LAB PRACTICAL 2 Flashcards
electromyography
a recording of the electrical activity of muscle tissue using electrodes attached to the skin or inserted into the muscle
surface EMG
electrodes placed on skin surface
intramuscular EMG
electrodes inserted into muscle; provides more insight
why do EMG signals look noisy?
EMG signals look noisy because motor units fire asynchronously
Nerve conduction study
detects neuropathies and can help with diagnosis of nerve compression or injury (carpal tunnel, sciatica)
signal conditioning
done by PowerLab; signal is modified by amplification and filtering
digital conversion
after signal conditioning, the analog voltage is sampled at regular intervals and converted from analog to digital before transmission to the attached computer
Raw EMG
records the potential difference detected at the electrode; often looks noisy when muscles are contracting
Integrated EMG
records the potential difference detected at the electrode, often looks noisy when muscles are contracting
reciprocal activation
activation of the agonist muscle and inactivation of antagonist muscle during goal-oriented movements
co-activation
during contraction of the agonist muscle, the antagonist muscle is slightly contracted as well for joint stability
co-contraction
activation of an antagonist and agonist muscle around a joint to maintain a given posture
What happens to your EMG signal when you increase the contraction strength?
when you increase the contraction strength, the EMG amplitude increases
During reciprocal activation, why is the antagonist muscle not completely silent?
during reciprocal activation, the antagonist muscle is not completely silent because of a phenomenon called co-activation, which simultaneously slightly contracts the antagonist muscle to stabilize the joint
Why is the electromyogram waveform irregular?
The EMG is irregular because it is recording asynchronous electrical activity because signals from multiple muscle fibers are being recorded. This contrasts electrocardiograms because the cardiac muscles fire synchronously to maintain a steady heartbeat.
Brett ate poisonous wild mushroom, which partially paralyzed his motor unit. What would a normal EMG trace look like?
A normal EMG from Brett would have higher amplitudes. If his motor unit was partially paralyzed, its functions would be inhibited and therefore it would be less efficient at propagating action potentials and stimulating muscle fibers. With decreased electrical signaling from the motor unit, the EMG trace has smaller amplitudes
When we placed electrodes on the bicep and tricep, what data were we collecting?
electrical activity of the muscle via electromyograms
Transduction
the process of converting one energy type to another
force transducer
converts an input mechanical force into an electrical output signal
raw input of data inquisition
analog signal
powerlab
data inquisition hardware that measures electrical signals
muscle used in frog lab
gastrocnemius
muscle twitch
a single contraction-relaxation cycle in a muscle fiber
twitch
response to a single threshold stimulus; can vary in height, duration, and rising slope
recruitment
multiple motor unit summation; if a stronger stimulus is applied, a graded response results from the summation of contractile forces from multiple muscle fibers
recruitment
refers to twitches in all of the fibers of several motor units
maximum excitation voltage
stimulus voltage that will recruit all muscle fibers
supramaximal excitation voltage
1.5X the maximal stimulus; ensures all motor units are recruited
threshold stimulus
the force (mV) at which the first muscle twitch is observed
summation
an increase in contractile force with multiple stimuli in a short period of time, especially when effects from previous stimuli have not completely subsided
tetanus
a sustained muscle contraction evoked when the motor nerve that innervates a skeletal muscle emits action potentials at a very high rate; as stimuli frequency increases and tension remains fairly constant
incomplete tetanus
where each stimulus causes a contraction to be initiated when the muscle has only partly relaxed from the previous contraction
complete tetanus
when muscle has reached a state of maximal sustained contraction
why is tetanic tension much greater than twitch tension?
In a twitch action potential: release of Ca2+ saturates troponin and exposes active sites with one stimulus. Because there is a single stimulus, Ca2+ availability is small.
During tetanus: continuations of action potentials provide enough Ca2+ to saturate troponin at all times.
Three mechanisms of fatigue
conduction failure
lactic acid buildup
buildup of ADP and inorganic phosphate
Conduction failure
action potentials repeatedly fire in muscle and extracellular potassium levels increase in the T-Tubule from repeated depolarization, upsetting ion concentration balance and leading to failure of another action potential
lactic acid buildup
during anaerobic respiration, muscle proteins may be altered
buildup of ADP and Pi
inhibits cross bridge cycling and delaying cross bridge attachment on actin
why is calibration of the force transducer essential?
this process zeros out the transducer by removing any tension on the string that is not the result of muscle contraction and allows measurements following this procedure to be comparable
as you increase the voltage to the muscle, how does it respond to the increased stimulus?
