Biology 30
Providence Christian School
2013-14
Mr. Schooten
Unit A: The Nervous &
Endocrine Systems
Chapters 11-13
Chapter 11:
The Nervous System
Section 11.1
Structures and Processes of the Nervous System
• Homeostasis – the
tendency of the body
to maintain a
relatively constant
internal environment
• The nervous system
regulates body
structures and
processes to maintain
homeostasis despite
changes in both the
internal and external
environment.
A. Organization of the Nervous System
a. Central Nervous System
(CNS)
• Located centrally – consists of
the brain and spinal cord
• Integrates and processes
information sent by nerves
b. Peripheral Nervous System (PNS)
•
•
Located peripherally – consists of nerves that
carry sensory messages to the CNS and nerves
that return information to muscles and glands
Divided into two systems
•
Somatic system
• Sensory receptors in the head and extremities
• Under conscious control or voluntary
•
Autonomous system
• Controls glandular secretions as well as smooth
and cardiac muscles
• Not under conscious control or involuntary
• Has two divisions, sympathetic and
parasympathetic, that work against each other to
regulate involuntary processes such as heartbeat
and peristalsis
Organization of the Nervous System
studyblue.com
B. Cells of the Nervous System
a. Glial Cells
• The support cells for neurons
(glial is Greek for ‘glue’)
•
•
•
•
Nourish the neurons
Remove waste
Defend against infection
Provide a supporting framework
http://med.stanford.edu
#1, 5, and 6 are types of glial cells
b. Neurons
•
•
The basic structural and functional units of the
nervous system, organized into tissues called
nerves that are made up of hundreds of neurons
Three main types of neurons form the basic
impulse-transmission pathway of the entire
nervous system:
•
•
•
en.wikipedia.org
Sensory neurons gather information from sensory
receptors (ie. senses) and transmit the information
to the CNS
Interneurons act as a link between sensory and
motor neurons by processing and integrating
incoming information and relaying outgoing
motor information
Motor neurons transmit information from the CNS
to the effectors such as muscles, glands, and other
organs
c. Special Case: The Reflex Arc
• Reflex arcs are simple
connections of neurons that
allow for sudden, reflexive
behaviours such as blinking
your eye when an object comes
towards it.
•
•
Very few neurons are used to
transmit messages
A reflex arc moves directly to and
from the brain or spinal cord
before the part of the brain
involved with voluntary control
has time to process the sensory
information
C. The Structure of a Neuron
• In general, each neuron
contains:
• Dendrites
•
Short, branching terminals that
receive impulses from sensory
receptors or other neurons and
relay the impulse to the cell body
• Cell body (soma)
•
•
Contains the nucleus and performs
metabolic reactions
Processes input from dendrites,
and if input is large enough, relays
it to the axon which begins an
impulse
tutorvista.com
• Axon
•
•
Conducts impulses away from the cell body
where it branches into many fibres
The axon terminal releases chemical signals
to the receptors or dendrites of
neighbouring cells.
•
Some axons are covered in a fatty insulating
layer called the myelin sheath (myelinated)
• the myelin sheath is made up of Schwann
cells, a type of glial cell, and protects the
neuron and speeds the rate of impulse
transmission
•
naturalhealthschool.com
Myelinated neurons form the white matter in
the CNS and unmyelinated neurons form the
gray matter. Most PNS neurons are
myelinated.
D. Unmyelinated Nerve Impulse
•
Luigi Galvani (1737-1798) discovered the
electrical nature of nerve tissue by using
two metal rods and some wire to cause a
frog’s leg to twitch. In 1952, A.L. Hodgkin
and A.F. Huxley performed experiments
on the giant axon of a squid to determine
more about the mechanisms by which
nervous tissue transmitted electrical
information.
• Nerve conduction differs from
electrical conduction along a wire in
that it depends on movement of ions
across the cell membrane of the
axon.
•
•
In a resting neuron, the inside (cytoplasmic)
of the membrane is negatively charged
relative to the extracellular side. The
separation of charge across the membrane
is potential energy, called membrane
potential.
