SLE1/MODULE 4- Muscle Architecture + Mechanics Flashcards
external brain structures (4)
-cerebrum
-cerebellum
-cerebral hemisphere
-brainstem
how is cerebrum split
into 2- left + right
-each side is called a hemisphere
what is each side of cerebrum called
hemisphere
what is below the cerebrum
cerebellum
what is below the cerebellum
brainstem
brainstem
leads us down into the spinal cord + eventually connects/projects into the muscular system
what is the cerebrum’s surface called
neocortex
neocortex
the cerebrum’s surface, convoluted into hundreds of folds/grooves
what happens at the neocortex
where all the HIGHEST brain functions take place
-cognition
-language
-abstract thinking (where we think about what we do, what it means, etc.)
describe the makeup of the neocortex
thin layer of cells about 1.5-4 mm thick
neocortex contains how many neurons
25 billion
neocortex contains how many miles of axons
62,000 miles of axons
neocortex contains how many synapses
300,000,000,000,000
where do the highest cognitive functions take place
neocortex
what is the largest portion of the brain
cerebrum
where are the 2 hemispheres of the cerebrum connected
at the corpus callosum
cerebrum is often divided into how many lobes
5 lobes
-each responsible for different brain functions
5 lobes of the cerebrum
-frontal lobe
-temporal lobe
-limic lobe
-parietal lobe
-occipital lobe
frontal lobe- functions
-problem solving
-memory
-motivation
-judgement
-impulse control
-social + sexual behavior
temporal lobe- functions
-emotions
-smelling
-tasting
-perception
-memory
-aggressiveness
-sexual behavior
limbic lobe- functions
-regulates emotion + memory
-directly connects the lower + higher brain functions
parietal lobe- functions
-processes sensory + spatial awareness
-key component in eye-hand coordination + arm movement
occipital lobe- functions
-vision
-object recognition
where is the Wernicke’s area
in the back part of the temporal lobe
function of Wernicke’s area
-language speaking
-written comprehension
where is the Broca’s area located
in the frontal lobe
-usually on the left side
functon of Broca’s area
-speech production
-being able to form words + communicate with auditory speech
Wernicke’s area + Broca’s area are connected by what
large bundles of nerves called arcuate fasciculus
within the frontal lobe, what is there
specific areas that have to do with coordination, cognition, + behavioral processes
-premotor cortex + motor cortex
where are premotor cortex + motor cortex found
frontal lobe
motor cortex
has to do with planning, control, + execution of voluntary movement
-if I voluntarily send a command to clench my fist, it will be planned then executed through that motor cortex within the frontal lobe
premotor or motor cortex is more anterior
premotor cortex
premotor or motor cortex is more posterior
primary motor area
-motor cortex
premotor cortex is responsible for what
repetitive motions of learned motor skills
primary motor area is responsible for what
control of skeletal muscles
what are different areas of the brain associated with
different parts of the body
injury to the motor cortex can result in what
motor disturbance in the associated body part
cerebellum is connected to what
brainstem
brainstem controls what
basic life functions
cerebrum is center for what
body movement + balance
what does cerebellum do
integrates motor + sensory information
what is cerebellum associated with
timing of movements + transformation of sensory information into space-time coordinates
thalamus is also called what
“the gateway to the cerebral cortex”
thalamus
nearly all sensory inputs pass through this to get to higher levels of the brain
basal ganglia
a group of nuclei located deep in the cerebral cortex
6 parts of the basal ganglia
-caudate
-putamen
-nucleus accumbens
-globus pallidus
-substantia nigra
-subthalamic nucleus
function of basal ganglia
-integration of sensory motor centers
-unconscious motor behavior (ex: maintaining muscle tone by sitting with good posture)
-gross body movements
what occurs within the basal ganglion that influences how we move/motor control
excitation + inhibition
a patient comes to the neurologist’s office reporting that they’re experiencing falls. the patient is not successful in performing a basic reach-out-and-touch nose with finger test. a follow-up includes a brain scan, which reveals lesions. in which region are the lesions most likely?
