Neuro Lab Exam 1

medial longitudinal fissure

separates the right and left cerebral hemispheres

transverse fissure

separates the cerebellum and the cerebrum

cruciate/ansate sulcus

separates the frontal and parietal lobes in sheep brain

central sulcus

separates the frontal and parietal lobes in the human brain

lateral sulcus

separates the temporal lobe from the other cerebral lobes

frontal lobe

motor function, language production, personality, working memory, higher-order thinking

parietal lobe

somatosensation

occipital lobe

primary visual perception

temporal lobe

primary auditory sensation, language comprehension

insula lobe

taste, pain, interoception

limbic lobe

emotion, memory, olfaction

midbrain

stimulus orientation and auditory perception

pons

acts as a bridge between the cerebellum and the brain stem

medulla

responsible for life functions such as breathing, HR, BP, reflexes and sleep

cerebellum

motor memory and coordination, posture, balance

spinal cord

neuron axons that carry sensory and motor information

cerebral peduncles

communication pathways between the brain stem and the cerebrum

infundibulum

facilitates communication between the hypothalamus and the pituitary gland

pituitary gland

endocrine gland that contributes to the maintenance of homeostasis by influencing growth, metabolism, and reproductive processes

trapezoid body

helps determine the spatial direction of sound

pyramidal tracts

contain motor fibers that carry information for muscle movement

optic chiasm

crosses visual field information to corresponding hemisphere so that it is processed into a single image

optic tracts

carry contralateral visual field information to the lateral geniculate nucleus

mammillary bodies

emotion and memory

rhinencephalon

olfactory processing center

pyriform area/lobe

smell perception

olfactory tract

connects the olfactory bulbs to the cortex for processing smells

rhinal fissure

separates the pyriform area of the rhinencephalon from the rest of the cerebrum

dura mater

physically protects the brain

arachnoid mater

contains CSF and filters it back into the blood

pia mater

maintains the blood-brain barrier

cingulate gyrus

involved in emotion, learning, and memory

hippocampus

learning, memory, spatial orientation/navigation

fornix (and fimbria)

transmits information from the hippocampus to the mammillary bodies

hypothalamus

maintains homeostasis by regulating hormones, body temperature, and appetite/thirst; involved in emotion and memory

thalamus

relays sensory and motor information to the cerebrum

lateral ventricles

produce, circulate, and store CSF

3rd ventricle

produce, circulate, and store CSF

cerebral aqueduct

produce, circulate, and store CSF

4th ventricle

produce, circulate and store CSF

corpus callosum

connects the left and right cerebral hemispheres

pineal body

secretes melatonin that plays a role in the sleep-wake cycle

superior colliculus

responsible for visual orientation to stimuli

inferior colliculus

responsible for auditory perception

internal capsule

relays information between the putamen and the caudate nuclei of the basal ganglia

corona radiata

carry sensory and motor information between the cerebrum and the brain stem

caudate nucleus

part of the dorsal striatum of the basal ganglia which is involved in initiating movement, suppressing unwanted movement, reward, and motivation

putamen

part of the dorsal striatum of the basal ganglia which is involved in initiating movement, suppressing unwanted movement, reward, and motivation

sheep vs. human CNS

• smaller cerebral cortex in sheep

• sheep spinal cord extends posteriorly (quadrupedal), human spinal cord extends inferior (bipedal)

  • nervous system adapted to these forms of movement over evolutionary time

• larger olfactory bulb to cerebrum size ratio in sheep

  • processing smells in environment more important for sheep than humans

• less prominent temporal and occipital lobes in sheep

  • humans have better vision, and language and emotion processing than sheep

• both have sulci and gyri

  • larger surface area of neural tissue in both animal cortexes

cerebrospinal tract (CST) pathway

primary motor cortex (located in pre-central gyrus) → cerebral peduncles in the midbrain → pyramids in the medulla → spinal cord → upper motor neurons → lower motor neurons → skeletal muscle fibers → voluntary movement

cerebrospinal fluid (CSF) flow

choroid plexus in lateral ventricles produces CSF → 3rd ventricle where more CSF is produced → cerebral aqueduct → 4th ventricle where even more CSF is produced → some through central canal of spinal cord, most into subarachnoid space → arachnoid granulations → dural sinuses → blood

mouse spinal cord sections

• ventral horns have large motor neuron cell bodies in them

  • ventral horns look larger in the lumbar sections because more motor neurons are needed to innervate the lower limbs since they contain lots of musculature

• less white matter in sacrum and coccyx sections because most axons exit the spinal cord in prior sections

• white matter (outside) = oligodendrocytes that produce myelin for axons in CNS, grey matter (inside) = cell bodies