as the voltage increases from threshold to maximum:
- Greater force in the muscle contraction
- Once maximal voltage reached, further increase in stimulus will show no effect on force of muscle contraction
how does the isolated muscle respond as the stimulus interval was decreased progressively?
summation of stimuli and stronger contractile forces in the isolated muscle
How did the isolated muscle respond as it was stretched progressively?
as the gastrocnemius was stretched, the muscle contracted with greater force and the strength of contraction increased up to a certain length
how did the muscle respond to high frequency stimulation?
the isolated muscle experienced complete tetanus and its contractile force progressively declined until 35 seconds when it failed and gave out
how can you explain the graded response in light of the “all-or-none” law of muscle contraction?
the all or none law of muscle contraction refers to individual muscle fibers contracting. the graded response refers to the number of motor units that have been recruited to contract.
at which stimulus interval did you observe tetanus?
tetanus is a sustained muscle contraction elicited from frequent stimuli. With continuous and frequent stimuli, APs are generated in the muscle at a similar rate, preventing the muscle from relaxing in between these stimuli. The muscle is unable to relax because with frequent action potentials, calcium ions are released in the cell which continuously bind to troponin and expose the actin binding site. Without enough time to pump the Ca2+ ions out of the cytoplasm, the muscle continuously contracts
what stretch resulted in the highest contraction force?
when the muscle was stretched to 2mm, it generated the highest contractile force because actin and myosin filaments had optimal overlap. As it was increasingly stretched, its ability to contract and generate force decreased because the actin and myosin filaments had less overlap and therefore contracted with less force
rigor mortis
lack of ATP in a corpse does not allow myosin heads to unbind from actin binding sites
resting membrane potential
the electrical membrane potential difference between the exterior and interior of the cell
resting membrane potential is determined by
a difference in ion concentrations
relative permeability of the cell membrane to the different ion species
equilibrium potential
each ion has a unique voltage when they are at equilibrium
characteristics of action potentials
regenerative, brief, stereotyped, all or none with refractory period, directional conduction of signals
nerve program
examines the generation and propagation of action potentials
setup of nerve
- stimulus electrode and one recording electrode are fixed
- other two recording electrodes can be moved up and down the axon
- different colored action potentials correspond to different nerves being stimulated
white matter
myelinated nerve fibers
grey m atter
nerve cell bodies, unmyelinated nerve fibers
corpus callosum
axons that connect the two hemispheres of the brain; roof of lateral ventricles
fornix
floor of lateral ventricles, output tract of hippocampus to mammillary body
choroid plexus
lines ventricles, produces CSF
aqueduct of sylvius
mesencephalic aqueduct
diencephalon
relays sensory information and connects nervous system structures with endocrine system
brainstem
midbrain, pons, medulla oblongata
frontal lobe
behavior, personality, learning, motor control
parietal
sensory information
temporal
hearing and sound, language and understanding
occipital
vision
central sulcus
divides frontal lobe from parietal
lateral sulcus
divides frontal lobe from temporal
olfactory
smell (sensory)
optic
vision (sensory)
oculomotor
eye movement and focusing; elevates eyelid (motor)
trochlear
nerve supply to eye muscle; superior oblique (motor)
trigeminal
3 main branches:
maxillary
mandibular
ophthalmic nerves
chewing, sensation from forehead, eyes, teeth, tongue, gums, nose, lips (sensory and motor)
abducens
eye movement; lateral rectus (motor)
facial
facial expression, tongue, taste buds, salivary glands (sensory and motor)
vestibibulocochlear
posture, heraing (sensory)
glossopharyngeal
taste sensation and back of tongue, swallowing, visceral sensory from carotid bodies (sensory and motor)
vagus
most pharyngeal and laryngeal muscles; visceral sensory information from pharynx, larynx, carotid bodies, heart, lungs, abdominal organs; general sensory information from external acoustic meatus, eardrum, and pharynx (sensory and motor)
accessory
head movement (sternocleidomastoid and trapezius muscles) (motor)
hypoglossal
speech, swallowing (tongue muscles) (motor)
cerebral cortex
6 layers
giant pyramidal cells and Betz cells are most numerous in layer 5
axons leave the cortex via tracts of white matter (cerebral corpuscles) and run caudally to spinal cord via corticospinal or pyramidal tract
betz cell dendrites are different from purkinje cell dendrites
cerebellum
3 layers
molecular layer
purkinje layer
granule layer
molecular layer
close to the surface, contains axons from many sensory systems; dendrites of purkinje cells extend to this layer
purkinje cell layer
somas of purkinje cells located here
granule cell layer
cell bodies of interneurons whose axons make up molecular cell layer
differences between human and sheep brain
olfactory bulb: sheep has larger
mammillary bodies: human has 2, sheep has large one
size: human is 3-4lbs, sheep isi 140-180 grams
sulci: human has more which increases surface area and complexity
how does the relative size of the fornix in the sheep brain compare with the human fornix?
the fornix is larger in the sheep because it connects the hippocampus to mammillary body which connects their sense of smell to their emotions, allowing them to sense food and danger
How does Vrest change in response to concentration changes of K and Na?
