APSM 2441 Exam #3

The phenomenon in which stimuli arriving at different times cause larger contractions is called...

wave summation

Describe the nerve and blood supple of skeletal muscle.

well vascularized, highly innervated, somatic motor neurons contract muscle

fused tetanus

when a skeletal muscle fiber is stimulated at a higher rate of 80 to 100 times per second, it does not relax at all

unfused tetanus

when a skeletal muscle fiber is stimulated at a rate of 20 to 30 times per second, it can only partially relax between stimuli

neuromuscular junction

where muscle action potentials arise; the synapse between a somatic motor neuron and a skeletal muscle fiber

axon hillock

where the axon joins the cell body

trigger zone

where the nerve impulse begins

nebulin

wraps around actin filament which anchors the actin to the Z discs

PNS

-12 cranial nerves -31 pairs of spinal nerves

fast oxidative glycolytic fibers (type IIa)

-contraction time: moderately fast -size of motor neuron: medium -fatigue resistance: fairly high -type of activity: long-term aerobic -max duration use: <30min -force production: medium -mitochondrial density: high -capillary density: intermediate -oxidative capacity: high -glycolytic capacity: high -major storage fuel: PCr, glycogen

slow oxidative fibers (type I)

-contraction time: slow -size of motor neuron: small -fatigue resistance: high -type of activity: aerobic -max duration use: hours -force production: low -mitochondrial density: high -capillary density: high -oxidative capacity: high -glycolytic capacity: low -major storage fuel: triacylglycerol

fast glycolytic fibers (type IIb)

-contraction time: very fast -size of motor neuron: very large -fatigue resistance: low -type of activity: short-term anaerobic -max duration use: <1min -force production: very high -mitochondrial density: low -capillary density: low -oxidative capacity: low -glycolytic capacity: high -major storage fuel: PCr, glycogen

motor neurons (efferent)

-convey info from CNS to effector organs in the periphery -most are multipolar

muscular atrophy

-decrease in diameter of muscle fibers -wasting away of muscles -loss of myrofibrils -caused by disuse and denervation

Explain how neurons display great diversity in size and shape.

-dendritic branching pattern is varied and distinctive -some have long or short axons altogether

creatine phosphate

-energy-rich molecule found in muscle fibers -when muscle fibers are relaxed they produce an excess of ATP which is used to synthesize creatine phosphate. - 3-6 times more plentiful than ATP in the sarcoplasm of a relaxed muscle fiber

interneurons

-in CNS -integrate sensory info and stimulate motor response -most are multipolar

peripheral fatigue

-inadequate release of Ca2+ from the SR -depletion of creatine phosphate -insufficient oxygen -depletion of glycogen and other nutrients -buildup of lactic acid and ADP -failure of the motor neuron to release enough ACh

sensory neurons (afferent)

-sensory receptors at distal end -send info to CNS through cranial/spinal nerve -most are unipolar

slow axonal transport

1-5mm per day, axoplasm moves in one direction (from the cell body toward the axon terminals-anterograde), moves mostly axoplasm and cytoskeletal proteins

Name the 4 functions of muscular tissue.

1. producing body movements - movements of the whole body and localized movements such as grasping a pencil is the result of muscular contraction, and integrated function of skeletal muscles, bones, joints and the nervous system 2. stabilizing body positions - when awake postural muscles continuously contract, holding your head upright 3. storing and moving substances within the body - sphincters are rings of smooth muscles whose sustained contractions store substances, preventing them from moving out of a hollow organ; smooth and cardiac muscle, skeletal muscle moves fluids through lymph and veins 4. generating heat (thermogenesis) - involuntary contractions of skeletal muscles, known as shivering, can increase the rate of heat production; muscle contraction generates heat (ATP production releases heat)

Everything done in the nervous system involves 3 fundamental steps...

1. sensory function 2. integrative function 3. motor function

What are the 4 sources of muscle energy?

