Block 8 H&N

Tentorium Cerebelli

tent-like dural partition between the cerebral hemispheres and the Cerebellum, with a hiatus between the left and right sides, allowing the brainstem to connect with the Cerebrum.

Tentorial notches

edges of the tentorium

Kernig’s Test & Sign

1. Passive flexion of hip

2. Passive extension of knee

3. Pain with knee extension

Brudzinski’s Test & Sign

1. With passive flexion of neck

2. Patient feels pain in neck

3. Pain is spontaneous, involuntary hip and knee flexion

4. Reflexive response to neck flexion and pain is possibly an unconscious compensatory response dural tension and pain induced by the neck flexion

4 major arteries supplying Brainstem & Cerebellum

superior cerebellar artery

anterior inferior cerebellar artery

posterior inferior cerebellar artery

anterior spinal artery

Anterior Cerebral Artery (ACA)

supplies medial and dorsolateral parts of frontal and parietal lobes

Posterior Cerebral Artery (PCA)

supplies ventral and some lateral surface of temporal and occipital lobes

excluded from entering the brain

dopamine, adrenal epinephrine, some medications like penicillin

thrombotic occlusion

formation of a blood clot and occlusion at that location

embolic occlusion

embolism is formed at some location and travel distally in an artery until it lodges and occludes blood flow.

thrombotic vs. embolic occlusion

thrombotic mechanisms are recurring events so a prodrome may be generated

Epidural

rupture of meningeal artery, typically due to head trauma

Subdural

rupture of bridging veins: cerebral veins as they extend in to dural sinus

more vulnerable to rupture in elderly, with alcohol abuse, or any condition involving brain atrophy

Subarachnoid

diffuse spread of blood through subarachnoid space, detectable by lumbar puncture

exceptionally painful, “worst headache of my life”

increases intracranial pressure, can clog arachnoid villi

arteriovenous malformations

failure to form capillary bed leads to arteries/arterioles becoming entangled with veins/venules

Neural tube

differentiates into CNS

Neural crest

gives rise to cells that form most of the PNS and ANS

neuroprogenitor cells of the neural tube (neural canal) thicken and form

ventricular system of the brain

central canal of the spinal cord

alar plate cell bodies

form dorsal gray columms/horns

= afferent nuclei

basal plate cell bodies

form ventral and lateral gray columns/horns

= efferent nuclei, motor

CSF flow

produced in choroid plexuses of the ventricles, exits the fourth ventricle, circulates in the subarachnoid space, and enters the superior sagittal sinus via the arachnoid granulations

What brains regions comprise the cerebrum?

Cerebrum = frontal, parietal, occipital, temporal lobes

What brain regions does the term telencephalon refer to?

includes cerebral cortex, basal ganglia, and limbic system

What brain regions does the term diencephalon refer to?

thalamus, hypothalamus, epithalamus (includes pineal gland), subthalamus

telencephalon + diencephalon

= forebrain

List the major brain regions in caudal to rostral order

Caudal to Rostral:

1. Spinal cord

2. Medulla oblongata

3. Pons

4. Midbrain (mesencephalon)

5. Diencephalon (including thalamus, hypothalamus, epithalamus, and subthalamus)

6. Telencephalon (cerebrum)

Spatial Relationship between pons and cerebellum

Pons is more anterior and inferior to cerebellum

Deepest parts of each of the ventricles

telecephalon - lateral ventricles

diencephalon - third ventricle

midbrain - cerebral aqueduct

between pons and cerebellum - fourth ventricle

between medulla and cerebellum - fourth ventricle

inside spinal cord - central canal of the spinal cord

Falx cerebri

A sickle-shaped fold of dura mater that descends vertically in the longitudinal fissure between the cerebral hemispheres, separating them.

Falx cerebelli

A small midline dural fold that runs vertically along the vermis of the cerebellum, separating the two cerebellar hemispheres.

What is the normal range for intracranial pressure?

The normal range for intracranial pressure (ICP) is typically considered to be between 5 and 15 mmHg (millimeters of mercury) when measured in adults

Pathway of manometer into a lateral ventricle

skull, epidural space, dura mater, subdural space, arachnoid mater, subarachnoid space, lateral ventricle

What clinical problem does papilledema indicate?

increased intracranial pressure, which can occur due to various conditions such as intracranial tumors, hydrocephalus, meningitis, or cerebral edema.

Which specific meningeal layer contains pain-sensitive nerve fibers?

meningeal layer that contains pain-sensitive nerve fibers is the dura mater

What specific nerves carry this sensory information from the meninges to the CNS?

sensory information from the meninges to the central nervous system (CNS) is carried primarily by the branches of the trigeminal nerve (cranial nerve V), specifically the ophthalmic (V1), maxillary (V2), and mandibular (V3) divisions.

What kinds of stimuli can activate these sensory fibers?

1. Mechanical stimuli: Such as pressure or stretching of the meninges, as may occur with intracranial hypertension or traction on the dura mater during surgical procedures.

