07: Fatigue and Finesse

Fatigue

Muscle accomplishes less contractile force or fails to contract due to use

Causes of fatigue

• Local accumulation of ADP and Pi

• Accumulation of waste

• Accumulation of EC K+

• Depletion of glycogen

Types of accumulated waste products

Heat and H+

How does K+ contribute to fatigue

Inhibits depolarization in the muscle cell

Central fatigue

Decrease in CNS stimulation of motor neurons

Why do animals breathe a lot after activity

Heat dissipation

Why do animals have an increased rate of oxygen metabolism after activity

• Replenishing CrP

• Converting lactate back into pyruvate and glucose

• Replenishing glycogen

Why is oxygen needed for post exercise recovery

ATP!!!

Muscle fiber types

• I

• IIA

• IIX

What determines the type of muscle fiber

Myosin heavy chain isotype

How do the myosin isotypes differ

Ability to hydrolyze ATP and cross bridge cycling

Speed of the different fiber types

• I: slow twitch

• IIA: fast-ish

• IIX: FAST

Speed of fiber types related to energy production

• I: slow oxidative

• IIA: fast oxidative

• IIX: fast glycolytic

What type of fiber has lots of mitochondria

Type I

What type of fiber relies more on glycolysis

Type IIX

The center of a muscle belly tends to be what type of fiber

Type I

The periphery of a muscle belly tends to be what type of fiber

Type IIX

How are axons and muscle fiber types organized

All the fibers associated with an axon will be the same fiber type

What type of fiber do we want most in beef cattle

IIX → LOTS of glycogen!

Red muscle fibers

Type I

Why are red muscle fibers red

Lots of mitochondria means lots of myoglobin needs to be present

White muscle fibers

IIX and IIB

Why are white muscle fibers white

Less myoglobin and more sugar

Why might different breeds of horses have different susceptibilities to muscle diseases

Different breeds have been engineered to have a different distribution of muscle fiber types

Ways to cause a muscle to adapt

• Ask it to produce more power that it is suited to (resistance training)

• Ask it for long term metabolic stress (aerobic conditioning)

What is crucial for muscle remodeling

REST

Why does muscle remodeling require rest

De novo protein synthesis takes time

What NT transmits nerve signal to muscle cells

Ach

What type of neurons control locomotion

Lower motor neurons

Myosin activity during eccentric contraction

Just enough activation to counteract the force being applied

How is muscle finesse facilitated/informed

Stretch receptors that communicate with sensory neurons (afferent)

Where is the sensory signal integrated to then inform locomotion

Brain, sometimes spinal cord

When does a signal get integrated at the spinal cord

For known and repetitive processes

What does it mean that the CNS is plastic

Constantly learning, and keeps track of repeated processes

What happens if the pressure in a joint changes

Your brain has no clue what is going on in the joint → less informed movement → lameness

Causes for lameness

• Peripheral issues: joint or neurons

• Central issues: integration or drunk

Spinal walking

Cyclic stimulation of opposing muscle groups to allow crude locomotion even if the brain is out of commission

How does spinal walking become normal walking

Fine tuning by the brain

How is the forelimb primarily propelled during locomotion

Stored energy in the stance passively released when the limb comes up (like a spring)

How is the hindlimb primarily propelled during locomotion

Muscle generating power (motor)

Primary mode of locomotion for gazelles

Almost all passive E and tendon stretch

Primary mode of locomotion for cheetahs

Muscular propulsion

How does a gazelle survive a cheetah

Starts zig zagging within the first three steps