Module 2 Flashcards
- is situated in the posterior cranial fossa and is covered superiorly by the tentorium cerebelli
- largest part of the hindbrain and lies posterior to the 4th ventricle, pons and medulla oblongata
- somewhat ovoid in shape and constricted in its median part
Cerebellum
Cerebellum consists of two cerebellar hemispheres joined by a narrow median __
vermis
The cerebellum is connected to the posterior aspect of the brainstem by three symmetrical bundles of nerve fibers called the ___
superior, middle, and inferior cerebellar peduncles
The cerebellum is divided into three main lobes:
- Anterior lobe
- Middle lobe
- Flocculonodular lobe
– superior surface of the cerebellum and is separated from the middle lobe by a wide V-shaped fissure called the primary fissure
Anterior lobe
– sometimes called the posterior lobe
– is the largest part of the cerebellum, is situated
between the primary and uvulonodular fissures.
Middle lobe
– is situated posterior to the uvulonodular fissure
Flocculonodular lobe
– found along the margin of the cerebellum separates the superior from the inferior surfaces
Horizontal fissure
The cerebellum is composed of an outer covering of gray matter called ____
cortex and inner white matter.
Embedded in the white matter of each hemisphere are three masses of gray matter forming the ____
intracerebellar nuclei
3 Functional Divisions of the Cerebellum
- Paleocerebellum
- Neocerebellum
- Archicerebellum
- Consists of the vermis of the anterior lobe, the pyramids, the uvula, and the paraflocculus
- Also known as the spinocerebellum
- Plays a role in the control of muscle tone and the axial and limb movements.
Paleocerebellum
- Corticocerebellum or cerebrocerebellum
- Consists of the middle portion of the vermis and most of the cerebellar hemispheres
- Also known as pontocerebellum
- Projects fibers to the cerebral cortex through the thalamus
- Plays a role in the planning and initiation of movements, as well as regulation of fine limb movements.
Neocerebellum
- Corresponds to the flocculonodular lobe
- Also called the vestibulocerebellum
- Receives input from areas of the brain concerned with eye movements
- Plays a role in the control of body equilibrium and eye movements.
Archicerebellum
A section made through the cerebellum parallel with the median plane divides the folia at right angles, and the cut surface has a branched appearance, called the ____
arbor vitae
The gray matter of the cortex throughout its extent has a uniform structure. It may be divided into three layers:
- an external layer, the molecular layer
- a middle layer, the Purkinje cell layer
- an internal layer, the granular layer
Cerebellar Output
Spinocerebellum fastigial>>medial descending systems>> motor execution interposed>>lateral descending systems>> motor execution Cerebrocerebellum dentate>>areas 4 and 6>>motor planning Vestibulocerebellum vestibular nuclei>>balance and eye movements
Internal Structure of the Cerebellum
Gray matter – outside and inside (Small aggregations of gray matter in the interior, called cerebellar nuclei)
White matter – inside
Gray matter of the Cerebellum: 3 Layers
Molecular layer – stellate cells, basket cells
Purkinje cell layer – Purkinje cells, which are large Golgi type 1 neurons
Granular layer – granule cells (fibers of which form parallel fibers), neuroglial cells, Golgi cells
Gray matter of the Cerebellum
- Purkinje cell – output
- Mainly inhibitory except granule cells (utilizes glutamate)
- Main neurotransmitter: γ-ABA
- Output of the cerebellar nuclei is excitatory but is modulated by an inhibitory cortical loop, effected by Purkinje Cell output
White matter of the Cerebellum
- Intrinsic fibers
- Afferent fibers
- Efferent fibers
– connect different regions WITHIN the cerebellum (folium-folium; hemisphere-hemisphere)
Intrinsic fibers
– form the greater part of the white matter, PROCEED to the cerebellar cortex; enter though the INFERIOR and MIDDLE cerebellar peduncles
– 3 types: mossy (predominantly), climbing (olivocerebellar tracts), multilayered
Afferent fibers
– constitute the OUTPUT of the cerebellum; commence as the axons of the Purkinje cells, which synapse with the neurons of the cerebellar nuclei; exit mainly through the SUPERIOR and INFERIOR cerebellar peduncle
Efferent fibers
Cerebellar Peduncles
Inferior Cerebellar Peduncle – connects to the medulla oblongata; restiform body
Middle Cerebellar Peduncle – connects to the pons; brachium pontis
Superior Cerebellar Peduncle – connects to the midbrain; brachium conjunctivum
Inferior Cerebellar Peduncle: Afferent tracts
- The dorsal spinocerebellar tract
- The cuneocerebellar tract
- The olivocerebellar tract
- The vestibulocerebellar tract
- The reticulocerebellar tract
- The arcuatocerebellar tract
Inferior Cerebellar Peduncle: Efferent tracts
