Midterm Part 3 Functional Neuro-muscular Units Flashcards
Functional Neuro-muscular Units
Order of the organization of functional skeletal muscle:
Muscle -> Fascicle -> Muscle Fibers -> Myofibrils -> Thick and Thin Filaments (sarcomere)
skeletal muscle surrounded by _____ and contains _______
epimysium, muscle fascicles
muscle fascicles surrounded by ______ and contains ______
perimysium, muscle finbers
muscle fiber surrounded by ______ and contains _______
endomysium, myofibrils
sarcomere contains ______
thick and thin filaments
Neuromuscular Junction.
where is it?
what are its components?
site where axon and muscle fiber communicate.
Five basic components:
- motor neuron - motor end plate - synaptic cleft - synaptic vesicles - neurotransmitters
Muscle Contraction
motor nerve impulses cause release of ACh from synaptic vesicles which bind to receptors on motor end plate and generate muscle contraction
Muscle Relaxation
acetylcholinesterase breaks down ACh, motor neuron impulses stop, Ca moves back into sarcoplasmic reticulum, myosin and actin binding prevented
motor unit
a single motor neuron and all the muscle fibers it controls
true or false?
when a motor unit fires all the muscle fibers contract together
true
true or false?
one muscle fiber may be innervated by several motor neurons
true
small amount of muscle fibers makes for fine or strength control?
fine: extraocular muscles (20 fibers)
Twitch
a single brief stimulus to a muscle that produces a quick cycle of contraction and relaxation lasting less than 1/10 sec. aka a single muscle contraction. 3 phases: latent, contraction, relaxation
Is a single twitch contraction strong enough to do any useful work?
no. normal activities require more tension - sustained muscle contraction of the whole muscle!
Treppe
relaxation is complete before next stimulus occurs. ea contraction a little stronger than previous. 10-20 stimuli/sec.
Wave summation
temporal summation.
if a second stimulus is applied before relaxation is complete, the second contraction is greater. rapid sequence of stimuli cause twitches to fuse together – more strength of contraction.
20-40 stimuli/sec
Tetanus
w higher frequency of stimulation, muscle relaxation between contractions is reduced.
incomplete or complete tetanus?
sustained maximal contraction at peak tension
complete
incomplete or complete tetanus?
produces peak tension during rapidly alternating cycles of contraction and partial relaxation
incomplete
ea stimulus produces an identical twitch response. true or false?
true
twitch, treppe, summation or tetanus?
ea subsequent contraction is stronger than previous until after a few stimuli, all contractions are equal.
treppe
twitch, treppe, summation or tetanus?
ea stimulus arrives before the previous twitch is over.
wave summation. as the frequency of stimulus increase, frequency of contraction increases.
twitch, treppe, summation or tetanus?
20-40 stimuli/sec
wave summation or incomplete tetanus
twitch, treppe, summation or tetanus?
muscle fibers partially relax between contraction
incomplete tetanus
twitch, treppe, summation or tetanus?
10-20 stimuli/sec
treppe
twitch, treppe, summation or tetanus?
up to 10 stimuli/sec
twitch
twitch, treppe, summation or tetanus?
no relaxation
complete tetanus
twitch, treppe, summation or tetanus?
40-50 stimuli/sec
complete tetanus
twitch, treppe, summation or tetanus?
twitches fuse into smooth, prolonged contraction
complete tetanus
Sensory Neuron
afferent. transmit impulses from receptors to brain or spinal cord
Motor Neuron
efferent. transmit impulses from brain or spinal cord to effector sites such as muscles, glands, or organs
Interneuron
association neuron. transmit impulses from one neuron to another
Which fibers are myelinated? A, B, C
A and B
A, B, or C? if A, which kind?
sympathetic preganglionic
B
A, B, or C? if A, which kind?
unmyelinated
C
A, B, or C? if A, which kind?
fastest!
A alpha
A, B, or C? if A, which kind?
smallest diameter
C
A, B, or C? if A, which kind?
7ms
B
A, B, or C? if A, which kind?
motor efferents
A alpha, A gamma
A, B, or C? if A, which kind?
both efferents and afferents
A alpha
A, B, or C? if A, which kind?
muscle spindle afferents
A alpha
A, B, or C? if A, which kind?
motor efferent to muscle spindle
A gamma
A, B, or C? if A, which kind?
largest diameter
A alpha
A, B, or C? if A, which kind?
sympathetic postganglionic
C
A, B, or C? if A, which kind?
15 ms
A delta
A, B, or C? if A, which kind?
skin temperature and pain (noxious stimuli)
A delta
A, B, or C? if A, which kind?
touch and pressure afferents (mechanoreceptors)
A beta
A, B, or C? if A, which kind?
50ms
A beta
A, B, or C? if A, which kind?
100ms
A alpha
A, B, or C? if A, which kind?
pain (burning, aching, itch) 1ms
C
A, B, or C? if A, which kind?
20 ms
A gamma
A, B, or C? if A, which kind?
7ms
B
A, B, or C? if A, which kind?
proprioceptors of skeletal muscle
A-alpha
What is the basic functional unit of the nervous system?
Spinal Cord Reflex Arc
automatic response to stimuli wo conscious thought
Spinal Cord Reflex Arc: 5 basic components:
- sensory receptor
- sensory neuron
- interneuron
- motor neuron
- effector organ
Proprioception
the sense of position and movement of one’s own limbs and body wo using vision (somatosensory)
body & limb position, speed and direction or limb joint movement, muscle length and tension
3 types of mechanoreceptors that detect proprioception:
- muscle spindle receptors
- golgi tendon organs
- joint kinesthetic receptors
Where are muscle spindle receptors located?
fleshy part of muscle
What are intrafusal muscle fibers?
modified muscle fibers enclosed in a capsule within extrafusal muscle fibers (voluntary skeletal muscle) that make up Muscle Spindle Receptors. the ends of the intrafusal fibers attach to extrafusal and are contractile.
