A and P Exam 3

Muscle Function

Turn chemical energy into mechanical force

Maintain

Posture

Stabilize joints

Generate heat

Muscle Excitability

Ability to receive and respond to stimuli

Muscle Contractibilty

Ability to shorten

Muscle Extensibility

Ability to lengthen

Muscle Elasticity

Ability to recoil and return to original shape

Types of muscle - all come from ______

Mesoderm

Skeletal muscle

Cardiac muscle

Smooth muscle

Myoblasts

Precursors to skeletal muscle

Multi-nucleated Myotube

Phase in between myoblast and myofiber

Myofiber

Cylindrical, multinucleated mature muscle cell

Nervous system must form a synapse/motor end plate in order for myotube to become myofibril

Skeletal Muscle

Fibers: striated, tubular, multi nucleated

Voluntary

Usually found attached to skeleton

Vascularized and innervated by a plexus (network of blood vessels and nerves)

Direct (A) Attachment Type

Straight attachment from muscle to bone

• Attachment via periosteum

• Attachment via perichondrium during development

Indirect (B, C) Attachment Type

Attachment via tendon

• Attachment via tendon to bone

• Aponeurosis attachment: sheet of connective tissue usually for wider-sheet like muscles; attaches sheet like muscles needing a wide area of attachment (lumbar, abs, scalp)

Cardiac Muscle

Fibers: Striated, branched, and mono or multinucleated

Involuntary

Calcium mainly from caveolae

Only found covering walls of the heart

Smooth Muscle

Fibers: Non-striated, spindle-shaped, uninucleated, no sarcomeres, no troponin/tropomyosin, has calmodulin and myosin light chain kinase, intermediate filament cytoskeleton,

Calcium mainly from caveolae

Involuntary

Usually found covering the walls of internal organs

Organization of Muscle

Epimyseum

Outermost sheath that surrounds the entire muscle

Perimyseum

Dense irregular connective tissue sheet that surrounds fascicles

Endomysium

Smallest sheath, loose areolar connective tissue surrounding each muscle fiber

Fasicle

Bundle of muscle cells with motor units

Motor unit - A motor neuron and all of the muscle fibers that it innervates

Muscle Fiber

Individual muscle cell. Extremely large. Has sarcoplasm (cytoplasm for muscle cells). Has sarcolemma (cell membrane for muscle cells). Made of myofibrils

Myofibril

Organelle, only in striated muscle. Consists of sarcomeres, rod shaped

Sarcomere

Smallest unit of muscle, contractile unit of muscle with actin and myosin

Sarcomere photo

Second sarcomere photo

H-Zone

No actin overlap, no thin filaments, only thick filaments. Shortens during contraction

M-Line

Represents the middle of the sarcomere Structural proteins, anchors thick filament and whole sarcomere

Z-Disk

Represents the edges of the sarcomere. Tolerates a lot of mechanical stress

A-Band

• Represents the Portion of Myosin

• Anisotropic” Lack of light, lots of proteins + mitochondria. Thick and thin filaments

I-Band

Represents the portion of actin that has no myosin overlap

“Isotropic”. Allows light. Less proteins. Z-Disk + some actin filaments

Shortens when muscle contracts

Thin Filaments

String of globular actin proteins

Has myosin binding sites

Binding sites blocked by tropomyosin - regulatory protein, allows muscles to relax

Troponin complex - positions tropomyosin, relaxed = actin binding sites covered, contract = pull on tropomyosin to uncover myosin binding sites

Thick Filaments

Myosin

2 proteins

Binds to actin, pulls, causes contraction

Sarcoplasmic Reticulum

Where muscles stores, releases, and sequesters calcium (initiates contraction)

It is a special Ed smooth endoplasmic reticulum

T-Tubule

Perpendicular to sarcomere

Part of sarcolemma (cell membrane)

Where EC coupling occurs

Allows action potential into muscle fiber

Terminal Cisternae

Where calcium is stored + released

Has calcium pumps that use and active transport calcium pump to sequester it

Triad

Two terminal cisternae + one T tubule

E-C Coupling

1. Acetylcholine released from the axon terminal binds to receptors on the sarcolemma, causing them to change shape and sodium and potassium ions to cross the membrane.

2. More sodium crosses the membrane than potassium, more positive ions move in than out and the membrane potential. Sodium voltage gated channels are opened in the neuron, and an action potential is generated and travels across the membrane and down the T tubule. This occurs in a series, not one action potential.