- Fastigiobulbar tract
- - Cerebelloreticular tracts
Middle Cerebellar Peduncle: Afferent tracts
Fibers from the pontocerebellar tract (corticopontocerebellar tract)
Superior Cerebellar Peduncle: Afferent tracts
The ventral spinocerebellar tract
The tectocerebellar tract
The trigeminocerebellar tract
The cerulocerebellar tract
Four Masses of Gray matter
- Dentate Nucleus – largest of the cerebellar nuclei; has a shape of a crumpled bag with the opening medially
- Emboliform Nucleus – ovoid and is situated to the dentate nucleus, partially covering its hilus
- Globose Nucleus - consists of one or more rounded cell groups that lie medial to the emboli form nucleus
- Fastigial nucleus - lies near the midline in the vermis and close to the roof of the fourth ventricle; it is larger than the globose nucleus
Clinical Features of Cerebellar Dysfunction
- Incoordination (ataxia) of volitional movement
- A characteristic tremor (“intention” or ataxic tremor)
- Disorders of equilibrium and gait
- Diminished muscle tone
- “Cerebellar sign par excellence”
- May affect the limbs, trunk or gait
- Asynergia ; Dysmetria Adiodochokinesis; Dysdiadochokinesis
Ataxia or dystaxia
– lack of synergy of the various muscle components in performing more complex movements so that movements are disjointed and clumsy and broken up into isolated successive parts
Asynergia
- Abnormalities in the rate, range and force of movement
Dysmetria
– abnormality in the rhythm of rapid alternating movements
Adiodochokinesis; Dysdiadochokinesis
- It is related to a depression of gamma and alpha motor neuron activity
- The least evident of the cerebellar abnormalities
- More apparent with acute than with chronic lesions
- Failure to check a movement - a closely related phenomenon (impairment of the check reflex)
Hypotonia
- Hypermetria – overshooting the target
- When the finger approaches the target, there is a side-to-side movement of the finger before reaching the target.
- Titubation - A rhythmic tremor of the head or upper trunk (three to four per second)
Intention or ataxic tremor
- Scanning dysarthria – variable intonation (prosody) and abnormalities in articulation; described also as staccato, explosive, hesitant, slow altered accent, and garbled speech.
- Speech production is often labored with excessive facial grimacing.
- Thought to be a result of generalized hypotonia.
Cerebellar Dysarthria
Disturbances of Ocular Movement (Cerebellum)
- Inability to hold eccentric gaze
- Slower smooth pursuit movements with “catch-up” saccades
- Nystagmus
- Other “cerebellar” eye signs – ocular flutter, opsoclonus, ocular bobbing, square wave jerks at rest, skew deviation, failure to suppress the vestibulo-ocular reflex
– usually gaze-evoked, upbeat, rebound with abnormal kinetic nystagmus if with midline cerebellar lesions; periodic alternating nystagmus with lesions of the uvula, nodulus; downbeat nystagmus with posterior midline lesions
Nystagmus
Disorders of Equilibrium and Gait
- Standing with feet together may be impossible
- In walking, the patient’s steps may be uneven and placement of the foot may be misaligned
- Wide-based stance with increased trunk sway, irregular stepping with a tendency to stagger as if intoxicated
- Impaired tandem walking
The 4 Cerebellar Syndromes
- Hemispheric syndrome
- Rostral vermis syndrome
- Caudal vermis syndrome
- Pancerebellar syndrome
- Incoordination of ipsilateral appendicular movements
- -* Usual etiologies: Infarcts, neoplasms, abscesses
Hemispheric syndrome
- A wide-based stance and titubating gait
- Ataxia of gait, with proportionally little ataxia on the heel-to-shin maneuver with the patient lying down
- Normal or only slightly impaired arm coordination
- Infrequent presence of hypotonia, nystagmus, and dysarthria
Rostral vermis syndrome
- Axial disequilibrium (truncal ataxia) and staggering gait
- Little or no limb ataxia
- Sometimes spontaneous nystagmus and rotated postures of the head
Caudal vermis syndrome
– Bilateral signs of cerebellar dysfunction affecting the trunk, limbs, and cranial musculature
– Some etiologies: infectious and parainfectious processes; hypoglycemia; hyperthermia; paraneoplastic cerebellar; degeneration associated with small cell lung cancer
Toxic processes
Pancerebellar syndrome
Disorders of the Cerebellum
V – Vascular – strokes, hemorrhage, vasculitis
I – Infectious – cerebellitis, post-infectious, abscesses
T – Traumatic, Toxic – gross trauma, intoxication with drugs
A – Autoimmune
M – Metabolic
I – Inflammatory
N – Neoplastic, Nutritional – alcoholism, paraneoplastic
D – Degenerative, Developmental (including Congenital), Demyelinating – Multiple sclerosis, spinocerebellar degeneration, Chiari malformations
- Around 20% of metastases occur in the posterior fossa.
