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UIUC / Molecular Cell and Developmental Biology / MCB / what is Chromatophilic substance (Nissl Bodies)?

what is Chromatophilic substance (Nissl Bodies)?

what is Chromatophilic substance (Nissl Bodies)?

Description

School: University of Illinois at Urbana - Champaign
Department: Molecular Cell and Developmental Biology
Course: Human Anatomy & Physiology I
Term: Fall 2019
Tags: anatomy and Physiology
Cost: 50
Name: MCB 244 Exam 3 Study Guide
Description: Completed Chapter 10 and 12 Study Guide
Uploaded: 11/16/2019
17 Pages 11 Views 13 Unlocks
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MCB244: EXAM 3 STUDY GUIDE


what is Chromatophilic substance (Nissl Bodies)?



Chapter 12: Nervous Tissue (Sections 12.1 – 12.4; 12.6-12.9)

1. Know the overall organization of the nervous system. Be able to distinguish between the structural components of the CNS vs PNS. Be able to distinguish between the afferent and efferent divisions: know the source(s) where they originate and source(s) where they end.

The nervous system is organised in two ways: Structural and Functional

Structural

Functional

CNS (central) and PNS (peripheral)

→ brain → nerves

→ spinal cord → ganglia

Afferent (Input)

- Sensory NS: detects stimuli and

transmits information from receptors to CNS

- Somatic Sensory: sensory

input that is consciously

perceived from receptors of Don't forget about the age old question of thea 101

blood vessels and internal

organs (eyes, ears, skin)

- Visceral Sensory: sensory


what is Perikaryon?



input that is not consciously

perceived from receptors of

blood vessels and internal

organs (<3)

*Enteric NS also part of efferent → → - ‘Second brain’ the gut- nerves to spinal cord

Efferent (Output)

- Motor NS: initiates and transmits from the CNS to effectors

- Somatic Motor: motor output

that is consciously or

voluntarily controlled; effector

is skeletal muscle

- Autonomic Motor: motor

output that is not consciously

or involuntary controlled;

effectors are cardiac muscle,

smooth muscle, and glands

MCB244: EXAM 3 STUDY GUIDE

2. Know the various structural components of a typical multipolar neuron that were addressed in class including: If you want to learn more check out vi-trade test

Multipolar Neuron- multiple process extend directly from the cell body; typically has many dendrites, one axon (most common)


what is Axon hillock?



Axons can be insulated with myelin sheath which is formed by glial cells (neurolemmocytes or oligodendrocytes)

● Dendrites (not insulated w/ myelin): they transmit graded potentials along plasma membranes; more dendrites means more input a neuron can receive

● Soma- cell body that contains the nucleus, connects with dendrites

● Chromatophilic substance (Nissl Bodies): cell bodies contain this made of free and bound ribosomes- ‘grey matter’

● Perikaryon- plasma membrane encloses cytoplasm

● Axon- initiate and propagate action potentials along their axolemma, which trigger synaptic vesicles to release neurotransmitters from the synaptic knobs ● Axon hillock- area that controls the initiation of the neuron’s chemical impulse after processing the incoming signals from other neurons; connects to cell body with axon

● Axolemma- plasma membrane of an axon

● Axoplasm- cytoplasm within an axon

● Synaptic terminal/terminal extension 

● Synaptic knobs- extreme tips of of the terminal extensions; within are numerous synaptic vesicles containing neurotransmitter

3. Know the various types and functions of glial cells of the CNS and PNS.

Glial Cells- non excitable, found in CNS and PNS; small in size but outnumbers the amount of neurons We also discuss several other topics like ksu 125

- Unlike neurons (esp in CNS) glial cells are mitotic

- Function: protect and nourish neurons, provide physical structural support for nervous tissue and facilitate neuronal structural guidance during development. Critical for normal function at neural synapse.

