Skeletal Muscles

What are the 3 primary tissue types found in muscles

• Cardiac muscle (heart)

• Smooth muscle - walls of hollow organs

• Skeletal muscle - makes up half of the nody’s mass and most muscle in the body

4 Properties of Muscle Tissue

• Excitability

• Contractility

• Extensibility

• Elasticity

Excitability

• muscle cells can respond to signals that are sent from the nervous system, allowing them to generate electrical impulses and leading to muscle contractions.

Contractility

• muscles can contract, so this allows for the muscle fibres to shorten and it generate force, and that’s what causes movement

Extensibility

• muscles can also stretch, so this is important for the muscle to be able to extend its fibres.

Elasticity

this allows the muscle to return to their original shape and length after theyve been stretched out or contracted

Primary Function of Muscle Tissue

• movement

• Posture and Stability

• Heat Production

• Support and protection

• Control of openings

What percentage of body mass is made up of skeletal muscles?

Skeletal muscles make up about 40% of body weight

How do muscle cells respond to signals from the nervous system?

Muscle cells respond to signals from the nervous system, which triggers electrical impulses and leads to muscle contraction

4 components to the skeletal muscles

• Skeletal muscle tissue

• Connective tissue

• Blood vessels

• Nerves

Skeletal muscle

• attach to the bony skeleton

• Produced movement

• Each muscle is an organ

Muscle structure Components and what they are

• Muscle: a bundle of fascicles

• Fascicles: bundles of muscle fibres and they’re wrapped in a layer called perimysium

• Muscle fibre: bundles of myofibrils. They are long, contract and what creates movement

• Myofibril: responsible for contraction

  • Actin & Myosin are proteins found in myofibril

Structural Connective tissue compnents

• Epimysium

• Perimysium

• Endomysium

• Bone

• Tendon

• Fascia

Epimysium

a dense regular connective tissue around the entire muscle and in the outer layer

Perimysium

a fibrous connective tissue around each fascicle

Endomysium

a fine connective sheath around each muscle fibre on the inside

Bone

a framework for muscle attachment and enables movement

Fascia

a connective layer surrounding muscles and organs and provides support

Support Systems for Muscle

• Nerves

• Blood vessel

Nerves

transmit electrical signals to muscle fibres and trigger contractions

Blood vessel

delivers oxygen and nutrients and removes waste

Innervation of skeletal Muscle

• Motor neurons

• Neuromuscular junction

• axon terminal’

• Synaptic cleft

Motor Neurons

innervate the skeletal muscle tissue

Neuromuscular junction

where nerve ending meets muscle fiber

Axon terminal

stores neurotransmitters

Synaptic cleft

the space between the axon terminal and sarcolemma

What three factors influence muscle action?

• Fascicle arrangement

• lever mechanics

• muscle position relative to the joint

Fascicles arrangement in circular muscles

• Fascicles are arranged in concentric rings

• surrounding external body openings (sphincter)

Examples of circular muscles

Orbicularis oris and orbicularis oculi

How do circular muscles function?

They work like a drawstring; when they relax, the opening gets larger, and when they contract, it closes

What are the types of Fascicle Arrangement

• circular

• convergent

• parallel

• Pennate

Fascicle Arrangement on Convergent muscles

• Broad origin, with fascicles converging toward the tendon of insertion

• ex: pectoralis major

Fascicle Arrangement in Parallel muscles

Fascicles run along the muscle’s long axis

2 types of Parallel muscle

• Fusiform: biceps

• Straplike: supinator

Fascicle Arrangement in Pennate Muscle

Fascicles are arranged on an angle to a central tendon and run through the middle of the msucle

3 types of Pennate Muscle

• Unipennate

• Bipennate

• Multipennate

Unipennate

the fascicle insert into one side of tendon

Bipennate

inserts on both sides

Multipennante

the fasicles inserts into tendon from all sides

Origins & Insertions

• Origin: less movable attachment

• Insertion: more movable attachment

most skeletal muscles span between two bones

Muscle Attachment

• muscles are attached by connective tissue

• There are direct and Indirect attachments

Direct Attachment

Connective tissue fuses to the bone

Indirect attachment

Connective tissue forms a tendon or aponeurosis

Aponeurosis

a sheet of pearly white fibrous tissue that takes the place of a tendon in flat muscles having a wide area of attachment.

Ligaments

Connects bone to bone

Tendon

Connects muscle to bone

4 Lever System

• lever - a rigid bar that moves

• fulcrum- a fixed point

• effort - applied force

• load - resistance

Function of Levers

• move a heavier load

• move a load farther

What is the mechanical advantage of levers?

effort arm > (longer) load arm

• make it easy to lift heavier things

What are the mechanical disadvantage of levers?

effort arm is < load arm

What are the lever systems in the body?

• Bones: levers

• Joints: fulcrums

• Muscle contraction: provides effort at muscle

• Load: body part moved

Describe a first-class lever

• effort at one end and load at the other

• Fulcrum between load and effort.

