Download UNIT 4 – HOMEOSTASIS 8.1 – Human Body Systems and H

UNIT 4 – HOMEOSTASIS
8.1 – Human Body Systems and Homeostasis
(Taken from Biology 12, MHR, 2011)
The Human Body
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The human body is organized in a hierarchy of levels.
Cells (smallest unit)  Tissues  Organs  Organ System (largest unit)
The human body systems transport blood and lymph, digest food, excrete wastes, move
and protect the body and maintain homeostasis.
Homeostasis
Homeostasis:
the tendency of the body to maintain a relatively constant internal
environment despite changes in the external environment.
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This system of active balance requires constant monitoring and feedback signals about
body conditions:
 evaporation of water helps regulate body temperature
 kidneys maintain water balance
 blood distributes heat throughout the body
 pancreas regulates blood sugar
 muscles contract and release heat, etc
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A feedback system is a cycle of events in which a variable (e.g., temperature) is
continuously monitored, assessed and adjusted.
All homeostatic control systems have 3 functional components: a sensor, a control
centre, and an effector.
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Sensors
- Special sensors located in the organs of the body send a signal to the contol centre once
an organ begins to operate outside its normal limits.
Control Centre
- Receives information from the sensors and relays the information to the appropriate
effector, which helps to restore the normal balance.
- Ex:
CO2 levels
when CO2 levels increase during exercise, chemical receptors in the brain
stem are stimulated.
nerve cells from the brain then carry impulses to muscles that increase the
depth and rate of breathing.
Flushing out the excess CO2
Effectors
- Receives signals from a control centre and responds.
- Muscles, glands, or organs that restore the normal balance.
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Homeostasis is often referred to as a dynamic equilibrium – condition that remains stable
within fluctuating limits.
Negative and Positive Feedback
Negative Feedback
- Mechanisms that make adjustments to bring the body back within the acceptable range
are referred to as negative feedback systems.
- Ex: Thermostat
- thermometer: sensor
- thermostat: control centre
- furnace: effector
- Negative feedback mechanisms prevent small changes from becoming too large.
- Most homeostatic mechanisms in animals operate on this principle of negative feedback.
For example, body temperature, blood sugar levels, responses to stress, etc.
- See Figure 8.3, pg 346
Positive Feedback
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Positive feedback systems are less common in the body. Positive feedback reinforces
internal change.
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Ex 1: Birth process (progesterone)
drop in progesterone will initiate contractions of the uterus
these contractions, in turn, release another hormone, oxytocin, which
causes stronger contractions
as contractions build, the baby moves toward the opening of the uterus
once the baby is expelled, the uterine contractions stop, which in turn stops
the release of oxytocin
See Figure 8.4, pg 347
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Ex 2: Pepsin
autocatalysis, occurs in some digestive enzymes, such as pepsin
pepsin is a protein-digesting enzyme that works in the stomach, however,
the stomach does not secrete pepsin -> it secretes the inactive form,
pepsinogen
when one pepsinogen molecule becomes activated, it helps to activate
other pepsinogens nearby, which in turn, can activate others.
HOMEWORK:
pg 348 #1 – 10
Thermoregulation
(Taken from Biology 12, Nelson, 2003)
Thermoregulation:
maintenance of body temperature within a range that enables cells
to function efficiently
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Each animal species possesses its own unique temperature range.
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Ectotherms: metabolic rates are regulated by the air temperature in their external
environment, which makes metabolic rates vulnerable to the elements
Ex: invertebrates, as well as most fish, amphibians, and reptiles
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Endotherms: able to maintain a constant internal body temperature regardless of their
surroundings
Ex: mammals (including humans) and birds
The “thermostat” for the thermoregulation is the hypothalamus.
For humans, our internal body temperature (core temperature) is set at about 37oC, give
or take a degree.
The temperature setting actually varies throughout the day, falling slightly at night.
