Physiology 241 Unit 3

Major types of muscle fibers

*CHART* Slow twitch = back Fast twitch = eye and fingers

Transverse Tubules

*T-tubules* Run perpendicularly from surface of muscle cell membrane to central portions of the muscle fiber Action potential on surface membrane spreads down into the T-tubule Spread of action potential down a T-tubule triggers release of calcium from sarcoplasmic reticulum into cytosol

Actin

*Thin filaments* consist primarily of the protein *actin* Actin interacts with the myosin cross-bridges Two other proteins, *tropomyosin and troponin* lie across the surface of actin In relaxed muscle, they prevent cross-bridge interaction

2 divisions of peripheral nervous system

1 Autonomic Nervous System 2 Somatic Nervous System

2 primary factors which can be adjusted to accomplish gradation of whole-muscle tension

1 Number of muscle fibers contracting within muscle 2 Tension developed by each contracting giber

Contraction-relaxation steps requiring ATP

1 Splitting of ATP by myosin ATPase provides energy for power stoke of cross bridge 2 Binding of fresh molecule of ATP to myosin lets bridge detach from actin filament at end of power stroke so cycle can be repeated 3 Active transport of calcium back into sarcoplasmic reticulum during relaxation depends on energy

Two subdivisions of Autonomic nervous system

1 Sympathetic nervous system (fight or flight) 2 Parasympathetic (resting and digesting

3 filaments in smooth muscle

1 Thick myosin filaments Longer than those in skeletal muscle 2 Thin actin filaments Contains tropomyosin *but lacks troponin* 3 Filaments of intermediate size Do not directly participate in contraction Form part of the cytoskeletal framework that supports cell shape

What kind of drug would be used to treat an overactive bladder?

Acetylcholine antagonist: blocks acetylcholine (bladder usage)

Sliding filament theory

Actin and myosin interact at cross-bridges Cross-bridge formation leads to *power stroke* *Z-lines* move inward, sarcomere shortens Actin and myosin slide past one another shortening sarcomere

Adrenal Medulla

Adrenal medulla is a modified part of sympathetic nervous system Stimulation of medulla by sympathetic system produces secretion of 2 hormones into blood About 20% hormone released is norepinephrine About 80% of hormone released is epinephrine (adrenaline) Adrenal medulla intensifies the activity of the sympathetic system.

Relaxation

Alpha motor neuron stops signaling muscle to contract, decreases ACh release *Acetycholinesterase* is an enzyme in neuromuscular junction that breaks down ACh Muscle fiber action potential stops Calcium moves back to sarcoplasmic reticulum Regulatory proteins return to blocking position Relaxation occurs

Where do the preganglionic and postganglionic fibers communicate?

Autonomic ganglion

What kind of drug would be used to treat fast heart rate?

Beta 1 antagonist: Blocks beta 1 (beta 1 would increase the heart rate)

What kind of drug would be used to treat asthma?

Beta 2 agonist: mimics beta 2 (dilating lungs)

Autonomic agonists

Bind to receptor as Neurotransmitter Elicit an effect that mimics that of neurotransmitter "mimetic" Mimics the NT it binds to

Autonomic Antagonists

Bind to receptors Blocks neurotransmitters response "lytic" Blocks NT and decrease NT

ATP

Binds to myosin head and detaches it from actin Hydrolysis of ATP transfers energy to myosin head and reorients it Reenergized head now capable of another power stroke

Muscle receptors

Both activated by muscle stretch, but monitor different types of information 1 Muscle spindle 2 Golgi tendon organs = in tendon, detects strength and tension in muscle

Which autonomic system utilizes chains of two neurons ?

Both sympathetic and parasympathetic

What neurotransmitter do the sympathetic and parasympathetic preganglionic fibers release?

Both sympathetic and parasympathetic preganglionic fibers release Acetylcholine

Which of the following is released by the sarcoplasmic reticulum?

