Cog Neuro Exam 1

gray matter

gray matter

cell bodies, dendrites

white matter

myelinated axons

• white matter tracts - 'highways of the brain"

types of neurons

• multipolar

• unipolar

• bipolar

central nervous system

includes brain and spinal cord

peripheral nervous system

includes everything except the brain and spinal cord

glial cells

glial (glue) cells support neuronal activity

astrocytes

star-shaped glial cells with many processes that receive neuronal input and monitor activity

microglial cells (microglia)

small cells that remove debris from injured cells

oligodendrocyte

myelinates axons in the CNS

• cytoplasm of oligodendrocyte wraps around the axon) (Schwann cells in PNS)

cranial nerves

connected directly to the brain

• 12 total, with sensory and motor functions

spinal (somatic) nerves

connected to the spinal cord

• 31 pairs

• input comes in the dorsal side

• output goes out ventral side

superior/inferior

superior up, towards the top of the skull inferior = down, towards the spine *can also use dorsal/ventral

dorsal/ventral

dorsal = up, towards top of skull ventral = down, towards spine *makes more sense if you imagine humans walking on all 4's

• means the same as superior/inferior

rostral/caudal

rostral = font, towards the face caudal = back, away from the face *means the same as anterior/posterior

anterior/posterior

anterior = font, towards the face posterior = back, away from the face

• can also use rostral/caudal

medial/lateral

medial = inwards, towards the midline lateral = outwards, toward the ears

autonomic nervous system

division of the peripheral nervous system into sympathetic and parasympathetic

• primarily controls glands and internal organs

  • involuntary actions of smooth muscles and heart and glands

sympathetic and parasympathetic nervous system

sympathetic: flight or flight

• norepinephrine (adrenaline) parasympathetic: rest and digest

• acetylcholine

views of the brain

• horizontal

• coronal - vertical, front/back view of brain

• sagittal - vertical, side view of brain

frontal lobe

part of the cerebral cortex on the anterior part of the brain

• borders temporal lobe in the lateral/ventral/posterior side, and the parietal lobe to the posterior sides

• lies right behind the forehead

parietal lobe

part of the cerebral cortex on the posterior, dorsal part of the brain -borders frontal lobe in the anterior side, temporal lobe in the lateral/ventral side, and the occipital lobe in the posterior/ventral side

• lies below the crown of the head

occipital lobe

part of the cerebral cortex on the posterior part of the head

• borders parietal lobe in the dorsal/anterior side, and the temporal lobe in the lateral/anterior side

• lies in the back of the head

temporal lobe

part of the cerebral cortex on the lateral sides of the brain

• borders the frontal lobe in the dorsal/anterior/medial side, the parietal lobe in the dorsal/posterior/medial side, and the occipital lobe in the posterior side

• lies inside the temples of the head

olfactory bulb

one of two enlargements at the terminus of the olfactory nerve at the base of the brain just above the nasal cavities

• on the ventral side of the frontal lobes

precentral gyrus

on the posterior edge of the frontal lobe (border w/ parietal lobe), bounded in the back by the central sulcus

• contains the motor area

central sulcus

sulcus dividing the frontal and parietal lobes

• anterior side: precentral gyrus (frontal lobe)

• posterior side: postcentral gyrus (parietal lobe)

postcentral gyrus

on the anterior edge of the parietal lobe (border w/ frontal lobe), bounded in the front by the central sulcus

sylvian fissure

separates the temporal lobe from the frontal and parietal lobes

• dorsal to the temporal lobe

gyrus and sulcus

gyri (singular - gyrus): the folds or bumps in the brain sulci (singular - sulcus): the indentations or grooves in the brain

• folding of the cortex increases surface are

brain structures

locations of motor, visual, auditory, and somatosensory corteces (and more)

• motor cortex: movement

• somatosensory cortex: somatic sensation (sense of touch)

• visual/striate cortex: vision

• auditory cortex: hearing

Brodmann areas

division of the brain based on (cyto)architecture

• (cytoarchitecture -cellular composition of the central nervous system's tissues under the microscope)

basal ganglia structures

several motor-related structures

• thalamus - sesory processing

• tail of caudate, head of caudate (caudate nucleus)

