Chapter 9: Muscular System: Histology and Physiology

skeletal muscle

9.1: Functions of the Muscular System

• attached to bones

• very long and cylindrical

• multinuclear, peripherally located

• striations

• voluntary and involuntary control (reflexes)

• controls body movement

smooth muscle

9.1: Functions of the Muscular System

• walls of hollow organs, blood vessels, eyes, glands, and skin

• spindle-shaped

• uninuclear, centrally located

• gap junctions join some visceral cells together

• involuntary control

• some are capable of spontaneous contraction

• moves food through the digestive tract, empties the urinary bladder, regulates blood vessel diameter, moves hair, etc

cardiac muscle

9.1: Functions of the Muscular System

• located in the heart

• cylindrical and branched

• uninuclear, centrally located

• intercalated disks join cells to one another

• striations

• involuntary control

• capable of spontaneous contraction

• pumping blood; contractions provide the major force for propelling blood through blood vessels

functions of the muscular system

9.1:

• movement of the body

• maintenance of posture

• respiration

• production of body heat

• communication (speaking, gesturing, writing, etc)

• constriction of organs and vessels

• contraction of the heart

contractility

9.2: General Properties of Muscle Tissue

the ability of the muscle to shorten forcefully

excitablity

9.2: General Properties of Muscle Tissue

the capacity of muscle to respond to an electrical stimulus

extensibility

9.2: General Properties of Muscle Tissue

• muscle can be stretched beyond its normal resting length and still be able to contract

• builds contractility

elasticity

9.2: General Properties of Muscle Tissue

the ability of the muscle to recoil to its original size after it has been stretched

connective tissue layers covering skeletal muscle

9.3: Skeletal Muscle Anatomy

• epimysium

• perimysium

• endomysium

muscle fascia

9.3: Skeletal Muscle Anatomy

the layer of connective tissue between adjacent muscles and between muscles and the skin

epimysium

9.3: Skeletal Muscle Anatomy

Fibrous envelope surrounding a skeletal muscle; surrounds muscles

fascicles

9.3: Skeletal Muscle Anatomy

• little groups of muscle fibers that are bundled together

• wrapped in the perimysium

perimysium

9.3: Skeletal Muscle Anatomy

Fibrous sheath enveloping a bundle of skeletal muscle fibers; surrounds fascicles

endomysium

9.3: Skeletal Muscle Anatomy

Fine connective tissue sheath surrounding a muscle fiber; surrounds muscle fibers

tendon

9.3: Skeletal Muscle Anatomy

band or cord of dense connective tissue that connects a muscle to a bone or another structure.

aponeuroses

9.3: Skeletal Muscle Anatomy

a flattened fibrous membrane binding the muscles together or connecting them to other parts of the body such as bone or skin

muscle fiber

9.3: Skeletal Muscle Anatomy

muscle cell

myoblasts

9.3: Skeletal Muscle Anatomy: Fibers

Primitive, multinucleated cell with the potential to develop into a muscle fiber

striated

9.3: Skeletal Muscle Anatomy: Fibers

Striped; marked by stripes or bands

hypertrophy

9.3: Skeletal Muscle Anatomy: Fibers

an increase in the size or volume of muscles due to the enlargement of individual cells

two main aspects to muscle contraction

9.3: Skeletal Muscle Anatomy: Fibers

• an electrical component

• a mechanical component

electrical component structures

9.3: Skeletal Muscle Anatomy: Fibers

• sarcolemma

• Transverse tubules (T tubules)

• sarcoplasmic reticulum

sarcolemma

9.3: Skeletal Muscle Anatomy: Fibers ⚡

The plasma membrane of a muscle fiber; an electrical component

Transverse tubules (T tubules)

9.3: Skeletal Muscle Anatomy: Fibers ⚡

• injection point for the sarcoplasmic reticulum to get its contents (calcium) into the cell

• conduct action potentials deep into the muscle fiber

• an electrical component

sarcoplasmic reticulum

9.3: Skeletal Muscle Anatomy: Fibers⚡

• Endoplasmic reticulum of muscle; an electrical component

• storage and release of calcium ions

triad

9.3: Skeletal Muscle Anatomy: Fibers⚡

Two terminal cisternae (sarcoplasmic reticulum) and a T tubule between them

sarcoplasm

9.3: Skeletal Muscle Anatomy: Fibers

The cytoplasm of a muscle fiber, excluding the myofilaments.

