Final Exam Flashcards
what does somatic sensation enable?
enables us to feel, ache, and sense temp and pressure
how is the somatic sensory system different from other systems?
broadly distributed receptors and responds to multiple different stimuli
types of skin
hairy and glabrous
layers of skin
epidermis (outer) and dermis (inner)
what are the functions of skin?
protects, prevents evaporation of bodily fluids, and provides direct contact with the world
what are most somatosensory receptors? what are they sensitive to?
mechanoreceptors; physical distortion
what are the difference mechanoreceptors?
pacinian corpuscles, ruffini’s endings, meissner’s corpuscles, and merkel’s disks
pacinian corpuscles
highest densities in the fingers, lies deep, mm size
meissner’s corpuscles
in the ridges of glabrous skin, 1/10 size of p.c.
what are merkel’s disks made up of?
a nerve terminal and a flattened non-neural epithelial cell
how do mechanoreceptors vary?
stimulus frequencies, pressures, receptive fields, and responses to long-lasting stimuli
what are Pacinian corpuscles sensitive to?
vibrations of ~ 200-300 Hz
what are Meissner’s corpuscles sensitive to the best?
vibrations around 50 Hz
how do mechanoreceptors convert mechanical force to a change in ion current?
they have unmyelinated axon terminals with ion channels that are connected to proteins. when mechanical stimuli is present, a release of second messengers is tiggered
two-point discrimination
ability to discriminate the detailed features of a stimulus (between two points) varies throughout the body
how much does two-point discrimination vary across the body?
20-fold
why are fingertips good for Braille reading?
higher density of mechanoreceptors, enriched in receptor types with small receptive fields, more brain tissue, and there may be special neural mech.s for high-res discriminations
where are primary afferent axons primarily located?
dorsal root of spinal cord; enter cord through there.
characteristics of C fibers (primary afferent axons)
- mediate pain, temp, and itch
- no myelin & ~1 um in diameter
- slowest (0.5-1 m/sec)
what do Abeta primary afferent axons mediate?
touch sensations
4 divisions of the spine and their vertebral adjacents
cervical (1-8)
thoracic (1-12)
lumbar (1-5)
sacral(1-5)
total spinal segments?
30
dermatones
area of skin innervated by right and left dorsal roost of spinal segment; one-to-one correspondence with spinal segments (vertebrae)
what is shingles and what is it’s connection to sensation?
herpes virus (chickenpox) that remains in primary sensory neurons and revives; restricted to skin innervated by axons of affected dorsal root
how many branches do the Abeta axons have and what do they do?
2 branches. one is on second-order sensory neurons & does rapid unconscious reflexes. other is responsible for perception
where do the Abeta axons enter the spinal cord?
in the ipsilateral dorsal column
where do the axons of the dorsal column go in the brain?
dorsal column nuclei @ junction of spinal cord and medulla
what is special about dorsal column axons?
some of the longest axons
where do the axons of the dorsal column decussate to?
VP nucleus of thalamus and primary somatosensory cortex (S1)
what are the sections of the somatosensory areas?
- postcentral gyrus of somatos. cortex (1, 2, 3a)
- Brodmann’s area of somatos. cortex (3b)
- posterior parietal cortex (5 and 7)
what is considered the primary somatic sensory cortex and why?
area 3b (Brodmann’s)
- receives dense inputs from VP nucleus
- very responsive
- lesions impair somatic sensation
- evokes somatic sensory experiences when electrically stimmied
what info does area 3b send to area 1?
texture info
what info does area 3b send to area 2?
emphasizes shape and size
where do thalamic inputs to 3b (S1) terminate
mainly in layer IV
how are S1 (3b) neurons organized?
alternating layers stacked vertically into 6 columns
what is the main difference between the two types of cortical layers in S1?
one has rapidly adapting sensory responses and one has slowly adapting sensory responses
what did Wilder Penfield discover?
electrical stimulation of S1 surface can map somatic sensations localized across the body
somatotopy
mapping of the body’s surface sensations onto the brain (think that really weird cartoon about the different regions of sensation on the brain)
barrel cortex
sensory signals from each vibrissa follicle go to one clearly defined cluster of S1 neurons
how many maps of the body does the somatic sensory system have? what are some examples?
many maps; some are mirrored (owls monkey hand area)
what happens when someone looses a digit (in owl monkey)?