• globulus pallidus

• nucleus accumbens

• putamen -subthalamic nucleus etc. *amygdala is definitely anatomically connected, but not really part of it

limbic system

several structures related to emotional processing

• hippocampus - very important for memory

• amygdala -olfactory bulbs

• cingulate gyrus - reward processing

• thalamus etc.

ventricles

protection and supplies

• fluid filled

• shock absorbers

• exchange of nutreints etc. between blood vessels and brain tissue

• choroid plexus crucial for producing cerebrospinal fluid

  • network of blood vessels and cells in the ventricles that are covered by a thin layer of cells that make cerebrospinal fluid -CSF drains out of the bottom of the ventricles and surrounds the brain and spinal cord and it is also gradually recycled into the blood

blood vessels

oxygen supply

• internal carotid arteries are connected to many blood vessels in the brain

• anterior cerebral artery - feeds the medial, anterior, and dorsal parts of brain

• middle cerebral artery - feeds the lateral parts of the brain

• posterior cerebral artery - feeds dorsal and posterior parts of the brain

• circle of Willis: the joining area of several arteries at the bottom (inferior) side of the brain (forms a 'circle')

brain imaging techniques

• MRI (magnetic resonance imaging) - uses strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body -fMRI (functional MRI) - measures brain activity by detecting changes associated with blood flow

• CT (computed tomography) - combines a series of X-ray images taken from different angles around the body and uses computer processing to create cross-sectional images (slices) of the bones, blood vessels and soft tissues inside the body

• EEG (electroencephalogram) - records/measures electrical activities through electrodes attached to the scalp

neurophysiology

the study of electrical and chemical processes in neurons

• information flow:

  • within neurons - electrical signals

  • between neurons - chemical signals

electrical signaling

• fast over long distances

• neurons contain mostly anions --> inside of a neuron more negatively charged than the outside

ion channels

membrane-spanning transport protein for ions

• cell membrane itself is impermeable for water soluble molecules such as ions that are present intra- and extracellularly

• selective permeability of a neuron

• ex: non-gated potassium (K+) channels selectively allow K+ into the cell

  • passive transport: does not cost energy

membrane resting potential

difference in electrical potential across the membrane of a cell when it is inactive - about -65mV in neurons

• reflects 'balancing act' between opposing forces that drive K+ in and out of the cell

  • diffusion - movement of molecules from areas of high concentration to low concentration

  • electrostatic forces - tendency of charged molecules or ions to move towards areas with the opposite charge

• ions constantly moving back and forth across membrane through ion channels and pumps (ex. K+ channels, Na+/K+ pumps)

  • but, at some point, the opposing forces are at equilibrium and there is no net flow

important ions for neural signaling

• sodium: Na+

• potassium: K+

• chloride: Cl-

• calcium: CA++ or CA2+

• magnesium: Mg++ or Mg2+

at rest: more K+ inside the cell more Na+ and Cl- outside the cell

sodium/potassium pump (Na+/K+)

exchanges 3 Na+ for 2 K+ ions

• K+ is pumped in

• Na+ is pumped out *active transport: costs energy

• can move ions across membrane, creating a large concentration difference (gradient)

equilibrium potential

voltage difference across a permeable membrane needed to counterbalance diffusion forces

• The electrical potential at which a given concentration gradient across the membrane is stable, when the membrane is permeable for X.

  • voltage difference needed to counteract diffusion forces

membrane resting potential of a neuron (value)

about ~65 mV

• K+, Cl-, and Na+ are all fighting to reach their equilibrium potential, but there are more passive K+ channels, than Cl- and Na+ channels, so K+ is "winning"

  • K+ has an EP of -85 mV, but the movement of Cl- and Na+ brings the MRP to about -65mV

• there is constant movement of ions passively through channels, since non of the ions are at their EP

hyperpolarization

increasing negativity of membrane potential

depolarization

decreasing negativity of membrane potentail

generating a potential

-potentials/neuronal electrical activity - deviations from the resting potential

• caused by temporarily changing, very locally, the permeability for an ion by opening gated ion channels

