Ex Phys Exam 2 Old Stuff

Reciprocal Inhibition

The reflex relaxation of the antagonist muscle in response to the contraction of the agonist.

Muscle Tonus

A state of low-level muscle contraction at rest

Gamma Motor Neurons

Contract the distal poles of intrafusal fibers, causing a stretch in the central portion of the Intrafusal fibers that is sensed by the Flower-Spray & Annulospiral Neurons

Annulospiral Neurons (Bag & Chain)

-Senses rate of length change

-Dynamic Response (knee-jerk, head-jerk)

-Static Response

Flower-Spray Neurons (Chain)

-Senses Muscle length

-Static Response

Intrafusal Fibers

-Nuclear Bag fibers: thick and extend beyond capsule and attach to connective tissue

-Nuclear Chain fibers: thin and short

Myotatic (Stretch) Reflex

Stimulus Stretches Quadriceps

Afferent neuron(2) transmits stimulus to CNS and bifurcates within CNS, synapsing with interneuron(3) and alpha motor neuron(4a)

Alpha motor neuron(4a) activates the agonist muscle

Interneuron(3) synapses with the efferent fiber(4b) and inhibits the antagonist muscle resulting in knee extension(5)

Gamma efferent neurons(6) innervate the muscle spindles and help provide smooth, coordinated movements

Golgi Tendon Orgrans

•Consists of a thin capsule of connective tissue enclosing collagenous fibers

•In series with skeletal muscle fibers

1)Protection against muscle damage

2)Flexibility: Muscles that are relaxed can be stretched further by opposing muscles or external force

3)Provides sensory information regarding muscle tension to the cerebellum, which allows for smooth movement during activities such as running, which involve rap cycling between flexion and extension

•Both static and dynamic components

Inverse Myotatic Reflex

•Increased tension stimulates the Golgi Tendon Organ(1), and afferent neurons transmits this impulse to the spinal cord(2)

•Within the spinal cord, the afferent neuron synapses with the inhibitory association neuron and an excitatory motor neuron(3)

•Inhibitory association neuron synapses with a motor neuron innervating the agonist(4a)

•Excitatory association neuron synapses with a motor neuron innervating antagonist(4b)

•Resulting in agonist relaxation and antagonist contraction(5)

4 Stages of Carbohydrate Cellular Respiration

•Stage I: Glycolysis

•Stage II: Formation of Acetyl Coenzyme A

•Stage III: Krebs Cycle

•Stage IV: Electron Transport and Oxidative Phosphorylation

Glycogen Synthase

Rate limiting enzyme of glycogen synthesis

Glycogen Phosphorylase

Rate limiting enzyme of glycogen breakdown

Hexokinase

Glucose entering the cell is trapped by phosphorylation using ATP (ATP->ADP)

This enzyme is inhibited by glucose 6-phosphate

Phosphofructokinase 1

Rate Limiting Step of glycolysis

Fructose-6-Phosphate is Phosphorylated to Fructose-2,6-Biphoshate (ATP->ADP)

Glyceraldehyde 3-Phosphate Dehydrogenase

Catalyzes an oxidation and addition of inorganic phosphate to its substrate

Reduction of NAD⁺ -> NADH

3-Phosphoglycerate Kinase

Step 7 Enzyme

Substrate level phosphorylation (ADP->ATP)

Pyruvate Kinase

Step 10 Enzyme 

Substrate level phosphorylation (ADP->ATP)

Lactate Dehydrogenase

Step 11 Enzyme

Reoxidzes NADH -> NAD⁺

“Anaerobic” Glycolysis

•When oxygen is not present (anaerobic)  Pyruvate cannot move forward in the energy metabolism steps and is converted to Lactate.

oCatalyzed by lactate dehydrogenase (LDH)

Cori Cycle

Lactate is converted back to glucose in the Liver

Muscle Contraction (Factors in Lactate Production)

•Ca release during the coupling action of actin and myosin causes Glycogenolysis and the released muscle glycogen is processed by fast glycolysis which results in lactate production regardless of oxygen levels

Enzyme Activity (Factors in Lactate Production)

•Lactate dehydrogenase and pyruvate dehydrogenase, are used to convert pyruvate to lactate or pyruvate to acetyl Co A, respectively

•LDH has one of the highest rates of any other glycolytic enzyme, so lactate production is an inevitable consequence of glycolysis. 

•The more pyruvate provided, the more lactate is produced, because LDH is much faster then PDH

Muscle Fiber Type (Factors in Lactate Production)

•Fast twitch fibers are preferentially recruited during high intensity exercise and due to LDH isosome (facilitate pyruvate to lactate) and low mitochondrial density in these fibers, lactate is produced in these fibers regardless of oxygen availability

SNS Activation (Factors in Lactate Production)

•During heavy exercise the SNS is activated, triggering a cascade of actions resulting in an increase in glycogen breakdown, which results in high levels of G6P

•High levels of G6P increase the rate of glycolysis, which increases level of pyruvate, which ultimately increases lactate production as we discussed previously

Insufficient Oxygen (Factors in Lactate Production)

•High intensity exercise or static exercise where muscle contraction actually can impede blood flow

•A reduction is blood flow reduces oxygen delivery, which ultimately leads to an increase in lactate production

GLUT 1

Glucose transporter that is non-insulin regulated

Exercise will stimulate the use of GLUT 1

GLUT 4

Glucose transporter that is insulin regulated

Insulin signaling will stimulate the use of GLUT 4

MCT1

Take up Lactate from circulation

Shuttle lactate between and within muscle fibers

MCT4

Cell membranes of glycolytic skeletal fibers and is especially suited for lactate export