Download Nervous Systems - VCE Biology Units 1 and 2

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The nerve cell or neuron, is the functional unit
of the nervous system. It reacts using sensory
cells, by sending an electrical signal along two
or more neurons to reach an effector cell.
Effector cells are the cells that produce a
response.
The neural response pathways are very
specific. The receptor cells only respond to a
specific signal.
Because of the directness and speed or neural
responses, control via nerves is usually
extremely rapid, short in duration and very
precisely located.
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Nervous responses require more energy than
hormonal responses. Hormones are sent using
the circulatory system, nervous responses are
electrical signals sent down neurons, and it
requires a lot of energy to restore the ion
balance after a signal is sent.
Basic structure and neuron function is very
similar in all groups of the animal kingdom.
In nervous systems nerve cells connect to form
pathways between sensory receptors, a central
brain and a responsive organ.
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Evolution has led nerves to form the
development of complex nervous systems
made up of coordinating groups of nerve cells
connected to path-ways of sensory (receptor)
and motor (muscle or gland)nerve fibers.
More complex animals have nerve cells
grouped together, forming one or more
structures similar to small-brains called
ganglia. Which can receive and coordinate
information from sensory cells in all parts of
the body to create the appropriate response.
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Over the course of evolution animals
developed to have their sensory organs in the
front of their body, as it would be the first to
meet the new environment.
It also lead to having a coordinating brain
closer to all these sensory organs (ie a head).
In mammals coordination largely occurs in the
brain and spinal cord which are known as the
central nervous system.
Information is relayed to and from the CNS by
neurons lying outside the spinal cord and brain
called peripheral nervous system.
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The ability to detect and quickly respond to
changes in internal and external environments is
essential for an animals survival.
Pain is what you feel as a result of excessive
stimulation of sensory receptors in the skin.
A reflex is a action that occurs before your brain
processes the information.
For example if you step on a pin, your foot will
pull away before your brain even realizes you have
stepped on it.
This kind of reflex protects us from further injury.
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Stimulation of sensory receptors in the skin
send a message to the spinal cord, from there
the message is passed on to nerves to respond
and pull away from the signal. At the same
time a message is sent to the brain so you
become away of the pain.
Reflexes are the simplest type of nervous
response in animals and may involve as little as
2 or 3 cells.
The response is unconscious and automatic, it
is not modified by information received from
any other part of the body.
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Reflexes are important as they cause a reaction
often in defense of injury. Ie. Falling, the knee
jerk to overstretched tendons.
If you concentrate you can often overcome
some of the reflex, or the reflex entirely. The
brain can overcome the unconscious reaction if
you know it is coming and focus consciously to
send signals and repress the reflex.
For example most people don’t pull away
during an injection.
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Reflexes are occurring all the time, especially in
regards to posture. These small reflexes will
take cues from your ears, eyes, joints and
muscles.
Try standing on one foot.
Now try standing on one foot with your eyes
closed. That shows you the importance of
visual cues in posture.
Stretch receptors in tendons and muscles give
the body information about the length of
muscles and precise position of muscles (These
are known as kinesthetic receptors).
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A good example of these muscle and tendon
reflexes in posture is when you are standing
up, our body will sway slightly, and as it goes
forward our calf muscles are stretched and the
reflex is to contract them. This pulls your body
back to a stable upright position.
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Reflexes are also involved in some homeostatic
regulations in the body such as the circulatory
system.
For example the baroreceptor-heart rate reflex
helps maintain blood pressure.
An increase in blood pressure increases the
stretch on barorecptors in many arteries
causing these receptors to increase activity.
This in turn leads to a decrease in heart rate,
and that decreases blood pressure.
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When interneurons are added to a pathway,
the possibility of coordination and integration
increases.
For example most movements at joints use
actions of opposing sets of muscles of flexion
and extension.
Your biceps cause the flexion, and your triceps
will extend your arm. However when your
biceps are activated to contract, your triceps
receive a signal to inhibit their flexion. This
prevents the opposing muscles from flexing at
the same time.
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Most reflexes are even more complex as they
need to coordinate full body movement to get
away from the stimulus, for example if you
step on a nail or pin, you have to shift your
body weight and force to the other foot. If you
simply moved the foot on the nail you would
fall on your face.
Interneurons allow for coordinated responses
and in the human body 97% of human neurons
are interneurons.
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Most integration in humans occurs in the CNS
(brain and spinal cord). Different regions of the
brain are responsible for particular functions.
Cerebral cortex: Associated with motor
activity, sensory input, speech, sight and
breathing.
Hypothalamus: Receives info relating to the
well-being of the body, functions in
maintaining homeostasis.
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Cerebellum: is involved in the coordination of
muscle activity, including posture, balance and
movement.
Brainstem: is associated with control of the
heart, blood vessels and lung ventilation.
Along with coordinating information from the
body to create the appropriate responses. The
brain also stores information so that responses
can take into account past experiences.
Pg 282
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The PNS is made up of sensory nerves (carry
signals to CNS) and motor nerves (carry signal
to the effector organs).
The motor component of the PNS has 2
divisions, autonomic (involuntary) and somatic
(voluntary).
The voluntary or somatic system involves
functions over which you have control
(movement).
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The autonomic or involuntary nervous system
is involved in the unconscious responses such
as constriction of pupils, secretion from glands,
heart rate changes.
It sends signals to heart muscle, smooth muscle
(internal organs), glandular tissue and
regulates the digestive, cardiovascular,
endocrine, respiratory and excretory systems.
