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Flashcards in Neuro Anatomy Deck (71)


"cerebral hemispheres"

consists of 6 lobes on each side


Frontal lobe

Precentral gyrus: primary motor cortex for voluntary muscle activation

Prefrontal cortex: controls emotions and judgements

Broca's area: controls motor aspects of speech


Parietal lobe

Postcentral gyrus: primary sensory cortex for integration of sensation
-receives fibers conveying touch, proprioception, pain and temperature sensations from OPPOSITE side of the body


Temporal lobe

Primary auditory cortex: receives/processes auditory stimuli

Associative auditory cortex: processes auditory stimuli

Wenicke's area: language apprehension


Occipital lobe

Primary visual cortex: receives/processes visual stimuli

Visual association cortex: processes visual stimuli



deep within lateral sulcus, associated with visceral functions


Limbic system

consists of the limbic lobe (cingulate, parahppocampal and subcallosal gyri), hippocampal formation, amygdaloid nucleus, hypothalamus and anterior nucleus of the thalamus

phylogenetically the oldest part of the brain- concerned with instincts and emotions contributing to preservation of the individual

Basic functions: feeding, aggression, emotions and endocrine aspects of sexual response


White matter

myelinated nerve fibers located centrally

1-Transverse (commissural) fibers: interconnect the 2 hemispheres, including corpus callosum (the largest), anterior commissure and hippocampal commissure.

2-Projection fibers: connect cerebral hemispheres with other portions of the brain and SC

3- Association fibers: connect different portions of the cerebral hemispheres, allowing cortex to function as integrated whole

Anterior, lateral and posterior white columns or funiculi in the SC


Basal ganglia

masses of gray matter deep within cerebral hemispheres
-includes: striatum (caudate nucleus, nucleus accumbuns, putamen), globus pallidus (external & internal segment), subthalamic nucleus and substantia nigra.

"Lenticular nucleus" = putamen and globus pallidus

forms an associated motor system (extrapyramidal system) with other nuclei in the subthalamus and the midbrain

consists of multiple circuits:
1- oculomotor circuit (caudate loop)
2- motor loop (putamen loop)
3-limbic circuit


Oculomotor circuit

"caudate loop"
associated motor system of the BG

originates in frontal and supplementary motor eye fields

projects to caudate

functions with saccadic eye movements


Motor loop

"Putamen loop"
associated motor system of the BG

originates in precentral motor and postcentral somatosensory areas

projects to and excites putamen neurons; putamen cells inhibit globus pallidus neurons, which in turn boosts activity in the ventral lateral nucleus and supplemental motor area

functions to scale amplitude and velocity of movements reinforces selected pattern, suppressed conflicting patterns; preparatory for movement


Limbic circuit

associated motor system of the BG

originates in prefrontal and limbic areas of cortex to BG to prefrontal cortex

functions to organize behaviors (executive functions, problem solving, motivation) and for procedural functions


Diencephalon consists of:




sensory nuclei: integrate and relay sensory information from body, face, retina, cochlea, and taste receptors to cerebral cortex and subcortical regions
*smell (olfaction) is only exception

Motor nuclei: relay motor info from cerebellum and globus pallidus to percentile motor cortex

Other nuclei: assist in integration of visceral and somatic functions



involved in control of several functional pathways for sensory, motor and reticular function



integrates and controls the functions of the ANS and the neuroendocrine system

maintains body homeostasis



habenular nuclei: integrate olfactory, visceral and somatic afferent pathways

pineal gland: secretes hormones that influence the pituitary gland and several other organs; influences circadian rhythm


Brainstem consists of:

1-midbrain (mesencephalon)
-connects pons to cerebrum
-superior peduncle connects midbrain to cerebellum

2- pons
-connects medulla oblongata to midbrain- allows passage of important ascending and descending tracts

3- medulla oblongata
-connects SC to pons



connects pons to cerebrum

superior peduncle connects midbrain to cerebellum

contains cerebral peduncles (2 lateral halves), each divided into an anterior part or basis (crus cerebra and substantia nigra) and a posterior part (tegmentum)

Tegmentum contains all ascending tracts and some descending tracts; the red nucleus receives fibers from the cerebellum; is the origin for the rubrospinal tract, important for coordination;
-contains CN nuclei: oculomotor and trochlear

Substantia nigra is a large motor nucleus connecting with the BG and cortex; important in motor control and muscle tone

