CNS development

1. A somewhat general overview of CNS development

In the beginning……

• zygote – fertilized egg; – undergoes a number of divisions with overall size

unchanged and divisions resulting in smaller and smaller cells (cleavage) to form the BLASTULA

• blastula invaginates giving rise to 3 layers – called gastrulation and the structure is now called a gastrula

• blastula invaginates giving rise to 3 layers – gastrulation

– endoderm• guts, lungs, liver, internal organs

– mesoderm• muscles, skeleton, connective tissue, cardiovascular

system, urogenital system

– ectoderm

• neural groove flattens and forms the neural plate – this folds into a tubular structure called the neural tube

The 3 dimensions of the neural tube

longitudinal –

caudal end – spinal cordcaudal end – spinal cordrostral end – brainrostral end – brain

if neural tube fails to closeif neural tube fails to closecaudal – spina bifidacaudal – spina bifidarostral – anencephalyrostral – anencephaly

• cavity of the neural tube forms the ventricular system

During neurula stage – see further specialization of neural tube

cephalic end differentiates into 3 primary vesicles

1.

During neurula stage – see further specialization of neural tube

3 swellings at rostral end1. prosencephalon – forebrain vesicle

2. mesencephalon – midbrain vesicle

3. rhombencephalon – hindbrain vesicle

After 3 vesicles are formed – we see 2 flexures:

1. cervical (sc and hindbrain)

2. cephalic (hindbrain and midbrain)

when neurulation is complete – when neurulation is complete – considered an embryo!considered an embryo!

See further specialization of neural tube

further divisions – 1. prosencephalon – forebrain vesicle

telencephalon - cortexdiencephalon – thalamus, hypothalamus

2. mesencephalon – midbrain vesicle

3. rhombencephalon – hindbrain vesiclemetencephalon- pons and cerebellummyelencephalon - medulla

corticogenesis

• - develops from inside out

Axon and dendrite development

• When does dendritic growth occur?

• Environmental influence?

Synaptogenesis

general terms

• nerves• tracts• ganglion• nucleus

myelination

• What is responsible for myelination?

• How long does myelination take?

Autonomic NS

Somatic NS

• 31 pairs of spinal nerves

label the diagram

• sensory neurons– clustured in DRG

– pseudo unipolar neurons• bifurcated axon with central and peripheral branches

components of SC

• dorsal horn – – sensory relay neurons

• ventral horn –– motor nuclei

• white matter – – longitudinal tracts of myelinated axons

components of SC (con’t)

• white matter –– dorsal columns

• contains ascending axons carrying somatosensory info

– lateral columns• both ascending axons and descending axons

– ventral columns• ascending somatosensory and descending axons

• corticospinal tract– humans - ~ 1,000,000 axons – originate in motor cortex; pyramidal motor system– makes monosynaptic connections with motor neurons

• The corticospinal tract mostly contains motor axons.

• The rubrospinal tract – 2ndairy motor system - responsible for large muscle movement such as the arms and the legs (flexor and extension, muscle tone).

• The spinothalamic tract is a sensory pathway originating in the spinal cord that transmits information about pain, temperature, itch, some measures of touch to thalamus.

ways to determine region of spinal cord• relative white to gray matter• configuration of gray matter• specific nuclei- clarkes nucleus

Cranial nerves primarily serve head and face

Brain

• hindbrain, midbrain and forebrain

hindbrain

• medulla

• pons

• cerebellum

hindbrain (con’t)

• medullastructure

resembles SC

contains:early relay nuclei in taste, hearing, maintenance of

balance, neck and facial muscles

• pons– ventral portion – pontine nucleus – info about movement and

sensation from cc to cerebellum– dorsal portion – respiration, taste, sleep

hindbrain

• medulla• pons• cerebellum

– roles:

midbrain

• structures:

midbrain

diencephalon (part of the forebrain)

• thalamus– role:

• hypothalamus– role:

The thalamus communicates with much of the cerebral cortex - serving as a sensory and motor information relay.

components of the thalamus

• nuclei– relay or diffuse projections- classified based on location

• internal capsule– large bundle of fibers carrying most of axons

running to and from cerebral hemispheres• massa intermedia

– connects left and right thalamus

• reticular nucleus– role – feedback to output nuclei of thalamus - GABA

telencephalon

• basal ganglia

• limbic system

• cerebrum (cerebral hemispheres)

telencephalon

• cerebrum (cerebral hemispheres)– SOME TERMS: – fissures – large grooves on cerebrum surface– gyrus – outswelling observed on cerebrum– sulci – smaller grooves on cerebrum

cerebral cortex layers

• distinctive laminar structure of certain cortices provides information regarding region of cortex

– ex. Layer IV – main target of sensory info from thalamus

telencephalon

• cerebrum (cerebral hemispheres)– 4 lobes

• primary and association cortices

– key differences in primary cortices

• What do we know about the extent of innervation as it relates to sensory information?

• Explain the statement that functional systems are hierarchically organized.

Some questions…..

• Differentiate between unimodal association areas and multimodal association areas

Prefrontal association area

• functions of prefrontal cortex

• lesions –

• tests of frontal lobe function