topic 9 - sensory systems

Abiotic changes in environment

Temperature, humidity, sunlight

Biotic changes in environment

Abundance of food, presence of competitions, predators/pathogens/parasite, reproductive partners

Signal

Any acts or structure that influences the behaviour of other organisms (receivers), and which evolved specifically because of that effect

ie

Cue

An incidental source of information that may influence the behaviour of a receiver, despite not having evolved under selection for that function — although cues may provide information to a receiver, they have not necessarily evolved to do so.

ie. mouse making rustle in the bushes, cues to predators that there is food nearby

Types of receptors:

Chemo-, Thermo-, Mechano-, Photo-

Chemo-

Detect chemical stimuli in the environment or within the body.

Functions by binding specific molecules or detecting changes in chemical concentrations, which then trigger electrical signals (nerve impulses) sent to the brain for processing.

Eg. Tongue (taste buds), nose (olfactory receptors).

Thermo-

Temperature changes on the skin (external environment) - feeling hot or cold air, objects, etc.

Changes in the core body temperature (internal).

Thermoreceptors ion channels. Ion flow changes: these channels open or close depending on temperature, altering the flow of ions like Na+ or Ca2+ into the cell.

Electrical signals generated: this change in ion flow can trigger action potentials, which are sent to the central nervous system (CNS).

Mechano-

Detects stimuli such as touch, pressure, vibration, stretch, sound waves, body position.

Detected by skin mechanoreceptors (eg merkel discs, Meissner’s corpuscles) - feeling objects or textures with your fingers.

Photo-

Detect light (photons) they are essential for vision and are located primarily in the retina of the eye.

Light hits the retina: light enters the eye and reaches the photoreceptors at the back of the retina.

Photopigments are activated: rods contain rhodopsin, cones contain photopsin causes a chemical change in these pigments.

Plants photoreceptors Pr and Pfr

Photoreceptors contain a protein component bound to a light-absorbing pigment called the chromophore.

Responds to a range of wavelengths. Absorbs light of particular wavelength. Activation of photoreceptors, triggers cascade.

Gene expression for plant growth. Phytochrome photoreceptors: Pr inactive, Pfr active

Pr

Absorbs red light; when exposed to red light, converted back to Pfr

Pfr

Absorbs far-red light, is the active form of phytochrome, can be converted back to Pr under far-red light or in darkness.

Pfr can activate cytoplasmic molecules, or translocate to the nucleus and regulate gene expression.

When a plant is partially shaded, the light quality differs on each side.

The lit side receives direct sunlight, rich in red light, which converts more Pr to Pfr

The shaded side received filtered light, where red light is absorbed by overhead leaves, and far-red light is enriches, converted more Pfr back to Pr

Stratocytes

Gravity sensing cells in the root cap of roots. Contain statoliths.

Statoliths

Starch-filled amyloplasts.

The sedimentation of these heavy statoliths to the bottom of the cell in response to gravity serves as a signal, triggering the redistribution of hormones like auxin, and leading to differential growth that causes roots to grow downward and shoots to grow upward.

Thigmotropism

The directional growth exhibited by plants in response to touch.

Positive thigmentropism

Threadlike tendrils of climbing plants grow toward objects they touch, sometimes rapidly coiling around them. Tendrils are highly touch sensitive.

Contact with a stimulus induces the contraction of cells at the contact side and the elongation of cells at the non-contact side.

The differential growth eventually causes tendrils to twine around the abject, thereby securing the plant.

Negative thigmentropism

Roots generally grow away from objects they touch, allowing them to follow the path of least resistance through the soil

Circadian rhythm

Natural process in animals and plants that controls when things such as sleeping, eating or growing happen during a 24 hour period

Somatosensory system (3 main levels)

Receptor, circuit, perceptual

Receptor level

First level, where sensory receptors (like mechanoreceptors, thermoreceptors), detect specific stimuli. These receptors convert the stimulus electrical signal; into nerve impulses and send them along sensory neurons toward the spinal cord (CNS)

Circuit level

Second level. Primary somatosensory area, or cerebellum. Signals are relayed through the spinal cord and brain stem to the appropriate area of the brain.

Often involves multiple neurons and synapses, which help refine, filter, or amplify the signal as it ascends toward the brain.

Perceptual level

Final level. Where the brain (especially the somatosensory cortex in the parietal lobe) processes the incoming information, allowing the organism to consciously perceive the type, location and intensity of the stimulus