A&P 12: The Central Nervous System Flashcards
Central nervous system (CNS)
brain and spinal cord
Cephalization
elaboration of the anterior portion of the CNS, along with an increase in the numbers of neurons in the head; reaches its highest level in the human brain
Brain
unimpressive in humans; 2 good fistfuls of quivering pinkish gray tissue, wrinkled like a walnut, with a consistency somewhat like cold oatmeal; average mass of about 1500g
Neural tube
the brain and spinal cord begin as this embryonic structure
Primary brain vesicles
prosencephalon, mesencephalon, and rhombencephalon
Prosencephalon
forebrain
Mesencephalon
midbrain
Rhombencephalon
hindbrain
Secondary brain vesicles
primary brain vesicles give rise to these, which include the telencephalon, the diencephalon, and the hindbrain constricts forming the metencephalon and myelencephalon
Telencephalon
endbrain
Diencephalon
interbrain
Metencephalon
afterbrain
Myelencephalon
spinal brain
Cerebrum
2 cerebral hemispheres
Brain stem
all of the midbrain and hindbrain structures (except the cerebellum) form this
Ventricles
continuous with one another and with the central canal of the spinal cord; have hollow chambers filled with CSF and lined by ependymal cells, a type of neuroglia
Lateral ventricles
paired, one deep within each cerebral hemisphere; large C-shaped chambers that reflect the pattern of cerebral grwoth; anteriorly, lie close together, separated only by a thin median membrane called the septum pellucidum
Septum pellucidum
thin median membrane separating the lateral ventricles; “transparent wall”
Third ventricle
each lateral ventricle communicates with this narrow ventricle in the diencephalon via an interventricular foramen
Interventricular foramen
each lateral ventricle communicates with the narrow 3rd ventricle in the diencephalon via this channel
4th ventricle
3rd ventricle is continuous with this via the cerebral aqueduct
Cerebral aqueduct
canal that runs through the midbrain
Lateral apertures
2 of 3 openings that mark the walls of the 4th ventricle; connect the ventricles to the subarachnoid space
Median aperture
1 of 3 openings that mark the side walls of the 4th ventricle; connect the ventricles to the subarachnoid space
Cerebral hemispheres
form the superior part of the brain; most conspicuous part of an intact brain, together, they account for 83% of total brain mass
Gyri
elevated ridges of tissue
Sulci
shallow grooves that separate the gyri
Fissures
deeper grooves that separate large regions of the brain
Longitudinal fissure
this median fissure separates the cerebral hemisphere
Transverse cerebral fissure
large fissure that separates the cerebral hemispheres from the cerebellum below
Central sulcus
lies in the frontal plane; separates the frontal lobe from the parietal lobe
Frontal lobe
part of the brain that overlies the frontal bone
Parietal lobe
part of the brain that overlies the parietal bone
Precentral & postcentral gyrus
borders the central sulcus anteriorly and posteriorly
Parieto-occipital sulcus
located more posteriorly on the medial surface of the hemisphere, separates the occipital lobe from the parietal lobe
Occipital lobe
part of the brain the overlies the occiptal bone
Lateral sulcus
deep groove that outlines the flaplike temporal lobe and separates it from the parietal and frontal lobes
Temporal lobe
part of the brain that overlies the temporal bone
Insula
5th lobe of the brain; “island”; buried deep with the lateral sulcus and forms part of its floor; covered by portions of the temporal, parietal, and frontal lobes
Cerebral cortex
“executive suite” of the nervous system; where our conscious mind is found; enables us to be aware of ourselves and our sensations, to communicate, remember, understand, and initiate voluntary movements; composed of gray matter (neuron cell bodies, dendrites, associated glia and blood vessels but no fiber tracts); 40% of brain mass even though only 2-4mm thick
Contralateral
each hemisphere is chiefly concerned with the sensory and motor functions of the opposite side of the body
Motor areas
parts of the cortex which control voluntary movement; lie in the posterior part of the frontal lobes - primary ___ cortex, pre____ cortex, Broca’s area, and the frontal eye field
Primary (somatic) motor cortex
located in the precentral gyrus of the frontal lobe of each hemisphere
Pyramidal cells
these large neurons in the gyri allow us to consciously control the precise or skilled voluntary movements of our skeletal muscles
Somatotopy
mapping of the body in CNS structures
Motor homunculus
“little man” in the brain representing various regions of motor control throughout the body
Premotor cortex