Na: increase intracellularly, membrane is more hyperpolarized
K: increase intracellularly, membrane hyperpolarizes
does K+ or Na+ have a bigger effect on Vrest?
K+ dominates at rest with potassium leak channels and has a greater conductance so changing its concentration has a bigger effect
MetaNeuron: Vrest = -64.81
Experimental data: Vrest = -73.06
WHY?
the data calculation was different from MetaNeuron because the data calculation included the involvement of Cl- anions in the membrane resting potential in addition to Na+ and K+
When conductance is shown on the graph, why are both traces positive?
both traces are positive because both ion channels have opened and increased the permeability to the ions
when ionic currents are shown on the graph, why is the K+ trace positive while the Na+ trace negative?
The K+ trace is positive because it is going outside of the cell (up) whereas the Na+ trace is negative because it is going inside the cell (down)
When TTX is applied to the neuron, there is still a small depolarization. Why?
the cell can still depolarize but it cannot initiate an action potential because the sodium voltage gated channels are blocked.
what is the cause of the blip in the Na+ trace for currents?
When the membrane is depolarizing, the membrane voltage reaches closer to ENa. When closest to ENa, the driving force for Na+ is the least and the Na+ current starts decreasing in response to the lowered driving force. This slowdown of the current causes the upward deflection. When K+ channels open, the membrane returns to its resting conditions and results in an increase in the driving force and subsequent increase in Na+ current.
what is the maximum temperature to generate and action potential? what trends do you notice as temp decreases?
Maximum temp: 22 degrees (C)
as temperature decreases, the cellular action potential response time decreases. This occurs because colder temperatures tend to slow down most cellular processes, so a neuron firing slows down as well
TTX symptoms
numbness in lips, tongue, face, neck
pains in stomach and throat, nausea and vomiting
difficulty breathing, complete paralysis and irregular heartbeat
Mechanism of TTX
blocks the acetylcholine receptors on the muscle fiber so acetylcholine does not depolarize the cell and initiate a contraction –> paralysis
batrachotoxin symptoms
numbness in fingers, lips, mouth
batrachotoxin mechanism
causes a conformational change that prevents voltage gated sodium channels from closing
ventral nerve cord
nerve that runs the length of the worm on the inner ventral surface
three giant axons
one medial fiber and two lateral fibers
lateral fiber characteristics
have higher stimulus thresholds, require increased voltages
conduct slower than medial fiber, so longer latent period
intracellular recordings
measures single transmembrane potential by inserting a glass pipette into one cell and recording potential changes
extracellular recording
small potential differences recorded by placing an electrode in living tissue in close proximity to an excitable cell; no direct access to membrane potentials
biphasic extracellular recording
AP propagation:
passes under first electrode (negative), region is more negative in relation to second electrode; - and - makes a positive deflection
as it recovers, the region under the second electrode (positive) becomes negative; + and - records a negative deflection
extracellular recording characteristics
size and shape of waveform depend on the distance between the two recording electrodes, the length of the axon segments, and the conduction velocity of the axon
conduction velocity
speed at which an electrochemical impulse propagates down a neural pathway
absolute method (conduction velocity)
determined by distance and latency period
difference method (conduction velocity)
determined from both original set up and when both recording electrodes are moved away or closer to the stimulus
refractory period
longest interpulse interval at which a second action potential cannot be evoked
what is the relationship between stimulus strength and response amplitude in a single axon?
the stimulus strength does not influence response amplitude because it is all or nothing
an intracellularly recorded nerve action potential approximates 80 mV. Why is your action potential smaller?
