Biology 3201
Unit 1: Nervous System
What are the major parts of the
Nervous System?
1. Brain
2. Spinal Cord
3. A series of neurons that transmit impulses
throughout the body.
The Nervous System
DRAW 
FIG. 12.3
PG. 393
What is the function of the Nervous
System
- To help maintain homeostasis (remembersteady internal state).
- It does this by regulating body temperature,
blood-glucose levels, motor coordination,
among other body processes.
Structures of the Nervous System:
• There are two main sections:
1. The Central Nervous System (CNS):
– The Brain
– The Spinal Cord
2. The Peripheral Nervous System (PNS):
- The nerves that lead into and out of the central
nervous system
Function of the CNS:
• To receive sensory information, interpret that
information and initiate responses such as
motor responses.
Protection of the CNS:
• Four structures are used to protect the CNS.
They include (i) the skull (ii) the vertebrae (iii)
meninges (iv) the cerebrospinal fluid.
• The skull forms an enclosure around the brain
and the vertebrae enclose the spinal cord.
• Meninges are protective membranes that
surround both the brain and spinal cord.
• The cerebrospinal fluid fills the spaces within the
meninges to create cushion and provide further
protection.
Protection of CNS
The Spinal Cord
• The function of the spinal cord is to provide
communication between the brain and the
peripheral nervous system (PNS).
• The spinal cord extends from the vertebrae in
the back though the bottom of the skull into
the base of the brain.
• Spinal nerves will pass through the vertebrae
and out to the PNS.
Spinal Cord Structure:
• A cross section of the spinal cord show the (i)
central canal containing cerebrospinal fluid (ii)
grey matter and (iii) white matter.
• DRAW fig 12.3 p. 393.
Grey Matter and White Matter
• The grey matter is brownish-grey in color and contains
sensory neurons, motor neurons and interneurons. It
also contains cell bodies and non-myelinated fibres.
The grey matter is found in the center of the spinal
cord in the form of a letter H.
• The white matter is found around the grey matter. It
contains the myelinated axons of interneurons that run
together in tracts. Ascending tracts carry information
to the brain whereas descending tracts carry
information from the brain.
The Brain- 4 Lobes
The Brain- 2 Hemispheres
Structure and Function of the Brain
• Cerebrum
– Controls complex behaviour and intelligence.
– Makes decisions and stores memories.
– Controls voluntary muscles (ones you can
consciously move).
– Collects info from our senses and sorts it.
– Makes us different from other mammals (we have
more cerebrum tissue).
– Very convoluted to increase surface area.
Cerebrum
Cerebellum
• Controls motor coordination and balance.
• Contains 50% of the brains neurons.
• The physical skills we learn are slowly taken over by
the cerebellum and are not consciously controlled,
eg. Walking, running, etc.
Medulla
• Controls involuntary life processes, heart rate,
blood pressure, breathing rate.
• Swallowing, hiccuping, vomiting, coughing.
Thalamus
• Sensory relay center
• Receives sensations of heat, touch, pain, cold as well
as info from muscles.
• Relays mild sensations to cerebrum
• Relays strong sensations for immediate action to the
hypothalamus.
Hypothalamus
• Hypothalamus
• acts as the main control center for the autonomic nervous
system.
• Controls the sympathetic and parasympathetic responses.
• Controls hunger, temperature, aggression and other aspects
of metabolism and behavior.
Midbrain
• Short section of brainstem between the
cerebrum and the pons. It is involved in sight
and hearing.
Pons
• contains bundles of axons traveling between
the cerebellum and rest of CNS.
• It works with the medulla to regulate
breathing rate and has reflex centers involved
in head movement.
Corpus Callosum
• is a series of nerve fibers that connects the left
and right hemispheres of the brain.
The Nervous System
Images with permission of Eric Chudler <chudler@u.washington.edu>
The Nervous System
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Neurons
Soma
Axon
Dendrite
Myelin sheath
Schwann cells
Synapse
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Motor neurons
Interneurons
Sensory neurons
Neurotransmitters
Action potential
Reflex arc
Nerve tissues respond to stimuli and
are composed of individual cells called
neurons and their associated support
cells.
Nerve cells can measure up to two meters
in length and are well suited to
transmitting messages. These cells convert
stimuli into electrochemical impulses and
transmit the signals down their lengths.
