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 NEUROBIOLOGY Molecules, Cells and Systems
Gary G. Matthews
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Glossary
[ A-E ] [ F-L ] [ M-R ] [ S-Z ]
Glossary
- M -
- M line
- In the sarcomere of a striated muscle cell, the transverse line at the midpoint of the sarcomere. The M line consists of filaments connecting the thick filaments at their midpoint.
- mammillothalamic tract
- A fiber tract containing axons projecting from the mammillary bodies of the hypothalamus to the thalamus in the limbic system.
- marginal zone
- The relatively cell free region at the outer edge of the neural tube.
- mechanoreceptors
- Sensory receptor neurons that respond to mechanical displacement of the sensory surface. Examples are muscle spindle receptors and hair cells.
- medial geniculate nucleus
- The portion of the thalamus that processes auditory information. The medial geniculate nucleus receives synaptic input from the inferior colliculus and sends axons to the primary auditory cortex.
- medial lemniscus
- A fiber tract carrying ascending somatosensory information from the dorsal column nuclei of the brainstem to the thalamus in the diencephalon.
- medulla oblongata
- The most posterior part of the brainstem, at the border between the brain and the spinal cord.
- Meissner corpuscle
- A rapidly adapting skin mechanoreceptor that is sensitive to touch and pressure.
- membrane potential
- The electrical voltage difference between the inside and the outside of a cell.
- Merkel receptor
- A slowly adapting skin mechanoreceptor that signals sustained pressure.
- mesencephalon
- The midbrain.
- midbrain
- The middle of the three brain vesicles that arise from the neural tube during embryonic development. In the adult brain, the midbrain consists of brain structures such as the superior colliculus, the inferior colliculus, and parts of the reticular formation.
- miniature end-plate potential
- A small postsynaptic depolarization at the neuromuscular junction, arising from spontaneous fusion of a single synaptic vesicle in the synaptic terminal.
- motor neuron
- A neuron that makes synaptic contact with the final target cell, such as a skeletal muscle cell.
- motor unit
- A single motor neuron and all of the muscle cells that receive synaptic connections from that motor neuron.
- muscarinic acetylcholine receptor
- A type of G protein-coupled receptor, activated by acetylcholine.
- muscle fiber
- A muscle cell.
- muscle spindle
- An encapsulated sensory structure activated by stretch of skeletal muscles.
- myelin
- The insulating sheath around axons, formed by certain types of glial cells.
- myofibril
- A bundle of thick and thin filaments that forms an organizational unit within a single muscle cell, which contains several myofibrils.
- myosin
- The protein that makes up the thick filaments of a myofibril. ATP hydrolysis by myosin provides the energy to drive filament sliding during muscle contraction.
- myotatic reflex
- The spinal reflex triggered by activation of muscle spindles.
- N -
- neocortex
- A type of cerebral cortex characterized by multiple layers of cells. Most of the cerebral cortex in the human brain consists of neocortex. Examples of neocortex are the primary somatosensory cortex and the primary motor cortex.
- Nernst equation
- The equation used to calculate the equilibrium potential for a permeant ion.
- nerve growth factor
- A protein neurotrophin that stimulates neurite outgrowth and influences gene expression in neurons by activating trkA receptors (tyrosine receptor kinase type A).
- neural crest
- The portion of the neural plate and neural groove containing cells that give rise to the peripheral nervous system. At the neural groove stage, the neural crest occupies the lateral margins of the groove. At the neural tube stage, the neural crest separates from the neural tube.
- neural groove
- An indentation along the midline of the developing embryo, formed by the proliferation of neuronal precursor cells in the neural plate.
- neural plate
- The portion of ectoderm overlying the notochord, containing cells that will give rise to the nervous system during further embryonic development.
- neural tube
- A tubular structure formed by fission of the neural groove from overlying ectoderm. The brain and spinal cord develop from neural tube.
- neurite
- A collective term for the dendrites and axons of a neuron.
- neuritic plaque
- A pathological feature found in the brains of patients with Alzheimer's disease. Neuritic plaques are extracellular accumulations of protein, consisting largely of beta-amyloid protein.
- neurofibrillary tangle
- A pathological feature found in the brains of patients with Alzheimer's disease. Neurofibrillary tangles are abnormal intracellular accumulations of a microtubule-associated protein called tau.
- neurogenesis
- The stage of neural development when neuronal precursor cells proliferate to produce neurons.
- neurohypophysis
- The posterior part of the pituitary gland, where nerve terminals of hypothalamic magnocellular neurosecretory cells release the hormones oxytocin and vasopressin.
