Anatomy, embriology: general Flashcards
WM tracts
cingulum
Cingulate gyrus to the entorhinal
cortex
Affect, visceromotor control;
response selection in skeletomotor
control; visuospatial processing
and memory access
X: Left-sided lesions cause verbal amnesia, whereas right-sided lesions alter visuospatial (location) memory; bilateral damage causes global amnesia.
Fornix
Hippocampus and the septal area to
hypothalamus
Part of the Papez circuit; critical in
formation of memory; damage or
disease resulting in anterograde
amnesia
Superior longitudinal
fasciculus
Frontotemporal and frontoparietal
regions
Integration of auditory and speech
nuclei
SLF + FA
Originally, the AF was first described as a component of the SLF, and their names were used as a synonym of each other. Recently, researchers have separated these bundles as the SLF and the AF that connect the frontal cortex to the occipital and parietal cortex, respectively (Dick & Tremblay, 2012; Gierhan, 2013; Petrides & Pandya, 2009). Damage to this tract can cause speech impairments such as anarthria and dysarthria
Inferior longitudinal
fasciculus
Ipsilateral temporal and occipital
lobes
The role of the ILF is therefore central in all activities involving processing complex visual information, from objects, faces, and word perception to emotion recognition and semantics (ffytche et al., 2010). Some of the behavioral and cognitive deficits described in patients with anterior temporal lobe damage are due to disconnection of the ILF fibers that prevent visual inputs to reach the limbic, paralimbic, and temporopolar cortex.
X: object recognition, visual agnosias, prosopagnosia
Cholinerg projection brain
Dopamine projection brain
GABA pathway brain
Noradrenergic projection of the brain
Serotonin pathway brain
Limbic system Papez circuit
Neuralation
Neurulation is a multistep process leading to the development of the central nervous system.
*
It starts at 21-day postfertilization in humans.
*
Neurulation is a process divided into primary neurulation and secondary neurulation.
*
Primary neurulation is a discontinuous process that starts at different points along the rostrum–caudal axis necessary for the neural tube closure.
*
The secondary neurulation permits the formation of the spinal cord at the lower sacral and caudal level.
Basal plate give rise to…
Periferial nerves
Axonal injury
Neurapraxia (“Nerve Dysfunctional”)
Neurapraxia Overview:
Nerve injury causing temporary interruption of action potential conduction without permanent damage.
Preservation of axon with no axonal degeneration.
Mild and reversible pathological changes.
Full and rapid recovery expected, typically within days to a few months.
Variability in Nerve Susceptibility:
Motor nerves are most susceptible to injury.
Pain and autonomic nerves are least susceptible.
Proprioception, light touch, and temperature modalities show intermediate susceptibility to injury.
Axonotmesis (“Axon Cut”)
Neurotmesis (“Nerve Cut”)
In neurotmesis, there is complete loss of axonal continuity. The cut ends of the nerve either remain separated, or they may reconnect through a bridge of scar tissue consisting of fibroblasts, Schwann cells, and regenerating axons. In any event, recovery is negligible. Hope for any functional recovery requires surgery
Axonotmesis regeneration
In axonotmesis, degeneration occurs distal to the injury
site, while the proximal segment exhibits few histologic or
pathologic changes. Distal segment degeneration is called
Wallerian degeneration, or anterograde degeneration, the
principal histologic change of which is a breakdown of both
axons and myelin, leaving only ghost-like endoneurial
sleeves. Schwann cells, and later macrophages, consume
the axonal and myelin debris. The complete process
unfolds over a period of weeks, ultimately reducing nerve
fibers to a mass of Schwann cells and endoneurial sheaths.
When the endoneurium is disrupted (Sunderland
type III) Wallerian degeneration proceeds (as described
above), with this difference: intrafascicular injury impairs
axonal regeneration. That is, damage to the endoneurium
causes shrinkage, fibrosis, and ultimately obliteration
of the endoneurial tubes, limiting axonal regeneration.