Body core temperatures are higher than peripheral body temperatures.
Ex: Core temperatures, found in the chest cavity, the abdominal cavity, and the central
nervous system, are usually higher than 37oC. The peripheral temperatures can be as
much as 4oC lower on very cold days.
Response to Heat Stress
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Thermoreceptors in the skin send messages to the brain that the body is getting too hot.
In the brain, the hypothalamus co-ordinates a response by sending a signal to sweat
glands to initiate sweating.
The evaporation of the water from the surface of the skin draws heat from the body,
thus cooling it down.
At the same time, a nerve message is sent to the blood vessels in the skin, causing them
to dilate  this increases blood flow to the surface of the skin.
The warm blood heats up the sweat droplets on the surface of the skin and loses heat to
evaporate them, returning to the core of the body much cooler.
Unfortunately, sweat carries valuable salts with it, so when the body sweats, it loses
these dissolved substances.
Response to Cold Stress
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Thermoreceptors in the skin send messages to the brain that the body is getting too
cold.
The hypothalamus sends a signal to organs and tissues to increase body temperature.
There are 3 responses to cold stress:
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1)
 Nerves going to the arterioles of the skin cause smooth muscles to contract and the
arterioles to constrict, limiting blood flow.
 The blood is shunted away from the extremities and goes to the core of the body,
bathing internal organs – this is why our fingers, toes, nose, and ears feel numb when
we’re out in the cold for very long.
2)
 Nerve messages are also carried to the smooth muscle that surrounds the hair follicles in
your skin, causing the hair to stand up, causing goosebumps.
 When the hair is erect, it traps warm, still air next to the surface of the skin and helps
reduce heat loss.
3)
 The hypothalamus also sends a message that initiates shivering – a rhythmic contraction
of skeletal muscle that generates ATP production, while at the same time, releasing heat.
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An extreme response to cold stress is the ability to slow down the heart rate and divert
blood to the brain and other vital organs  this is how some people have survived
sustained exposure to cold temperatures.
8.2 - Structures and Processes of the Nervous System
(Taken from Biology 12, MHR, 2011)
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Both the nervous system and the endocrine system control the actions of the body.
Responses to change in internal and external environments are made possible by
either electrochemical messages relayed to and from the brain, or by a series of
chemical messengers (hormones), many of which are carried by the blood, are
produced by glands, and require more time for response than nerves require.
Overview of the Nervous System
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The nervous system has two main divisions: central nervous system (CNS) and
peripheral nervous system (PNS).
central nervous system: the body’s coordinating centre for mechanical and chemical
actions; made up of the brain and spinal cord
peripheral nervous system: all parts of the nervous system, excluding brain and
spinal cord, that relay information between the central nervous system and other
parts of the body
The peripheral nervous system can be further subdivided into somatic and
autonomic nerves.
The somatic nervous system controls the skeletal muscle, bones, and skin. Sensory
somatic nerves relay information about the environment to the central nervous
system, while motor somatic nerves initiate an appropriate response.
The autonomic nervous system contains special motor nerves that control the internal
organs of the body. The two divisions of the autonomic system – the sympathetic
nervous system and the parasympathetic nervous system – often operate as
“on-off” switches.
See Figure 8.6, pg 350
Cells of the Nervous System
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The nervous system is composed of only two main types of cells: neurons and cells
that support the neurons, which are called glial cells.
Neurons are the basic structural and functional units of the nervous system.
They are specialized to respond to physical and chemical stimuli, to conduct
electrochemical signals, and to release chemicals that regulate various body
processes.
Individual neurons are organized into tissues called nerves.
Glial cells nourish the neurons, remove their wastes, and defend against infection.
They are provide a supporting framework for all nervous-system tissue.
