BSCI201 Exam 3

Contraction Steps.

1. Nerve impulses stimulate release of neurotransmitter called Acetylcholine.
2. When receptors have been stimulated, the sarcolemma exhibits electrical changes (Negative to neutral charges).
3. The Electrical changes spreads until it reaches the sarcoplasmic reticulum.
4. Sarcoplasmic reticulum stimulates the release of Ca+ ions into sarcomere, which causes myofilaments to undergo a conformational change and slide over one another.

What are the functions of the muscles?

Movement
Maintaining posture and body position
Stabilizing joints
Heat generation (especially skeletal muscle)

Dangerous heat levels are prevented by radiation of heat from the ___ and _____

Skin and sweating

Skeletal muscle tissue is attached to ______.
Is it striated?
Voluntary or not?

Attached to bones and skin
Striated
Voluntary

Cardiac muscle tissue is found where? Is it striated?

Only in the heart
Striated

Where is smooth muscle found? Is it striated? Voluntary?

Walls of hollow organs, stomach, urinary bladder, airways
Not striated
Involuntary

What are special characteristics of muscle tissue?

Vascularized and inverted, excitability, contractility, extensibility, elasticity

Myosin has ___ heads and is ____

Globular heads and is at an angle

Actin ____overlaps with myosin

Partially

Actin forms ____ strands

Double twisted

Thick filament has ___ molecules whose head protrude at _______

many myosin molecules.....protrude at opposite ends of the filament

tropomyosin

blocks the attachment site for the myosin crossbridge, thus preventing contraction

Troponin

____ is attached to the protein tropomyosin

Thin filament consists of ____ strands of ____ twisted in a helix plus two types of regulatory proteins: ______ and ______

two strands of actin subunits....regulatory proteins: troponin and tropomyosin

When calcium is present, myosin heads bind to ____. What is formed?

Actin, forms a cross bridge (ATP-->ADP)

Next, myosin heads __1___ and return to normal state, then they __2___ again and under go___3__

1. Detach
2. Bind again
3. Conformational change

What is the sliding filament theory

The actin (thin) filaments of muscle fibers slide past the myosin (thick) filaments during muscle contraction, while the two groups of filaments remain at relatively constant length.

During the sliding filament theory, what happens to the size of:
I Band
A Band
H zone
M line

I Band: decrease (could disappear)
A Band: (No change)
H zone: Disappears (could just decrease)
M line: No change

What ATP is used first in skeletal muscle contraction?

Stored ATP

This ATP is produced from direct phosporylation of ADP by CP using the enzyme Creatine Kinase

Creatine phosphate (CP)

What process produces the most ATP

Aerobic catabolism of glucose

Pyruvic acid is converted into lactic acid and ATP

Anaerobic catabolism of glucose

What are the three purposes of ATP in muscle contraction?

1. To activate myosin heads (enable cross bridge attachment)
2. Crossbridge detachment
3. Sequestration of calcium ions back into the SR for storage and active transport

Why does rigor mortis happen?

Caused by storage of calcium and ATP that stimulate myosin head to bind to actin sites. The binding of the head contracts the muscle but then because no more ATP and C+ are being made, the muscle can't relax and this leads to the body becoming rigid and stiff.

Acetylcholine:

(Neurotransmitter)
Diffuses across synaptic cleft and binds to receptors on sarcolemma.

Motor Unit:

The motor neuron and all of the skeletal muscles it innervates.

One motor neuron innervates...

many muscle fibers

One muscle fiber is innervated by...

only ONE neuron

Small motor Units:

Fine movements. Ex. Fingers, eyes.

Large motor units:

Large weight bearing muscles and gross movement. (Thighs, hips).

The force of muscle contraction is affected by:

The number of muscle fibers stimulated.
Relative size of the fibers-hypertrophy of cells increase strength.
Frequency of stimulation.
Sarcomere length.

Muscle Tension:

Force exerted by a contracting muscle.

Load:

Opposing force exerted on the muscle by weight of the object to be moved.

Contraction is...

The generation of force (tension).

Contraction does NOT necessarily cause...

shortening of the
fiber.

Shortening occurs when...

tension generated by crossbridges on the thin filament exceeds forces opposing shortening.

Isotonic Contractions:

Muscle changes in length and moves the load. (Bicep Curl)

Isotonic contractions are either...

Concentric or eccentric.

Concentric Contractions:

The muscle shortens and does work.

Eccentric contractions:

The muscle contracts as it lengthens.

Isometric Contractions:

The load is greater than the tension the muscle is able to develop.
(Pushing a wall)

Tension increases to the muscle capacity but the muscle ______

Neither shortens or lengthens

Speed of Contraction:

Speed at which Myosin ATPase hydrolyzes ATP.
Either Slow or Fast.

Major Pathway for ATP production are...

Aerobic respiration & Anaerobic respiration using more glycogen.

Aerobic respiration:

oxidative fiber

Anaerobic respiration using more glycogen:

Glycolytic fiber

What are the 3 major skeletal muscle types?

i) Slow Oxidative Fibers
ii)Fast Oxidative Fibers
iii) Fast Glycolytic fibers

Aerobic (endurance) exercise leads to increased...