Superior and inferior colliculi

Periaqueductal gray: contains endorphin-producing cells (important for the suppression of pain) and descending autonomic tracts


Superior vs. inferior colliculi

Superior: important relay station for vision and visual reflexes

Inferior: important relay station for hearing and auditory reflexes



connects the medulla oblongata to the midbrain, allowing passage of important ascending and descending tracts

middle cerebellar peduncle -anterior basal acts as a bridge to cerebellum

midline raphe nuclei project widely and are important for modulating pain and controlling arousal

tegmentum contains several important CN nuclei: abducens, trigeminal, facial, vestibulocochlear


Medulla oblongata

connects SC with pons

contains relay nuclei of dorsal columns (gracilis and cuneatus); fibers cross to give rise to medial lemniscus

inferior cerebellar peduncle relays dorsal spinocerebellar tract to cerebellum

corticospinal tracts cross (decussate) in pyramids

Medial longitudinal fasciculus arises from vestibular nuclei and extends t/o brainstem and upper cervical SC; important for control of head movements and gaze stabilization (vestibular-ocular reflex)

olivary nuclear complex connects cerebellum to brainstem and is important for voluntary movement control

contains several important CN nuclei: hypoglossal, dorsal nucleus of vagus and vestibulocochlear

contains important centers for vital functions: cardiac, respiratory and vasomotor centers



located behind dorsal pons and medulla in posterior fossa
-joined to brainstem by 3 pairs of peduncles
-comprises 2 hemispheres and midline vermis


1-Archicerebellum (flocculonodular lobe)
-connects with vestibular system
-concerned with equilibrium and regulation of muscle tone; helps coordinate vestibule-ocular reflex

2- Paleocerebellum (rostral cerebellum, anterior lobe; spinocerebellum)
-receives input from proprioceptive pathways
-concerned with modifying muscle tone and synergistic actions of muscles
-important in maintenance of posture and voluntary movement

3-Neocerebellum (cerebellar hemisphere, posterior lobe, pontocerebellum)
-receives input from cortiopontocerebellar tracts and olivocerebellar fibers
-concerned with the smooth coordination of voluntary movements
-ensures accurate force, direct and extent of movement
-important for motor learning, sequencing of movements and visually triggered movements
-may have role in assisting cognitive function and mental imagery


central gray matter consists of:

Anterior horns: contain cell bodies that give rise to efferent (motor) neurons
-alpha motor neurons to affect muscles
-gamma motor neurons to affect muscle spindles

Posterior horns: contain afferent (sensory) neurons with cell brides located in the dorsal root ganglia

Central gray commissure with central canal

2 enlargements: cervical and lumbosacral for origins of nerves of UE and LEs

Lateral horn is found in thoracic and upper lumbar segments for preganglionic fibers of the ANS


Ascending fiber systems/sensory pathways

1- Dorsal columns/medial lemniscal system:

2- Spinothalamic tracts

3-Spinocerebellar tracts

4- Spinoreticular tracts


Dorsal columns/medial lemniscal system:

convey sensations of proprioception, vibration and tactile discrimination

divided into:
1-fasciculus cuneatus (UE tracts, laterally located)
2- Faciculus gracilis (LE tracts, medially located

neurons ascend to medulla where fibers cross = lemniscal decussation) to form medial lemniscus as ascend to thalamus and then to somatosensory cortex


Spinothalamic tracts:

convey sensations of pain and temperature (lateral spinothalamic), and crude touch (anterior spinothalamic)

tracts ascend 1 or 2 ipsilateral SC segments (Lissauer's tract), synapse and cross in SC to opposite side and ascend in ventrolateral spinothalamic system


Spinocerebellar tracts

convey proprioception info from muscle spindles, GTO and touch and pressure receptors to cerebellum for control of voluntary movements

Dorsal spinocerebellar tract ascends to ipsilateral inferior cerebellar peduncle

Ventrospinocerebellar tract ascends to contralateral and ipsilateral superior cerebellar peduncle


Spinoreticular tracts

convey deep and chronic pain to reticular formation of brainstem via diffuse, polysynaptic pathways


Descending fiber systems (motor pathways)

1- Corticospinal tracts

2- Vestibulospinal tracts

3- Rubrospinal tracts

4- Reticulospinal system

5- Tectospinal tract


Corticospinal tract

arise from primary motor cortex, descend in brainstem, cross in medulla (pyramidal decussation), via lateral corticospinal tract to ventral gray matter (anterior horn cells)

