pyrogen Substance that causes marked increases in body temperature.
quarternary polypeptide Formed when different polypeptide chains assemble to become a large protein molecule; each polypeptide is called a subunit.
quiet biting (predatory) attack A form of aggressive behavior (premeditated murder and hunting behavior in humans) in which an animal will stalk and then bite the back of the neck of the prey object, ultimately killing it; lacks autonomic signs characteristic of defensive rage and, in nature, constitutes a form of hunting behavior.
radionuclide A natural or artificial nuclear (atomic) species that exhibits radioactivity.
rami communicantes White or gray communicating branches between spinal nerves and a sympathetic trunk.
raphe nuclei Midline nuclei situated in the brainstem that give rise to serotonin neurons that supply the brain and spinal cord.
rapsyn Cytoplasmic protein subunit required, in addition to agrin, for muscle-specific kinase to be effective and for signaling in the process of differentiation of the neuromuscular junction.
Rathke’s pouch An ectodermal diverticulum from which the anterior lobe of the pituitary is derived.
Raynaud’s disease Characterized by spasmodic vasoconstriction of arteries in the fingers and toes of upper and lower limbs, respectively; precipitated by the activation of sympathetic nervous system in response to cold or emotional stress; the digits appear cyanosed periodically due to the deoxygenation of stagnant blood.
receptive field Space in which a sensory receptor is located and where it produces the transduction of the stimuli in the somatic nervous system.
receptive field of a bipolar cell A circular area of the retina that, when stimulated by a light stimulus, changes the membrane potential of the bipolar cell; consists of "the receptive field center," which provides a direct input from the photoreceptors to the bipolar cells, and "receptive field surround," which provides an indirect input from the photoreceptors to the bipolar cells via horizontal cells; changes in membrane potential of bipolar cells in the receptive field center and surround are opposite.
receptors 1. Membrane-spanning proteins that serve as recognition sites for the binding of a neurotransmitter. 2. Cells that mediate sensory perception.
recruiting response Distinctive cortical electrical pattern characterized by a surface negative wave, which reaches a maximum amplitude rapidly and then slowly decreases in size produced by low-frequency stimulation of nonspecific thalamic nuclei; behavioral response from such stimulation is drowsiness.
rectifying synapse Type of synapse at which the current can pass in one direction (from presynaptic to postsynaptic neuron) but not in the reverse direction.
recurrent collaterals Collateral branches arising from the axon near their cell body in some neurons. See also Schaffer collaterals.
recurrent inhibition Type of inhibition resulting from activation of an alpha-motor neuron in spinal cord; mechanism involves excitation of a Renshaw cell (interneuron) via excitatory (cholinergic) collaterals of the alpha-motor neuron; Renshaw cells, in turn, inhibit (via glycinergic synapses) the activity of the same alpha-motor neuron.
referred pain Pain arising from deep visceral structures that is perceived as coming from a site different from its true origin. The phenomenon can be explained by the fact that the same dorsal horn neuron receives afferent signals from deep visceral, cutaneous, and skeletal muscle nociceptors; higher centers incorrectly ascribe the pain stimuli to the skin or skeletal muscle instead of coming from a deeper visceral structure.
refractory period Time required for the sodium channel to revert from inactivated to resting state (de-inactivation) of the neuron.
regeneration Recovery of neuronal injury.
relative refractory period Time immediately after the absolute refractory period, during which an action potential can be generated, but more depolarizing current is needed to shift the membrane potential to threshold level.
relay nuclei Serve to transmit sensory information to different sensory receiving areas of the cerebral cortex.
releasing hormones Hypothalamic peptides that regulate the release of pituitary hormones.
REM (paradoxical) sleep Phase of sleep characterized by a beta-type encephalographic rhythm (i.e., low voltage, fast frequency) and rapid eye movements. Renshaw cells Interneurons that make inhibitory (glycinergic) synapses on the alpha motor neurons and receive excitatory (cholinergic) collaterals from the same neurons. See also recurrent inhibition.
residual phase Time between psychotic episodes in schizophrenia, in which the patient is in touch with reality; however, the patient displays a flat affect, is withdrawn, and continues to have bizarre or eccentric (deviating from the normal pattern) thinking.
