Anatomy and Physiology 2: Sensory Systems

Anatomy and Physiology 2

• Sensation is the process of receiving information from the environment, including touch, sight, hearing and other senses.
• Taste and smell provide enjoyable flavor and warning of spoiled or dangerous food.
• Senses also provide information about internal body states, like hunger and thirst.

Sensory Pathway

• The sensory pathway involves structures that detect stimuli and transmit information to the brain.
• Receptors detect changes, producing nerve impulses that travel to sensory neurons in the central nervous system (CNS).
• Sensory neurons transmit the impulses to the brain (or spinal cord).
• Sensory tracts carry the nerve impulses to specific areas of the brain.
• Sensory areas in the brain process the information. Most of these areas are located in the cerebral cortex.

Cutaneous Senses

• The skin (dermis and subcutaneous tissue) contains receptors for touch, pressure, heat, cold, and pain.
• These senses provide information about the external environment and the skin itself.
• Much of this information is processed subconsciously by the thalamus.

Referred Pain

• Pain resulting from an internal organ, but perceived in a different cutaneous area, is referred pain.
• This is because sensory tracts in the spinal cord can transmit impulses from both cutaneous and internal sources.
• Examples include: heart attack pain referred to the left arm, and gallstone pain referred to the right shoulder.
• The pain is perceived by the brain, which interprets the signal from the internal organ in a cutaneous location.

Sense of Taste

• Taste receptors are located on the tongue.
• Common taste types are sweet, sour, salty, bitter, and savory.
• Impulses from taste buds are transmitted by cranial nerves (facial and glossopharyngeal) to taste areas in the brain's cortex.

Sense of Smell

• Olfaction receptors (chemoreceptors) in the upper nasal cavity detect vaporized chemicals.
• Humans possess several hundred different smell receptors.
• Impulses from these receptors are carried by the olfactory nerves to the temporal lobes of the brain.
• The brain can distinguish amongst approximately 10,000 different scents.

Hunger and Thirst

• Receptors for both hunger and thirst are specialized cells located in the hypothalamus.
• Hunger receptors detect changes in blood nutrient levels (hormones and enzymes secreted by the stomach and small intestine), and hormones released by fat tissue.
• Thirst receptors detect changes in the body's water-to-salt proportion.
• Hunger and thirst sensations are not felt in the hypothalamus, but rather are projected to the stomach (hunger) and mouth/pharynx (thirst), resulting in reactions like stomach contractions or reduced saliva production.

Vision and the Eye

• The eye is the organ of vision.
• Light receptors (photoreceptors) in the retina detect light.
• Refracting lenses focus light rays onto the receptors.
• The eye has two components:
  • eyeball: contains the refractive system and receptors
  • accessory structures: eyelids, lacrimal apparatus, and eye muscles.

Eye Structure (Layers)

• The eye has three layers:
  • Outer layer (sclera and cornea)
  • Middle layer (iris and pupil, lenses)
  • Inner layer (retina)
• The sclera is tough protective tissue.
• The cornea is the transparent part of the outer layer.
• The choroid and iris/pupil regulates light entering the eyes.
• The lens focuses light entering the eye.
• The retina is the light-sensitive tissue.
• Impulses generated in the retina by light are passed via the optic nerve to specific areas in the brain.

The Ear

• The ear is made up of three parts: outer ear, middle ear, and inner ear.
• The receptors for hearing and equilibrium are in the inner ear.
• The outer ear (auricle and ear canal) captures and amplifies sound waves, directing them to the middle ear.

Middle Ear

• The middle ear is connected to the outer ear by the tympanic membrane (eardrum).
• The middle ear contains three bones (malleus, incus, and stapes) that amplify sound vibrations.
• The middle ear maintains pressure balance with the nasopharynx through the Eustachian tube.

Inner Ear (Cochlea)

• The cochlea is a snail-shaped structure containing fluid.
• The basilar membrane within the cochlea vibrates in response to sound waves.
• Hair cells on the basilar membrane generate nerve impulses that are sent to the brain, where sounds are interpreted.

Mechanism of Hearing

• Sound waves enter the ear canal and cause vibrations in the eardrum.
• The vibrations are passed to the middle ear bones (malleus, incus, and stapes), amplifying the vibrations.
• Vibrations in the bones are transmitted to the inner ear's fluid (cochlear fluid).
• Vibrations in the fluid cause the basilar membrane to vibrate, stimulating hair cells.
• Hair cells generate nerve impulses that are transmitted to the brain for interpretation.

Explore the intricate details of anatomy and physiology focusing on the sensory systems. This quiz covers the processes of sensation, the sensory pathways, and the cutaneous senses. Test your knowledge about how our body receives and processes sensory information.