Head and Neck: The Nervous System

What structure does the Neural Tube differentiate into?

Central Nervous System (CNS)

Into which secondary brain vesicles does the Forebrain (Prosencephalon) divide at the 5th week of development?

Telencephalon and Diencephalon

Does the Midbrain (Mesencephalon) divide into secondary vesicles at the 5th week of development?

No division (remains Mesencephalon)

Into which secondary brain vesicles does the Hindbrain (Rhombencephalon) divide at the 5th week of development?

Metencephalon and Myelencephalon

Which primary embryonic structure gives rise to the PNS, ANS, and cranial/spinal/autonomic ganglia?

Neural crest

What are the main derivatives of the Neural Crest?

Sensory ganglia of cranial and spinal nerves, neurilemmal sheath of peripheral nerves, meninges, pigment cells of retina, and cells of adrenal medulla

What is the underlying embryological cause and genetic mutation of Hirschsprung Disease (congenital megacolon)?

Failure of neural crest migration secondary to a RET mutation

Which enteric nerve plexuses are absent in the distal colon in Hirschsprung Disease, and what is the outcome?

Auerbach and Meissner plexuses are absent; leads to failure of peristalsis in the aganglionic segment resulting in congenital megacolon

What is the typical clinical history of a newborn with Hirschsprung Disease?

Bilious emesis, abdominal distention, and failure to pass meconium within 48 hours of birth

What key physical examination finding (on DRE) is classic for Hirschsprung Disease?

Squirt sign (explosive expulsion of feces on digital rectal examination)

What is the definitive treatment for Hirschsprung Disease?

Surgical resection

How is the human body positioned in normal anatomical position?

Body erect, head directed anteriorly, and forearm on sides supinated

The Medulla Oblongata is a derivative of which secondary brain vesicle?

Myelencephalon

From which germ layer and during which week of development does nervous tissue develop?

Develops from the ectoderm in the 3rd week of development

What is the functional unit of the nervous system?

Neuron

What are alternative names for the neuronal cell body?

Perikaryon or soma

What are the characteristic features of a neuron's nucleus, neuroplasm, and Nissl bodies?

Nucleus: large, euchromatic with a prominent nucleolus; Neuroplasm: cytoplasm with many polyribosomes and RER; Nissl bodies: basophilic regions of many ribosomes and RER

What is the direction of impulse transmission in an Axon?

Transmits impulses away from the cell body ("Axon Away")

What is the Axon Hillock?

Region of the cell body where the axon originates

What is a Terminal Bouton?

Distal dilation that contacts another neuron

What is the composition of Axoplasm?

Cytoplasm rich in mitochondria, microtubules, neurofilaments, and transport vesicles

In which nervous system division is the Neurilemmal Sheath enveloped by a basal lamina?

PNS only

Which myelinating cell type forms the neurilemmal sheath in the PNS vs CNS?

Schwann cells in the PNS; Oligodendrocytes in the CNS

What is Myelin?

Compacted layers of cell membrane internal to the neurilemmal sheath

What is the direction of impulse transmission in a Dendrite?

Transmits impulses toward the cell body

What are Dendritic Spines and why are they clinically important?

Dynamic membrane protrusions in dendrites that are important for neural plasticity

What is the morphology of a Unipolar neuron, and what is a primary example?

Morphology: Single process that bifurcates; Example: Most sensory neurons

What is the morphology of a Bipolar neuron, and what are primary examples?

Morphology: One axon and one dendrite; Examples: Vestibular and cochlear ganglia, Olfactory epithelium

What is the morphology of a Multipolar neuron, and what is its prevalence?

Morphology: One axon with two or more dendrites; Prevalence: Most common type of neuron

What is the morphology and function of an Anaxonic neuron, and what are primary examples?

Morphology: Many dendrites but no true axon; Function: Regulates charges of adjacent neurons; Examples: Some CNS neurons, Retina (amacrine and horizontal cells)

What is Neuropil?

Intercellular network of processes from neurons and neuroglia

Which neuroglial cells originate from the Neural Tube (ectoderm)?

Astrocytes, oligodendrocytes, and ependymal cells

Which neuroglial cells originate from the Neural Crest (ectoderm)?

Schwann cells and satellite cells

Which neuroglial cell originates from Bone Marrow (mesoderm)?

Microglia

What is the structure and function of Astrocytes in the CNS?

Structure: Star-shaped, largest and most numerous glial cell; Function: Structural and metabolic support/repair

What is the structure and function of Oligodendrocytes in the CNS?

Structure: Condensed nucleus, scanty cytoplasm, predominant glia in white matter; Function: Forms myelin and neurilemmal sheath around several axons

What is the tissue origin of Microglia?

Monocyte origin

How are Microglia distributed throughout the CNS?

Evenly distributed throughout the CNS

What are the main functions of Microglia?

Defense, immunity, and phagocytosis

What is the histological shape of Ependymal Cells?

Simple cuboidal

Which cavities are lined by Ependymal Cells?

Ventricles and central canal of the spinal cord

Do Ependymal Cells possess a basal lamina?

