Neuroscience Concepts

Central nervous system (CNS)

Brain

• Cerebrum (telencephalon): Cortex, subcortical structures
• Diencephalon: Thalamus, hypothalamus
• Brain stem: Midbrain, pons, medulla oblongata
• Cerebellum

Spinal cord

• Cervical
• Thoracic
• Lumbar
• Sacral

Functions

Forebrain (telencephalon and diencephalon)

Responsible for higher order processing (language memory, thought, emotion), sensory processing, motor output to skeletal muscle and viscera, autonomic glands

Brain stem

Responsible for lower level functions (breathing, cardiac regulation) as well as some sensory and motor functions

Spinal cord

Facilitates sensory and motor functions via cranial and spinal nerves (PNS)

Peripheral Nervous System (PNS)

Composed of cranial and spinal nerves which connect the CNS to muscles, glands, organs, and sensory tissue.

Sensory (afferent - arrive) neurons: Send signal to CNS
Motor (efferent - exit) neurons: Send signal from CNS

For a more detailed primer, see here: Peripheral Nervous System (PNS)
For anatomical detail, see here: Nervous System Primer > Autonomic nervous system

Autonomic nervous system

Responsible for involuntary movement, carries signal from CNS

• Sympathetic nervous system: Flight or flight
• Parasympathetic nervous system: Rest and digest
• Enteric nervous system: GI tract

For general effects, see here: Autonomic Nervous System Effects Primer

Somatic nervous system

Responsible for voluntary muscle movement in skeletal muscle

White and Gray Matter

White matter contains myelinated axons whereas gray matter contains unmyelinated axons.

Gray matter

CNS: Makes up the outer cortex and are arranged as nuclei
PNS: Organized into ganglia

White matter

CNS: Organized into tracts (axon bundles) or columns (several tracts)
PNS: Organized into nerves (axon bundles)

Nerves

Nerves reside in the horn roots 😈 of gray matter. Rootlets emerge from horns.

Sensory neuron in dorsal horns. On-ramps.
Motor nuclei reside ventral horns. Off-ramps.

Rootlets emerge from horns and form dorsal/ventral roots. These combine to form spinal nerves which branch. Spinal nerves branch into rami, the dorsal ramus and ventral ramus. Because it is both dorsal and ventral, it has both motor and sensory info.

Dorsal ramus: Intrinsic muscles of back and skin of back
Ventral ramus: Everything else

The dorsal root ganglion is a good way of finding dorsal direction.

Spinal nerves

Named by vertebral region and the number in region.
Spinal cord ends at L1/L2. The conus medularis is the official end to the spinal cord. The filum terminale emerges from the tip of the conus medularis and continues as the cauda equina.

Dermatomes

Provide sensory innervation to the skin. Mostly ventral rami. These will follow the naming vertebrae of the spine. A rash following a particular dermatome may indicate pathology of the corresponding spinal nerve (e.g. shingles).

There are no dermatomes for the face as sensory information for the head and neck is picked up by cranial nerves. The exception to this is cranial nerve X (vagus nerve) which goes everywhere (heart, lungs, GI, etc.)

Neuron Classification

Multipolar: Most common variant in humans. Dendrites > Cell Body > Axon.
Bipolar: Dendrites > Axon > Cell Body > Axon > Dendrites
Pseudounipolar: Cell Body > Two Axons > Dendrites
Unipolar: Cell Body > Axon > Dendrites

Functions

Excitation: Increase the likelihood the target will fire (e.g. glutamate)
Inhibitory: Decrease the likelihood the target will fire (e.g. gamma-aminobutyric acid GABA)
Modulatory: Modify the probability the target neuron will fire (e.g. dopamine, serotonin, acetylcholine)

Glial Cells

See here for more information on myelin: Ion channels and Action Potentials > Nodes of Ranvier

Other Cell Types

Ependymal cells: Make up choroid plexus lining the ventricles of the brain. Produces cerebrospinal fluid (CSF)
Pial cells: Make up pia mater lining the surface of the brain (innermost lining of meninges)
Vascular cells: Blood circulation

Clinical Pearls

CNS disorders

• Alzheimer's Disease: Atrophy of brain tissue, affects memory and cognitive functioning
• Glioblastoma: Aggressive form of cancer affecting astrocytes in the brain
• Multiple Sclerosis (MS): Demyelination (loss of white matter) in the brain and spinal cord

PNS disorders

• Diabetic neuropathy: Chronically elevated glucose which can damage nerves (usually of hands and feel)
• Schwannoma: Benign tumor affecting Schwann cells
• Sciatica: Pain radiating along sciatic nerve