The Muscular System

Part 2: Support & Movement

Muscle Tissue

Muscle: One of the 4 basic human tissuesDefined by its ability to contract & provide

movement Composition of muscle tissue will be

discussed in next chapter Current chapter will cover location,

function, & classification

3 Types of Muscle Tissue

Skeletal Muscle: Striated - associated with unstriated muscle Voluntary Attaches to the bones of the skeleton

Multinucleated Smooth Muscle:

Involuntary Found in digestive system, blood vessel walls, urinary & reproductive

systems Cardiac Muscle:

Involuntary Only found in the heart Has rhythmicity – will beat without outside stimulation Sources of energy that moves blood through the blood vessels

Smooth & Cardiac Muscle are controlled by the autonomic nervous system.

Common Traits

Proteins Needed: Actin Myosin

Four Essential Ions Needed: Calcium Sodium Chloride Potassium

Common Characteristics: Excitability Conductivity Contractility Extensibility Elasticity

Skeletal Muscles: Function

Functions: MovementStabilityCommunication

Expressions, Speech

Provides primary source of body heat Through muscle contractions – thermogenesis

Roughly 600 skeletal muscles in the human body

Skeletal Muscles: Properties

Contractility: Ability to forcefully contract when stimulated

Extensibility: Ability of the tissue to stretch without damage

Elasticity: Ability to return to its original shape after contraction or extension

Excitability: Ability to respond to stimuli Action Potentials: Electrical signals prompted by

neurotransmitters or by autorhythmic signals arising within the muscle tissue

Skeletal Muscles: Connective Tissue Components

Fascicles: Bundles of muscle fiber that make up skeletal musclesEnveloped by connective tissue

Fascia: Thin fibrous sheet of connective tissue that surrounds muscles & provides protectionSuperficial Fascia: Separates the skin from

muscle; subcutaneous layerDeep Fascia: Holds individual muscles

together

Skeletal Muscles: Connective Tissue

3 Types of Connective Tissue protecting muscles: Endomysium: Layer of areolar tissue

surrounding individual muscle fibersPerimysium: Sheath of connective tissue

surrounding the fasciclesEpimysium: Outer layer of connective tissue

covering the entire muscle & blending into the fascia

Skeletal Muscles: Attachment

Collagen Fibers: Connects muscle directly to bone Attaches using epimysium & periosteum

Tendons: Extensions of connective tissue, primarily from the deep fasciaAttaches to the periosteum of the bone

Skeletal Muscles: General Anatomy

Points of Attachment: Origin: Point of attachment at the stationary

end of an individual muscle. Usually medial

Insertion: Point of attachment at the more mobile end of the muscle.

Belly: Middle region of the muscle; very thick.

Skeletal Muscles: Classification

Intrinsic Muscles: Entirely contained within a particular region, e.g. the tongue.

Extrinsic Muscles: Act upon a certain region, but their origin is elsewhere.

Skeletal Muscles: Classification

Classification based on the orientation of fascicles: 5 Types Circular: Surround body openings; e.g. sphincter

muscles Convergent: Fan shaped; e.g. pectoralis major Fusiform: Tapered at the ends but thicker in the

middle; e.g. digrastric muscles Parallel: Relatively long & uniform in width, look like

straps with parallel fascicles; e.g. stylohyoid muscle. Pennate: Short, feather-shaped bundles with tendons

running almost the entire length; have unipennate, bipennate, multipennate forms; e.g. deltoid muscles.

Muscle Action & Coordination

Muscles act together as coordinated groups to produce movement

Muscles are often paired against muscles of an opposing joint. Prime Mover or Agonist: The muscle that produces the most

force. Antagonist: The muscle that yields to the effects of the prime

mover; acts opposite to it. Synergist: A muscle that aids the prime mover and prevents

unwanted movement at the joints. Fixator: A muscle that prevents bone from moving and

stabilizes the movement itself. Example: Flexing the forearm at the elbow – biceps

brachii is the prime mover & triceps brachii is the antagonist.

Muscle Innervation

Innervation: Every muscle fiber has a single motor neuron which innervates several other muscle fibers.

Threshold: The level of stimulus needed for the neuron to fire… It will not fire until this is reached, and will instantly fire once it is reached. Without nerves, skeletal muscles will not move.

Atrophy: Without innervation & movement, muscles will waste away & form scar tissue.

Skeletal Muscle Names

Skeletal muscles are named according to their distinctive features!

Named for size, shape, action, & number of origins.

Skeletal Muscle Names

Named by Size: Maximus: Largest muscles

E.g. gluteus maximus

Minimus: Smallest muscles E.g. gluteus minimus

Longus: Long muscles E.g. adductor longus

Major: Larger muscles E.g. pectoralis major

Skeletal Muscle Names

Named by Shape: Trapezius: Trapezoid shaped

E.g. Trapezius muscle

Rhomboid: Diamond shaped E.g. Rhomboid major

Quadratus: Square shaped E.g. Quadratus femoris

Skeletal Muscle Names

Named by Action: Flexor: Decreases angle

E.g. flexor carpi radialis

Levator: Elevates E.g. levator scapulae

Tensor: Makes rigid E.g. tensor fasciae latae

Skeletal Muscle Names

Named by Number of Origins: Biceps: Two origins

E.g. biceps brachii

Triceps: Three origins E.g. triceps brachii

Quadriceps: Four origins E.g. quadriceps femori