Muscular System Anatomy of Muscle Fibrils Physiology of Muscle Contraction

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Did you know that ?

- More than 50% of body weight is muscle !

- Muscle is made up of proteins and water

The Muscular System

• Muscles are responsible for all movement of the body

• There are three basic types of muscle • Skeletal (Striated or Voluntary) • Cardiac (Heart) • Smooth (Involuntary)

3 Types of Muscles

Info About Muscles • Only body tissue able

to contract • Create movement by

flexing and extending joints

• Body energy converters (many muscle cells contain many mitochondria)

Functions of Muscles

• Produce external movement • Maintain posture – hold body still or in a

particular position • Stabilize joints

• Movement of substances inside the body – cardiac and smooth (visceral) muscles transport blood and food

• Generate heat by contractions – High metabolic rate of contracting produces lots of waste heat; small contractions to maintain body temperature

Three types of muscle Skeletal Cardiac Smooth

Muscle Terms

All muscles share some terminology • Prefixes myo and mys refer to

muscle • Prefix sarco refers to flesh

Classification of Muscle Skeletal Cardiac Smooth

Limbs Heart Viscera Movement Heartbeat

Move food & and other substances through the body

Striated Multi- nucleated Fibers in bundles

Striated and Branched Uni-nucleated Lots of mitochondria

Not striated Uni-nucleated Fibers in sheets

Voluntary Contracts in short, strong bursts

Involuntary All fibers contract at the same time

Involuntary Contracts slowly, but steadily

Skeletal Muscle • Also called Striated Muscle • Always connect to skeleton in at least one place

• Most attached to two bones by a tendon

• Act independently of neighboring muscle fibers

Skeletal or Striated Muscle

• Striated - have stripes, banding • Multi-nucleated - cells have more than

one nucleus • Voluntary - subject to conscious

control, CNS • Long cylindrical fibers are arranged in

bundles

Muscles move Bones

• Muscles move by shortening their length, pulling on tendons, and moving bones closer to each other. • Tendons – strong collagen fibers

• One bone is pulled toward the other bone, which remains stationary.

How are Muscles Attached to Bone?

• Muscle connected to stationary bone by tendons at the Origin. The basis for the action.

• Muscle connected to moving bone by tendons at the Insertion. The effects of the action.

• Muscles are always attached to at least 2 points

• Movement is attained due to a muscle moving an attached bone

Muscle Attachments

Origin

Insertion

Naming Muscles

• Location •Origin and Insertion •Number of Origins •Shape, Size and Direction •Function

Three types of Connective Tissue

The layers of connective tissue are the cement that holds the muscle cells and bundles together

• Epimysium – surrounds the whole muscle • Perimysium – surrounds the Fascicle

(individual bundles of muscle cells) • Endomysium – surrounds the Muscle

Fiber (Muscle Cell)

Bone to Muscle Fiber / cell

Progression of Anatomy

Structure of skeletal muscle

• Each Muscle Cell or Fiber is long and cylindrical

• 50-60 mm in diameter, and up to 10 cm long (length is greater than width)

• The contractile elements of skeletal muscle cells are Myofibrils

• Sarcolemma – special cell membrane that conducts electrochemical signals

Sarcotubular System

Vesicles and Tubules that surround the Muscle Fiber (cell)

• T-System or Tubules – connect to sarcolemma and transmits the nerve impulse to the middle of the cell and all the thousands of myofibrils that make up the muscle cell

• Sarcoplasmic Reticulum - forms a curtain around each myofibril and a storehouse of the calcium ions (Ca + 2) that are part of the contraction mechanism

Sarcomere

Dark and Light Bands

Myofibrils – muscle fiber structure; contractile elements

A Bands - Dark and thick – Myosin H Band (zone) – darker area in the middle of the A Band

I Bands – Light and thin – Actin Z Line (band, disc) – narrow, dark band in the central region of the I Band Sarcomere – area between two Z Lines – functional unit of muscle fiber

3 Factors cause a Muscle Contraction

1. Neuroelectrical Factors – Nerve impulse causes Potassium ions (K +) and Sodium ions (Na¯ ) to switch places across the cell membrane and create an Action Potential that travels along the T-System.