a) corpus callosum
b) cerebrum
c) brainstem
d) cerebellum
e) basal ganglia
d) cerebellum
2 aspects of spinal cord
-dorsal
-ventral
dorsal is sensory/motor
sensory
ventral is sensory/motor
motor
what is located next to the dorsl root ganglion
dorsal horn
dorsal root ganglion
bulge/pile/collection of nerves that have to do with sensation
what goes through the dorsal horn
afferent sensory information
what travels through the ventral horn
efferent signals to muscles + glands via the ventral root
where do motor neurons originate
originate in the VENTRAL HORN + comes out to send efferent signals to muscles + glands via the ventral root
afferent
sends information in
efferent
sends information out
lateral white column refers to what
myelination
-white due to a high % of nerves in that area are myelinated
where do we find gray matter
cervical + lumbar regions of spinal cord
where are sensory neurons located in spinal cord
towards back side of spinal cord
where are motor (efferent) neurons located in spinal cord
towards front of spinal cord
what do motor neurons in the anterior gray columns do
send axons to innervate skeletal muscle (lower motor neurons)
-this is the FINAL COMMON PATHWAY to the muscle
another name for neurons in anterior gray columns
lower motor neurons
what are lower motor neurons constantly bombarded with
impulses from the motor cortex, midbrain, medulla, + pons
upper motor neurons
supraspinal neurons that form the descending tracts to the alpha motor neurons
-also FINAL COMMON PATHWAY NEURONS
what 2 neurons are final common pathway neurons
-lower motor neurons
-upper motor neurons
if you want to do a contraction with your muscles…
you have to activate a motor neuron that connects to skeletal muscle
in its simplest form, the descending pathway consists of how many neurons
3
3 neurons of the descending pathway
-1st order neuron
-2nd order neuron
-3rd order neuron
descending
1st order neuron
upper motor neuron
descending
where is the 1st order neuron (upper motor neuron) found
motor cortex
descending
where does 1st order neuron (upper motor neuron) connect with 2nd order neuron (interneuron)
anterior gray column in the spinal cord
descending
2nd order neuron
interneuron
descending
where are 2nd order neurons (interneurons) located
spinal cord
descending
describe the axon of 2nd order neurons (interneurons)
short axon
descending
3rd order neuron
-alpha motor neuron
-somatic motor neuron
-final common pathway neuron
-spinal motor neuron
-lower motor neuron
descending
where are 3rd order neurons located
anterior gray column that forms the motor unit
ascending pathway
pathway to consciousness (our ability to cognitively think + interpret things)
in its simplest form, the ascending pathway consists of how many neurons
3
3 neurons of ascending pathway
-1st order neuron
-2nd order neuron
-3rd order neuron
ascending
1st order neuron
cell body in posterior root ganglion
ascending
what does the 1st order neuron connect
sensory receptor ending + 2nd order neuron in spinal cord
ascending
2nd order neuron does what
gives rise to an axon that decussates + ascendings to a higher level of the CNS + synapses with a 3rd order neuron
ascending
3rd order neuron is located where
typically in the thalamus
ascending
what does the 3rd order neuron do
gives rise to projection fibers that passes to a sensory region of the cerebral cortex
ascending
when neurons are in the brain
2nd + 3rd order neurons
presynaptic inhibtion projected by an inhibitory interneuron on an alpha motor neuron is likely which type of neuron?
