PSY290 - Neurons and the Nervous System

Cells of the nervous system and general organizational principles of the nervous system

Central Nervous System

Central Nervous System

brain and the spinal cord, encased in bone

Peripheral Nervous System

everything else that is outside of the central nervous system

microglia

small cells that respond to injury and disease states by multiplying and engulfing debris (cleaning)

• regulate cell death and synapse formation /elimination

astroglia

• affinity for blood vessels

• regulate flow of materials into the CNS to provide nutritional support for neurons

• vital for injury response

• have receptors, release transmitters and influence neuronal activity

astrocytes

• experience increase in intracellular calcium once activated

• can enhance or inhibit synaptic activity

• neurotransmitters are also taken up by astrocytes

what cells myelinate neurons in the CNS?

oligodendroglia

what cells myelinate neurons in the peripheral nervous system?

Schwann cells

neurons

excitable cells that generate and conduct electrochemical signals

• activate at different rates and generate different behavioral states

neuronal membrane

phospholipid bilayer separating the intracellular region from the extracellular region

what allows the neuronal membrane to control what can enter or leave the cell?

selective permeability

what ions have a higher concentration in the intracellular region of the neuronal membrane?

A- and K+ ions

what ions have a higher concentration in the extracellular region of the neuronal membrane?

Cl - and Na + ions

Na+/K+ exchanger

• exchanges 3 Na+ for 2 K+ ions

• ATP/ energy dependent

Resting membrane potential

when there is no active potential the resting is at -60 to -70 mv due to the potential difference across the membrane due to the restriction of charged substances

what happens when channels are open?

• ion flow across the membrane will occur

• membrane voltage will change and electrochemical impulses will be generated

K+ concentration gradient

• chemical: high to low (outward)

• electrical: positive to negative (inward)

what is the net electrochemical driving force of K+?

outward

Na+ concentration gradient

• chemical: high to low (inward)

• electrical: positive to negative (inward)

what is the net electrochemical driving force of Na+?

inward

what channels are operational at the resting membrane potential?

Na+/K+ exchanger and leak k+ channels

neurotransmission

when the neuron receives a chemical signal from another cell

ligand gated channel

opens in response to a specific extracellular neurotransmitter

voltage gated channel

opens transiently in response to change in the membrane potential (when action potential is initiated)

Ligand-gated Na+ channel

transmitter released by cell A binds to receptors on cell B and the activation of receptors triggers excitement of cell B

• when channel opens, Na+ ions enter and neuron is excited by ions

what channels are open during excitatory transmission?

ligand gated channels and voltage gated Na+ channels

Depolarization of Vm

when transmitter glutamate binds to AMPA receptor channel opens and allows the flow of Na+ ion which cause excitatory post synaptic potential that depolarizes the voltage membrane

inhibitory post synaptic potentials

• vital to controlling cell activity

• hyperpolarizes the neuron making it less likely to achieve threshold and fire action potential

Glutamate

excites the neuron (GO)

GABA

inhibits the neuron (STOP)

what happens at threshold -55 mv ?

• the membrane voltage is - 55 mV and action potential starts

what channels open at threshold?

Voltage-gated channels which allow Na+ ions into the cell

what is happening at the gaps of myelination?

nodes of Ranvier are present and there is a high density of voltage-gated Na+ channels

why are nodes of Ranvier so beneficial to the neuron?

• makes signal conductance faster and more energetically favorable because you don’t have to depolarize the full axon

saltatory conduction

impulses jump from one node to the next

what is the defining feature of multiple sclerosis?

damaged myelination (white matter lesions)

how does the signal leave the axon?

• depolarization at axon terminal

• influx of Ca2+

• triggers vesicular fusion and transmitter into extracellular space

• travels across synapse to stimulate target

what channels are open at the axon terminal?

voltage gated Ca 2+ channels

ionotropic receptors

signal quickly

metabotropic receptors

signal slowly via a messenger cascade

endorphins

• natural painkillers

• mediate pain by acting on targets in the nervous system

u-opioid receptors

highly responsive to opioid drugs like morphine

gray matter

cell bodies nuclei

white matter

axon tracts

ganglia

groups of cell bodies

nerves

groups of axons

meninges

membrane covering the brain that cushions it against the skull

what are 3 layers of the meninges called

dura, arachnoid and pia

cerebrospinal fluid

supports and cushions against impact

• generated by choroid plexus and flows through ventricles

• tightly regulated

choroid plexus

generates cerebrospinal fluid

Telencephalon

higher order functioning

• cortex, the basal ganglia and the limbic system

limbic system

• cingulate cortex

• hippocampus

• amygdala

• mamillary body

• septum

cortex

mostly gray matter and is the outer layer of cells

what are the two types of cortex

• the neocortex and the allocortex

neocortex

makes up 90% of the cortex in humans and explains the majority of our higher order behaviors

allocortex

makes up 10% of our brain and is part of the hippocampus and the olfactory system

what are the bumps of the brain called?

Gyri

what are the folds of the brain called?

sulci

longitudinal fissure

divides the hemispheres

central fissure

frontal and parietal lobes

lateral fissure

separates top half (frontal + parietal) from bottom half (temporal)

basal ganglia

• dorsal striatum

• globus pallidus

• nucleus accumbens

dorsal striatum

caudate and the putamen

globus pallidus

important for movement

ventral striatum

nucleus accumbens which plays a role in reinforcement learning and habit formation which is relevant to addiction

diencephalon

• thalamus

• hypothalamus

thalamus

relay center for incoming sensory information

• exception (olfactory input)

hypothalamus

key drive center

• fighting

• fleeing

• feeding

• loving

Mesencephalon

• superior colliculus

• inferior colliculus

• substantia nigra

• reticular formation

• periaqueductal

metencephalon

pons and cerebellum

myelencephalon

medulla

what part of the brain deals with sensory information and motor instruction (incoming and outgoing tracts)

the metencephalon and the myelencephalon

key principles of brain function

• localization of function

• collaboration is significant

• balance is critical and lack of it causes dysfunction

• reorganization is possible with limitations

what divisions of the peripheral nervous system?

• somatic nervous system

• autonomic nervous system

• enteric system

what are the nerves of the PNS?

• afferent and efferent neurons

afferent neurons

sensory information

efferent neurons

motor information

parasympathetic nervous system

rest and digest

sympathetic nervous system

fight or flight

rostro lateral frontal cortex

rostro = front and lateral = outer part of the frontal cortex

dorsolateral frontal cortex

dorso = top , lateral = outer

ventromedial hypothalamus

ventro = bottom , medial = middle

posteromedial hypothalamus

postero = posterial , medial = middle

what are the 3 axis’ of the nervous system?

• medial-lateral axis

• rostral-caudal axis

• dorsal-ventral axis

what responses are dominant in the parasympathetic nervous system

• heart rate variability and galvanic skin resistance

what responses are dominant in the sympathetic nervous system?

• respiration

• heart rate

• blood pressure

• catecholamines