MCB244: EXAM 3 STUDY GUIDE

Glial Cells in CNS

Ependymal Cells (physical protector)- lines internal cavities of the brain and spinal cord, forms choroid plexus (produces CSF) with nearby capillaries, ciliate (helps circulates CSF) simple cuboidal or simple columnar epithelial cells 

Astrocytes (chemical protector)- starshaped; most numerous in CNS. Functions: Don't forget about the age old question of uop chemistry

- helps form blood brain barrier- regulated substances that enter NS from blood - Regulates the neuronal environment in CNS (interstitial fluid composition) - Form structural framework: strong cytoskeleton helps support nearby neurons - Secrete chemicals that regulate synapse formation

Microglia (immunological)- small, rare cells that wander CNS and replicate in infection

- Eat pathogens in CNS and play roll in general “tissue” repair in NS

- Immune phagocytic cells that engulf infectious agents

- Remove debris from damaged CNS tissue and maintain structural integrity (synaptic pruning)

Oligodendrocytes- large cells with slender extensions that wrap around axons of neurons forming myelin sheath (acts as electrical insulation to speed up action potential conduction/propagation)

*not all neurons are myelinated

Glial Cells in PNS

- Overall regulation of environment

Satellite Cells- arranged around neuronal cell bodies in a ganglion (nerve cell bodies located in the autonomic NS and sensory system, mostly outside the central NS). Function: electrically insulate and regulate the exchange of nutrients and wastes between neuron and interstitial fluid

Schwann Cells (Neurolemmocytes)- elongated, flat cells that cover PNS axons with myelin. Function: allows for faster action potential/propagation Don't forget about the age old question of donatello accomplishments

**Neurolemmocytes myelinate axons in the PNS, and oligodendrocytes myelinate axons in the CNSDon't forget about the age old question of parian wreath

MCB244: EXAM 3 STUDY GUIDE

4. Understand the concept of the electrochemical gradient and know the factors that influence it specifically for sodium and potassium ions.

Na+ ions: ECG drives Na+ INTO THE CELL at normal resting potential K+ ions: ECG drives K+ OUT OF THE CELL at normal resting potential If left unbothered, Na+ and K+ diffuse down ECG

5. For sodium and potassium know the following:

● Their relative distributions across the cell membrane

● Their relative permeabilities across the cell membrane under resting conditions ● Their equilibrium potentials - know the magnitude and sign as well as what it represents.

Sodium Na+

● Distribution: enters cells

● Permeability under RMP: less permeable than K+

● Equilibrium potential: 60mV

Potassium K+

● distribution : exits cell

● Permeability: more permeable than Na+; reaches equilibrium faster

● Equilibrium potential: -90mV

6. Be able to distinguish between chemical and electrical synapses.

Synapse- where neuron connects to another neuron or effector

Chemical Synapse- most common in CNS

- Release and transmission of chemical from neuron to effector 

- Presynaptic neuron’s axon terminal: produces signal

- Postsynaptic neuron/effector: receives signal

- Synaptic cleft: small fluid-filled gap between neurons

Electrical Synapse (limited regions of the brain and the eyes)

- Presynaptic and postsynaptic neurons bond together by gap junction (direct exchange of intracellular components. The cells act as though they shared a plasma membrane. - No synaptic delay in electrical signal

MCB244: EXAM 3 STUDY GUIDE

7. Be familiar with the anatomy of a typical chemical synapse including the pre-synaptic neuron, post-synaptic neuron, synapse, synapse cleft etc.

a. At the axon terminal the electrical impulse passes to another cell at a cellular connection called the synapse

b. The space between the presynaptic neuron and a postsynaptic cell is called the synaptic cleft. The presynaptic neuron contains signal molecules called

neurotransmitters that are packaged inside vesicles.

c. When an action potential reaches the end of a neuron, neurotransmitters are released by exocytosis from the neuron into the cleft.

d. The neurotransmitters bind to the adjacent cell at the receptor sites attached to ion channels.

e. The channel opens, allowing movement of ions into or out of the effector cell, which alters its membrane potential, thereby transmitting the signal from the neuron to the effector cell.

