NEURO 523 > Neurulation > Flashcards

Neurulation Flashcards

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1
Q

Mammalian Brains

A

Look very different but actually just slight
modifications of the same theme
Subcortical areas common amongst vertebrates

Similar structures in all mammalian brains

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2
Q

Central Nervous System (CNS)

A

Cell bodies in the brain and spinal cord

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3
Q

Peripheral Nervous System (PNS)

A

Cell bodies outside the brain and spinal cord

Cerebrum, cerebellum. brainstem, spinal cord

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4
Q

Anatomical references

A

Rostral – Latin for beak
Caudal – Latin for tail
Dorsal – Latin for back
Ventral – Latin for belly

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5
Q

Cerebrum

A

Split into two hemispheres by sagittal fissure. Largest and most rostral part of the brain
HEMISPHERES MEDIATE SENSATION AND MOVEMENT IN CONTRALATERAL BODY.

LEFT HEMISPHERE – RIGHT BODY; RIGHT HEMISPHERE – LEFT BODY

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6
Q

Cerebellum

A

LATIN FOR LITTLE BRAIN
CONTAINS AS MANY NEURONS AS THE CEREBRAL HEMISPHERES DESPITE BEING SMALLER
IT IS THE MOVEMENT CONTROL CENTER AND HAS EXTENSIVE CONNECTIONS
ROSTRALLY TO CEREBRUM AND CAUDALLY TO SPINAL CORD
CONTROL IN THE CEREBELLUM IS IPSILATERAL

RIGHT CONTROLS RIGHT SIDE OF BODY; LEFT CONTROLS LEFT SIDE OF BODY

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7
Q

Brain stem

A

Pathway to spinal cord.
Also the area of regulation of vital organs.
MOST PRIMITIVE PART OF THE BRAIN
COMPLEX NEXUS OF FIBER TRACTS AND NUCLEI
FIBER TRACTS CONNECT CEREBRUM TO SPINAL CORD AND CEREBELLUM
NUCLEI CONTROL BASAL BODY FUNCTIONS INCLUDING: BREATHING, CONSCIOUSNESS, BODY TEMPERATURE, ETC.

DAMAGE TO THE BRAIN STEM IS TYPICALLY FATAL

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8
Q

Spinal cord

A

MAJOR CONDUIT BETWEEN BODY AND BRAIN
ENCLOSED BY BONY VERTEBRAL COLUMN
NERVES ENTER AND EXIT THE CENTRAL NERVOUS SYSTEM FROM THE BODY IN THE SPINAL CORD

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9
Q

Dorsal Root

Sensory info enters the spinal cord

A

Cell bodies of sensory neurons situated outside the spinal cord in Dorsal Root Ganglia.
Central projection leave cell body and enter dorsal horn of the spinal cord

These are afferent (“carry to”) projections

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10
Q

Ventral root

Motor info leaves the spinal cord

A

Cell bodies of neurons in the ventral horn of the spinal cord.
Axons of these neurons exit the spinal cord to innervate muscle in the periphery

These are efferent (“carry from”) projections

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11
Q

Neural tube formation

Neurulation: process by which the neural plate becomes the neural tube

A

Endoderm - viscera (internal organs)
Mesoderm - muscle and bone
Ectoderm - NS, neural crest, and skin

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12
Q

Neural crest

Formed by the ectoderm

A

Specialized tissue that gives rise to pigment cells, peripheral glia, some peripheral neurons, enteric nervous sustem, and craniofacial bones

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13
Q

Neurulation

A

The process by which the neural plate becomes the neural tube

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14
Q

Primary Neurulation

A

Cells surrounding the neural plate direct the plate cells to proliferate, invaginate, and pinch off from the surface to form a hollow tube

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15
Q

Secondary Neurulation

A

Neural tube arises from cells that coalesce into a solid cord that subsequently hollows to eventually form a hollow tube

Only occurs caudal to the sacral vertebrae in mammals

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16
Q

The Steps of Primary Neurulation

A

1) After neural plate formation, edges thicken and move up to form neural folds.
2) Neural groove appears in center of plate.
3) Neural folds migrate towards the embryonic midline.
4) Neural folds fuse creating a hollow tube.

In humans, evidence that neural tube closure begins in ~3 places

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17
Q

Open Ends of the Neural Tube

A

At the end of neurulation, open ends of the neural tube are: Anterior neuropore
Posterior neuropore

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18
Q

Folic acid

Neurulation happens within the first few weeks of pregancy

Often before pregnancy is known

A

Estimated 90% of birth defects due to lack of folic acid. The exacr reason for its importance is unknown.

No Anterior closure - anencephaly
No posterior closure - spina bifida

1/500 births has neurulation defect due to nutritional deficits

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19
Q

3 Primary Brain Vesicles

Entire brain develops from these primary vesicles

A

Prosencephalon - forebrain
Mesencephalon - midbrain
Rhombencephalon - hindbrain

First steps of neural differentiation are swelling of anterior neural tube leading to formation of primary vesicles

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20
Q

Differentiation

A

The process by which structures become functionally specialized

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21
Q

Differentiation of the Forebrain

A

1) Vesicles sprout off the sides of the prosencephalon.
Two telencephalic vesicles, two optic vesicles
Residual central structure that remains is diencephalon
2) Retina develops from the optic vesicle.
Part of forebrain, not PNS

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22
Q

Formation of the Retina from the Optic Vesicle

A

1) Optic vesicles grow and invaginate
2) Form the optic stalks and the optic cups
3) These become the optic nerves and the retinas in the adult
4) Retinas and optic nerves are derived from the neural tube

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23
Q

Telencephalon

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A

Differentiates into the cerebral hemispheres, olfactory bulbs, basal telencephalon.
Grows lateral and posterior to cover diencephalon.