- - Usual neoplasms that metastasize to the brain parenchyma: lung, breast, melanoma, GI, kidney
Cerebellar Neoplasms
- a primary cerebellar neoplasm that arises in the posterior part of the vermis and neuroepithelial roof of the fourth ventricle
- ~20% of childhood brain tumors
- Occur in children around 4-8 years of age
- Males> females
Medulloblastoma
- Arises from the lining in the walls of the ventricles
- ~70% originate from the 4th ventricle
- Tumor of childhood
Ependymoma and Papilloma of the 4th ventricle
- May occur anywhere in the neuraxis
- - ___ in the posterior fossa and optic nerves are more frequent in children and adolescents
Astrocytoma
- Occur most often in association with von Hippel-Lindau disease
- May have an associated retinal angioma, or hepatic and pancreatic cysts
- Tendency to develop malignant renal or adrenal tumors
- Pxs may have polycythemia due to elaboration of erythropoietic factor
Hemangioblastoma
- Congenital anomalies at the base of the brain, consisting of:
1. Extension of a tongue of cerebellar tissue into the cervical canal
2. Displacement of the medulla into the cervical canal
- Congenital anomalies at the base of the brain, consisting of:
- Chiari II- associated with a meningomyelocoele
- Hydomyelia, syringomyelia are common associated findings
Arnold-Chiari Syndrome
- Almost always secondary to a purulent focus elsewhere in the body
- ~40% are related to diseases of the paranasal sinuses, middle ear, mastoid cells
- From otogenic sources, around 1/3 lie in the anterolateral part of the cerebellar hemisphere; the remainder occur in the middle and inferior parts of the temporal lobe
Brain Abscesses
- Result from thrombotic or embolic occlusion of a cerebellar vessel
- Symptoms: vertigo, dizziness, nausea, vomiting, gait unsteadiness, limb clumsiness, headache, dysarthria, diplopia and decreased level of alertness
- Prominent signs: limb and gait ataxia, dysarthria, nystagmus, altered mental status
Cerebellar Strokes
Cerebellar Strokes (Artery affected and Percentage)
PICA 40%
AICA 5%
SCA 35%
Cortical watershed and deep cerebellar whitematter borderzone infarcts 20%
Clinical tests for arm dystaxia
- Ask the patient to extend the arms straight out front
- Do the finger to nose test
- Rapid pronation-supination test, thigh-slapping test
Clinical tests for leg dystaxia
- Heel-to-shin test
- - Heel-tapping test
Clinical tests for dystaxia of station and gait
- Observe the patient’s stance
- Ask the patient to walk
- Tandem-walk
Clinical demonstration of hypotonia
- Inspect for hypotonia – rag doll posture
- Checking for hypotonia
- Pendulous or hypotonic muscle stretch reflexes
Overshooting and checking tests of arms
- Wrist-slapping test
- - Arm-pulling test
Eye movements, speech
- Check smooth pursuit
- - Listen to patient’s speech
Types Of Circulation
Anterior circulation – is supplied by the internal carotid Posterior circulation – is supplied by the anterior vertebral artery
Two most important arteries are the
Internal Carotid
Vertebral Artery
Arterial Supply Of The Brain
- Consumes 15% of the cardiac output
- 20% of oxygen in the body goes to the brain
- Normal blood flow 50-100ml/g of the brain per
minute - Consists of two pairs of major vessels, Internal carotid
arteries and Vertebral arteries.
– Found within the subarachnoid space
– Enters skull through foramen magnum
At the junction between the medulla and the pons the two vertebral arteries fuse to form the ___
Basilar Artery
Branches Of The Internal Carotid Are:
- Caroticotympanic artery (inconsistent)
- Pterygoid (30%)
- Meningohypophyseal trunk
- Anterior meningeal
- Artery to inferior portion of cavernous sinus
- Capsular artery
- Ophtalmic artery
- Superior hypophyseal artery
- Posterior communicating
- Anterior Choroidal
There are three most important branches of the
carotid artery that we must know; these are:
ophthalmic artery
posterior communicating
anterior choroidal
• It enters orbit via the orbit canal and lateral to the
optic nerve
• Supplies eyes and orbital contents
• Terminal branch supply the frontal area of the scalp,
the ethmoid and frontal sinuses and the
ophthalmic artery
- is a branch of the ophthalmic artery
- provides the only blood supply to the five layers of the retina
- is an end artery; its occlusion results in blindness
Central artery of the retina
– Arises from the carotid siphon, runs posteriorly
above the oculomotor nerve and joins the posterior
cerebral artery; part of the circle of Willis
– Connection between internal carotid system and vertebral artery system through the posterior
cerebral artery
– Stroke of this area results in bitemporal hemianopsia
(Loss of vision on the outer half of each eye) as it
supplies the optic chiasm)
– is a common site for berry aneurysms
Posterior communicating artery (PCoA)
- it is formed because the two anterior cerebral arteries usually meet over short distance of midplane. At the medial aspect of the brain.
- is the most common site of berry aneurysms
Anterior communicating artery (ACA)
– arises from the internal carotid artery
–supplies the choroid plexus of the temporal horn of the lateral ventricle, hippocampus, amygdala, optic tract, lateral geniculate body, globus pallidus, and ventral part of the posterior limb of the internal capsule
– supplies the proximal portion of optic radiations as they leave the lateral geniculate
body to form Meyer loop
Anterior choroidal artery
– originates at the terminal bifurcation of the internal carotid artery.