resting membrane potential Potential difference across the cell membrane during the resting state. restless legs syndrome A syndrome in which the patient complains of drawing pains in the calves and thighs that may also include creeping or crawling feelings. reticular activating system Pertains to the region of the teg-mentum of the brainstem (i.e., the reticular formation), which, when stimulated from sensory or other inputs, can cause arousal (and modulate sleep and wakefulness) by exciting neurons in the cerebral cortex.
reticular formation Central core of the brainstem extending from the medulla through the midbrain; consists of the numerous cell groups and ascending and descending axons; functions include: control of sensory, motor, and visceral processes, as well as states of consciousness.
reticular nucleus Nucleus situated in the lateral margin of the thalamus containing gamma aminobutyric acid (GABA)-ergic neurons that project to other thalamic nuclei.
reticulospinal tracts Pathways arising from the medulla (lateral tract) and pons ( medial tract) that pass to different levels of the spinal cord and modulate muscle tone. reticulotegmental nucleus Nucleus situated in the tegmentum of the pons whose axons project to the cerebellum.
retina Innermost layer of the eye. Consists of the following layers: (1) the pigment epithelium layer, which is the outermost layer consisting of melanin-containing cells that provide nutrition (glucose and essential ions) to photoreceptors and other cells associated with them; (2) the layer of rods and cones (photoreceptors); (3) the external limiting membrane, which contains the processes of rods and cones and Muller cells (homologous to the glial cells of the central nervous system [CNS]); (4) the outer nuclear layer, which contains the cell bodies of rods and cones; (5) the outer plexiform layer, which contains the axonal processes of rods and cones, processes of horizontal cells, and dendrites of bipolar cells (synaptic interaction between photoreceptors and horizontal and bipolar cells takes place in this layer); (6) the inner nuclear layer, which contains the cell bodies of amacrine cells, horizontal cells, and bipolar cells (amacrine and horizontal cells, sometimes called association cells, function as interneu-rons); (7) the inner plexiform layer, which contains the axons of bipolar cells, processes of amacrine cells, and dendrites of ganglion cells (synaptic interaction between different retinal cells takes place in this layer); (8) the layer of ganglion cells, which contains the cell bodies of multipolar ganglion cells (the final output from the retina following visual stimulation is transmitted to the CNS by the ganglion cells via their axons in the optic nerve); and (9) the optic nerve layer, which contains the axons of ganglion cells that form the optic nerve exiting from the eye. Neural retina is concerned with sensing and processing of light stimulus and includes the layer of rods and cones, external limiting membrane, outer nuclear layer, outer plexiform layer, inner nuclear layer, inner plexiform layer, layer of ganglion cells, and optic nerve layer. The retina is supplied by the central artery of the retina, which arises from the ophthalmic artery.
retinal detachment Disorder in which the pigment epithelium layer becomes detached from the neural retina; this occurs because the contact between the pigmented epithelium layer and the neural retina is mechanically unstable; the photore-ceptors can be damaged in this disorder because they may not receive nutrition that is normally provided by the pigment epithelium layer.
retinitis pigmentosa Visual disorder encompassing a diverse group of hereditary visual defects characterized by night blindness and a gradual loss of vision caused by degeneration of photoreceptors.
retinohypothalamic fibers Optic fibers that terminate in the region of the suprachiasmatic nucleus and are important in regulating the sleep-wakefulness cycle and circadian rhythms that govern endocrine functions.
retrograde amnesia Refers to difficulty in retrieving old memories.
retrograde degeneration Degenerative changes in the cell body and proximal part of the axon after damage to the axon.
retrograde messenger A substance (e.g., the neurotransmitter nitric oxide) that diffuses from the postsynaptic neuron into the presyn-aptic terminal and elicits further release of the neurotransmitter.
retrograde tracing technique Involves microinjection of a marker (e.g., horseradish peroxidase, fluorescent dyes, cholera toxin, or viruses) at the predicted terminal region of neurons whose cell bodies are to be determined. The marker is taken up by axon terminals and transported retrogradely into the neuronal cell bodies; the neurons labeled with the marker are visualized.
retrograde transneuronal degeneration Occurs in neurons sending inputs to an injured neuron: Terminals of the neuron syn-apsing with a chromatolytic neuron withdraw and are replaced by processes of glial cells; the neuron, from which the inputs to the chromatolytic neuron arise, eventually degenerates.