- neuromuscular junction
- The synaptic junction between the motor neuron and its postsynaptic skeletal muscle cell.
- neuron
- A nerve cell.
- neurotransmitter
- The chemical messenger released from a synaptic terminal to influence a postsynaptic target cell.
- neurotrophins
- A soluble molecule secreted into the external space that promotes the survival of neurons and stimulates neurite outgrowth.
- nicotinic acetylcholine receptor
- A type of ligand-gated acetylcholine receptor molecule in which ACh directly binds to the channel protein and opens the channel.
- nitric oxide
- A small, membrane-permeant molecule that is thought to serve as a cellular signal. Nitric oxide (NO) is formed by the enzyme nitric oxide synthase from the amino acid arginine.
- NMDA receptor
- A subtype of glutamate receptor. NMDA receptors require glutamate binding and depolarization to allow cations to enter the postsynaptic cell. Open NMDA receptors also allow calcium ions to enter the postsynaptic cell.
- nociceptor
- A sensory neuron that is activated by stimuli that damage tissue, leading to the sensation of pain.
- nodes of Ranvier
- Periodic breaks in the myelin sheath, where voltage-dependent sodium channels are clustered and sodium influx occurs to support action potential propagation.
- norepinephrine (noradrenaline)
- A neurotransmitter released by sympathetic motor neurons and by some neurons in the central nervous system.
- notochord
- A long, rod-shaped group of cells formed in the mesoderm during gastrulation of the early embryo. The notochord defines the longitudinal axis of the body plan and induces formation of neural tissue in the overlying ectoderm.
- nucleus (plural: nuclei)
- A cluster of neuronal cell bodies within the central nervous system.
- O -
- olfactory bulb
- The part of the central nervous system that receives synaptic projections from olfactory sensory neurons, via the olfactory nerve.
- oligodendrocyte
- A type of glial cell that myelinates axons in the central nervous system.
- optic chiasm
- The cross over point of the optic nerve, where ganglion cell axons from the temporal and nasal portions of the retina are sorted to ipsilateral or contralateral projections to the lateral geniculate nucleus.
- organ of Corti
- The sensory structure within the cochlea, where sensory hair cells are located.
- osmosis
- The movement of water down its concentration gradient.
- otolith organ
- A sensory structure containing hair cells that detect the organism's orientation with respect to gravity.
- oxytocin
- A hormone released in the posterior pituitary by hypothalamic neurosecretory neurons.
- P -
- Pacinian corpuscle
- A rapidly adapting skin mechanoreceptor that is sensitive to touch and pressure.
- paleocortex
- A form of cerebral cortex characterized by two layers of cells, as opposed to the multiple layers of cells found in the neocortex. Entorhinal cortex of the olfactory system is an example of paleocortex.
- Papez circuit
- The central core of the limbic system, consisting of a loop from the cingulate gyrus, entorhinal cortex, hippocampus, hypothalamus, thalamus, and back to the cingulate gyrus.
- parasympathetic division
- The acetylcholine-releasing division of the autonomic nervous system.
- paravertebral ganglia
- The chain of sympathetic ganglia that parallel the spinal column.
- Parkinson's disease
- A human disease characterized by muscle tremor and difficulty in initiating and sustaining locomotion. The disease results from degeneration of dopamine-releasing neurons of the substantia nigra.
- phosphodiesterase
- An enzyme that inactivates cyclic nucleotide molecules, such as cyclic AMP or cyclic GMP.
- phospholipase C
- An enzyme that acts on phospholipid molecules in the plasma membrane to release the intracellular messenger molecules inositol trisphosphate and diacylglycerol. Inositol trisphosphate increases the intracellular calcium concentration, while diacylglycerol activates protein kinase C.
- phospholipid
- A type of lipid molecule that forms the lipid barrier of cell membranes. A phospholipid molecule includes a hydrophilic portion and a hydrophobic portion.
- phosphorylation
- Attachment of a phosphate group to specific amino acid residues of a target protein, carried out by a kinase enzyme.
- pituitary gland
- A master control endocrine gland at the base of the brain. The pituitary gland is controlled in turn by the hypothalamus.
- plasma membrane
- The external cell membrane separating the interior and the exterior of the cell.
- pons
- A major subdivision of the hindbrain.
- portal vessels
- Blood vessels that transport release factors secreted by hypothalamic neurons to the anterior pituitary gland, where they control the release of pituitary hormones.
- postcentral gyrus
- The gyrus located just posterior to the central sulcus, consisting of the primary somatosensory cortex.
- postsynaptic cell
- The target cell at a synapse.
- post-tetanic potentiation
- Synaptic potentiation that follows a sustained, high-frequency burst of presynaptic action potentials.