Calcium

Excitation-contraction coupling

Calcium inside cell 1 *Acetylcholine* binds to motor neuron and is sent to skeletal muscle (neural-muscular junction) Opens sodium and potassium pumps Action potential T-tubules SR, calcium, tropomyosin and troponin, cross-bridge When calcium goes back into SR, can no longer form a cross-bridge

Central nervous system control of autonomic activities

Can be influenced by prefrontal association complex through its involvement with emotional expression characteristic of individual's personality. Hypothalamus plays a role in integrating autonomic, somatic, and endocrine responses that automatically accompany various emotional and behavioral states Medulla within brain stem is region directly responsible for autonomic output. Same autonomic reflexes, such as urination, defecation, and erection are integrated at spinal chord level.

Involuntary muscles

Cardiac muscles and smooth muscles

Which of the following is NOT characteristic of smooth muscle?

Cells contain actin and myosin organized into sarcomeres

Peripheral Nervous System

Communication link by which central nervous system controls activities of muscles and glands.

Myosin

Component of *thick filament* Protein consists of 2 identical subunits 1 tail ends are intertwined 2 Globular heads project out at one end Heads form cross-bridges between thick and thin filaments Cross-bridge has 2 important binding sites: 1 *actin-binding site* 2 *myosin ATPase site* Cross bridges project from each thick filament in six directions toward the surrounding thin filaments.

Muscle spindle structure

Consist of collections of specialized muscle fibers known as intrafusal fibers Lie within spindle shaped connective tissue capsules parallel to extrafusal fibers Each spindle as its own private efferent and afferent nerve supply Plays key role in stretch reflex

Types of contractions: Isometric

Constant length = the muscle length remains constant as tension increases

Types of contractions: Isotonic

Constant tension = the load remains constant as the muscle changes length

Types of contractions: Isokinetic

Constant velocity = the velocity remains constant as the muscle changes length

Muscles that produce precise, delicate movements

Contain fewer fibers per unit.

Myofibrils

Contractile elements of muscle fiber Regular arrangement of thick and thin filaments (proteins) Thick = myosin Thin = actin Viewed microscopically myofibril displays alternating dark (the A bands) and light bands (the I bands) giving appearance of striations Dark = A band, myosin Light = I band, actin

Muscle Twitch

Contractions of whole muscle can be of varying strength: Twitch: Brief, weak contraction Produced from single action potential Too short and too weak to be useful Normally does not take place in body

Muscle function

Controlled muscle contraction allows: Purposeful movement of the whole body or parts of the body Manipulation of external objects Propulsion of contents through various hollow internal organs Emptying of contents of certain organs to external environments Posture Heart generation Joint stability

Review of energy sources

Creatine phosphate gives phosphate to ADP to make ATP (1-6 seconds) Oxidate phosphorylation = Krebs cycle and ETC, needs oxygen Glycolysis = burning sugar, not much ATP, occurs quickly, high intensity (10-15 seconds)

Autonomic nervous systems- exceptions

Exceptions to the general rule of dual innervation by the 2 branches of Autonomic Nervous System: Most arterioles and veins receive only sympathetic nerve fibers Most sweat glands are innervated only by sympathetic nerves Salivary glands are innervated by both autonomic nervous system divisions but activity is not antagonistic-- both stimulate salivary secretion

Autonomic nerve pathway

Extends from central nervous system to an innervated organ Two neuron chain: 1 Preganglionic fiber (synapses with cell body and second neuron). Located in spinal chord, sends axon out 2 Postganglionic fiber (innervates effector organ). Sends axon to target tissue to release neurotransmitter

A muscle stretched to 150% of its resting length can still generate normal tension

False

Acetylcholine is associated with the autonomic "fight or flight" response

False

Every visceral function is controlled by both sympathetic and parasympathetic output ?