1. stored ATP - 3 sec 2. energy transferred from creatine phosphate - 12 sec 3. anaerobic glycolysis - 2 min max 4. aerobic respiration - minutes to hours *all except for aerobic respiration are anaerobic processes

astrocytes

1. structural support of neurons 2. wrap around blood capillaries and secret chemicals to prevent the entry of harmful substances to reinforce the blood brain barrier 3. maintain ISF environment 4. in embryos, regulate growth and interconnections among neurons in the brain 5. role in learning and memory by influencing the formation of new neural synapses

Maximum tension (force) is dependent on...

1. the rate at which nerve impulses arrive (frequency of stimulation) 2. the size of the motor unit (gradation of force) 3. the amount of stretch before contraction (length-tension relationship) 4. the nutrient and oxygen availability (anaerobic and aerobic respiration)

fast twitch=

10 msec

relaxation period

10-100 msec, when Ca2+ is actvely transported back to the SR

In response to a single action potential, cardiac muscle contracts ____ times longer than skeletal muscle.

10-15

slow twitch=

100 msec

A single muscle cell from a biceps may contain ____ sarcomeres.

100,000

Delayed onset muscle soreness can take how long?

12-48hrs

fast axonal transport

200-400mm per day, uses motor proteins to carry material along the axon; anterograde (provides supply of organelles and neurotransmitter containing synaptic vesicles); retrograde (degradation of materials)

Describe the events that occur at the neuromuscular junction.

1. ACh is released from synaptic vesicle. 2. ACh binds to ACh receptor (in the junctional fold). 3. Muscle action potential is produced. 4. ACh is broken down.

Name the characteristics of muscular tissue.

1. excitability 2. contractibility 3. extensibility 4. elasticity

What are the 4 steps of the contraction cycle (cross-bridge cycling)?

1. myosin head hydrolyzes ATP and becomes energized and oriented. 2. myosin head binds to actin, forming a cross-bridge. 3. myosin head pivots, pulling the thin filament past the thick filament toward center of the sarcomere (power stroke). 4. as myosin head binds ATP, the cross-bridge detaches from actin.

When can the contraction cycle begin?

At the onset of contraction, the sarcoplasmic reticulum releases calcium ions into the sarcoplasm. There, they bind to troponin. Troponin then moves tropomyosin away from the myosin-binding sites on actin.

The epimysium, perimysium, and endomysium are all extensions of the ____ of the ____.

CT; tendons

contraction period

Lasts 10-100 msec, when Ca2+ binds to troponin, myosin-binding sites on actin are exposed, and cross-bridges form

The ____ is a reinforcement of the fascia lata.

IT band

The Sliding-Filament Mechanism

Muscle contraction occurs because myosin heads attach to and "walk" along the thin filaments at both ends of a sarcomere, progressively pulling the thin filaments toward the M line. As a result, the thin filaments slide inward and meet at the center of the sarcomere (may even overlap), and the Z discs (which are attached to the thin filaments) get closer together which shortens the sarcomere (this causes the shortening of the whole muscle fiber). As the thin filaments slide inward, the I band and H zone narrow and eventually disappear when the muscle is maximally contracted. The width of the A band and the individual lengths of the thin and thick filaments remain unchanged.

Muscle action potential

Na+ gates open during the depolarization phase and K+ gates open during the repolarization stage. Since the Na+ is higher outside of the call then inside, when Na+ channels open Na+ rushes into the cell causing a positive charge in the transmembrane potential (depolarization). After the Na+ gates close, K+ gates open. Since K+ is higher inside of the cell than outside, the K+ rushes out of the cell causing a negative drop in the transmembrane potential (repolarization).

multiple sclerosis

autoimmune disease attacks the myelin sheath in the CNS; nerves send unreliable and often effectively conduct signals

When is the number of skeletal muscle fibers set?

before you are born

Small motor units are recruited ____ large motor units. This allows for increasing ____.

before; gradations of strength

The amount of myelin increases from ...

birth to maturity

botulinum toxin

blocks release of ACh from synaptic vesicles and may cause death by respiratory muscle paralysis; may be found in improperly canned foods *botox

axon collaterals

branches of an axon

latent period

brief delay between the time of stimulation and the beginning of contraction; during the latent period the muscle action potential sweeps over the sarcolemma and Ca2+ is released into sarcoplasmic reticulum

Because of the ____ , the peak tension generated during fused tetanus is 5 to 10 times larger than the peak tension produced during a single twitch.

