Brain and behavior

dendrites

• receive signals via ligand gated receptors

axon hillock

• site of action potential initiation

• dense voltage gated channels

myelin sheath

• insulates axon for faster signal transmission

• made out of lipid bilayer

node of ranvier

• gaps in myelin sheath

• dense in voltage grated channels

oligodendrocytes

• CNS

• forms and wraps myelin sheath

• can wrap multiple cells at once

schwann cells

• PNS

• forms and wraps myelin sheath

• only wraps one cell at a time

astrocytes

• CNS

• scaffolding for axons

• forms blood brain barrier

  • wraps end feet around vessels

• buffer extracellular fluid

microglia

• CNS

• cleans up cell

neuro filaments and micro filaments

make up cytoskeleton

kinesin

a motor protein, anterograde - away from soma, walks along micro tubules in axons

dyenin

a motor protein, retrograde - to soma, walks along micro tubules in axons

K⁺/Na⁺ pump

2 K⁺ in, 3 Na⁺ out

nernst potential

the voltage of equilibrium between chemical and electrical forces, the voltage the cell wants to be at, usually a constant

relativity in the nernst equation

higher concentration of positive ions outside the cell, higher nernst

difference between nernst and ghk

nernst is for a single ion, ghk is for the whole cell

ghk equation

factors in all ions, includes relative conductance and concentration so takes into account relative permeability, calculates resting potential of a cell

Driving force =

membrane potential (V_m) - nernst of Ion (E_ion)

Typical resting potential of neuron

-65 mV

process of action potential

• slight depolarizations add up to pass the threshold

• V-gated na channels open, Na rushes in, further depolarizes the cell as Na tries to get membrane potential to E_na

• Na channels inactivate (ball and chain), K channels open

• K rushes out to bring membrane potential back down,

• Na channels deinactivate, K channels close

Is active potential binary or spectrum

Binary (all or nothing)

How does initial depolarization occur to trigger action potential

receptor activation allowing na and/or k into cell

How does action potential get down axon

jumps from node to node esentially being regenerated at each node, decays in between the nodes

The flow of information between neurons via chemical transmission.

• NT binds to receptors on dendrites

• ligand gated channels open, influx of an travels to hillock

• Vm reaches threshold and generates action potential that travels down axon

• influx of an at axon terminal open Ca2+ v-gated channels

• Ca2+ influx triggers release of NT into synaptic cleft

• NT binds to receptor proteins on post synaptic cell

differnce between elctrical and chemical transmission

electrical is faster, rarer and doesnt include NTs or Ca2+, movement is bidirectional

temporal vs spatial summation

temporal - summation of multiple EPSPs potentials from a single axon

spatial - summation of single EPSPs from multiple axons

Process of electrical transmission at synapse

• NTs are synthesized and packaged into vesicles in terminal or soma (if in soma, transferred by kinesin)

• AP reaches terminal

• depolarization of presynaptic terminal opens Ca2+ channels

• influx of Ca2+ causes synaptobrevin and synaptotagmin to dock vesicle

• SNARE and syntaxin fuse membranes

• NT released into cleft

• NT binds to postsynaptic receptors

• receptors open or close causing epsp or ipsp

Peptide NTs

• made of amino chains

• synthesized in ER

• activated in Golgi

• packaged into vesicles and then transported down axon to terminal

• ex: oxytocin, insulin

small molecule NTs we should know

• Glutamate - primary excitatory NT

• GABA - primary inhibitory NT

• Norepinephrine

• Serotonin

• Dopamine

• ACh
  

GABA-A receptors

• inhibitory

• allow Cl- in

• GABA is NT

NT for AMPA and NMDA receptors

glutamate

Reversal potential

voltage when net flow = 0 (Na= and K+ are going in and out equally)

Ionotropic vs metabotropic receptors

Ionotropic

• ligand gated

• receptor and effector are the same

• ex: AMPA and NMDA, GABA

Metabotropic

• receptor and effector are different

• extra steps

• GPCRs

• ex: protein kinases that open or close ion channels by phosphorylating them

• G-proteins subunits activate downstream effectors for slower, larger, longer lasting changes

Agonist vs. antagonist

Agonist activates receptor, antagonist block receptor

Different ways to clear NTs

• reuptake - taken back into presynaptoc cell by transporter proteins

• diffusions - NTs diffuse away or are taken up by astrocytes at the far ends of he cleft

• destructions - enzymes breakdown NT molecules

Meninges

• Dura Mater

  • hard outer layer

• Arachnoid

• subarachnoid space

• pia mater

Telencephalon (adult brain derivatives and associated ventricular space)

• cerebral cortex and Basal ganglia, hippocampus, olfactory bulb, basal forebrain

• lateral ventricles

Diencephalon (adult brain derivatives and associated ventricular space)

• Thalamus and hypothalamus

• third ventricle

Mesencephalon (adult brain derivatives and associated ventricular space)

• Midbrain (superior and inferior colliculi)

• cerebral acueduct

Mentencephalon (adult brain derivatives and associated ventricular space)

• Cerebellum and Pons

• Fourth ventricle

myelencephalon (adult brain derivatives and associated ventricular space)