- neurons devoted to amputated digit will respond to others
- rep of remaining digits expand to compensate in map
- phantom limb possible
red muscle fibers
large # of mitochondria and enzymes, slow to contract, can sustain contraction; antigravity muscles of leg and torso
white muscle fibers / fast fibers
fewer mitochondria, anaerobic metabolism, contract and fatigue rapidly; human arm muscles
fatigue-resistant fast fibers
white fibers with moderate strength and fast contractions
fast fatigue fibers
fastest, strongest white fibers but rapidly fatiguing
motor unit
motor neuron + the muscle fibers it innervates
how many types of muscle fibers can a motor unit have?
only one
how many muscle fiber types do most muscles have?
all three (red, fatigue-resistant, and fast fatigable)
two types of motor units
slow and fast
repeated trains of APs lead to different….
rates of fatigue
what did the crossed-innervation experiment discover?
switched nerve input -> switch in muscle phenotype
how can you switch muscle phenotype?
switching the activity of the motor neuron
can a switch in neuron phenotype happen irl?
yes, with changes in synaptic activity with experience
when are muscle fibers formed?
early in fetal development by fusion of muscle precursor cells
basic anatomy of muscle fiber
- each cell has >1 nucleus
- fibers enclosed in sarcolemma (excitable membrane)
- layers of contractable myofibrils inside
excitation-contraction coupling
alpha motor neurons release ACh -> ACh induce EPSP -> EPSP invoke AP -> AP release Ca+2 -> fiber contracts -> calcium reuptake -> fiber relaxes
sarcomere anatomy
alternating I and A bands, I contains Z line, A contains H zone. sarcomere extends from one Z line to another
how does muscle contraction occur in regards to the filaments?
thin filaments slide along thick filaments, bringing Z lines together and shortening the sarcomere
muscle spindles
deep in skeletal muscles; contain stretch receptor; example of proprioceptors
proprioceptors
“body sense”
how do stretch receptors cause the muscle to shorten/contract?
stretching leads to depolarization of Ia axon -> opening of mechanosensitive ion channels -> AP discharge from Ia depolarizes alpha motor neurons -> contraction
stretch reflex
muscle wants to pull back when it’s being pulled
discharge of Ia sensory axons is closely related to …
length of the muscle
example of stretch relfex?
knee-jerk
many inputs to motor neurons are mediated by…
spinal interneurons
reciprocal inhibition
contraction of one muscle set is accompanied by relaxation of anatgonist muscle
reciprocal inhibition is done because…
inhibitory spinal interneurons are between the Ia axon from the contracting muscle and the alpha motor neuron going to the antagonist muscle
flexor reflect
withdraw a limb from an aversive stimulus; excitatory interneurons
crossed-extensor reflex
activation of extensor muscles and inhibition of flexors on opposite side during flexor reflex
when would crossed-extensor reflex be used?
to brace the other leg when you step on something sharp
central pattern generators
circuits that give rise to rhythmic motor activity
examples of central pattern generators
spinal motor programs for walking (circuitry in the spinal cord and rhythmic activity in interneurons)
how does rhythmic activity in spinal interneurons occur?
glutamate activates NMDA channels to open, allowing Ca+2 influx. calcium then activates K+ channels to open, causing K+ efflux. Mg+2 comes in to clog the NMDA channel, and less calcium causes K+ channel to close. reset!
what is a possible circuit for alternating rhythmic activity?
continuous input from brain goes into two excitatory interneurons that are connected by an inhibitory interneuron. because they can inhibit each other, the activity alternates
example of when alternating rhythmic activity would occur?
flexion in one limb is accompanied by extension in the other
electrical rhythms of the cerebral cortex
sleeping, walking, hibernation, and breathing
classical method of recording brain rhythms
EEG
circadian rhythms
changes in physiological functions according to brain clock
when was first EEG?