8. Know the important physiological functions of and be able to distinguish between the following types of potentials:

● Resting membrane potential

○ Passive ion movement- Na+ and K+ ions diffuse down the

electrochemical gradient to reach equilibrium

● Graded potentials

○ Dependant upon magnitude of stimulus (graded)

○ Occur in receptive segment of a neuron (dendrites and cell bodies) due to the opening of chemically gated channels

○ Diffusion of ions across membrane changes the electrical potential

occurring in either depolarization (more positive) or repolarization (more negative)

■ If Na+ channels open→ depolarization (cell is less negative than

RMP)

■ If Cl- channels open→ hyperpolarization (cell is more negative

than RMP)

■ If K+ channels open→ hyperpolarization (cell is more negative

than RMP )

● Action potentials

○ Generated within the initial segment and propagated along the conductive segment of a neuron

○ Action potential is initiated when voltage-gated channels open in response to a minimum voltage change (threshold value)

MCB244: EXAM 3 STUDY GUIDE

○ Voltage gated Na+ channels open first allowing depolarization and then K+ voltage gated channels open allowing K+ out to cause repolarization

(return membrane from positive to negative)

● Equilibrium potential

○ There is no net driving force for an ion to move in or out of the cell (ions are evenly distributed)

○ Na+ has eq potential of 60mV and K+ an eq potential of -90mV

9. Know the difference between a pump and a channel in terms of membrane potentials and ion movements across the plasma membrane. Know the various states channels can exist in (e.g. open/activated; closed/deactivated vs inactivated).

Pumps- require energy to move ions AGAINST their concentration gradient to maintain the concentration gradient (K+ into the cell, Na+ out of the cell)

Channels- protein pores in membrane that allows for diffusion of ions DOWN their concentration gradient

- Resting (closed but can be opened) – activation gate closed, inactivation gate open - Activation (open) – activation gate opens due to voltage change, inactivation gate open - Inactivation (closed but can’t be opened) – activation gate open, inactivation gate closed

10. Be able to compare and contrast the 3 types of gated channels (mechanically, voltage and ligand) as well as leak channels and their roles in neuronal activity.

- Voltage gated – normally closed, open when membrane charge changes; Voltage gated channels has 3 states

- Mechanically gated – opens and closes in response to mechanical vibration or pressure

- Ligand gated – bind neurotransmitters and open in response to ligand binding; Control synaptic transmission between two neurons or neuron and muscle - Leak (passive) – always open for continuous diffusion

- Chemically gated – normally closed, opens when neurotransmitter binds

MCB244: EXAM 3 STUDY GUIDE

11. For the resting membrane potential

a. Know the sign and magnitude of the resting membrane potential as well as the active and passive forces (e.g. channels, ions etc.) responsible for setting it. i. Na+ and K+ subjected to concentration gradient and electrical gradients produced electrochemical gradient

ii. Active transport helps return to RMP

b. Know all of the major components which contribute to it, specifically, know the importance of the Na/K-ATPase pump and how it works.

i. The Na/K-ATPase pump is active transport and helps maintain the

concentration gradient

c. Know the importance of Na+ and K+ with regard to their relative contributions to the resting membrane potential

i. 3Na+ out and 2K+ in

12. Know in detail the sequence of steps involved in the generation of action potentials with specific reference to the movement of Na+ and K+ ions during the various phases (depolarization, repolarization etc.), gating of membrane channels and refractory periods. a. A threshold stimulus opens voltage gated Na+ channels (phase 1)

b. Na+ ions diffuse INTO the axon DEPOLARIZATION it to +30mV (making it LESS negative which causes other Na+ channels to open)

c. Inactivation gates of Na+ channels then close

d. Voltage gated K+ channels open causing K+ ions to diffuse OUT of the axon REPOLARIZING it to a negative value (beyond -70mV)

e. Phase 3 starts; Membrane potential briefly HYPERPOLARIZES. Voltage gated K+ channels close

f. Na+ channels are released from inactivation

g. Membrane potential returns to resting stage of -70mV because ions only move through LEAK CHANNELS until RMP is back to -70mV

13. Be able to distinguish between and know the characteristics of excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs). How does each affect membrane potentials?