3. Ca²+ is released from the sarcoplasmic reticulum in response to the change in voltage.

4. Ca²+ binds troponin; Cross-bridges form between actin and myosin.

5. Acetylcholinesterase removes acetylcholine from the synaptic cleft.

6. Ca²+ is transported back into the sarcoplasmic reticulum.

7. Tropomyosin binds active sites on actin causing the cross-bridge to detach.

Jacobs EC Coupling Explanation

Ch 1) The Neuron

• A stimulus strong enough to reach threshold triggers an AP to travel from the motor cortex, spinal cord, to motor neuron.

• Sodium VGCs open. Na+ enters axon causing membrane potential to increase/depolarize. This occurs in a series along the length of the membrane.

• Na+ travels to buton/axon terminals. Causes Ca2+ VGCs to open. Triggers exocytosis

• Vesicles storing neurotransmitter ACh attach to T-snares on membrane with V-snares.

• ACh is released from neuron (exocytosis) into the neuromuscular junction/synaptic cleft

• Behind the AP, K+ channels open, repolarizing the cell. Na/K pump restores resting potential

Ch 2) The Muscle Fiber

• ACh attaches to ACh receptors on the sarcolemma in the synaptic cleft. These open, allowing sodium to enter the cell. This raises membrane potential, causing the AP to be transferred to the muscle fiber.

• Na+ Channels open in a series along the length of the sarcolemma(depolarization), down the length of the sarcolemma and down the T Tubule

• As AP propagates down T Tubule, triggers Ca2+ VGCs to open which connect the T tubule to the SR. Calcium now is released from cisternae into cytosol

Ch 3) Sarcomere Shortening

• Calcium binds to troponin which causes sarcomeres to shorten

• Thin filaments slide past thick filaments

• I Bands decreases in length

• H zone decrease in length

• Z- discs decrease in length

Ch 4) Cross Bridge Cycling

• Calcium binds to troponin C on the troponin complex, this causes troponin T to pull on on tropomyosin exposing the myosin binding sites on actin.

• Myosin heads in a high energy state attach, release ADP + Pi and pull on the actin thin filaments towards the M line

• ATP attaches to myosin, releasing it from actin

• ATP is hydrolyzed by ATPase to ADP and Pi. Restores myosin to high energy
  "cocked" position.

• Cycle repeats in presence of calcium

Epilogue) Relaxation

• Stimulus ends, AP ends. Neuron restored back to resting. ACh no longer released. ACh in synaptic cleft is broken down by enzymes or sequestered.

• Membrane potential similarly restored in muscle cell via Na/K pump.

• Calcium is sequestered via calcium pumps on the terminal cisternae back into the SR. Pumps are called SERCAs

• ATP detaches myosin from actin

• Muscle relaxes

Action Potentials

Stimulation Frequency

Neural Recruitment

Length-Tension Relationship

Powerstroke

Movement of the myosin head, bound to actin, towards the M-Line of the sarcomere

• This pulls actin towards the center of the sarcomere, shortening the I-Band, H-zone, and the entire sarcomere

Cross-bridge Cycle

Arrange the following structures from largest to smallest: myofibril, whole muscle, muscle fiber, fascicle, and sarcomere.

Whole muscle → fascicle → muscle fiber → myofibril → sarcomere. A muscle fiber is one muscle cell containing many myofibrils, each composed of repeating sarcomeres.

What structures mark the boundaries of a sarcomere?

Describe what happens to the distance between these boundaries during contraction.

A sarcomere extends from one Z disc to the next.

During contraction, the Z discs move closer together, shortening the sarcomere.

Identify the main protein in each type of filament.

How do these proteins interact to cause muscle contraction?

Thick filaments consist primarily of myosin, while thin filaments consist primarily of actin. Myosin heads bind to actin and pull the thin filaments toward the center of the sarcomere.

What does the sarcoplasmic reticulum store, and how does releasing this substance help initiate muscle contraction?

It stores calcium ions (Ca?*). Released calcium binds to troponin, causing tropomyosin to move and expose myosin-binding sites on actin, allowing contraction to begin.

During contraction, do the thick and thin filaments become shorter? Explain how their movement changes the length of the sarcomere.