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There are two main subdivisions of the ANS,
the sympathetic and parasympathetic. They
work in similar but generally opposite ways.
Sympathetic: typically increases energy use
and prepares the body for action in emergency
situations by increasing HR and metabolic rate.
Parasympathetic: typically enhances activities
that conserve energy, such as digestion, and
slowing the HR.
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The enteric nervous system is an extensive
network of cells (and reflexes) within the wall
of the gut that coordinate the functions of the
gut.
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Animals have sensory receptors to detect
aspects of their environment that may affect
their ability to survive and reproduce.
The type of receptors present and their
sensitivity differ between animals and are
related to their lifestyle.
Humans have 5 special senses: vision, hearing,
taste, smell, and touch.
They are perceived through sense organs (eyes,
ears, nose, tongue and skin)
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These receptors can be classified into three
main types. Photoreceptors (vision),
Chemoreceptors (taste, smell, communication)
or Mechanoreceptors (hearing, balance,
pressure, touch).
The other receptors in the body or on the
surface provide the information for the general
senses such as pressure, pain, and joint position
and some internal states such as BP and blood
chemistry. These are known as visceral
receptors or enterorecptors.
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Visual stimulus in the form of light enters a
human eye through the cornea and passes
through a lens where it is focused onto the
retina.
The retina contains two kinds of
photoreceptors; cones and rods which contain
light-sensitive pigments.
Fibres from both cones and rods lead to the
optic nerve from the back of the eye and carry
coded information to the brain in the form of a
nerve impulse.
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Cone cells function in the highest light
intensities, and can detect colour and detail.
Cones are most concentrated in the central
region of the retina.
Cones provide us with our central vision which
is used when a person looks straight at an
object.
Rod cells detect light of low intensity and can
detect movement of an object. Rods do not
distinguish colour or detail, and occur at the
highest concentration in the outer areas of the
retina.
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In humans taste receptors are located in taste
buds located on the tongue.
Each taste bud is a collection of about 50
receptor cells.
Nerves from these receptors transmit impulses
that carry info about the taste of a dissolved
substance that enters the mouth. This info is
then decoded and interpreted in the brain.
Taste receptors can detect chemical substances
that are in solution in the water saliva of the
mouth.
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There are 5 basic tastes which have been
identified: Sour, salt, bitter, sweet and umami.
Umami is a taste sensation produced by
monosodium glutamate (MSG) and other
glutamates found in fermented foods.
The traditional tongue map have been found to
be wrong. All taste buds can detect all 5 tastes.
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We smell something when vapours consisting of
small lipid-soluble molecules bind to receptors.
This triggers an impulse to signal the brain.
Olfactory receptors in the nose can detect
substances at a concentration of 10,000 times less
than that required for detection in taste receptors.
People do however vary in the smell sensitivity.
There is a particularly large difference in sensing
the odour of steroid-type substances, women are
about 1000 times more sensitive to it.
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The ‘taste’ of many foods is a complex
sensation, as it is a combination of several
sensory imputs.
They include olfactory stimuli from odour
(before and while in the mouth), tactile stimuli
from the texture of the food, gustatory stimuli
arising from the taste of the dissolved food,
and temperature stimuli.
We use a combination to get the general taste
of food. And often use both the taste and smell
to determine if we need to reject the food if it
has gone off or spoiled.
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Receptors to detect stimuli that produce the
sensation of touch, pressure, temperature and
pain are distributed over the entire skin
surface. To stimulate a tactile receptors an
object must make physical contact with the
body.
Whiskers and bristles around the face of many
mammals have touch receptors at their base.
These acted as extensions of the body surface to
increase a mammals ability to collect
information.
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congenital insensitivity to pain with
anhidrosis," referred to as CIPA.
His family was shocked when Roberto started
teething. He gnawed on his own tongue, lips
and fingers to the point of mutilation.
Can’t sweat.
These genetic disorders affect the autonomic
nervous system -- which controls blood
pressure, heart rate, sweating, the sensory
nerve system and the ability to feel pain and
temperature.
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For some children it's a mild degree such as
breaking a leg, they'll get up and walk on the
leg. They feel that something is uncomfortable
but they keep on moving," she said. "For other
children, the pain loss is so severe that they can
injure themselves repetitively and actually
mutilate themselves because they don't know
when to stop.
part of this sensory disorder is difficulty
"telling where they are in space."
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1.
The ears of all mammals share a common
structure. Three regions are commonly
identified.
The outer ear consists of an external ear, made
of cartilage, that leads into an ear canal. The
canal ends in a delicate membrane (eardrum).
The purpose of the outer ear is to gather sound
waves.
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2. The middle ear is an air filled cavity that
contains three tiny bones that are joined by
elastic ligaments. Sound waves cause the
eardrum to vibrate, and this vibration is then
conducted across the middle of the ear by these
three bones to the inner ear. The force of the
vibration is magnified because it is transmitted
from a relatively large area of the eardrum to a
much smaller one in the inner ear. The middle
ear functions to magnify sound vibrations.
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3. The inner ear consists of a small coiled
structure, known as the cochlea, which is filled
with fluid. Vibrations that reach the inner ear
produce pressure waves in this fluid. The
sound receptors are minute hair cells located
on a membrane inside the cochlea. Information
about the sound stimulus is encoded into nerve
impulses and sent to the brain. The inner ear is
what receives the sound stimulus.
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The human ear also functions in maintaining
balance, but we will not be discussing the
structures and mechanisms of this process.
Not all mammals have an external ear, and
those that do vary in size and shape.