See Figure 8.7, pg 351
The Structures of a Neuron
Structure
Function
neuron
dendrite
*nerve cell that conducts nerve impulses
*projection of cytoplasm that carries impulses toward the cell body
*are numerous and highly branched (increase surface area to receive
information)
*contains the nucleus and is the site of the cell’s metabolic reactions
*extension of cytoplasm that carries nerve impulses away from the cell
body
*vary in length from 1 mm to 1 m
*insulated covering over the axon of a nerve cell (provides protection)
*speeds the rate of nerve impulse transmission
*composed of Schwann cells (type of glial cell)
*regularly occurring gaps between sections of myelin sheath along the
axon where nerve cells are transmitted
*delicate membrane that surrounds the axon of some nerve cells
*promotes regeneration of damaged axons
cell body
axon
myelin sheath
nodes of Ranvier
neurilemma
Classifying Neurons According to Structure
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Structurally, neurons are classified based on the number of processes that extend from
the cell body.
There are 3 types of neurons based on structure:
1) Multipolar Neuron
- has several dendrites
- has a single axon
- found in the brain and spinal cord
2) Bipolar Neuron
- has a single main dendrite
- has a single axon
- found in inner ear, retina of the eye, and olfactory area of the brain
3) Unipolar Neuron
- has a single process that extends from the cell body
- dendrite and axon are fused
- found in the peripheral nervous system
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See Table 8.1, pg 352
Classifying Neurons According to Function
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There are three main types of neurons based on function: sensory input, integration,
and motor output.
1) Sensory Input (Sensory Neurons)
- Sensory receptors receive stimuli and form a nerve impulse.
- Sensory neurons transmit impulses from sensory receptors to the central nervous
system.
2) Relay Neurons (Interneurons)
- Interneurons carry impulses within the central nervous system.
- They act as a link between the sensory and motor neurons.
3) Motor Output (Motor Neurons)
- Motor neurons transmit information from the central nervous system to effectors.
- Effectors include muscles, glands, and other organs that respond to impulses from
motor neurons.
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See Figure 8.9, pg 352 and Figure 8.10, pg 353
Definitions
stimulus:
a change in the environment, either internal or external, that is detected by a
receptor and elicits a response
response:
a change in an organism, produced by a stimulus
reflex:
a rapid unconscious response to a stimulus
(IB Syllabus, 2007), (Allott and Mindroff, 2010, pg321), (Damon, McGonegal, Tosto, Ward,
2007, pg 461)
Reflex Arc
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The reflex arc contains five essential components: the receptors, the sensory
neurons, the relay neurons, the motor neurons, and the effectors.
receptors: detect a stimulus; can be sensory cells or nerve endings of sensory neurons
sensory neurons: receive messages across synapses from receptors and carry them to the
central nervous system (spinal cord or brain) via the dorsal root
relay neurons (interneurons): receive messages, across synapses, from sensory neurons
and pass them to the motor neurons that can cause an appropriate
response
motor neurons:
effectors:
receive messages, across synapses, from relay neurons and carry them to
an effector
carry out a response after receiving a message from a motor neuron; effectors
can be muscles or glands
(Allott, 2007, pg 132)
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An example of a pain withdrawal reflex is pulling away the hand after touching a
sharp object.
Receptors in the skin sense the pressure of the sharp object and initiate an impulse in a
sensory neuron. The impulse carried by the sensory neuron then activates the relay
neuron (interneuron) in the spinal cord. The relay neuron (interneuron) signals the
motor neuron to instruct the muscle to contract and withdraw the hand.
See Figure 8.11, pg 353
(Carter-Edwards, Gerards, Gibbons, McCallum, Noble, Parrington, Ramlochan, Ramlochan,
2011), (Allott, 2007, pg 132)
Electrochemical Impulse
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Nerves conduct electrochemical impulses from the dendrites along the axon to the end
plates of the neuron.
These nerve impulses involve the change in the amount of electric charge across a cell’s
plasma membrane.