PowerLab

an analog-to-digital converter, meaning that it takes a continuous and smooth analog signal input and converts it into a discrete digital signal output that is easier to interpret in the Lt software

PowerLab input

• input sensors- responsible for collecting physiological data and transferring it to the PowerLab hardware in the form of an electrical, analog signal

  • pulse transducer- detects changes in pressure from the pulse of the finger and converts that information into an electrical analog signal that serves as input for the PowerLab hardware to convert into a digital signal that is ultimately used by the Lt software to calculate heart rate

  • bioamplifier- measures and magnifies the amplitude of small physiological voltages

    • Bio Amp cable- brings afferent information to the Powerlab

Powerlab output

stimulating bar electrode- used to deliver a stimulus to a nerve or muscle

sampling rate

• how many times per second an analog signal is sampled to create a digital signal

• ECGs are typically 1000 samples per second while slowly changing signals like breathing are typically 200 samples per second

motor unit

• a group of muscle fibers that is innervated by a single LMN

• large muscles have multiple motor units and thus multiple LMNs innervating them

neuromuscular junction (NMJ)

• facilitates neurotransmitter release and binding that leads to muscle contraction

• AP reaches the synapse → calcium ions enter pre-synaptic neuron terminal and bind with synaptic vesicles → ACh is released into the synaptic cleft and diffuses across it → ACh binds with nAChRs → nAChRs open → sodium ions enter and depolarize the postsynaptic muscle cell → calcium ions are released into the muscle cell cytoplasm from the SR → muscle contraction → acetylcholinesterase breaks down ACh remaining in cleft

disorders affecting muscle contraction

amyotrophic lateral sclerosis (ALS), myasthenia gravis, botulism, and muscular dystrophy

amyotrophic lateral sclerosis (ALS)

• progressive degeneration of motor neurons

• DNA-binding protein dysfunction that results in its mislocalization and aggregation that leads to degeneration

• can affect both the CNS (UMNs) and the PNS (LMNs)

myasthenia gravis

• an autoimmune disorder in which antibodies attack nAChRs on muscle cells making it difficult for muscle contraction to occur

• causes facial drooping, muscle weakness, fatigue

botulism

involves the neurotoxin botulinum A that causes muscle paralysis by entering the presynaptic neuron terminal of NMJs and preventing the formation of synaptic fusion complexes so that ACh is not released into the synaptic cleft and muscle contraction does not occur

muscular dystrophy

genetic condition caused by a gene mutation that makes muscle fibers leaky to calcium ions resulting in excess intracellular calcium ion concentration that damages the mitochondria of muscle cells which leads to muscle cell death and muscular atrophy

surface EMG measure and analysis

• use electrodes placed on the skin over the muscle of interest to detect the electrical activity produced when the muscle is activated → Bio Amp carries electrical analog signal from electrodes to PowerLab hardware → bioamplifier amplifies the analog signal → PowerLab converts analog signal into digital signal that is displayed in the Lt software as a waveform

• an EMG can be analyzed based on the timing of contractions versus relaxation, the pattern of motor unit recruitment, and the amplitude of its resulting waveforms which reflects the strength of contractions

  • increase in amplitude when force of contraction increases because more motor units are recruited to increase contraction → more motor neurons firing → more electrical activity detected

electromyography (EMG)

• EMG is a technique that measures the electrical activity of skeletal muscles

• EMGs are recorded either using surface electrodes placed on the skin or needle electrodes inserted into the muscle through the skin

• EMGs represent the overall electrical activity of the different motor units within the muscle

  • stronger EMG signal = more motor units firing

root mean square (RMS)

• square each voltage value so they are all positive → average together the squared values → take the square root of that average

• quantifies the overall magnitude of the EMG signal which provides an estimate of muscle activation → higher RMS = larger EMG signal = greater muscle activation and vice versa

muscle coactivation

• contraction of an agonist (primary muscle) results in minor activity in the antagonist (opposing muscle)

• thought to help stabilize joints

• biceps contraction has a large amplitude EMG signal paired with a small amplitude EMG signal from the triceps

surface vs. intramuscular EMG

• surface EMG

  • records the overall electrical activity of the muscle

  • limited application in clinical settings but can be used for performance analysis and monitoring of muscle activation

    • less accurate, more general information

    • can be affected by presence of adipose tissue

  • non-invasive but restricted to superficial muscles

• intracellular EMG

  • records the individual electrical activity of a motor unit within a muscle

  • produces consistent and accurate information useful for clinical diagnosis

  • invasive

biopotentials

voltages produced by physiological processes that involve excitable cells (i.e. muscle contraction or nerve stimulation)

compound action potential (CAP)

