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
