Sense-organ neurons {afferent nerve} {afferent fiber} send to ganglia outside brain along spinal cord. Ganglia sense neurons send one axon to brain and one axon to peripheral nerve.
Axons to brain synapse on brain secondary sense neurons. Secondary sense neurons send to cerebellum or thalamus. Thalamus neurons send to neocortex. Neocortex neurons send back to thalamus and to cortex association areas. Association cortex neurons send to hippocampus and amygdala. Hippocampus and amygdala neurons send to hypothalamus.
All these cortical regions send to corpus striatum. Corpus striatum neurons send to globus pallidus. Globus pallidus neurons send to reticular formation and thalamus.
muscle
Muscle sense-cell afferent is wide axon and has one synapse, because large axons have lower thresholds.
skin
Skin afferent is fine axon with several synapses, because fine axons have higher thresholds.
Brain neurons {efferent nerve} {efferent fiber} send to sense organs, muscles, and glands.
Large myelinated axons {A fiber} can come from motor or sense neurons. A fibers {A-alpha nerve} {alpha fiber} can be for proprioception or be somatic motor axons. Sensory A fibers {A-beta nerve} {beta fiber} can be for touch or pressure and travel in spinal cord from trigeminal nucleus. Intermediate-size myelinated sensory A fibers {A-delta nerve} {delta fiber} can be for pain, temperature, or touch and travel in spinal cord to trigeminal nucleus. Motor A fibers {A-gamma fiber} {gamma fiber} can be for muscle spindles.
Small myelinated axons {B fiber} are preganglion autonomic nerves.
Small unmyelinated axons {C nerve} {C fiber} are postganglion sympathetic autonomic nerves or are dorsal root nerves for pain, temperature, and reflexes. Unmyelinated sense-nerve axons travel from spinal cord dorsal roots to trigeminal nucleus. Unmyelinated axons have few branches.
Dopamine-secreting neurons {dopamine neuron} are for goals.
Sensory axons {Ia fiber} can be for muscle spindle and annulospiral endings.
Sensory axons {Ib fiber} can be for Golgi tendon organ.
Sensory axons {II fiber} can be for muscle spindle, flower spray ending, touch, or pressure.
Sensory axons {III fiber} can be for pain, temperature, and touch.
Neurons {interneuron}| can connect across two nerve pathways. After pathway neuron excites them, interneurons typically inhibit or excite other-pathway neurons. Interneurons can detect correlations among local neuron signals. They note constancies and covariances between pathways. Symmetric connections coordinate pathway neurons in ganglia and cortex, especially in topographical maps. Asymmetric inhibitory connections among neurons and interneurons allow associative learning. Interneurons arose from neuron duplication.
Sensory axons {IV fiber} can be for pain or other receptors.
Fruitfly brain cells {Kenyon cell} receive from electric-shock dopamine cells and from odor cells and possibly send to motor neurons.
Unmyelinated C fibers and slightly myelinated A-delta fibers {nociceptive fiber} go to trigeminal nucleus for noxious stimuli, pain, or punishment.
Medulla respiratory center sends excitatory signals along nerve {phrenic nerve} to diaphragm.
Legs have a main nerve {sciatic nerve}|.
Body neurons {somatic neuron} can connect to striated muscles to perform voluntary actions and can be active or quiet, depending on will.
Spinal cord nerves {spinal nerve} are two per vertebra and include dorsal nerves, ventral nerves, and visceral autonomic nerves.
Spinal nerves include visceral branches {autonomic nerve}.
Spinal nerves can be on back {dorsal nerve}.
Spinal nerves can be on side and front {ventral nerve}.
Head has cranial nerves 1 through 12 {cranial nerve}.
Cranial nerve 1 {olfactory nerve} {cranial nerve 1} {cranial nerve I} has axons from nose olfactory-sense neurons, through cribriform plate, to olfactory bulb. Vertebrate smell uses first cranial nerve.
Cranial nerve 2 {optic nerve} {cranial nerve 2} {cranial nerve II} is from retina to thalamus. It leaves the retina at a location with no receptors {optic disk}.
Cranial nerve 3 {oculomotor nerve} {cranial nerve 3} {cranial nerve III} sends to extrinsic eye muscles, upper eyelid elevator muscle, ciliary muscle, and pupil sphincter muscle. Extrinsic eye muscles are inferior oblique, superior rectus, inferior rectus, and medial rectus, but not lateral rectus or superior oblique.
Cranial nerve 4 {trochlear nerve} {cranial nerve 4} {cranial nerve IV} sends to superior oblique eye muscles.
Cranial nerve 5 {trigeminal nerve} {cranial nerve 5} {cranial nerve V} is from face and carries smell coolness or hotness.
Cranial nerve 6 {abducens nerve} {cranial nerve 6} {cranial nerve VI} sends to lateral rectus eye muscles.
Cranial nerve 7 {facial nerve} {cranial nerve 7} {cranial nerve VII} is from face and has branch {chorda tympani nerve} from anterior mobile tongue that travels with trigeminal-nerve lingual branch as it leaves tongue, goes to middle ear, goes to brain, and signals taste.
Cranial nerve 8 {auditory nerve} {vestibulocochlear nerve} {cranial nerve 8} {cranial nerve VIII} is from inner ear and has cochlear-nerve axons, from hair cells to brain, and vestibular-nerve axons, from vestibule to brain.
Cranial nerve 9 {glossopharyngeal nerve} {cranial nerve 9} {cranial nerve IX} is from pharynx and controls swallowing, tasting, and saliva release.
Cranial nerve 10 {vagus nerve, cranial nerve}| {cranial nerve 10} {cranial nerve X} goes from heart, lungs, stomach, intestine, larynx, esophagus, and aorta to nucleus tractus solitarius. It connects brain to lungs, heart, and intestines.
Cranial nerve 11 {spinal accessory nerve} {cranial nerve 11} {cranial nerve XI} is from shoulder.
Cranial nerve 12 {hypoglossal nerve} {cranial nerve 12} {cranial nerve XII} is from tongue.
Outline of Knowledge Database Home Page
Description of Outline of Knowledge Database
Date Modified: 2022.0225