Nervous System and Neural Cell Structure

• The central nervous system (CNS) consists of the brain and spinal cord
• The brain is divided into cerebral hemispheres, diencephalon, cerebellum, and brainstem

Neural Cell Structure:

• The neural cell features dendritic spines where inputs from other axon terminals are received
• Synapses are the junctions where neurons communicate
• The soma is the cell body
• The axon initial segment (AIS) is the beginning of the axon
• The node of Ranvier is a gap in the myelin sheath
• The axon carries signals away from the soma
• The axon terminal is where the neuron communicates with other cells
• Dendrites branch into apical dendrites and basal dendritic tree

Neuron Types

• Neurons are classified by morphology (structure), function, and neurotransmitter
• Morphology includes unipolar, bipolar, multipolar, and pseudounipolar types

Neuron Function

• Neurons can be sensory, motor, or interneurons
• Interneurons include projection neurons and local-circuit neurons

Neurotransmitters

• Neurotransmitters are the chemical messengers that neurons to communicate
• Types of neurotransmitters include Glutamatergic, GABA-ergic, Adrenergic, Noradrenergic, and Dopaminergic, etc.

Functional Features of Neurotransmitters

• Acetylcholine (ACh) has an excitatory postsynaptic effect
• ACh uses choline + acetyl CoA as precursors
• CAT is the rate-limiting step in synthesis, AChEase is used for removal, and vesicles are small and clear
• Glutamate is excitatory
• Glutaminase is the rate-limiting step in synthesis, transporters are used for removal, and vesicles are small and clear
• GABA is inhibitory
• GAD is the rate-limiting step, transporters are used for removal, and vesicles are small and clear
• Glycine is inhibitory
• Phosphoserine is the rate-limiting step, transporters are used for removal, and vesicles are small and clear
• Catecholamines are excitatory and use tyrosine as a precursor
• Tyrosine hydroxylase is the rate-limiting step, transporters, MAO, and COMT are used for removal, and vesicles are either small dense-core or large irregular dense-core
• Serotonin (5-HT) is excitatory and use tryptophan as a precursor
• Tryptophan hydroxylase is the rate-limiting step, transporters and MAO are used for removal, and vesicles are large, dense-core
• Histamine is excitatory and use histidine as a precursor
• Histidine decarboxylase is the rate-limiting step, transporters are used for removal, and vesicles are large, dense-core
• ATP is excitatory and use ADP as a precursor
• Mitochondrial oxidative phosphorylation and glycolysis are rate-limiting steps, hydrolysis to AMP and adenosine is used for removal, and vesicles are small and clear
• Neuropeptides are excitatory and inhibitory and are synthesized by amino acids (protein synthesis)
• Enzymatic modification of lipids are used for removal, and vesicles are large, dense-core
• Endocannabinoids are inhibitory and use membrane lipids are precursors
• Hydrolasis by FAAH is used for protein synthesis, vesicles are none
• Nitric oxide is excitatory and inhibitory and use arginine as a precursor, Nitric-oxide synthase is the rate-limiting step, has spontaneous oxidation for removal and vesicles are none

Glial Cells

• Glial cells in the CNS include Astrocytes, Ependymal cells, Radial glia, Oligodendrocytes, and Microglia
• Glial cells in the PNS include Schwann cells, Satellite cells, and Enteric glial cells

Astrocytes

• Astrocytes play a regulatory role in neurogenesis and synaptogenesis
• Astrocytes help in the control of the blood-brain barrier permeability
• Astrocytes maintain extracellular homeostasis
• Astrocytes regulate synaptic activity

Oligodendrocytes

• Oligodendrocytes are myelinating cells of the CNS
• Oligodendrocyte pathologies are involved in neurodegenerative and neurodevelopmental diseases

Microglia

• Microglia eliminate microbes, dead cells, redundant synapses, and protein aggregates
• Microglia mediate neuroinflammatory processes
• Microglia have different morphological phenotypes

Ependymal Cells

• Ependymal cells have a critical role in CSF homeostasis
• Ependymal cells regulate brain metabolism
• Ependymal cells clear waste from the brain

Radial Glia

• Radial glia have a fundamental role in neurogenesis and brain development
• Radial glia are progenitor cells
• Radial glia guide neuronal migration

White and Gray Matter in the CNS

• In the brain, gray matter is on the outside
• White matter is on the inside
• In the spinal cord, gray matter is on the inside
• White matter is on the outside

Brain Lateralization

Cerebrum

• The cerebrum includes the frontal lobe, parietal lobe, temporal lobe, insular lobe, and occipital lobe

Cerebral Cortex:

• Motor Areas: Primary motor cortex, premotor cortex, supplementary motor area
• Sensory Areas: Primary somatosensory cortex, primary visual cortex, primary auditory cortex
• The cortex also has Association Areas: Prefrontal association area, parietotemporal association area, limbic association area, Broca's area, Wernicke's area,etc.