10% of fibers do not cross and travel in anterior corticospinal tract to cervical and upper thoracic segments

important for voluntary motor control


Vestibulospinal tracts

arise from vestibular nucleus and descend to SC in lateral (uncrossed) and medial (crossed and uncrossed) vestibulospinal tracts

important for control of muscle tone, antigravity muscles and postural reflexes


Rubrospinal tracts

arise in contralateral red nucleus and descend in lateral white columns to spinal gray

assist in motor function


Reticulospinal system

arises in the reticular formation of the brainstem and descends (crossed and uncrossed) in ventral and lateral columns

terminates both on dorsal gray (modifies transmission of sensation, especially pain) and on ventral gray (influences gamma motor neurons and spinal reflexes)


Tectospinal tract

arises from superior colliculus (midbrain) and descends to ventral gray

assists in head turning responses to visual stimuli


Autonomic Nervous System (ANS)

concerned with innervations of involuntary structures: smooth muscle, heart, glands

helps maintain homeostasis- constant internal body environment

DIVISIONS: (both have afferent and efferent nerve fibers; pre & post ganglionic fibers)

1- Sympathetic (thoracolumbar division, T1-L2)
-prepares body for fight or flight, emergency responses
-increases HR and BP, constricts peripheral blood vessels and redistributes blood
-inhibits peristalsis (intestinal contraction)

2-Parasympathetic (craniosacral division, CN III, VII, IX, X; pelvic nerves)
-conserves and restores homeostasis
-slows HR and reduces BP
-increases peristalsis and glandular activity

Autonomic plexuses: cardiac, pulmonary, celiac (solar), hypogastric, pelvic

Modulated by brain centers:
1- Descending autonomic system: arises from control centers in hypothalamus and lower brainstem (cardiac, respiratory, vasomotor) and projects to preganglionic ANS segments in thoracolumbar (sympathetic) and craniosacral (parasympathetic) segments
2- CN: visceral afferent sensations via glossopharyngeal and vagus nerves; efferent outflow via oculomotor, facial, glossopharyngeal and vagus nerves



3 membranes that envelop the brain

1- dura mater: outer, tough, fibrous membrane attached to inner surface of cranium
-forms falx and tentorium

2- Arachnoid: delicate, vascular membrane

Subarachnoid space: contains cerebrospinal fluid (CSF) and cisterns, major arteries

3- Pia mater: thin, vascular membrane that covers the brain surface
-forms tela chloridea of ventricles


brain ventricles

4 cavities/ventricles filled with CSF and communicate with each other and with SC canal

2 lateral ventricles: large, irregularly shaped with anterior, posterior and inferior horns
-communicates with 3rd ventricle through foramen of Monro

3rd ventricle: located posterior and deep between the 2 thalami
-communicates with 4th ventricle through cerebral aqueduct

4th ventricle: pyramid-shaped cavity located in the pons and medulla
-foramina of Luschka and Magendie communicate with 4th ventricle through subarachnoid space


Cerebrospinal fluid

provides mechanical support (cushions brain)

controls brain excitability by regulating ionic composition

aids in exchange of nutrients and waste produces

produced in choroid plexuses in ventricles


Blood brain barrier

selective restriction of blood borne substances from entering the CNS

associated with capillary endothelial cells


Blood supply

brain= 2% of body weight with a circulation of 18% total blood volume

Carotid system: internal carotid arteries arise off common carotids and branch to form anterior and middle cerebral arteries
-supplies a large area of brain and many deep structures

Vertebrobasilar system: vertebral arteries arise off subclavian arteries and unite to form the basilar artery
-this vessel bifurcates into 2 posterior cerebral arteries
-supplies the brainstem, cerebellum, occipital lobe and parts of thalamus

Circle of Willis: formed by anterior communicating artery
-connecting the 2 anterior cerebral arteries and the posterior communicating artery, connecting each posterior and middle cerebral artery

Venous drainage: includes cerebral veins and dural venous sinuses


Neuron structure

cell bodies: genetic center
-dendrites: receptive surface area to receive info via synapses

axons: conduct impulses AWAY from cell body (1 way conduction)

Synapses: allow communication between neurons
-chemical neurotransmitters are release (chemical synapses)
-electrical signals pass directly from cell to cell (electrical synapses)

neuron groupings/types
-nuclei are compact groups of nerve cell bodies; in the peripheral NS these groups are call ganglia
-projection neurons carry impulses to other parts of the CNS
-interneurons are short relay neurons
-axon bundles are called tracts or fasciculi; in the SC, collections of tracts are called columns or funiculi