a) 1st order neuron of the descending pathway
b) 2nd order neuron of the descending pathway
c) 3rd order neuron of the descending pathway
d) 1st order neuron of the ascending pathway
e) 2nd order neuron of the ascending pathway
b) 2nd order neuron of the descending pathway
what connects muscle fibers
3-level network of collagenous connective tissue
3 levels of CT connecting muscle fibers
-epimysium
-peripmysium
-endomysium
epimysium
covers the whole muscle
perimysium
collects bundles of fibers into fascicles
endomysium
surrounds individual muscle fibers
sarcoplasm
fluid enclosed within the fiber + sarcolemma
sarcolemma
excitable cell membrane of muscle fiber
myofibril
series of sarcmeres, that contain contractile elements
what do sarcomeres have
thin + thick filaments
a single skeletal muscle fiber contains many ____
myofibrils
what is found within the myofibril
sarcomeres
sarcomere
the basic functional unit for each myofibril
how are sarcomeres aligned within the myofibril
in series (one after the other)
-thousands of sarcomeres making up the myogibril
describe myofibrils in terms of muscle fiber
myofibrils run the length of the muscle fiber + thus vary from 1-400 mm in length + 1 mm in diameter
a 10 mm myofibril contains how many sarcomeres in series
4000
sarcomere definition
the longitudinally repeating pattern of dark + light bands (striations) from z disk to z disk
thick + thin filaments are called ____
myofilaments
how many thin filaments connect to each z band
3000-6000
thick filaments consist of what
myosin
thick filaments terminate in ____
large globular heads
thin filaments include what
actin + 2 regulatory proteins (toponin + tropomyosin)
excitation-contraction coupling
process of converting a muscle fiber AP into muscle fiber force
excitation-contraction coupling steps
AP propagation along muscle fiber ->
AP propagation down T-tubule ->
AP coupling to the change in calcium conductance of the SR (sarcoplasmic reticulum) ->
release of calcium from SR ->
reuptake of calcium into SR ->
calcium binding troponin ->
interaction of contractile protein
ATP stands for
adenosine triphosphate
contractile force is produced by the interaction between what
thick + thin filaments
cross bridge cycle
mechanism of sarcomere shortening during contraction
-involves cyclical attachment + detachment of myosin heads to adjacent thin filaments (actins)
what 2 things are required by cross bridge cycle
-ATP
-Ca2+
sliding filament hypothesis
thick + thin filaments slide past each other in cross bridge cycle
who came up with the sliding filament hypothesis
Huxley et al. 1950s
steps to muscle contraction (cross bridge)
myosin heads hydrolyze ATP + become reoriented + re-energized ->
myosin heads bind to actin, forming cross bridges ->
myosin cross bridges rotate toward center of sarcomere (powerstrike) ->
as myosin heads bind ATP, the cross bridges detach from actin
isotonic
muscle length is changing
isometric
muscle length isn’t changing
2 types of isotonic contractions
-concentric
-eccentric
concentric: muscle torque or load is greater
muscle torque > load
concentric: muscle shortens/lengthens
shortens
concentric: load is lowered/lifted
lifted
eccentric: muscle torque or load is greater
muscle load > torque
eccentric: muscle shortens/lengthens
lengthens
eccentric: load is lowered/lifted
lowered
eccentric/concentric requires the most force
eccentric
slower you move, more/less force
MORE
faster you move, more/less force
LESS
what does movement require
unequal muscle + load torques
isometric ratio of (muscle / load) torque
muscle / load torque = 1
concentric ratio of (muscle / load) torque
muscle / load torque > 1
eccentric ratio of (muscle / load) torque
muscle / load torque < 1
concentric/eccentric requires more muscle activation to achieve a given muscle froce
concentric
electromyography (EMG)
an extracellular recording technique that measures the change in the potential difference in the extracellular space due to the activation of many motor units
what does EMG indicate
when a muscle is active
what does EMG procide an estimate of
the force produced by the contraction
EMG is a _____ comparison
extracellular space comparison
what does EMG suggest
fatigue-related changes in motor unit activity
how does EMG estimate force production by a muscle?