  • Depending on where the fulcrum is it can either cause a mechanical advantage or disadvantage

Examples of a First-Class lever

seesaws, scissors, lifting your head of your chest

Describe the Second-Class Lever

• Effort at one end and Fulcrum at the other

• The load is between the effort and fulcrum

• a Mechanical advantage

Example of Second-class Lever

• wheelbarrow

• standing on your tiptoe

Describe a Third-Class Lever

• Effort is closer to the fulcrum than the load

• Fast

• Always at a mechanical disadvantage

Examples of Third-Class lever

• biceps brachii

Muscle Action and Interactions

• muscles can’t reverse their own movements

• Require opposing muscles

  • Muscles with opposite action on opposite sides of a joint

Roles in Muscle Movement

• Prime mover (agonist)- a major role in the movement

• Antagonist- opposes or reverses movement

• Synergist - helps prime mover, and adds force or reduces unwanted movement

• Fixator: sygernist that stabilizes

Prime mover

• a major role in the movement

• has an opposing muscle compartment with the antagonist

Antagonist

opposes or reverses the movement

• has an opposing muscle compartment with an agonist

Synergist

helps prime mover and adds force or reduces unwanted movement

• has the same muscle compartment

Fixator

synergist that stabilizes the bone

Example of the prime mover and Antagonist

When you bend your elbow the biceps brachii contracts, So it lifts the forearm, That makes It the prime mover for the action. While we're bending our elbow, the triceps brachii acts as the antagonist. So it's responsible for straightening that elbow, and it has to be relaxed for

the bicep to be able to bend.

Limb Muscles

• Extensors - dorsal to limb bones

• Flexors - ventral to limb bones

Extensor and Flexor in the Upper limb

Extensors are posterior and Flexors are anterior

Extensors and Flexors in the Lower limb

Extensors are anterior, and flexors are posterior

What divides limb muscles into compartments?

Dense connective tissue

4 Muscle Compartments of the Upper Limb

• Anterior arm component

• Anterior forearm compartment

• Posterior arm compartment

• Posterior forearm compartment

Anterior arm Component

• Flexes shoulder/arm

• Innervation is the musculocutaneous nerve

Anterior forearm compartment

• Flexes wrist and digit

• The Innervation is the median and ulnar nerve

Posterior Arm compartment

• Extends the elbow

• Innervation is the radial nerve

Posterior Forearm Compartment

• Extends the wrist and digits

• Innervation is the radial nerve

3 Muscle Compartments of the Thigh

• Posterior compartment

• Anterior Compartment

• Medial Compartment

Posterior Compartment of the thigh

• Extends the hip and Flexes the knee

• Innervation is the tibial branch of the sciatic nerve

Anterior Compartment of the thigh

• Flexes the hip and extend the knee

• Innervation in the femoral nerve

Medial Compartment of the thigh

• Adduct Thigh

• Innervation is the obturator nerve

3 Muscle Compartment of the leg

• Posterior compartment

• Anterior compartment

• Lateral compartment

posterior compartment of the leg

• Digital and plantar flexors

  • help point the foot down and flex the toes

• Innervation is the tibial nerve

Anterior compartments of the leg

• Digital extensors and dorsiflexors

  • lifts the foot and extends the toes

• Innervation is the deep fibula nerve

Lateral Compartment of the Thigh

• Plantar flexes and everts foot

  • turns the foot outwards, and points it down

• Innervation is the superficial fibular nerve

7 Facial expression muscles

• Epicranius

• Corrugator Supercilii

• Zygomaticus major

• Orbicularis oris

• Orbicularis oculi

• Mentalis

• Platysma

What are the two components of Epicranius

• Frontalis - at the front of your head

• Occipitalis - Base of skull

Epicranius - Frontalis- Action

• Raises eyebrows, wrinkles forehead and assists in lifting eyelids

Frontalis - Origin & insertion

Origin - Galea aponeurotica

Insertion: Skin of eyebrows and bridge of noes

Epicranius - occipitalis, Action

Pulls scalp (flatten forehead) and raises eyebrows

Occipitalis - Origin & Insertion

Origin- Superior nuchal line, and mastoid process

Insertion: Galea aponeurotica

Galea aponeurotica

a fibrous, tough sheet of fascia that connects the muscles of our scalp

Corrugator Supercilii

• Deep to the frontalis

• helps with facial expressions

Action of the Corrugator Supercilii

pulls the eyebrow down and medially, which creates forehead wrinkles

Origin and Insertion of the Corrugator Supercilii

Origin- at the medial end of the superciliary arch

Insertion- Skin of eyebrow and orbital fascia

Orbicularis Oculi

a circular muscle around the eye, and it closes the eyelids

Origin and Insertion of the Orbicularis Oculi

Origin- frontal bone, maxilla and the orbit ligaments

Insertion- Skin around the eyelids and lateral palpebral raphe (the ligamentous band near the eye)

Zygomaticus Major

A diagonal muscle from the cheek (zygomatic bone) to the mouth corners

Origin and Insertion of the Zygomatic Major

Origin- zygomatic bone

Insertion- skin and muscles at an angle of the mouth

Action of the Zygomatics Minor

• elevates the upper lip and exposes teeth

• draws the upper lip backward and up

• used for smiling and sneering

Origin and Insertion of Zygomaticus minor

Origin: Zygomatic bone (anterior part)

• Insertion: Skin of upper lip (medial to the zygomaticus major)

Orbicularis Oris

Surrounds the mouth and forms most of the lips

action of the Orbicularis Oris

• closes and protrudes lips for speech

• could be used for kissing and whistling

Origin and Insertion of Orbicularis Oris

• Origin: Maxilla and mandible;

• Insertion: Skin and mucous membrane at the lips