• other ion channels briefly open (ex. Na+), so the membrane potential changes -gets closer to EP of K+, +67 mV ---> depolarization ---> potential

electrotonic conduction

passive propagation of a potential

• signals spread along the membrane in all directions extremely fast

• but, it also leaks away because of non-gated ion channels that are trying to restore membrane resting potential (it is 'lossy')

• passive process, and signals decrease over space

structure of a (multipolar) neuron

• dendrites

• cell body + nucleus

• axon hillock - base of the axon where action potential starts

• axon

• axon terminal

graded local potentials

spread passively from synapses (dendrites) to axon hillock, and from the tend of the axon to axon terminals

• electrotonic conduction

• flexible in shape and magnitude

action potential

brief but radical changes in polarization that send an electrical charge down the neuron - threshold: about -40mV

• fundamental unit for electrical communication

• uniform in shape and magnitude

  • larger depolarizations produce more action potentials, not bigger or longer ones

  • information is encoded in the (change in) frequency of action potentials

• action potentials propagate actively over the axon

generating an action potential

1. neurotransmission causes depolarization at the synapse

2. electrotonic conduction of graded potential (charge flows through the inside of the neuron)

3. axon hillock: voltage-gated Na+ channels open ---> action potential starts here

absolute vs. relative refractory periods

after an action potential passes through, it is impossible (or difficult) for that section of membrane to fire again

• absolute refractory period: Na+ channels already open, or they are INactivated for 1ms

  • a new action potential absolutely can not be produced

• relative refractory period: when Na+ channels DEactivate, the membrane potential is hyperpolarized at -80 mV, so a larger depolarization is needed to trigger a new action potential

Hodgkin-Huxley cycle

• Na+ channels open at threshold membrane potential (about -40 mV) --> Na+ rushes into the cell

  • after about 1 millisecond (at +30 mV) the Na+ channel is inactivated (not closed) --> absolute refractory period

• now K+ channels open --> K+ leaves the cell (concentration and electrical gradient)

  • membrane potential decreases, then becomes negative until about -80 mV, and K+ channels close

  • Na+ channels are now deactivated (closed) ---> relative refractory period

• normal resting potential is restored at -65 mV

action potential propagation

electrotonic conduction not sufficient

• the depolarization of an action potential is strong enough to cause threshold depolarization in the next adjacent segment --> the action potential is regenerated along the axon

• the action potential cannot flow 'backwards' because the previous segment is in the refractory period

myelin

oligodendrocytes produce myelin that insulate the axon (cytoplasm of oligodendrocyte wraps around the axon)

• node of Ranvier - small gaps between myelinated sections

  • action potential 'jumps' from node to node

• action potential can travel farther in a myelinated axon -prevents 'leakage' of ions during electrotonic conduction

• very important for communication between neurons

saltatory conduction

action potential 'jumps' from node to node (nodes of ranvier)

• electrotonic conduction of AP along myelinated sections, then the AP is regenerated at the node

• faster way to travel down an axon than traveling in an axon without myelin.

toxins

some toxins block ion channels and prevent neuronal signaling

• ex: tetrodoxin (found in puffer fish) - voltage-gated Na+ channel blocker

multiple sclerosis

autoimmune disease in which the immune system attacks the myelin sheath or the cells that produce and maintain it

• particularly the optic nerve, the deep cerebral white matter, the cerebellar peduncles, and particular parts of the brainstem and spinal cord.

how many neurons are there in the brain?

100 billion neurons -10,000 connections each

• 1 quadrillion (10^15, or 1,000,000,000,000) total synapses in the brain!

2 types of synapses

• electrical (gap junction)

• chemical

electrical synapse (gap junction)

current just flows between cells - it is 'passive'

• bi-directional

• fast (no delay)

• used for synchronization (ex. heart cells, release of neural hormomes - a bunch of cells need to do the same thing)

• about ~2 nanometers of space between neurons

• minority in the brain

• disadvantage: no computations take place. not doing anything complex, just creating more of the same signal across more cells.

chemical synapse (definition)

new potential created in postsynaptic cell - it is 'active'

• one-directional

• slow - about ~0.5-1.0 ms of delay between arrival of the action potential at axon terminal and the creation of a postsynaptic action potential.

