Ch. 10 - Muscle Gross Anatomy

Functions of Muscles

1. Movement

2. Stability

3. Control of openings

4. Heat production

5. Glycemic control

How muscles help with movement:

they allow us to move from place to place, they move body parts, and they move body contents in breathing, circulation, and digestion

In communication: speech, writing, facial expressions and other nonverbal communications

How muscles help with stability:

• Maintains our posture by preventing unwanted movements

• work as “antigravity” muscles by preventing us from falling over

• Stabilize our joints by maintaining tension

How muscles help control openings and passageways:

there are muscles called sphincters shaped in a ring that control the movement of food, blood, and other materials within body

• these muscles open/close openings

How muscles help with heat production:

the friction of our skeletal muscles produces as much as 85% of our body heat

How muscles help with glycemic control:

Muscles absorb and store glucose which helps regulate blood sugar concentration within a normal range

• can store but cannot release into blood stream like liver tissue can

Approximately how much body weight do our muscles constitute?

half of our body weight

What is the major purpose of muscles?

to convert the chemical energy in ATP into the mechanical energy of motion

Myology

the study of the muscular system

Epimysium

connective tissue surrounding entire muscle

• is continuous to the fascia

• holds fascicles together

Fascia

thick layer of collagen that leads into the tendon

• separates neighboring muscles or muscle groups from each other and the subcutaneous tissue

Perimysium

Thicker layer of connective tissue that wraps fascicles and holds them together

• Carries nerves, blood vessels, and stretch receptors

Fascicles: bundles of muscle fibers wrapped together

Endomysium

Thin sleeve of loose connective tissue around each muscle fiber/cell

• Electrically insulates muscle cells

• Allows room for capillaries and nerve fibers

• Provides chemical environment for muscle fiber

Strength of a muscle and the direction of its pull are determined partly by….

the orientation of its fascicles

Fusiform Muscles

thick in the middle and tapered at each end

Parallel Muscles

uniform width and parallel fascicles

• most parallel muscles have the word rectus in the name

Triangular (Convergent) Muscles

broad at one end and narrow at the other

Pennate Muscles

feather shaped

• pennate muscles are the strongest shape

• can pack the most muscle together

• includes:

  • Unipennate

  • Bipennate

  • Multipennate

Unipennate

fasciles approach tendon from one side

Bipennate

fascicles approach tendon from both sides

Multipennate

bunches of feathers converge to single point

Circular Muscles (Sphincters)

form rings around body openings

• weakest muscles in the body

Muscle Compartment

A group of functionally related muscles enclosed by fascia

• Also contains nerves and blood vessels that supply the muscle group

• these compartments are good bc they slow/stop the spread of pathogens from one compartment to another

Intermuscular Septa

very thick fascia that separate one compartment from another

Indirect Attachment to Bone

muscles attaching to bone indirectly using tendons

Tendons

connects muscles to bones

• Collagen fibers of the endomysium, perimysium, and epimysium continue into the tendon all the way into the periosteum and matrix of the bone

Aponeurosis

tendon is a broad, flat sheet (palmar aponeurosis)

ex) abdomen, top of the head (frontalis to occipitalis)

Retinaculum

connective tissue band that tendons from separate muscles pass under

• keeps tendons from getting tangled

Direct (fleshy) Attachment to Bone

• no visible tendon

• Little separation between muscle and bone

• Muscle seems to emerge directly from the bone

Some muscles attach on the fascia or tendon of another muscle or on collagen fibers of the dermis instead of bone

Origin

the end of the muscle that is closer to the heart

Insertion

the end of the muscle farther away from the heart

Intrinsic Muscle

muscle that is entirely contained within a region, such as the hand

Extrinsic Muscle

acts on a designated region, but has one attachment elsewhere

ex) extrinsic muscles in the forearm help move the wrist

Action

an effect produced by a muscle to produce or prevent movement

Four categories of muscle action:

• prime mover

• synergist

• antagonist

• fixator

Prime Mover (agonist)

Muscle that produces most of the force during a particular joint action

Synergist

muscle that aids the prime mover

• can contribute additional force, modify the direction of movement, or stabilize a nearby joint

Antagonist

opposes the prime mover

• Prevents excessive movement

• Sometimes relaxes to give the prime mover control over an action

Antagonistic pairs—muscles that act on opposite sides of a joint

• ex) elbow flexion: biceps brachii is the prime mover (agonist) and the triceps brachii is the antagonist

Fixator

muscle that prevents movement of bone

• joint stabilization

Innervation

Innervation of a muscle refers to the identity of the nerve that stimulates it

• Knowing innervation enables the diagnosis of nerve, spinal cord, and brainstem injuries from muscle tests

Spinal Nerves

arise from the spinal cord

• emerge through intervertebral foramina

• Immediately branch into posterior and anterior rami (branches of spinal nerves)

• Innervates muscles below the neck

• includes plexus

Plexus

web-like network of spinal nerves next to the vertebral column

Cranial Nerves

arise from the base of the brain

• Emerge through skull foramina

• Innervate the muscles of the head and neck

• Numbered CN I to CN XII

Blood Supply

• the muscular system receives 1/4 of the blood pumped by the heart per minute at rest

• During heavy exercise, total cardiac output rises and the muscular system’s gets more than ¾ of the blood from the heart per minute

Capillaries branch through the endomysium to reach every muscle fiber