– gives direct branches to the optic chiasm.
– supplies the medial surface of the frontal and parietal lobes and corpus callosum.
– supplies part of the caudate nucleus and putamen and anterior limb of the internal
capsule via the medial striate artery of Heubner
– supplies the leg and foot area of the motor and sensory cortices (paracentral lobule)
Anterior cerebral artery
– largest branch of the ICA; supplies many deep structures as much as the lateral aspect of the cerebrum, it breaks up into several branches that course in the depth of the lateral fissure , over the insula before reaching the convexity of the hemisphere.
– Supplies the lateral convexity of the hemisphere and underlying insula
– Supplies the trunk, arm, and face areas of the motor
and sensory cortices
– Supplies the Broca and Wernicke speech areas
– Supplies the caudate nucleus, putamen, globus
pallidus and the anterior and posterior limbs of the
internal capsule via lateral striate arteries
Middle cerebral artery (MCA)
– it is the largest medial artery.
– It is also the most important since it supplies blood to the
Caudate Nucleus, Putamen, Outer Globus Pallidus, and
Anterior Limb of the internal capsule
– Branch of the anterior cerebral artery
– Once there’s an injury it’ll show collateral face and
arm weakness
– Expressive aphasia in the dominant hemisphere
Recurrent Artery of Heubner
- It is the branch of the 1st part of the subclavian
artery - Joins its opposite partner to form basilar artery at
the level of pons (vertebrobasilar system)
Gives rise to the following: Anterior Spinal Artery, Posterior Spinal Artery and Posterior Inferior Cerebellar Artery
Vertebral Artery
- supplies the anterior two-thirds of the spinal cord, including the anterior and lateral horns.
- supplies the pyramids, medial lemniscus, and intra-axial fibers of the hypoglossal nerve (cranial nerve [CN] XII) in the medulla.
Anterior spinal artery
- supply the posterior third of the spinal cord, including the posterior horns and columns.
- supply the gracile and cuneate fasciculi and nuclei in the medulla.
Posterior spinal arteries
– gives rise to the posterior spinal artery.
– Largest branch
– Supplies the dorsolateral zone of the medulla
– Supplies the inferior surface of the cerebellum and the choroid plexus of the fourth ventricle.
– Supplies the medial and inferior vestibular nuclei, inferior
cerebellar peduncle, nucleus ambiguus, intra-axial fibers of the glossopharyngeal nerve (CN IX) and the vagal nerve (CN X), spinothalamic tract, and spinal trigeminal nucleus and tract.
– Supplies the hypothalamospinal tract to the ciliospinal center of Budge at T1–T2 (Homer Syndrome)
Posterior Inferior Cerebellar Artery
- is formed by two vertebral arteries
- gives rise to: Pontine arteries; Labyrinthine artery, Anterior inferior cerebellar artery, Superior Cerebellar Artery and Posterior Cerebellar Artery
Basilar Artery
– include penetrating and short circumferential branches.
– Supplies corticospinal tracts and the intraaxial
exiting fibers of the abducent nerve
(CN VI).
Pontine arteries
– also called the auditory artery or internal auditory artery
– arises from the basilar artery in 15% of the population.
– Perfuses the cochlea and the vestibular
apparatus.
Labyrinthine artery
– Supplies the inferior surface of the cerebellum.
– Supplies the facial nucleus and intra-axial fibers, spinal trigeminal nucleus and tract, vestibular nuclei, cochlear nuclei, intraaxial fibers of the vestibulocochlear nerve,
spinothalamic tract, and inferior and middle cerebellar peduncles.
– Gives rise to the labyrinthine artery in 85% of the population.
– Supplies the hypothalamospinal tract (Horner syndrome)
Anterior inferior cerebellar artery
- supplies the superior surface of the cerebellum and the cerebellar nuclei (dentate nucleus).
- supplies the rostral and lateral pons, including the superior cerebellar peduncle and spinothalamic tract.
Superior cerebellar artery
• originates from the internal carotid (fetal origin) in 20% of the population.
• is formed by bifurcation of the basilar artery.
• provides the major blood supply to the midbrain
supplies the posterior half of the thalamus and the medial and lateral geniculate bodies.
• supplies the occipital lobe, visual cortex, and inferior surface of the temporal lobe, including the hippocampal formation.
• gives rise to the lateral and medial posterior choroidal arteries, which supply the dorsal thalamus, pineal body, and choroid plexus of the third and lateral ventricles.
Posterior cerebral artery
–Arises from the vertebral and segmental arteries
Arteries of the Spinal Cord
- is a branch of the subclavian artery
- Gives rise to the anterior spinal artery and posterior spinal artery
- joins its opposite partner to form the basilar artery
Vertebral Artery
- supplies the anterior two-thirds of the spinal cord, including the anterior and lateral horns.
- Supplies the pyramids, medial lemniscus, and intra-axial fibers of the hypoglossal nerve (cranial nerve [CN] XII) in the medulla.
Anterior spinal artery
- supply the posterior third of the spinal cord, including the posterior horns and columns.
