Download Option E Review

Option E Review
Syllabus Statements
• E.1.1 Define the terms stimulus, response and reflex in
the context of animal behavior.
• E.1.2 Explain the role of receptors, sensory neurons,
relay neurons, motor neurons, synapses and effectors in
the response of animals to stimuli.
• E.1.3 Draw and label a diagram of a reflex arc for a pain
withdrawal reflex, including the spinal cord and its spinal
nerves, the receptor cell, sensory neuron, relay neuron,
motor neuron and effector.
• E.1.4 Explain how animal responses can be affected by
natural selection, using two examples.
Terms
• Stimulus =
– a change in the environment (internal or
external) that is detected by a receptor and
elicits a response
• Response =
– a change in the organism based on the
stimulus that is received
• Reflex =
– a rapid unconscious response
Nervous systems are used in response to
stimuli.
Behavior is the pattern of responses in an
animal.
The 5 parts of the reflex arc and
their roles
• 1. receptors: to detect a stimulus;
receptors can be sensory cells or nerve
endings of sensory neurons.
• 2. sensory neurons: to receive messages
across synapses, from receptors and carry
them to the central nervous system (spinal
cord or brain).
• 3. relay neurons: to receive messages,
across synapses, from sensory neurons,
and pass them to the motor neurons that
acan cause an appropriate response.
Reflex arc continued:
• 4. motor neurons: to receive messages,
across synapses, from relay neurons and
carry them to an effector.
• 5. effectors: to carry out a response after
receiving a message from a motor neuron;
effectors can be muscles, which respond
by contracting, or glands, which respond
by secreting.
Sequence of events in response to
pain.
1.
2.
3.
4.
•
•
Nerve endings in the skin of the rabbit’s nose detect the pain caused by the stings.
These cells are called pain receptors. The pain receptors are nerve endings of
sensory neurons.
These sensory neurons carry impulses from the nose of the rabbit to its central
nervous system.
The impulses travel to the ends of the sensory neurons where there are synapses
with relay neurons. Messages are passed to the relay neurons by synaptic
transmission.
The relay neurons have synapses with motor neurons, which carry impulses out of
the central nervous system, to muscles in the rabbit’s body.
5. Messages are passed across synapses from motor neurons to muscle fibers,
which contract and pull the rabbit’s nose away from the nettle. It is the connections
between sensory, relay and motor neurons that ensure the response is appropriate
to the stimulus –that is known as coordination.
Taken from IB Biology: Course Companion by Allott and Mindorff. 2007
Draw a Spinal Reflex Arc
Natural Selection and Responses
(Directly from the syllabus)
• The blackcap species of bird (Sylvia
atricapilla) breeds during the summer in
Germany.
• Until recently, this species migrated
southwest to Spain or other Mediterranean
areas for winter.
• Recently, studies show that 10% of
blackcaps now migrate west to the UK
instead.
Blackcap: The Blackcap breeds throughout most of Europe and into North
Africa and western Siberia. During the winter birds from the north and east
of Europe move south, many as far as sub-Saharan Africa. Some
continental birds, however, winter in Britain
Testing hypothesis that genetics and,
therefore, natural selection a factor:
• Eggs were collected from parents who had migrated to the UK
in the previous winter.
• Eggs were also collected from parents who had migrated to
Spain.
• The young were reared and the direction in which they set off,
when the time for migration came, was recorded.
• Birds whose parents had migrated to the UK tended to fly west,
wherever they had been reared, and birds whose parents had
migrate to Spain tended to fly southwest.
• Despite not being able to follow their parents at the time of
migration, all the birds tended to fly in the direction that would
take them on the same migration route as their parents.
Conclusion from this study:
• Blackcaps are genetically programmed to
respond to stimuli when they migrate so
that they fly in a particular direction.
• Speculation: the increase in numbers of
blackcaps migrating to the UK for the
winter may be due to warmer winters and
greater survival rates in the UK.
2nd Example of animal responses
affected by natural selection.
• Note that a key to all of
these studies involves first
demonstrating that a trait is
under genetic control. Only
then, is the trait subject to
natural selection.
• Parus major (great tit)
mentioned in review guide.