What is more, Wallerian degeneration is now accompanied by an additional pathologic process: degeneration of
the proximal segment in a retrograde direction.
Axonal and cell body degeneration
Degenerative changes in the cell body may include migration of the nucleus to the periphery of the cell and the
breakdown and dispersal of Nissl granules in a process
named chromatolysis. This process depresses cell body
protein synthesis. Regeneration of the cell body reverses
this process, reinstating protein synthesis, which in turn
facilitates axonal regeneration.
Lesion of cervical plexus
Plexus brachialis
Polio
Guillan Barré
Spinal nerve
GM in spine
Rexed Laminae
Hippocampal fibers
WM tracts and striatum
Thalamic fibers
Thalamus vascular supply
Cerebellar neurons and inputs
Types of cerebellar neurons and their inputs: mossy fiber pro-
jections from pontine n., vestibular n., red n., deep cerebellar n., spinal cord, reticular formation; climbing fiber projections from inferior olive.
Anterior mesenchephalis syndromes
Mid pons lesion
Lower pons lesions
Superior medulla
Inferior medullar lesion
Spinal trigeminal tract; medial lemniscus
Central herniation
Long tracts of spinal cord
reticulospinal tract
Course
Medial Reticulospinal Tract (Pontine): Descends ipsilaterally in the anterior funiculus [1] Responsible for controlling axial and extensor motor neurons e.g enable extension of the legs to maintain postural support ; Stimulation of the midbrain locomotor centre can result patterned movements (e.g. stepping)[3]
Lateral Reticulospinal tracts (Medullary): Descends bilaterally in the lateral funiculus [1] Responsible for flexor motor neurons [2]; Inhibits the medial reticulospinal tract and therefore extensor motor neurones enabling modulation of the stretch reflex [4]
Both the lateral and medial tracts act via interneurons shared with the corticospinal tract on proximal limb and axial muscle motor neurons.[1]
reticulospinal tract lesion
Pathology
Spastic paraplegia
Lesions to the cortico-reticulospinal system can result in decreased postural control and reduced selectivity of postural control.[3] If the excitatory fibres in the reticular formation have a leison this can result in hypotonia by the loss of descending excitatatory impulses to the spinal cord. Conversly in the inhibitory fibres are disrupted in the reticular formation this could result in hypertonia (spasticity) As the lateral reticulospinal’s is involved in inhibition, if this pathway is disrupted it can result in spasticity [4]. In addition due to the lack of descending inhibition, the medial reticulospinal tract would then maintain spasticity in the musculature.[4]
vestibulospinal tr
Upright Posture Maintenance: Performed by both the medial and the lateral vestibulospinal tracts. The medial tract supplies the muscles of the head and neck whereas the lateral tract supplies the muscles located in other parts of the body. When the head of the person moves, signals are sent by these vestibular tracts to specific antigravity muscles. These muscles contract and maintain the upright posture of the body.
Vestibulospinal Reflexes: A vestibulospinal reflex is the one that uses organs of the vestibular system and the skeletal muscles in order to maintain balance and posture[1]
vestibulo ocular reflex
Medial Vestibulospinal Tract
Vestibulo-ocular reflex lateroflexion of neck
Head and Eye Coordination: Performs the synchronization of the movement of the eyes with the movement of the head so that eyes do not lag behind when the head moves to one side. This function is very important for maintaining the balance of the body.
