bio 462 ch 1

overview of the nervous system

why brain

behavior, processing info

old conception

brain is part of a sensory motor system

output is the consequence of input (reflex loops)

exception to old conception (what made it wrong)

dreams and cognition

current conception

brain makes a representative model of our world through our senses

evidence for current conception

appearance of neurons coincided with appearance of movement during hunting

learning

prediction-action model = brain builds a virtual model of the future (prediction), which is compared with a movement physically entering the future (action)

some connections get stronger, others get weaker

neuronal ensembles

independent units of neurons that are grouped together and become activated together to build internal thoughts, memories, ideas, etc

organized into hierarchies

modules

specific diagrams that must be precise

wiring of neurons links different…

modules

precise connections

neurons connect only with set particular ones

distributed connectivity

many connections are pruned and tweaked through learning

neurons are lost until the perfect wiring is created

two types of wiring

precise and distributed

learning is which type of wiring?

distributed

Hebb’s rule

associative learning

when two or more neurons are activated at the same time, their connections are strengthened, which is how memories are built

associative learning

association of separate stimuli when neurons fire together and form a unit

spatial topographic maps

ex. position of object in space correlates to specific position in retina

wiring diagrams are organized in…

maps, which provide representations

control theory

compare output with the prediction

error signal causes fine-tuning of output

(feedback control)

optimization

work must be performed effectively at minimal energy cost

machinery of the nervous system is extremely optimize

how many of total genes are expressed in the nervous system

2/3

how many of total genes are expressed UNIQUELY in nervous system

1/3

signal in neurons

electricity provided by ion currents

axon

extends out for long distance signaling

usually connect to dendrites of another neuron

converge

diverge

action potential

generated as a signal for the neuron

all or none, on or off

shape is similar in many species

results from integration of several inputs if threshold of depolarization is reached

constant amplitude

neurons connect to other neurons through…

synapses

chemical synapse

secretion of neurotransmitter between a pre-synaptic and a post-synaptic terminal

vesicles carrying neurostransmitter exocytose through membrane into synapse and bind to receptors

post-synaptic cell

expresses the receptor of the neurotransmitter

electrical synapse

direct link between neighboring cytoplasms

gap junction

closer joining of the two membranes, much faster

local potentials

slow and graded

amplitude depends on intensity of the input

ionotropic receptors

ion channels open with ligand binding

fast acting

metabotropic receptors

coupled to second messengers that cause chemical cascades

slow acting

EPSP

local excitatory post-synaptic potential caused by the movement of ions

IPSP

local inhibitory post-synaptic potential caused by the movement of ions

dendritic spines

contact of axons of excitatory terminals

soma

contact of axons of inhibitory terminals

central nervous system (CNS)

brain and spinal cord

cell bodies

peripheral nervous system (PNS)

cell bodies outside of brain and spinal cord

sensory systems

receive and process information from environment (input)

sensory ganglia and nerves, sensory receptors

motor systems

generate movement (output)

sympathetic, parasympathetic, enteric

autonomic ganglia and nerves

motor nerves

associational systems

complex brain functions

astrocytes

maintain a balanced environment around neurons and synapses

oligodendrocytes

form myelin around axons in CNS

multiple axons at once

schwann cells

form myeling around axons in PNS

one axon at once

myelin

multilayered membrane around axons

provides insulation and structural support, speeds up electrical signal

microglia

immune cells of CNS

mediate inflammation

same origin as macrophages (mesoderm)

prune synapses