Chapter 3: The Anatomy of the Nervous System
General Layout of the Nervous System:
Central Nervous System (CNS)
Brain (in the skull)
Spinal Cord (in the spine)
- Think of this system as the core
Peripheral Nervous System (PNS)
Located outside of the skull and spine
Serves to bring information into the CNS and carry signals out of the CNS
1) Somatic NS
- Afferent Nerves (Sensory) into
- Efferent Nerves (Motor) out of
- Have both of these nerves
- Tie this back to CNS, afferent nerves into the CNS (touch, joint angles,
muscles, internal organs sending signals to the CNS)
- Efferent sensing signals out of the CNS, sending signals to the motor
signals so you can move and adapt to the environment
2) Autonomic Nervous System
a) Sympathetic Nerves b) Parasympathetic
- Thoracic and Lumbar - Cranial (out of skull area) and sacral (low
- “Fight or Flight” back)
- Second stage- neurons are far from the - “Rest and Restore”
target. - Out of the CNS - Second Stage -neurons are near the target
- Both are efferent sending signals to sweat glands, lungs, and heart, taking
signals out of CNS to out of the organs so your body can react to the
environment in appropriate ways.
- Both have opposite effect
- 2-stage neural Paths, neurons exiting the CNS synapses on a second-stage
neuron before the target organ
- Sympathetic- prepare body for demands, sympathetic to what you‟re going
through and going to be sympathetic to the changes that need to happen.
Telling body to get ready
- Para- does the opposite; it counters the effect of the sympathetic nerves.
Heart pounding, sweating-- slowly quiet things down.
- The way the signals are carried, they use a 2-stage arrangement, signals
coming out of spinal cord; those neurons are going to synapse on another
neuron and then on an organ itself.
- Fight or Flight- you saw the bear, blood flow pattern are going to change,
you need all blood to go to muscles, instead to go to the digestive system for
you to run away from the bear. I need stress hormones kicking in (adrenaline) pupillary
response, breathing, and
heart rate to make body
ready. And once you get
Parasympathetic gets you
down to an everyday state.
Meninges, Ventricles and Cerebrospinal Fluid (CSF)
- CNS ANATOMY
- We have several layers of membrane that help protect the CNS Meninges/ Meninx
CNS encased in bone and covered by three meninges help protect the brain
If you want to investigate them in mammals, remove section of skull, we first hit
a thick tough membrane called the Dura Mater
Dura mater – tough outer membrane, and then below that directly underneath you
have the arachnoid.
Arachnoid membrane – web-like, also has a space underneath that house thins in that
region- dorsal sinuses
For keeping the brain from hitting the skull, we need this shock absorption system,
web like fluid in it. From helping it slamming into the skull
Pia mater – adheres to CNS surface
Cerebrospinal fluid (CSF)
Fluid serves as cushion
Act as a shock absorber that is created in the ventricles of the brain.
We have 4 ventricles where the fluid passes
We have internal and external shock absorption
We need a certain amount of fluid to do that job.
Anybody that has had a spinal tap done - you‟re removing the fluid and removing that
natural absorption and you get a horrible headache.
You can develop problems if you have tumors forming near the aqueduct
Some researchers has investigated that neurogenesis can happen in the ventricles
Brain Chemical protection
The blood-brain barrier – tightly-packed cells of blood vessel walls prevent entry of
We have ways to protect brain and spinal cord from calatogenes, can be chemicals,
and can be proteins, viruses and other bacteria. So in our body the blood stream, the
vascular that we have outside the CNS, the cells that make up these vessels are sloppy in
nature, the cell spacing is larger, so many things can be leaked out and wastes can be go
back in - the peripheral
But in the spinal cord and brain the cells are more compact. This is a good thing
because the immune function in the CNS is bad.
If you get an infection in the CNS, you need aggressive treatment because there is not
substantial immune response there
Reason why we tell pregnant women to stay away form things is because some of
these things are teratogens that can be passed through and can go to the brain.