reuptake A mechanism in which the neurotransmitter (e.g., dopamine, norepinephrine) released in the synaptic cleft is actively transported back into the neuronal terminal where it is recycled for release or destroyed. reuptake-1 Process by which dopamine is released into the synaptic cleft and actively transported back into the neuronal terminal. reuptake-2 Process by which 10% of the dopamine that is released into the synaptic cleft (about 10%) is actively transported into the effector cells.
rhodopsin A photoreceptor pigment present in the rods; consists of a protein called opsin that is attached with a light-absorbing component, called retinal (an aldehyde form of vitamin A).
rhombencephalon Developing hindbrain, which will later form the metencephalon (pons) and myelencephalon (medulla).
rhombic lips Cells on the narrow roof plate of the developing fourth ventricle, which become the vermis.
rhombomeres Series of swellings that appear along the neural tube in development of the brainstem; contain neurons (sensory and motor) that innervate the various branchial arches.
ribosomes Cell organelles where amino acids assemble to form proteins according to instructions provided by messenger RNA; the amino acids are connected by peptide bonds to form a chain.
Rinne’s test Compares hearing by air conduction versus bone conduction. A vibrating tuning fork is held in the air near the affected ear and then the base of the tuning fork is placed on the mastoid process. If the sound perceived by the patient is louder when the tuning fork is placed on the mastoid process, when compared to the sound of the tuning fork held in the air, the patient is diagnosed as suffering from conductive hearing loss. If the sound perceived by the patient is louder when the tuning fork is placed in the air near the affected ear, the patient is diagnosed as suffering from sensorineural hearing loss. rising phase of the action potential See action potential. rods Rod-shaped photoreceptors that are highly sensitive and can detect dim light; specialized for night vision.
Romberg test Test of position sense in which the patient is asked to stand with feet together and eyes closed.
roof plate Aspect of the developing nervous system whose cells lie along the dorsal midline of the neural canal.
rostral Above the midbrain, rostral means "toward the front of the brain," and below the midbrain, rostral means "toward the cerebral cortex."
rostral basal pontine syndrome Disorder characterized by con-tralateral hemiplegia, loss of facial sensation, and loss of ability to chew; caused mainly by occlusion of paramedian branches of the basilar artery, affecting the corticospinal tract and sensory and motor components of cranial nerve V.
rostral interstitial nucleus Region for vertical gaze movements situated in the ventrolateral aspect of the rostral midbrain periaqueductal gray matter.
rostral pontine tegmental syndrome Characterized by ipsilat-eral loss of sensation to the face and ability to chew; contralat-eral loss of pain, temperature, and conscious proprioception from the body; as well as possible ataxia of movement; associated mainly with occlusion of the long circumferential branches of the basilar artery affecting sensory and motor nuclei of cranial nerve V, medial lemniscus, spinothalamic tracts, and possibly cerebellar afferent fibers contained in the middle cerebellar peduncle.
rostral spinocerebellar tract Arises from the cervical cord and supplies the anterior lobe of the cerebellum, conveying whole limb movement (from the Golgi tendon organ) to the anterior lobe from the upper limb.
rostral ventrolateral medullary pressor area (RVLM) Located caudal to the facial nucleus; involved in the maintenance of sympathetic tone of arteries.
rough endoplasmic reticulum Endoplasmic reticulum with ribo-somes attached to its membrane.
round window Secondary tympanic membrane in the inner ear.
rubrospinal tract Pathway from the red nucleus of midbrain to spinal cord, which facilitates spinal cord flexor motor neuron activity.
Ruffini’s corpuscles Low-threshold, slowly adapting receptors sensitive to stretching of the skin; provide information about the magnitude and direction of stretch.
saccadic movements Horizontal eye movements that occur quite rapidly, the duration of which is less than 50 milliseconds.
saccule An ovoid sac-like structure in the ear that is connected to the cochlea and the utricle; detects linear acceleration.
sacral cord Most caudal aspect of spinal cord situated between the thoracic cord rostrally and cauda equina caudally, containing five pairs of spinal nerves (S1-S5).
sacral plexus Consists of nerve roots from L4-S2, emerging from the lumbar enlargement. The sacral spinal nerves emerging from the conus medullaris contain parasympathetic fibers and motor fibers innervating the bladder and its sphincters, respectively.
sacral sparing Phenomenon in which damage to the spinotha-lamic tracts leaves pain, temperature, and simple tactile sensations intact in sacral dermatomes.
saltatory conduction Rapid conduction of an action potential along the axon when the action potential jumps from one node of Ranvier to another; the action potential becomes regenerated at the nodes of Ranvier, which are uninsulated, have a lower resistance, and are rich in Na+ (sodium) channels.
satiety center Medial hypothalamus, stimulation of which suppresses feeding behaviorand lesions of which result in hyperphagia.
scala tympani Lower division of the cochlear canal.
scala vestibuli Upper division of the cochlear canal.