- EPSP- depolarization caused by cation (usually Na+ but sometimes Ca2+) entry - Make membrane potential more positive

- IPSP- hyperpolarization caused by cation exit (K+) or anion (Cl-) entry - Makes membrane potential more negative

MCB244: EXAM 3 STUDY GUIDE

14. Know in detail the various ways for propagation of action potentials down an axon. Be able to distinguish between continuous conduction and salutatory conduction. Are there any advantages/disadvantages of one vs the other? What physical/structural requirement is needed to have salutatory conduction? Understand how axon diameter affects the propagation of action potentials and how it, along with myelination.

- Regeneration continues in one direction to axon terminals- unidirectional propagation.

- After Na+ channels close and K+ channels open, it renders the segment temporarily insensitive or REFRACTORY to another stimulus. However, Na+ channels downstream segment are close and receptive to the depolarizing stimulus

- In UNMYELINATED axons- continuous conduction occurs; charge opens up voltage-gated channels, change enters, then spreads to adjacent regions and opens more channels

- In MYELINATED axons- propagation is different; propagating in a saltatory or leaping fashion. Myelinated cells use less ATP to remain RMP. Action potentials occur only at Node of Ranvier (where axons voltage gated channels are

concentrated); rapid current jumping node to node

- The LARGER the diameter the FASTER the action potential because there is less resistance of movement of ions

15. Know in detail the sequence of steps involved in neurotransmitter release at a typical chemical synapse.

a. At the axon terminal the electrical impulse passes to another cell at a cellular connection called the synapse

b. The space between the presynaptic neuron and a postsynaptic cell is called the synaptic cleft. The presynaptic neuron contains signal molecules called

neurotransmitters that are packaged inside vesicles.

c. When an action potential reaches the end of a neuron, neurotransmitters are released by exocytosis from the neuron into the cleft.

d. The neurotransmitters bind to the adjacent cell at the receptor sites attached to ion channels.

e. The channel opens, allowing movement of ions into or out of the effector cell, which alters its membrane potential, thereby transmitting the signal from the neuron to the effector cell.

16. Be able to distinguish between temporal and spatial summation and their effects on action potential generation.

MCB244: EXAM 3 STUDY GUIDE

a. Spatial Summation- occurs when multiple presynaptic neurons release neurotransmitter at various locations onto the receptive segment, this generating EPSP’s, IPSP’s or both in the postsynaptic neuron

i. two EPSPS are added together and both move the membrane potential toward threshold

ii. two IPSPs are added together to move the membrane potential away from the threshold

iii. If an EPSP and IPSP arrive simultaneously toward the threshold, is

canceled out by the IPSP which moves the membrane potential away from threshold

b. Temporal Summation- occurs when a simple presynaptic neuron repeatedly releases neurotransmitter to produce either multiple EPSPS or IPSPS in the postsynaptic neuron at the same location within a very short amount of time

i. One presynaptic neuron rapidly establishes two postsynaptic potentials (because they are established by the same presynaptic neuron it must

either be two EPSPS or two IPSPS)

ii. Two EPSPS are added together and both move the membrane potential toward threshold

iii. Two IPSPS are added together to move the membrane away from

threshold

c. Typically BOTH spatial and temporal summation are occuring simultaneously. When graded potentials arrive at the initial segment within a small period of time, they can either contribute to (if EPSPS) or interfere with (if IPSPS) the threshold value being reached

i. If threshold value is reached, action potential is initiated

ii. Change below the threshold is not sufficient to open voltage gated

channels and is called a subthreshold value; channels remain closed

and no action potential is initiated.

MCB244: EXAM 3 STUDY GUIDE

Chapter 10 Skeletal Muscle Physiology 

1. Know the functions skeletal muscle tissues perform.

a. Movement (body) – bones, speak, breathe, swallow

b. Maintenance of posture – stabilizes joint

c. Protection and support – package internal organs and hold them in place d. Regulating elimination of materials – circular muscle bands (sphincter) control passage of materials at orifices (digestive system)

e. Heat production – help maintain body temperature

2. Be familiar with the structural and functional organization of skeletal muscles from the whole muscle to fascicles to fibers etc. down to the level of myofibrils and myofilaments.

