ANAT 100 Module 3

What are muscles?

Contractile organs; through muscle contraction, these organs perform a number of important functions

What are the three types of muscle?

skeletal, cardiac, smooth

Skeletal muscle

Help human body move. Most skeletal muscle is attached to bones via tendons.

Cardiac muscle

Found in heart. Contract rhythmically, and is modulated by neural activity and hormones.

Smooth Muscle

controlled by nervous system or hormones. It may be either generally inactive and then respond to stimulation, or it may be rhythmic.

How can muscles be categorized?

morphology (form) or how they function.

What are the two morphologically categorized groups?

Striated and Smooth muscle

straited muscle

Striated muscle is marked by both light and dark bands (striations). Striated muscle is found in heart and skeletal muscles.

How is striated muscle characterized?

Is characterized by long muscle fibres (cells) with multiple nuclei which are located peripherally for skeletal muscle or centrally for cardiac muscle. Cardiac muscle also has intercalated discs: connect heart muscle cells to each other.

Smooth muscle

Found in blood vessels, the digestive system, and other viscera. Each smooth muscle fibre (cell) contains a single centrally located nucleus. Smooth muscle has fusiform-shaped (spindle-like) cells without striations.

What are the two functionally categorized groups?

Voluntary & Involuntary

Voluntary Muscle

is consciously controlled in order to perform a specific function, such as the muscle that move the skeleton for walking, reaching, talking, etc.

What type of muscle is voluntary?

skeletal muscle

involuntary muscle

involuntary muscle is not consciously controlled

What type of muscle(s) is involuntary?

smooth muscle and cardiac muscle

What are the two basic properties of muscle?

excitability and contractility

Excitability

Ability of muscle tissue to receive and respond to electrical signals from nerves or stimulation from hormones

Contractility

When a muscle cell is excited by a nerve or hormone, this causes the muscle to shorten, resulting in contraction.

How many muscles are apart of the skeletal system and what are they composed of?

700 named muscles; skeletal muscle tissue, epithelial, connective, and nervous tissue.

What are most skeletal muscles attached to?

Most skeletal muscles are attached to 2 bones across a joint, such that when contracted, the muscle brings parts of those 2 bones closer to each other

What are the five functions of skeletal muscle?

Produce movement, maintain posture and stabilize joints, control excretion (elimination of urine and feces) and swallowing, produce heat, support and protect internal organs.

What does skeletal muscle consist of?

Skeletal muscle consists of muscle tissue and connective tissue.

What does connective tissue surround?

Connective tissue surrounds the muscle tissue and attaches the ends of each muscle to bone.

What are the three layers connective tissue is categorized into?

epimysium, perimysium, and endomysium

Epimysium

surrounds an entire muscle and is continuous with the tissue that becomes the tendon.

Perimysium

Layer of connective tissue surrounding a bundle of muscle fibres (fascicle) within a muscle.

Endomysium

surrounds the individual muscle cells (muscle fibres) within a muscle bundle

What are the units of contraction for the muscle cell?

myofilaments

What are myofilaments organized into?

repeating structural units known as sarcomeres

What happens when the sarcomeres are shortened.

Contraction of muscle.

What does each unit consist of?

actin (thin) and myosin (thick)

Why does skeletal muscle have a striated appearance?

due to arrangement of actin and myosin into organized sarcomeres that form distinct lines and bands.

A-band

Made up of thick and thin filaments. Appears darker when views histologically.

Z-line

Composed of protein that makes a "zig-zag" line marking the beginning and end of each sarcomere. It lies in middle of the I-band and is where the thin filaments attach.

M-line

Composed of protein down the center of sarcomere ('mid-line'). This is where the thick filaments attach.

