Neuroscience: CNS, PNS, Neural Development, and Synaptic Plasticity

Central Nervous System (CNS)

Brain, spinal cord, cranial nerves (1 and 2)

Peripheral Nervous System (PNS)

Cranial nerves (3-12), spinal nerves (31), ganglia

Autonomic Nervous System (ANS)

Provides communication between the brain and visceral muscles and secretory glands

Somatic Nervous System (SNS)

Transmits information from brain to skeletal muscles

Gray Matter

Neuron cell bodies

White Matter

Axons wrapped in myelin

Spinal Nerves Connection

Cervical plexus, brachial plexus, lumbosacral plexus

Midbrain

Visual and auditory processing and eye movement

Pons

Relay for signals between the cerebrum and cerebellum

Medulla Oblongata

Controls autonomic functions including heart rate, blood pressure, respiration, & swallowing

Brainstem Damage

Destroys pathway of nerve communication and autonomic functions that keep the body and systems alive

Cranial Nerve Roots in Brainstem

Forebrain: 1-2, Midbrain: 3-4, Pons: 5-8, Medulla: 9,10,12, Spinal cord: 11

Cerebellum Subdivisions

Right and left cerebellar hemispheres, vermis

Diencephalon Structures

Thalamus, hypothalamus, epithalamus, subthalamus

Cortical Lobes

Frontal lobe, temporal lobe, parietal lobe, occipital lobe, limbic, insular

Internal Capsule

A bundle of axons connecting cortex and subcortical structures

Corpus Callosum

White matter that connects/communicates the left and right cerebral hemispheres

Cerebrospinal Fluid (CSF)

Modified filtrate of blood plasma, secreted by the choroid plexus within the ventricles of the brain

Blood Vessels of Spinal Cord

Posterior spinal artery, posterior medullary artery, segmental artery, anterior medullary artery, anterior spinal artery

Anterior Circulation of Brain

2 internal carotid arteries: supply the anterior, superior, and lateral cerebral hemispheres

Posterior Circulation of Brain

2 vertebral arteries: supply the brainstem, cerebellum, occipital, and inferior lobes in cerebrum

Bipolar Neuron

Glial radial cells with a single axon

Pseudounipolar Neuron

Afferent sensory neuron with two axons and no dendrites

Major Chemicals for Action Potential

Sodium: positively charged, Potassium: positively charged, Calcium: positively charged, Chlorine: negatively charged

Depolarization

A change in the cell membrane potential making it less negative

Repolarization

Return of the cell membrane potential to a more negative value after depolarization

Hyperpolarization

An increase in the membrane potential, making it more negative than the resting potential

Refractory Period

The time following an action potential during which a neuron is less excitable

Resting K+ channel (leak channel)

Always open.

Voltage gated channel

Opens transiently in response to change in the membrane potential.

Ligand-gated channel

Opens (closes) in response to a specific extracellular neurotransmitter.

Signal-gated channel (modality gated)

Opens (closes) in response to a specific intracellular molecule.

Resting membrane potential

Maintained by the electrochemical gradient or the difference in polarity between internal and external surface of the membrane.

Local potential

Small, graded amplitude; either depolarize or repolarize membrane; passive propagation; sensory neuron end-receptor; modality-gated channel postsynaptic membrane: ligand-gated channel.

Action potential

Large, all or none amplitude; depolarizing effect on membrane; active and passive propagation; voltage gated channels responsible for the change in membrane potential.

Graded

Means the potential's size is proportional to the stimulus strength (stronger stimulus = larger potential change), unlike all-or-none action potentials.

Temporal summation

Multiple graded potentials occur at the same synapse in rapid succession. Each new potential adds onto the previous one before it dissipates, allowing them to combine and reach threshold.

Spatial summation

Graded potentials from different synapses (on different locations of the membrane) occur at the same time. Their effects add together, increasing depolarization enough to reach threshold.

Threshold of action potential

Considered normal at -55 mV.

Conduction velocity of action potential

Promoted by myelination.

Backward flow prevention of action potential

The refractory period makes it so the voltage-gated sodium channels become inactivated and cannot reopen, ensuring that the depolarization cannot re-excite the same patch of membrane right away.

Macroglia

Cells that include astrocytes, oligodendrocytes, ependymal cells, radial cells, Schwann cells, and satellite cells.

Microglia

Cells that include macrophages.

Astrocytes

Most abundant in CNS; function to connect neurons and blood vessels which provide additional nutrition, make up blood-brain barrier, guide axons to repair nervous system tissue, and transmit signals by up-taking, releasing and exchanging chemicals.

Oligodendrocytes

Myelinate CNS.

Schwann cells

Myelinate PNS.

Ependymal cells

Type of macroglial cell.

Radial cells

Type of macroglial cell.

Satellite cells

Type of macroglial cell.

Microglial cells

Normally function as phagocytes, attracted to dying cells that secrete proteins, and help create a glial scar while cleaning up debris.

Glial scars

Created by glial cells and astrocytes, they inhibit the spread of damage but also inhibit the process of regeneration after nervous system damage.

Axosomatic synapse

Consists of a presynaptic terminal, synaptic vesicles containing neurotransmitter, a synaptic cleft, and postsynaptic receptors on the soma membrane.

Axodendritic synapse

Includes a presynaptic terminal, synaptic vesicles with neurotransmitter, a synaptic cleft, and postsynaptic receptors on the dendritic membrane.

