2-Neuroanatomy Primer

No!

However increases variability of behavioral response

nervous system contains of

• afferent neurons —> receive input from sensors

• efferent neurons —> contact actuators (muscles, organs, …)

1. Sensors respond to stimulus with changes of their membrane potential

2. Afferent neurons relay signals as series of action potentials to integration center

3. Interneurons in integration center compute incoming information

4. Efferent neurons send signals as seriies of action potentials two effectors (muscles, organs, glands, ..)

concentration of neurons (and glia cells)

if located in front of animal —> called brain

• Ganglion (greek for knot)

  clusters of neuron cell bodies outside of CNS

  in ganglia, cell bodies (somata) of neurons are located

• Laminae

  layers of neuronal tissue organized for specific functions (often alternating with fiber layers e.g cortex)

• Neuropil structures

  composed of axonal and dendritic structures, without cell bodies

concentration of cell bodies in CNS, with clear boundary to surrounding tissue

organizes sensory (afferent) input and motor (efferent) output in highly structured way

• Gray matter in Butterfly structure

  —> ‘Wings’ of butterfly referred as horns (dorsal and ventral)

• White matter surrounds gray (contains axons to and from other brain areas)

• Dorsal horn (Sensory Input)

  receives afferent fibers from sensors in muscles (enter via dorsal roots)

• Ventral horn (Motor Output)

  contains motor neurons that send signals to muscles via ventral roots

= superior colliculus (upper bulge) in mammals

= optic tectum (optic roof) in rest of vertebrates

receives input from all spatially organized sensory organs

—> forms representation of inputs: neuroanl maps of outer world

—> enables quick, spatially correct motor responses to sensory stimuli

• 6 layers (Isocortex)

• surrounds basal ganglia

• gray area = cortex with somata

• white matter = axonal connections

in many mammals cortex not folded

largest amount of cortical neurons is found in humans

largest brain: sperm whale (9kg), smallest shrew (300 mg)

human brain: 1400 gr

• Frontal lobe

• Parietal lobe

• Temporal lobe

• Occipital lobe

• large lobes

• functional regions

• histological details (Broadmann-Areas), similar to functional regions

• Sulci —> grooves between folds

• Gyri —> folds

locations are quites constant —> basic localization

• e.g primary motor cortex in gyrus in front of central sulcus

• forebrain hemispheres seperated by deep sagittal groove

• both hemispheres connected via corpus callosum

corpus callosum

No, brains grow and shrink

• gray matter (neurons) peaks in late childhood

• white matter (connections) peaks in young adulthood

• ventricles (cavities filled with liquid) peak in late adulthood

  —> protect brain mechanically

No, thickness of sections can vary

e.g. primary visual cortex has thick layer IV

Input recipient layer 4 (L4) sends projections to layers 2/3 (L2/L3), which in turn drives layer 5 (L5)

2nd characteristic cell type (after neurons) in brain

at least as numerous as neurons (some say 10x more)

• Astrocytes (mechanical)

• Oligodendrocytes (insulation)

• Microglia (repair and immune function)

• Ependymal cells (fluid composition)

regular body cells in most aspects (molecular, metabolic, cytoskeleton, …)

‘typical neuron’ consists of

• Cell body (soma)

• Dendrites extending in all directions (multipolar)

• long Axon with several to many synaptic endings

BUT: only few neurons in brain look like this

not easy, but usually:

• Axons

  • much thinner and dont taper over their extent (dünner werden)

  • not always originate at soma

  • may carry boutons or en-passant synapses

• Dendrites

  • much thicker and taper

  • may carry spines

• typically receive input from single synapse, mostly excititory

• cells can have thousands of spines (dynamic and change with time)

—> spines are small computational modules, where changes in synaptic strength take place

function: memory formation, learning

1. Converting airborne sound to fluid movement (Middle Ear)

   • Sound waves (air pressure changes) vibrate the tympanum (eardrum)

   • three middle ear bones (ossicles) transfer movement to oval window of cochlea (fluid filled)

2. Converting fluid movement to frequency-specific excitation (Inner Ear)

   • movement of ossicles creates pressure waves in cochlear fluid —> basilar membrane vibrates at specific locations depending on sound frequency

   • Hair cells along basilar membrane detect vibrations —> convert into action potentials —> travel along auditory nerve towards brain

   (Different frequencies activate specific parts of the basilar membrane —> sounds are seperated)

3. Computing input patterns to determine sound position and to classify sounds (Auditory pathway)

   • processes signals to extract sound paramters (timing, intensity, frequency)

   • brain computes time and amplitude differences to determine sound direction

Small muscles at ossciles that contract and dampen the transfer

1. Sensory transduction

   • light enters eye —> detected by 2 types of photoreceptors in retina

     • Rods: night vision

     • Cones: day and color vision

   • generate electrical signals (action potentials)

2. Retinal Computation

   • receptors (Rods and Cones) transmit signals to bipolar cells —> contact ganglion cells (axons form optic nerve) —> project to brain (chain srtongly modulated by multitude of interneurons horizontal/amacrine cells)

3. Networks in the brain

   • Retianl output formed by retinal ganglion cells

   • target several structures in di- and mesencephalon

Rods = very sensitive and for night vision

Cones = three variants that sense different wavelength —> allow color vision during day

Retina is inverse:

• lights enters retina from ganglion cell layer

• consists of several layers with specialized interneurons of many different types

Fovea: first layeres pulled aside —> light directly accesses photoreceptors

Signals from Retina —> Optic Nerve —> Optic chiasm —> project to lateral geniculate nucleus (LGN) in Thalamus

Signals sent to primary visual cortex (V1) —> further processed into

• What Pathway (Ventral Stream): identifies objects (form and color)

• Where Pathway (Dorsal Stream): determines spatial location and motion