Neuro Anatomy Flashcards
Telencephalon
“cerebral hemispheres”
consists of 6 lobes on each side frontal parietal temporal occipital insular limbic
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
Insula
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:
1-thalamus
2-subthalamus
3-hypothalamus
4-epithalamus
thalamus
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
Subthalamus
involved in control of several functional pathways for sensory, motor and reticular function
Hypothalamus
integrates and controls the functions of the ANS and the neuroendocrine system
maintains body homeostasis
Epithalamus
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
midbrain
“mesencephalon”
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
Pons
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
Cerebellum
located behind dorsal pons and medulla in posterior fossa
- joined to brainstem by 3 pairs of peduncles
- comprises 2 hemispheres and midline vermis
Lobes:
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
meninges
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
LMN
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)
sensations:
- 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)
CN I
Olfactory nerve
smell
Anosmia= inability to detect smells
-seen with frontal lobe lesions
CN II
Optic nerve
- vision- central and peripheral visual acuity
- pupillary reflexes
blindness
myopia= impaired far vision
presbyopia= impaired near vision
homonymous hemianopsia= visual field deficit
CN III
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
CN IV
Trochlear nerve
-turns adducted eye down
eye can’t look down when adducted
diplopia looking down- difficulty with stairs
CN V
Trigeminal nerve
- Sensory: face, cornea
- Motor: temporal and masseter muscles
CN VI:
Abducens
-pulls out laterally
Esotropia= pulls eyes inward
CN VII:
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
CN VIII
Vestibulocochlear nerve
- vestibular: eye head coordination, vestibular-ocular reflex
- cochlear function: auditory acuity
vertigo
dysequilibrium
nystagmus
deafness/impaired hearing
tinnitus
sensorineural loss: sound heard in good ear
conductive loss: sound heard through bone is equal to or longer than air
CN IX
Glossopharyngeal nerve
- phonation
- swallowing
- palatal, pharynx control
- gag reflex
- posterior 1/3 of tongue taste
dysphonia= difficulty with speech dysphagia= difficulty swallowing
CN X
Vagus nerve
- phonation
- visceral sensations and reflexes
- cardiac depressor
- bronchoconstrictor
- GI tract peristalsis and secretion
palpitation, tachycardia, vomiting, slowing of respiration, ipsilateral paralysis of soft palate and larynx, hoarseness, anesthesia of the larynx
CN XI
Spinal Accessory nerve
- Carotid/cranial part: deglutition and phonation
- Spinal part: trapezius and SCM innervation
CN XII
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
dermatome
specific segmental skin area innervated by sensory spinal axons
myotome
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.