- precentral gyrus
- The gyrus located just anterior to the central sulcus, consisting of the primary motor cortex.
- premotor cortex
- Part of the frontal lobe anterior to the primary motor cortex, containing neurons that encode complex movements.
- preoptic area
- Part of the telencephalon just anterior and superior to the anterior end of the hypothalamus. The preoptic area is closely associated with the hypothalamus and is usually considered to be part of the hypothalamus.
- presynaptic cell
- The input cell at a synapse.
- prevertebral ganglia
- Sympathetic ganglia located in the abdominal cavity.
- primary visual cortex
- The visual cortical area that receives direct input from the lateral geniculate nucleus. The primary visual cortex (area V1; striate cortex) is located at the posterior pole of the occipital lobe.
- process
- Another name for a neurite.
- proprioceptor
- A sensory receptor neuron that detects limb or joint position, muscle length, or muscle tension.
- prosencephalon
- The forebrain.
- protein kinase A
- A kinase enzyme that is activated by cyclic AMP. The active kinase phosphorylates target proteins, such as ion channels.
- protein kinase C
- A kinase enzyme that is activated by an intracellular messenger, diacylglycerol, together with calcium. Diacylglycerol is produced from membrane lipid by the enzyme phospholipase C.
- proteoglycans
- A constituent of the extracellular matrix, formed by the combination of protein and glycosaminoglycan molecules.
- Purkinje cell
- The output cells of the cerebellum.
- putamen
- One of the basal ganglia of the forebrain. Together, the putamen and the caudate nucleus form the striatum.
- pyramidal cell
- A type of cortical neuron shaped like a pyramid, with a long apical dendrite originating from the narrow end of the cell.
- pyramids
- The fiber bundles consisting of descending axons from the primary motor cortex.
radial glial cell. A glial cell that extends from the ventricular zone to the marginal zone during early neural development. Migrating neurons leaving the ventricular zone follow the long thin radial glial cells.
- R -
- raphe nucleus
- A nucleus located near the midline of the brainstem, containing (among other neurons) the omnidirectional pause neurons that allow saccades to proceed.
- receptive field
- The portion of the sensory surface where stimuli affect the activity of a sensory neuron.
- receptor potential
- The change in membrane potential in a primary sensory receptor neuron in response to a sensory stimulus.
- receptor tyrosine kinase (or tyrosine receptor kinase)
- A membrane protein whose extracellular portion binds a neurotrophin. The intracellular portion of the molecule includes a tyrosine protein kinase region, which phosphorylates target proteins when the receptor is occupied.
- red nucleus
- A brainstem motor control nucleus that gives rise to the rubrospinal tract. Activation of the rubrospinal tract promotes limb flexion.
- release factor
- A substance released into portal vessels by hypothalamic neurosecretory neurons to control release of anterior pituitary hormones.
- Renshaw cell
- An inhibitory interneuron in the spinal cord that receives excitatory input from a motor neuron and makes inhibitory synapses back onto the same motor neuron.
- resting potential
- The steady state membrane potential of a neuron in the absence of incoming synaptic or sensory influences.
- reticular formation
- A diffuse network of neurons in the midbrain and hindbrain, involved in a variety of sensory and motor functions.
- reticulospinal tract
- A fiber tract consisting of descending axons from neurons in the reticular formation to spinal interneurons and motor neurons.
- retina
- The multilayered structure at the back of the eye responsible for light reception and processing of visual information. The retina consists of the neural retina, containing the neurons and glial cells, and the retinal pigmented epithelium, which absorbs stray light and supports the outer segments of photoreceptor cells.
- retinal (retinaldehyde)
- The light-absorbing chromophore group that is chemically attached to the opsin protein to form a visual pigment molecule.
- retinal ganglion cell
- The output cells of the retina, whose axons form the optic nerve and project to the lateral geniculate nucleus of the thalamus, the accessory optic system, and the suprachiasmatic nucleus of the hypothalamus.
- retinohypothalamic tract
- The fiber tract consisting of axons of retinal ganglion cells projecting to the suprachiasmatic nucleus of the hypothalamus.
- rhodopsin
- The visual pigment molecule of rod photoreceptors.
- rhombencephalon
- The hindbrain.
- rods
- A subtype of photoreceptor found in the vertebrate retina. Rods are more sensitive to light than cones are responsible for vision under dim illumination.
- rubrospinal tract
- The fiber tract containing axons descending to the spinal cord from the red nucleus of the brainstem.
- Ruffini corpuscle
- A slowly adapting skin mechanoreceptor that signals sustained pressure.
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