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 cord rostral end – brain if neural tube fails to close caudal – spina bifida rostral – 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 end 1. 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 – considered an embryo!

See further specialization of neural tube further divisions – 1. prosencephalon – forebrain vesicle telencephalon - cortex diencephalon – thalamus, hypothalamus 2. mesencephalon – midbrain vesicle 3.rhombencephalon – hindbrain vesicle metencephalon- pons and cerebellum myelencephalon - 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) medulla structure 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