No basal lamina

What are the primary functions of Ependymal Cells?

CSF production and movement

What is the alternative name for Schwann Cells?

Neurolemmocytes

What is the physical description of Schwann Cells?

Small, flat cells

How many axons can a single Schwann Cell myelinate at one time?

A single axon

What are the primary functions of Schwann Cells in the PNS?

Forms myelin and neurilemmal sheath around a single axon

What are the alternative names for Satellite Cells?

Mantle cells or amphicytes

Where are Satellite Cells located?

Wrapped around neuronal cell bodies in ganglia

What are the primary functions of Satellite Cells?

Structural and metabolic support of neurons

Which secondary brain vesicle develops from the Telencephalon?

Telencephalon

Which adult brain structures develop from the Telencephalon?

Cerebrum (cerebral hemispheres, cortex, white matter, basal nuclei)

Which adult neural canal regions develop from the Telencephalon?

Lateral ventricles

Which adult brain structures develop from the Diencephalon?

Diencephalon (thalamus, hypothalamus, epithalamus) and retina

Which adult neural canal region develops from the Diencephalon?

Third ventricle

Which adult brain structure develops from the Mesencephalon?

Brain stem: midbrain

Which adult neural canal region develops from the Mesencephalon?

Cerebral aqueduct

Which adult brain structures develop from the Metencephalon?

Brain stem: pons and cerebellum

Which adult neural canal region develops from the Metencephalon?

Fourth ventricle

Which adult brain structure develops from the Myelencephalon?

Brain stem: medulla oblongata

Which adult neural canal region develops from the Myelencephalon?

Central canal

Which adult brain structure develops from the caudal neural tube?

Spinal cord

Which adult neural canal region develops from the caudal neural tube?

Central canal

What defines the boundary of the Supratentorial level?

Located above the tentorium cerebelli

Which cerebral structures are located at the Supratentorial level?

Cerebrum, basal ganglia, thalamus, and hypothalamus

Which cranial nerves are located at the Supratentorial level?

CN I and CN II

What defines the anatomical boundaries of the Infratentorial level?

Located below the tentorium cerebelli but above the foramen magnum

Which brainstem structures are located at the Infratentorial level?

Midbrain, Pons, and Medulla Oblongata

Which cerebellar structure is located at the Infratentorial level?

Cerebellum

Which cranial nerves are located at the Infratentorial level?

CN III to CN XII

What defines the anatomical boundaries of the Spinal level?

Located below the foramen magnum but contained within the vertebral column

Which CNS structures are located at the Spinal level?

Spinal cord and spinal nerves within the vertebral column

What defines the location of the Peripheral level?

Neuromuscular structures located outside the skull and outside the vertebral column

Which nerves belong to the Peripheral level?

Cranial nerves, spinal nerves, and their peripheral branches

What higher cognitive functions are governed by the Cerebrum?

Perceives sensations, commands skilled movements, awareness of emotions, memory, thinking, and language abilities

Which lobe of the cerebrum contains the primary motor area?

Frontal lobe

Which lobe of the cerebrum is considered the seat of mental activities?

Frontal lobe

What is the primary functional center of the Parietal lobe?

Somesthetic center

What is the primary functional center of the Occipital lobe?

Visual center

What is the primary functional center of the Temporal lobe?

Hearing center

What functional cortical area is located in the pre-central gyrus?

Primary Motor Area

What is the Brodmann Area designation for the Primary Motor Area?

BA 4

What functional cortical area is located in the post-central gyrus?

Primary Somesthetic Area

What is the Brodmann Area designation for the Primary Somesthetic Area?

BA 3, 1, 2

What functional cortical area is designated as Brodmann Area 17?

Primary Visual Area

In which cerebral gyrus is Wernicke's Area located?

Superior temporal gyrus

What is the Brodmann Area designation for Wernicke's Area?

BA 22

What functional type of aphasia results from damage to Wernicke's Area?

Sensory aphasia

In which cerebral gyrus is Broca's Area located?

Inferior frontal gyrus

What is the Brodmann Area designation for Broca's Area?

BA 44, 45

What functional type of aphasia results from damage to Broca's Area?

Motor aphasia

What is the auditory comprehension ability of a patient with Wernicke's Aphasia?

Patient hears but does not understand (cannot comprehend)

What is the speech characteristics pattern in Wernicke's Aphasia?

"Word salad" (speaks fluent but nonsensical sentences)

What is the auditory comprehension ability of a patient with Broca's Aphasia?

Patient CAN comprehend language

What is the speech characteristics pattern in Broca's Aphasia?

"Broken speech" (speech is slow, deletes many words, difficulty putting words together)

What is the comprehension ability of a patient with Conduction Aphasia?

Patient CAN comprehend

What is the fluency of speech in Conduction Aphasia?

Patient is fluent in speech

What is the primary deficit in Conduction Aphasia?

Difficulty repeating words

What two aphasia types combine to form Global Aphasia?

Broca's aphasia and Wernicke's aphasia

Which gyrus houses the primary motor cortex?

Precentral gyrus