Resting Membrane Potential
resting membrane potential: potential difference across the membrane in a resting neuron
(-70 mV  millivolts)
Polarization is the process of generating a resting membrane potential of -70 mV.
polarized membrane:
membrane charged by unequal distribution of positively charged ions
inside and outside the nerve cell
- Three main factors influence resting membrane potential.
1) Large, negatively charged proteins are located inside the cell.
2) Channels in the membrane allow potassium (K+) to diffuse out of the cell more easily
than sodium (Na+) can move into the cell. This makes the interior of the cell more
negative relative to the exterior.
3) The sodium-potassium pump moves sodium and potassium ions across the cell
membrane in different ratios.
See Figure 8.12, pg 354
sodium-potassium pump:
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system involving a carrier protein in the plasma membrane that
uses the energy of ATP to transport sodium ions out of and
potassium ions into animal cells; important in nerve and muscle
cells
The sodium-potassium pump actively transports three sodium ions (Na+) outside of the
cell for every two potassium ions (K+) moved inside the cell.
The overall result of the active transport of sodium and potassium ions across the
membrane, and their diffusion back across the membrane, is a constant membrane
potential of -70 mV.
See Figure 8.13, pg 355
Action Potentials
action potential: in an axon, the change in charge that occurs when the gates of the K+
channels close and the gates of the Na+ channels open after a wave of
depolarization is triggered (caused by inflow of sodium ions)
depolarization:
a change from the negative resting potential to the positive action potential
repolarization:
the change in the electrical potential from the positive action potential back
to the negative resting potential
threshold potential:
repolarization:
miminum level of a stimulus required to produce a response (usually 50 mV)
the change in the electrical potential from the positive action potential back
to the negative resting potential
refractory period: recovery time required before a neuron can produce another action
potential
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An action potential consists of two phases: depolarization and repolarization.
When the membrane potential rises to the threshold potential (-50 mV), sodium channels
are going to open while the potassium channels remain closed.
The movement of sodium ions into the nerve cell causes a depolarization of the
membrane and signals an action potential in that area.
As a result of influx of sodium ions the membrane potential rises to a positive value of
approx. +30 - +40 mV.
When the membrane potential reaches its peak, potassium channels open and allows
potassium ions to diffuse out of the neuron. This is known as repolarization.
Repolarization causes the membrane potential to fall below the normal resting membrane
potential of -70 mV.
The drop of membrane potential below -70 mV is called hyperpolarization.
This area of the neuron is not ready for another action potential until the resting
membrane is restored.
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The resting potential is restored by the sodium-potassium pump pumping sodium and
potassium ions across membrane to rebuild concentration gradients.
The time is takes for the resting potential to be restored in known as the refractory
period.
See Figure 8.14, pg 357
(Allott and Mindroff, 2010, pg 254-255), (Damon, McGonegal, Tosto, Ward, 2007, pg 177),
(Burrell, J. G. (2002-11) Click4Biology (version 0820.2011). Thailand: Bangkok; URL
http://click4biology.info)
Movement of the Action Potential in Unmyelinated Neurons
- The movement of sodium ions into the nerve cell causes a depolarization of the
membrane and signals an action potential in that area.
- This area of the axon then initiates the next area of the axon to open up the sodium
channels. This results in the movement of the action potential down the axon.
- The action potential moves along the nerve cell membrane, creating a wave of
depolarization and repolarization.
- The action potential can be described as a self-propagating wave of ion movements in
and out of the neuron membrane.
- Once the impulse starts at the dendrite end of the neuron, the action potential will selfpropagate itself to the far end of the axon.
(Damon, McGonegal, Tosto, Ward, 2007, pg 177)
Myelinated Nerve Impulse
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Myelinated neurons have exposed areas known as nodes of Ranvier.
Nodes of Ranvier contain many voltage-gated sodium channels.
The nodes of Ranvier are the only areas of myelinated axons that have enough
sodium channels to depolarize the membrane and initiate an action potential.