Head righting reflexes. These are responsible for keeping the head and gaze horizontal
Eye righting reflex (Vestibulo-ocular reflex) This origniates in the ascending medial longitudinal fasciulus and extends to the extraocular muscles of the eyes. The horizonal position of the eyes when the head is an upright postural set is caused by cancelling of the tonic acitiy of the deiteroocular pathways.[2] It is therefore able to keep the eyes still while the head moves, allowing images to focus on the retina [4]
Spinal grey matter somatotopy
vascular watershed zones of SC
Facial nerve components
bered 1 through 5) cause different neuro
-
logical symptoms because of the involved nerve components: 1
, facial weakness + impaired hearing + vestibular dysfunction; 2
, facial weakness + impaired taste sensa-
tion + decrease lacrimal & salivary secre-
tion; 3
, facial weakness + impaired taste sensation + decreased salivary secretion + hyperacusis; 4
, facial weakness + impaired taste sensation + decreased salivary secre-
tion; 5
, facial weakness. Greater petrosal nerve carries parasympathetics to the lac-
rimal and nasal glands. Stapedius nerve acts to dampen the tympanic membrane oscillation. Chorda tympani carries taste sensation from the anterior tongue
accessorius
Bladder disfunctions
retinal representation
CN III-VI
oculomotor nucleus
nystagmus types and patterns
less common nystagmus types
nystagmus types III
Bony jugular foramen
Jugular foramen contents
detailed jugular foramen
acustic meatus
Facial visceral motor
IX visceral
CNX visceral
visceral CN nuclei
Medial column motor nuclei
his column, which is not continuous longitudinally, is immediately adjacent to the midline, just below the floor of the ventricular system. It contains nuclei composed of neurons that innervate the striated muscles of the head and neck derived from embryonic myotomes (i.e., the extraocular muscles and the muscles of the tongue). In rostrocaudal order, the nuclei contained in this column include the following four structures
Paramedian motor nuclei in BS
This column is located lateral and ventral to column 1. It contains nuclei composed of neurons that innervate the striated muscles of the head and neck derived from the **branchial arches **(i.e., the muscles of mastication, the muscles of facial expression, the muscles of the pharynx and larynx, and the sternocleidomastoid and trapezius muscles). I
Immediately paramedian nuclei (Column 3)
This column is located immediately lateral to column 1. It contains nuclei of preganglionic parasympathetic neurons that innervate the smooth muscles and glands of the head and neck, as well as the thoracic and parts of the abdominal viscera. (Preganglionic parasympathetics originating in sacral segments of the spinal cord supply the rest of the abdominal and pelvic viscera.)
BS Lateral Columns Contain Three Sensory Nuclei
The lateral columns are composed of sensory nuclei. Unlike most motor nuclei, whose axons are carried in a single corresponding cranial nerve, each sensory nu-cleus receives input from several different cranial nerves
Long tract: ST
The lateral and anterior spinothalamic tracts are re-sponsible for pain, temperature, and light touch sensa-
tion. They are located in the lateral aspect of the teg-
mentum throughout the brainstem, adjacent to the descending sympathetic tract. They occur in essentially the same position they occupy in the spinal cord. The spi-
nothalamic tract consists of second-order neurons that originate in the dorsal gray horn
of the spinal cord, cross the midline in the anterior white commissure
, and project to the ventral posterolateral (VPL) nucleus of the thalamus
. Third-order neurons in the VPL thalamus send axons to the postcentral gyrus
. Because of the close proximity of the spinothalamic tract to the descending sympathetic fibers, both systems are typically impaired as a result of damage to the lateral tegmentum, where they represent important landmarks. An ipsilateral Horner syndrome (descending sympathetic lesion) is thus often associated with a contralateral hemisensory loss (spinothalamic le-
sion), which may be caused by a lesion in the lateral me-
dulla or pons
Long tract: ML
The medial lemniscus, which is the rostral continu-ation of the dorsal columns of the spinal cord, medi-
ates position sense and discriminative touch. It consists of second-order neurons that originate in the nucleus cuneatus