Scarpa’s (vestibular) ganglion Consists of two ganglia; neurons located in these ganglia innervate receptors (hair cells) in the vestibular labyrinth in the ear.
Schaffer collaterals Collaterals of axons arising from CA3 hippocampal pyramidal cells, which project back to the CA1 field of the hippocampus.
schizophrenia Disorder characterized by a dysfunction in the thought process in which the ability to correctly test reality is lacking; includes delusional thought processes (i.e., false beliefs); disturbances in speech, appearance, and behavior; hallucinations (i.e., false perceptions, which are mostly auditory such as hearing voices); apathy; a paucity of emotion; and the presence of a catatonic posture.
Schwann cells Supporting cells of the peripheral nervous system responsible for the formation of myelin.
sclera Outermost layer of the eye; consists of a tough white fibrous tissue.
second-order neurons (neuron II) Carry sensory or motor stimulus orders down spinal cord tracts to synapse with third-order neurons.
secondary visual cortex Brodmann’s area 18.
sedatives Agents that have a generally depressive effect on central nervous system functions, and might produce a mild elevation of mood, sedation, sleep, behavioral disinhibition, and a decrease in anxiety (e.g., alcohol, barbiturates, and benzodiazepines).
seizures Paroxysmal events in which there is a significant change in the electroencephalogram that correlates with a change in behavior and/or consciousness.
serotonin-norepinephrine reuptake inhibitors (SNRIs) Class of antidepressant drug used to treat major depression, anxiety disorders, obsessive-compulsive disorder, and other phsycho-logical disorders
selective serotonin reuptake inhibitors (SSRIs) Drugs that inhibit reuptake of serotonin into the presynaptic terminal and increase the extracellular level of the serotonin available for binding to the postsynaptic receptor; used for the treatment of depression, anxiety disorders, and some personality disorders. Also known as serotonin-specific reuptake inhibitors.
sella turcica A saddle-like bony prominence on the upper surface of the sphenoid bone; with its dural covering, it forms the hypophyseal fossa in which the pituitary gland (hypophysis) is located.
semaphorins Class of secreted and membrane proteins that act as axonal growth cone guidance molecules; inhibitory signalers.
semicircular canals Three canals (anterior or superior, posterior and lateral or horizontal semicircular canals) in the labyrinth of the ear that lie in different planes and are perpendicular to each other; they detect angular acceleration.
sensorimotor cortex Where axons of the third-order neurons terminate.
sensorineural deafness Result of pathological lesions in the cochlea, cochlear nerve, or central auditory pathways.
sensory neglect (anosognosia) Disorder in which the patient denies having a disease condition or is unaware of it. It is caused by damage to the right posterior parietal cortex and can be demonstrated when the patient is asked to draw a clock and the numbers on the clock are all drawn on the right side of the clock.
sensory threshold Smallest intensity at which a particular sensation is detected in the somatic nervous system.
septa (septum) Sheet-like processes extending from the menin-geal layer of the dura deep into the cranial cavity, forming freely communicating compartments, which prevent displacement of the brain when the head moves.
septal area Limbic structure representing a major relay nucleus of the hippocampal formation.
septal rage Intensified aggressive response following lesions placed in the septal area of rats. Lesions of the region of the septal area and septum pellucidum in humans have also been reported to be associated with aggressive behavior as well.
septum pellucidum A structure that lies immediately ventral to the corpus callosum, is most prominent anteriorly, and consists of two thin-walled membranes separated by a narrow cleft, forming a small cavity (cavum of septum pellucidum).
serine One of the amino acids present in proteins.
serotonin (5-hydroxytryptamine; 5-HT) A small-molecule neurotransmitter synthesized from tryptophan (a nutritionally essential amino acid present in proteins).
serotonin hypothesis Theory that the etiology of schizophrenia involves deficiencies in serotonin.
serotonin receptors Group of six metabotropic and one ionotro-pic receptors located in central and peripheral neurons.
set-point Value at which the hypothalamus regulates food intake; governed by such factors as metabolic rate of the organism, immediate past history of food intake, and present level of food intake.
