Neural Control

• Two main classes of cells in the nervous system:

1.Nerve cells (neurons): ‒ specialized for electrical signaling

transmission over a long distance;

2.Glial cells (glia), or supporting cells: ‒ not capable of electrical signal

transmission

Overview: Nervous system and the perception of sensation

Structure of a neuron

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• Dendrites: – Input – Provide sites for the synaptic contacts

made by the terminals of other nerve cells – Specialized for receiving information.

• Axons: – Output. – Transmit information that impinges on the

dendrites of other neurons – Specialized for transmitting signal

Structure of a neuron

Action potential

The axonal mechanism that carries signals over such distance is called “action potential”.

Photo: public domain

Action potential

Perception of sensations

Stimuli (hot, pain, cold, light, sound, odor, sweet, bitter…)

Specific sensory receptor cells

Different areas of the brain

Action potentials carried by the nerve cells

Sensory Input

Detailed introduction to different senses will be given in the following lectures

Type of sensations Type of stimuli Type of sensory receptor cells Taste Salt, sweet, sour,

bitter, umami Taste sensory cells present in taste buds

Smell Aroma Olfactory receptor cells Sight Light Photoreceptors

(Rods and Cones) Touch Temperature,

pressure, etc…. Different types of receptors present in our skin

Sound Sound waves Auditory receptor cells (hair cells)

Perception of sensations

All five senses are integrated at the same time!

Light travels the fastest. Sight: • visual appearance such as colors, size,

shape, smoothness of the surface, blemishes, defects….

Demonstration: Visual Discrimination

Which senses will be involved in the enjoyment of food?

2. Taste and Odor: • Odor perceived before and after the

food is placed in the mouth

• Along with the perception of taste, form part of the perception of overall flavor

Which senses will be involved in the enjoyment of food?

Chemical travels by diffusion in air and liquid.

3. Touch: • Texture such as hardness, cohesiveness,

viscosity, springiness, adhesiveness, fracturability, chewiness, gumminess, particular size, shape and orientation, moisture, oiliness, greasiness…

4. Sound: • crunchiness, crispiness… Demonstration: Sound and texture

Which senses will be involved in the enjoyment of food?

Somatosensory perception comes last.

• Studies imply that food flavor improves nutrient metabolism and influences satiety.

Physiological effects of flavor perception

• 5-min exposure to sensory stimuli resulted in a 33% decrease in postprandial (after the meal) glucose levels owing to a significant increase in postprandial insulin release

• After swallowing 50g of fat in capsules, only sham-feed with full-fat cream cheese resulted in significantly higher postprandial triacylglycerol levels than were found when no oral stimulus was provided.

Effects of flavor on nutrient metabolism