2. Chemical stimuli: Release of inflammatory mediators or metabolic byproducts due to tissue injury, inflammation, or infection within the meninges.

3. Vascular stimuli: Changes in blood flow or vascular integrity within the meninges, such as with vasodilation or vasoconstriction, can lead to pain sensation.

sequence of dural sinuses that venous blood can flow through to drain the brain and exit the cranium

superior sagittal sinus, inferior sagittal sinus, straight sinus, confluence of sinuses, transverse sinuses, sigmoid sinuses, internal jugular veins

Atherosclerosis

Accumulation of plaque (composed of cholesterol, fat, and other substances) on the inner walls of arteries can narrow the arterial lumen and lead to occlusion, reducing blood flow to downstream tissues.

Arterial Dissection

Tear in the inner lining of an artery (intima) can cause blood to enter the arterial wall, leading to the formation of a dissecting hematoma that narrows or occludes the arterial lumen.

Vasculitis

Inflammatory conditions affecting the blood vessels, such as giant cell arteritis or systemic lupus erythematosus, can cause vessel wall damage and subsequent occlusion.

Intraparenchymal Hemorrhage (IPH)

1. Type of Vessel Involved: Typically involves small penetrating arteries or arterioles, commonly associated with hypertension or cerebral amyloid angiopathy.

2. Location of Vessels: The bleeding occurs directly within brain tissue, rather than within the subarachnoid space.

3. Common Causes: Hypertension, cerebral amyloid angiopathy, trauma, bleeding disorders, and vascular malformations are common causes of intraparenchymal hemorrhage.

neuroimaging techniques typically used to evaluate a patient suspected of having a stroke

CT, MRI, Perfusion Imaging, Transcranial Doppler Ultrasound

Where are the lateral ventricles found? Where is CSF produced? What are some circumventricular organs?

largest ventricles in the brain and are situated deep within the cerebral hemispheres

CSF is primarily produced by the choroid plexus

Circumventricular organs (CVOs) are specialized structures located around the third and fourth ventricles in the brain

What is the difference between communicating and noncommunicating hydrocephalus? How is idiopathic intracranial hypertension different?

communicating hydrocephalus involves impaired CSF absorption or circulation outside the ventricular system

noncommunicating hydrocephalus involves obstruction within the ventricular system itself

idiopathic intracranial hypertension involves elevated intracranial pressure without hydrocephalus

normal composition of CSF

Water, Electrolytes, Glucose, Proteins, Cells

increase in red blood cells (RBCs) in the CSF

Traumatic Tap, Subarachnoid Hemorrhage, Intraventricular Hemorrhage, Meningitis or Encephalitis, Tumor Bleeding

developmental origin of CNS

neural plate - ectoderm

neural tube - consists of a single layer of neuroepithelial cells, becomes spinal cord

what induces the neural plate to form?

Shh - plays a role in inducing the formation of the notochord

Wnt - contibute to neural plate induction

what are the neuroectodermal cells not included in the neural tube that remain between the neural tube and surface ectoderm

neural crest cells move away from neural tube and differentiate into: peripheral nervous system, craniofacial structures, cardiovascular system, pigment cells, and endocrine system

what does mesencephalon become

aka the midbrain, becomes the tectum and cerebral peduncles

what does the hindbrain give rise to

Metencephalon: pons and cerebellum

Myelencephalon: medulla oblongata

What is the origin of unipolar neurons in the dorsal root ganglia?

These reside in the dorsal root ganglia and originate from neural crest cells. They play a critical role in transmitting sensory information from the periphery to the central nervous system contributing to perception, reflexes, and motor control.

What causes spinal bifida cystica?

incomplete closure of the neural tube during embryonic development, leading to malformation of the spinal cords and its protective coverings

What is an example of a major birth defect incompatible with life?

Meroencephaly - sever calvaria and brain defect resulting from failure of the rostral neruopore to close

What is an example of a severe birth defect that causes a functional disability (e.g., muscle paralysis in the lower limbs)?

Spina bifida is a neural tube defect that occurs when the neural tube, which forms the spinal cord and the brain, fails to close properly during embryonic development.

most severe forms of spina bifida is called myelomeningocele, where the spinal cord and its covering membranes (meninges) protrude through the opening in the spine and form a sac or cyst on the baby's back.

importance of vitamin A

retinoic acid is key in the development of the spinal cord

During the fifth week, what do the three primary brain vesicles become?

Prosencephalon - telencephalon and diencephalon

Mesencephalon

Rhombencephalon - metencephalon and myelencephalon

What is blockage of CSF flow in the ventricular system called?

hydrocephalus

What is the blockage of CSF flow in the subarachnoid space called?

obstructive hydrocephalus

What is congenital hydrocephalus associated with in most cases?