When the sodium ions move into the cell, the charge moves quickly through the
cytoplasm to the next node.
When the sodium ions reach the next node of Ranvier, the positively charged sodium
ions causes the membrane at that node to become depolarized to threshold.
The same process occurs until the impulse reaches the end of the neuron.
The conduction of an impulse along a myelinated neuron is called salutatory
conduction.
Saltatory comes from the Latin word that means to jump or leap.
The transmission of an impulse along an unmyelinated axon is much slower than the
salutatory conduction along a myelinated axon – about 0.5 m/s, compared with as
much as 120 m/s in a myelinated axon.
See Figure 8.15, pg 358
Synaptic Transmission
- Small fluid-filled spaces between neurons, or between neurons and effectors, are known
as synapses.
- A neuromuscular junction is a synapse between a motor neuron and a muscle cell.
- Sometimes one presynaptic neuron can synapse with one postsynaptic neuron.
- Other times one presynaptic neuron can form a synapse with many postsynaptic neurons
or vice versa many presynaptic neurons can form a synapse with one postsynaptic
neuron.
- See Figure 8.16, pg 359
- A nerve impulse (action potential) travels down the length of the axon until it reaches the
axon terminus or terminal button.
- An action potential cannot cross the synaptic cleft between neurons therefore the nerve
impulse is carried across by chemicals called neurotransmitters.
- Once an action potential reaches the area of the terminal button, it initiates the following
sequence of events.
1) Calcium ions (Ca2+) diffuse into the terminal buttons.
2) The calcium influx causes vesicles containing neurotransmitters to fuse with the
presynaptic membrane.
3) Neurotransmitter is released into the synaptic cleft by exocytosis.
4) The neurotransmitter diffuses across the synaptic cleft from the presynaptic neuron to
the postsynaptic neuron.
5) Neurotransmitter binds with a receptor protein on the postsynaptic neuron membrane.
6) This results in ion channels opening and sodium ions diffusing into the postsynaptic
neuron through these channels.
7) This depolarizes the postsynaptic neuron membrane and the action potential begins
moving down the postsynaptic neuron.
8) To prevent continuous synaptic transmission, the neurotransmitter is degraded or broken
down by specific enzymes and is released from the receptor protein. For example,
acetylcholinesterase breaks down the neurotransmitter acetylcholine.
9) The ion channel closes to sodium ions.
10)Neurotransmitter fragments diffuse back across the synaptic cleft to be reassembled in
the terminus buttons of the presynaptic neuron.
(Damon, McGonegal, Tosto, Ward, 2007, pg 179), (Allott and Mindroff, 2010, pg 257), (Allott,
2007, pg 52)
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See Figure 8.16, pg 359
Neurotransmitters
Not all transmissions across a synapse are excitatory. Some are inhibitory.
Some presynaptic neurons excite postsynaptic neurons and others inhibit postsynaptic
transmissions.
The neurotransmitter, acetylcholine, may act as an excitatory neurotransmitter on one
postsynaptic membrane and could act as an inhibitory neurotransmitter on another.
Other neurotransmitters include: serotonin, dopamine, and glutamic acid (found in
the central nervous system) and norepinephrine (found in the peripheral nervous
system).
See Table 8.2, pg 360 (Neurotransmitters and their functions)
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The interaction of excitatory and inhibitory neurotransmitters is what allows you to throw
a ball.
As the triceps muscles on the back of your arm receives excitatory impulses and
contracts, the biceps muscle on the front of your arm receives inhibitory impulses and
relaxes.
This ensures that the two muscles of the arm do not pull against each other.