False

Nerve and muscle cells occasionally come into direct contact at a neuromuscular joint

False- cells do not touch the joint

A motor neuron interacts with many muscle cells

False- with one muscle cell

Single unit smooth muscle

Fibers can act as single unit Self excitable (does not require nervous stimulation for contraction) hormones Also called visceral smooth muscle Fibers become excited and contract as single unit Cells electrically linked by *gap junctions* Can also be described as a functional syncytium Contraction is *slow* and energy-efficient Well suited for forming walls of distensible, hollow organs, digestive system, uterus, bladder

Smooth muscle

Found in walls of hollow organs and tubes No striations Filaments do not form myofibrils Not arranged in sarcomere pattern found in skeletal muscle Spindle-shaped cells with single nucleus Cells usually arranged in sheets within muscle \Have dense bodies containing same protein in Z lines.

Cardiac muscle

Found only in heart walls Striated Cells are interconnected by gap junctions Fibers are joined in branching network Innervated by autonomic nervous system

Sarcomere

Functional unit of skeletal muscles Found between 2 Z lines, how muscles contract Regions of sarcomere: 1 *A Band* thick filaments along with portions of thin filaments that overlap on both ends of thick filaments 2 *I band* consists of remaining portion of thin filaments that do not project into A band. When muscles contract, A and I bands length changes,

During the contraction of a skeletal muscle that produces shortening, which of the following would occur in the sarcomere?

I band narrows (becomes shorter)

Adrenergic receptors: Alpha 2

Inhibitory, located on digestive organs, when activated the digestive system turns off

Autonomic Nervous System

Involuntary branch of peripheral nervous system Innervates cardiac muscle, smooth muscle, most exocrine glands, some endocrine glands, and adipose tissue

Which of the following is NOT associated with myosin?

It is the major component of the thin filament (that is actin)

*Tropomyosin*

Lies along side groove of actin spiral Covers actin sites, blocking cross-bridge binding

Energy sources of contraction

Limited stored ATP in muscle Muscle fibers have alternate pathways for forming new ATP Transfer of a high-energy phosphate from *creatine phosphate* to ADP Oxidate phosphorylation Glycolysis

Sympathetic adrenergic receptors: Alpha 1

Located on blood vessels, cell is activated to contract, higher blood pressure

Adrenergic receptors: Beta 2

Located on smooth muscle, respitory airways (lungs), *only* sensitive to epinephrine coming from adrenal medulla, cause relaxation

*Troponin*

Made of 3 polypeptide units: 1 binds to tropomyosin 1 binds to actin 1 binds with calcium Cross bride = muscle contraction No calcium then tropomyosin blocks actin, so myosin cannot come in With calcium troponin moves tropomyosin, so myosin can interact with actin Calcium is a key step in muscle contraction

Sarcoplasmic Reticulum

Modified ER Consists of fine network of interconnected compartments that surround each myofibril Stores and *releases calcium* to promote muscle contraction Stimulated by electrical signals flowing through muscle cell membrane

Effects on organs

Most visceral organs innervated by both sympathetic and parasympathetic fibers. In general produce opposite effects in a particular organ Dual innervation of organs by both branches of autonomic nervous system allows precise control over organ's activity.

Motor units

Motor unit; motor neuron and the muscle fibers it innervates Number of muscle fibers varies among different motor units. Number of muscle fibers per motor unit and number of motor units per muscle vary widely More motor units, stronger contractions

Muscle cell (fiber)

Muscle consists a number of muscle fibers lying parallel to one another and held together by connective tissue Single muscle cell is known as muscle fiber Multinucleated Large, elongated, and cylindrically shaped Fibers usually extend entire length of muscle Units of myofibrils

Alpha motor neurons

Muscle contracts

Which event is NOT associated with the binding of acetylcholine to receptors on the muscle membrane?

Muscle relaxation

Review of last two cards

Myosin and actin are proteins Myosin = thick, has a head and 2 binding sites When actin and myosin interact it is called a cross-bridge Myosin head = ATP site, makes energy for myosin

Power Stroke

Myosin head binds to actin Myosin head swivel toward center of sarcomere (power stroke) ATP binds to myosin head and detaches it from actin Hydrolysis of ATP transfers energy to myosin head and reorients it Contraction continues if ATP is available and calcium level in cytoplasm is high.

