Sensory Receptors

Sensory Receptors

• There are 6 types of receptors: - Proprioceptors - Chemoreceptors - Photoreceptors - Mechanoreceptors - Thermoreceptors - Nociceptors  • A sense organ is a group of sensory receptors grouped together in a way to maximise the reception of a stimulus. • All sense organs share basic features:    - Contain receptor cells that are particularly sensitive to one class of stimulus energies    - Usually respond to a retraced range of intensity    - The sensitive mechanism is localised at a specific location    - The sensory neurons in the receptor pass information directly to a sensory nerve which will carry that information directly to the brain. • A sensory receptor will code for four aspects of a stimulus:    - Type (Modality): Only specific receptors will respond to specific stimuli    - Intensity: The receptors send info in different patterns to inform the brain of the intensity of the stimulus    - Location: Often determined by the location of the receptor in the body - eg. sound receptors in the ear    - Duration: determined by the firing sequences of the receptors 

Proprioceptors

• Found throughout the body and signal information to the CNS about the position and movement of the body parts. • These help your brain know where you are in space • Give your body warning that you are about to roll your ankle if you land incorrectly • Basically, the main internal sense receptors in the body

Chemoreceptors

• Located on the tongue and back of the nose which change shape when they bond to a particular 'flavour' molecule. 1. Distance Chemoreceptors:    - Found at the back of the nasal cavity and respond to chemical molecules carried in the air. Do not need to be in contact with the source of stimulus to detect it. 2. Direct Chemoreceptors - Do come in contact with the source of the stimulus and are found in groups on the tongue, palate, and throat (taste buds). Taste buds are little swellings of skin called papillae and each group can detect a different quality. - Can detect the following 5 qualities: 1. Sour 2. Salt 3. Sweet 4. Bitter 5. Umami • There are other important chemoreceptors in the body too. Some detect respiratory gases in the blood, which is used to control the rate and depth of breathing. • Basically chemoreceptors play a vital role in homeostasis.  

Photoreceptors

• Sensitive to light. • Transform light energy into action potential and then interpreted in the brain as visual images. • Depending on the amount and types of photoreceptors, and animal may be adapted to night activity or day activity. • Cone cells are sensitive to colour - they provide clear and accurate distinctions between objects. • Rod cells are sensitive to light rather than colour. Distinguish between sizes and shapes.

Mechanoreceptors

• Respond to mechanical forces such as pressure or distortion • Can be found in hair cells but mostly in skin cells. Three main types: 1. Slowly adapting types may have either a small or large receptive field.    a. Small receptive field detect form and roughness    b. Large receptive field detect stretching. 2. Rapidly adapting receptors have a small field and perceive slipping 3. Pacinian receptors detect high frequency vibrations

Thermoreceptors

• Detect changes in temperature • Two types in mammals: 1. Those that detect and increase in body temperature 2. Those that detect a decrease in body temperature • The way the body reacts to temperature change varies depending on the type of animal

Nociceptors

• Respond to damaging stimuli by sending signals to the spinal cord and brain that result in the perception of pain. • Found in the skin and organs  • Only respond to a potentially damaging situation or to actual damage, and their activation threshold is high. • Respond to a variety of stimuli: - Extreme temps - Excessive pressure or distortion - Wide variety of chemicals