NEURO-204 Unit 1

human nervous system components

brain, spinal cord, nerves, ganglia

central nervous system

brain and spinal cord

peripheral nervous system

all nerves and sensory structures outside of the CNS

PNS - somatic

voluntary control of skeletal muscle

PNS - autonomic

involuntary control of glands and smooth muscle

sympathetic - “fight or flight”

parasympathetic - “rest and digest”

planes of the brain

coronal, sagittal, axial (horizontal)

rostral / anterior

front of brain

caudal / posterior

back of brain

dorsal / superior

above

ventral / inferior

below

forebrain

cerebrum and diencephalon

brainstem

midbrain, pons, medulla

blood brain barrier

surrounds arteries in brain, prevents toxins from getting to brain

neural hierarchy

flexible/abstract vs. reflexive/specific

grey matter

consists of somas (cell bodies)

white matter

composed of myelinated axons

cerebellum

balance, coordination, fluid movement, motor activity

medulla

cranial nerve cell body site, connects brain and spinal cord, vital functions, motor nerves decussate, reticular activation system

reticular activating system

neurons receive input from cranial nerves and project diffusely to other regions of the brain; important for arousal, attention, and regulating sleep-wake cycles

midbrain

superior and inferior colliculi, integration and orienting

diencephalon

hypothalamus and thalamus

hypothalamus

helps maintain equilibrium - homeostatic functions including body temp, eating/drinking, sex, circadian rhythm, stress

thalamus

relay point for information leaving from and entering the cortex; sensory relay center that separates nuclei for each sense and projects to the limbic system and cortex; region where neurons from one brain area synapse onto neurons that will synapse somewhere else

basal ganglia

motor control and habitual behavior

limbic system

integration of emotion information

amygdala: threat, novelty detection

hippocampus: memory

cingulate cortex: behavior regulation (selecting actions and motivation)

cortex

gyri - protrusions

sulci - creases/folds

fissure - deep sulci

longitudinal fissure separates right hem. from left; lateral (Sylvian) fissure separates dorsal and ventral hemispheres

ventricles

contain cerebrospinal fluid, allows nutrients to reach neurons, provides cushioning

PNS: schwann cells and CNS” oligodendrocytes

produce myelin

nodes of ranvier

gaps between myelinated sections of axon

axon hillock

produces the action potential

myelin sheath

fatty, white insulating substance to help propagate action potential; larger sheath leads to faster speed of propagated electrical signal

terminal bouton

end of road for action potential, contains synaptic vesicles

types of glia

microglia, astrocyte, ependymal, oligodendrocyte/schwann cells

microglia

immune function, helps remove potentially harmful debris

astrocyte

connect w/ capillaries, providing nutrients

ependymal

produce cerebral spinal fluid (CSF)

action potential steps

resting potential: -70 mV

threshold of excitation: -55 mV, Na+ channels open

depolarization as mV approaches zero

peak action potential: +30 mV, Na+ channels close, K channels open

repolarization/falling phase as it becomes more negative

hyperpolarization: becomes more neg. than resting potential, K channels close

back at resting potential

features of action potentials

• self-propagating at a constant speed

• signal doesn’t dissipate, always has the same strength

• all-or-nothing (once started, it won’t stop)

• magnitude/intensity = firing rate

• speed influenced by axon diameter and myelin

synapse

region of contact between neuron containing terminal bouton, synaptic cleft, and postsynaptic region

T or F: axons can only synapse with one neuron

false - axons can have many branches and can synapse with 1,000 different neurons!

synaptic transmission

• action potential reaches axon terminal

• calcium ion channels open, allowing Ca 2+ ions in

• Ca 2+ causes synaptic vesicles to release from microtubules

• synaptic vesicles fuse with axon membrane at release sites in presynaptic neuron

• vesicles open, releasing neurotransmitters into synaptic cleft

• neurotransmitter binds with receptor on postsynaptic neuron

• vesicle material is recycled

• vesicles either return to neuron cell body via retrograde transport or are refilled at axon terminal

post-synaptic neurotransmitter modulation

• reuptake - neurotransmitters are taken up into terminal bouton of presynaptic neurons via transporter molecules

• enzymatic deactivation - deactivating the enzyme so that NT’s can’t bind, leading to an increased amount of NT