and nucleus gracilis
. These nuclei receive input from the spinal cord via the cuneate and gracile fasciculi (dorsal columns), which carry impulses from the upper and lower extremities, respectively. After synapse in the ipsilateral cuneate and gracile nuclei, these axons act as the internal arcuate fibers and ascend to the contralateral VPL thalamus. From here they ascend to the sensory cor-
tex. The medial lemniscus is situated in the medulla close to the midline between the posteriorly situated medial longitudinal fasciculus (MLF) and the anteriorly situated corticospinal and corticopontine tracts. In its rostral as-
cent, the medial lemniscus moves laterally but remains an important landmark of the medial aspect of the me-
dulla and pons
Long tract: CS
The corticospinal tract transmits motor-related im-pulses from the cerebral cortex to laminae IV through IX (few fibers synapse directly with IX motor neurons in laminae IX) of the spinal gray matter. The fibers of this tract traverse the corona radiata
and the posterior limb of the internal capsule
and continue in the middle of the midbrain crura cerebri, flanked by more numerous cor-
ticopontine fibers on each side. At the level of the pons, the corticospinal tract is broken up into small bundles by transverse pontocerebellar fibers, which cross the mid-
line to reach the contralateral cerebellar hemisphere via the middle cerebellar peduncle. At lower pontine levels, the corticospinal fibers come together again and form the medullary pyramids
. As they reach the caudal medulla
, approximately 85% of corticospinal fibers cross the mid-
line in the decussation of the pyramids to form the lateral corticospinal tract
(the other 15% of fibers continue in the uncrossed anterior corticospinal tract
, which later de-
cussates in the anterior commissure at cervical and up-
per thoracic levels). Separate from direct corticopontine fibers, numerous collateral branches of the corticospinal fibers innervate the pontine nuclei, including those of the reticular formation. Like the medial lemniscus, the cor-
ticospinal tract courses close to the midline throughout the pons and medulla, providing an important medial brainstem landmark
Long tract: CB
The corticobulbar tract comprises fibers projecting from the cerebral cortex to the lower brainstem. Among the neurons that receive these projections are several motor cranial nerve nuclei, including the trigeminal, fa-cial, and hypoglossal nuclei. Except for part of the facial motor nucleus, the cortical input to these nuclei is more or less symmetrically bilateral. The muscles that receive their supply from these nuclei include the laryngeal, pha-
ryngeal, palatal, upper facial, extraocular, and muscles of mastication. Because of their bilateral innervation, uni-
lateral lesions interrupting the corticobulbar supply of these muscles cause only mild signs of paresis, whereas bilateral lesions are usually significant (pseudobulbar palsy). The clinically familiar contralateral paralysis of lower facial muscles (sparing the forehead) is evidence of predominantly crossed corticobulbar innervation of part of the facial motor nucleus. In addition to this direct corticobulbar pathway, corticoreticular fibers innervate neurons of the reticular formation, which serve to relay impulses indirectly from the cortex to the motor cranial nerve nuclei. As a landmark of the medial brainstem, the corticobulbar tract is associated with the medial lemnis-
cus and the corticospinal tract
Afferent cerebellar path
Efferent cerebellar pathw
CN3
CN3 palsy
CN4
CNVI
Horizontal gaze
supranucleas gaze palsy
nuclear gaze palsy
INO
CN7
CN9
Foster Kennedy sy
Gradenigo sy (itis)
Tolosa Hunt sy
Ramsay Hunt sy
Vernet sy
cortical leyer cells
Brd 4
Brd 6
Brd 6 pre motor
Brd 9-11 prefrontal
Brd 3-1-2 SS
Second SS
Cerebello-thalamic and
Pallido-thalamic fibers
Essential tremor DBS EANS
Pupil symp psy
Optic pathway vascular supply
Sympathetic innervation of pupil
PSY pupil
Marcus Gunn pupil
CN.III. compression
Argyll Robertson pupil
Eyelid “drop”
coma breathing patterns
caloric stimulation
foramen ovale rotundum contents
foramen lacerum contents
zona incerta
The zona incerta (ZI) is a horizontally elongated region of gray matter in the subthalamus below the thalamus. Its connections project extensively over the brain from the cerebral cortex down into the spinal cord.