• medulla

• fourth ventricle

Spinal Cord (adult brain derivatives and associated ventricular space)

• Spinal cord

• central canal

Taste (stimuli, receptor cell, ganglia, nerve, brainstem relay, thalamic nuclei, Primary cortical region)

• molecules from food

• Type II or III cells

• n/a

• Central nerves 7,9,10

• Gustatory nucleus of medulla

• VPM

• Primary gustatory cortex

Smell (stimuli, receptor cell, ganglia, nerve, brainstem relay, thalamic nuclei, Primary cortical region)

• chemicals in air

• olfactory epithelial cells

• glomeruli in olfactory bulb

• Olfactory nerve (CN 1)

• n/a

• Medial Dorsal (MD)

• Primary olfactory cortex

Vision (stimuli, receptor cell, ganglia, nerve, brainstem relay, thalamic nuclei, Primary cortical region)

• Lightwaves

• Rods/cones

• Retinal ganglia

• Optic nerve (CN 2)

• n/a

• LGN

• Primary visual cortex (striate cortex)

Hearing (stimuli, receptor cell, ganglia, nerve, brainstem relay, thalamic nuclei, Primary cortical region)

• Soundwaves

• Haircells

• Spiral ganglia

• Vestibulochlear (CN 8)

• Dorsal and ventral cochlear nuclei, inferior colliculus

• MGN

• Primary auditory cortex

Vestibular (stimuli, receptor cell, ganglia, nerve, brainstem relay, thalamic nuclei, Primary cortical region)

• Movement of fluid

• Haircells

• Scarpa’s ganglia

• Vestibulochlear (CN 8)

• Medial and lateral vestibular nuclei

• VPN

• projects to cerebellum and motor neurons but doesn’t map anywhere

Taste type II vs type III cells

type II

• receptors are GPCRS

• ATP acts as NT

• sweet, bitter, umami

type III

• receptors are ion channels

  • detect high Na+ (salty) or protons/H+ ions (sour)

• form a typical synapse

• can respond to multiple tastants

transcription for taste

one afferent axon from each cell on a taste bud, population coding

olfactory receptors process

• dendrites stick out into olfactory epethilium

• GPCR metabotropic receptor,

• GPCR activates channels to allow Ca2+ and Na+ in, Ca2+ activates channel to let Cl- out

olfcatory transcription

• 1:1 Glomeruli to receptor

• each smell is a specific combo of glomeruli

Vision receptors

• rods and cones with disks of rhodopsin

• rhodopsin detects light, GPCR opens Na+ channels

parvocellular cells

• red/green

• see detail

• small, few receptor cells

Magnocellular cells

• see large objects and movement

• large, many receptors

• not color selective

nonM nonP type cells

• Discriminate between blue and yellow (red and green)

• large objects and movement

• small, few cells

visual pathway

• optic nerve - all axons from each eye

• optic chiasm - nasal nerves cross over

• optic tract - left visual field goes to right hemisphere and vice versa

higher order visual processing pathway

• magnocellular

  • goes through MT cortex and ends in parietal cortex

  • spacial awareness and movement

  • “where”, ”action”

• Parv/Koniocellular

  • goes through V4 and ends in temporal lobe

  • object identity, facial awareness

  • “what”, “who”

structure of the ear (out—>in)

Pinna —> auditory canal —> tympanic membrane —> ossicles —> labyrinth and cochlea —> auditory vestibular nerve

structure of cochlea

• spaces (top —> bottom)

  • scala vestibuli

  • scala media

    • tectorial membrane

    • organ of corti

    • basilar membrane

  • scala tympani

• conch shell shape

Auditory receptors

• mechanically gated hair cells

• when depolarized (towards tallest hair) all mechanoreceptors pulled open by tip link and lets K+ in, when hyperpolarized, all closed, when resting some open

• depolarization opens ca2+ channels, ca2+ helps vesicles with excitatory NT dock and secrete

Auditory transcription

tonotopy by pitch on cochlear nucleus

sound wave structure

• low frequency - phase locked and on every cycle

• medium frequency - phase locked but not on every cycle

• high frequency - not phase locked, not on every cycle

location of sound (low pitches)

• interaural timing difference

• the bigger the time difference, the more lateral the sound

  • if the sound is right in front of you, no time difference

• excitation-excitation

location of sound high pitches

• interaural intensity difference

• strong excitation and week inhibition from the side the sound came from

  • equal and opposite intensity from the other side

• excitation-inhibition

detection of head tilt and acceleration

• otoliths drag on gelatinous layer which open or close mechanoreceptors on the hair cells

detection of head rotation

• turning head moves extracellular fluid in ampula that pushes against hair bundle in cupula

• three planes of movement, three ampula

touch receptors

mechanoreceptors open when you push against skin or when extracellular proteins pull on them, allow in ca2+ and na+

touch: location and intensity detection

• location

  • receptive fields

  • smaller receptive fields have more dense receptors and take up more (relatively) of the cortex

• intensity

  • high intensity, high firing rate

structure of spinal cord

• dorsal = sensory

• ventral = motor

• gray matter

  • dorsal horn

  • intermediate grey

  • ventral horn

• white