- Tendon (attaches muscle to bone) composed to dense regular CT

- Muscle fibers are bundled with in a fascicle and many fascicles are bundled within the whole skeletal muscle

- The entire muscle is ensheathed in a tough outer connective tissue called the epimysium (dense irregular CT). Each fascicle is wrapped in a connective tissue layer called the perimysium (dense irregular CT). Within fascicles, each muscle fiber is surrounded by a delicate connective tissue layer called the endomysium (areolar CT- electrically insulate the muscle fibers).

- The plasma membrane of muscle fibers is the sarcolemma, cytoplasm is sarcoplasm, specialized smooth ER which stores, releases, and retrieves calcium ions is called the sarcoplasmic reticulum SR.

- A functional unit of skeletal muscle is the sarcomere, a highly organized arrangement of contractile myofilaments actin (thin filaments) and myosin (thick filaments), along with other support proteins

- Striations are created by the organization of actin and myosin resulting in the banding pattern of myofibrils. Individual contractile subunits myofibrils, each is surrounded by SR. The SR contains Ca+ ions.

- Myofibrils contain thick and thin filaments. Subunits called sarcomeres made up of actin and myofilaments (protein filaments)

MCB244: EXAM 3 STUDY GUIDE

3. Know the following components of connective tissue sheaths (epimysium, perimysium & endomysium). What structural units do they cover, what are they composed of, and what structures do they come together to form at the end of muscles? Connective Tissue Sheaths – come together to form tendon or fascia

a. Epimysium – covers entire whole skeletal muscle

 i. Composed of dense irregular CT

b. Perimysium - covers fascicles

 i. Composed of dense irregular CT

 ii. Contains nerves and blood vessels (arteries and veins) c. Endomysium – covers muscle fibers

 i. Composed of areolar CT

 ii. Provides capillary support to muscle fiber cells

4. What cells fuse to form skeletal muscle fibers during development? How does this relate to the fact that skeletal muscles are multinucleated cells.

Formation of skeletal muscle fibers during development

a. Myoblast cells – fuse together to form muscle fibers, maintain nucleus causing muscle fiber to be multinucleated

5. What are myosatellite cells and what is/are their function(s)? How do these cells relate to the fact that muscle fibers are amitotic and how do these cells play a role in muscle hypertrophy? Myosatellite cells - Do not go to form muscle fiber

a. Fuse w/ and attempt to repair damaged muscle fibers

b. Muscle Hypertrophy – satellite cells repair old/damaged muscle fibers so that they can regrow and increase in size.

6. Be able to identify the functions and characteristics of skeletal muscle fiber components: motor-end plate, t-tubules, sarcoplasm, sarcolemma, thick and thin filaments, sarcoplasmic reticulum, terminal cisterna, sarcomeres, triads, etc.

Skeletal Muscle Fiber components: 

a. Sarcolemma (plasma membrane) –

i. has t-tubules (transverse tubules): contains voltage-gated ion channels

b. Sarcoplasm (cytoplasm) – Has typical organelles, plus contractile proteins c. Sarcoplasmic reticulum (SR) – Internal membrane complex; multinucleated  i. Terminal cisternae – blind sacs of SR

- Stores Calcium ions until muscle fiber is stimulated; arranged in groups of 2 to border T-tubules to form Triad

MCB244: EXAM 3 STUDY GUIDE

- Contains channels that allow for Calcium diffusion when muscle fiber is stimulated and calcium pumps (actively transports Calcium from

sarcoplasm to SR)

d. Myofibrils

i.Thick filaments – myosin (contractile protein)

1. Each myosin molecule has 2 heads and 2 intertwined tails

2. Heads have binding site for actin (thin filament) & ATPase site

3. Heads point towards end of filament

ii. Thin filament – actin (contractile protein)