just anterior to the precentral gyrus in the frontal lobe; helps plan movements; can control voluntary actions that depend on sensory feedback
Broca’s area
lies anterior to the inferior region of the premotor area; has long been considered to be (1) present in 1 hemisphere only (usually the left) and (2) a special motor speech area that directs the muscles involved in speech production
Frontal eye field
located partially in and anterior to the premotor cortex and superior to Broca’s area; controls voluntary movement of the eyes
Primary Somatosensory cortex
resides in the postcentral gyrus of the parietal lobe, just posterior to the primary motor cortex
Spatial discrimination
ability of neurons to identify the body region being stimulated
Somatosensory homunculus
part of the “little man” in the brain that governs senses
Somatosensory association cortex
lies just posterior to the primary somatosensory cortex; has many connections with it; major function: integrate sensory inputs (temperature, pressure, etc) relayed to it via the primary somatosensory cortex to produce an understanding of an object being felt (size, texture, & relationship of its parts)
Primary visual (striate) cortex
seen on the extreme posterior tip of the occiptal lobe; most of it is buried deep in the calcarine sulcus in the medial aspect of the occipital lobe; = largest coritcal sensory area; receives visual information that originates on the retina of the eye; there is a contralateral map of visual space on this, analagous to the body map on the somatosensory cortex
Visual association area
surrounds the primary visual cortex and covers much of the occipital lobe; uses past visual experiences to interpret visual stimuli
Primary auditory cortex
located in the superior margin of the temporal lobe abutting the lateral sulcus; sound energy exciting the hearing receptors of the inner ear causes impulses to be transmitted to this, where they are interpreted as pitch, loudness, and location
Auditory association area
more posterior than the primary auditory cortex; permits the perception of the sound stimulus, which we “hear” as speech, a scream, music, thunder, noise, etc.; memories of sounds heard in the past appear to be stored here for reference
Primary olfactory cortex
lies on the medial aspect of the temporal lobe in a small region called the piriform lobe which is dominated by the hooklike uncus; afferent fibers from smell receptors in the superior nasal cavities send impulses along the olfactory tracts that are ultimately relayed to the olfactory cortices; outcome = conscious awareness of different odors
Rhinencephalon
olfactory cortex is part of this primitive part, which includes all parts of the cerebrum that receive olfactory signals - the orbitofrontal cortex, uncus, and associated regions located on or in the medial aspects of the temporal lobes, and the protruding olfactory tracts and bulbs that extend to the nose
Gustatory cortex
region involved in perceiving taste stimuli; located in the insula just deep to the temporal lobe
Multimodal association areas
complexly connected areas that make up most of the cortex and receive inputs from multiple senses and send outputs to multiple areas
Anterior association area
in the frontal lobe; also called the prefrontal cortex; most complicated cortical region of all; involved with intellect, complex learning abilities (cognition), recall, and personality; contains working memory (necessary for abstract ideas, judgment, reasoning, persistence, and planning)
Posterior association area
large region encompassing parts of the temporal, parietal, and occipital lobes; plays a role in recognizing patterns and faces, localizing us and our surroundings in space, and binding different sensory inputs into a coherent whole
Limbic association area
area including the cingulate gyrus, parahippocampal gyrus, and hippocampus; part of the limbic system; provides the emotional impact that makes a scene important to us; the hippocampus establishes memories that allow us to remember an incident
Lateralization
hemispheres’ division of labor; each hemisphere has abilities not completely shared by its partner
Cerebral dominance
designates the hemisphere that is dominant for language
Cerebral white matter
2nd of 3 basic regions of each cerebral hemisphere; internal; responsible for communication between cerebral areas and between the cerebral cortex and lower CNS centers
Association fibers
connect different parts of the same hemisphere; short ones connect adjacent gyri; long ones are bundled into tracts and connect different cortical lobes
Commissural fibers
connect corresponding gray areas of the 2 hemispheres
Commissures
allow the 2 hemispheres to function as a coordinated whole
Corpus callosum