Its function is unknown, though several potential functions related to “limbic–motor integration” have been proposed, such as controlling visceral activity and pain; gating sensory input and synchronizing cortical and subcortical brain rhythms. Its dysfunction may play a role in central pain syndrome. It has also been identified as a promising deep brain stimulation therapy target for treating Parkinson’s disease.
Its existence was first described by Auguste Forel in 1877 as a “region of which nothing certain can be said”.[1][2] A hundred and thirty years later in 2007, Nadia Urbain and Martin Deschênes of Université Laval noted that the “zona incerta is among the least studied regions of the brain; its name does not even appear in the index of many textbooks.”[
cerebellar cell layers
pupil reflex
ethmoidal artery
Origin: Ophthalmic artery.
Course: Passes within the anterior ethmoidal canal and enters the anterior cranial fossa via the anterior ethmoidal foramen.
Branches: Anterior meningeal, anterior septal, and anterior lateral nasal branches.
Supplied Structures: Anterior ethmoidal cells, frontal sinus, dura mater, and nose.
cerebellar nuclei
cerebellar efferents
the dentate nucleus that receives information form the cerebellar neocortex and projects to the motor areas of the cortex using a polysynaptic pathway.
the nucleus interpositus and fastigial nuclei, that receive messages from the cortex of the vermis and influence brainstem nuclei that project to the spinal cord.
inferior olivar nucl
The Inferior Olivary Nucleus is the source of the powerful climbing fibres that project to the cerebellum. Groups of these neurones are linked by gap junctions so they fire synchronously; and each of thee groups is at the centre of a cerebellar module or microzone - the functional unit within the cerebellum.
The exact nature of the processing of motor information by the olive is not entirely clear. However, the Inferior Olivary Nucleus is known to have inputs from the red nucleus (see the diagram opposite) and also from the motor cortex, via collaterals of the corticospinal tract.
It also contains a somatotopic map of the body surface, and has inputs from the dorsal column nuclei as well as the dorsal and ventral spino-cerebellar tracts. So proprioceptive and cutaneous information, which can be used to tell the position of the limb and when the limb is touching an object, can be fed into the cerebellum by this route.
So although the rubro-olivary tract is outside the cerebellum it appears to play a part in its function. It has been suggested that the olive can compare the commands from the motor cortex with their effects on spinal centres.
cerebellar somatotopy
movement pathway
histologic layers of cerebellum
The cerebellar cortex has three layers - a surface (molecular) layer of parallel fibres, consisting of the axons of granule cells and the dendrites of Purkinje cells; the cell bodies of the granule cells are densely packed in the innermost layer - the granular layer; and the Purkinje cell layer, one cell in thickness, between them, and is the main output pathway for the cerebellum.
The axons of granule cells pass towards the surface of the molecular layer and bifurcate, sending their collaterals in opposite directions within the folia where they become parallel fibres, and make excitatory, glutamatergic, synapses on the dendrites of hundreds of Purkinje Cells.
The planar arbors of Purkinje cell dendrites are oriented perpendicular to the parallel fibers, and this arrangement resembles wires running between electricity pylons. Purkinje cells can therefore extract information from the molecular layer, and pass it to the deep cerebellar nuclei, where they release GABA and have inhibitory effects.
**Inputs to Purkinje Cells
**
Purkinje cells have two types of input: (a) the parallel fibres of the molecular layer (the axons of granule cells), and (b) climbing fibres which originate in the inferior olive and have a very strong excitatory influence on the Purkinje cells.
Climbing fibres
The name ‘climbing fibers’ is used because the axons wrap themselves around the Purkinje cell dendrites. Every Purkinje cell receives a very powerful excitatory synaptic input from each climbing fibre, each of which innervates ony a small number of Purkinje cells; this is in contrast to the very large number of weaker excitatory inputs Purkinje cells receive from parallel fibres. Climbing fibres arise from the contralateral inferior olivary nucleus and excite Purkinje cells AND an associated cluster of neurones in the deep cerebellar nuclei.