1. Consist of fibrous actin (F-actin)

2. Each strand of F-actin composed of actin globules (G-actin)

3. Each g-actin has a myosin binding site, which myosin heads attach to during contraction

 iii. Tropomyosin (regulatory protein) – twisted string-like protein covering actin in a non contractile muscle

iv. Troponin (regulatory protein) – globular protein attached to tropomyosin 1. Binding of Ca2 to troponin pulls off tropomyosin, allowing

contraction

v. Sarcomere – composed of overlapping thick & thin filaments

1. Separated at both ends by Z-discs, which anchor thin filaments

e. Energy production of muscle fiber –

 i. Mitochondria – abundant mitochondria for aerobic ATP production

 ii. Glycogen – stored for quick release of energy

 iii. Creatine Phosphate – quickly gives up Phosphate group to replenish ATP supply

MCB244: EXAM 3 STUDY GUIDE

7. Know the components of a sarcomere including thin and thick filaments and all the contractile, stabilizing and regulatory proteins [actin, troponin, tropomyosin, myosin, titin] as well as all of the different regions, zones and bands of the sarcomere (A, I & H bands, Z & M lines and the zone of overlap).

a. Z-Disc: Ends of thin filaments

b. I-bands: contain only thin filaments, intersected by Z-disc (light region)  i. Gets smaller when muscle contracts

c. A-bands (only overlapping zone): contains thick filaments and overlapping thin filaments

 i.Central region of sarcomere

d. H-zone: only thick filaments; no thin filament overlap

 i. Disappears with maximal muscle contraction

 ii. Central portion of A-band

e. M-line: Protein meshwork structure

 i. Attachment site for thick filaments

f. Connectin – stabilizes thick filament and has “springlike” properties (passive tension) g. Dystrophin – anchors some myofibrils to sarcolemma protein

 i. Abnormalities of this protein causes muscle dystrophy

8. How does the morphology(size)of the different regions zone of the sarcomere change during contraction? What is the basis of muscle shortening according to the sliding filament theory? - When the sarcomere contracts: the H zone disappears, the I hand narrows in width and may disappear, and the Z discs in each sarcomere move closer together. However, thin and thick filaments do not shorten. A description of the repetitive movement of thin filaments sliding past thick filaments is called the sliding filament theory. Muscle Shortening – Sarcomere shortens when Z-discs move closer together; thick and thin filaments stay the same length but slide past each other.

9. Know the major 3 major phases of skeletal muscle contraction.

(Z line goes closer to M line)

MCB244: EXAM 3 STUDY GUIDE

1. Events at Neuromuscular Junction

2. Sarcolemma, T-tubules, and Sarcoplasmic Reticulum- Excitation-contraction coupling

3. Cross-bridge cycling

11.Know the steps in detail that occur at the neuromuscular junction and all important molecular proteins involved (e.g. voltage-gated channels, presynaptic vesicles etc.). 1. Events at Neuromuscular Junction

a. A nerve signal triggers voltage gated Ca2+ channels to open-- Ca2+ enters synaptic knob and binds to synaptic vesicles

b. ACh is released by exocytosis into synaptic cleft

c. ACh binds to ACh receptors

12. Know the steps in detail that occur in EC coupling beginning with the generation of the end-plate potential (what causes it) up to the increases in Ca2+ levels in the sarcoplasm (where does this calcium come from and what is the signal for its entry into the sarcoplasm).

2. Sarcolemma, T-tubules, and Sarcoplasmic Reticulum- Excitation-contraction coupling

a. ACh binding causes Na+ to rapidly enter the skeletal muscle fiber and K+ to slowly exit the skeletal muscle fiber, which may result in an end-plate potential (EPP)

b. The EPP initiates an action potential along the sarcolemma and T-tubules c. Action potential triggers Ca2+ release from SR terminal cisternae

13. Know the steps in detail involved in cross-bridge cycling. You should know the roles of both contractile and regulatory proteins, ATP and calcium. Know at what step in the cycle does sarcomere shortening occur and what is ATP’s role in the overall process.

3. Cross-bridge cycling - Ca2+ binding to troponin triggers cross-bridge cycling a. Ca2+ binds to troponin exposing myosin binding sites on actin

b. Attach: Crossbridge formation between myosin and actin

c. Pull: Power stroke motion of myosin head pulls thin filament past it

d. Release: ATP binds to myosin head releasing myosin head from actin e. Reset: ATP split and myosin head is reset

14.Muscle fiber relaxation is considered a passive event but what ‘active’ process is responsible for its occurrence?