buildup of Ca2+

triad

a T-tubule and two terminal cisterns on either side

nerve

a bundle of hundreds to thousands of axons plus associated CT and blood vessels that lie outside the brain and spinal cord

sarcoplasmic reticulum

a fluid-filled system of membranous sacs that encircles each myofibril

curare

a plant poison used by South American Indians on arrows and blowgun darts that blocks ACh receptors inhibiting Na+ ion channels; causes muscle paralysis derivatives of curare are used during surgery to relax skeletal muscles

rheumatism

a problem affecting joints and surrounding CT

unmyelinated axons

a schwann cell "protects"a group of axons, but it does not speed up the rate of nerve impulse

extensibility

ability of muscular tissue to stretch, within limits, without being damaged

Muscle spasms can cause cramps and are usually brought on by...

alcoholism dehydration heavy exercise hypothyroidism kidney failure medications muscle fatigue metabolic problems pregnancy reduced levels of Mg or Ca

central fatigue

caused by the CNS and psychological mechanisms and manifests as feeling "tired" or not wanting to go on

fibromyalgia

chronic, painful, nonarticular rheumatic disorder that affects the CT of muscles, tendons and ligaments; may cause fatique, poor sleep, headaches, depression, and IBS

ependymal cells

ciliated cells that line brain ventricles and central canal of spinal cord and aid in the circulation of cerebrospinal fluid (CSF)

Maximum tension is developed when the sarcomere length is ____ where the zone of overlap is ____.

close to resting length; optimal

motor unit

composed of a motor neuron plus all of the muscle cells it innervates

titin

connects Z disc to M line of sarcomere stabilizing the thick filament position

gray matter

contains neuronal cell bodies, dendrites, unmyelinated axons, axon terminals, and neuroglia

white matter

primarily myelinated axons

muscular dystrophy

progressive degeneration of skeletal muscle fibers

axon

propagates the nerve impulse

structural proteins

provide sarcomere alignment, elasticity and extensibility; titin, alpha-actinin, myomesin, nebulin, dystrophin

Dendrites

receiving or input portion of neuron

troponin

regulatory protein that is a component of thin filament; when calcium ions bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin

tropomyosin

regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin

Muscle fibers ____ the cells damage and more ____ are formed.

repair; myofibrils

endomysium

separates individual muscle fibers within the fascicles; reticular fibers

multipolar neurons

several dendrites and one axon (ex. most neurons in the brain, and motor neurons)

graded potentials

short distance communication

synapse

site of communication between a neuron and its effector

What are the 3 types of muscular tissue?

skeletal, cardiac, and visceral smooth muscle

Anticholinesterase agents

slow the enzymatic activity of acetylcholinesterase; can strengthen weak muscle contractions (ex. Neostigmine)

How is muscle tone sustained?

small groups of motor units are alternatively active and inactive in a constantly shifting pattern to sustain muscle tone

myofilaments

smaller protein structures within myofibrils (thin or thick)

The myofibrils of ____ are not arranged into sarcomeres.

smooth muscle cells

The myelin sheath increases the...

speed of nerve conduction

axoplasm

cytoplasm

As the sarcomeres of a muscle fiber are stretched to a longer length, the tension the fiber can produce ____.

decreases

excitation-contraction coupling

steps that connect excitation of the muscle cell by a motor neuron, to the contractile mechanism of the muscle cell; it involves the events at the junction between a motor neuron and a skeletal muscle fiber

alpha-actinin

structural protein of Z discs that attaches to actin molecules of thin filaments and to titin molecules

myomesin

structural protein that forms M line of sarcomere; binds to titin molecules and connects adjacent thick filaments to one another

Both ____ and ____ features are used to classify the various neurons in the body.

structural, functional

unipolar neuron

dendrites and one axon form a continuous process that emerges from the cell body (ex. sensory receptors detect stimuli such as touch, pressure, pain, thermal; cell bodies in ganglia outside the spinal cord

terminal cisterns

dilated end sacs of the sarcoplasmic reticulum

Neurotransmitter, organelles, cytoplasm and other substances created in the cell body must be moved...