• involves neurotransmitters

• used for integration/computation in the postsynaptic neuron

chemical synapse (overview)

presynaptic part:

• depolarization from action potential triggers voltage-gated Ca2+ channels -Ca2+ influx leads to vesicles releasing neurotransmitter into the cleft

synaptic cleft:

• released neurotransmitter binds to receptor on postsynaptic membrane

• neurotransmitter is then either degraded by enzymes or taken up again in the presynaptic part

postsynaptic part:

• neurotransmitter activates the receptor to do something, for example to open an ion channel, leading to a postsynaptic potential, either excitatory (EPSP) or inhibitory (IPSP).

neurotransmitter degradation and reuptake

degradation: neurotransmitters are rapidly broken down / deactivated by a special enzyme -NTs may be recycled to make more NT in the axon terminal

reuptake: neurotransmitters are rapidly cleared from the synaptic cleft by being taken up into the presynaptic cell

• special receptors (transporters) bring the NT back inside the cell

• may be repacked into newly formed synaptic vessicles

excitatory post synaptic potential (EPSP)

local postsynaptic membrane DEpolarization in the postsynaptic neuron

• caused by excitatory synapses

• pushes the postsynaptic cell a bit closer to threshold membrane potential (Na channels open, Na+ into cell) -EPSPs caused by many neurons that converge on the postsynaptic cell --> action potential

inhibitory postsynaptic potential

local postsynaptic membrane HYPERpolarization in the postsynaptic neuron

• caused by inhibitory synapses

• pulls the postsynaptic cell further away from threshold membrane potential (Cl channels open, Cl- into cell)

postsynaptic potential (PSP)

neurotransmitters released into the synapse briefly alter the membrane potential of the postsynaptic cell

• graded potential: bigger stimulus --> more hyper/depolarization. longer stimulus --> longer lasting hyper/depolarization (no increase in size)

• PSPs last much longer than action potentials (more than 10 ms)

• (a neuron can receive 100s of synapses from other cells --> 100s or 1000s of PSPs

• a balance of excitatory and inhibitory ESPS is vital in neural processing of information (over-excitation --> seizure. under-excitation --> coma/death)

• excitatory/inhibitory effects are sometimes caused by which neurotransmitter is present.

• action potential generation in the postsynaptic cell is determined by the (im)balance of the number of excitatory and inhibitory signals received.

botox

prevents fusion of vesicles to the presynaptic membrane by splitting SNARE proteins, hence no transmitter release (exocytosis)

• botox is a neuromodulator

neurotransmitter

a chemical released from the presynaptic axon terminal that serves as the basis of communication between neurons

• generally easy to synthesize from amino acids in diet

• amino acids are most common NT in the brain

• amines - based on modifications of a single amino acid by enzymes

amino acid neurotransmitters

glutamate: fast excitatory, memory

• main excitatory NT in the brain

GABA: fast inhibitory, memory

• main inhibitory NT in the brain

• subtypes of GABA receptors exhibit quite different properties

• GABA A, GABA B, GABA C receptors (gamma-aminobutyric acid)

amine neurotransmitters

dopamine (DA): reward,

• involved in schizophrenia and Parkinson's disease norepinephrine (NE) epinephrine (EP) serotonin (5-HT): mood, sleep depression

acetyl choline (ACh)

neurotransmitter: neuromuscular

• first NT to be identified

• receptors: nicotinic (nACh): ionotropic (muscles) and muscarinic (mACh) metabotropic

• Alzheimer's disease: widespread loss of cholinergic neurons

ligand

a molecule that can bind to a receptor protein

• can activate or block it

endogenous ligands: neurotransmitters and hormones made inside of the body

• agonist exogenous ligands: drugs and toxins from outside the body

• receptor agonist

• competitive antagonist

• non-competitive agonist/antagonist (neuromodulator): does not bind to the same receptor site

antagonist (ligand)

an exogenous ligand that all together stops the receptor from producing a response

• ex: poisons can block acetylcholine (ACh) receptors in the brain

agonist (ligand)

molecules (can be drugs) that bind to receptors and mimic the action of a neurotransmitter.