Frontal Lobe

• Functions involving voluntary movements, language, higher-level executive functions, emotional control, and personality

Prefrontal cortex Functions:

• Attention, working memory, cognitive control processes, planning, goal attainment, and problem-solving, and emotion regulation

Functions of the Primary motor cortex:

• Task: move fingers in pattern
• Brain activity: premotor area + primary motor cortex + prefrontal cortex
• Functions of the Primary motor cortex: imagine moving the fingers in a pattern
• Brain activity: Premotor area and prefrontal cortex

Broca's Area

• Broca's area is involved in language
• Broca's aphasia is characterized by diminished spontaneous speech output and loss of normal grammatical structure

Parietal Lobe

• Functions of the parietal lobe include spatial awareness and navigation, sensory integration & processing, body perception and movement, language and mathematics, attention allocation, and perception of the environment and manipulation

Somatosensory Cortex

• Touch, temperature, pain, Propiroception, Bodily sensations, Sensation of pressure and weight, Object recognition through touch, and storing sensory information

Occipital Lobe

• Visual object recognition, color processing, spatial processing and depth perception, motion detection, visual integration, hand-eye coordination, and visual imagery processing

Temporal Lobe

• Functions of the left temporal lobe: Auditory Processing, Language Comprehension, Verbal Memory, Speech Production, Music perception, and Emotional response
• Functions of the right temporal lobe: Auditory Processing, Visual Memory, Processing of Non-verbal Sounds, Emotional processing, Spatial processing, and facial Recognition

Temporal Lobe Substructures

• Wernicke's aphasia results in impaired language comprehension, difficulties with repetition and naming, and problems with understanding
• Limbic system region, Wernicke's Area, auditory cortex, superior temporal gyrus, middle temporal gyrus, and inferior temporal gyrus

Limbic System

• This includes the cingulate gyrus, thalamus, hypothalamus, the amygdala and the hippocampus

Basal Ganglia

• Includes the motor cortex, caudate nucleus, globus pallidus internus and externus, substantia nigra, subthalamic nuclei, putamen, and thalamus

Pineal Gland

• This regulates the sleep-wake cycle and melatonin secretion.

Pituitary Gland

• This regulates growth, reproduction, the response to stress and trauma, lactation, water and sodium balance, and labor and childbirth

Brainstem

• Located between the cerebrum and spinal cord
• Contains the thalamus, midbrain, pons, and medulla

Cranial Nerves

• Optic nerve (CN II), Oculomotor nerve (CN III), Trochlear nerve (CN IV), Trigeminal nerve (CN V), Abducens nerve (CN VI), Facial nerve (CN VII), Vestibulocochlear nerve (CN VIII), Glossopharyngeal nerve (CN IX), Vagus nerve (CN X), Hypoglossal nerve (XII), and Accessory nerve (XI)

Cerebellum

• This maintains balance and posture, coordinates voluntary movements, learning and congitive functions

Spinal Cord

• The spinal cord has cervical, thoracic, lumbar, sacral, and coccygeal regions
• C1-C4 controls breathing
• C2 controls head and neck movement
• C4-C6 controls heart rate
• C6 controls shoulder movement
• C5 controls wrist and elbow movement
• C7-T1 controls hand and finger movement
• T1-T12 controls sympathetic tone and and temperature regulation
• T2-T12 controls trunk stability
• T11-L2 controls ejaculation
• L2 controls hip motion
• L3 controls knee extension
• L4-S1 controls foot motion
• L5 controls knee flexion
• S2-S3 controls bowel and bladder activity
• S2-S4 controls sexual function
• S5 controls bowel and bladder activity
• C0 innervates coccygeus and levator ani muscles and the skin over the coccyx

Circle of Willis

• The circle of willis provide blood flow to the brain
• Anterior communicating artery, anterior cerebral artery, internal carotid artery, middle cerebral artery, posterior communicating artery, basilar artery, posterior cerebral artery, superior cerebellar artery, vertebral artery, posterior inferior cerebellar artery and anterior spinal artery

The Blood-Brain Barrier (BBB)

• The BBB includes astrocystes, pericyctes, neurons, microglia, and endothelial cells

Meninges

• The meninges are made up of the Bone of Skull, Eipdural Space, Dura mater, Subdural Space, Arachnoid Mater, Subarachnoid space, pia mater, brain and Skull