Parus caeruleus (blue tit)
example 1996 Royal
Society article.
Adaptive differences in the timing of egg laying
between different populations of birds result from
variation in photoresponsiveness.
• Parus major breeds in spring or early summer
throughout much of Europe.
• Timing of egg laying is genetically determined
(experiment used non-domesticated birds bred in
captivity).
• Day length is used to determine the time of year.
• Recent studies in the Netherlands have shown that
the mean date of egg laying is becoming earlier.
• Adults that breed earlier enjoy greater reproductive
success.
• This is due to the earlier opening of leaves on
deciduous trees and an earlier peak in the biomass of
invertebrates feeding on tree leaves.
• These invertebrates are the main food that adults
collect and feed to offspring.
• Results of work with blue tit of Southern
France, indicate that some island
populations reproduce 3 weeks earlier
than mainland varieties. Differences
persist even if island populations are
raised in outdoor aviaries on the mainland.
E.2s Perception of stimuli
• E.2.1 Outline the diversity of stimuli that can be detected
by human sensory receptors, including mechanoreceptors,
chemoreceptors, thermoreceptors and photoreceptors.
• E.2.2 Label a diagram of the structure of the human eye.
• E.2.3 Annotate a diagram of the retina to show the cell
types and the direction in which light moves.
• E.2.4 Compare rod and cone cells.
• E.2.5 Explain the processing of visual stimuli, including
edge enhancement and contralateral processing. Edge
enhancement occurs within the retina and can be
demonstrated with the Hermann grid illusion. Contralateral
processing is due to the optic chiasma, where the right
brain processes information from the left visual field and
vice versa. This can be illustrated by the abnormal
perceptions of patients with brain lesions.
• E.2.6 Label a diagram of the ear. Include pinna, eardrum,
bones of the middle ear, oval window, round window,
semicircular canals, auditory nerve and cochlea.
• E.2.7 Explain how sound is perceived by the ear, including
the roles of the eardrum, bones of the middle ear, oval and
round windows, and the hair cells of the cochlea.
Perception of Stimuli
• Stimuli are detected by receptors. Some
receptors are nerve endings of sensory
neurons, e.g. pain receptors.
• Other receptors are special cells located in
a sense organ, e.g. hair cells in the
cochlea of the ear.
• Animals can detect a wide variety of
stimuli, using different types of receptors.
Human receptors: All convert energy from a
stimulus into electrical energy of a nerve impulse --energy transducers.
• Mechanoreceptors: perceive mechanical energy in the form of
sound waves e.g. hair cells in the cochlea of the ear; perceive
movements due to pressure or gravity e.g. pressure receptor
cells in the skin.
• Chemoreceptors: perceive chemical substances dissolved in
water (tongue) e.g. receptor cells in the tongue; chemical
substances as vapors in the air (nose) e.g. nerve endings in the
nose.
• Thermoreceptors: perceive temperature e.g. nerve endings in
skin detect warm or cold.
• Photoreceptors: detect electromagnetic radiation, usually in the
form of light e.g. rod and cone cells in the eye.
The Human Ear: Mechanoreception
Olfaction in humans.
Sensory transduction by a taste receptor.
Photoreceptors in the vertebrate
retina
A
B
C
D
E
F
The vertebrate retina
Photoreceptor layer of neural
retina
• Human retina contains 120 million rod cells, 6 million cone
cells  photoreceptors = specialized to transduce light rays
into receptor potentials.
• Rods: more sensitive to light (all wavelengths), used night
vision, no color vision; shapes and movement
• Cones: can distinguish color in daylight
– 3 types – red, green & blue; high visual acuity in bright
light.
• Lifestyle of organism dictates proportion of each in retina
• Humans: cones near fovea; rods on periphery (see better at
night if not looking directly at an object).
Difference between rods and
cones
• Outer segments of
cones are tapered or
cone-shaped
• Visual Acuity
• Color vision (R, G, B)
So each cone contains
1 of 3 different kinds
of photopigments.
• Outer segments of
rods are cylindrical or
rod-shaped.
