For Wednesday (4/412), Read: Raven and Johnson, pages 957-959, 964-965; and IB text, pages 331-333.

Section postponed until 4/4/12

4/4/12 (Introduction)
Autonomic Nervous System video
E.5.4 Sympathetic and Parasympathetic Nervous system
For more detailed information on the control of heart rate see section H.5.3
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Heart rate is controlled by the autonomic system which is also divided into two parts, the sympathetic and parasympathetic nervous system.
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Sympathetic (Fight-or-flight) response


See also: Hypothalamic–pituitary–adrenal axis
Catecholamine hormones, such as adrenaline or noradrenaline, facilitate immediate physical reactions associated with a preparation for violent muscular action. These include the following:[6[[|]]]

Parasympathetic (relax and renew) response


Parasympathetic Stimulation
Iris (eye muscle)

Pupil constriction
Salivary Glands

Saliva production increased
Oral/Nasal Mucosa

Mucus production increased

Heart rate and force decreased

Bronchial muscle contracted

Gastric juice secreted; motility increased
Small Intestine

Digestion increased
Large Intestine

Secretions and motility increased


Increased urine secretion
Adrenal medulla


Wall contracted
Sphincter relaxed
4/5/12 (Pupil reflexes as sympathetic and parasympathetic responses, introduction to sensory reception)

E.5.5 The pupil reflex

Pupil constriction in bright light- a parasympathetic response: Animation
    • The iris reflex is under the control of the autonomic system.
    • If light is particularly bright the receptors cells of the retina can be come over stimulated.
    • To prevent over stimulation the iris is able to reduce the amount of light entering through the constriction of the pupil that as much light as possible reaches the retina the pupil dilates.
    • The mechanisms in the eye is based on two sets of muscles, the circular and radial muscles.
    • This antagonistic pair of muscles makes up the iris
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E.5.6 Death and the pupil reflex

Descriptions of death at the biological level:
  • external image e.5.6.jpg

E.2.1 Outline the diversity of stimuli that can be detected by human sensory receptors.

Receptors detect the changes in both internal and external environment.
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E.2.2 Label a diagram of the structure of the human eye.

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HW: Read pages 323-324 in IB text


Contralateral processing is the way in which the brain collects and integrates information from the eyes to create the perception of seeing.

Stimuli from the left visual field enter both eyes.

The stimulated receptive fields of the left and right eye stimulate the ganglion cells which provide neural activity along the optic nerve.

Look closely, the left visual field information from ganglion in BOTH eyes goes to the right side of the brain.
Equally for the right visual field object, the information ends up in the left side of the brain.

The cross over point for optic nerves is the Optic Chiasm.
The optic nerves for synapses in the lateral geniculate nucleus with neurones from the primary visual cortex.

The brain is able to integrate the 2 dimensional information of the retina back into a 3 dimensional perception of the ‘real world’.

E.2.3 Annotate a diagram of the retina to show the cell types and the direction in which light moves.

General organization:
        • external image neuroneseye.jpg

rretina structure
rretina structure

  • (a)Bipolar cell forming synapses with more than one photoreceptor.
  • (b) Bipolar cells connecting together rods and cones
  • (c)Ganglion cell collecting input from a group of photoreceptors (receptive field)
  • (d)Axon of the ganglion cell forming the optic nerve at (i)
  • (e)Summation of rod photoreceptors gives low visual acuity (resolution) Non-fovea arrangement
  • (f)Another form of summation
  • (G)The arrangement of cones in the fovea provides a high level of visual acuity (resolution).

HW: Read Raven and Johnson (980-987) and IB Text (325)


E.2.4 Compare rod and cone cells.

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E.2.5 Explain the processing of visual stimuli, including edge enhancement (See below) and contralateral processing (See above).
  • Edge enhancement is a ‘pre- central nervous system ‘processing of information on the retina itself. This processing is not carried out by part of the brain but by the organisation of the retinal cells.
  • Contralateral processing is the way in which the brain collects and integrates information from the eyes to create the perception of seeing. Both these processes require a more detailed knowledge of the retina and brain. It should also be noted that this biology is still the subject of much research and the ideas presented are hypothetical.

Edge Enhancement:

edge enhancement
edge enhancement

Stare at the square; you might notice that there is a kind of ‘white glow’ around the outside.

This glow is called edge enhancement and it results from retinal processing of information.

The purpose is to provide a greater contrast at the edges of objects.

The scintillating grid illusion

  • The scintillating grid illusion is an optical illusion constructed by superimposing white discs on the intersections of orthogonal gray bars on a black background.
  • Dark dots seem to appear and disappear rapidly at random intersections, hence the label “scintillating”. When a person keeps his or her eyes directly on a single intersection, the dark dot does not appear.
  • The effect is explained by the facts that: 1) ganglion cells are stimulated by a group of receptors in the retina that form a receptive field; and 2) ganglion cells are more stimulated if the edge of a light/dark area is within the receptive field.
Explain visual stimuli processing/edge enhancement/contralateral processing - IB Biology Syllabus
Explain visual stimuli processing/edge enhancement/contralateral processing - IB Biology Syllabus

4/13/12 (Auditory system: structure and function)

(Good review article on auditory system)

Structure of the human auditory system

Optical/Auditory Illusions activity

Test on Autonomic Nervous System, Sensory perception, Eye and Ear structure/function.