The potential difference across the
membrane in a resting neuron is called the
resting membrane potential and is -70 mV
(millivolts). This potential provides the
energy for a nerve impulse.
• In order to generate and maintain a
resting membrane potential of -70
mV, three mechanisms contribute to
polarization:
•
•
•
Large negatively charged protein molecules
are found in the intracellular fluid but not
outside the cell and are too large to pass
through the membrane.
The membrane is nearly impermeable to
some smaller negative charged ions such as
chloride ions that are also inside the cell
The main mechanism is the sodiumpotassium exchange pump
•
•
This system uses energy from ATP to remove
sodium ions and bring potassium ions into the
cell. Three sodium ions leave for every two
potassium ions that enter, thereby decreasing
the net positive charge on the inside of the
cell
Mechanism found in Figure 11.12 on pg. 374
medic4u.webs.com
E. Action Potential
•
•
A nerve impulse consists of a series of action potentials
In myelinated neurons, action potentials exist only at the gaps in the myelin sheath, the nodes
of Ranvier, because the myelin insulates the membrane elsewhere
•
•
When the transmembrane potential is reduced to less than the resting potential of -70 mV, the
membrane is depolarized.
If it is depolarized past the threshold potential a significant change occurs called an action potential
•
This threshold potential for most neural cells is close to -55
mV. It is an “all-or-none” event because nothing changes if
the potential remains between the threshold potential and
the resting potential.
•
•
•
•
•
•
When the threshold is reached, voltage-gated sodium
channels open to make the membrane very permeable to
sodium ions, allowing sodium to rush in because of the
concentration gradient
Within a millisecond or less the potential difference across
the membrane is +35 mV
This causes voltage-gated potassium channels to open and
potassium ions rush out of the cell according to the
concentration gradient
The membrane is thus repolarized to a potential of -90 mV.
The sodium-potassium exchange pump then restores the
potential to the resting potential of -70 mV
The membrane cannot be stimulated to undergo another
action potential for a few milliseconds which is called the
refractory period
F. Myelinated Nerve Impulse
•
When the sodium ions rush into the axon
through the voltage-gated sodium channels
during an action potential, they spread out in
both directions within the axon.
•
•
•
www.as.wvu.edu
These sodium ions reach neighbouring nodes
of Ranvier and depolarize to threshold and
stimulates an action potential at the next node
of Ranvier
The impulse only travels in one direction,
however, since one of the neighbouring nodes
of Ranvier is still in the refractory period
This process of one action potential stimulating
the next is a nerve impulse
bio1152.nicerweb.com
• Action potentials “jump” from one node of Ranvier to the next so it is called
saltatory conduction, which is Latin for jump or leap.
• In unmyelinated neurons action potentials can occur everywhere along the
axon so the impulse is much slower (about 0.5 m/s compared to up to 120
m/s in myelinated neurons)
Multiple Sclerosis
•
Multiple sclerosis is caused by a body’s immune
system breaking down the myelin sheath
surrounding the axons in the CNS which
prevents neurons from efficiently carrying
impulses between the brain and body.
•
Symptoms include blurred vision, loss of
balance, muscle weakness fatigue and slurred
speech
blogs.mcgill.ca
G. Signal Transmission across a Synapse
•
•
cs.brown.edu
When an impulse reaches the terminal of a
neuron it must jump a gap or a synapse in
order to have the impulse continue. The
synapses between motor neurons and muscle
cells are called neuromuscular junctions.
Chemical messengers called neurotransmitters
carry the neural signal from the presynaptic cell
across the synaptic cleft to the postsynaptic
cell.
•
•
•
•
•
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When an action potential arrives at the synaptic terminal it
causes sacs, called synaptic vesicles, which contain
neurotransmitters to fuse with the membrane of the axon.
The contents of these vesicles are released into the synaptic
cleft and diffuse across the synapse in between 0.5 ms to 1
ms and reach the dendrites of the postsynaptic cell.
The neurotransmitters bind to specific receptor proteins in
the postsynaptic membrane which triggers ion-specific
channels to open.