Protects chemicals form getting through.
But again not all things are kept out, THC and weed, cocaine goes right through but if
it stayed there then nothing would happen
Cerebrospinal fluid (CSF)
Cells of the Nervous System:
Specialized cells for the reception, conduction, and transmission of
electrochemical signals in CNS AND PNS
That collect signals from other neurons and send signals to other neurons.
They receive and transmit. By electrical signals and chemical
Many sizes and shapes Cell Membrane
- composed of a lipid bilayer, or 2 layers
of fat molecules.
- Protein molecules are embedded in the
bilayer and are the basis of the
membrane‟s functional properties
- Some membranes are channel proteins,
through whithc molecules can pass
- Others, are signal proteins, which
transfer a signal to the inside of the
neuron when some molecules bind to
them on the outside of the membrane
- in general, there are 2 gross neural structures: 1) those composed primarily of cell
bodies and 2) those primarily composed of axons.
- In the CNS, clusters of cell bodies are called nuclei
- In the PNS, clusters of cell bodies are called ganglia
- in the CNS bundles of axons are called tracts
- in the PNS bundles of axons are called nerves
Glial Cells- the forgotten ones - supportive cells
- Originally we thought they were outnumbering, but now it‟s said to have equal
numbers of cells.
- We thought they just supported the neurons, 1 they help create the blood barrier,
they myelinated axons, they create a structure that the neurons can grow on and
keep them arrange properly. But they also do other things
- We found that there are signals between them and between neurons, and a neuron
modulatory affect, can turn up and down
Outnumber neurons 10:1
Recent evidence for glial communication and modulatory effects of glia
on neuronal communication
Four classes of Glial cells:
Oligodendrocytes – extensions rich in myelin create myelin sheaths in
CNS have long processes and have pancake ends that wrap around the
axons of nerves in the CNS, create the installation in the axon only in the
CNS. Help neurotransmission to go faster.
Schwann cells – similar to function of oligodendrocytes but in PNS, can
guide axonal regeneration In the PNS, its not done by one cell that sends
many msgs to different cells, but its multiple cells sending msgs to other
many cells. If we damage a neuron and it dies, some neuron can continue growth
of axon and regenerate itself. In the PNS the Schwann cells, if it dies, the
Schwann cells are still there. After other glial cells come in and take away
the dead tissue. You have a channel for regeneration to follow. In the PNS
but doesn‟t happen in the CNS
Astrocytes – largest glia, star-shaped, many functions
Microglia – involved in response to injury or disease
In the CNS we don‟t refer to it as nerve we refer to them as Tracts.
Myelin-providing gilia Oligodendrocytes Schwann cells
Clusters of Cell bodies Nuclei Ganglia
Clusters of Axons Tracts Nerves
- Only difference between the
two (uni and bi) is how many
processes are coming off of it
- Bipolar- Multipolar
interneuron is just the cell body Neuroanatomical Techniques and Directions
- We have astrocytes, all these cells and when you look at it under a microscope its
hard to see. Your magnification is limited because the more you magnify the more it
dims, and their all tissue of the same colour
- So you can stain cells to know what it is there.
- They do two different contrast way of making special cells stand out more.
- Golgi Stain: allows for visualization of individual neurons, they will stain the
entire neuron. But doesn‟t stain all of them stains selectively ones here and there.
- They will stain the whole neuron, which is good you can see the dendrites and the
whole picture. But the problem there is you don‟t know how many there are or
cell densities. This is where nissl stains come in
- In the picture, it does not show all the neurons that are actually there.
- Nissl Stain: selectively stains cell bodies, stains all the cells but ONLY the cell
bodies. Now you can see the cell densities. And see different layers. And can
identify the different layers because they have different shapes. But I can‟t really
get at the synapse to see what‟s going on there.
- In the pic, you don‟t see the axons or the dendrites but you se