I-band

Made up of thin filaments. It appears lighter in colour, and transverses 2 sarcomeres

Sarcolemma

cell membrane surrounding a muscle cell

What is beneath the sarcolemma?

nuclei, myofibrils, and the sarcoplasm (cellular fluid)

What does it mean when said, "skeletal muscle cells are multinucleated"?

they have more than one nucleus. These nuclei are located towards the outside of the myofiber

Myofibris

structural units of the muscle cell and contain the contractile myofilaments

Sarcoplasmic Reticulum

surrounds each myofibril and is where the muscle cell stores calcium, which is necessary for muscle function

Transverse tubules (t-tubules)

Extensions of the sarcolemma that surround the myofibrils and transmit nerve stimulation to the sarcoplasmic reticulum within the cell

What happens with actin and myosin when muscle contracts?

the actin and myosin filaments slide over each other, which shortens the sarcomere. This increases muscle tension grossly resulting in the movement of structures.

How are the muscles of the body generally organized?

superficial (shallow), intermediate, or deep

What are the four muscles involved in facial expression?

frontalis, orbicularis oculi, zygomaticus, orbicularis oris

Frontalis

muscle that covers the frontal bone and lifts eyebrows, causing forehead to wrinkle

Orbicularis oculi

muscle surrounding the eye that forcefully closes the eye when contracted. It originates on the frontal and maxillary bones.

Zygomaticus

Extends from the zygomatic arch to the corners of the mouth. It draws the angle of the mouth superiorly and posteriorly, causing one to smile.

Orbicularis oris

Surrounds mouth and enables the puckering of lips. Originates on the maxillary bones of mandible and sometimes referred as a kissing muscle.

What are the two muscles involved in mastication (chewing)?

temporalis and masseter

Temporalis

fan-shaped muscle that extends from the temporal fossa of the parietal bone to the coronoid process of the mandible. The temporalis muscle elevates and pulls the mandible posteriorly (retract).

Masseter

Powerful muscle that extends from the zygomatic arch to the angle of the mandible (lower jaw). Its action is to elevate and protract (move forward) the jaw.

What are the anterior muscles of the head and neck?

The sternocleidomastoid muscle

The sternocleidomastoid muscle

flexes the neck with bilateral contraction, and rotates the head to the opposite site with unilateral contraction

What are the posterior muscles of the head and neck?

the semispinalis capitis and the splenius capitis

Semispinalis capitis

Extends the neck with bilateral contraction, and turns the face slightly to the opposite side with unilateral contraction

Splenius capitis

Extends the neck with bilateral contraction, and causes flexion and lateral rotation of the neck with unilateral contraction.

What muscles of the thorax aid in the process of breathing?

the intercostal muscles

What are the two main intercostal muscles focused on?

the external and internal intercostals

External

Most superficial, and their fibres run anteriorly and inferiorly between the ribs. They aid in inspiration

Internal Intercostals

Lie deep to the externals, and their fibres run superiorly and anteriorly. Aid in expiration

What group of muscles help to keep the spine erect?

The erector spinae muscles; they run down both sides of spinal column

What do the abdominal wall muscles do?

facilitate movement of the trunk, and aid in breathing

What is the external oblique?

most superficial of the anterolateral wall musculature. Its fibres run anteriorly and inferiorly

What are the external oblique's functions?

flexes the vertebral column and compresses the abdominal wall (Bilateral) (used in forced expiration); lateral flexion and rotation of the vertebral column (unilateral).

What is the internal oblique?

lies deep to the external oblique, and its fibres run anteriorly and superiorly

What are the internal oblique's functions?

lexes the vertebral column and compresses the abdominal wall (bilateral); lateral flexion and rotation of the vertebral column (unilateral).

What is the transversus abdominis?

Runs horizontally, deep to the internal oblique.

What are the transversus abdominis' functions?

flexes the vertebral column and compresses the abdominal wall (Bilateral) (used in forced expiration); lateral flexion and rotation of the vertebral column (unilateral).

What is the rectus abdominis?

lies on either side of linea alba (a line of connective tissue down middle of abdomen for muscle attachment) and is separated by tendinous intersections

What are the rectus abdominis' functions?

Flexion of trunk and forced expiration.