What do muscle spindle receptors detect?
rate at which the muscle fibers are stretched and how much it’s stretched
Two types of Intrafusal Fibers (part of muscle spindle receptor)
nuclear bag fibers and nuclear chain fibers
why is it called Nuclear Bag Fibers?
nuclei concentrated in central “bag” part of intrafusal fiber
why is it called a Nuclear Chain Fiber?
nuclei are spread in a “chain-like” fashion in the center of the fiber
Intrafusal Fibers: nuclear chain or nuclear bag?
sensitive to steady changes of length of muscle (tonic) … static
chain
Intrafusal Fibers: nuclear chain or nuclear bag?
sensitive to sudden rate of change in muscle length (phasic) … dynamic
bag
Intrafusal Fibers: nuclear chain or nuclear bag?
contractile ends receive input from gamma motor neurons
bag
Intrafusal Fibers: nuclear chain or nuclear bag?
contractile fibers are attached to ends of nuclear bag muscle fibers
chain
Intrafusal Fibers: nuclear chain or nuclear bag?
contractile fibers are attached to the extrafusal fibers
bag
Intrafusal Fibers: nuclear chain or nuclear bag?
ends of fibers are striated and contractile
bag and chain
Intrafusal Fibers: nuclear chain or nuclear bag?
the central non-contractile region is wrapped by sensory nerve endings that send input about length of spindle to CNS
bag and chain
Two types of sensory nerve endings that wrap around non-contractile regions of intrafusal fibers:
primary endings type la fiber and secondary endings type ll fiber
primary endings type la fiber or secondary endings type ll fiber?
annulospiral sensory endings
primary endings type la fiber
primary endings type la fiber or secondary endings type ll fiber?
smaller diameter, conduct impulses more slowly
secondary endings type ll fiber
primary endings type la fiber or secondary endings type ll fiber?
flower spray sensory endings
secondary endings type ll fiber
primary endings type la fiber or secondary endings type ll fiber?
larger diameter, conduct impulses faster (100ms)
primary endings type la fiber
primary endings type la fiber or secondary endings type ll fiber?
respond to rate of change in muscle fiber length
primary endings type la fiber
primary endings type la fiber or secondary endings type ll fiber?
respond to overall length of muscle fiber
secondary endings type ll fiber
Stretching activates the sensory neurons of the spindle. signals to brain and spinal cord. What happens next?
CNS activates alpha motor neurons that cause muscle extrafusal to contract resisting further stretching
Muscle spindles sense changes in muscle _______ and _______.
tension and length
What motor neurons let the brain preset the sensitivity of spindle to stretch?
gamma motor neurons. when brain signals gamma to fire, intrafusal fibers become tense so that little stretch is needed to stimulate sensory endings - balance reflexes. INVOLUNTARY MUSCLE CONTRACTION
Response to stretching can be either…
monosynaptic spinal reflex - makes rapid adjustment to prevent fall
or
controlled by cerebellum - regulate muscle tone i.e. the steady force of a non-contracting muscle to resist stretching
What are the encapsulated nerve endings located at the junction of tendon and muscle called? sensory neurons!
Golgi Tendon Organs GTOs
GTOs detect…
GTOs prevent… how?
GOTs play a role in…
detect:
- force of muscle contraction
- tension applied to tendon
GTOs respond to slow stretch by resetting a muscles’ length and inhibiting its synergistic stabilizers while facilitating its antagonist (important!)
prevent:
- prevent a contracting muscle from applying excessive tension to tendons
how?
- produces sudden relaxation of muscles INVOLUNTARY MUSCLE RELAXATION
roles:
- muscle tone balance
- muscle spasm
- tender points
How do GTOs cause a muscle to relax? protect the tendons and muscles!
only intense stretch! -> lb sensory neurons from GTOs stimulated –> to spinal cord to synapse w inhibitory interneurons –> inhibitory neurotransmitters released –> alpha motor neurons inhibited
GTO: Dynamic Response vs Static Response
sudden increase in muscle tension causes a decrease in muscle tone
via involuntary muscular relaxation, quick stretch = Dynamic
postural tone = Static
Where are joint kinesthetic receptors located?
What do they detect?
3 types?
- located in and around synovial joint capsules.
- detect direction of movement, acceleration/deceleration, pressure of joint, excessive joint strain, postural changes, input from skin receptors - ruffini and merkel’s discs
- 3 types: Pacinian corpuscles, Ruffini corpuscles, Free nerve endings
Which type of Joint Kinesthetic Receptor: Pacinian, Ruffini, or Free Nerve Endings?
- located in CT and synovial joint capsules
- responds to rapid pressure changes, stretch, acceleration and deceleration of joint movement
Pacinian Corpuscles
Which type of Joint Kinesthetic Receptor: Pacinian, Ruffini, or Free Nerve Endings?
- located in most body tissues
- respond to rapid and sustained pressure
Free Nerve Endings
Which type of Joint Kinesthetic Receptor: Pacinian, Ruffini, or Free Nerve Endings?
- located in synovial capsules and ligaments
- respond to deep rapid, sustained pressure, lateral stretch
Ruffini Corpuscles
Which type of Joint Kinesthetic Receptor: Pacinian, Ruffini, or Free Nerve Endings?
- detects changes in joint angles
- ligament receptors adjust muscle tone
Ruffini Corpuscles