largest commissure; lies superior to the lateral ventricles, deep within the longitudinal fissure
Anterior & posterior commissures
less prominent than the corpus callosum
Projection fibers
either enter the cerebral cortex from lower brain or cord centers or descend from the cortex to lower areas; sensory information reaches the cerebral cortex and motor output leaves it through these fibers
Internal capsule
at the top of the brain stem, the projection fibers on each side form a compact band called this, that passes between the thalamus and some of the basal nuclei
Corona radiata
“radiating crown”; beyond the basal nuclei, the projection fibers radiate fanlike through the cerebral white matter to the cortex
Basal nuclei (basal ganglia)
deep within the cerebral white matter is the 3rd basic region of each hemisphere; a group of subcortical nuclei; includes the caudate nucleus, putamen, and globus pallidus
Caudate nucleus
comma-shaped part of the basal nuclei/ganglia; arches superiorly over the diencephalon; with the putamen, forms the striatum
Putamen
with the caudate nucleus, forms the striatum; “pod”; with the globus pallidus forms the lens-shaped mass called the lentiform nucleus
Striatum
named because the fibers of the internal capsule passing through them creates a striped appearance
Globus pallidus
“pale globe”; with the putamen, forms a lens-shaped mass, sometimes called the lentiform nucleus
Diencephalon
forming the central core of the forebrain and surrounded by the cerebral hemispheres, it consists largely of 3 paired structures - the thalamus, the hypothalamus, and epithalamus
Thalamus
consists of bilateral egg-shaped nuclei, which form the superolateral walls of the 3rd ventricle; Greek for “inner room”; deep well-hidden brain region that meks up 80% of the diencephalon
Interthalamic adhesion
in most people, this intermediate mass connects the nuclei of the thalamus
Hypothalamus
named for its position below the thalamus; caps the brain stem and forms the inferolateral walls of the 3rd ventricle; merges into the midbrain inferiorly; extends from the optic chiasma to the posterior margin of the mammillary bodies; main visceral control center of the body; vitally important to overall body homeostasis
Mammillary bodies
paired pealike nuclei that bulge anteriorly from the hypothalamus; = relay stations in the olfactory pathways
Infundibulum
between the optic chiasma and mammillary bodies; a stalk of hypothalamic tissue that connects the pituitary gland to the base of the hypothalamus
Pituitary gland
neuroendocrine gland located beneath the brain that serves a variety of functions including regulation of gonads, thyroid, adrenal cortex, lactation, and water balance
Epithalamus
most dorsal portion of the dienchephalon; forms the roof of the 3rd ventricle
Pineal gland
extending from the posterior border of the epithalamus; also called ___ body; secretes melatonin and along with hypothalamic nuclei, helps regulate the sleep-wake cycle
Midbrain
located between the diencephalon and the pons; on its ventral aspect, has 2 bulging cerebral peduncles that form vertical pillars that seem to hold up the cerebrum
Cerebral peduncles
“little feet of the cerebrum; 2 bulges on the midbrain that form vertical pillars that seem to hold up the cerebrum
Corpora quadrigemina
“quadruplets”; the largest midbrain nuclei; raise 4 domelike protrusions on the dorsal midbrain surface
Superior coliculi
superior pair of the “quadruplets”; = visual reflex centers that coordinate head and eye movements when we visually follow a moving objects, even if we are not consciously looking at it
Inferior coliculi
inferior pair of the “quadruplets”; part of the auditory relay from the hearing receptors of the ear to the sensory cortex; also act in reflexive responses to sound such as the startle reflex
Substantia nigra
1 of 2 pigmented nuclei embedded in each side of the midbrain white matter; located deep to the cerebral peduncle; dark color reflects a high content of melanin, a precursor of the neurotransmitter (dopamine) released by these neurons; functionally linked to the basal nuclei; degeneration of its neurons = ultimate cause of Parkinson’s
Red nucleus
1 of 2 pigmented nuclei of the midbrain white matter; oval; lies deep to the substantia nigra; reddish hue due to its rich blood supply and to the presence of iron pigment in its neurons; = relay nuclei in some descending motor pathways that effect limb flexion; embedded in the reticular formation (system of small nuclei scattered through the core of the brain stem)
Pons
bulging brain stem region wedged between the midbrain and the medulla oblongata; dorsally, the 4th ventricle separates it from the cerebellum; chiefly composed of conduction tracts oriented in 2 directions (deep = longitudinally; superficial = transversely/dorsally)
