Nervous System: Neurons, Ion Channels & Neurotransmitters

• A neuron's resting membrane potential is -70mV.
• Cytoplasm has high concentrations of nucleic acids, phosphate, and proteins.
• Sodium (Na+) is the primary positively charged ion outside the cytoplasm.
• Hyperpolarization occurs when the charge within a neuron becomes more negative.

Ion Channels

• Ligand-gated ion channels open when a ligand binds and are located in dendrites, the cell body, or the axon plasma membrane.
• Mechanically gated ion channels open in response to pressure, stretch, or vibration and are found in dendrites of sensory neurons.
• Voltage-gated ion channels respond to specific voltages in the cytoplasm near the axon plasma membrane.
• Voltage-gated Potassium channels open at +30mV.
• An action potential involves rapid depolarization followed by rapid repolarization in a neuron's axon.

Neurotransmitter Effects

• Released neurotransmitters can activate neurotransmitter receptors on the postsynaptic cell.

Drug Effects on the Nervous System

• Agonists mimic the body's neurotransmitters by binding to and activating receptors (e.g., opioids like morphine).
• Antagonists block receptor activation by binding to receptors (e.g., Narcan blocking endorphins).
• Reuptake inhibitors prevent neurotransmitters from being transported back into axon terminals (e.g., SSRIs like Prozac).
• Enzyme inhibitors block enzymes that break down neurotransmitters in the synapse, increasing the time neurotransmitters remain active.
• Channel blockers clog ion channels in the neuron axon, preventing action potentials (e.g., Novocaine blocking VG Na+ channels).
• Neural Regeneration occurs along myelinated axons in the PNS (Peripheral Nervous System).
• Neurogenesis is the formation of new neurons.
• The central nervous system (CNS) consists of the brain and spinal cord.

Ventricles

• Ventricles are cavities within the brain filled with cerebrospinal fluid (CSF).
• The brain contains four ventricles.
• Ventricle walls are lined with ependymal cells.

Cerebrospinal Fluid (CSF)

• CSF circulates nutrients and ions.
• CSF helps stabilize ion concentrations.
• CSF flushes waste from the brain and spinal cord.
• CSF absorbs shocks to the brain and back.
• CSF is produced in the Choroid Plexuses.

Cerebrum

• The cerebrum is the largest part of the brain.
• Gyri are the bumps on the brain's surface.
• Sulci are the grooves on the brain's surface.
• Fissures are deep grooves, such as the longitudinal fissure separating the hemispheres.

Parts of the Cerebrum

• The cerebral cortex is the superficial, outer layer of gray matter and is responsible for consciousness.
• Cerebral white matter tracts are bundles of axons in the CNS; In the PNS these are called Nerves.
• Basal nuclei are involved in the initiation and termination of conscious thought.
• The primary somatosensory cortex is located in the front of the parietal lobes on the postcentral gyrus.
• Association areas of the cerebral cortex are responsible for associative functions like language.

Aphasia

• Aphasia is a language disorder affecting comprehension or communication.
• Nonfluent aphasia results from damage to Broca's area, impairing control of vocal cords.
• Fluent aphasia is caused by damage to Wernicke's area, impairing language comprehension.
• Functional areas in the cerebral cortex: Sensory, motor, and association areas.

Primary Cortexes

• Primary Olfactory Cortex processes smells and is near the temporal lobe.
• Primary Gustatory Cortex processes taste and is near the frontal operculum areas.
• Primary Visual Cortex processes visual information and is located at the back of the brain near the occipital lobe.
• Primary Auditory Cortex processes sound and is located in the temporal lobe.
• The diencephalon is the central core region of the brain.

Thalamus

• The thalamus is located in the central portion of the diencephalon.
• The thalamus is made of gray matter.
• The thalamus give rise to emotions.
• The thalamus is egg-shaped.
• The thalamus relays sensory information to the cerebral cortex.

Hypothalamus

• The hypothalamus is located in the lower portion of the diencephalon.
• The hypothalamus is made of gray matter.
• The hypothalamus give rise to emotions like hunger, thirst, and sex drive.
• The hypothalamus regulates the autonomic nervous system.
• The hypothalamus produces hormones.

Epithalamus

• The epithalamus is located in the upper portion of the diencephalon.
• The epithalamus includes the pineal gland.
• The epithalamus give rise to emotions.
• The epithalamus regulates the sleep-wake cycle.
• The epithalamus secretes melatonin.
• The brain stem is the lower stalk of the brain that connects the brain to the spinal cord.

Midbrain

• The midbrain is the upper part of the brain stem.
• The midbrain is mostly white matter with some gray matter.

Midbrain Parts

• Substantia nigra works with basal nuclei to regulate skeletal muscle contractions and is dysfunctional in Parkinson’s disease.
• Superior Colliculi integrates reflexes that move the head and upper body in response to visual stimuli.
• Inferior Colliculi respond to auditory stimuli, similar to the superior colliculi but triggered by loud noises.
• The pons is the middle part of the brain stem and is mostly white matter.
• The Pons contains nuclei which control consciousness and breathing.
• Neural regeneration is the repair of damaged nerves/axons and only occurs in the PNS.
• The Cauda Equina is the spinal nerves that hang down from the conus medullaris.
• Sensory receptors in the body's periphery synapse with first-order neurons; some receptors are dendrites of these neurons.
• First-order neuron cell bodies are located in the dorsal root ganglion and synapse with second-order neurons in the dorsal horn.
• Second-order neuron axons extend to the spinal cord, cross over, and extend through the RAS before synapsing with third-order neurons in the thalamus.
• Third-order neurons are located in the thalamus.

Senses

• Special senses involve complex sensory structures such as vision, hearing, smell, and taste, with receptors in dendrites or specialized cells.
• General senses include blood pressure, pain, and body temperature.
• Sensory receptor adaptation involves changes in sensitivity and neurotransmitter release.
• Upregulation increases sensitivity when receptors are understimulated.
• Downregulation decreases sensitivity when receptors are overstimulated.

Meninges Layers

• Dura is the surface layer of the meninges.
• Arachnoid is the middle layer of the meninges.
• Pia is the lower layer of the meninges.
• Nerve plexuses are networks of interconnected nerves outside the spinal cord.
• Somatic reflexes are involuntary muscle responses involving skeletal muscles.
• The crossed extensor reflex involves withdrawing from a painful stimulus while the opposite limb provides support.