2. Chemical Interactions – Actin unites with Myosin to form Actomyosin.

3. Energy Sources – ATP

Where Does the Energy Come From? • This all happens in the Mitochondria

• Energy is stored in the muscles in the form of ATP

• ATP comes from the breakdown of glucose during Cellular Respiration

Neurotransmitters

• Acetylcholine – released from synaptic vesicles, stimulates a muscle impulse

• Cholinesterase – enzyme that stops action of acetylcholine

Steps in a Contraction 1

• More Potassium ions inside the cell than outside. More Sodium ions outside the cell than inside. Inside the cell is negatively charged and outside is positively charged – Resting Potential

• At the neuromuscular junction (end of the axon), a nerve impulse causes release of acetylcholine from the synaptic vesicles into the synaptic cleft.

• Acetylcholine diffuses across the neuromuscular junction and binds to receptors on the sarcolemma (muscle cell membrane).

Action Potential

Steps in a Contraction 2

• Impulse spreads across sarcolemma and increases the permeability to K+ ions (depolarization) - the potassium ions rush outside the cell and the sodium ions rush inside the cell. This creates an electrical potential - and the Action Potential is generated.

• Action Potential travels by way of the T-Tubules to

all the cells and causes the Sarcoplasmic Reticulum to release Calcium ions that diffuse into the sarcoplasm.

Steps in a Contraction 3

• The Calcium ion concentration at the myofilaments increases and negates the troponin and tropomyosin which keeps the filaments apart. This causes the formation of cross bridges between the actin and myosin filaments and they slide between each other and make Actomyosin. The Z Lines move together.

• Contraction – the formation of the Actomyosin

shortens the myofibril which shortens the muscle fibers which shortens the muscles

Actin and Myocin

Steps in a Contraction 4

• Sodium –Potassium Pump operation restores the Na and K distribution to the resting potential. Calcium ions are actively reabsorbed (Calcium Pump using ATP) into the Sarcoplasmic Reticulum and the concentration in the myofilaments decreases.

• Contraction stops. The Z Lines move apart. The muscle cell relaxes and lengthens. Enzyme Cholinesterase stops action of the Acetylcholine.

Too Little Oxygen & ATP Too Much CO₂

• Muscle Fatigue - a muscle is tired and unable to contract because of lack of oxygen, energy (ATP) and too many waste products.

• Oxygen Debt - the amount of oxygen that the body needs to restore muscle cells to resting state. You feel out of breath!

Contraction Physiology

• Motor Unit – one motor neuron and the muscle fibers (cells) that it sends impulses to; they all contract together • Average 150 muscle cells • 200 muscle cells for gross movement (hand) • 10 muscle cells for fine movement (eye)

• Muscle Cells have four properties: • Excitability – stimulated by a nerve cell (neuron) • Conductivity – response can travel throughout cells • Contractility – the response to the stimulus • Elasticity – return to original shape after contraction

Contractions

Contraction Cycle - Latent Period to Contraction Period (Shortening of fibers) to Relaxation Period Strength of contraction depends on:

• Number of Motor Units sending signals • Strength of stimulus • Duration of stimulus • Speed of application • Weight of the load (table vs. coffee cup) • Temperature of the body (98.6⁰)

All or None Law

A stimulus that elicits a response will produce a maximum contraction. The contraction occurs or it does not.

Muscle Twitch

Single nerve impulse of a motor neuron will cause a motor unit to contract briefly before relaxing

• A single brief small contraction • Not a normal muscle function

Muscle Tetanus

Motor neuron provides many nerve impulses in rapid succession, the muscle has a complete and lasting contraction.

• One contraction immediately followed by another • Effects are compounded • Remains in tetanus until the nerve signal slows or

the muscle too fatigued to continue • Muscle never completely returns to a relaxed

state

Muscle Tone

A natural condition of in which a muscle stays partially contracted at all times.

• Some muscle cells will always be contracting while other muscle cells are at rest.

• Maintain body posture without tiring • Slight and steady pull on attached bones • Pressure on abdominal contents • Blood pressure in arteries and veins • Assists in digestion in stomach and intestines • Prevents damage to muscle and joints from sudden

movements

Two types of Contractions

• Isotonic Contraction – tone or tension remains the same; the muscles become shorter and thicker; lifting a weight

• Isometric Contraction – muscles remain at a constant length while the tension against the muscle increases; push against a wall or lift a large rock

Exercise and Muscles

• Isotonic - muscles shorten and movement occurs ( most normal exercise)

• Isometric - tension in muscles increases, no movement occurs (pushing one hand against the other); help develop tone or firmness in muscles

More or Less

• Hypertrophy – increase in size due to repeated forceful contractions (exercise); 75% maximum effort

• Atrophy – disuse or very low intensity use causes muscle to shrink – fibers shorten and replaced with fat and connective tissue (CT).