mechanical component structures

9.3: Skeletal Muscle Anatomy: Fibers

• myofibrils

• myofilaments

myofibrils

9.3: Skeletal Muscle Anatomy: Fibers ⚙

• bundles of protein filaments

• each muscle fiber has many of these in its sarcoplasm

• long threadlike structures extending the entire length of the muscle fiber

• protein filaments in this interact to shorten the muscle fiber during contraction

myofilaments

9.3: Skeletal Muscle Anatomy: Fibers ⚙

Extremely fine molecular thread helping form the myofibrils of muscle; thick [term] are formed of myosin, and thin [term] are formed of actin

actin myofilaments

9.3: Skeletal Muscle Anatomy: Fibers ⚙

• Thin filament of muscle fibrils

• composed primarily of the protein actin

• found in the sarcomeres

myosin myofilaments

9.3: Skeletal Muscle Anatomy: Fibers ⚙

• Thick filament of muscle fibrils

• composed of myosin molecules

• found in the sarcomeres

sarcomeres

9.3: Skeletal Muscle Anatomy: Fibers ⚙

• structural and functional contractile unit of the skeletal muscle fiber.

• Part of a myofibril between adjacent Z disks

• Each one is composed of two main protein filaments—actin and myosin

titin filaments

9.3: Skeletal Muscle Anatomy: Sarcomeres

links thin filaments to Z disks

Z disks

9.3: Skeletal Muscle Anatomy: Sarcomeres

Delicate, membranelike structure found at each end of a sarcomere to which actin myofilaments attach

I band

9.3: Skeletal Muscle Anatomy: Sarcomeres

• The area between the ends of two adjacent myosin myofilaments within a myofibril

• Z disk divides this into two equal parts.

A band

9.3: Skeletal Muscle Anatomy: Sarcomeres

• Length of the myosin myofilament in a sarcomere

• the darker-staining band in the center of each sarcomere

• contains both actin and myosin myofilaments overlapping, except in the center of the [term]

H zone

9.3: Skeletal Muscle Anatomy: Sarcomeres

• area in the center of the A band in which there are no actin myofilaments

• contains only myosin

• only found in relaxed muscle

M line

9.3: Skeletal Muscle Anatomy: Sarcomeres

The line in the center of a sarcomere made of delicate filaments that hold the myosin myofilaments in place in the sarcomere of muscle fibers.

myosin head

9.3: Skeletal Muscle Anatomy: Actin Myofilaments

the part of a myosin molecule that binds to actin filaments and generates force for muscle contraction

G actin (active sites)

9.3: Skeletal Muscle Anatomy: Actin Myofilaments

Globular protein molecules that, when bound together, form fibrous actin (F actin)

tropomyosin

9.3: Skeletal Muscle Anatomy: Actin Myofilaments

chain that goes across the surface of the actin sites, not allowing the myosin heads to hook up with the actin

troponin

9.3: Skeletal Muscle Anatomy: Actin Myofilaments

the padlock that holds the tropomyosin (chain) in place

calcium

9.3: Skeletal Muscle Anatomy: Actin Myofilaments

• released by the sarcoplasmic reticulum

• injected through the T tubules, into the myofibrils

• this mineral then binds to troponin and unlocks it, which removes tropomyosin from the actin sites, allowing the myosin heads to connect to the actin site to form a cross-bridge and undergo a power stroke, which pulls the z disks closer to the M line

sliding filament model

9.3: Skeletal Muscle Anatomy: Fibers

explains how muscles contract at a cellular level, describing the process where thin actin filaments slide past thick myosin filaments within a muscle fiber, causing the muscle to shorten and generate force, powered by the energy from ATP molecules

resting membrane potential (RMP)

9.4: Skeletal Muscle Fiber Physiology

The electric charge difference inside a plasma membrane is measured relative to just outside the plasma membrane.

ion channels

9.4: Skeletal Muscle Fiber Physiology

act as selective pores in the cell membrane, allowing specific ions to flow in and out of the cell, which in turn creates electrical changes across the membrane that form the basis of a nerve impulse

action potential

9.4: Skeletal Muscle Fiber Physiology

• occurs when the excitable cell is stimulated

• reversal of the resting membrane potential such that the inside of the plasma membrane becomes positively charged compared with the outside

• a rapid change in the electrical charge of a muscle cell's membrane that triggers contraction

action potential phases

9.4: Skeletal Muscle Fiber Physiology

depolarization and repolarization

depolarization phase

9.4: Skeletal Muscle Fiber Physiology

• phase of the action potential in which the membrane potential moves toward zero, or becomes positive.