Presynaptic
Neuron
Excitatory
Neurotransmitter
Inhibitory
Neurotransmitter
Effect
 Increases permeability of
postsynaptic membrane to positive
ions
 Influx of sodium ions (Na+)
 Depolarizes the postsynaptic
membrane
 Possibly reaches threshold potential
 Generates a new action potential
 Inhibits action potentials
 Hyperpolarizes postsynaptic
membrane (inside more negative)
 Makes it more difficult to reach
threshold
 Difficult to generate action potential
 Influx of chloride ions (Cl-) or loss of
potassium ions (K+)
 Lowers resting potential
Example of Transmitter
Substance
Acetylcholine
Gamma-aminobutryic acid
(GABA)
(Burrell, J. G. (2002-11) Click4Biology (version 0820.2011). Thailand: Bangkok;
URL http://click4biology.info), (Damon, McGonegal, Tosto, Ward, 2007, pg 483)
Disorders Associated With Neurotransmitters
Parkinson’s Disease
characterized by involuntary muscle contractions and tremors
caused by inadequate production of dopamine
Alzheimer’s Disease
associated with the deterioration of memory and mental capacity
has been related to decreased production of acetylcholine
HOMEWORK:
pg 362 #1 – 11
8.3 - The Central Nervous System
(Taken from Biology 12, MHR, 2011)
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The central nervous system consists of the brain and spinal cord.
It is the structural and functional centre for the entire nervous system.
In the central nervous system, myelinated neurons form the white matter while the
unmyelinated neurons form the grey matter.
Grey matter consists of cell bodies, dendrites, and short, unmyelinated neurons. It
is found around the outside areas of the brain and forms the H-spaced core of the
spinal cord. Grey matter lacks myelin sheaths and neurilemma (cannot regenerate
after injury). Damage to grey matter is usually permanent.
White matter contains myelinated axons and neurilemma. It forms in the inner
region of some areas of the brain and the outer area of the spinal cord.
The Spinal Cord
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The spinal cord is a column of nerve tissue that extends from the brain downward
through a canal within the backbone.
Within the spinal cord, sensory nerves carry messages from the body to the brain for
interpretation, and the motor nerves relay messages from the brain to the effectors
(muscles or glands).
See Figure 8.18, pg 364
The spinal cord is protected by cerebrospinal fluid, soft tissue layers and the spinal
column (series of vertebrae).
Sensory nerves enter the spinal cord through the dorsal root ganglion, and the motor
nerves leave through the ventral root ganglion.
The Brain
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The human brain comprises three distinct regions: the hindbrain, the midbrain, and
the forebrain.
The forebrain contains paired olfactory lobes and the cerebrum. The midbrain is less
developed and acts as relay centre for some eye and ear reflexes. The hindbrain
contains the cerebellum, pons, and medulla oblongata.
The brain is protected by the skull and meninges.
The meninges are three layers of tough, elastic tissue within the skull and spinal
column that directly enclose the brain and spinal cord.
Cerebrospinal fluid circulates throughout the spaces within the brain and spinal
cord carrying hormones, white blood cells, and nutrients.
It also acts a shock absorber to cushion the brain.