Axoaxonic synapse

Comprises a presynaptic terminal, synaptic vesicles with neurotransmitter, a synaptic cleft, and postsynaptic receptors on the axon membrane.

Postsynaptic inhibition

Involves hyperpolarization at the postsynaptic receptors, making the postsynaptic neuron less likely to fire an action potential, while neurotransmitter release from the presynaptic neuron remains unaffected.

Presynaptic inhibition

Decreases Ca influx during the action potential, reducing the amount of neurotransmitter released into the synaptic cleft.

Calcium ions (Ca^2+)

Influx into the axonal terminal stimulates the release of neurotransmitters from synaptic vesicles into the synaptic cleft.

EPSP (Excitatory postsynaptic potential)

A graded depolarization of the postsynaptic membrane caused by excitatory neurotransmitters binding to receptors, usually opening Na and sometimes Ca channels.

IPSP (Inhibitory postsynaptic potential)

A graded hyperpolarization of the postsynaptic membrane caused by inhibitory neurotransmitters binding to receptors, usually opening Cl channels (influx) or K+ channels (efflux).

Generation of EPSP or IPSP

Mainly occurs at axodendritic and axosomatic synapses.

Neurotransmitter

Released by a presynaptic neuron, acts directly on postsynaptic ion channels or activates proteins inside the postsynaptic neuron, and is fast acting.

Neuromodulator

Released into extracellular fluid, adjusts the activity of many neurons, and is slow acting.

G-protein gated channel

A channel that opens in response to the activation of a G-protein, leading to a slower and more prolonged effect on the postsynaptic neuron.

Ligand-Gated Ion channels

Neurotransmitter binds directly to the channel protein. The channel opens immediately, allowing ions to flow. This is a very fast process which mediates rapid EPSPs or IPSPs.

G-Protein gated channels

Neurotransmitter binds to a G protein coupled receptor which activates a G protein which indirectly opens or closes ion channels. This can either increase or decrease ion conductance, modulate enzymes or alter cellular signaling cascades. It is much slower than that of ligand gated channels but the effects are longer and more wide-spread.

Mechanism of action of G-proteins

G-proteins dissociate from the receptor and travel along the membrane to activate enzymes or distant channels. Each can transmit signals to multiple effector molecules and spread signals farther along the membrane. This means they have the ability to dramatically amplify and diversify signals.

Effect of neurotransmitter on ion channel opening

The effect of a neurotransmitter on opening an ion channel is determined by the type of receptor it binds to, not the neurotransmitter alone.

Receptors on neuron membrane

No, they can change through upregulation, downregulation or a dynamic process like learning, memory formation, synaptic plasticity and disease.

Agonist

Enhance/mimic neurotransmitter action.

Antagonist

Block neurotransmitter action.

Principal stimulator of muscle contraction

Acetylcholine.

Pathology from acetylcholine deficiency

Deficiency leads to muscle weakness and paralysis or even myasthenia gravis: destruction of Ach receptors at the neuromuscular junction.

Neurotransmitter increasing heart muscle contraction

Norepinephrine.

Side effects of excessive norepinephrine release

Increased alertness, attention, sensitivity and cognitive processing speed at the cost of panic, fear, anxiety, and sleep disturbance.

Functions of dopamine in CNS

Depending on the sequence of release, movements and intensity can either be inhibited or excited by dopamine release.

Disease associated with dopamine deficiency

Parkinson's Disease.

Neurotransmitters contributing to well-being

Dopamine and serotonin.

Blockage of reuptake pump and depression

Allows for a larger quantity of readily available excitatory neurotransmitters to be in the extracellular space rather than being 'recycled' by the reuptake pumps.

Function of substance P

Functions as the neurotransmitter for the sensation of pain but also helps with respiratory and cardiovascular control as well as mood regulation.

Endogenous neurotransmitters for muscle relaxation

GABA, Glycine, Endogenous opioids (endorphins, enkephalins, dynorphins).

Exogenous neurotransmitters for muscle relaxation

Benzodiazepines, Baclofen, Propofol, barbiturates.

Endogenous opioids

Endorphins: inhibit neurons in the CNS that are involved in perception of pain.

Endorphins

Inhibit neurons in the CNS that are involved in perception of pain.

Glutamate

Activates NMDA and AMPA receptors which are crucial for long-term potentiation (LTP).

Ach (Acetylcholine)

Critical for attention, focus, and encoding new information.

Dopamine

Enhances alertness and arousal, increasing signal-to-noise ratio in cortical circuits.

Serotonin

Modulates plasticity, mood, and flexibility in learning strategies.

Pre-embryonic stage

Conception to 14 days.

Embryonic stage

Day 15 to week 8.

Fetal stage

Week 9 to birth.

Neural induction

The notochord signals the overlying ectoderm to thicken and form the neural plate.

Neurulation

The process where the neural plate folds to form the neural tube.

Notochord

A structure that signals the ectoderm to form the neural plate.

Neural crest

Cells at the crest of the folds detach and migrate to form diverse structures, including peripheral nerves, ganglia, and parts of the face and heart.

Mesoderm

The embryo layer that later develops into muscles and the skeleton.

Neuropores

Open ends of the neural tube that close during development.

Spina bifida

A developmental abnormality that may occur when the inferior neuropore fails to close.

Ependymal/neuroepithelial layer

The most deep layer of cells in the developing neural tube.

Mantle layer

The middle layer of cells in the developing neural tube that forms future gray matter.

Marginal layer

The most superficial layer of cells in the developing neural tube that forms future white matter.