Review of power stroke

Myosin heads move and bend Z line is pulled toward the center Every time a myosin head moves, it uses all of its energy to bind to head (cross-bridge breaks) The cross bridge has to break to reenergize

Which autonomic system controls the activity of skeletal muscles that move the arms and legs?

NEITHER

Multiunit smooth muscle

Neurogenic Consists of discrete units that function independently of one another Units must be separately stimulated by nerves to contract

Cross bridges in smooth muscle

No troponin Calcium and calmodulin complex Activates enzyme myosin kinase adds phosphate to myosin, so it can interact with actin

Frequency of stimulation: tetanus

Occurs if muscle fiber is stimulated so rapidly that it does not have a chance to relax between stimuli Contraction is usually 3 or 4 times stronger than a single twitch Constant contraction

Central fatigue

Occurs when CNS no longer adequately activates motor neurons supplying working muscles Often a psychologically based Mechanisms involved in central fatigue are poorly understood

Muscle fatigue

Occurs when exercising muscle can no longer respond to stimuli with some degree of contractile activity Defense mechanism that protects muscle from reaching point at which it can no longer produce ATP Underlying causes of muscle fatigue are unclear

Adrenergic receptors: Beta 1

On the heart, excitatory response when stimulated, faster heart rate

What is the difference between to sympathetic and parasympathetic nervous systems to where they originate?

Originate = where preganglionic fibers originate Sympathetic originates in thoracic and lumbar Parasympathetic originates in cranial and sacral areas of central nervous system.

Asynchronous recruitment of motor units helps delay or prevent fatigue.

Other factors influencing extent to which tension can be developed: 1 Frequency of stimulation 2 Length of fiber at onset of contraction

Which autonomic system has ganglia found very close to the target organ?

Parasympathetic

Which autonomic system has the Vagus nerve as its major output nerve?

Parasympathetic

Which autonomic system stimulates urinary bladder contractions?

Parasympathetic

Force as a function of muscle length

Resting muscle length = highest contraction Short muscle= decrease ability of force Lengthened muscle = harder to contract Pulling actin and myosin apart - less cross bridges

Frequency of stimulation: twitch summation

Results from sustained *elevation of cytosolic calcium*

Striated muscles

Skeletal and cardiac muscles

Voluntary muscles

Skeletal muscles

Which statement concerning muscle contraction is true?

Smooth muscle does not rely on troponin and tropomyosin for contraction regulation

Unstriated muscles

Smooth muscles

Gamma motor neurons

Spindle shortens

If you wanted to pick up something heavier than your pencil (such as your book), you would need to develop elevated muscle tension. In what way might you accomplish this?

Stimulate more motor units

Somatic Nervous System

Subject to voluntary control Innervates skeletal muscle

Which autonomic system has cells that originate in the thoracic-lumbar region of the spinal chord?

Sympathetic

Which autonomic system is also known as the adrenergic system?

Sympathetic

Which autonomic system promotes activity of the adrenal medulla?

Sympathetic

Which autonomic system use NE to affect target structures?

Sympathetic

Which autonomic system uses a neurotransmitter that interacts with beta receptors ?

Sympathetic

What neurotransmitter do the sympathetic and parasympathetic postganglionic fibers release?