Sodium ions rush in and depolarizes the postsynaptic
membrane stimulating an action potential.
Neurotransmitters can have excitatory or inhibitory effects
and the cell body must integrate all incoming signals. If the
combined effects are excitatory enough, an action potential
will be generated through the axon and the impulse will be
carried on.
Enzymes break down neurotransmitters after they have had
their effect in order to inactivate it so it can be reabsorbed
by the presynaptic cell.
cwx.prenhall.com
Neurotransmitters
•
Some common neurotransmitters include:
•
Dopamine
•
•
Serotonin
•
•
Act as natural painkillers in synapses in the
brain
Norephinephrine
•
www.drfrancescott.com
Involved in mood control
Endorphins
•
•
Linked to sensations of pleasure, such as eating
Readies the body to respond to danger or other
stressful situations
Chapter 11:
The Nervous System
Section 11.2
The Central Nervous System
• The CNS is the structural and
functional centre for the entire
nervous system. It is composed of
grey matter and white matter
• Grey matter is found around the
outside areas of the brain and
forms the H-shaped core of the
spinal cord.
• White matter forms the inner
region of some areas of the brain
and the outer area of the spinal
cord.
nlm.nih.gov
A. The Spinal Cord
•
•
A column of nerve tissue that extends out
of the skull from the brain down through
a canal within the backbone
A vital communication link between the
brain and the PNS
•
•
•
csuchico.edu
Sensory nerves carry message from
the PNS to spinal cord and motor
nerves relay messages from the brain
to the effectors
The primary reflex centre, coordinating
incoming and outgoing neural
information
The spinal cord is protected by
cerebrospinal fluid, soft tissue layers, and
the spinal column or backbones
(vertebrae)
•
•
•
B. The Brain
Plays a central role in maintaining
homeostasis and is the centre for
intelligence, consciousness, and
emotion
It is very fragile and has a gelatinlike consistency. It is protected by
the skull and the meninges, three
layers of tough, elastic tissue
within the skull and spinal column
that enclose the brain and spinal
cord.
Can be divided into three general
regions: the hindbrain, the
midbrain, and the forebrain.
Hindbrain
•
•
•
sites.google.com
Cerebellum is a walnut-shaped structure
involved in unconscious coordination of
posture, reflexes, and body movements,
as well as fine, voluntary motor skills such
as those used to play the piano or hit a
tennis ball
The medulla oblongata connects the brain
to the spinal cord and controls automatic,
involuntary responses, such as heart rate,
constriction or dilation of blood vessels,
rate and depth of breathing, swallowing
and coughing
The pons serves as the relay centre
between the neurons of the right and left
halves of the cerebrum, the cerebellum,
and the rest of the brain
Midbrain
• It relays visual and auditory
information between areas of
the hindbrain and the
forebrain and plays an
important role in eye
movement and control of
skeletal muscles
wfpsychbrainwiki.wikispaces.com
Forebrain
•
•
•
morris.umn.edu
The thalamus contains neurons that are
connections mainly between the forebrain
and hindbrain, and between areas of the
sensory system and the cerebellum (except
for sense of smell)
The hypothalamus regulates the body’s
internal environment by coordinating the
actions of the pituitary gland by producing
and regulating the release of certain
hormones. The hypothalamus controls
blood pressure, heart rate, body
temperature, basic drives such as thirst and
hunger, and emotions.
The cerebrum is the largest part of the brain
and is divided into right and left
hemispheres which contain centres for
intellect, memory, consciousness, and
language and interprets and controls
responses to sensory information
The meninges protects the CNS by
preventing direct circulation of blood
through the cells of the brain and spinal cord
through the blood-brain barrier. The
capillaries that bring blood to the brain and
made of tightly fused epithelial cells that
block many toxins and infectious agents but
allow glucose and oxygen through. Other
lipid-soluble substances can also pass
through such as nicotine, caffeine, alcohol,
heroin and some other drugs.
addiandcassi.com
• Approximately 150 mL of
cerebrospinal fluid is circulating
through the spaces or ventricles
within the brain and spinal cord at
any time. This fluid is replaced 4
times daily. It transports
hormones, white blood cells, and
nutrients across the blood-brain
barrier and also acts as a shock
absorber to cushion the brain.
daviddarling.info
C. The Structure and Function of the Cerebrum
•
•
The cerebral cortex is the outer covering of grey matter on the cerebrum that is responsible for
language, memory, personality, vision, conscious thought, and other thinking and feeling
activities.
