Download Figure 9-1 - Center for Invertebrate Biology

Chapter 9
Part 1
Central Nervous System
Exam 1 has been graded
Class average = 79%
Figure 9-1
Evolution of the nervous system: same basic principles
action potentials, neurotransmitters at synapses, etc.)
apply to all nervous systems
Copyright © 2010 Pearson Education, Inc.
CNS Development
Early embryo, nervous system cells lie in a flattened area
called the neural plate
Day 20: Neural Plate cells along the edge migrate toward
midline (Fig. 9-2a, p. 299)
Neural Plate cells are purple in the figure
Neural Crest cells are red
Day 23: Neural Plate cells fuse, creating the Neural Tube
(Fig. 9-2b, p. 299)
Figure 9-2a
Copyright © 2010 Pearson Education, Inc.
Figure 9-2b
Copyright © 2010 Pearson Education, Inc.
CNS Development
Neural Tube then develops into the entire CNS
Lumen of neural tube remains hollow, becomes the central
cavity of the CNS
Cells forming the lining of the tube will differentiate into
ependymal cells or remain as neural stem cells
Outer cell layers of the tube become the neurons and glia
Neural crest cells become the sensory and motor neurons of
the PNS
Figure 9-3a
At 4 weeks,
anterior end of tube
has specialized into
3 brain regions:
Forebrain
Midbrain
Hindbrain
Copyright © 2010 Pearson Education, Inc.
Figure 9-3b
Brain
at
6 weeks
Central
cavity
becomes
the ventricles
Copyright © 2010 Pearson Education, Inc.
Figure 9-3c
Brain at 11 weeks
Cerebrum
expanding
rapidly
Copyright © 2010 Pearson Education, Inc.
Figure 9-3d
At birth, cerebrum developing furrows and ridges
Copyright © 2010 Pearson Education, Inc.
Figure 9-3e
Due to flexion in neural tube during development,
“dorsal and ventral” are different
Copyright © 2010 Pearson Education, Inc.
CNS Structure
Composed of neurons and glial cells

Interneurons are only found in the CNS

Afferent and Efferent neurons link interneurons to
peripheral receptors and effectors

CNS divided into gray matter and white matter
(Fig. 9-4c, p. 302)

Figure 9-4, part 2
Copyright © 2010 Pearson Education, Inc.
CNS Structure
Gray matter: unmyelinated nerve cell bodies, dendrites
and axon terminals

Cell bodies are organized into either layers or
clusters, depending on where they are in the CNS

Clusters are known as nuclei in the brain and spinal
cord

Nuclei often have names:

Lateral geniculate nucleus: processes visual
information

CNS Structure
White matter: mostly myelinated axons; also has a
few cell bodies

It is white because of the myelin

Tracts: bundles of axons in the CNS

Tracts are the equivalent of nerves (PNS)

Bone and connective tissue in the CNS
Bone provides support and protection
Brain is encased in the skull or cranium

Spinal cord runs through a canal in the vertebral
column

Each vertebra is separated by disks of connective
tissue

PNS nerves enter and leave the spinal cord through
notches between the vertebrae (Figure 9-4c)