Coronal section contains lateral ventricles

24
Q

Diencephalon

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A

Gives rise to the thalamus and hypothalamus

Coronal section contains third ventricle

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White Matter Systems
Bundle with 3 main systems: cortical white matter corpus callosum internal capsule | Axons extended from developing forebrain to other parts of NS
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Cortical white matter
All axons that run to and from the neurons within the cerebral cortex
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Corpus Callosum
Continuous with the cortical white matter. Forms a bridge that links the 2 hemispheres
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Internal capsule
Also continuous with the cortical white matter. Links cortex with brainstem
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# Forebrain structure-function relationships Cerebral cortex
Analyze sensory input and command motor output
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# Forebrain structure-function relationships Thalamus | Gateway to the cortex
Sensory neuron connections all pass through on route to the cortex. Axons from thalamus to cortex are in the internal capsule. Information is relayed contralaterally | Left foot stimulation is recieved by right cortex
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2 Main Cortex to Spinal Cord Routes
1) Direct route from cortex to brain stem is corticospinal tract. 2) Other path system first on basal ganglia. Critical for voluntary movement Multiple nuceli make basal ganglia Lost in neurodegenerative diseases
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Huntington's Disease
Largely caldate and putamen
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Parkinson's Disease
Substantia nigra More posterior Derived from mesencephalon | Symptoms due to loss of DA signaling from SN to striatum and other areas
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Differentiation of the Mesencephalon | Small changes in midbrain relative to forebrain
Dorsal surface becomes tectum ("roof") Floor becomes tegmentum Center remains open as the cerebral aqueduct - connected to ventricular system
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Tectum | Superior and inferior colliculus
Critical relays for ensory info on route to thalamus. Superior (optic tectum) - recieves input from eye Inferior - recieves input from ear
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Tegmentum | Substantia nigra and red nucleus
Substantia nigra - degenerates in Parkinson's Disease Red nucelous - limb movement critical for infant crawling
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Rostral Hindbrain
Differentiates into 3 parts: pons medulla oblongata cerebellum | 4th ventricle between dorsal and ventral hindbrain derivatives
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Stages of Hindbrain Development
1) Rostral hindbrain is a simple tube 2) Dorsal-lateral wall of the tube grows dorsally and medially to form rhombic lips 3) This expands into the cerebellum 4) The ventral wall (below 4th ventricle) becomes the pons
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Differentiation of Caudal Hindbrain
1) Medulla oblongata develops from caudal hindbrain 2) Ventral and lateral walls swell leaving only a thin layer of non-neural cells 3) Medullary pyramids are present on lateral edges of the ventral medulla. These are white matter tracts
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Pons
Develops from rostral hindbrain (metencephalon). Switchboard connecting cerebral cortex to cerebellum to coordinate movement. | Pons nuceli: sleep, respiration, swallowing, bladder, hearing, posture
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Medulla Oblongata
Develops from the caudal hindbrain (myencephalon). Carries axons of the corticospinal tract. Where the medulla joins the spinal cord, these tracts cross | Medulla oblongata: heartrate, respiration, BP, reflexes (vomit, cough) ## Footnote Direct connection from brain to spinal cord
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Cerebellum
Develops from the rostral hindbrain (metencephalon). | Movement control
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Pyramidal Decussation | Explains contralateral control of movement
Where the axons in the CST cross from ipsilateral to contraleteral | Occurs near where medulla (hindbrain) joins spinal cord
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Pyramidal (Corticospinal) Tract
Descending axons that pass through the midbrain/pons into the spinal cord through the medullary pyramids
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Rat and Human CNS
Similarities in basic arrangement of structures. Rat has larger olfactory bulb. Humans have gyri and sulci to allow expansion of cortical size while fitting in the skull and defined cortical regions based on sulci landmarks.
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Frontal Lobe
Reasoning, impulse control, integration. Contains motor and premotor cortex for higher order motor control and voluntary movement
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Parietal Lobe
Processing somatosensory information
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Occipital Lobe
Vision and visual processing
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Temporal Lobe
Language, auditiory processing, memory, visual perception
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Cerebral Cortex
Cell bodies of cortical neurons are always arranged in layers or sheets that lie parallel to the surface of the brain. Layer 1 (most superficial) below the pia matter (meninges) has no neurons and is primarily made of neuronal processes. At least 1 cell layer has pyramidal cells with large apical dendrites that extend up to layer 1.
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Neocortex | Unique cortical region of mammals ## Footnote Cortex amount has evolved. Structure has not and is conserved. Thickness has not changed substantially
Hippocampus is critical for learning and memory. Olfactory cortex or bulb is for smell. | Cortical regions can be distinguished by cytoarchitecture ## Footnote Primary sensory areas, secondary sensory areas, motor areas, and more recently evolved association areas of cortex
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Bodmann's Areas
Divided cortex into regions based on similarities in cytoarchitecture. Later determined divisions reflected functional divergence between cortical regions.
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Brodmann Area 17
Visual cortex that recieves information from retina after traversing thalamus
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Brodmann Area 4
Motor cortex that projects axons through to ventral horn in the spinal cord for voluntary movement
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Brodmann Area 44/45 | Broca's Area
Language production
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Brodmann Area 42/22 | Wernicke's Area
Language comprehension
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