Physiology Lecture 9 - Muscle Mechanics/Exercise Physiology

Proprioceptive sense (proprioception)

the sense of self-movement and body position, generated as a result of our own action, which is important for fine control of movements

Afferent neurons

Nerve cells that carry impulses towards the central nervous system

Efferent neurons

Nerve cells that conduct impulses away from the central nervous system

Proprioceptors

these are located inmsucles joints and skin in order to sense proprioception

Muscle spindles

these are part of the skeletal muscle and change muscle LENGTH

Golgi tendon organs

Receptors sensitive to change in tension of the muscle and the rate of that change

Extrafusal fibers

these are ordinary muscle fibers

Intrafusal fibers

modified muscle fibers within the spindle, with a non-contractile central portion

detect changes in muscle length 

maintain spindle stretch sensitivity during voluntary contractions

What is the primary function of the muscle spindles?

Muscle Length

muscle spindles monitor changes in ______________ ____________

Stretch Reflex

the contraction of a muscle in response to stretch of that muscle, using muscle spindles

to protect the muscle from stretching too quickly

support body structure

Why do we have the stretch refle

stretches, muscle spindles

Tapping the patellar ligament ______________ the quadricepts and excites its ____________ __________________

Afferent sensory impulses

the ________________ _________________ ________________ travel to the spinal cord when the patellar ligament is tapped, making monosynaptic excitatory synapses on alpha motor neurons and intraneurons

Alpha motor neurons

these send activating impulses to the quadricepts, causing it to contract, leading to knee extension

Interneurons

these make inhibitory synapses on alpha motor neurons that innervate antagonist muscles

Extrafusal (ordinary) muscle fibers

These receive efferent stimulation from alpha motor neurons in stretch reflex

Intrafusal muscle fibers

these are activated by the efferent gamma motor neurons that innervate the contractile ends of spindle fiber in stretch reflex

Co-Activation

____-______________ of alpha and gamma motor neurons coordinates shortening of both intrafusal and extrafusal fibers, to maintain spindle sensitivity to stretch, during reflex and voluntary contractions

alpha and gamma

Co-activation of ____ and ____ motor neurons coordinates shortening of both intrafusal and extrafusal fibers. This maintsin spindle fiber sensitivity to stretch, during reflex and voluntary contractins

golgi tendon organ

A _______ _______ ______ consists of endings of a single afferent sensory nerve fiber intertwined within bundles of connective tissue that makes up the tendon

muscle length

muscle spindles are sensitive to changes in _____ ______

muscle tension

Golgi tendon organs detect and respond to changes in _____ _____ that are caused by muscular contraction but not passive stretch

The brain

Information from the tendon organs is sent to where for processing?

Motor-unit recruitment

twitch summation

length-tension relationship

These are the 3 primary factors that can be adjusted to accomplish gradation of whole-muscle tension

Motor unit

this is defined as a single motor neuron and all of the muscel fibers innervated by it

Motor unit recruitment

this mechanism allows more motor units to be stimulated simultaneously to result in a stronger contraction

Small

_____________(smalll/large) motor units allow for very precise adjustments in contraction strength

Large

______________(small/large) motor units alow less precise adjustments in contraction strength, but allow for stronger contractions in general

High frequency

when a muscle fiber is stimulated at a _________ __________________, the muscle tension builds up and reaches a maximal sustained contraction (tetanus)

Ca2+, cross bridge cycling

Twitch summation allows for sustained contraction because of the elevation in cytosolic _____(what ion?) level and continued ____________-_______________ __________________

Twitch summation

this results from two contributory contractions of a muscle, allowing for many action potentials in a short amount

Cross-bridge cycling, SERCA (Ca2+ pump)

these two things in skeletal muscle require ATP when contraction occurs

Creatine phosphate, Glycolysis, Oxidative phosphorylation

these three methods supply the additional ATP as needed during muscle contractions

Creatine phosphate

this acts as an accessible energy store in rested muscle, making it a major energy pool.

Creatine Kinase

Creatine can be used as ATP because the enzyme ___________ ___________ transfers a high energy phosphate from ATP to creatine, and vice versa

First few seconds

Creatine is used for ATP in the _________ _________ __________________ of exercise, so it cannot be used long term

Glycolysis

this anaerobic metabolic process doesn't require O2 and can be used for fast ATP production during exercise, however it only produces 2 ATP per glucose so it cannot be used long term

Lactic Acid

If there is a lot of glycolysis activity, there ends up being a build up of this in the muscle

Oxidative Phosphorylation

this production of ATP uses O2 in the muscles in order to produce ATP, but takes a longer amount of time so it is used for long term exercise, and breating is required

Type I fibers (Slow-oxidative)

this type of fiber has a lot of mitochondria and myoglobin, and derive energy primarily through aerobic oxidative phosphorylation of fatty acids. Used for continuous contractions over long periods, and marathon runners have a higher amount of these

Type IIa (fast-oxidative fibers)

these types of fibers have a lot of mitochondria and myoglobin, but a lot of glycogen as well. They use oxidative phosphorylation and anaerobic glycolysis for ATP, used for rapid contractions and short bursts of activity

Type IIx (glycolytic fibers)

these types of fibers have less mitochondria and less myoglobin, and A TON of glycogen, depending largely on glycolysis energy. These fibers are adapted for rapid contractions, but fatigue very quickly. Examples are the muscles that move the eyes or the digits

Broad

most humans have a ____________ distribution of muscle fiber types

Genetics

while most humans have a broad distribution of muscle fiber types, some humans based on their _____________ have a different distribution of fiber types, which might make them better in athletic performance

Aerobic exercise

this type of exercise can increase the number of mitochnodria and capillaries supplying blood to uscle fibers to increase the amount of O2 going to the muscle

Do not

in aerobic exercise, muscles __________(do/do not) change size

Anaerobic Exercise

this type of exercise uses weightlifting to increase the muscle size

Hypertrophy

this is the increase of musle size, specifically the fast-glycolytic fibers from increased synthesis of myosin and actin

Does not

Anaerobic exercise __________(does/does not) increase performance endurance

Muscle atrophy

lack of muscle activity; reduces muscle size, tone, and power

Disuse atrophy

this type of muscle atrophy occurs when a muscle is not sued for a long period, but innervation is intact (ex. broken bones, bed confinement, malnutrition)

Denervation atrophy

this type of muscle atrophy occurs after the innervation of a muscle is lost, usually from an injury or neurodegenerative disease

Age-related atrophy (sarcopenia)

this type of muscle atrophy occurs naturally with aging