Neuroglia= support cells that don't transmit signals
-important for myelin and neuron production
-maintenance of K+ levels and repute of neurotransmitters after neural transmission at synapses


Neuron function/ neuronal signaling

resting membrane potential: positive outside, negative inside (~ -70 MV)

action potential: increased permeability of Na+ and influx into cell with outflow of K+ results in polarity changes (inside to ~ +35 mV) and depolarization; generation of an action potential is all or none)

conduction velocity is proportional to axon diameter; largest myelinated fibers conduct fastest

repolarization results from activation of K+ channels

many axons are covered with myelin with small gaps (nodes of Ranvier) where myelin is absent; action potential jumps from one node to the next (saltatory conduction); myeline functions to increase speed of conduction and conserve energy


Nerve fiber types

A fibers: large, myelinated, fast-conducting
-alpha: proprioception, somatic motor
-beta: touch, pressure
-gamma: motor to muscle spindles
-delta: pain, temp, touch

B fibers: small, myelinated, conduct less rapidly; preganglionic autonomic

C fibers: smallest, unmyelinated, slowest conducting
-dorsal root: pain, reflex responses
-sympathetic: postganglionic sympathetics


peripheral nerves


motor/efferent fibers originate from motor nuclei (cranial nerves) or anterior horn cells (Spinal nerves)

sensory/afferent fibers originate in cells outside of brainstem or spinal cord with sensory ganglia (cranial nerves) or dorsal root ganglia (spinal nerves)

ANS fibers: sympathetic fibers at thoracolumbar spinal segments and parasympathetic fibers at craniosacral segments


Cranial nerves

12 pairs; all distributed to the head and neck (except CN X which is distributed to the thorax and abdomen)

I: Olfactory
II: Optic
III: Oculomotor
IV: Trochlear
V: Trigeminal
VI: Abducens
VII: Facial
VIII: Vestibulocochlear
IX: Glossopharyngeal
X: Vagus
XI: Spinal accessory
XII: Hypoglossal


CN: pure sensory

pure sensory, carry special senses of smell, vision, hearing and equilibrium

I: olfactory
II: optic
VIII: vestibulocochlear


CN: pure motor

pure motor, controlling eye movements and pupillary constriction

III: oculomotor
IV: trochlear
VI: abducens

pure motor, innervating SCM, trapezius and tongue
XI: spinal accessory
XII: hypoglossal


CN: mixed motor and sensory

mixed motor and sensory

involved in:
-chewing (V)
-facial expression (VII)
-swallowing (IX, X)
-vocal sounds (X)

-from head (V, VII, IX)
-alimentary tract, heart, vessels and lungs (IX, X)
-taste (VII, IX, V)


CN: carry parasympathetic fibers of ANS

III- oculomotor
VII- facial
IX- glossopharyngeal
X- vagus

involved in:
-control of smooth muscles of inner eye (III)
-salivatory and lacrimal glands (VII)
-parotid gland (IX)
-muscles of the heart, lung and bowel (X)



Olfactory nerve

Anosmia= inability to detect smells
-seen with frontal lobe lesions



Optic nerve
-vision- central and peripheral visual acuity
-pupillary reflexes

myopia= impaired far vision
presbyopia= impaired near vision
homonymous hemianopsia= visual field deficit



Oculomotor nerve
-extraocular movements: turns eye up, down and in
-pupillary reflexes
-lifts eyelid

stabismus= eye deviates from normal conjugate position (eye pulled outward by CN VI)
Mydriasis= dilated pupil
loss of light and accommodation reflexes
Ptosis= drooping eyelid



Trochlear nerve
-turns adducted eye down

eye can't look down when adducted
diplopia looking down- difficulty with stairs



Trigeminal nerve
-Sensory: face, cornea
-Motor: temporal and masseter muscles



-pulls out laterally

Esotropia= pulls eyes inward



Facial nerve
-Motor: facial expression (eyebrows, frown, smile, close eyes, puff cheeks)
-Sensation: anterior 2/3 taste of tongue; glands and mucosa of the pharynx, palate, nasal cavity, paranasal sinuses, submaxillary and sublingual gland

