lecture 3

4 functional groups of neurons

sensory, motor, principal, interneurons

neurons function

send electrical signals over short and long distances in the body
electrically and chemically excitable

neuron structure

dendrites: branches on which other neurons form synapses
axons make connections with other neurons

sensory neurons

afferent, transform a specific type of input or stimulus into electrical and chemical signals
inform the nervous system of internal or external environmental events

motor neurons

responsible for the direct or indirect control of effector organs (muscles and glands)

principal neurons

excitatory neurons that use glutamate
integrate and process information within a brain region, project output to a different region

pyramidal neurons

throughout the cortex, found mainly in layers 3 and 5
primary excitatory neurons, release glutamate
information processing units

inhibitory interneurons

interact with and control pyramidal cells, prevent over excitation in neuronal networks
found exclusively in brain and spinal cord
non pyramidal

inhibitory interneurons distinguished by

structure of axonal arbour, typically innervate selective domains of their target cells

cortical organization

cerebral cortex divided into six distinct layers

non pyramidal cells

found throughout all 6 layers of cerebral cortex
project out to sympathetic nervous system
inhibitory, use GABA

rosehip neurons

inhibitory neuron found in the cerebral cortex, highly specialized brake on brain activity

dendrites

receiving portion of incoming signals from other cells
electrical and biochemical signals channeled to cell body

dendritic spines

small protrusions along branches, site of some synaptic contacts
are where nervous system is able to change (plasticity)

axon

main output extension of the neuron
propagates signals in all-or-none fashion

information flow through neurons

dendrites: collect electrical signals
cell body: integrates incoming signals and generates outgoing signal to axon
axon: passes electrical signals to dendrites of another cell or to an effector cell

myelin

coating on axon, produced by glial cells

nodes of ranvier

gap in the myelin sheath of a nerve
allows axon potential to travel quickly down the axon
contains sodium and potassium ion channels

axonal transport

organelles from soma travel along axon to terminals
microtubule proteins give structure and allow proteins to travel to the terminal

presynaptic terminals

ends of an axon that release neurotransmitters to transmit signals to other neurons, muscles, or glands
consists of specialized swellings

glial cells

non-neuronal components of the nervous system, make up space and gaps in the brain

astrocytes

regulatory role in brain functions (neurogenesis, synaptogenesis, control BBB permeability, maintain extracellular homeostasis)

protoplasmic astrocytes

grey matter, fine elaborate processes
processes contact blood vessels, form perivascular end feet and form multiple contacts with neurons
bridge between blood vessel and neuron, takes in glucose and oxygen to feed neuron

astrocytes and the BBB

end feet wrap round blood vessels and signal to endothelial cells
endothelial cells lining blood vessels from tight junctions which maintain blood brain barrier

fibrous astrocytes

white matter
perivascular endfeet contact axons at nodes of ranvier
sites of exchange, soak up extra potassium, control ion balance

astrocytes and principal cells

astrocytes keep principal cells in check
end feet in synapse
once glutamate has done its job, will break it down so cells dont hyperexcite

oligodendrocytes

myelinating glial cells in the CNS, can myelinated different axons and several internodes per axon
endfeet on blood vessels, feed themselves

Schwann cells

myelinating cells in the PNS, can myelinated a single internode in a single axon

myelinating glial cells

oligodendrocytes of schwann cells form myelin sheath by wrapping their membrane several times around the axon

microglia

immune cells derived from progenitors that migrated from periphery, from mesoderm

microglia precursors

invade CNS, disseminate homogeneously throughout the neural tissue
acquire a specific phenotype which distinguishes them from precursors (blood-derived monocytes)

microglia role

brain infection and disease: phagocytosing debris and secreting factors to modify disease progression
homeostasis: regulation of cell death, synapse elimination, neurogenesis, neuronal surveillance
maturation and plasticity of neural circuits

blood brain barrier

highly selective semipermeable membrane
separates circulating blood from the brain and extracellular fluid in the CNS

BBB formation

formed by brain endothelial cells

what can pass through the BBB

water, some gases, lipid soluble molecule by passive diffusion
selective transport of glucose and amino acids that are crucial to neural function

M1

inflammatory microglia
causes neuroinflammmation or neuronal loss, disrupt BBB
releases proinflammatory factors, ROS, performs immune stimulation

M2

anti-inflammatory microglia
support neuronal survival
restrict BBB

cytokines

small proteins that help control the growth of and activity of immune and blood cells