1929
are walking and sleeping EEGs the same?
no! distinctly different
unit of measurement used in EEG
microvolts (uV), usually in tens
amplitude of EEG signal measures…
synchronous activity of underlying neurons
what generates the electrical fields detected by EEG?
currents that flow during synaptic excitation of dendrites of many pyramidal neurons; thousands have to activate together to generate signal strong enough to be detected
how do we describe EEGs?
relative amplitude (suggests how synchronous underlying activity is)
how are EEG rhythms categorized?
based on their frequency range; 7 catagories
what are the 7 categories of EEG rhythms?
alpha, beta, gamma, delta, theta, spindles, and ripples
alpha EEG
8-13 Hz; quiet, walking state
beta EEG
15-30 Hz; an activated or attentive cortex
gamma EEG
30-90 Hz; an activated or attentive cortex
delta EEG
< 4 Hz; deep sleep
theta EEG
4-7 Hz; some sleep and walking states
spindles EEG
brief 8-14 Hz waves associated with sleep
ripples EEG
brief bouts of 80-200 Hz oscillations; in hippocampus, sleep
are EEGs specific to species?
no, they’re similar across mammalian brains
what are high-frequency, low-amplitude EEGs associated with?
alertness and walking, or dreaming stages of sleep
what are low-frequency, high-amplitude EEGs associated with?
non-dreaming sleep states, certain drugged states, or pathological condition of coma
what are high synchrony, high amplitude EEGs associated with?
deep sleep
what is a pacemaker in regards to rhythms?
the collective behavior of all participants (in this case neurons)
how does pacemaker work in leading a synchronous rhythm?
- take cues from a central clock
- share or distribute timing function among themselves by mutually exciting or inhibiting one another
basic features of a neural oscillator
- source of constant excitatory drive
- feedback connections
- synaptic excitation and inhibition (usually one excitatory and one inhibitory neuron)
what are some causes of seizures?
tumor, trauma, genetics, infection, vascular disease, and other unknown causes
seizures can be defined as…
the most extreme form of synchronous brain activity (accompanied by very large EEG)
generalized seizure
entire cerebral cortex, complete behavior disruption, loss of consciousness
partial seizure
circumscribed cortex area, abnormal sensation/aura (odd smell, sparking lights)
absence seizure
> 30 sec of generalized 3 Hz EEG waves, characterize a childhood form of epilepsy, motor signs strangely subtle
what are the characteristics of the EEG of a generalized seizure?
- beings abruptly
- synch. across entire head
- ends abruptly
whats the purpose of sleep?
dunno
sleep is defined as
a readily reversible state of reduced responsiveness to, and interaction with, the environment
how long do we spend sleeping?
1/3 of lifespan
what are the three functional brain states?
awake, REM sleep, and non-REM sleep
rem sleep
EEG looks like awake, body immobilized, dreams
non-rem sleep
no dreams usually, slow large/high voltage EEG
we know we go through all 5 stages of sleep, but what happens as we repeat them?
non-rem stages get shorter and shallower and rem stage periods get longer
what are some physiological changes during REM periods?
increases in heart rate, respiration rate, and erections (lmao)
non-REM sleep stage 1
- transitional sleep
- relaxed EEG
- slow, rolling eye movements
non-REM sleep stage 2
- slightly deeper
- occasional 8-14 Hz EEG oscillation called sleep spindle
- high-amp sharp K complex
- almost no eye movement
non-REM sleep stage 3
- EEG begins large-amp, slow delta rhythms
- few eye and body movements
non-REM sleep stage 4
- deepest stage
- large EEG rhythms of 2 Hz or less
do we go straight from stage 4 non-REM sleep into REM sleep?
no, we go back to stages 3 and 2 before suddenly entering REM
what is special about the way dolphins sleep?
they sleep with one cerebral hemisphere at a time
what are the two main theories of sleep function?
restoration and adaptation
restoration sleep function theory
sleep to rest, recover, and prepare to be awake again; possible some brain regions achieve form of essential rest only during sleep
adaptation sleep function theory
sleep to keep out of trouble, hide from predators
Sigmund Freud dream theory
dream functions - wish fulfillment, conquer anxieties
Hobson and McCarley dream theory
activation-synthesis hypothesis; dreams are seen as associations and memories of the cerebral cortexthat are elicited by the random discharges of the pons during REM
Karni dream theory
certain memories require strengthening time period, that period being REM. sleep learning
neurons most critical to control of sleeping and waking are part of the…
diffuse modulatory neurotransmitter systems
what do the diffuse modulatory neurotransmitter systems control?
rhythmic behaviors of the thalamus -> EEG rhythms of cerebral cortex
how are sleep and the branches of diffuse modulatory systems connected?
sleep involves activity in the branches, i.e. inhibition of motor neurons during dreaming
what did Cirelli and Tononi discover about sleep?