a) EMG tells us about how much a single motor unit is discharging action potentials, which tells us about how much force that motor unit produces
b) EMG describes the sum of the motor unit action potentials, which increases with greater force
c) EMG will be reduced in amplitude as target force increases
b) EMG describes the sum of the motor unit action potentials, which increases with greater force
study “fluctations in acceleration during voluntary contractions lead to greater impairment of movement accuracy in old adults” was done by which professor
Evangelos Christou
study
study- to assess the effect of movement velocity on the relation between FLUCTUATIONS IN ACCELERATION + the ABILITY TO ACHIEVE A TARGET VELOCITY during voluntary contractions performed by young + older adults
15% MVC
-6 movement velocities
study
EMG amplitude increased with ____
velcoity
-BUT ONLY FOR CONCENTRIC CONTRACTIONS
study
for study on acceleration +target velocity, were concentric + eccentric results statistically significant
concentric were statistically significant
-eccentric weren’t
study
what did study find for concentric + eccentric contractions
more steadiness with slower contractions vs faster contractions for BOTH
study
does velocity affect steadiness/force fluctuations for eccentric contractions
NO
-average EMG/muscle activity are the same
study
given there wasn’t a change in EMG for eccentric, but there was for concentric, what does this suggest
sarcomeres are not shortening for eccentric, but they are for concentric
study
fluctuations in acceleration increased with velocity for eccentric/concentric
BOTH contractions
study
standard deviation of acceleration increased with movement velocity for eccentric/concentric
BOTH contractions
study
which can explain why EMG does not change with velocity during eccentric contractions?
a) gravity will promote the mechanical separation of thin + thick filaments
b) gravity will not promote the mechanical separation of thin + thick filaments
c) this lack of EMG change is not consistent in the rest of the literature (just this study)
d) false statement: EMG does change with velocity during eccentric contractions
a) gravity will promote the mechanical separation of thin + thick filaments
the force a muscle exerts depends on what 3 things
-the contractile properties of the activated muscle fibers
-the arrangement of the fibers in the muscle
-the attachment sites of the muscle on the skeleton
mechanical properties can be described at what 3 levels
-single fiber
-whole muscle
-joint
SINGLE FIBER LEVEL
what is force output related to
the number of cross bridges occurring at the same time
-the more cross bridges you have engaged, the more force you should be outputting
-this is why when you lift a lot of weight you lift slowly so that you don’t miss any cross bridges
SINGLE FIBER LEVEL
as the length of the muscle changes + the thick + thin filaments slide past each other, what happens
the number of actin-binding sites available for the cross bridges changes
SINGLE FIBER LEVEL
what does tension mean in terms of muscle
the number of crossbridges that can be bound
SINGLE FIBER LEVEL
when is tension maximal
at intermediate lengths
-at middle segment
SINGLE FIBER LEVEL
when does tension decrease
at shorter + longer lengths
MUSCLE LEVEL
force output is related to what 2 things
-an active component
-a passive component
MUSCLE LEVEL
active component of force output
-voluntary activation
-number of cross bridges occurring concurrently
MUSCLE LEVEL
passive component of force output
-no voluntary activation
-connective tissues
MUSCLE LEVEL
where is tension maximal
at longer lengths
MUSCLE LEVEL
why is tension maximal at longer lengths
because of the contribution of active + passive components; sum of active + passive components
JOINT LEVEL
where is tension maximal
at intemediate lengths
-decreases at shorter + longer lengths
does joint level tension relationship correspond to whole muscle relation
NO
-rather, it mimics the single fiber force-length relation
how do muscle fibers that do not span the length of the muscle contribute to force produced by the muscle?
a) force-generating capabilities can jump between fibers wtihin a muscle
b) force is transmitted laterally via connective tissue
c) most muscle fibers within a muscle do not actually contribute to force
d) this is not the case in all humans; most muscle fibers span the entire length of the muscle
b) force is transmitted laterally via connective tissue
contractile proteins
thick + thin filaments
what are contractile proteins (thin + thick filaments) connected to
cytoskeletal proteins (desmin, skelemin, etc.)
how are contractile proteins connected to cytoskeletal proteins
through connective tissue
cytoskeletal proteins involved in longitudinal transmission
-titin
-nebulin
-MARP
-MLP
cytoskeletal proteins involved in lateral transmission
-titin
-dystrophin
-integrins
cytoskeletal proteins involved in linking the 2 modes of force transmission (longitudinal + lateral) + play a role in both processes
-desmin
-alpha-actinin
what is special about titin
involved in both lateral + longitudinal transmission
-shares information between them
a loss in lateral force transmission appears to lead toward what
sarcolemma damage + membrane disruption
can you think of a disease that involves the disruption of connective proteins?