1. aqueductal stenosis: narrowing or blockage of the cerebral aqueduct which connects the third and fourth ventricles

2. dandy-walker malformation: cystic enlargement of the fourth ventricle

3. arnold-chiari malformation: herniation of the cerebellar vermis and brainstem through foramen magnum

4. neural tube defects

5. intraventricular hemorrhage

What are some causes of prenatal and postnatal cognitive deficits?

1. pre-natal causes: genetic/chromosomal abnormalities, maternal illness, premature birth, hypoxic-ischemic injury

   1. post-natal causes: brain injury, infectious diseases, neurodevelopmental disorders

most common cause of NTDs

vitamin B9 (folate) deficiency

Explain what the term dermatome means

area of skin that is primaryly innervated by the sensory fibers of a single spinal nerve root

Explain why referred pain happens in terms of neural mechanisms.

misinterpretation of visceral sensory signals as originating from somatic structures

What aspect of motor function is served by the Corticospinal System?

control of voluntary movement, particularly fine and skilled movement of distal musculature

Describe how a muscle spindle works to sense muscle stretch

they detect changes in muscle length and provide feedback to the central nervous system (CNS) regarding muscle position and movement

Explain the function of the nociceptive withdrawal reflex. How is it useful clinically?

protective mechanism that helps to minimize injury in response to noxious stimuli, primary function of the nociceptive withdrawal reflex is to rapidly remove the affected body part from the stimulus source

Spinal Lower Motorneurons, different levels of cord and body region served

Cervical Plexus: C1-C4

Brachial Plexus: C5-T1

Lumbosacral Plexus: L1-S5

Concept of mytotomes

lateral horn

only present T1-L2 and contains sympathetic neurons for output

stretch reflex arch

stretch provides feedback to activate the LMN, which triggers active muscle contraction

LMN lesion abolishes reflex arch

UMN lesion enhances reflex (hyper-reflexive)

UMN lesion

firm stroking of the sole of the foot causes dorsiflexion of the ankle, extension, and spreading of the toes

lateral corticospinal pathway

controls muscles of the distal limbs

responsible for precise, highly skilled movements

Trigeminal Nerve Pathway

UMNs bilaterally innervate the LMNs

LMNs in the masticator nuclei of the Pons control the ipsilateral muscles of mastication - via the mandibular division of the CN V3

Function Test: patient protrudes their jaw

1 degree neuron

pseudounipolar with its cell body located in the DRG of the PNS

cell body is in the trigeminal ganglion for the face

axons ascend ipsilaterally in the fasciculus gracilis

2 degree neuron

cell body is located in the dorsal horn of the spinal cord OR a brainstem nucleus

then decussates and its axon projects to the contralateral thalamus

ascend contralaterally in the medial lemniscus

3 degree neuron

cell body located in the VP nucleus of the thalamus and projects to the somatosensory cortex

Anterior Spinothalamic Tract

carries information involving crude touch sensation

Lateral Spinothalamic Tract

carries information involving pain and temperature sensation

Primary Motor Cortex Damage

UMN damage: ALS, cerebral palsy (hypoxia/ischemia), Ischemic stroke

Upper Cervical Damage

UMN damage: brainstem infarcts (UMN axons)

Lower Cervical/Upper Thoracic Damage

UMN damage: white matter disease, spinal cord injury

Lower Lumbar/Mid-Sacral Damage

LMN damage: spinal cord pathology, peripheral neuropathy, neuromuscular junction, myopathy (muscle disease)

Sympathetic NS: Urinary Storage

inhibits detrusor (beta mediated)

activates internal sphincter (alpha 1 mediated)

Sacral Parasympathetics: Urinary Voiding

activates detrusor (muscarinic)

inhibits internal sphincter

Sacral Anterior Horn Motorneuron: Urinary Retention

activates external sphincter (muscarinic)

urination requires inhibiting this pathway

mesencephalic

located in the midbrain

onion skin pattern of pain loss

more caudal the damage, the larger the area of the mouth is spared

corneal blink reflex

afferent limb in CN V

efferent limb in CN VII

Jaw Jerk Reflex

mediated through the trigeminal nerve V3

Merkel’s touch domes

fine/discriminative touch

hairs: motion

pick up light pressure, edges, texture

Pacinian corpuscles

vibration

Meissner’s

tap, flutter, texture

Ruffini

proprioception, skin stretch, joint movement

Free nerve endings

pain and temperature

Friedreich’s ataxia

neurodegenerative disease, autosomal recessive

sensory ataxia is most evident as impaired coordination of walking

romberg’s sign:

primary gaze

each of the six extra-ocular muscles works in coordination to maintain alignment and stability of the eyes

medial rectus muscle is affected

diplopia is worse when looking toward the affected side

primary muscle “looking in”

lateral rectus muscle is affected

diplopia is worse when looking toward the unaffected side

key muscle used when looking out

Cranial Nerve VI (Abducens Nerve) Damage

the affected eye typically deviates inward toward the nose due to unopposed action of the medial rectus muscle

Diplopia is typically worst when looking laterally toward the affected side (abduction is impaired), as the eyes cannot properly align to maintain single binocular vision