Ch. 2

Neuroembryology: developmental stages

1. Preembryologic
2. Embryonic
3. Fetal

Preembryologic

(1st stage)

Occurs: conception to 2 weeks

Three layers from the embryonic disc (embryo)


1. Ectoderm (forms nervous tissue (blue)
2. Mesoderm
3. Endoderm

Embryonic

(2nd stage)

occurs 2-8 weeks

days 18-26 (3 weeks) happens:

* Ectoderm will start to fold and thicken forming a neural plate running along the dorsal side of the developing embryo
* neural plate folds to forms neural groove
* edges fuse to form neural tube
* cells that seperate from the neural tube form autonomic ganglia and most of PNS (neural crest)

The neural tube forms how many layers ?

2 layers


1. Mantle layer (inner layer)
* Alar plate- forms dorsal gray matter
* Basal plate -forms ventral gray matter
2. Marginal layer (outer layer)
* become white matter of the spinal cord

How is the central canal formed ?

the neural tube narrows to form the central canal of the spinal cord

Anencephaly

anterior neuropore fails to close leading to a neural tube defect

* the brain cannot form
* can occur day 28 (4 weeks)

Spina bifida

Failure of the posterior neurpore to close leads to neural tube defect

* area of the spinal cord doesn’t form properly
* day 30

the developing brain has how many prominent swellings?

Three


1. Prosencephalon
2. Mesencephalon
3. Rhombencephalon

Cephalic flexure

between brain and brain stem

cervical flexure

end of brain stem to spinal cord

Fetal

(3rd stage)

* occurs 8 weeks to birth

Brain stems consist of _____ (three things)

* midbrain
* pons
* medula

cranial nerve development

* 14 week -sucking and swallowing
* 25 weeks- vision
* 28 weeks - hearing
* 31-32 weeks - olfaction (sense)

Meninges

three membranous protective layer covering the entire CNS

* encompass the spinal Cord

layers of the meninges

PAD

* Pia mater
* arachnoid mater
* dura mater

Cerebrospinal fluid

CNS is bathed in CSF formed by the choroid plexus

* provides stable chemical environment

dendrites

short processes which receive inputs

axon

long process which carry outputs

Multipolar

several dendrites and axons

Bipolar

single dendrite and axon

* most sensory neurons

Myelin

formed by glial cells to insulate axons

Oligodendrocytes

myelin forming glial cells in CNS

Schwann cells

myelin forming glial cells in PNS

Unipolar

both axon and dendrite arise from a single process coming off the cell body

Primary CNS neurotransmitters (NT)

* excitatory- glutamate
* inhibitory- GABA

primary ANS neurotransmitters (NT)

acetylcholine (parasympathetic) and norepinephrine (sympathetic)

Primary PNS neurotransmitter

acetylcholine

Gray matter

* cell bodies
* most local synaptic communication between neurons in CNS

Cerebral cortex

\-outermost layer

* gray matter that cover the surface of cerebral hemispheres

White matter

transmit signals over long distance in the CNS

* myelinated axons- carry and send out signals to and from the brain

white matter names

* tract- long
* commisure- connect right and left sides

peripheral nerves

bundles of axons in the peripheral nervous system (PNS)

Afferent pathway

toward the structure, to brain

Efferent pathway

Away from structure, to muscle

where does the spinal cord end?

L1-L2 vertebrae column

Conus Medullaris

end of spinal cord

sulci

infolding of cerebral cortex

gyri

ridges of cerebral cortex

central sulcus

seperates frontal and parietal lobes

sylvian (lateral fissure)

superior border of temporal lobe

Parieto-occipital sulcus

separate parietal and occipital lobes

Precental gyrus

anterior to central sulcus

postcentral gyrus

posterior to central sulcus

corpus callosum

giant commissure between hemispheres

consist of :

* rostrum
* genu
* splenium
* body

Calcarine fissure

occipital lobe

parahippocampal gyrus

temporal lobe

insular cortex

deep to lateral/ sylvian fissure

“ finger like”

primary motor cortex (precentral gyrus)

movement on opposite side of the body

primary sensory cortex (postcentral gyrus)

sensation from opposite side of the body

primary visual cortex

posterior occipital lobes

primary auditory cortex

transverse gyri of Heschl (posterior part of insular cortex)

