kinase) increase as they are released from damaged muscle

Imbalances of Homeostasis

• Spasm

– A sudden involuntary contraction of a single muscle within

a large group of muscles – usually painless

• Cramp

– Involuntary and often painful muscle contractions

– Caused by inadequate blood flow to muscles (such as in

dehydration), overuse and injury, and abnormal blood

electrolyte levels


• Disease States and Disorders– Fibrosis (myofibrosis)

• Replacement of muscle fibers by excessive amounts of connective tissues (fibrous scar tissue)

– Myosclerosis• Hardening of the muscle caused by calcification

– Both myosclerosis and muscle fibrosis occur as a result of trauma and various metabolic disorders


• Aging– In part due to decreased levels of physical

activity, with aging humans undergo a slow, progressive loss of skeletal muscle mass that is replaced largely by fibrous connective tissue and adipose tissue

– Muscle strength at 85 is about half that at age 25

– Compared to the other two fiber types, the relative number of slow oxidative fibers appears to increase


Naming Muscles

• Location

– tibialis anterior

Tibialis anterior

• Size

– gluteus maximus

• Number of

Attachments

o biceps; triceps

Naming Muscles

• Location/Direction of

Fibers

– transversus abdominus

Naming Muscles

• Attachments

(origin &

insertion)

o sternocleidomas

toid

Naming Muscles

Styloid process

Hyoid bone

• Muscle action

– levator scapulae

– adductor magnus

– tensor tympani

Naming Muscles

Levator scapulae

• Combination of above– Fibularis longus

Naming Muscles

Chapter 10&11

Science

Transcript of Chapter 10&11