Nakamura Human Physiology Lecture 7 Flashcards
(25 cards)
Skeletal muscle actions
Extensor: increases the angle at a joint Flexor: decreases the angle at a joint Abductor: moves limb away from the midline of the body Adductor: moves limb toward the midline of the body Levator: moves insertion upward Depressor: moves insertion downward Rotator: rotates a bone along its axis Sphincter: constricts an opening
Types of muscle contractions
Twitch Summation Incomplete tetanus Complete tetanus Treppe: staircase effect
Twitch
-Muscle is stimulated with a single electrical shock from nerve (above threshold).
–Quickly contracts and then relaxes. (1 contraction 1 relaxation)
–Increasing stimulus increases the strength of the twitch (up to maximum).
Summation
.–If second electrical shock is administered before complete relaxation of muscle
- slight relaxation then second shock
- increases the strength of contraction
Incomplete tetanus
-Stimulator delivers an increasing frequency of electrical shocks.
–Relaxation period shortens between twitches.
–Strength of contraction increases.
Complete tetanus
-Fusion frequency of stimulation.
–No visible relaxation between twitches.
–Smooth sustained contraction
Treppe
Staircase effect
–Electrical shocks are delivered at maximal voltage.
–Each shock produces a separate, stronger twitch (up to maximum).
–Due to an increase in intracellular calcium
-gradual increase
Isometric and isotonic contractions
.•In order for a muscle to shorten, it must generate a force greater than the opposing forces that act to prevent movement.
•Isometric Contractions (a)
–Length of muscle fibers remain constant
-if the number of muscle fibers activated is too few to shorten the muscle (or load is too large)
•Isotonic Contractions (b)
–Force of contraction remains constant throughout the shortening process
Length - tension relationship
-The sarcomeres are at the optimum length to develop maximum tension when the fiber is relaxed (2.25 um)
•At shorter sarcomere lengths, contraction strength is less (1.65 um, etc)
•At very long sarcomere lengths, contraction strength is less (3.65 um)
ATP usage
-ATP synthesized by the muscle is used as the energy source for:
–Muscular contraction (Myosin ATPase)
–The Ca2+ pumps in the sarcoplasmic reticulum (follows concentration gradient so can be used for the next cycle)
Another source of power for muscular activity
-A muscle may use ATP faster during sustained activity than it can replace through respiratory metabolism (referring to the electron transport chain in mitochondria)
•Phosphocreatine is a high energy reserve of phosphate that can be donated to ADP to form ATP
•Skeletal muscle has about 3X more phosphocreatine than ATP
-creatine kinase is the enzyme that makes ATP from ADP and phosphocreatine
-phosphate is used, creatine is left
-creatine is removed by the kidneys, if kidneys damaged creatine content in blood would be high
Slow oxidative/type 1 (red)
Diameter: small Z line thickness: wide Glycogen (stored glucose) content: low Resistance to fatigue: high Capillaries: many Myoglobin (O2 carrier in muscle) content: high Respiration: aerobic Oxidative capacity: high Glycolytic capacity: low Twitch rate: slow Myosin ATPase content: low
Fast oxidative/ type IIA (red)
.Diameter: intermediate Z line thickness: intermediate Glycogen (stored glucose) content: intermediate Resistance to fatigue: intermediate Capillaries: many Myoglobin (O2 carrier in muscle) content: high Respiration: aerobic Oxidative capacity: high Glycolytic capacity: high Twitch rate: fast Myosin ATPase content: high
Fast glycolytic/ type IIx (white)
.Diameter: large Z line thickness: narrow Glycogen (stored glucose) content: high Resistance to fatigue: low Capillaries: few Myoglobin (O2 carrier in muscle) content: low Respiration: anaerobic Oxidative capacity: low Glycolytic capacity: high Twitch rate: fast Myosin ATPase content: high
Oxidative capacity
.a measure of a muscle’s maximal capacity to use oxygen in microlitres of oxygen consumed per gram of muscle per hour. Factors which affect the oxidative capacity of muscles include the activity of oxidative enzymes .
Major metabolic pathways
Digestion: proteins, polysaccharides and lipids broken down (stage 1)
Cytoplasm: (stage 2) pyruvic acid to lactic acid and acetyl CoA
Mitochondria: (stage 3) Krebs cycle, then electron transport and oxidative phosphorylation
Study diagram
Summary of glycolysis and respiration
Glycolysis takes place in cytoplasm, yields 2 ATP
Krebs cycle yields 2 ATP and in mitochondria
Electron transport yields 34 ATP
Aerobic: 38 ATP
Anaerobic: 2 ATP
Without oxygen pyruvic acid can’t go any further/ can’t go to mitochondria
Motor control of muscles
.Upper Motor Neurons in brain (location of cell body)
•Lower Motor Neurons in spinal cord that innervate the muscle
•Alpha Motor Neurons innervate extrafusal (normal) muscle fibers
•Gamma Motor Neurons innervate intrafusal (inside muscles, esp larger ones and ones in the lower limb) (muscle spindle) fibers
Sensory control
Muscle spindles: change muscle length/tension bcuz they sense how heavy something is
Two types of muscle spindle fibers
-nuclear bag fibers
-nuclear chain fibers
-Annulospiral endings is the sensory neuron that controls both
-Flower spray endings is the sensory neuron that controls just the chain fiber
-Golgi tendon organs: tendon part of sensory control. Relaxes muscle tension
Muscle spindle
-sensory device within muscle
-controls by both sensory and motor
Muscle Spindles (in parallel)
•Nuclear bag fibers: nuclei arranged loosely in the center of the fiber
•Nuclear chain fibers: nuclei are in a row
•Sensory neurons
•Annulospiral endings (Primary) are wrapped around central region of nuclear bag and chain fibers, respond to rapid changes in length
•Flower-spray endings (Secondary) are inserted into the contracting poles of nuclear chain fibers, respond to sustained stretch
Monosynaptic (stretch) reflex
Ex) knee jerk reflex
-Passive stretch of the muscle activates the annulospiral endings on the spindles
•The annulospiral endings synapse onto alpha motor neurons
•Activation of the alpha motor neurons stimulates the extrafusal muscle fibers to contract
Coactivation
Motor only
-Upper motor neurons in the brain stimulate the lower motor neurons (alpha and gamma in in spinal cord) to contract simultaneously.
-Stimulation of the alpha motor neurons causes extrafusal muscle fibers to contract (shorten)
-stimulation of the gamma motor neurons causes the intrafusual fibers to shorten and eliminate the slack that would develop
Upper to lower, alpha stimulate extrafusal, gamma stimulate intrafusal
Golgi tendon organs
-In series with the extrafusal muscle fibers
•Monitor muscle (tendon) tension and protect the muscle from overstretch via the disynaptic reflex (action is inhibitory).
•Relaxation of a muscle’s extrafusal fibers.
Steps of Golgi tendon organ
- Tension on tendon activates sensory neuron
- Sensory neuron stimulates interneuron (+ charge)
- Interneuron inhibits(-charge) motor neuron (alpha motor neuron)
- Tension in tendon is reduced (muscle relaxation)