• occurs when there is a rapid influx of sodium ions into the plasma membrane

repolarization phase

9.4: Skeletal Muscle Fiber Physiology

Phase of the action potential in which the membrane potential moves from its maximum degree of depolarization toward the value of the resting membrane potential

all-or-none principle

9.4: Skeletal Muscle Fiber Physiology

When a stimulus is applied to a cell, an action potential is either produced or not. In muscle cells, the cell either contracts to the maximum extent possible (for a given condition) or does not contract.

neuromuscular junction (NMJ)

9.4: Skeletal Muscle Fiber Physiology

• Specialized synapse between a motor neuron and a muscle fiber.

• consists of a group of enlarged axon terminals (the end of the axon) that rests in an invagination of the sarcolemma, this contact results in an action potential

• the stimulus for the action potential is the release of acetylcholine from the motor neuron

synaptic cleft

9.4: Skeletal Muscle Fiber Physiology

the fluid-filled space between a neuromuscular junction

excitation-contraction coupling

9.4: Skeletal Muscle Fiber Physiology

• occurs at the triad

• links the electrical component of muscle contraction to the mechanical component

• the link between an action potential on the sarcolemma and the sarcomere shortening

cross-bridge movement

9.4: Skeletal Muscle Fiber Physiology

• the mechanical component of muscle contraction

• causes sarcomeres to shorten and the muscles to contract

• requires energy from one ATP molecule for each cycle

• before each cycle, the myosin head is in its resting (high-energy) position

• the myosin heads connecting to the actin sites

• [study this image]

muscle relaxation

9.4: Skeletal Muscle Fiber Physiology

• occurs when acetylcholine is no longer released at the neuromuscular junction

• calcium ions are transported into the sarcoplasmic reticulum

muscle twitch

9.5: Whole Skeletal Muscle Physiology

Contraction of a whole muscle in response to a stimulus that causes an action potential in one or more muscle fibers.

force of contraction

9.5: Whole Skeletal Muscle Physiology

• a stimulus of increasing frequency increases the…?

• Treppe

treppe

9.5: Whole Skeletal Muscle Physiology

Series of successively stronger contractions that occur when a rested muscle fiber receives closely spaced stimuli of the same strength but with a sufficient stimulus interval to allow complete relaxation of the fiber between stimuli.

wave summation

9.5: Whole Skeletal Muscle Physiology

• results when many action potentials are produced in a muscle fiber

tetanus of muscles

9.5: Whole Skeletal Muscle Physiology

results from wave summation; frequency of stimulus is higher than for treppe

incomplete tetanus

9.5: Whole Skeletal Muscle Physiology

occurs when the action potential frequency is low enough to allow partial relaxation of the muscle fibers

complete tetanus

9.5: Whole Skeletal Muscle Physiology

occurs when the action potential frequency is high enough that no relaxation of the muscle fibers occurs

active tension

9.5: Whole Skeletal Muscle Physiology

• tension is produced by the contraction of a muscle

• as the length of a muscle fiber increases, its [term term] also increases. If stretched passed optimal length, it declines

isometric contractions

9.5: Whole Skeletal Muscle Physiology

• a muscle produces increasing tension as it remains at a constant length

• this is a characteristic of postural muscles that maintain a constant tension without changing their length

isotonic contractions

9.5: Whole Skeletal Muscle Physiology

• a muscle produces a constant tension and shortens during contraction

• this is a characteristic of finger and hand movements

• includes concentric and eccentric contractions

  • concentric - a muscle produces tension as it shortens

  • eccentric - a muscle produces tension as it resists lengthening

slow twitch muscle fibers

9.6: Muscle Fiber Types

• a type of muscle fiber that breaks down ATP slowly and have well-developed blood supply, many mitochondria, and myoglobin

• muscle fibers used for mundane, simple tasks

• dark meat

fast twitch muscle fibers

9.6: Muscle Fiber Types

• break down ATP rapidly,

• for powerful movements

• white meat

  • Type IIa muscle fibers have a well-developed blood supply, more mitochondria, and more myoglobin

  • Type IIx muscle fibers have large amounts of glycogen, poor blood supply, fewer mitochondria, and little myoglobin

four sources of energy for ATP production in muscles

9.6: Muscle Fiber Types

1. conversion of two ADP to one ATP and one adenosine monophosphate (AMP) by the enzyme adenylate kinase

2. Transfer of phosphate from a molecule called creatine phosphate by the enzyme creatine kinase from ADP to form ATP

3. Anaerobic production of ATP during intensive short-term exercise

4. Aerobic production of ATP during most exercise and normal conditions