See Figure 8.19, pg 365
THE HINDBRAIN: COORDINATION AND HOMEOSTASIS
A) Cerebellum
Walnut-shaped structure located below and behind the cerebrum
involved in the unconscious coordination of posture, reflexes, body movements and
fine, voluntary motor skills
B) Medulla Oblongata
sits at base of brainstem
connects brain with spinal cord
coordinates many reflexes and automatic bodily functions that maintain homeostasis
C) Pons
found above and in front of medulla oblongata in the brainstem
relay centre between neurons of right and left halves of the cerebrum, the
cerebellum, and the rest of the brain
THE MIDBRAIN: PROCESSING SENSORY INPUT
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D) Midbrain
found above pons in the brainstem
involved in processing information from sensory neurons in the eyes, ears, and nose
THE FOREBRAIN: THOUGHT, LEARNING, AND EMOTION
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E) Thalamus
sits at base of the forebrain
known as “the great relay station”
consists of neurons that connect hindbrain and forebrain and connect sensory system
with the cerebellum
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F) Hypothalmus
lies just below thalamus
helps to regulate body’s internal environment
contains neurons that control blood pressure, heart rate and body temperature
major link between the nervous system and the endocrine system
coordinates the actions of the pituitary gland by producing and regulating the release
of certain hormones
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G) Cerebrum
largest part of the brain
divided into right and left cerebral hemispheres
contains centres for intellect, learning and memory, consciousness, and language
interprets and controls the response to sensory information
The Structure and Function of the Cerebrum
cerebral cortex:
thin outer covering of grey matter that covers each cerebral hemisphere of
the brain; responsible for language, memory, personality, conscious
thought, and other activities that are associated with thinking and feeling
corpus callosum: bundle of white matter that joins the two cerebral hemispheres of the
cerebrum of the brain; sends messages from one cerebral hemisphere to
the other, telling each half of the brain what the other half is doing
Lobes of the Cerebral Cortex
Lobe
Frontal lobe
Temporal lobe
Parietal lobe
Occipital lobe
Function
*integrates information from other parts of the brain and controls
reasoning, critical thinking, memory, and personality
*motor areas control movement of voluntary muscles (e.g., walking and
speech)
*processes visual and auditory information
*linked to understanding speech and retrieving visual and verbal
memories
*receives and processes sensory information from the skin
*helps to process information about the body’s position and orientation
*receives and analyzes visual information
*is needed for recognition of what is being seen
See Figure 8.22, pg 368
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HOMEWORK:
pg 369 # 1 - 19
8.4 - The Peripheral Nervous System
(Taken from Biology 12, MHR, 2011)
The Somatic System
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The somatic nervous system controls voluntary movement of skeletal muscles.
The somatic system includes 12 pairs of cranial nerves and 31 pairs of spinal nerves (all
are myelinated).
The sensory neurons carry information about the external environment from the
receptors in the skin, tendons and skeletal muscles.
The motor neurons carry information to the skeletal muscles.
The Autonomic System
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The autonomic nervous system is under automatic or involuntary control.
It either stimulates or inhibits the glands or the cardiac or smooth muscle.
The hypothalamus and medulla oblongata control the autonomic system.
The autonomic system maintains the internal environment of the body (homeostasis) by
adapting to the changes and demands of an external environment.
Ex: Once carbon dioxide or oxygen levels exceed or drop below the normal range,
autonomic nerves act to restore homeostasis.
The autonomic system is made up of the sympathetic nervous system and the
parasympathetic nervous system.
The Sympathetic Nervous System
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The sympathetic nervous system prepares the body for stress. The response is often
referred to as the fight-or-flight response.
The neurotransmitter, norepinephrine, is released from the sympathetic system which
has an excitatory effect on its target muscles.
The Parasympathetic Nervous System
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The parasympathetic nervous system returns the body to a resting state. It acts to
restore and conserve energy
The parasympathetic system releases the neurotransmitter, acetylcholine, to control
organ responses.
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 can act as either stimulants or depressants by directly affecting the
sympathetic and parasympathetic nervous systems.
Functions of the Sympathetic and Parasympathetic Nervous Systems
Effector
Tear ducts
Pupils
Salivary glands
Lungs
Heart
Liver
Effect of Sympathetic
Inhibits tears
Dilates pupils
Inhibits salivation
Dilates air passages
Speeds heart rate
Stimulates the release of glucose
Kidneys, stomach,
pancreas
Adrenal gland
Small and Large
intestine
Urinary bladder
Inhibits activity of kidneys,
stomach, and pancreas
Stimulates adrenal secretion
Decreases intestinal activity
Parasympathetic
Stimulates tears
Constricts pupils
Stimulates salivation
Constricts air passages
Slows heart rate
Stimulates gall bladder to release
bile
Increases activity of stomach and
pancreas
No known effect
Increases intestinal activity
Decreases urination
Increases urination
HOMEWORK:
pg 373 #1 - 12