down the axon of a neuron to the axon terminal

Neurons have ____. Define.

electrical excitability-capacity to respond to stimuli and produce action potentials

Schwann cells

encircle PNS axons; each cell myelinates a single axon; axon regeneration

axon terminals

end point of an axon (telodendria)

Type I fibers are used for...

endurance like running a marathon

In groups of muscles the ____ continues to become ____, forming ____ which covers many muscles.

epimysium; thicker; fascia

The ____ envelops the entire group of quadriceps and hamstring muscles.

fascia lata

More precise movements are controlled by muscles with...

few muscle fibers per neuron (ex. muscles of the larynx and eye) 2-20 fibers/neuron

Muscle tone keeps skeletal muscles ____.

firm

What is used to show the terminal processes of a single neuron which terminate on a few muscle fibers?

florescent dye

oligodendrocytes

form and maintain the myelin sheath of multiple axons

Nodes of Ranvier

gaps in myelin sheath

To meet this demand, cardiac muscle uses the rich supply of O2 delivered by the coronary circulation to ____.

generate ATP through aerobic respiration

contractile proteins

generate force; actin and myosin

Name the connective tissue components of skeletal muscle.

hypodermis fascia epimysium perimysium endomysium tendon

aerobic respiration

if sufficient oxygen is present, the pyruvic acid formed by glycolysis enters the mitochondria and undergoes a series of oxygen-requiring reactions that produce ATP, CO2, water and heat

Myasthenia gravis

immune system disorder in which antibodies block ACh receptors, causing muscle weakness

Tay-Sachs disease

improper alignment of the myelin sheath in CNS; multiple rigidity, seizures, eventual blindness, dementia, and lack of coordination; life span 3-4 years

spasm

sudden involuntary contraction of a single muscle (usually painless)

neuroglia

supportive cells of the nervous system: the "glue" that holds the nervous tissue together; smaller but more abundant than neurons; undergo cellular division and act as "scar tissue" in cases of neural damage or disease; present in CNS and PNS

satellite cells

surround cell bodies in the ganglia; support the cell body; regulate exchange of fluid between ISF and neuronal cell bodies

synaptic end bulbs

swollen axon terminals containing vesicles storing neurotransmitter

contractibility

the ability of muscular tissue to contract forcefully when stimulated by an action potential

elasticity

the ability of muscular tissue to return to its original length and shape after contraction and extension

excitability

the ability to respond to certain stimuli by producing electrical signals called muscle action potentials (impulses)

sarcomere

the basic functional unit of skeletal muscle fibers; an arrangement of thick and thin filaments sandwiched between two Z discs

neurology

the branch of medical science that deals with the normal functioning and disorders of the nervous system

twitch contraction

the brief contraction of all the muscle fibers in a motor unit in response to a single action potential in its motor neuron (lasts from 20-200 msec)

What are measurable markers of muscle damage?

increased plasma myoglobin (red-colored protein binds oxygen molecules that diffuse into muscle fibers from interstitial fluid; releases oxygen when needed by mitochondria for ATP) and creatine kinase

length-tension relationship

indicates how the forcefulness of muscle contraction depends on the length of the sarcomeres within a muscle before contraction begins

Botox

inhibits exocytosis of ACh from nerve ending

Type II is used for...

intense anaerobic activity of short duration

Cross-bridge cycling cannot occur without ____.

intracellular Ca2+ release from its storage sites in the sarcoplasmic reticulum

cramp

involuntary, painful muscle contraction caused by inadequate blood flow to muscles (such as in dehydration), overuse and injury, or abnormal blood electrolyte levels (potassium)

What is the general function of the nervous system?

keeps controlled conditions within limits that maintain homeostasis; responsible for all our behaviors, memories, and movements

The motor end plate is rich in ____ that respond to Acetylcholine.

ligand-gated sodium channels

dystrophin

links thin filaments to proteins of sarcolemma

action potentials

long distance communication

Skeletal muscle fibers are very ____ cells and are ____.

long; multi-nucleated

Large-scale, powerful movements are controlled by muscles with...

