Ventricular System, Action Potential, and Basal Ganglia Structures

Largest ventricle

third ventricle

Ventricular System Function

produce, transport, and secrete cerebrospinal fluid

Role of CSF

decrease friction, decrease weight of brain, cushion, blood brain barrier

CSF Composition

correct mix of chemicals tailored to CNS function

Choroid plexus

found in lateral and 4th ventricles, makes CSF

Pathway through ventricles

lateral ventricles, intraventricular foramina, 3rd ventricle, cerebral aqueduct, 4th ventricle, central canal, reabsorption into blood vessels

Action potential

rapid sequence of changes in voltage across a membrane potential, roughly 1ms

Resting Potential

-70mV. Na+ EQ is +60mV, K+ EQ is -85mV

Depolarization

Na+ rush into cell passively, Na+ voltage gated channels open quickly at -55mV
Net change negative to positive

Repolarization

Na+ channels shut quickly, K+ channels open slowly around 10mV

Hyperpolarization

K+ channels slow to close so K+ flows out excessively. Corrected by Na+/K+ pump

AP ends at axon terminal

Ca2+ gates snap open, Ca2+ binds to vesicles which then fuse with membrane to release NT via exocytosis

Glutamate

excitatory (EPSP), makes membrane potential less negative

GABA

inhibitory (IPSP), makes membrane potential more negative

Absolute refractory period

Na+ channels must reset before they can be opened

Relative refractory period

new AP can be generated but it takes a much stronger signal

Input Nuclei (afferent)

caudate and putamen

Intrinsic Nuclei

External Globus Pallidus, subthalamic nuclei, pars compacta (SNc)

Output nuclei (efferent)

internal globus pallidus, pars retinacula (SNr)

Caudate Nucleus function

movement planning, learning, memory, motivation,

Striatum

Caudate Nucleus + Putamen

Caudate Nucleus Afferent

input from ipsilateral frontal lobe

Caudate Nucleus Efferent

output to hippocampus, globus pallidus, thalamus

Putamen Function

learning, motor control, pain perception, speech articulation

Putamen Afferent

input from cortex

Putamen Efferent

output to cortex via thalamus

Globus Pallidus Internus (GPi) function

inhibitory tone on thalamus, relay for information, involved in indirect and direct pathway

Globus Pallidus Externus (GPe) Function

excitatory tone on thalamus, sends info to thalamus, involved only in indirect pathway

Overall Globus Pallidus Function

conscious and proprioceptive movements, input from multiple structures

Substantia Nigra

black substance from high melanin levels

Pars Compacts (SNc)

compact/dense, responsible for 80% of body’s dopamine, projections into striatum and synapses

Pars Reticulata (SNr)

net-like part of substantia nigra

DA1

excitatory projections in GPi, direct pathway only

DA2

inhibitory projections to GPe, indirect only

DA1 and DA2 Receptor types

metabotropic, creates signal cascade instead of opening a channel, long term impacts

GABAergic receptors open what?

K+-ligand gated channels

Glutamatergic receptors open what?

Na+ ligand gated channels

Subthalamic Nucleus

functionally related to basal ganglia

Subthalamic Nuclei Afferent

input from GPe

Subthalamic Nuclei Efferent

output to GPi, part of indirect pathway to put overall inhibitory tone on thalamus
primarily glutamatergic neuron