- in rats
- 0.5% of genes showed differences of expression levels when awake or asleep
- awake increased intermediate early and mitochondrial genes
- sleep increased genes that contribute to protein synth and plasticity
- changes specific to brain, no other tissues
what is the hallmark of an anxiety disorder / anxiety?
the occurrence of an inappropriate stress response either when a stressor is not present or when it is not immediately threatening
characteristics of a stress response
- avoidance behavior
- increased vigilance and arousal
- activation of symp. ANS
- release of cortisol from adrenal gland
HPA axis
hypothalamus secretes CRH -> anterior pituitary secretes ACTH -> adrenal gland secretes cortisol
what activates the HPA axis?
amygdala
what deactivates the HPA axis?
hippocampus via negative feedback; inhibits CRH release
what kind of receptors are sensitive to cortisol?
glucocorticoid receptors
what are available treatments for anxiety disorders?
psychotherapy and anxiolytic medications
how do anxiolytic medications treat anxiety disorders?
alter chemical synaptic transmission
types of anxiolytic medications?
GABA, benzoids, SSRIs (new drugs targeting CRH receptors)
affective disorders are defined as…
disorders of mood
major depression and dysthymia are part of ___ depression
recurrent
symptoms of major depression
- lowered mood, interest, pleasure, and appetite
- insomnia or hypersomnia
- fatigue
- feelings of worthlessness or guilt
- cant concentrate
- suicidal thoughts
dysthymia
milder than major depression, seldom disappears spontaneously
bipolar disorder
repeated episodes of mania, or mixed episodes of mania and depression
symptoms of mania
- inflated self-esteem or grandiosity
- decreased need for sleep
- increased talkativeness
- flight of ideas, subjective experience that thoughts are racing
- distractability
- increased goal-directed activity
type 1 bipolar
manic episodes with no depression
type 2 bipolar
hypomania; mild mania and hella depression
what is the monoamine hypothesis of affective disorders?
deficit in central diffuse modulatory systems; depression is a consequence of a deficit in one of these d.m.s.; treatments focus on central serotonergic and/or noradrenergic synapses
available treatments for affective disorders
psychotherapy, electroconvulsive therapy (ECT), and antidepressants
characteristics of electroconvulsive therapy
- unknown mechanism in relieving depression
- affects temporal lobe
- advantage: quick relief of depression and mania
- adverse affect: loss of prior memories, impaired storage of new information
what are the types of antidepressants?
MAO inhibitors, tricyclics, SSRIs, and NE-selective reuptake inhibitors
MAO inhibitors
reduce enzymatic degradation of serotonin and norepinephrine
tricyclics
block reuptake of norepinephrine and serotonin
SSRIs
act only on serotonin terminals (ex: fluoxetine)
adaptation of antidepressants
therapeutic actions take weeks to develop
what common drug is used to treat affective disorders (mainly major depressive disorder)?
ketamine
how does deep brain stimulation (DBS) help neurologic and psychological disorders?
in depression: stimmies anterior cingulate cortex to decrease brain activity in circuits that are chronically overactive
what is the first step in wiring the nervous system?
neurogenesis
when are the majority of neurons made? at what rate?
before birth. 250,000 cell/min
when will the neuron never divide again?
when neuronal fate is reached
what are the three stages of neuronal structure development?
cell proliferation, cell migration, and cell differentiation
subventricular zone (SVZ)
in the lining of the lateral ventricles; site where neuroblasts are formed
where do neuroblasts migrate to once formed?
to the olfactory bulb via the rostral migratory system (RMS)
subgranular zone (SGZ)
in the dentate gyrus of the hippocampus area
are radial glial cells only a scaffold?
no, they also give rise to neurons and astrocytes (aka neuro progenators)
how many rounds of division will a neuron go through?
2 - one symmetrical and one asymmetrical
how do pyramidal cells and astrocytes migrate out of the SVZ?
vertically by moving along thin radial glial fibers
how are inhibitory interneurons and oligodendroglia different in generation and migration?
they generate in a different place and migrate laterally
when does a cell look like a neuron? when is it programmed to be a neuron?
takes on characteristics of neuron once it reaches destination, but is programmed way before that
put the following in order from first to differentiate to last: astrocytes, oligodendrocytes, and neurons
neurons, astrocytes (peak @ time of birth), oligodendrocytes
chemoaffinity hypothesis
chemical markers on growing axons are matched with complementary chemical markers on their targets to establish precise connections
what are some growth guidance cues?
chemoattractant (ex: netrin) and chemorepellent (ex: slit)