many muscle fibers per neuron (ex. biceps brachii, gastrocnemius, quadriceps femoris) 2,000-3,000 fibers/neuron

electromyography

measures the electrical activity of muscles (resting muscles=no electrical activity; contracting muscles=the greater tension developed the more electrical activity)

The sarcolemma at the neuromuscular junction is called the ____.

motor end plate

myelin sheath

multilayered lipid and protein covering; surrounds some axons; insulator; increases the speed of nerve conduction

As a muscle action potential propagates along the sarcolemma and into the T tubules, it causes the release of Ca2+ from the SR into the sarcoplasm and this triggers ____.

muscle contraction

Z-disc

narrow, plate-shaped regions of dense protein material that separate one sarcomere from the next

action potential is a ____.

nerve action potential

Can significant skeletal muscle damage be repaired?

no; fibrosis occurs

bipolar neurons

one main dendrite and one axon (ex. retina of eye, inner ear, olfactory area of brain)

initial segment

part of axon closest to the axon hillock

refractory period

period of lost excitability after stimulus is applied

microglia

phagocytes that remove debris

axolemma

plasma membrane

myofibril

the contractile organelles of skeletal muscle

The repetition of the sliding filament mechanism is known as...

the contraction cycle

sarcoplasm

the cytoplasm of a muscle fiber

neuron

the functional unit of the nervous system

muscle fatigue

the inability of muscle to maintain force of contraction after prolonged activity

perimysium

the layer that surrounds the fascicles (bundle of muscle fibers); dense irregular CT

epimysium

the outer layer, encircling the entire muscle; dense irregular CT

sarcolemma

the plasma membrane of the muscle cell

motor unit recruitment

the process in which the number of active motor units increases

isometric contraction

the tension generated is not enough for the object to be moved and the muscle does not change its length

isotonic contraction

the tension remains constant while muscle length changes

transverse tubules

tiny invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber

True or False: the motor neuron sends the same strength of signal every time.

true

microtubules

tubules that transport proteins along the axon

regulatory proteins

turn muscle contractions on and off; troponin and tropomyosin

Most sensory neurons are ____.

unipolar

What are parts of a neuron?

1. Cell body-contains the nucleus 2. Dendrites-the receiving (input) portion of the neuron 3. Axon-a projection from the cell body along which a nerve impulse travels

muscular hypertrophy

-an increase in muscle fiber diameter -testosterone and human growth hormone -caused by repeated mechanical overload

muscular hyperplasia

-an increase in the number of muscle fibers -satellite cells (can fuse with damaged muscle cells, or with one another to regenerate functional muscle fibers)

CNS

-brain (85 billion neurons) -spinal cord (100 million neurons)

fascia

-connective tissue covering a group of skeletal muscles -sheath of fibrous tissue enclosing a muscle or organ; attaches, stabilizes, encloses and separates muscles and other organs -protective lining for vessels, nerve and lymph (reduces friction between contracting muscles and other structures)

all-or-nothing principle

The principle that once the electrical impulse reaches a certain level of intensity (its threshold), it fires and moves all the way down the axon without losing any intensity. The muscle cell must contract at full force, and all of the muscle fibers in that motor unit must all contract at the same time.

muscle tone

a small amount of continuous tension in the muscle due to weak contractions of motor units

Nerve fiber

any extension from the cell body of a neuron

actin

contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction

myosin

contractile protein that makes up thick filament; consists of a tail and 2 myosin heads, which bind to myosin-binding sites on actin molecules during muscle contraction

How does intense exercise damage muscle fibers?

tears sarcolemmas, damages myofibrils, and disrupts Z-discs

The muscle cell can vary in the amount of ____ depending on the ____.

tension it generates; number of signals sent per minute

anaerobic glycolysis

the entire process by which the breakdown of glucose gives rise to lactic acid when oxygen is absent or at a low concentration

Where is the mitochondria in muscle fiber cells?

the mitochondria lie in rows throughout the muscle fiber, strategically close to contractile muscle proteins that use ATP during contraction so that ATP can be produced as quickly as needed

eccentric isotonic contraction

the muscle elongates (the cross-bridges resist the movement of a load and slow lengthening)

concentric isotonic contraction

the muscle shortens (the tension developed by the muscle is greater than the load)