Neuro 3000 MT3

contralateral

the opposite side of the brain

Contralateral processing occurs in the cerebrum

ipsilateral

same side of the brain

ipsilateral processing occurs in the cerebellum

decussation

the crossing over of nerve fibers from one side of the CNS to the other

• allows integration of sensory/motor info from both sides of body

pyramidal decussation

descending tract from cortex (medulla) to the spinal cord

• motor fibers from the cortex cross over the midline at the lower medulla and go into the spinal cord

• allows for contralateral processing (occurs on both sides of the brain)

internal capsule

white matter tract in brain; carries outgoing fibers from cortex and incoming fibers from thalamus to cortex (beginning part of corticospinal tract)

corticospinal tract

consists of long pyramidal neurons that extend from cortex to spinal cord

allows for direct movement control

cerebrum

has two hemispheres that each get input from and control motor function for the contralateral side

cerebellum

ipsilateral movement control

• has many connections to spinal cord/cerebellum

• despite smaller size, has same number of cells as cerebrum (higher conc.)

CNS

brain and spinal cord; functions in info processing and distribution

dorsal root

sensory processing; root enters into the spinal cord and runs up

protected by meninges

ventral root

motor information; root exits the spinal cord and goes down into body part

protected by meninges

PNS

Everything out of the CNS; transmits sensory and motor info to/from the CNS

Motor nervous system

divided into autonomic (glands, adipose tissue, smooth/cardiac muscle) and somatic (skeletal muscle) nervous systems

anterior/rostral

front of brain

posterior/caudal

back of brain

lateral

far from midline

medial

near midline

dorsal

top of brain (mouse’s back)

ventral

bottom of brain (mouse’s belly)

superior (to)

found above a certain structure

inferior (to)

below a certain structure

superficial

closer to surface

deep

far from surface

sagittal plane

cuts into left/right halves along midline

• no bilateral symmetry

coronal/transverse plane

cuts into front/back halves

• bilateral symmetry visible

horizontal plane

cuts into top/bottom halves

• bilateral symmetry visible

gyri

sulci

brain ridges

spaces in between the ridges

bounds frontal lobe

lateral sulcus, central sulcus

bounds parietal lobe

lateral sulcus, central sulcus, parieto-occipital sulcus

bounds occipital lobe

parietal-occipital sulcus, transverse fissure

bounds temporal lobe

lateral sulcus, parieto-occipital sulcus

fissures

deeper than sulci; mark major brain divisions

longitudinal fissure

separates left and right hemispheres

transverse fissure

separates cerebrum and cerebellum

grey matter (cortex)

cell bodies; appear grey

white matter

myelin sheaths from axons

PNS

myelination occurs through Schwann cells

somatic NS

voluntary movements by skeletal muscles

Motor neurons: their cell bodies are located in CNS, axons in PNS

autonomic NS

unconscious movements (smooth muscle, heart muscle, glands)

sympathetic and parasympathetic

sympathetic NS: driven by norepinephrine

activates fight or flight response

dilates pupils, heart races, digestion slows

parasympathetic NS: driven by ACh

calms fight or flight response

breathing slows, digestion resumes, heart slows down

ganglion

collection of neuron soma in the PNS

ex: dorsal root ganglia, basal ganglia

preganglionic neuron

soma in CNS; innervate postganglionic neurons

in sympathetic NS: come from thoracic and lumbar spinal cord

parasympathetic NS: come from cranial nerves and sacrum

cranial nerves

12 total; relay info from brain to head, neck, GI tract

pseudo-unipolar neurons

Stages of neurodevelopment (post-fertilization)

Cleavage to blastocyst

Gastrulation and neural induction; formation of 3 germ layers

Neurulation, formation of neural tube

Organogenesis, brain patterning

Cleavage to blastocyst (days 2-10)

where ESCs come from

1. Neural induction (days 11-15)

occurs during gastrulation

formation of 3 germ layers: ectoderm, endoderm, mesoderm

ectoderm

nervous system, skin

endoderm

internal organs

mesoderm

muscle and skeleton; becomes bone/muscle around spine

produces the neural inducer noggin

noggin

neural inducer; makes the ectoderm become neural (otherwise, would just become skin)

generates neural tube from ectoderm

used to convert ESCs to neurons

Neurulation/neural tube formation (days 16-25)

neural tube becomes brain and spinal cord; closes off

neural crest develops and becomes sensory/autonomic neurons

still part of the neuroectoderm

endoderm becomes internal organs

Regionalization and patterning (days 28+): anterior-posterior patterning

controlled by RA, lipophilic molecule

3 brain vesicles appear: prosencephalon (forebrain), mesencephalon (midbrain), and rhombencephalon (hindbrain)

development goes from posterior to anterior; hindbrain first

default fate is forebrain; RA helps develop posterior fates

Regionalization and patterning (days 28+): dorsal-ventral patterning

controlled by Shh, protein

development goes from bottom up

initiates formation of nervous system

used to induce neurogenesis in iPSCs

Expansion of forebrain: day 36

prosencephalon expands and adds telencephalic vesicles

• later becomes telencephalon and diencephalon

rhombencephalon begins to develop

Expansion of forebrain: days 49-90

forebrain develops into telencephalon and diencephalon

telencephalon covers diencephalon

optic cup

develops from the optic vesicle, which originates in the diencephalon (prosencephalon)