Bell's palsy



Vestibulocochlear nerve
-vestibular: eye head coordination, vestibular-ocular reflex
-cochlear function: auditory acuity


deafness/impaired hearing
sensorineural loss: sound heard in good ear
conductive loss: sound heard through bone is equal to or longer than air



Glossopharyngeal nerve
-palatal, pharynx control
-gag reflex
-posterior 1/3 of tongue taste

dysphonia= difficulty with speech
dysphagia= difficulty swallowing



Vagus nerve
-visceral sensations and reflexes
-cardiac depressor
-GI tract peristalsis and secretion

palpitation, tachycardia, vomiting, slowing of respiration, ipsilateral paralysis of soft palate and larynx, hoarseness, anesthesia of the larynx



Spinal Accessory nerve
-Carotid/cranial part: deglutition and phonation
-Spinal part: trapezius and SCM innervation



Hypoglossal nerve
-tongue movement

dysarthria= difficulty articulating words
deviates to weak side on protrusion


Spinal nerves

31 pairs- correspond to vertebral segments; each has a ventral and dorsal root
8 cervical
12 thoracic
5 lumbar
5 sacral
1 coccygeal

Ventral root: efferent/motor fibers to voluntary muscles (alpha and gamma motor neurons), and to viscera, glands and smooth muscles (preganglionic ANS fibers)

Dorsal root: afferent/sensory fibers from sensory receptors from skin, joints and muscles; each dorsal root possesses a dorsal root ganglion (cell bodies of sensory neurons); no dorsal root for CI

nerve roots exit from the vertebral column through the intervertebral foramina
-Cervical spine: numbered roots exit horizontally above the corresponding vertebral body
-Thoracic, lumbar and sacral spine: roots exit below the corresponding vertebral body

after emerging from the intervertebral foramen, each spinal nerve divides into a large anterior ramis (supplying the muscles and skin of the ant/lat body wall and limbs) and a small posterior ramis (supplying muscles and skin of the back); each ramus contains motor and sensory fibers

Anterior rami joint at the root of the limbs to form nerve plexuses
-Cervical plexus: C1-4 nerve roots
-Brachial plexus: C5-T1
-Lumbar plexus: T12-L4
-Sacral plexus: L4-S3



specific segmental skin area innervated by sensory spinal axons



skeletal muscles innervated by motor axons in a given spinal root


spinal level reflexes

stretch (myotatic) reflex
-reciprocal inhibition
-reciprocal innervation

inverse stretch (myotatic) reflex

gamma reflex loop

flexor (withdrawal) reflex

Crossed extension reflex


Stretch (myotatic) reflex

stimulus: muscle stretch

reflex arc: afferent Ia fiber from muscle spindle to alpha motor neurons projecting back to muscle or origin (monosynaptic)

functions for maintenance of muscle tone, support agonist muscle contraction and provide feedback about muscle length

clinically, sensitivity of the stretch reflex and intactness of SC segment are tested by DTR

reciprocal inhibition: via an inhibitory interneuron, the same stretch stimulus inhibits the antagonist muscle

reciprocal innervation: describes the effects of a stretch stimulus on agonist (autogenic facilitation), antagonist (reciprocal inhibition) and synergistic muscles (facilitation)


Inverse stretch (myotatic) reflex

stimulus: muscle contraction

reflex arc: afferent Ib fiber from GTO via inhibitory interneuron to muscle of origin (polysynaptic)

functions to provide agonist inhibition, diminution of force of agonist contraction, stretch-protection reflex


gamma reflex loop

stretch reflex forms part of this loop

alows muscle tension to come under control of descending pathways (reticulospinal, vestibulospinal and others)

descending pathways excite gamme motor neurons, causing contraction of muscle spindle, and in turn increased stretch sensitivity and increased rate of firing from spindle afferents; impulses are then conveyed to alpha motor neurons


flexor (withdrawal) reflex

stimulus: cutaneous sensory stimuli

reflex arc: cutaneous receptors via interneurons to largely flexor muscles; multisegmental response involving groups of muscles (polysynaptic)

functions as a protective withdrawal mechanism to remove body part from harmful stimuli


crossed extension reflex

stimulus: noxious stimuli and reciprocal action of antagonists; flexors of one side are excited, causing extensors on same side to be inhibited; opposite responses occur in opposite limb

reflex arc: cutaneous and muscle receptors diverging to many SC motor neurons on same and opposite side (polysynaptic)

function: coordinates reciprocal limb activities such as gait.