Parts of the Neuron
Cell Body: contains a large centrally located
nucleus. Its cytoplasm contains mitochondria,
lysosomes , Golgi body and rough
endoplasmic reticulum
Dendrites: are the primary sites for receiving
information signals from other neurons
Axon: Long cylindrical extension of the cell body.
It ranges from 1mm-1m in length. It transmits
waves of depolarization when receiving an
impulse that is strong enough
Axon Terminal: Bud like extension of the axon. It is responsible for releasing
neurotransmitters.
Myelin Sheath(Schwann cells and Nodes of Ranvier): found in the CNS and PNS in
which speed is important.
It is a fatty layer that is formed by the Schwann cells that wrap around the
axon.
Schwann cells line the length of the axon in the PNS. The gap between the Schwann
cells is called the nodes of Ranvier. The axon is exposed in this gap and allows the
impulse to jump from one node to another thereby increasing the wave of
depolarization to 120m/s.
Schwann cells enable neurons to regenerate themselves in situations where
damage is not severe in the PNS
Neurons and The Reflex Response
• Recall the structure of a neuron:
Know the definitions for each part of the neuron.
DRAW 
Three Classes of Neurons
• 1. Sensory Neuron- take information from a
sensory receptor, such as a pain receptor, to
the CNS.
• 2. Interneuron- receives info from sensory
neurons and other interneurons and
exchanges the information among neurons in
the CNS.
• 3. Motor neuron- takes info from the CNS to
an effector, such as a muscle fiber or gland.
Receptors vs Effectors
Receptors
Effectors
Take in stimuli (pain, smell, etc.)
from the environment.
The muscles and glands of the
body that carry out actions as
instructed by the CNS.
Ex: Skin receptors are stimulated
by pain, heat, cold, pressure,
touch
Ex: pulling your hand out of hot
water.
Other receptors include the
sensory organs: nose, eyes, ears
and tongue
What is a Reflex?
• When a certain action sets off a specific
reaction automatically.
• Ex: Blinking when something moves close to
your eye.
Reflex Arc
• Sensory neuron, interneuron and motor neuron are
all involved in the reflex arc
• During the reflex our bodies react before our brain is
aware of the stimulus
• Nerve endings are the dendrites of the sensory
neuron and require a strong stimulus to activate it
• The impulse travels along the sensory neuron to the
spinal cord where the signal is passed along to the
interneuron
• The interneuron sends an impulse to the motor
neuron
• The motor neuron causes muscles to contract
and move the body away.
• Reflex action is involuntary ( but part of the
somatic nervous system).
• The interneuron sends a message to the brain
making the brain aware of what has happened
The Reflex ARC
DRAW  P. 396
LAB #1
• Answer the pre-lab question.
• Do a complete lab write-up:
Title, Problem, Hypothesis, Materials, Procedure,
Observations (table), Discussion (answer
questions), Conclusion.
• Pass in your lab report either in a lab notebook or
a duotang folder.
DUE:
How the Neuron Works
• 1. At Rest
• Not carrying an impulse.
• Membrane surface is polarized (overall
positive charge on outside, negative charge on
the inside).
• The difference in charge between the inside
and outside is approximately -70 mV, this is
the resting potential.
Diagram: on board
All-Or-None Principle
• If an axon is stimulated sufficiently (above the
threshold), the axon will trigger an impulse
down the length of the axon.
• The strength of the impulse will be uniform
along the entire length of the axon.
• The strength of the response is independent
of the strength of the stimulus.
2. Depolarization
• If the neuron is sufficiently stimulated, a wave of
depolarization is triggered.
• This involves sodium channels opening and
potassium channels closing. Sodium moves
inside, making the inside more positively charged
than the outside.
• This change in charge is called Action Potential,
and starts a chain reaction of depolarization
down the length of the axon.
(diagram)
3. Repolarization (2 steps)
• Immediately after the Na channels have
opened for depolarization, the gates of K
channels re-open, Na channels close and K
ions move out. This re-establishes the
polarization in the area.
• To restore the “resting” ion distribution, the
Na/K pump actively transports Na back
outside the membrane.
• The mitochondria in the neuron uses oxygen
and glucose to produce ATP, which releases
the energy that fuels the Na/K pump.
• Immediately after the wave of polarization,
there is a refractory period- approx. 0.001 s
before the axon is ready for another impulse.
Impulse Transmission and Membrane
Potential
• The membrane potential refers to the voltage
that is measured before, during and after the
impulse passes.