- Muscle capillaries
- Number of mitochondria
- Myoglobin synthesis
- May convert fast glycolytic fibers into fast oxidative fibers

Resistance exercise (typically anaerobic) results in..

- Muscle hypertrophy (due to increase in fiber size) (Myofibril).
- Increased glycogen stores.

A bigger muscle is a...

Stronger muscle (can elicit more force)

Smooth muscle has two layers called?

Longitudinal and circular

Are smooth muscles slow or fast to contract?

Slow-myosin ATPase 10-100 times slower than skeletal

Smooth muscles are ___ shaped and multi or uni nucleated?

Spindle shaped and uninucleate

In smooth muscles, thick filaments and thin filaments arrange..

Diagonally

Thick filaments have heads along...

their entire length

Smooth muscle lacks...

sacromeres & myofibrils

Smooth muscle CELLS lack...

Z lines

Dense Bodies:

Anchor the thin filaments.

Intermediate Filaments:

Attached to the dense bodies and resist tension.

Tropomyosin:

-Present in thin filaments, but does
not block myosin binding sites on actin.

If there is no troponin complex such as in smooth muscle, what happens?

Protein calmodulin binds Ca2+

Sarcolemma of smooth muscle cells lack...

T-tubules

Caveolae (caveoli)

Shallow cavities.
Contain extracellular fluid rich in calcium.

Steps of Excitation-Contraction Coupling in Smooth Muscle:

1. Opening of calcium channels in plasma membrane and sarcoplasmic reticulum (Calcium enters cytosol)
2. Calcium ions bind to calmodulin
3. Ca-Calmodulin activates (myosin light chain kinase) MLCK
4. MLCK activates (phosphorylates) myosin
5. Crossbridge cycling (sliding filament theory)

Contraction of smooth muscle:

- Slow, synchronized contractions.
- Gap junctions (Electrically couple cells)
- Some cells are self-excitatory

Rate and intensity of contraction may be modified...

by neural and chemical stimuli.

Peristalsis:

Series of wave-like muscle contractions that moves food to different processing stations in the digestive tract. The process of peristalsis begins in the esophagus when a bolus of food is swallowed.

Longitudinal layer contracts:

Organ dilates and shortens.

Circular layer contracts:

Organ constricts and elongates.

Cardiac Muscle: Intercalated Disks:

- Gap junctions.
- Desmosomes

Aerobic muscle:

Coronary circulation

No cell division after infancy:

Hypertrophy

Can have spontaneous electrical changes:

Pacemaker cells/autorhythmic cells

Autorhythmiccells Percentage:

1%

Contractile cells Percentage:

99%

Cardiac Muscle:

- Striated with sarcomeres.
- Troponin & Tropomyosin.
- T tubules.
- Sarcoplasmic reticulum.
- Similar to slow oxidative fibers.

How is it Similar to slow oxidative fibers?

Myoglobin
Mitochondria
Slow to fatigue

Cardiac Muscle: Similarities with Smooth Muscle:

Gap Junction.
Pacemaker cells: autorhyhmic
Innervated by autonomic nervous system (involuntary)
Influenced by hormones

Groups of myofibers make up a

Fascicle

In skeletal muscles, calcium is released from the

Sarcoplasmic reticulum

Slow oxidative fibers are what color?

Red

Functions of the Nervous System:

1. Sensory input
2. Integration
3. Output

Afferent nerve fibers:

Conduct signals TO CNS (Sensory)

Efferent nerve fibers:

Conduct signals AWAY from CNS (Motor neurons, effector neurons)

Central Nervous System (CNS)

Consists of the brain and the spinal cord.
Dorsal body cavity surrounded by meninges.

Peripheral Nervous System (PNS)

All neural structures outside of the CNS.
Cranial nerves, spinal nerves and sensory receptors.

Peripheral nervous system division: Sensory

Somatic afferent fivers and visceral afferent fibers

Peripheral nervous system division: Motor

Somatic nervous system (voluntary)
Autonomic nervous system (involuntary)

Autonomic nervous system

Sympathetic and para sympathetic

Two principal cell types:

Neurons
Neuroglia

_______ are the excitable cells that _________

Neurons, transmit electrical signals

_______ (glial cells) are the ______ cells.
(Vary based location)

Neuroglia, supporting cells

Special characteristics of neurons

Generally amitotic (no cell division after birth).
High metabolic rate.
Continuous supply of oxygen and glucose.

Components of a Neuron:

-Cell body (Soma)
-Dendrites: reception of incoming information
-Axon: transmits electrical impulses called action potentials
-Axon hillock

SUPPORTING CELLS IN THE CNS:

Astrocytes
Microglia
Ependymal cells
Oligodendrocytes

Astrocytes:

- Numerous extensions that wrap around neurons.
- Involved in forming the blood brain barrier.
- Regulate brain function

Microglia

Macrophages to engulf/destroy pathogens and cell debris.

Ependymal cells:

Ciliated columnar cells
Line the ventricles
Circulate cerebrospinal fluid

Oligodendrocytes:

Their extensions myelinate axons of neurons in the CNS

SUPPORTING CELLS IN THE PNS:

Satellite cells: surround neuron cell bodies in the PNS
- Schwann cells (neurolemmocytes)