• glial cell degradation (astrocytes): can break down NT into different chemicals

• autoreceptors: bind to NT’s, decrease the activity of the presynaptic neuron, inhibits NT activity (negative feedback)

• diffusion: NT's drift elsewhere, away from the synapse

reuptake transporter vs. autoreceptor

both

• types of proteins on presynaptic neuron axon terminal

• reduce NT in synaptic cleft by bringing back into presynaptic neuron

reuptake

• NT brought back into presynaptic neuron through transporter channel

autoreceptor

• NT binds to receptor and inhibits NT activity (negative feedback)

• when receptor is inhibited, excitation occurs and more NT is communicated

post-synaptic responses

excitatory postsynaptic potential (EPSP)

• makes cell’s electrical charge a bit more positive

• gets it closer to depolarization

inhibitory postsynaptic potential

• makes inside of cell a bit more negative than outside

• further from depolarization

responses:

• signals are summed and neurons choose to send a signal

• if terminal is slightly closer to axon hillock it can have a more controlling/influential role

neurotransmitters

chemicals exchanged during communication between neurons

classes of NT’s found in CNS

amino acids: molecules that make up proteins and can act as NTs

NT systems: NTs isolated and organized into specific pathways

two main amino acids in CNS acting like NT’s, used in immune system

GABA

• inhibitory - dampens/modulates the system

• 40% CNS neurons

• can be used as sleep/anxiety medication

• alcohol affects GABA receptors

Glutamate

• excitatory leading to depolarization

• 15-20% CNS neurons

• excitotoxicity: neurons get “fried” by too much stimulation, it’s good to have inhibitory control

transmitter: acetylcholine (ACh)

• NT system: cholinergic

• site of origin: basal forebrain

• projection sites: diffuse cortical regions

main behavioral effects

• attention, vigilance, arousal, memory

• cortical excitability

• motor excitation for muscle contraction

• autonomic communication

• anti-inflammatory in periphery

NT: norepinephrine (NE)

• also known as noradrenaline (british term)

• NT system: noradrenergic

main behavioral effects

• attention, vigilance, arousal

• sympathetic communication - fight or flight

NT: serotonin (5-HT)

• sleep, mood, sexual behavior, eating, pain, memory, arousal

• largely produced in gut

• MDMA (ecstasy) use leading to memory loss

serotonergic NT system has two subsystems:

• dorsal raphe nucleus → cortex and thalamus

• medial raphe nucleus → limbic system

NT: dopamine (DA)

NT system: dopaminergic

• working memory, novelty seeking, attention, psychotic symptomatology

• D1-like (postsynaptic) and D2-like (postsynaptic + presynaptic) dopaminergic receptors

nigrostriatal subsystem

• substantia nigra → dorsal striatum

• motor activity

mesolimbic subsystem

• ventral tegmental area → limbic regions, prefrontal cortex

• reward + reward-related behavior

mesocortical subsystem

• ventral tegmental area → prefrontal cortex

• working memory, planning - keep info “online” for tasks/strategy

vestibulation (in pons)

sense of balance and orientation, awareness of acceleration, related to inner ear function, overlaps with function of cerebellum

excitotoxicity

overstimulation of glutamate receptors to dangerous levels, can cause cell death

structure vs. function

structure - like a picture

• static, trait-like, somewhat stable

• ex: computerized tomography (CT), structural magnetic resonance imaging (MRI)

function: what happens

• activity, temporary, measuring how something is acting, during a specific response/behavior

brain perturbation (neurodisruption) functional approach

• perturbation (modification) of brain

• measure task performance

• examples

  • optogenetics - how neurons respond to light

  • transcranial magnetic stimulation (TMS) - currents to disrupt brain

  • stroke, trauma, disease (lesion)

neuromonitoring functional approach

• assign task / manipulate cognitive process / experiment

• measure neural variable - how the brain responds

• examples

  • electrophysiological recordings

  • electroencephalography (EEG)

  • positron emission tomography (PET)

  • functional magnetic resonance imaging (fMRI)

brodmann’s areas

fallen out of practice, grouping by anatomical cellular patterns but not function

motor and somatosensory corticies

• primary motor cortex in frontal lobe

• primary somatosensory cortex in parietal lobe

  • tactile stimulation, proprioception, pressure, pain

• separated by central sulcus

• contralateral processing

corpus callosum

• collection of nerves, enables contralateral processing

• communicates across the brain (connects L + R)

