anatomy ch 10-11

myology

study of muscles and associated diseases

skeletal muscle tissue

• moves bone

• striated

• voluntary

• NOT auto-rhythmic

• somatic nervous system

cardiac muscle tissue

• in wall of heart= myocardium

• striated

• involuntary

• auto-rhythmic

• autonomy nervous system & hormones (epithelium)

smooth muscle tissue

• in wall of hollow organs

• NOT striated

• involuntary

• auto-rhythmic

• autonomy nervous system & hormones

functions of muscle tissue

• produce body movements

• stabilize body position

• store and move substances within the body

• produce heat

• allow breathing to occur

excitability

to respond to a stimulus and to produce an action potential= nerve impulse= electrical signal

contractability

the ability to stretch w/out being damaged

elastictity

the ability to return to original shape/length after contraction or extension

skeletal muscle tissues

each muscle consists of numerous muscle cells → muscle fibers= myocytes

muscle belly= muscle body

attached to bones by tendons

tendons

a cord of dense regular connective tissue attaching the muscle to the periosteum

aponeuroses

a type of tendon → broad, flat sheet of dense connective tissue

endomsysium

connective tissue surrounding each muscle fiber

perimysium, epimysium

connective tissue that surrounds each muscle fascicle → bundles of muscle fibers

fascia

connective tissue sheets protecting group of muscles

capillaries

carry nutrients and wastes

neuromuscular bundle

includes the muscle fiber, nerves and blood vessels

neuromuscular junction (NMJ)

the connective between the muscle fiber and nerve

somatic motor neurons

send action potentials to stimuli muscle fiber to contract

muscle tone

• sustained, partial state of contraction

• in a constantly shifting pattern, a few motor units become active while others become inactive within skeletal muscle

• essential for maintaining posture

• loss of muscle tone= flaccidity of a skeletal muscle

microscopic anatomy of skeletal muscle / muscle fiber structure

• during embryonic development, a skeletal muscle fiber is formed by fusion of myoblasts and thus the muscle fibers are multinucleate

• skeletal muscle grows by hypertrophy after birth

• skeletal muscle grows by hyperplasia in utero

• skeletal muscles do have some regeneration due to the presence of satellite cells to repair or replace damaged muscle fibers

sarcolemma

• plasmalemma of satellite cells to repair or replace muscle fibers

• transverse tubules= T tubules

transverse tubules= T tubules

tunnel like infoldings that penetrate into the muscle fiber at right angles to myofilaments. these T tubules conduct muscle action potentials which cause the release of calcium ions from sarcoplasmic reticulum

sarcoplasm

• contains myoglobin → a protein that carries oxygen

• contains sarcoplasmic reticulum — with dilated end sacs called terminal cisterns with store Ca2+. the release of Ca2+ into the cytosol triggers muscle contraction

• contains numerous myofibrils

thin filaments

• made up of proteins called actin and 2 regulatory proteins= troponin + tropomyosin

• extends from z disc towards the center of the sarcomere

thick filament

• made up of proteins= myosin

• located in the center of the sarcomere

sarcomere

• basic functional unit of a muscle

• composition: structural proteins that provide elasticity and extensibility

z disc= z line

separate adjacent sarcomeres

A band

• dark, middle part of the sarcomere

• eastenders the entire length of the thick filament

• has overlapping of the thin filament

H zone

• region in the center of each A band

• only contains thick filaments

M line

• the region in the center of each A band

• only contains thick filaments together

I band

• light, less dense area of the sarcomere

• only contains thin filaments

• z disc passes through the center

red muscle fibers

have high content of myoglobin and mitochondria

white muscle fibers

have low content of myoglobin and mitochondria

slow oxidative fibers= type I fibers

use aerobic repiration

fast oxidative fibers= type II A fibers

• aerobic and anaerobic respiration

• type II B fibers → anaerobic respiration

cardiac muscle tissue

• location: heart

• striated

• involuntary muscle

• auto-rhythmic (at own pace)

• branching cylinders w/ usually 1 nucleus

• neighboring fibers are connected by intercalated discs that contain desmosomes & gap junctions

• under normal resting conditions, cardiac muscle tissue rhythically contracts and relaxes about 75 times per min. this rhythm may be increased or decresed by nerve or hormonal stimulation

• permits increase in heart rate, prevents the heart from undergoing tetanus

• hypertrophy (response to increased workload)

desmosomes

strongly hold fibers together

gap junction

allow muscle action potential to spread from 1 fiber to another

smooth muscle tissue

• involuntary

• uninucleate

• narrow fibers with tapering ends

• thick and thin filaments not arranged in orderly sarcomeres → no striations

• in sarcoplasm, contains intermediate filaments attached to dense bodies → function similar to Z disc in striated muscle fibers