• ex: nicotine

types of ion channels

-non-gated -voltage-gated -ligand-gated (also called chemically-gated ion channels or ionotropic receptors) -stretch gated (mechanosensitive)

non-gated ion channels

• resting membrane potential

• always open

voltage-gated ion channels

• triggered by a voltage change

• can open and close

mechanosensitive (stretch-gated) ion channels

sensitive to mechanical stress

different chemical synapses

• axo-dendritic

• axo-somatic

• axo-axonic: allows the presynaptic neuron to regulate neurotransmitter release of the postsynaptic neuron

• dendro-dendritic - allows coordination of cells' activities

ionotropic receptors

(also called chemically-gated or ligand-gated ion channels) postsynaptic receptor proteins that include an ion channel, which is opened when an agonist binds to it .

• fast communication

• open when some chemical binds to them (could be a neurotransmitter or some 2nd messenger)

metabotropic receptors

postsynaptic receptor proteins that do not contain an ion channel, but may (when activated) activate a G-protein

• G-protein: acts as a '2nd messenger' inside the cell. it amplifies the effect of the 1st messenger (the neurotransmitter) and can initiate processes that affect postsynaptic membrane potential

• slower communication

• amplify and prolong synaptic signals

different example of postsynaptic receptor: GABA A receptor, Cl- channel (and example of neuromodulation)

• alcohol and bind to it (noncompetitive ligand) and modulate the effect of neurotransmitters binding to the receptors

• alcohol is a neuromodulator

up-regulation

compensatory increase in receptor availability at the synapse of a neuron

down-regulation

compensatory decrease in receptor availability at the synapse of a neuron

spatial summation

summation of postsynaptic potentials from different synapses (different physical locations across the cell body) that overlap in time

• physically closer together --> increased summation (and vice versa)

temporal summation

summation of potentials from one synapse that overlap in time

• closer together in time --> increased summation (and vice versa)

information processing

• graded postsynaptic potentials spread passively from the dendrites ober the cell body towards the axon hillock (in multi-and bi-polar cells)

• if a depolarization is strong enough (exceeds the threshold) reaches the axon hillock --> action potential produced

• spatial and temporal summation determine whether an action potential is triggered

optogenetics

inducing EPSPs and IPSPs experimentally

• advantage over electrical stimulation: targets specific cells, controlled PSPs

convergence and divergence

convergence: neuronal connections in which many cells send signals to a single cell

• range fractionation: information from receptors of different sensitivities is sent to one cell and integrated to code for the intensity of a stimulus

divergence: one cell sends signals to many other cells

• allows for an impulse to be amplified in order to produce a response over a widespread area

neural chain

a simple kind of neural circuit in which neurons are attached linearly, end to end

• ex: knee jerk reflex: sensory neuron synapses directly onto motor neuron (synapse is in the spinal cord). involves myelinated axons of large diameter.

analog- vs. digital-like signals

• analog: vary in strength (ex. graded potential)

• digital: all-or-none, vary in frequency (ex. action potential)

event related potentials (ERPs)

(also called evoked potential) gross potential changes evoked by a discrete sensory stimulus, such as light flashes

• ex: auditory evoked potentials can be recorded with an EEG, and can diagnose deafness or hearing impairments in infants.

neurochemistry

branch of neuroscience concerned with the fundamental composition and processes OF the nervous system

• endogenous processes

neuropharmacology /(psychopharmacology)

the scientific field concerned with the discovery and study of compounds that selectively AFFECT the function of the nervous system

neuropeptide neurotransmitters

endorphins, orexin, oxytocin

four major pathways

• Cholinergic (ACh)

• Dopaminergic (DA)

• Noradrenergic (NE)

• Serotonergic (5-HT)

Cholinergic pathways

acetylcholine (ACh) From: basal forebrain, (PPT/LDT - pedunculopontine nucleus and laterodorsal tegmental nucleus) To: hippocampus, amygdala, cortex

Involved in muscle control and memory

• Alzheimer's disease: ACh deficiency

nicotinic receptors: ionotropic

• important in muscular system

• curare (antagonist) --> paralysis

muscarinic receptors: metabotropic

• atropine (antagonist) --> confusion, memory problems