Thin filaments slide past thick filaments toward the sarcomere center, increasing their overlap and bringing the Z discs closer together. H-Zone shortens

Cardiac Muscle

Specialized striated muscle developed from cardiomyocytes and only found in walls the heart. Mononucleated

Cardiomyocytes are small

Automaticity - Action potentials are created spontaneously by the heart, allowing it to depolarize and beat on its own without need for external stimuli

Cardiac Muscle Neural Control

Autonomic nervous system

• Parasympathetic - relaxes

• Sympathetic - stimulates

No neuromuscular junction

Intercalated Discs

Spread action potentials throughout the heart, which promotes the rhythmic contraction of the heart

Rich in Desmosomes - Membrane junction between cardiomyocytes swell suited for dealing with the high stress connection from contraction of heart

Rich in Gap Junctions - Allow communication between cardiomyocytes, so that if one depolarizes they all depolarize

Smooth Muscle

Non-striated, unvoluntary, mononucleated

Smaller than skeletal muscle, thin & thick filaments are arranged diagonally

Found in the walls of hollow visceral organs (stomach, bladder, etc.)

Peristalsis – waves of smooth muscle contraction followed by waves of relaxation that move substances through the GI tract

Smooth muscle has SLOW & SMOOTH sustained contractions

Smooth Muscle Neural Control

Autonomic Nervous System

• Parasympathetic

• Sympathetic

No neuromuscular junction, i.e. no synaptic cleft

• Instead, innervated with varicosities -Swollen bulbs of nerve bundles that release neurotransmitters

Smooth Muscle Structure

Cytoskeleton: criss-cross network of intermediate filaments, attached together via dense bodies

Caveolae: Ca2+ VGCs that diffuse calcium across plasma membrane

SR - poorly developed

One nucleus

Thick and thin filaments: more thick to thin, 1:13 (skeletal is about 1:6)

No troponin or tropomyosin

Varicosities - smooth muscle innervation

Smooth Muscle EC Coupling

1. AP travels from brain, spinal cord, autonomic axon, to varicosity. Neurotransmitter releases, binds to receptors. Increased membrane potential cause Ca2+ VGC to open at caveolae. Some is also released by SR.

2. Calcium binds to and activates calmodulin.

3. Calmodulin activates myosin light chain kinase (MLCK)

4. MLCK breaks down ATP to ADP + Pi, attaches Pi to myosin

5. Myosin now activated and forms cross bridge. Actin thin filaments slide across myosin thin filaments

Single Unit Type Smooth Muscle

“Visceral” muscle

Contraction rhythmically

Coupled via gap junctions

May have spontaneous potentials

Physic contractions - contraction to relaxation

Ex: peristalsis

Multi Unit Type Smooth Muscle

Gap Junctions Rare

Infrequent action potentials

Structurally independent (work on their own)

Lots of nerves

Graded contractions (force output varied rather than the entire muscle contracted/relaxed)

Tonic contractions (little to no energy needed) - contraction, hold, relaxation

Ex: Large arteries, arrector pili muscles

Smooth Muscle Response to Stretch/Stress Relaxation Response

When you stretch smooth muscle, it impulsively contracts

If you hold it, it will relax and adapt to its new length. Allows organs to store contents that change in volume. Ex: Your bladder

Sliding Filament Theory

During contraction the thin filaments slide past the thick filaments so that actin and myosin overlap to a greater degree

Cross-Bridge Cycling

Know this stuff about twitches

Fast (Unique) Twitches

Very oxidative

Uses carbs (glucose, aerobic metabolism)

Ex: extraocular muscle

Medium (considered fast if fast unique is not included) Twitch

Power (short sprint)

Relaxes relatively quickly

Uses carbs (glycogen / anaerobic metabolism)

Ex: Gastrocnemius

Slow Twitch

Endurance

Uses fates (aerobic metabolism)

Uses fats

Relaxes slowly

Postural

Ex: soleus

Explain why ATP is necessary for both muscle contraction and relaxation. How would a complete lack of ATP affect myosin attachment to actin and calcium transport, and how does this explain rigor mortis?

• ATP allows myosin to detach from actin. As ATP binds to the myosin head, causing it to release actin and break the cross-bridge.

• ATP is hydrolyzed into ADP and inorganic phosphate (Pi), energizing and repositioning (“cocking”) the myosin head.

• The energized myosin head binds to exposed sites on actin. Release of Pi triggers the power stroke, pulling actin toward the center of the sarcomere; ADP is then released. Another ATP is needed for detachment and repetition. Mention cross-bridge cycling

• Calcium binds to troponin, moving tropomyosin away from the myosin-binding sites on actin.