MCB244: EXAM 3 STUDY GUIDE

Muscle Fiber relaxation – passive event, but an “active” event is responsible for occurrence a. Any disturbance/reverse of sequence of events in NMJ, EC coupling, or cross-bridge

15. What is muscle tension and what factors influence it?

 Muscle Tension – force generated when a muscle is stimulated to contract a. Influencing factors – number of muscle fibers recruited

16. What is a muscle “twitch” and what are the three phases that comprise a twitch? You should be familiar with the events that occur during each of the phases as well. Muscle Twitch

a. Latent period – Time after stimulus, before contraction, no change in tension b. Contraction period – Tension is increasing,

i. Begins as power strokes pull thin filament

c. Relaxation period – Tension begins decreasing to baseline

 i. Begins with the release of crossbridge

17. Be familiar and be able to identify the different types of frequency stimulations (treppe, wave summation vs tetanus [complete/incomplete]). How do they differ from one another in terms of their contraction/relaxation properties at the level of contractile/regulatory proteins and regulatory elements (Ca2+)?

Types of frequency stimulation

a. Treppe – An increase in twitch tension (stimuli occur 10-20 times per sec) i. Voltage is the same for each stimulus

ii. Relaxation is complete for each twitch

iii. Twitches get stronger because insufficient time to remove Ca2+ between twitches

iv. Skeletal muscles don’t exhibit treppe graded summations in muscle contraction

b. Wave summation – occurs if stimulus occurs about 20 times per sec

MCB244: EXAM 3 STUDY GUIDE

 i. Relaxation is incomplete between twitches

ii. Contractile forces add up to produce higher tensions

c. Incomplete tetany – occurs when frequency is increased further

i. Tension increases and twitches partially fuse

d. Complete tetany – occurs when frequency is around 40-50 per sec.  i. No relaxation time

 ii. High frequency stimuli lead to fatigue (decreased tension production)

18. Be able to define what a motor unit is and what it is comprised of. Understand the phenomenon of recruitment and understand the relationship between the number of motor units activated and whole muscle tension generation.

Motor Unit – single motor neuron and all the muscle fibers it innervates a. Motor neuron – as voltage increases, more motor units/neurons are recruited i. More motor neurons allow for better force control

 ii. A motor neuron can innervate multiple muscle fibers

b. Recruitment - Recruitment of fewer/more motor units to lift lighter/heavier objects c. Size – determine degree of control (Size and control have inverse relationship) i. Small motor neuron – less than 5 muscle fibers, more control

 ii. Larger motor neuron – more muscle fibers, less control

d. Above a certain voltage, all units are recruited, and maximum contraction is reached

19. Be able to distinguish between isometric and isotonic contractions.

Isometric and Isotonic contraction

a. Isometric – muscle length stays the same

 i. Tension increases, but is insufficient to overcome

resistance

b. Isotonic – tone stays constant, length changes

 i. Tension overcomes resistance

 ii. Concentric – muscle shortens

 iii. Eccentric - muscle lengths

20. Understand how muscle/sarcomere length affects muscle tension.

Muscle and Sarcomere length

a. Contracted length – Filament movement is limited, weaker force

b. Resting length – maximum contractile force due to optimal overlap of myosin and actin, greatest muscle tension

c. Extended length – generates weaker force, lowest muscle tension 21.Be familiar with the factors that produce muscle fatigue.

MCB244: EXAM 3 STUDY GUIDE

Muscle Fatigue – reduced ability to produce muscle tension

a. Primary factor – decrease glycogen storage during prolonged exercise b. Neural fatigue – Insufficient Ca2+ to enter synaptic knob

 i. Ca2+ needed to release ACh to excite fibers for contraction

c. EC coupling – altered ion concentrations impair AP conduction and Ca2+ release from SR

i. Ca2+ needed to interact with myofilaments for contraction (crossbridge cycling)

d. Crossbridge cycling – Excessive Pi slows release from myosin head i. Less Ca2+ available to bind to troponin, can’t contract muscles

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