general definitions Flashcards
gray matter
A generic term for a collection of neuronal cell bodies in the CNS. When a freshly dissected brain is cut open, neurons appear gray.
Cortex
Any collection of neurons that form a thin sheet, usually at the brain’s surface. Cortex is Latin for “bark.” Example: cerebral cortex, the sheet of neurons found just under the surface of the cerebrum.
Nucleus
A clearly distinguishable mass of neurons, usually deep in the brain (not to be confused with the nucleus of a cell). Nucleus is from the Latin word for “nut.” Example: lateral geniculate nucleus, a cell group in the brain stem that relays information from the eye to the cerebral cortex
Substantia
A group of related neurons deep within the brain but usually with less distinct borders than those of nuclei. Example: substantia nigra (from the Latin for “black substance”), a brain stem cell group involved in the control of voluntary movement.
Locus
A small, well-defined group of cells. Example: locus coeruleus (Latin for “blue spot”), a brain stem cell group involved in the control of wakefulness and behavioural arousal.
Ganglion
A collection of neurons in the PNS. Ganglion is from the Greek for “knot.” Example: the dorsal root ganglia, which contain the cell bodies of sensory axons entering the spinal cord via the dorsal roots. Only one cell group in the CNS goes by this name: the basal ganglia, which are structures lying deep within the cerebrum that control movement.
Nerve
A bundle of axons in the PNS. Only one collection of CNS axons is called a nerve: the optic nerve.
White Matter
A generic term for a collection of CNS axons. When a freshly dissected brain is cut open, axons appear white.
Tract
A collection of CNS axons having a common site of origin and a common destination. Example: corticospinal tract, which originates in the cerebral cortex and ends in the spinal cord.
Bundle
A collection of axons that run together but do not necessarily have the same origin and destination. Example: medial forebrain bundle, which connects cells scattered within the cerebrum and brain stem.
Bundle
A collection of axons that run together but do not necessarily have the same origin and destination. Example: medial forebrain bundle, which connects cells scattered within the cerebrum and brain stem.
Capsule
A collection of axons that connect the cerebrum with the brain stem. Example: internal capsule, which connects the brain stem with the cerebral cortex.
Commissure
Any collection of axons that connect one side of the brain with the other side.
Lemniscus
A tract that meanders through the brain like a ribbon. Example: medial lemniscus, which brings touch information from the spinal cord through the brain stem.