The right and left hemispheres are linked by a bundle of white matter called the corpus callosum.
The corpus callosum lets each half of the brain know what the other half is doing.
• The right cerebral hemisphere
is associated with holistic and
intuitive thinking, visualspatial skills, and artistic
abilities.
stephenking.com
•
The left cerebral hemisphere is associated with
segmental, sequential, and logical ways of
thinking, and to linguistic and mathematical
skills.
•
The process of speech involves two
important areas on the left side of the
cerebral cortex:
•
•
Broca’s area coordinates the muscles
for speaking and translates thought
into speech
Wernicke’s area stores the
information involved in language
comprehension
es.wikipedia.org
The Stroop Effect – pg. 390
•
The cerebral cortex is divided into four
pairs of lobes:
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The occipital lobes receive and
analyze visual information
The temporal lobes share in the
processing of visual information but
are mainly linked to understanding
speech and retrieving visual and
verbal memories.
The parietal lobes receive and process
sensory information from the skin
and process information about the
body’s position and orientation.
The frontal lobes integrate
information from other parts of the
brain and control reasoning, critical
thinking, memory, and personality
Sheep Brain Dissection
D. Mapping Brain Functions
•
•
Positron-Emission tomography (PET) is
based on the fact that more active areas
of the brain require more energy. A person
intakes radioactively-labelled glucose and
a scanner monitors glucose consumption
within the brain and determines different
activity levels
Magnetic Resonance Imaging (MRI)
provides structural and functional images
of the brain based on a changing magnetic
field inducing hydrogen atoms in the brain
to emit radio signals that can be detected
and translated into an image.
nansenneuro.net
Chapter 11:
The Nervous System
Section 11.3
The Peripheral Nervous System
• The Peripheral Nervous System
(PNS) consists of nerves that link
the brain and spinal cord to the rest
of the body, including the senses,
muscles, glands, and internal
organs.
• The two main divisions of the PNS
are the somatic system and the
autonomic system.
visual.merriam-webster.com
A. The Somatic System
•
•
The somatic system is under voluntary
control and its neurons service the head,
trunk, and limbs.
It includes 12 pairs of cranial nerves and 31
pairs of spinal nerves which are
myelinated.
•
www.spineuniverse.com
Each nerve contains both sensory and
motor neurons which service the area of
the body where they are found.
B. The Autonomic System
• The autonomic system is under
automatic or involuntary control
and either stimulates or inhibits
glands or cardiac or smooth
muscle.
• The hypothalamus and medulla
oblongata control the autonomic
system by coordinating the
sympathetic and parasympathetic
divisions of the autonomic system.
www.kabelchiropractic.com
•
The sympathetic nervous system (fight-orflight) is activated in stressful situations and
release a neurotransmitter called
norepinephrine which has an excitatory effect
on its target muscles.
•
•
www.upstreamfitness.com
Sympathetic nerves also trigger the adrenal
glands to release epinephrine and
norepinephrine which function as hormones
that activate the stress response.
It also inhibits some areas of the body such as
increasing blood pressure and heart rate while
slowing down digestion.
•
The parasympathetic nervous system (restand-digest) is activated when the body is calm
and at rest in order to restore and conserve
energy.
•
The parasympathetic nervous system uses a
neurotransmitter called acetylcholine to
control organ responses.
www.upstreamfitness.com
•
Depending on the situation and organs involved, the sympathetic and parasympathetic systems work in
opposition to each other in order to maintain homeostasis.
•
Certain drugs act as either stimulants or depressants by directly affecting one of these systems.
medicalterms.info