- Supplies the gracile and cuneate fasciculi and nuclei in the medulla.
Posterior spinal arteries
- arise from the aorta, vertebral arteries, and common iliac arteries as medullary arteries, which supply the anterior and posterior spinal arteries.
- Provides the main blood supply to the spinal cord at thoracic and lumbar levels.
Segmental arteries
– The second lumbar artery gives rise to the great anterior medullary
artery of Adamkiewicz
– due to inadequate blood supply after injury (e.g., dissecting aneurysms, atherosclerosis, and arterial thrombosis). Segments T1 to T4 and L1 are poorly vascularized and are at risk.
- May explain the etiology of the anterior spinal artery
syndrome.
Segmental vulnerability
– is formed by the anterior communicating, anterior cerebral, internal carotid, posterior communicating,
and posterior cerebral arteries.
– gives off penetrating arteries to supply the ventral diencephalon (hypothalamus, sub thalamus, and thalamus) and the midbrain.
Arterial Circle of Willis
- Absence of valves and muscle tissue
- - Divided into: Superficial Venous System and Deep Venous System
Venous System of the Brain
- larger than their corresponding cortical arteries and tend to lie along side the arteries in the cerebral sulci
- empties into the more superfically located sinus especially the superior sagittal, inferior sagittal and the transverse sinuses via anastomotic or draining veins
Superficial Venous System
Superficial Venous System
the most prominent anastomotic veins are :
- superficial middle cerebral vein - drains into the cavernous or sphenoparietal sinus
- great anastomotic vein of Trolard drains into the superior sagittal sinus
- posterior anastomotic vein of Labbe drains into the transverse sinus
Deep Venous System
- Great vein of Galen
- Internal cerebral veins
- Basal vein of Rosenthal
- located beneath the splenium of the corpus callosum
- receives the paired internal cerebral veins, the basal vein and drainage from the medial and inferior parts of the occipital lobe
Great vein of Galen
– lie in the roof of the 3rd ventricle. Large tributaries include thalamostriate veins, choroidal and septal veins
Internal cerebral veins
- begins near the ant perforate substance, encircles the cerebral crus an ends in the great vein of the Galen
- drains the medial and inferior surface of the frontal and temporal lobes, insular and opercular cortices and region of the hypothalamus and midbrain
Basal vein of Rosenthal
- also known as somatrosensory pathway
- represent functional pathways that convey sensory information from soma or viscera to higher levels of the neuraxis
- usually consist of a chain of three neurons: first-, second, and third-order neurons. The first order neuron is always in the dorsal root ganglion.
- may decussate before reaching their final destination.
- give rise to collateral branches that serve in local spinal reflex arcs.
Ascending Pathway
General Senses/Common Sensation
- Light Touch
- Pressure
- Pain
- Temperature
- Proprioception = Vibration sense
- awareness and precise location of very delicate mechanical stimuli
- Includes: Two–point sense, Fine touch/Stereognosis and Graphesthesia
Tactile Sense
- ability to distinguish stimulation by one or two points applied to the skin
Two–point sense
- ability to recognize objects by touch alone
Fine touch / Stereognosis
- ability to recognize numbers or letters drawn on the skin
Graphesthesia
– part of dorsal column which subserves the lower extremity; medial side
Fasciculus gracilis
– part of the dorsal column which subserves the upper extremity; more laterally
Fasciculus cuneatus
- type of sensation within the body signal awareness of body position and movement in
- receptors: tendon and Muscle spindles
Proprioception
– stimuli applied to subcutaneous structures via: firmly pressing on the skin with a blunt object and squeezing subcutaneous structures
Pressure
– sensation that warns of potential injury and alerts the person to avoid or
treat it.
Pain
– within the body; detect sensory information concerning the status of the body’s internal environment, such as Stretch, blood pressure, pH, oxygen or carbon dioxide concentration and osmolarity
Enteroreceptors
o Sensory information from the external world
o respond to pain, temperature, touch, vibration and
pressure
o Further classified as :
– teloreceptors (G. tele, “distant”) - receptors that respond to distant stimuli (such as light or sound), and do not require direct physical contact with the stimulus for stimulation;
– contact receptors - transmit tactile, pressure, pain, or thermal stimuli, require direct contact of the stimulus with the body.
Exteroreceptors
– touch, pressure and proprioception
– activated following physical deformation of the skin, muscles, tendons,
ligaments, and joint capsules in which they reside
– classified as nonencapsulated or encapsulated
Mechanoreceptors
pain; rapidly adapting receptors that are sensitive to noxious or painful stimuli
Nocireceptors
– warm / cold
– Three Subtypes:
1. Cold receptors - consist of free nerve endings of lightly myelinated Aδ fibers.
2. Warmth receptors - consist of the free nerve endings of
unmyelinated C fibers; respond to increases in temperature.