because extracellular recordings detect small potential differences to indicate an action potential has occurred as opposed to intracellular recordings that measure single transmembrane potentials. Extracellular electrodes do not access these intracellular electrical signals
cockroach legs
locomotion and sensory receptors for tactile, auditory, and vibratory stimuli
sensory spine action potential
when the spine moves, the dendrite of the neuron is distorted, opening mechanically gated ion channels in the dendrite which creates a receptor potential and triggers an action potential
femoral spines
less abundant than tibial, two rows on ventral surface
tibial spines
highly abundant, diverse orientation
femoral tactile spine
single large spine that projects dorsally, contains a single bipolar sensory neuron
cell body
size of body and nucleus increases linearly with the axonal diameter of the tactile spine
spontaneous firing
observed in a small population of axons
extracellular triphasic action potentials
movement of spine produces burst of action potentials and demonstrates fast adaptation
setup of cockroach leg
positive: femur
ground: coxa
negative: coxa
large bin size
many spikes into one bin, false impression they originate from a single axon
small bin size
variability of AP combined with background noise from recording system distributed across several bins
hormone
chemical messenger produced by an organ that is released into circulation and targets cells on distant organs
endocrine glands
pancreas, thyroid, parathyroid, pituitary, adrenal, gonads, placenta
endocrine tissues within other glands
heart, liver, kidney, GI, adipose
tissues that modify hormones
lungs, skin, liver, kidney
pineal gland
secretes melatonin
hypothalamus
produces hormones that control secretions in anterior pituitary; produces ADH and oxytocin
thyroid
bilobed, pyramidal lobe
thyroid follicles and parafollicular/ c cells
thyroid follicles
lined with cuboidal epithelial cells
follicular colloid
follicular colloid
iodinated glycoprotein; fluid of lumen that produces thyroid hormones T3 and T4
T3 and T4
increase metabolic processes
parafollicular (c cells)
produces calcitonin
calcitonin
decreases blood calcium by depositing it into bones
pancreas
exocrine and endocrine tissue
exocrine tissues of pancreas
synthesizes and secretes digestive proenzymes and enzymes
endocrine tissues of pancreas
acinar cells, islets of langerhans, venule
acinar cells
secretes digestive enzymes
islets of langerhans
clusters of cells responsible for secreting different hormones
alpha cells and beta cells
alpha cells
produce glucagon
beta cells
produce insulin
glucagon
releases glucose by stimulating glycogenolysis in liver
insulin
increases glucose uptake and promotes protein synthesis
venule
drains pancreatic islet of langerhans secretions, provides blood supply to pancreatic acini
parathyroid
chief cells, oxyphil cells
chief cells (principal cells)
most numerous, produces parathyroid hormone (PTH)
parathyroid hormone (PTH)
increases level of calcium in the blood
oxyphil cells
larger cell type, abundant mitochondria, unknown function
adrenal gland
cortex and medulla
adrenal cortex
zona glomerulosa
zona fasciculata
zona reticularis
zona glomerulosa
produces mineralocorticoids
mineralocorticoids
maintain homeostasis by stimulating reabsorption of Na+ by kidney
zona fasciculata
most active; produces glucocorticoids
glucocorticoids
promote normal metabolism and body to resist stress; cortisol, cortisone, corticosterone
zona reticularis
produces sex hormones
adrenal medulla
produces epinephrine and norepinephrine
epinephrine
vasodilation
norepinephrine
vasoconstriction
pituitary gland
hypophysis; secretes hormones that regular other endocrine glands
anterior pituitary
adenohypophysis;
pars distalis
pars intermedia
pars tubercle
pars distalis
secretory portion; acidophils, basophils, chromophobes
pars intermedia
vesicles with colloid that separate anterior from posterior
acidophils
red / pink
somatotropin, prolactin
somatotropin
growth hormone, STH
prolactin
lactotropic hormone, LTH
basophils
blue / purple; least abundant
thyrotropin (TSH) and gonadotropic hormones
thyrotropin (TSH)
controls production of thyroid hormones
gonadotropic hormones
FSH and LH
follicle stimulating hormone (FSH)
stimulates development of the follicle, production of estrogen
luteinizing hormone (LH)
works with FSH to stimulate ovary follicle maturation, controls development and maintenance of interstitial cells of the testes
chromophobes
uniform, lightly stained cytoplasm, most abundant, smaller
ACTH and MSH
adrenocorticotropin (ACTH)
stimulates adrenal cortex which synthesizes and releases glucocorticoids
melanocyte-stimulating hormone (MSH)
stimulates pigment changes
posterior pituitary
neurohypophysis; composed of hypothalamic axons of unmyelinated nerve fibers, herring bodies, pituicytes, capillary network
stores and releases hormones produced by the hypothalamus
infundibulum
connects hypothalamus and pituitary
herring bodies
terminal ends of axons that store hormones
pituicytes
specialized glial cells in posterior pituitary
antidiuretic hormone (ADH)
vasopressin; stimulates reabsorption of water from urine in the distal tubules of the kidney
oxytocin
stimulates myometrium of the uterus during pregnancy; stimulates contraction of myoepithelial cells in the mammary gland, resulting in milk secretion
PTU
interferes with thyroid hormones by inhibiting synthesis of T3 and T4 which decreases metabolic processes