Mossy Fibres
The parallel fibres of the cerebellar cortex arise from granule cells and are excited by axons originating in the pontine nuclei, that carry a copy of the motor command sent to the motoneurones. These axon terminals on granule cells are called mossy fibres, because of the tufted appearance of their synapses, and they also have axon collaterals that end on neurones of the deep cerebellar nuclei.
radial nerve
Posterior interosseous nerve syndrome.
The posterior interosseous nerve (PIN) syndrome is
the most common syndrome caused by compression at
the arcade of Frohse. As the PIN passes under the arcade of Frohse, a fibrous arch at the origin of the supinator muscle the nerve may be pathologically constricted. The cardinal features of this syndrome are an inability to extend the fingers at the metacarpophalangeal joint, the absence of wrist drop, and normal sensation. Because the finger extensors at the interphalangeal joint are median
and ulnar innervated, the patient is able to extend the
fingers at this joint. Branches to the supinator muscle are given off proximal to the nerve entering the arcade of Frohse, causing the supinator muscle to be spared.
n. medianus
Pronator teres syndrome.
The pronator teres syndrome results from entrapment
of the median nerve as it passes between the two heads
of the pronator teres muscle and under the fibrous arch of
the flexor digitorum superficialis. Compression may be
caused by (1) a thickened lacertus fibrosus (an aponeurosis that overlies the median nerve just proximal to the
passage of the nerve between the two heads of the pronator teres), (2) a hypertrophied pronator teres muscle,
or (3) a tight fibrous band of the flexor digitorum superficialis.
The syndrome is characterized by pain in the forearm.
In addition, weakness in the hand grip and numbness
and tingling in the index finger and thumb are characteristically present. The symptoms are similar to those
of carpal tunnel syndrome (see p. 70), but nocturnal exacerbation of pain is conspicuously absent. In advanced
cases, the hand assumes a “benediction attitude” due to
impairment of flexion in the radial three digits. Findings
on muscle testing will vary depending on the degree of
compression, but often there is no measurable weakness
in the median nerve–innervated muscles.
anterior interosseus sy
Upper brachial plx injury
Lower brachial plx injury
Suntherland classification of perif. nerve injury
persistent trigeminal artery
CT/MR angiography
A characteristic tau sign 4 or trident sign is described as its appearance on sagittal CTA or MRA/MRI.
persistent trigeminal artery
Persistent primitive trigeminal artery (PPTA) is the most common type of the four persistent carotid-vertebrobasilar anastomoses. It is present in 0.1-0.6% of cerebral angiograms and is usually unilateral 2.
In utero, the trigeminal artery supplies the basilar artery before the development of the posterior communicating and vertebral arteries. The PPTA arises from the junction between petrous and cavernous segments of the internal carotid artery, and runs posterolaterally along the trigeminal nerve (41%), or crosses over or through the dorsum sellae (59%). Vertebral, posterior communicating and caudal basilar arteries are often hypoplastic.
tau sign
trigeminal artery
persistent hypoglossal artery
Persistent hypoglossal artery is one of the persistent carotid-vertebrobasilar anastomoses. It is present in 0.02-0.26% of individuals 2 and overall, is second in frequency to the trigeminal artery which is present approximately six times as often 3.
It arises from the distal cervical internal carotid artery segment, usually between the C1 and C3 vertebral level. After passing through an enlarged hypoglossal canal, it joins the basilar artery inferiorly. If large, the ipsilateral vertebral artery and posterior communicating artery are often hypoplastic or absent.
glasscock triangle
Phrenic nerve
ASA thrombosis
Horner syndrome
Bladder innervation
Bladder dysfunction
cauda et conus medullaris
syrinx
medulla vascular territory
PSY of CN3
CN7 visceral motor
CN7 syndromes
hypothalamus nuclei