Medulla oblongata (medulla)
most inferior part of the brain stem; blends imperceptibly into the spinal cord at the level of the foramen magnum of the skull; together with the pons, forms the ventral wall of the 4th ventricle
Pyramids
flanking the midline on the medulla’s ventral aspect are 2 longitudinal ridges called this, formed by the large corticospinal tracts descending from the motor c`ortex
Decussation of the pyramids
the crossing over of the fibers just above the medulla-spinal cord junction; as a result of this crossover, each cerebral hemisphere chiefly controls the voluntary movements of muscles on the opposite side of the body
Olives
oval swellings caused mainly by the wavy folds of gray matter of the underlying inferior olivary nuclei
Inferior olivary nuclei
relay sensory information on the degree of stretch in muscles and joints to the cerebellum
Cochlear nuclei
auditory relays
Vestibular nuclei
mediate responses that maintain equilibrium
Nuclei gracilis & nucleus cuneatus
most prominent of the nuclei associated with ascending sensory tracts; associated with the medial lemniscus tract; serve as relay nuclei in a pathway which general somatic sensory information ascends from the spinal cord to the somatosensory cortex
Cerebellum
cauliflower-like “small brain”; 11% of total brain mass; dorsal to the pons and medulla & to the intervening 4th ventricle; protrudes under the occipital lobes, from which it is separated by the transverse cerebral fissure; provides the precise timing and appropriate patterns of skeletal muscle contraction for smooth, coordinated movements and agility needed for daily living; activity occurs subconsciously
Vermis
wormlike part that connects the 2 apple-sized cerebellar hemispheres
Cerebellar hemispheres
2 halves of the cerebellum
Folia
surface of the cerebellum is heavily convoluted with fine, transversely oriented pleatlike gyri known as “leaves”
Anterior, posterior, and flocculonodular lobes
deep fissures subdivide each cerebellar hemisphere into these lobes; 3rd cannot be seen in a surface view
Purkinje cells
large cells with extensively branched dendrites; only cortical neurons that send axons through the white matter to synapse with the central nuclei of the cerebellum
Arbor vitae
the distinctive pattern of white matter in the cerebellum resembles a branching tree, a pattern fancifully called the “tree of life”
Ipsilateral
virtually all fibers entering and leaving the cerebellum are this, which means from and to the same side of the body
Superior cerebellar peduncles
stalks connecting the cerebellum and midbrain; carry instructions from neurons in the deep cerebellar nuclei to the cerebral motor cortex via thalamic relays
Middle cerebellar peduncles
stalks that carry on one-way communications from the pons to the cerebellum, advising the cerebellum of voluntary motor activities initiated by the motor cortex (via relays in the pontine nuclei)
Inferior cerebellar peduncles
stalks that connect medulla and cerebellum; convey sensory information to the cerebellum from (1) muscle proprioceptors throughout the body, and (2) the vestibular nuclei of the brain stem, which are concerned with equilibrium and balance
Limbic system
group of structures located on the medial aspect of each cerebral hemisphere and diencephalon; its cerebral structures encircle the upper part of the brain stem; includes the amygdaloid body
Amygdaloid body
an almond-shaped nucleus that sits on the tail of the caudate nucleus, and other parts of the rhinencephalon; especially important in emotions; critical to responding to perceived threats with fear or aggression
Fornix
“arch”; with other fiber tracts, link the limbic system regions together
Cingulate gyrus
part of the limbic system especially important in emotions; plays a role in expressing our emotions through gestures and in resolving mental conflicts when we are frustrated
Psychosomatic illnesses
emotion-induced illnesses (ex. high blood pressure, heartburn)
Hippocampus
part of the limbic system that plays a role in memory (along with the amygdaloid body)
Reticular formation
extends through the central core of the medulla, pons, and midbrain; composed of loosely clustered neurons in what is otherwise white matter
Raphe nuclei
column of neurons along the midline of the brain stem
Medial (large cell) group of nuclei; lateral (small cell) group of nuclei
columns of neurons that flank the raphe nuclei in the brain stem
Reticular activating system (RAS)
sends a continuous stream of impulses to the cerebral cortex, keeping it alert and conscious and enhancing its excitability
