Nerve cells neural circuitry and behaviour A.Alipour Conscioustronics Foundation

.1 mm to 2 m!! Length of An axon

Neuron has 10 thousand connections It projects only 1 thousand Does it mean that the neuron is an integrator?

After axon hillock the action potential propagates through the axon without distortion or failure. 1 to 100 m/s How much time it takes for an A.P to propagate through the skull?

First recorded action potential giant axon of squid (1mm diameter)

Neuron doctrin Ramon Cajal Are Quantum approaches right?

We have 3 main rules Neuron doctrine Principle of dynamic polarization(Unidirectional transmission) Connectional specificity

3 main type of cells Unipolar Bipolar multipolar

unipolar Unipolar Mostly in invertebrates and autonomous nervous system

bipolar Bipolars are aboundant in retina and olfactory epithelium of nose

Pseudo-unipolar cell These cell exist in our peripheral sensory system i.e. The sense of touch, pain pressure sensory system of skin and joint This cell body forms the ganglion

multipolar Many dendritic branches protruded out of the cell body and just 1 axonal branch projects out of the soma

example A spinal Motor neuron Gets 10 thousand of dendritic input(1000 on its soma) Purkinje cell in cerebellum gets millions of inputs!

Another classification functional Sensory Motor inteneuron

afferent V.S. sensory Every signal or pathway that brings information in whether it will be perceived or not or not (input) Sensory every afferent signal that will be perceived

efferent Every out put of the system commands of the CNS or spinal cord

interneurons We have 2 classes of them Relay or projection interneurons: They have long projections and connect different areas of the brain Local interneurons: they make short connections in local circuits

Glial cells Derived from the Greek word means “glue” But they don’t glue! They support the neurons We have 2 types of them Microglia macroglia

microglia They belong to the Immune system 20% of the glia

macroglia They are 3 types : Oligodendrocytes ~40% of all Astrocytes ~ 40% of all Schwann cells in periphery

Astrocytes and oligodendrocytes These guys insulate the axon branches Each of oligodendrocytes covers one to 30 axonal branches depending on their diameter

oligodendrocyte

Schwann

astrocytes Two main types of astrocytes Protoplasmic : in grey matter Fibrous : in white matter

Astrocytes No definite answer but: They take up neurotransmitters Astrocytes help nourish surrounding neurons by releasing growth factors they feed neurons, also BBB Astrocytes separate cells Because astrocytes are highly permeable to K+, they help regulate the K+ concentration in the space between neurons,… why?

Each Nerve Cell Is Part of a Circuit That has a specific function Knee jerk reflex

Knee jerk reflex

Some simple stuff each of which makes direct contact with 45 to 50 motor neurons. This pattern of connection, in which one neuron activates many target cells, is called divergence Conversely, a single motor cell in the knee jerk circuit receives 200 to 450 input contacts from approximately 130 sensory cells. This pattem of connection is called convergence

Divergence & convergence

Feed-forward inhibition

Feedback inhibition

4 components of every neuron Receptive component Integrative component Conductive component Out put

Some electrical stuff! Resting Membrane potential

Some electrical stuff! Action potential

Graded local potentials V.S. active action potential Receptor potential Synaptic potential IPSP and EPSP

Axon hillock or trigger zone It decides about the neuron’s firing HOW?

NEURAL CODE HOW information is transmitted through neural firing patterns? ISI? Frequency?

Out put component It releases the neurotransmitter

What is a neurotransmitter and how it works? It is a molecule that is being released from a presynaptic neuron to effect the post synaptic neuron

Examples

4 components of every neuron Receptive component: dendrites + soma be4 axon hillock, receptor and synaptic potentials Integrative component: trigger zone Conductive component axonal branches Out put neurotransmitter release

Nerve cells mostly differ at the molecular level Different ion channels: different spiking pattern Different receptors: different inhibitory/ excitatory effects

Knee jerk reflex demonstrates what we said up to here

Neural nets… One question be4 them In invertebrate animals, and in some lower-order vertebrates, a single cell (a so-called command cell) can initiate a complex behavioral sequence. But as far as we know no complex human behavior is initiated by a single neuron. Rather, each behaviour is generated by the actions of many cells.

Parallel processing: the paradigm of computation in the brain The deployment of several neuronal groups or pathways to convey similar information

Neural networks…. Help! elements of the system process information simultaneously using both feed-forward and feedback connections.

Neural connectivity ? How is behavior modified if the nervous system is wired so precisely? Neural connectivity can be altered through experience

Plasticity hypothesis Put forth by Cajal early in 1900 Then advanced by polish psychologist Jerzy Konorski in 1948 These days people have strong believes about it because it has many experimental evidences

Some examples of neural plasticity how scientists and engineers used it Changes in Synaptic effectiveness Growing new synapses

Last point Do not respect TEXTBOOK THEORIES Vincent Walsh, BCNC, 2013

Time is over? No? Watch the clip! Sebastian Seung…………. I’m my connectome