• smooth muscle contracts and turns like a corkscrew

• compared to skeletal contraction, smooth muscle contraction starts more slowly and lasts much longer

• prolonged presence of Ca2+ in the cytosol provide smooth muscle tone

• 2 types of smooth muscle tissue (visceral, multi-unit smooth muscle tissue)

• smooth muscle tissue exhibits the stress-relaxation response which allows it to be stretched considerably while still retaining the ability to contract effectively

• smooth muscle fibers can undergo hypertrophy

aging and muscular tissue

• with aging, there is a progressive decrease in skeletal muscle mass that is replaced by fibrous connective tissue and adipose tissue

• decrease in maximum strength and slowing of muscle reflexes

• in some muscles, there is a change in proportions of specific types of skeletal muscle fibers

fibromyalgia

chronic, painful, non-articular rheumatic disorder that affects fibrous connective tissue components of muscles, tendons, and ligaments

electromyography= EMG

test that measures electrical activity (muscle action potentials) in resting and contracting muscles

fasciculation

brief, involuntary twitch of the entire muscle that is visible under the skin

fibrillation

spontaneous contraction of a single muscle fiber that is not visible under the skin but can be recorder by electromyography

myalgia

pain in the muscle

origin and insertion of skeletal muscles

• contractions of the skeletal muscles produce movements by exerting a pulling force on tendons, which in turn pull on bones or other structures

• most muscles extended across at least 1 joint and are attached to articulating bones that form the joint

• when such a muscle contracts, one bone remains relatively stationary where the other moveable bone is pulled toward it

• types of attachments:

  • origin: the attachment of the muscle tendon to the stationary bone

  • insertion: the attachent of the muscle tendon to the movable bone

• during most contractions, the insertion is pulled toward the origin resulting in the observed movement

lever systems and leverage

• produce a body movement

• lever acts on 2 forces: effort, resistance

• leverage is either a mechanical advantage or disadvantage gain by the lever

• the leverage is responsible for muscles’s strength and range of motion → maximum ability to move bones of a joint through an arc

lever

• a rigid structure that moves

• bone

fulcrum

• a fixed point

• joint

effort

• the force exerted to achieve a movement

• muscle contration

load

• the weight that opposes the movement

• the body part that is being moved

first class lever (EFL)

• effort applied at one end

• load is at opposite end

• fulcrum is located between load and effort

• examples include seesaws, scissors, and lifting your head off your chest

second class lever

• effort applied at one end

• fulcrum is at opposite end

• load is located between the effort and fulcrum

• ex: wheelbarrow and standing tiptoe

third class lever (FEL)

• load applied at one end

• fulcrum is at opposite end

• effort is applied between the load and fulcrum

• most skeletal muscles are third class levers

  • fulcrum is the elbow joint

  • effort is exerted on the proximal region of the radius

  • load is the distal part of the antebrachium

effects of fascicle arrangment

• skeletal muscle fibers are arranged within a muscle in bundles called fascicles

• within each fascicles, the fibers are arranged in parallel fashion, but the arrangement of the fascicles with respect to the tendons may take one of the several characteristic patterns

parallel fascicle arrangement

• fascicles run parallel to the longitudinal axis of the muscle

• terminate at either end in flat tendon

• ex: sternohyoid, sternocleidomastoid

fusiform fascicle arrangement

• fascicles nearly parallel to longitudinal axis of the muscle

• terminate in flat tendons

• muscle tapers toward tendons where the diameter is less than the belly

• ex: bicep brachii and digastric muscles

circular fascicle arrangement

• fascicles in concentric circular arrangements form sphincter muscles that encloses an opening or orifice

• sphincter is a general name for a circular muscle

• ex: orbicularis oris and orbicularis oculi muscles

triangular fascicle arrangement

• fascicle spread over broad area coverage at thick central tendon

• gives muscle a triangular appearance

• ex: pectoralis major muscle

pennate fascicle arrangement

• short fascicles in relation to total muscle tendon

• tendon extends nearly entire length of muscle

• 3 types

  • unipennate

  • bipennate

  • multipennate

unipennate

fascicles are arranged on only one side of tendon → ex: extensor digitorum longus muscle

bipennate

fascicles are arranged on both sides of centrally positioned tendons

multipennate

• fascicles attach obliquely from many directions to several tendons

• ex: deltoid muscle

coordination within muscle groups

• most movement require several muscles contracting together

• muscles are arranged in antagonistic pairs at joints

• agonist= prime mover: muscle that causes the desired action

• antagonist: the muscle with the opposite action of the agonist

• synergist:

  • prevents unwanted movements

  • helps the agonist to function more efficiently

• fixator: stabilizes the origin of the agonist → so agonist can act more efficiently

how skeletal muscles are named

• direction of fascicles and muscle fibers

• size

• shape

• action

• number of origins

• location

• origins and insertions

spasm

sudden, involuntary contraction of one or more muscles

cramp

painful, spasmodic contraction caused by inadequate blood flow, overuse of a muscle, injury, holding a position of prolonged periods

tic

spasmodic twitch made involuntarily by muscles that are usually under conscious control such as twitching of an eyelid

muscle strain= muscle pull= muscle tear

tearing of fibers in a skeletal muscle or tendon that attaches the muscle to the bone

paralysis

loss of muscle function through injury, disease, or its nerve supply. most paralysis is due to a stroke or spinal cord injury

frontalis= frontal belly

• origin: epicranial aponeurosis

• insertion: skin superior to supraorbital margin

• facial expression: raises eyebrows and wrinkles the forehead

occipitalis= occipital belly

starts at occipital/temporal bones, ends at epicranial aponeurosis & pulls the scalp posteriorly

orbicularis oculi

• origin: medial wall of the orbit

• insertion: circular path around the orbit

• facial expression: closes the eyes

zygomaticus major

• origin: zygomatic bone

• insertion: skin at the corner of the mouth

• facial expression: draws angle of the mouth superiorly and laterally

zygomaticus minor

starts at zygomatic bone, ends at upper lip & elevates upper lips / exposes upper teeth

levator labii superioris

starts at the maxillary bones, ends at the skin in the corner of mouth & raises the upper lip

risourius

starts at the fascia over the parotid gland, ends at the skin at the corner of the mouth & draws the mouth laterally

depressor labii inferioris

mandible, attached to lower lips & depresses or lowers the lower lips

orbicularis oris

• origin: muscle fibers surrounding the opening of the mouth

• insertion: skin at the corner of the mouth

• facial expression: closes the lips and shapes the lips during speech

temporalis

starts at the temporal bone, ends at the mandible & elevates / retracts the mandible

masseter

• origin: zygomati arch and maxilla

• insertion: mandible

• facial expression: elevates the mandible

buccinator

starts at maxilla/mandible, bends with the fibers of orbicularis oris & draws the corner of the lips laterally / presses the cheeks against the teeth and lips

medial pterygoid

• origin: sphenoid and maxilla

• insertion: mandible

• facial expression: elevates and protracts mandible

lateral pterygoid

• origin: sphenoid

• insertion: mandible

• facial expression: depresses and protracts mandible

platysma

• origin: fascia of the chest

• insertion: mandible and mouth

• facial expression: depresses the mandible

sternocleidomastoid

• origin: sternum and clavicle

• insertion: temporal bone

• facial expression: flexes the head and neck

anterior scalene

• origin: cervical vertebrae 3-6

• insertion: first costa

• facial expression: elevates the ribs, flexes and rotates the neck

middle scalene

starts at cervical vertebrae 2-7, ends at the first costa, elevates the ribs + flexes / rotates the neck

posterior scalene

starts at the cervical vertebrae 4-6, ends at the second costa & elevates the ribs, flexes / rotates the neck

digastric

• origin: mandibular and temporal bones

• insertion: hyoid

• facial expression: elevates the hyoid, opens the mouth and depresses the mandible

stylohyoid

• origin: temporal bone

• insertion: hyoid

• facial expression: elevates and retracts the hyoid

mylohyoid

• origin: mandible

• insertion: hyoid

• facial expression: elevates the hyoid and tongue

sternohyoid

• origin: sternum and clavicle

• insertion: hyoid

• facial expression: depresses the larynx and hyoid

sternothyroid

• origin: sternum

• insertion: thyroid cartilage

• facial expression: depresses the thyroid cartilage

thyrohyoid

• origin: thyroid cartilage

• insertion: hyoid

• facial expression: elevates the thyroid cartilage

pectoralis major

clavicle/sternum/ribs 2-7, attached to humerus & adducts / medially rotates the arm

serratus anterior

• origin: ribs 1-9

• insertion: scapula

• facial expression: abducts and rotates the scapula

deltoid

starts at clavicle / scapula, ends at humerus & abducts / rotates the arm

pectoralis minor

• origin: ribs 2-5

• insertion: scapula

• facial expression: abducts and rotates the scapula