3. Temperature-sensitive - nociceptors sensitive to excessive heat or cold.
Thermoreceptors
– awareness of active or passive movements of the parts of
the body;
– tested by passively flexing and extending individual fingers and toes, hand and foot, forearm and leg
– with eyes closed → recognize the direction, speed and
range of the movement
Motion sense
o awareness of the position of parts of the body
o tested by passively moving a limb or one of its parts to a
certain position and moving the opposite limb to the same
position
Position / Posture sense
- mediates tactile discrimination, vibration, form recognition, and joint and muscle sensation.
- mediates conscious proprioception.
- receives input from Pacini and Meissner corpuscles, joint receptors, muscle spindles, and Golgi tendon organs (GTOs).
Dorsal column–medial lemniscus pathway
General Sensation Receptors
Touch – Meissner’s corpuscles , Merkel’s disc , Hair follicle endings , Golgi Mazzoni
Pressure – Pacinian corpuscles
Pain – Free nerve endings
Temperature – Cold - Krause end bulb; Hot – Ruffini’s corpuscles
Proprioception – Tendon and Muscle spindles
occlusion in this vessel will cause contralateral (CL) weakness LE>UE
Anterior Cerebral Artery Occulsion
occlusion in this vessel will manifest
- Unilateral occipital lobe infarction – homonymous hemianopsia
- Cortical blindness
- Thalamic pain syndrome
Posterior Cerebral Artery (PCA) occlusion
occlusion in this vessel will manifest Triad 1. [CL] hemiplegia 2. Hemihyperesthesia 3. Homonymous hemianopsia
Anterior choroidal artery (AChA) occlusion
- Lateral Medullary syndrome (Wallenberg Syndrome)
- The only location where a lesion will produce sensory loss on Ipsilateral face and contralateral sensory loss in the body. All in the absence of pyramidal tract findings (eg weakness)
Posterior Inferior Cerebellar Artery (PICA) occlusion
occlusion in the Superior cerebellar vermis and superior cerebellum
Superior Cerebellar Artery (SCA) Occlusion
occlusion in this artery will cause Hemiparesis UE>LE, proximal muscles weaker than distal
Recurrent artery of Heubner Occlusion
Functional Division of the Ascending Spinal Tracts
- Conscious Tracts – Dorsal Column and Anterolateral System
- Unconscious Tracts – Spinocerebellar Tracts
Somatosensory Receptor and their Peripheral Axons (Receptor Type and Information Processed) 1
- Muscle Spindle: Annulospiral endings – Muscle length and velocity
- Muscle Spindle: Flower Spray endings – Muscle length
- Golgi Tendon Organ – Muscle tension
- Joint: Pacinian – Joint movement
- Joint: Ruffini – Joint angle
- Joint: Golgi Tendon Organ – Joint torque
Somatosensory Receptor and their Peripheral Axons (Receptor Type and Information Processed) 2
- Meissner corpuscle – Touch, flitter or movement
- Pacinian corpuscle – Vibration
- Ruffini corpuscle – Skin stretch
- Hair follicle – Touch movement
- Merkel complex – Fine touch
- Free Nerve endings (Axon Group III) – Sharp pain or cool/cold
- Free nerve endings (Axon Group IV) – Dull or aching pain, or touch or warm
- Discriminating tactile sense (touch and pressure) and kinesthetic sense (position and movement)
- – Receptors: pacinian corpuscle, unencapsulated joint receptor, Golgi-Mazzoni corpuscle and Meissner’s corpuscle
Dorsal Column Pathway
Dorsal Column Pathway
First Order Neuron: Dorsal Root Ganglion
Fasciculus Gracilis: Lower Extremities
Fasciculus Cuneatus: Upper Extremities
Second Order Neuron: Nucleus gracilis
Nucleus cuneatus
Third Order Neuron: Ventral Posterolateral nucleus of thalamus
Anterolateral System
Anterior Spinothalamic Tract – carries the sensory modalities of crude touch and pressure
Lateral Spinothalamic Tract – carries the sensory modalities of pain and temperature.
- Largest number of spinothalamic fibers arise from cells in laminae I, IV, and V contra laterally
- Conveys impulses associated with “light touch”
- Receptors: Meissner’s corpuscle (tactile)
Anterior Spinothalamic Tract
Anterior Spinothalamic Tract
First Order Neuron: Dorsal Root Ganglion
Second Order Neuron: Substantia Gelatinosa
Third Order Neuron: Ventral Posterolateral nucleus of Thalamus
- Transmits impulses for pain and thermal sense
- Cells of origin largely in laminae I, IV and V
- Cross to the opposite side
- Fibers related to thermal sense ten to be posterior to those related to pain
- Receptors: free nerve endings (pain), cold and heat receptors of dermatome
Lateral Spinothalamic Tract
Lateral Spinothalamic Tract
First Order Neuron: Dorsal Root Ganglion
Second Order Neuron: Substantia Gelatinosa
Third Order Neuron: Ventral Posterolateral nucleus of Thalamus
- Spinal tract and Nucleus of V: pain and temperature sensation
- Chief sensory nucleus of V: vibration, proprioception and light touch/tactile discrimination
- Mesencephalic nucleus of V: unconscious proprioception
Trigeminothalamic Tract
- Facial equivalent of the dorsal column pathway
- Proprioception, touch and vibration form the face, head and neck
- Receptors: Meissner’s and Pacinian corpuscles
- Some fibers remain uncrossed
Trigeminal Leminiscus
- Serves as pain and temperature pathway of the face, head and neck
- Facial equivalent of the spinothalamic tract
Trigeminothalamic Tract
Trigeminothalamic Tract
Trigeminal Ganglion (1st order)»enter the pons and descend the medulla»form spinal trigeminal tract»synapse in the spinal trigeminal nucleus (2nd order)»cross midline»VPM of the thalamus»postcentral gyrus of the sensory cortex
Trigeminal Leminiscus
- 1st Order: Trigeminal Ganglion
- Enter the pons synapse in the principal sensory trigeminal nucleus (2nd order)»axons cross midline»VPM (3rd order)»postcentral gyrus sensory cortex
– Carries proprioceptive information from the lower limbs to the ipsilateral cerebellum.