• Resting Potential is – 70 mV. The negative
signs refers to the difference in charge
between the inside and outside of the axon. It
is more negative inside, hence, the – 70.
• Depolarization- As the sodium ions flood in,
the charges switch and therefore the voltage
increases to approximately +40 mV.
• Repolarization- As the potassium moves
outside the axon, the voltage decreases to just
below resting potential (hyperpolarized). Then
rises back to resting (-70mV).
The Synapes
DRAW 
Fig 12.16
pg.405
Synapses
• Neurons do not touch one another; there are
tiny gaps between them. These are synapses.
• Presynaptic neuron- the neuron that carries
the wave of depolarization towards the gap.
• Postsynaptic neuron- the neuron that receives
the stimulus.
What happens at the Synapse?
When the wave of depolarization reaches the
end of the presynaptic axon, it triggers the
opening of special calcium gates. The
presence of calcium triggers the release of
neurotransmitters from synaptic vesicles,
which are located at the ends of the axon.
• The neurotransmitter diffuses into the
synapse and causes either an excitatory or
inhibitory response.
• Excitatory response involves the opening of
sodium channels in the post-synaptic neuron
triggering the wave of depolarization.
• Inhibitory response will cause the impulse to
stop. It does this by opening chloride channels
and causing the inside of the membrane to be
more negative.
The Importance of Neurotransmitters
Neurotransmitter
Acetylcholine
Noradrenaline
Glutamate
GABA
Dopamine
Serotonin
Effects
Importance of Cholinesterase
• Cholinesterase is an enzyme that works in
conjunction with acetylcholine. After the
acetylcholine has binded to the receptors on
the postsynaptic neuron and has produced it’s
desired effect, cholinesterase is released from
the pre-synaptic neuron to break down the
acteylcholine and bring the neuron back to
rest.
STSE Drugs and Homeostasis
Diseases associated with the Nervous
System
• Give a description of the disease, causes,
effects and treatments of….
Meningitis
Multiple Sclerosis
Alzheimers
Parkinson’s
Huntington’s
Technology Used to Diagnose and
Treat N.S diseases
• 1. MRI- Magnetic Resonance Imaging
– Scans the brain using a combination of large
magnets, radio frequencies and computer aids to
produce a detailed image of the brain or body.
– Under the influence of the magnetic field the
protons of hydrogen atoms in the body line up
parallel to each other. The atoms have entered a
high-energy state and are unstable.
• A strong pulse of radio waves is used to knock
the protons out of alignment. As the protons
realign themselves, they return to a low
energy state and they produce radio signals
that the computer converts into a 2D or 3D
image.
• See youtube video: Understanding MRIs
• 2. EEG- Electroencephalogram
– Measures electrical impulse activity of the various
areas of the brain.
– Pioneered by canadian Dr. Wilder Penfield.
– Monitors the condition of patients during surgery.
Can be used to determine brain death.
– Can diagnose disorders such as brain tumors and
epilepsy.
– Used to study brain activity during sleep to help
doctors diagnose and understand sleep disorders
• 3. CAT scan- computerized Tomography
– Takes cross sectional x-rays to create a 3D image
of a part of the body. Can be rotated and viewed
“slice by slice” to look for abnormalities.
The EYE
• Complete the worksheets on the eye’s
structures and their functions.
The Eye
The Ear
• See notes handout on the ear.
Stroke and Spinal Injury
• A stroke is a sudden loss of brain function. It is
caused by the interruption of flow of blood to
the brain (ischemic stroke) or the rupture of
blood vessels in the brain (hemorrhagic
stroke).
• Treatment?
– Clot-busting drugs
– Surgery to remove pools of blood
Treatment of Spinal Injury
• Treatment starts with steroid drugs
to reduce inflammation in the
injured area and prevent further
damage to cellular membranes that
can cause nerve death.
• Each patient's injury is unique. Some
patients require surgery to stabilise
the spine, correct a gross
misalignment, or to remove tissue
causing cord or nerve
compression. Some patients may be
placed in traction and the spine
allowed to heal naturally.
Importance of Glucose to N.S
• Cells within the nervous system require
enormous amounts of energy to function. This
energy is provided by the processing of glucose
and the production of ATP within these tissues,
requiring an adequate supply of carbohydrates
and oxygen (Na+/K+ pump). ATP energy is
required to operate the sodium-potassium pump
which convert cellular chemical signals into
electrical signals along a nerve cell and in
between individual nerve cells (i.e., synapse).