Electroencephalogram (EEG)
a recording of the electrical activity of neurons; measures voltage differences between various cortical areas
Brain waves
patterns of neuronal electrical activity
Alpha waves
8-13 Hz; relatively regular and rhythmic, low-amplitude, synchronous waves; in most cases, indicate that a brain is “idling” - a calm, relaxed state of wakefulness
Beta waves
14-30 Hz; rhythmic, but less regular than alpha waves and with a higher frequency; occur when we are mentally alert (concentrating on a problem or visual stimulus)
Theta waves
4-7 Hz; irregular; common in children; uncommon in awake adults, but may appear when concentrating
Delta waves
4 Hz or less; high-amplitude waves seen during deep sleep and when the RAS is damped, such as during anesthesia; in awake adults, indicate brain damage
Epileptic seizures
reflect a torrent of electrical discharges by groups of brain neurons; during their uncontrolled activity, no other messages can get through; loss of consciousness, uncontrollable jerking
Aura
phenomenon in which many seizure sufferers experience a sensory hallucination, such as a taste, smell, or flashes of light just before the seizure begins; helpful because it gives the person time to lie down and avoid falling
Consciousness
encompasses conscious perception of sensations, voluntary initiation and control of movement, and capabilities associated with higher mental processing (memory, logic, judgment, perseverance, etc)
Fainting (syncope)
brief loss of consciousness; most often, indicates inadequate cerebral blood flow due to low blood pressure
Coma
significant unresponsiveness to sensory stimuli for an extended period
Brain death
a dead brain in an otherwise living body
Non-rapid eye movement (NREM) sleep
alternates with REM sleep; 1st 30-45 minutes of sleep = 1st 2 stages
Slow-wave sleep
NREM stages 3 & 4; most nightmares and night terrors occur in this stage; presumed to be restorative sleep
Rapid eye movement (REM) sleep
alternates with NREM sleep; oxygen use is tremendous during this stage (greater than when awake); most dreaming occurs during this stage
Narcolepsy
people with this condition lapse abruptyly into REM sleep from the awake state; these sleep episodes last about 15 minutes, can occur without warning, and are often triggered by a pleasurable event (joke, game, etc)
Insomnia
chronic inability to obtain the amount or quality of sleep needed to function adequately during the day
Sleep apnea
temporary cessation of breathing during sleep
Broca’s area
patients with lesions involving this area can understand language but have difficulty speaking (and sometimes cannot write, type, or use sign language)
Wernicke’s area
patients with lesions involving this area are able to speak but produce a type of nonsense often referred to as a “word salad”; have great difficulty understanding language
Memory
storage and retrieval of information; essential for learning and incorporating our experiences into behavior
Short-term memory (STM)
working memory; limited to 7 or 8 chunks of information
Long-term memory (LTM)
limitless capacity, however, our ability to store and retrieve info declines with aging; transferring info from STM to this influenced by emotional state, rehearsal, association, and automatic memory
Memory consolidation
fitting new facts into the categories of knowledge already stored in the cerebral cortex
Declarative (fact) memory
entails learning explicit info; related to conscious thought and our ability to manipulate symbols and language
Procedural memory
skill memory
Motor memory
memory of a particular motion, like riding a bike
Emotional memory
memory inspired by emotion
Long-term potentiation (LTP)
persistent increase in synaptic strength that has been shown to be crucial for memory formation
Meninges (singular = meninx)
3 connective tissue membranes that lie just external to the CNS organs; cover and protect the CNS, protect blood vessels and enclose venous sinuses, contain CSF, and form partitions in the skull
Dura mater
“tough mother” strongest meninx; 2-layered sheet of fibrous connective tissue that surround the brain
Dural venous sinuses
the brain’s 2 dural layers are fused together except in certain areas, where they separate to encloses these cavities that collect venous blood from the brain and direct it into the internal jugular veins of the neck
Dural septa
flat partitions that subdivide the cranial cavity; limit excessive movement of the brain within the cranium
Falx cerebri
large sickle-shaped fold that dips into the longitudinal fissure between the cerebral hemispheres; anteriorly it attaches to the crista galli of the ethmoid bone
Falx cerebelli
small midline partition that runs along the vermis of the cerebellum