Figure 9-4, part 2
Copyright © 2010 Pearson Education, Inc.
Meninges
3 layers

covers brain and spinal cord

offers additional protection

Outermost layer: Dura Mater

Very thick, durable

Middle layer: Arachnoid membrane

Looks like a spiderweb, loosely tied to pia mater

The space in between the 2 layers is the

subarachnoid space

Meninges
Innermost layer: Pia Mater

Very thin and delicate, carries arteries which
supply the brain

Figure 9-4, part 1
Copyright © 2010 Pearson Education, Inc.
Figure 9-4, overview
Copyright © 2010 Pearson Education, Inc.
Extracellular fluid in CNS (p. 301)
Cerebrospinal fluid
– Found in the brain ventricles and in the
subarachnoid space
Interstitial fluid
– Interstitial: “in between”
– In CNS, interstitial fluid is located inside the pia
mater
Figure 9-5a
Copyright © 2010 Pearson Education, Inc.
Cerebrospinal fluid (CSF)
Secreted by the Choroid Plexus (fig. 9-5, p. 304)
• Cells are similar to kidney cells
• They selectively pump Na+ and other solutes
from the blood plasma into the ventricles
• This sets up an osmotic gradient which allows
water to flow into the ventricles
Figure 9-5bc
Copyright © 2010 Pearson Education, Inc.
Cerebrospinal Fluid Circulation
CSF is made in the choroid plexus, inside the third
ventricle
From the ventricles, the CSF flows into the
subarachnoid space
Then, within the subarachnoid space, it circulates
around the CNS
CSF is reabsorbed by Arachnoid Villi in the cranium
(fig. 9-5d, p. 304)
Figure 9-5bd
Copyright © 2010 Pearson Education, Inc.
Figure 9-5d
Copyright © 2010 Pearson Education, Inc.
Cerebrospinal Fluid Functions
Brain and spinal cord “float” in the CSF
• CSF buoyancy reduces the weight of the brain
nearly thirty-fold, decreasing pressure on blood
vessels and attached nerves
• CSF provides additional padding in case of
blows to the head, etc.
CSF provides a closely regulated chemical
environment for CNS cells
Cerebrospinal Fluid Functions
Compared to blood plasma, CSF has different
concentrations of ions:
• Na+ conc is same as plasma
• CSF has higher conc of H+ ions
• CSF has lower conc of
K+, Ca++, HCO3-, glucose
HCO3- is the carbonate ion
Cerebrospinal Fluid
– CSF normally contains little protein and no blood
cells
Spinal tap or lumbar puncture
– Withdraw fluid from the subarachnoid space of the
lower vertebrae
– If proteins and or blood cells are present in the
CSF sample, then an infection may be present
Blood-Brain Barrier
Figure 9-6, p. 303-304
Brain capillaries are very highly selectively permeable.
They only allow certain substances to cross over into
the brain
The endothelial cells of the capillary form tight
junctions with one another
This keeps out toxins and other harmful substances
Blood-Brain Barrier
Figure 9-6, p. 303-304
Tight junction formation in the endothelial cells is
promoted by release of paracrines from the foot
processes of the astrocytes.
The foot-processes sit right on top of the brain
capillaries (fig. 9-6)
Figure 9-6
Copyright © 2010 Pearson Education, Inc.
Blood-Brain Barrier
Blood-brain barrier excludes water-soluble
substances, but some lipid-soluble substances can
diffuse across
– This is why some antihistamines make you sleepy
(they can diffuse across into the brain) while
others don't
– Most substances require carrier proteins to cross
the blood-brain barrier (see p. 303 for details)
Blood-Brain Barrier makes it difficult to treat many
diseases—often won't let the intended treatment cross
over into the brain
Example: Parkinson's disease
Dopamine (neurotransmitter) levels are too low due to
damaged/dead dopaminergic neurons
Can be treated by adding L-dopa, a precursor to
dopamine
Dopamine, administered as a pill or an injection, would
theoretically treat the problem, but dopamine can't
cross the barrier
L-dopa, a precursor to dopamine, can cross the bloodbrain barrier
Once in the brain, L-dopa is metabolized to dopamine
Several brain areas lack the blood-brain barrier since
these areas need to be in direct contact with the rest
of the body:
Hypothalamus
– Releases neurosecretory hormones into the
capillaries which then circulate over to the anterior
pituitary
Vomit center in the medulla oblongata
– Tests blood for toxins, induces vomiting if toxins
are found
Brain cells require constant supply of both glucose and
oxygen:
Glucose
• Requires transport proteins to move across into
the brain
• Only source of energy for neurons
• Brain uses one half of body's glucose
consumption
• During starvation, brain can metabolize ketones
produced by breaking down fat
Oxygen
• Freely diffuses across the barrier
• Brain receives 15% of the blood pumped by the
heart
Brain damage can occur after only a few minutes if the
brain is deprived of either oxygen or glucose
–
– Progressive hypoglycemia (low blood sugar) can
lead to confusion, unconsciousness, and death
Spinal Cord
Divided into 4 regions (same as vertebrae)
– Cervical
– Thoracic
– Lumbar
– Sacral
Regions are subdivided into segments
Each segment gives rise to a bilateral pair of spinal
nerves
Figure 9-7
Copyright © 2010 Pearson Education, Inc.
Spinal Cord
Spinal Nerves
– Just before joining the spinal cord, each nerve
divides into two branches or roots
– Dorsal root carries incoming sensory information
– Dorsal root ganglion has the cell bodies of the
sensory nerves
– Ventral root carries information from the CNS out
to the muscles and glands
Figure 9-7
Copyright © 2010 Pearson Education, Inc.
Gray matter:
– The butterfly or H-shaped center
– Dorsal horns: sensory fibers synapse with
interneurons here
– Ventral horns: cell bodies of motor neurons which
carry
White matter:
– The white area around the central butterfly
• Contains tracts (ascending, descending,
propriospinal)
Spinal Reflexes
Spinal cord can function as a self-contained
integrating center for simple spinal reflexes
Figure 9-7
Copyright © 2010 Pearson Education, Inc.
Figure 9-8
Copyright © 2010 Pearson Education, Inc.
Figure 9-9, overview
Copyright © 2010 Pearson Education, Inc.
Figure 9-9-1
Copyright © 2010 Pearson Education, Inc.
Table 9-1
Copyright © 2010 Pearson Education, Inc.
Figure 9-10
Copyright © 2010 Pearson Education, Inc.
Figure 9-13
Copyright © 2010 Pearson Education, Inc.
Figure 9-14
Copyright © 2010 Pearson Education, Inc.
Figure 9-15
Copyright © 2010 Pearson Education, Inc.
Figure 9-16
Copyright © 2010 Pearson Education, Inc.
Figure 9-17
Copyright © 2010 Pearson Education, Inc.
Figure 9-18
Copyright © 2010 Pearson Education, Inc.
Figure 9-11
Copyright © 2010 Pearson Education, Inc.
Figure 9-12
Copyright © 2010 Pearson Education, Inc.