duchene’s muscular dystrophy
what protein is involved in duchene’s muscular dystrophy
dystrophin
-this is the protein with the problem
what do dystrophin + integrins do
act like rivets + ties that couple the intracellular matrix to the extracellular matrix
-this prevents shear stress from damaging the sarcolemma
what happens when there is loss of dystrophin + integrins in muscular dystrophies
weakens the connection between the intracellular + extracellular matrices
-this renders individual fibers to be more susceptible to damage from shear forces
duchenne’s muscular dystrophy is what type of disorder
genetic
duchenne’s muscular dystorphy is characterized by what
progressive muscle degeneration + weakness
how many types of muscular dystrophy are there
9
what is duchenne’s msuscular dystrophy caused by
absence of dystrophin
-causes failure to keep muscle cells intact
single fiber level
as cross bridges slide past each other at SLOW VELOCITIES, why is their reattachment is faster
gravity is helping
-it is a mechanical separation + no need for ATP
single fiber level
as crossbridges slide past each other at FAST speeds, what happens
the binding sites are missed as the thick
+ thin filaments slide past eachother
muscle level
for shortening contractions, force output increases/decreases with velocity
decreases
muscle level
during shortening contractions, force ouput increases/decreases with velocity + why
decreases
-because some binding sites are missed as the thick + thin filaments slide past each other at a fast speed
joint level
during shortening contractions, force output increases/decreases with velocity
decreases
-the binding sites are missed as the thick + thin filaments slide past each other at a fast speed
joint level
during lengthening contractions, force output increase/decreases with velocity
IS CONSTANT with velocity
-maybe this is due to different activation of muscles during lengthening contractions
in series
muscle fibers placed one after the other
in series ROM
greater ROM
in parallel
muscle fibers arranged next to each other
in parallel ROM
less ROM
-but greater force generation
in pennation angle
maximize number of fibers in a given volume + thus force capacity
true/false: the deltoid muscle has multiple pennation angles, which enhances maximum force output
true
motions at joints are ____
rotary
-because joint is an axis of rotation
what type of forces do muscle produce
linear
rotary torque equation
rotary torque = linear force x moment arm
moment arm
distance from axis of rotation
force length relationship joints
anaogy- if I open a door right next to the hinge, the amount of force I have to produce to be able to open the door is a long more than if I move out + create a longer moment arm
shorter moment arm results in…
better involvement through ROM
longer moment arm results in…
greater muscle torque generation
why do we have a knee cap?
to increase moment arm
what type of bone is patella
seismoid
patella
-very important structurally
-helps to increase lever arm for knee movement
-if it doesn’t move properly, you must go in for surgery
stretch-shorten cycle
a method to stretch + store more energy
-bigger stretch results in more elastic energy stored
-SPRING-like mechanism
stretch-shorten cycle
pre-stretch causes what
eccentric lengthening of muscle, which builds tension (think rubber band)
stretch-shorten cycle
longer pre-stretch =
less tension
stretch-shorten cycle
increasing speed of coil compression or force applied =
spring jumping higher or further (“rate of loading”)
stretch-shorten cycle fast speed
<250 ms
stretch-shorten cycle slow speed
> 250 ms
work
product of force + the displacement of a body along the same line the force is acting
positive work
when force has a component in the same direction as the displacement of the body
negative work
when force has a component in the opposite direction to the displacement of the body
energy
ability of a body to perform work
power
performing work over a certain amount of time
-measures speed with which work is performed
-product of force and velocity of displacement of a body in the direction of the force
gross efficiency
how efficient a system is
-mechanical work/metabolic work
what is the most common method to measure metabolic energy
rate of oxygen consumption
2 joints is better/worse than 1 joint
BETTER
-when the movement of 2 joints is coupled, better + more efficient for coordination
the shortening velocity of a 2 joint muscle is more/less than that of a 1 joint synergist
LESS
-this is due to redistribution of muscle torque, joint power, + mechanical energy throughout the limb
mechanical factors that influence force generation
-length
-speed
-moment arm
-number of joints crossed