Tentorium cerebelli
resembling a tent over the cerebellum, this nearly horizontal dural fold extends into the transverse fissure between the cerebral hemispheres, which it helps to support, and the cerebellum
Arachnoid mater
middle meninx; forms a loose brain covering; never dips into the sulci at the cerebral surface; separated from the dura mater by a narrow serous cavity (subdural space) which contains a film of fluid; fine and elastic so blood vessels poorly protected
Subdural space
narrow serous cavity between the dura mater and the arachnoid mater, which contains a film of fluid
Subarachnoid space
beneath the arachnoid membrane is this wide space in which spiderlike extensions secure the arachnoid mater to the underlying pia mater; filled with CSF; contains the largest blood vessels serving the brain
Pia mater
“Gentle mother”; delicate connective tissue; only meninx that clings tightly to the brain
Pia mater
“Gentle mother”; delicate connective tissue; only meninx that clings tightly to the brain
Cerebrospinal fluid
Found in and around the brain & spinal cord; forms a liquid cushion that gives buoyancy to CNS structures
Choroid plexuses
Hang from the roof of each ventricle; form CSF
Blood brain barrier
Protective mechanism that helps maintain a stable environment for the brain
Concussion
Alteration in brain function, usually temporary, following a blow to the head
Contusion
More serious concussions can bruise the brain & cause permanent neurological damage, a condition called this
Subdural or subarachnoid hemorrhage
Bleeding from ruptured vessels under the dura mater or arachnoid
Cerebral edema
Swelling of the brain
Cerebrovascular accidents (CVAs)
Strokes; “brain attacks”; single most common nervous system disorder; 3rd leading cause of death in North America
Ischemia
“To hold back blood”; deprivation of blood supply to any tissue; impairs the delivery of oxygen and nutrients to cells
Transient ischemic attacks (TIAs)
Temporary episodes of reversible cerebral ischemia; last from 5-50 min
Alzheimer’s disease (AD)
Progressive degenerative disease of the brain, ultimately resulting in dementia
Dementia
Mental deterioration
Parkinson’s disease
Typically strikes people in their 50s & 60s; results from a degeneration of the dopamine-releasing neurons of the substantia nigra
Huntington’s disease
Fatal hereditary disorder, strikes during middle age; massive degeneration of the basal nuclei & cerebral cortex
Spinal cord
2-way conduction pathway to & from the brain
Spinal dura mater
Single layer; not attached to the bony walls of the vertebral column
Epidural space
Between the bony vertebrae & the spinal dura mater; filled with a soft padding of fat & a network of veins
Lumbar puncture (tap)
Subarachnoid space within the meningeal sac inferior to that point - ideal spot for removing CSF for testing
Conus medullaris
Inferiorly the spinal cord terminates in this tapering cone-shaped structure
Filum terminale
Fibrous extension of the conus covered by pia mater, extends inferiorly from the conus medullaris to the coccyx; anchors the spinal cord so it is not jostled by body movements
Denticulate ligaments
Saw-toothed shelves of pia mater; secure the spinal cord to the tough dura mater meninx throughout its length
Cervical & lumbar enlargements
Obvious enlargements in the cervical & lumbosacral regions, where the nerves serving the upper & lower limbs arise
Cauda equina
Collection of nerve roots at the inferior end of the vertebral canal; resembles a horse’s tail
Ventral (anterior) median fissure
Deeper of the two grooves marking the surface of the spinal cord
Dorsal (posterior) median sulcus
More shallow of the 2 grooves marking the surface of the spinal cord
Gray commissure
Mirror image lateral gray masses connected by a crossbar of gray matter; encloses the central canal
Dorsal (posterior) horns
2 dorsal projections of the gray matter
Ventral (anterior) horns
Two ventral projections of the gray matter of the spinal cord
Lateral horns
Thoracic & superior lumbar segments of the cord have this additional pair of gray matter columns
Ventral roots
Ventral rootlets fuse together to become the ___ ___ of the spinal cord
Dorsal roots
Afferent fibers carrying impulses from peripheral sensory receptors form the ___ ___ of the spinal cord that fan out b4 they enter the spinal cord
Dorsal root ganglion (spinal ganglion)
enlarged region of the dorsal root; cell bodies of associated sensory neurons are found here
Spinal nerves
the dorsal and ventral roots are very short and fuse laterally to form these
Zones of spinal gray matter
somatic sensory (SS), visceral sensory (VS), visceral autonomic (VM), somatic motor (SM)
White columns