Posterior Spinocerebellar
Posterior Spinocerebellar
1st Order Neuron: DRG
2nd Order Neuron: Dorsal nucleus of clarke, uncrossed
»Spinal Cord medulla, pons»inferior cerebellar peduncle»rostral and caudal vermis
Carries proprioceptive information from the upper limbs to the ipsilateral cerebellum.
Cuneocerebellar Tract
Cuneocerebellar Tract
1st Order Neuron: DRG
2nd Order Neuron: Dorsal nucleus of clarke, uncrossed
– Terminate on the cells of the accessory cuneate nucleus in the medullainferior cerebellar peduncle»lobule V of cerebellar cortex
– Carries proprioceptive information from the lower limbs.
– The fibres decussate twice – and so terminate in the ipsilateral cerebellum.
– 2 Decussations: anterior white commissure and cerebellum
– DRG (1st order)»_space;dorsal horn (2nd Order)»
synapse»cross via anterior white commissure»
lateral funiculi»medulla, pons»superior cerebellar peduncle»cerebellum»recross midline»
anterior lobe and vermis of posterior lobe
Anterior Spinocerebellar Tract
– Cells of the posterior horn
– Spinal cordreticular formation in the brainstem
– Behavioral awareness, modification of motor and sensory activities and in the modulation of electrocortical activity
Automatic responses to pain/directs attention toward painful stimuli
Spinoreticular Tract
- Carries proprioceptive information from muscles and tendons as well as cutaneous impulses to the olivary nucleus
- Axons enter spinal cord from the DRG terminate on unknown 2nd order neurons in the posterior gray column»cross midline»ascend as the spino-olivary tract» synapse in the inferior olivary nuclei (3rd order)
- -Cross midline and enter cerebellum via ICP
Spino-Olivary Tract
Dermatomes
Area of the skin supplied by a single nerve C2: hood distribution C3 and C4: cape distribution C5-T1: UE T4: Nipple T10: Umbilicus L1: Groin L5: large toe S1: small toe
Descending Pathwaysare composed of:
- Corticospinal Tract
- Reticulospinal Tract
- Tectospinal Tract
- Rubrospinal Tract
- Vestibulospinal Tract
- Olivospinal Tract
- Descending Autonomic Fibers
Descending pathway is what type of neuron?
Motor neuron
Ascending pathway is what type of neuron?
Sensory neuron
Kinds of sensation perceived by Ascending pathway
Pain, temperature and vibrations
Spinal Cord Organization: White Matter is located?
OUTSIDE
Spinal Cord Organization: Gray Matter is located?
INSIDE
Brain Organization: White Matter is located?
INSIDE
Brain Cord Organization: Gray Matter is located?
OUTSIDE
Why is white matter white and Gray matter gray?
CELL BODIES that clump together which makes it DARK
Cell bodies can only be found in
GRAY MATTER
Gray Matter is composed of
- Nucleus
* Ganglion
Size of the Cortex
4 to 5 mm
White matter of Spinal Cord is subdivided into
- Anterior Funiculus (motor)
- Lateral Funiculus ( Contains the Rubrospinal , Lateralspinal and Most important)
- Posterior Funiculus (sensory)
Anterior Funiculus is subdivided into
- Anteriorcorticospinal
- Vestibulospinal
- Tectospinal
- Reticulospinal
Motor cortex is what part of the brain?