Somatotopic maps

are called sensory or motor homunculus

homunculus= “little man”= HAL

(Lateral) corticospinal tract

function: major motor pathway responsible for voluntary movement

Begins in the pre central gyrus (primary motor cortex)

controls movement on the opposite side of the body

two neuron pathway AKA pyramidal tract

Brodmann’s areas

divides cortex into functional areas based on microscopic appearance

* 52 areas identified
* Areas 3,2,1 primary somatosensory cortex
* Area 4- primary motor cortex
* Area 17- primary visual cortex

main long tracts of the nervous system

* lateral corticospinal tract
* posterior columns
* anterolateral pathways

lateral corticospinal tract

* voluntary motor movement

extending from precentral gyrus (primary motor cortex) to skeletal muscle

posterior (dorsal) column pathway

sensory

* vibration, joint position (proprioception), light touch) from opposite side of the body
* location and intensity
* axons cross over in the medulla (internal arcuate fibers)

anterolateral pathways

sensory

* Spinothalamic tract


* pain, temperature, crude touch (for those who have a spinal cord injury)
* axon crosses over a few levels above the dorsal sensory root from which it entered (anterior commissure) in the spinal cord
* all axons do NOT cross over together at the same spot

pyramidal decussation

where the (lateral corticospinal tract) crosses

at the bottom of the medulla

upper motor neuron

motor neuron that projects from cerebral cortex to the spinal cord targeting lower motor neuron

lower motor neuron

makes up a peripheral nerve

front portion of grey matter in spinal cord

innervate skeletal muscle to fire

Lesion above the decussation

contralateral opposite sided weakness or paralysis

lesion below decussation

ipsilateral same side weakness or paralysis

Cerebellum

“biggest snoop in town”

* little brain
* dorsal/posterior to pons
* responsible for refining movement
* lesion- ataxia “lack of order” uncoordinated movement

Thalamus

* right above the brain stem
* 2nd biggest snoop in town
* multiple nuclei located deep in the cerebrum
* major relay center for pathways traveling to the cortex

Basal Ganglia

stop or start movement

lesion- problems with start and or stopping movement

Ex: parkinson’s disease, huntington’s disease

two main sensory pathways

posterior (dorsal) column pathway

anteriorlateral pathway (spinothalamic tract)

* three neuron pathways

Monosynaptic stretch reflex

* reflex-arc providing local feedback for motor control
* sensory neuron (afferent) synapses on lower motor neuron
* responsible for motor responses
* testing - motor and sensory neuron integrity of PNS

CN I

olfactory nerve

function: olfaction (smell)

CN II

optic nerve

function: vision

CN III

oculomotor nerve

function: eye movements; pupil constriction

CN IV

trochlear nerve

function: specific eye movements that its involved with

* acts as a pulley

CN V

trigeminal nerve

function: facial sensation (pain, temperature, proprioception) ; muscle of mastication (chewing)

CN VI

Abducens nerve

Function: eye movements (abduction)

CN VII

facial nerve

Function: muscles of facial expression; taste; salivation

CN VIII

vestibulocochlear nerve

Function: hearing; equilibrium sense

CN IX

glossopharyngeal

function: pharyngeal muscles; carotid body reflexes; salivation

CN X

vagus nerve (to wonder)

function: parasympathetics to most organs; laryngeal muscles (voice)

(speaking + swallowing)

CN XI

Spinal accessory nerve

function: head turning (trapezius and sternomastoid muscles)

CN XII

hypoglossal nerve

function: eye movement

Brainstem

* contain numerous nuclei and white matter tracts
* contains reticular formation (RF)

Upper RF

* midbrain and upper pons
* regulating level of consciousness (LOC)

Lower RF

* lower pons and medulla
* motor, reflex, and autonomic functions (breathing, respiration, cardiac)

Limbic system

Function:

HOME

* homeostasis
* olfaction
* memory
* emotions and drives

the association cortex breaks down into what two things ?

1. Unimodal association cortex
2. Heteromodal association cortex

Unimodal association cortex

process a single sensory or motor modality

Heteromodal association cortex

Integrates function from multiple sensory and/or motor modalities

Ex: bring emotions and memories and attach to it

Wernicke’s area

temporal lobe

in left hemisphere

function: language comprehension (understand spoken or written language)

Broca’s area

frontal lobe

in left hemisphere

function: language production: write, talk, speak

An impairment in language is called ___?

Aphasia

Parietal lobe function

primary

process a lot of sensory and spacial info

important role in sensory perception and integration and spatial awareness (R>L)

sensation and comprehension of speech and reading

Lesion in right parietal lobe

* can exhibit hemineglect (neglect one side of the body)
* anosognosia (unawarness of the deficit) do not realize anything is wrong

lesion in left parietal lobe

* can exhibit apraxia
* inability to perform a movement in response to a verbal command

frontal lobe function

important role in personality and cognitive functioning

* voluntary movement, motor integration, language production (broca’s area) social functioning, initiative, inhibition of impulses, emotions

Lesion in left frontal lobe

effects:

depression- like symptoms

apraxia

Lesion in right frontal lobe

effects:

mania-like symptoms (wound up)

hemineglect

which two arteries supply the whole brain ?

1. internal carotid arteries - anterior circulation
2. vertebral arteries - posterior circulation

both join at the brain stem form the basilar artery

circle of willis

ring of arteries formed at the base of the brain by the anterior and posterior blood supplies

where is the vertebrobasilar system located ?

brain stem and cerebellum

how does blood get out of the brain?

internal jugular veins

* network of dural sinuses collect blood to drain into the internal jugular veins