3 funiculi; white matter on each side of the spinal cord, named according to their position as dorsal (posterior), lateral, and ventral (anterior)
First-order neurons
neurons with cell bodies residing in a ganglion (dorsal root or cranial); conduct impulses from the cutaneous receptors of the skin and from proprioceptors to the spinal cord or brain stem, where they synapse with 2nd-order neurons
Second-order neurons
neurons with cell bodies that reside in the dorsal horn of the spinal cord or in medullary nuclei; transmit impulses to the thalamus or to the cerebellum
Third-order neurons
neurons with cell bodies in the thalamus; relay impulses to the somatosensory cortex of the cerebrum (none of these in the cerebellum)
Dorsal column-medial lemniscal pathways
mediate precise, straight-through transmission of inputs from a single type (or a few related types) of sensory receptor that can be localized precisely on the body surface, such as discriminative touch and vibrations
Dorsal white column
dorsal column-medial lemniscal pathways are formed by the paired tracts of the ___ ___ ___ of the spinal cord - fasciculus cuneatus, fasciculus gracilis, and the medial lemniscus
Spinothalamic pathways
receive input from many different types of sensory receptors and make multiple synapses in the brain stem
Lateral & Ventral (Anterior) Spinothalamic Tracts
Spinothalmic pathways consist of these tracts; fibers in these pathways primarily transmit impulses for pain and temperature but also for coarse touch and pressure
Ventral & Dorsal Spinocerebellar tracts
3rd ascending pathway consists of these tracts; convey info about muscle or tendon stretch to the cerebellum, which uses this info to coordinate skeletal muscle activity; these pathways do not contribute to conscious sensation
Indirect (multineuronal) pathways
brain stem motor nuclei and all motor pathways except the pyramidal pathways; formerly called the extrapyramidal system
Reticulospinal & vestibulospinal tracts
maintain balance by varying the tone of postural muscles
Rubrospinal tracts
control flexor muscles
Tectospinal tracts
with the superior colliculi, mediate head movements in response to visual stimuli
Paralysis
loss of motor function
Parasthesias
abnormal sensations
Flaccid paralysis
severe damage to ventral root or ventral root horns results in this of the skeletal muscles served
Spastic paralysis
when only the upper motor neurons of the primary motor cortex are damaged, this type of paralysis occurs
Paraplegia
if transection of the spinal cord occurs between T1 and L1, both lower limbs are affected and this type of paralysis occurs
Quadriplegia
if an injury occurs in the cervical region, all 4 limbs are affected, and this type of paralysis occurs
Spinal shock
anyone with a spinal cord transection must be watched for symptoms of this transient period of functional loss that follows the injury; immediately depresses all reflex activity caudal to the lesion site; bowel/bladder reflexes stop, blood pressure falls, and all muscles (somatic and visceral) below the injury site are paralyzed and insensitive
Postpolio syndrome
many survivors of the great polio epidemic of the late 1940s and 1950s have begun to experience extreme lethargy, sharp burning pains in their muscles, and progressive muscle weakness and atrophy
Neural plate
the ectoderm (cell layer at the dorsal surface) thickens along the dorsal midline axis of the embryo to form this
Neural groove
the neural plate invaginates, forming this, flanked by neural folds
Neural crest
small groups of neural fold cells migrate laterally from between the surface ectoderm and the neural groove, forming this; give rise to some neurons destined to reside in ganglia
Neural tube
as the neural groove deepens, the superior edges of the neural folds fuse, forming this, which soon detaches from the surface ectoderm and sinks to a deeper position
Alar & basal plates
by the 6th week of pregnancy, each side of the developing spinal cord has these 2 recognizable clusters of neuroblasts that have migrated outward from the original neural tube
Cerebral palsy
neuromuscular disability in which the voluntary muscles are poorly controlled or paralyzed as a result of brain damage; may be caused by temporary lack of oxygen during a difficult delivery
Anencephaly
“without brain”; the cerebrum and part of the brain stem never develop because the neural folds fail to fuse rostrally; child is vegetative, unable to see, hear, or process sensory inputs; muscles are flaccid, and no voluntary movement is possible
Spina bifida
“forked spine”; results from incomplete formation of the vertebral arches and typically involves the lumbosacral region; laminae and spinous processes are missing on at least 1 vertebra