later becomes the retina

dorsal telencephalon becomes:

neocortex

basal telencephalon becomes:

amygdala, basal ganglia (striatum)

diencephalon (ventromedial forebrain) becomes:

thalamus, hypothalamus

forebrain

seat of perception, cognition, and voluntary action

thalamic axons:

project from the thalamus (CNS) via the internal capsule

ex: if you are hurt on your right foot, the pain signals go to your left cortex

corpus callosum

white matter tract; allows communication between hemispheres

cortical neurons (which project downward) can project to:

corticospinal tract (all the way down the spinal cord)

basal ganglia for movement control

• includes striatum (basal telen) and substantia nigra (midbrain)

  • takes in dopamine input

dorsal midbrain (mesencephalon)

Becomes the tectum

• superior colliculus: visual processing

• inferior colliculus: auditory processing

ventral midbrain

becomes tegmentum

cerebral aqueduct

connects diencephalon and hindbrain

dorsal rostral hindbrain

becomes cerebellum

ventral rostral hindbrain

becomes pons, pontine nuclei

• pons connects cerebral cortex and cerebellum using mossy fibers

medullary pyramids (caudal hindbrain)

carry corticospinal projection axons going to the spinal cord (corticospinal tract)

• pyramidal decussation

neurogenesis

neurons, astrocytes, glia, etc are generated

proliferation, migration, differentiation

proliferation:

to start, the brain’s vesicles only have 2 layers: ventricular zone and marginal zone

contain radial glia (neuron/glia precursors)

at first, cell division is done symmetrically to generate more radial glia

note that the nuclei initially move up into the marginal zone before coming back down

migration:

later in development, some cells develop asymmetrically; the daughter cell further from the ventricle migrates along a radial glia to reach its spot in the cortex

• this cell becomes a neuron/glia

final result: one postmitotic cell, one premitotic cell

once the postmitotic cell reaches its destination, only then does it differentiate

order of differentiation (after migration is finished):

pyramidal neurons are made first, then astrocytes

inhibitory interneurons and oligodendrocytes come from somewhere else

cell fate

driven by gene expression in development (daughter cells have certain genes turned on/off); depends on what plane the cells are cleaved

vertical cleavage

parent cell is cleaved symmetrically

daughter cell has both Notch 1 and Numb expression; continues to differentiate

horizontal cleavage

one daughter cell only has Notch 1; this migrates to MZ and differentiates

other daughter cell only has Numb; stays behind and continues to proliferate

cortical layers are developed inside out

layer VI forms first, then layer V, etc

differentiation only starts once the cells have reached their location and stop migrating

once one layer is finished, then the cells will migrate up from the VZ to the next layer

differentiation

once a cell has reached its final destination, it becomes a specialized neural cell

attracted to cortical surface by semaphorin 3A, which determines axon polarity

chemoattraction, chemorepulsion

semaphorin 3A: drives pyramidal polarity

high concentration in the marginal zone, but low expression in deeper layers

axons repulsed by sema3A, which is why they extend down from the cell body

synaptogenesis

formation of synapses

target-dependent cell death (apoptosis?)

more neurons are generated than actually needed

to determine which are lost, a limited amount of NGF/BDNF (growth factors) is produced; neurons need to compete

synaptic pruning

eliminates uneeded circuits

synaptic plasticity

learning and memory; related to synaptogenesis

frontal lobe

complex human behavior

prefrontal cortex, primary motor cortex

prefrontal cortex

planning, organizing, impulse control, learning, decisions

primary motor cortex

voluntary movement

primary motor/somatosensory cortex

primary motor: caudal frontal lobe

somatosensory: rostral parietal

frontal lobe and language

broca’s area: language-related motor functions

wernicke’s area: language comprehension

temporal lobe

language, hearing, memory

auditory cortex, wernicke’s area

ventral stream (temporal lobe)

“what” pathway

lets you identify and recognize *what* an object is

originates in occipital lobe

parietal lobe

sensation, spatial awareness

receives sensory input from the body

identify objects by touch; body’s position in space

primary somatosensory cortex, dorsal stream

sensorimotor cortex

primary somatosensory cortex

skin senses (touch, warmth, cold, pain)

inform about body position/movement

dorsal stream

“where” pathway

visual-motor control

occipital lobe

processes visual info

detects individual parts of a scene (color, movement, etc)

afterward, puts them together and sends them to be processed in temporal/parietal lobes

thalamus

sensory relay center

hypothalamus

controls emotion and motivated behaviors (eating, drinking, sex)

maintains homeostasis through control of autonomic NS

• links endocrine and nervous systems (HPA axis)

midbrain

contains structures with secondary roles in: vision (superior colliculum/optic tectum), hearing (inferior colliculum/auditory tectum), and movement/motivation (tegmentum, VTA)

hindbrain

made of pons (motor/sensory function, corticopontocerebellar tract, sleep/arousal), medulla, cerebellum

cerebellum

refines movements from the motor cortex (coordination)

motor learning

non-motor cognition and emotion