• white-matter (axon) tracts shuttle info between distinct brain regions

homunculus (somatosensory and somatomotor cortex)

• different body parts represented across the brain

• size corresponds to density of touch receptors (sensitivity to touch)

• larger area → fine motor control of body part (precision)

• inversion L-R and top-bottom

fMRI

• active tissue (gray matter) increases blood-oxygen-level-dependent (BOLD) response

  • identifies brain regions where neurons are active

• detects differences in the magnetic properties of oxygenated and deoxygenated blood

• can show more oxygenated blood moving to a part of the brain

frontal lobe

• planning, guidance, evaluation of behavior / olfactory processing

• prefrontal region, premotor region, primary motor region

• subsections of pre-frontal cortex

  • dorsolateral: memory + executive functions

  • orbital: emotional processing

  • medial: judgement, error detection

parietal lobe

• integration of internal/external sensations and memory

• combo of sensory inputs from inside and outside of the body

limb apraxia

• deficits in skilled movements; related to impairment in parietal and frontal regions

• e.g., perturbation study, examining stroke patients and comparing those with action production impairment to action recognition impairment

occipital lobe

visual processing

positron emission tomography (PET)

• structural - gray matter

• injection of radioactive tracer into bloodstream to measure physiological activity of different brain regions

• expression of tracer reveals tissue metabolism, indicative of activity levels

temporal lobe

memory, emotion, object recognition, auditory processing

electroencephalography (EEG)

• summed electrical signals of postsynaptic neuronal dendrites that was received from presynaptic neuron

• recorded on scalp using a cap; waveforms have specific voltages and frequencies (signal size + oscillation rate)

• useful for determining states of alertness/sleepiness

• not highly localized; EEG electrode collects info about a broad area

• recognition of syntax violation demonstrated in P600 EEG signal (recognition of incorrect syntax)

JC1 research question/hypotheses

maguire et al. (2000)

• taxi drivers have larger hippocampi than controls, time driving and hippocampal volume are positively related

• correlational / cross-sectional study

wollett & maguire (2011)

• taxi drivers show change in hippocampal structure as a result of acquisition of the “knowledge” from before to after completion of training

• longitudinal design

JC1 methods

• sMRI - electromagnetic signals emitted from hydrogen atoms after being stimulated by magnetic and radio waves

  • strength measured in Teslas (T)

  • radio frequency pulses emitted at a resonant frequency to stimulate protons

  • protons absorb/release energy from RF pulse differently depending on tissue type

JC1 results

maguire et al. (2000)

• posterior of hippocampus was a bit larger in taxi drivers and the anterior smaller compared to those who weren’t taxi drivers

• posterior → spatial awareness, anterior → images

• reported measures, not a before + after

wollett & maguire (2011)

• limited the confounding variables

• difference in training time per week across the groups

• only saw a posterior change, so anterior change may happen later; wasn’t captured

sensation

encoding of sensory information (how info is computed)

perception

representation of sensory information (how the brain organizes the info / how we understand it)

examples of sensation without perception and vice-versa

• hallucinations

• bug “crawling” on you

• phantom limb pain

• sleeping through alarm

retina

• network of neurons on back interior of eye

• contains photoreceptors, other neurons conveying specific information

• first step in visual transduction pathway

transduction

translation a sensory signal into something meaningful

photoreceptors

• receptor-specific pigment absorbs light wave

• light triggers depolarization through chemical change in receptor

• depolarization signals the next cell layer

• signaling pattern on ganglion cells serves different functions

rods

• photo pigment - rhodopsin

• many rods feed into each ganglion cell

• signal is a summation

  • low precision/resolution

  • stronger (summed) signal can persist in low light conditions

cones

• wavelengths

  • short - blue

  • medium - green

  • long - red

• few inputs to ganglion cells; signal maintains distinctiveness

  • high precision/resolution

  • weaker signal (comprised of less cells) does not depolarize ganglion cell in low light conditions

  • less summation → higher precision

ganglion cells

• the “output”; eye→brain

• cell bodies in retina

• axons form optic nerve

• output to thalamus

• center-surround (center is on)

two of the many types

• magnocellular (M) cells - large

  • coarse patterns (less precision)