Smooth Muscle

• No striations • Spindle shaped • Single nucleus • Involuntary - no conscious

control, ANS • Found mainly in the walls of hollow

organs

Location of Smooth Muscle

• Lines walls of viscera • Hollow Structures

• Intestines • Blood Vessels • Urinary Bladder

Hollow Organs

Intestines

• 2-Layer Arrangement • longitudinal and

circular layers • Alternate contraction

of circular & longitudinal muscle in the intestine leads to peristalsis

Structure of smooth muscle

• Elongated Spindle shaped

uni-nucleated cells • Striations not observed • Actin and myosin filaments are

present (protein fibers) but not as regularly arranged

Physiology of Smooth Muscle

• Slower and more rhythmic contractions

• Greater extensibility of the muscle • Slow wave of contraction over the

entire muscle mass

Cardiac Muscle

• Striations – very strong cells • Branching or y-shaped cells • Involuntary – ANS – autorhythmic • Uni-nucleated • Found only in the heart – responsible for

pumping blood • Cells connected by Intercalculated Discs

that spread signals quickly from cell to cell to beat as a unit

Cardiac muscle

• Main muscle of heart • Pumping mass of heart • Critical in humans • Heart muscle cells

behave as one unit • Heart always contracts

to full extent

Structure of cardiac muscle • Cardiac muscle cells (fibers) are short,

branched and interconnected • Cells are striated & usually have 1

nucleus • Adjacent cardiac cells are joined via

electrical synapses (gap junctions) • These gap junctions appear as dark

lines and are called Intercalated Discs

Contractions of Cardiac Muscle

• Rapid rhythm of contractions • Impulse – contract – relax - another

impulse – contract… • About 75 contractions per minute • Fibrillation – rapid uncontrolled

contractions of individual cells; blood is not pumped properly

Muscle Control Type of muscle

Nervous control

Type of control

Example

Skeletal Skeletal Controlled by CNS

Voluntary Lifting a glass

Cardiac Regulated by ANS

Involuntary Heart beating

Smooth Controlled by ANS

Involuntary Peristalsis

END OF ANATOMY AND PHYSIOLOGY

Flexion

Types of Musculo-Skeletal Movement

Extension

Hyperextension

Abduction, Adduction & Circumduction

Rotation

More Types of Movement……

• Inversion- turn sole of foot medially • Eversion- turn sole of foot laterally • Pronation- palm facing down • Supination- palm facing up • Opposition- thumb touches tips of fingers on the same

hand

The Skeletal Muscles There are about 650 muscles in the human body. They enable us to move, maintain posture and generate heat. In this section we will only study a sample of the major muscles.

Sternocleidomastoideus Flexes and Rotates Head

Masseter Elevate Mandible

Temporalis Elevate & Retract Mandible

Trapezius Extend Head, Adduct, Elevate or Depress Scapula

Latissimus Dorsi Extend, Adduct & Rotate Arm Medially

Deltoid Abduct, Flex & Extend Arm

Pectoralis Major Flexes, adducts & rotates arm medially

Biceps Brachii Flexes Elbow Joint

Triceps Brachii Extend Elbow Joint

Rectus Abdominus Flexes Abdomen

External Oblique Compress Abdomen

External Intercostals Elevate ribs

Internal Intercostals Depress ribs

Forearm Muscles

• Flexor carpi—Flexes wrist • Extensor carpi—Extends wrist • Flexor digitorum—Flexes fingers • Extensor digitorum—Extends fingers • Pronator—Pronates • Supinator—Supinates

Diaphragm Inspiration

Gluteus Maximus Extends & Rotates Thigh Laterally

Rectus Femoris Flexes Thigh, Extends Lower Leg

Gracilis Adducts and Flexes Thigh

Sartorius Flexes Thigh, & Rotates Thigh Laterally

Biceps Femoris Extends Thigh & Flexes Lower Leg

Gastrocnemius Plantar Flexes Foot & Flex Lower Leg

Tibialis Anterior Dorsiflexes and Inverts Foot