• ATP powers calcium pumps (SERCA) that move calcium from the cytosol back into the sarcoplasmic reticulum.

• Calcium dissociates from troponin, allowing tropomyosin to cover actin binding sites again.

• No ATP, Cross-bridges become locked, and normal cycling stops.

• No ATP, calcium cannot be actively pumped back into the sarcoplasmic reticulum. Calcium remaining in or leaking into the cytosol keeps actin binding sites exposed.

• After death, ATP production stops and remaining ATP is depleted. Calcium accumulates in the cytosol, and myosin–actin cross-bridges become locked, producing muscle stiffness.

• Decomposition breaks down muscle proteins and the locked cross-bridges; ATP production does not resume.

Mouth (Buccal Cavity

Stratified squamous epithelium

Site of mastication

Saliva turns food into a bolus

Some chemical digestion and absorption

Important structures

• Tongue

• Teeth

• Hard palate

• Soft palate

• Frenulum - attached lips and tongue to mouth

• Palatine ridge - divides food laterally

Tongue

Controlled by skeletal muscle

• Intrinsic muscles - only muscle in body with no origin or insertion. Change shape, length, width

• Extrinsic muscles - inserts on mandible. Change tongue position

Secretes lipase (fat breakdown)

Filiform papillae - inc surface area, holds things

Tastebuds: fungiform, vallate, and foliate

Lingual tonsils: Immune system surveillance, has WBCs

Teeth

Masticate (chew)

20 baby (deciduous) teeth

32 adult (permanent) teeth

4 types

• Incisors: cut/snip

• Canines: tear

• Premolars (bicuspid): grind, crush

• Molars: grind, crush

Two regions, crown and root

Crown

Enamel - Hydroxyapatite, hard

Dentin - Calcified protein

Pup Cavity - Blood vessels and nerves

Crown

Enamel - Hydroxyapatite, hard

Dentin - Calcified protein

Pup Cavity - Blood vessels and nerves

Root

In jaw bone, fixed via cement and ligament

Canines, premolars, incisors - 1 root

Molars - 2-3 roots

Salivary Glands

3 Glands: parotid (associated with mumps), submandibular, sublingual

Secrete saliva with 1-2 cell types: Serous cells, Mucus Cells (not in parotid)

Functions: cleanse mouth, dissolve food chemicals for taste, aides in bolus formation, contains amylase for starch digestion

Composition: 99% water, amylase, mucin, IgA antibodies, lysozymes, and defensins

Neural Control: Parasympathetic control of autonomic nervous system, Activated by chemoreceptors (taste receptors) and pressoreceptors (pressure receptors)

Esophagus

Pharynx to upper third is skeletal muscle (voluntary - swallowing)

Short transition zone - mix of skeletal and smooth

Rest is smooth muscle

Leads to stomach

Collapses when not in use

No serosa. Has adventitia instead

2 sphincters

• Upper esophageal sphincter

• Lower esophageal sphincter (cardiac sphincter)

How do the teeth, tongue, and saliva work together to begin digestion and form a bolus?

Teeth primarily aide in mastication. The tongue helps with mastication but also secretes lipase chemically break down triglycerides. Saliva moistens food and secretes amylase to chemically break down starches.

What are the two regions of a tooth? What role does each play?

Crown: hard part of tooth, mastication

Root: insertion into bone, innervation/blood supply

After picking up/delivering nutrients from digestive organs, where must blood go before returning to the heart to be reoxygenated? What is this circuit called?

The liver. Splanchnic portal system/hepatic portal system

A person begins chewing a flavorful piece of food.

Which receptors stimulate salivation, and which division of the autonomic nervous system promotes saliva secretion?

Chemoreceptors. Parasympathetic

What is the deepest membrane of the alimentary canal called when found in the abdominal cavity. What is it called when found outside the abdominal cavity?

Peritoneum/Serosa. Adventitia

T/F, the esophagus is made up of entirely smooth muscle

False

Types of Mechanical Breakdown

Mastication (chewing), churning (stomach), segmentation (small and large intestine food mixing)

Types of Chemical Breakdown

The different enzymes.

Mouth - lipase from salivary glands breaks down fats

Stomach: cell ty

Small intestine: cell types in crypt that secrete enzymes

• Enterocytes - intestinal juice

• Paneth cells - lysozyme and defensin to destroy bacteria

• Goblet cells - secrete mucus

• Enteroendocrine cells - secretin and cholecystokinin