  • rapid motion

  • faster

• parvocellular (P) cells - small

  • color

  • higher spatial resolution

  • slower

suprachiasmatic nucleus (SCN) pathway

in hypothalamus; related to circadian rhythms

tectopulvinar projection pathway/site

• retina → superior colliculus → pulvinar (in thalamus)

• mostly magnocellular (receives most input from M cells)

• processing motion quickly in a coarse way, not very detailed

• orientation/localization

geniculostriate projection pathway

• retina → lateral geniculate nucleus (LGN) in thalamus → V1 (striate cortex)

• more detailed analysis, mostly parvocellular

optic chiasm

switch-over point for contralateral processing of vision

V1 pathways

• dorsal (where) pathway

  • posterior parietal cortex

  • spatial location, sensory integration - where?

• ventral (what) pathway

  • inferior temporal cortex

  • identification

  • simple → complex qualities

  • posterior → anterior along stream

  • simple: color/texture/orientation/motion features

  • complex: specific objects

receptive field

• area in space to which a given cell responds - what is it receptive to?

• ganglion cell RF depends on which photoreceptors project to it

• not directly getting stimulated from light, rather via signals from photoreceptors (ganglion) and/or other downstream cells (RFs for other neurons)

LGN organization

• conservation of info via projections occurring in layers

• preserving where the info is coming from and what it is

• ganglion cells → LGN → thalamus

V1 organization

• primary visual cortex; striate “striped” cortex

• retinotopic layered columns

  • spatial location

  • orientation

  • motion

  • ipsilateral vs. contralateral eye of origin

striate cortex cells

• respond to bars of light in particular ways

• receptive field with center being off-area

• more complex cells can respond to a variety of inputs

grandmother cell theory

• one neuron responds to a certain person

• certain cells in ventral stream fire to single individuals or objects with great specificity

• flaw: recognition abilities would theoretically be easily disrupted

habituation/adaptation

• after repeated presentations, a cell becomes less sensitive to the stimulus

• a kind of desensitization

• neurons don’t keep responding to the same stimulus

• helps to be more efficient and to process stuff that matters

specialized regions in the “what” pathway

FFA: fusiform face area

• highly responsive to faces

• larger negative signal N170 for faces

• may be modified by experience

PPA: parahippocampal place area

• connected to “where” pathway, and gets sent to ventral “what” pathway

functional organization of visual system

• qualities of visual stimuli are represented spatially by different types and groupings of cells

• qualities and spatial mapping are preserved from retina to brain

• cells fire in response to qualities they are “tuned” for, indicating the intensity/magnitude of this quality in the stimulus

• cells fire in relation to background patterns (weaker cell response if part of background)

cortical blindness

• cortical origin rather than the eye or optic nerve

• unilateral or bilateral hemispheres

• some visual abilities maintained

  • stationary/moving, line orientation, color, emotion

• vision can still be possible if V1 is damaged

  • secondary pathways, like extrastriate cortex

  • affective blindsight: pulvinar → amygdala

  • LGN - extrastriate pathway

  • tectopulvinar pathway

prosipagnosia

• face blindness

• EEG signal sensitive to stimuli that stand out

• patient showed signal to familiar face despite no memory of it

• FFA

• strategies: paying attention to peoples’ voice, mannerisms, walking, social affiliations, pitches, and previous experiences

proprioception

the perception of the position of body parts and their movement

somatosensory cortex organization

based on qualities in spatial patterns

olfaction

• odorants bind to odor receptors and encode qualities through firing of cells in the olfactory bulb

• olfactory bulb

  • to the limbic system

  • or to the thalamus → primary olfactory cortex

• only ipsilateral projections

• strong limbic projection

• primary cortex is in temporal cortex

• overlap of smell + taste

gustation

• ipsilateral and contralateral

• limbic projection

• temporal cortex; insula

• taste buds

  • to limbic system

  • and to primary sensory cortex in insula

• info from tongue → medulla → cortex (via thalamus)

insula: emotions and visceral sensations

• anterior → emotional processing

• posterior → sensation representation + processing that particular sense

• visceral sensations: sensory representation of senses internally

• overlap in understanding our senses