Sympathetic postganglionic release Norepinephrine Parasympathetic postganglionic releasers Acetylcholine

Describe the sympathetic and parasympathetic effects on the blood vessels

Sympathetic: constriction of all blood vessels Parasympathetic: Dilation of vessels supplying the penis and clitoris only

Describe the sympathetic and parasympathetic effects on the digestive tract

Sympathetic: decreased movement, contraction to prevent further movement of contents, inhibition of digestive secretions Parasympathetic: increased movement, stimulation of digestive secretions

Describe the sympathetic and parasympathetic effects on the lungs

Sympathetic: dilation of airways, inhibition of mucus secretion (fight or flight) Parasympathetic: constriction of airways, stimulation of mucus secretion (resting and digesting)

Describe the sympathetic and parasympathetic effects on the eye

Sympathetic: dilation of pupil, far vision Parasympathetic: constriction of pupil, near vision

Describe the sympathetic and parasympathetic effects on the heart

Sympathetic: increased heart rate, increased force of contraction of whole heart (fight or flight) Parasympathetic: Decreased heart rate, decreased force of contraction, of atria only (resting)

Describe the sympathetic and parasympathetic effects on the urinary bladder

Sympathetic: relaxing Parasympathetic: contraction or emptying bladder

Review of t-tubules

T-tubule extends plasma membrane interior of the cell to go to sarcoplasmic reticulum to release calcium Allows electricity (action potential) into cell to get SR to release calcium.

Muscle tension

Tension produced internally within sarcomeres Tension must be transmitted to bone by means of connective tissues and tendons before bone can be moved (series-elastic component) Muscle typically attached to at least 2 different bones across joint: 1 Origin = end of muscle attached to more stationary part of skeleton 2 Insertion = end of muscle attached to skeletal part that moves

Which event of skeletal muscle contraction is NOT stated correctly?

The muscle cell becomes hyperpolarized when stimulate by acetylcholine

The smallest functional unit of skeletal muscle is

The sarcomere

Which statement concerning alpha-motor neurons is correct?

They promote contraction of extrafusal skeletal muscle fibers

Composition of thin filaments

Thin filament has 3 components: 1 Actin = bead- like, main one 2 Tropomyosin = doesn't contract, but regulates contractions by allowing cross-bridges to happen 3 Troponin = interacts with calcium

Autonomic neurotransmitter receptors

Tissues innervated by autonomic nervous system have *one or more of several different receptor types* for postganglionic chemical messages. 1 Cholinergic receptors- bind to Ach 2 Adrenergic receptors- bind to norepinephrine and epinephrine, two types: 1 Alpha receptors 2 Beta receptors

During relaxation of a skeletal muscle this protein blocks the cross-bridge binding sites between the contractile proteins

Tropomyosin

Autonomic ganglia are the site where autonomic preganglionic and postganglionic cells interact

True

Constriction of the pupil when light is shined into the eye is a parasympathetic reflex?

True

Fast-glycolytic muscle fibers do not require as much oxygen as slow-Oxidate fibers

True

Most arterioles and veins receive only sympathetic innervation?

True

Motor neurons can only stimulate skeletal muscles

True

Muscles that have fine degree of control have small motor units

True

The adrenal medulla releases less norepinephrine than epinephrine

True

The creatine phosphate system is the first system utilized to supply ATP to a contracting muscle

True

The somatic system is considered to be under voluntary control

True

Visceral afferent input is used to direct autonomic output

True

Function spindle

Two fibers in muscle 1 extrafusal muscle fiber = old stuff (myosin and actin) 2 Intrafusal muscle fiber = spindles located inside They are parallel Contraction = spindle folds up and shortens, determines length

Graded contractions

Variations in the degree of muscle contraction Required for proper control of skeletal movement Reponses are graded by changing the frequency of stimulation and changing the strength of the stimulus

Multiunit smooth muscle found in

Walls of blood vessels and airways (controls diameter) Eyes ton adjust lens for near and far vision Iris of eye (contracts pupil size) Hair follicles (causes goose bumps)

Changes in banding pattern during shortening

When muscle contracts A band does not change width I band narrows (actin) Z lines get closer because actin is sliding across molecule

Sympathetic trunk

Where sympathetic nervous system preganglionic fibers and postganglionic fibers communicate

Muscles performing powerful, coarsely controlled movement

have larger number of fibers per motor unit