• Wider field of view
• Black and white vision
• Best in dim light
• For movement and
shape determination
Processing of Visual Stimuli
• Reception at the level of Rods and Cones
• Processing begins in the retina
• At a simple level when multiple rods fee to
a bipolar or when horizontals and
amacrines connect inputs you have
processing
• In the retina you also have receptive fields
that organize groups of photoreceptors
We see this with Edge enhancement: The
Herman grid illusion.
When looking at a grid of black squares on a white background, one will have
the impression that there are “ghostlike” grey blobs at the intersections of the
white lines. The grey blobs disappear when looking directly at an intersection.
Stage 2: Edge enhancement
• The explanation of the Herman grid illusion rests in a
type of processing called edge enhancement.
• The intensity at a point in the visual system is not
simply the result of a single receptor, but the result of
a group of receptors called a receptive field.
• In the center of the receptive field, the receptors act
excitatory on the resulting signal, and the receptors in
the surrounding area act inhibitory on the signal.
• Since a point at an intersection is surrounded by more
intensity than a point at the middle of a line, the
intersection appears darker.
• In a person’s eyes, the nerve cells of the retina
associate and interact with each other, which results in
the illusion that there are dots, when there really
aren’t.
Another way to say this:
• Each ganglion cell is stimulated when light falls
on a small circular area of retina called the
receptive field.
• There are 2 types of ganglion cell. In one type
the ganglion is stimulated if light falls on the
center of the receptive field, but this stimulation
is reduced if light also falls on the periphery.
• In the other type, light falling on the periphery of
the receptive field stimulates the ganglion cell,
but this stimulation is reduced if light also falls on
the center.
• Both types of ganglion cell are therefore more
stimulated if the edge of light/dark areas is within
the receptive field. White areas of the Herman
grid look whiter if they are next to a black area.
Neural
pathways
for vision.
Stage 3: Contralateral
processing.
• Left and right optic nerves meet at optic
chiasma. Neurons from ½ of retina
nearest nose cross at optic chiasma to
opposite optic nerve
• Left portion of the visual field from each
eye sent to the right side of the brain and
vice versa.
• This allows the brain to deduce distances
and sizes.
Visual Processing continued
• Neurons continue to the thalamus where
processing begins
• Processed info carried to the visual cortex at the
back of the brain
• Further processing leads to image formation
here
• Estimated 30% of cerebral cortex used in
processing vision
• How these cells process images, then add in
motion, depth, shape and more is still largely
unknown
Perception of sound.
• 1. Eardrum: when sound waves reach
the eardrum at the end of the outer ear,
they make it vibrate with the same
frequency as the sound. These vibrations
consists of rapid movements of the
eardrum, towards and away from the
middle ear.
• The role of the eardrum is to pick up
sound vibrations from the air and transmit
them to the middle ear.
2. Bones (ossicles)of the middle
ear
• Each ossicle touches the next one…the first one
(malleus) is attached to the eardrum while the
stapes is attached to the oval window. The role
of the ossicles is to amplify the sound waves and
transmit sound waves from the eardrum to the
oval window. They reduce the amplitude of the
waves while increasing their force, which
amplifies sounds by about 20 times.
• The oval window’s small size helps with
amplification. Muscles attached to the ossicles
protect the ear from loud sounds, by contracting
to damp down vibrations in the ossicles.
3. Oval window
• This membrane transmits sound waves to
the fluid filling the cochlea. This fluid is
incompressible, so a second membranous
window is needed, called the round
window. When the oval window moves
toward the cochlea, the round window
moves away from it, so the fluid in the
cochlea can vibrate freely, with its volume
remaining constant.
4. Hair cells of the cochlea
• The cochlea consists of a tube, wound to form a spiral
shape. Within the tube are membranes, with receptors
called hair cells attached. These are the
mechanoreceptors of the ear and they are contained in the
organ of Corti.
• These cells have hair bundles, which stretch from one of
the membranes to another. When the sound waves pass
through the fluid in the cochlea, the hair bundles vibrate.
Because of graduation variations in the width and
thickness of the membranes, different frequencies of
sound can be distinguished, because each hair bundle
only resonates with particular frequencies.
• When the hair cells vibrate, the hair cells send messages
across synapses and on to the brain via the auditory
nerve.