Senses. Sequence of steps.

1. Stimulus (change in environment
2. Sensory receptor eg: EYE (Energy to Electrical Energy)
3. Signal/Nerve Impulse is conducted along neurones to the brain/Spinal cord.
4. Perception: brain trabslates message & sensation is percieved.

Sensitivity of area 

Receptor = Sensory neurone + receptor endings at the tips of DENDRITES.

 Stimulation anywhere in RECEPTIVE FIELD results in nerve impulse.

Nerve impulses 

Fixed size.

Receptor fires several impulses for strong Stimulus

Few for weak

Stimulus strength=frequency of impulses sent to brain.

why do you stop noticing background noise or the pressure of your clothing on the skin or the smell in a room?

The receptors  have become less responsive (they adapt) and they stop sending out nerve impulses. In general, our senses respond better to changing rather than constant stimulation

factors that determine the sensitivity of an area of the body

size, density and degree of overlap of the receptive fields of our sensory receptors that determine how sensitive an area of our body is and how well we can localise a stimulus.

type of stimulus.

compression, stretch etc

chemical

light

receptor type

mechanoreceptor

   chemoreceptor
    photoreceptor
      thermoreceptor

5 special senses. 

 sense     sense organ

taste    tongue

smell    nose

vision  eyes

hearing    ear

List the two main differences between special and general senses

Special-localised & complex receptors;

General-widely distributed & simple

Our special senses of taste and smell have similarities in both the receptor structures and the mechanisms involved:

·        the stimulus in both cases is chemical in nature

·        A chemoreceptor is activated to cause a nerve impulse

·        the stimulus must be in solution to reach the chemoreceptor

There are four basic tastes.

bitter

sour

salty

sweet 

taste buds 

• on the tongue at the base of the papillae (pin based dots) are the taste buds.
• contain individual cells. Some cells have “hairs”  protruding through  tongue epithelium. These belong to the gustatory (taste) cells which are the specific receptor cells.
• Chemicals in our food must first dissolve in saliva  in order to reach the taste “hairs

taste buds 2 

• At other end of the taste bud, nerve fibres leave receptor cells
  
• For some tastes, chemical binds to protein on the "hair" and the cell produces nerve impulse which tavels cranial nerves to brain 
• activation of a combination of chemoreceptors which gives us the variety of flavours. 

receptors for smell and how they work.

Receptor cells for smell (olfactory cells) are located in the olfactory nasal epithelium.

Mucus from adjacent support cells dissolves the odour chemicals inhaled.

These then bind to chemoreceptor proteins on cilia of the olfactory cells causing a nerve impulse in olfactory nerve fibres.

sense of smell

• very sensitive – it only takes a few molecules of a chemical to activate an olfactory cell. It also readily adapts to odours
• translated in the temporal lobe
•