• the sum of the action potentials recorded from a whole nerve that contains numerous nerve fibers

  • represents the overall electrical activity of an entire nerve

  • compared to an individual action potential from one nerve fiber

  • shape does not correspond to the form of a single intracellular AP recording (monophasic)

  • artifact a result of current that spreads passively through water contained in tissues

• recorded by using two external electrodes (1 reference, 1 recording) that measure the changes in polarity between them as the signal passes beneath them (+ then 0 then - → biphasic)

  • low signal strength (2-4 mV CAP vs. 80-100 mV AP)

evoked EMG

• an evoked EMG because stimulated nerve to cause it to fire CAPs and then also recorded EMG

  • different from previous lab because recording electrical activity of an intentionally stimulated nerve over milliseconds versus recording electrical activity of a voluntarily activated muscle over seconds

• as nerve stimulation increased, the evoked EMG amplitude increased until reaching a maximum response where it stopped increasing

  • amplitude determined by the number and frequency of nerve fibers firing

  • maximum response reached when all nerve fibers are firing at their highest possible frequency

• at lower levels of stimulation myelinated fibers that are larger in diameter and have a higher NCV are stimulated first

  • greater diameter = lower internal resistance = current spreads more easily and more quickly through axon = lower stimulation threshold so recruited first

  • myelination = higher membrane resistance = less current leakage = current spreads farther

nerve conduction velocity

• the rate at which an AP travels along a nerve

  • impacted by axon diameter (determines internal resistance, lower = higher NCV) and myelination (determines membrane resistance, higher = higher NCV)

• calculated by comparing distance traveled to time it took to travel that distance

  • stimulation spot at elbow distance from stimulation spot at wrist / latency of elbow - latency of wrist

earthworm median and lateral fibers

• earthworms have a ventral nerve cord that contains a median giant nerve fiber and two lateral giant nerve fibers that lie on either side of the medial giant nerve fiber as well as segmental sensory and motor fibers that do not run along the complete length of the animal

  • “giant” because they achieve speed via their large diameter rather than via myelination

  • each giant fiber is made up of individual cells (1 per segment) that are electrically coupled through gap junctions → rapid conduction of APs from cell-to-cell behavior of a single continuous fiber

  • lateral fibers are extensively linked to one another via cross-connections so behave like a single fiber

• allow the earthworm to respond rapidly to threatening situations with a variety of escape behaviors

earthworm APs recording

• same extracellular recording set-up as PNS function lab except this specific set-up is measuring the evoked EMG of a single nerve fiber versus a whole nerve, so APs are all-or-nothing and not graded CAPs

• recording set-up

  • reference (-) electrode followed by recording (+) electrode

    • differential amplifier used to amplify the small changes in voltages between the two electrodes

    • depolarization under reference electrode = positive inflection, depolarization under recording electrode = negative deflection, no difference between membrane potential under electrodes = zero deflection → biphasic

    • extracellular recording so cannot determine exact membrane potential of nerve fibers only if they fired an AP or not

    • electrodes placed closer to the nerve likely to have a higher amplitude, reversing electrodes (recording then reference) would flip polarity of biphasic signal (- then +), and increasing distance between stimulating and recording electrodes increases latency

  • ground electrode helps to reduce electrical interference called “noise” from the recording equipment and from the environment

• stimulating set-up

  • red cable (+ anion) anterior to black cable (- anion)

  • ground cable connecting to mat worm is on

determining earthworm measurments

• threshold is determined by gradually increasing strength of stimulus until an AP occurs

  • affected by myelination, nerve diameter, membrane properties (differences in membrane potential, ion channel distribution)

  • different from worm to worm due to fiber distance to electrode and tissue condition

• latency determined by measuring time it takes AP to occur after stimulation has occurred

  • affected by NCV (higher HCV = lower latency) and distance between stimulator and recording electrodes

  • different from worm to worm due to NCV differences

• nerve conduction velocity is determined by comparing distance traveled by signal to electrode with latency

  • affected by axon diameter, myelination, temperature, tissue condition, membrane properties

  • different from worm to worm due to nerve fiber diameter, temperature, tissue condition, and accuracy of electrode placement and distance measurements

• refractory period is determined by decreasing time in between two stimuli until only one action potential occurs instead of two → absolute refractory period when impossible for another AP to occur

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bidirectionality and orthodromic direction

• bidirectionality shown in lab by eliciting an AP from the medial giant fiber in both the orthodromic and antidromic directions

• orthodromic direction is determined by the anatomical connections of neurons and their normal function (i.e. the medial giant fiber in earthworms controls reflex response of head so propagates anterior to posterior)