2 Intro to Neuroatonomy

• Nervous systems interface between sensory stimuli and the responses of an organism such as muscle activation, gland production etc.

• For animals with bilateral body plan, the anterior end first comes into contact with novel stimuli, and therefore contains the majority of sensors.

• Neurons that compute these inputs are likewise concentrated at the anterior pole, forming a central nervous system or brain. Most animals have quite elaborate brains, with different building plans (insects, etc.).

• The vertebrate brain is always located in the midline and can be differentiated into a series of subdivisions, starting with the spinal cord and ending in the Telencephalon.

Central nervous systems (CNSs) are concentrations of neurons (and glia cells) and, if located at the front of the animal, are called brains

Ganglion: usually a neuronal cell mass with many cell bodies outside of the central nervous system. In ganglia the cell bodies (somata) of neurons are located.

Nucleus: concentration of cell bodies in the CNS, often with a clear boundary to the surrounding tissue.

Lamina: a layered arrangement of cell bodies, often alternating with fiber layers (e.g., Cortex)

Neuropil structures are composed of axonal and dendritic structures, without cell bodies.

• butterfly structure

• ‘wings’ are called horns (dorsal: to back, ventral: to belly) and contain cell bodies

• The ventral horns contain motor neurons, that make axonal connections via the ventral roots towards their muscle targets.

• Many reflexes consist of direct connections between afferents and motor neurons; these monosynaptic reflex arches are fast and control muscles for postural control etc.

• big cell means long

• control the attention

• The vertebrate midbrain is called optic tectum (optic roof) in all vertebrates except the mammals where the term is superior colliculus (upper bulge).

• receives input from all spatially organized sensory organs and forms an orderly representation of these inputs: neuronal maps of the outer world.

• These maps are in register and form a multisensory world representation that enables quick, spatially correct motor responses to sensory stimuli.

Gray area = cortex with somata, white matter = axonal connections.

The largest amount of cortical neurons is found in humans.

Very prominent is the increase of the ven tricles– cavities filled with liquid (cerebro spinal fluid) that protects the brain mechani cally, and serves as diffusion space.

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

• clean up

• repair

• keep structure

• most brain cancers start in glia cells and not in neurons

• 10x more glia than neurons

• mechanic stabilization

• nourishment of neurons

• „immune system“ of the brain

• electrical insulation of neurons

• clearance of neurotransmitters

• guidance structures in development

• repair functions after injury

• control of extracellular fluid composition

• Sensors respond to stimuli with changes of their membrane potential (sensory transduction).

• Afferent neurons relay the signals as a series of action potentials towards integration center(s).

• Interneurons within the integration center compute the incoming information.

• Efferent neurons send signals as a series of action potentials towards effectors such as muscles, glands etc.

• „head and neck“ appearance

• spines are small computational modules where changes in synaptic strength can take place.

• Their function is thus in the area of memory formation and learning.

1.Converting airborne sound to fluid movement.

2.Converting fluid movement to frequency-specific excitation.

Movement of the last ossicle leads to pressure waves in the canals of the cochlea.

Sensory elements along the basilar membrane will be excited by motion of the basilar membrane at their position and fire action potentials along the auditory nerve towards the brain.

3. Computing input patterns to determine sound position and to classify sounds.

The brain computes various parameters, e.g., the interaural time and amplitude difference, to determine sound direction.

1. sensory transduction

• Rods and cones are specialized retinal neurons that carry light sensing molecules and transduce photon influx to electrical excitation.

• Rods are very sensitive and for night vision. Cones come in three variants that sense different wavelength and allow colour vision during the day.

2. retinal computation

• The human retina is inverse: light enters the retina from the ganglion cell layer.

• The retina is not just a relay station, but consists of several layers with specialized interneurons of many different types.

• In general, receptors contact bipolar cells, that contact ganglion cells, that project to the brain.

• This chain is however strongly modu lated by a multitude of interneurons (horizontal and amacrine cells).

3. networks in the brain

• Retinal output is formed by retinal ganglion cells, the axons of which travel in the optic nerve, partly cross at the optic chiasm, and target several structures in the di- and mesencephalon.

• Apart from several areas that control pupil diameter, eye reflexes etc., two major projection systems towards the cortex originate there.

• In humans, the most important route to reach the cortex goes: retina – lateral geniculate nucleus (LGN) – primary visual cortex (V1).

• From V1, two major processing streams originate, dealing with „what“ and „where“ of the visual input. However, what „seeing“ really means remains to be understood.