Pre-central Gyrus (where commands come from)
The axons will descend along with other axons of other cell bodies into
Internal Capsule
Fibers that command the lower extremity lies on
Medial part
Fibers that command the upper extremity lies on
Lateral part
Internal capsule contains
Fibers of face, arms, legs, pharyngeal and eye muscles
Corona radiata descend into
Internal Capsule
Descending pathway: In order
• Internal capsule • Cerebral peduncle • Midbrain • Pons • Medulla (pyramids of medulla) • Cervicomedullar decussation (Right goes to Left, Left goes to right) • Spinal Cord • Stops descending in C6 • Ventral horn • Anterior horn • Synapse at 2nd cell bodies • Axon • Ventral root (motor) • Join the Dorsal root (mixed)
Connects hemisphere into the brainstem
Cerebral peduncle
Percentage of fibers crossed (innervates PERIPHERAL MUSCLES)
95%
Percentage of fibers uncrossed (innervates AXIAL MUSCLES)
10%
Fiber that has crossed goes into
Lateralcorticospinal tract
Fibers that has uncrossed goes into
Anteriorcorticospinal tract
Fibers that descend on the spinal cord is in the
White matter (lateral funiculus)
Combination of Ventral root and Dorsal root equals
Peripheral Nerve
Peripheral Nerve has this type of neuron
Motor and Sensory neurons
Type of neuron when it has already passed the Dorsal root
Mixed (motor and sensory)
Lesion on the Peripheral Nerve will cause
- Both motor and sensory finding
* Weak and Numb
From the Cortex to the Peripheral Nerve, how many neurons are there?
2 cell bodies (upper and lower motor neurons)
Motor Cortex Lesion
- Half of the brain has no blood supply
* Not conscious
Type of MRI where you can draw on the images where Corticospinal tract fibers are
Functional MRI
Outpatient procedure, uses high powered laser which burns the tumor
Gamma Knife
Cranial nerves are what kind of neuron?
Motor neuron
Facial nerves have what kind of symmetry?
Ipsilateral symmetry
Tracts that leaves the same time
- Corticospinal tract
* Corticobulbar tract (leaves earlier)
True or False
Corticobulbar tract is not a part of Descending pathway because is not seen in Spinal Cord
TRUE
Tract that controls the movement
Corticospinal trat/ Lower Motor Neuron
Pathway that governs the Reflex, autonomic fibers
Reticulospinal tract
Small islands in Reticulospinal tract that is important in CONSCIOUSNESS
Reticular Formation
Patellar Reflex is governed by
Reticulospinal tract
Pathway that commands the eye and neck movement
Tectospinal tract
Pathway that governs the FLEXION build and INHIBIT EXTENSORS
Rubrospinal tract
Pathway that governs EXTENSTION build and INHIBITS FLEXION; for balance
Vestibulospinal tract
Tests for BRAIN DEAD confirmation
Doll’s eye movement
Pupil size test to know where the damage are in
- Midbrain- 4mm
- Medulla- 6mm
- Pons- pinpoint
Pathways by which the motor signals are sent from the brain to LMN
Descending tract
Ascending Pathways
- Posterior Columns
- Spinothalamic Tracts
- Spinocerebellar Tract
White Matter of Spinal Cord divisible into:
Anterior Funiculus
Posterior Funiculus
Lateral Funiculus
Descending Tracts
Lateral corticospinal Rubrospinal Lateral reticulospinal Medial reticulospinal Vestibulospinal Tectospinal Anterior corticospinal
Motor Pathway
Motor Cortex Corona radiata Internal capsule Cerebral peduncle Brainstem Cervicomedullary junction Corticospinal tract Anterior horn cell Ventral root Peripheral nerve Neuromuscular junction Muscle
- Coming from the RETICULAR FORMATION of the midbrain, pons and medulla
- Descend to the anterior and lateral white columns and enter the gray matter
- These tracts influence the motor neurons
- INFLUENCE VOLUNTARY AND REFLEX MOTOR ACTIVITIES
- Also include the DESCENDING AUTONOMIC FIBERS from the hypothalamus
Reticulospinal Tract
- Arise from the neurons in the SUPERIOR COLLICULUS OF THE MIDBRAIN
- Fibers descend close to the MEDIAL LONGITUDINAL FASCICULUS of the midbrain
- Descends thru the anterior white column and synapse with the internuncial neurons and terminate in the anterior gray matter of the upper cervical spinal cord
- Concerned with REFLEX POSTURAL MOVEMENTS in response to VISUAL STIMULI
Tectospinal Tract
- Arise from the RED NUCLEUS of the tegmentum of the midbrain
- Descend thru the pons and medulla to the lateral white column of the spinal cord
- Receives afferent impulses from the CEREBRAL CORTEX and the CEREBELLUM
- An indirect pathway to influence the motor neurons
- Facilitates the activity of the flexor muscles and inhibits the activity of extensor muscles
Rubrospinal Tract
- Arises from the VESTIBULAR NUCLEI in the pons and medulla
- Receives afferents from the vestibular nerve and the cerebellum
- Descend thru the anterior white column
- Synapse with the interneurons of the anterior gray matter
- This is a means by which the inner ear and the cerebellum facilitate the activity of extensor muscles and inhibit flexor muscles
Vestibulospinal Tract
- Arises from the INFERIOR OLIVARY NUCLEUS of the medulla
- Descends thru the lateral white column
- Influences the activity of the motor neurons
Olivospinal Tract
Dorsal Column lesion will cause:
Ipsilateral loss of light tough, vibration, and position sense generalized below the lesion level.
Fasciculus Cuneatus Lesion will cause:
Ipsilateral loss of light touch, vibration, and position sense in the right arm and upper trunk.
Lateral Spinothalamic tract lesion will cause
Contralateral loss of pain and temperature sense
