L24 Sensory system (Intro)

Question 1

Name the 3 basic types of sensory receptors present in higher vertebrates and for each explains how stimulation of the receptor generate the action potentials in the afferent nerve?

Answer 1

1. mechanoreceptor:
2. Chemoreceptor:
3. photoreceptor:

Question 2

Describe the major sensory systems present in vertebrates?

Answer 2

1. Somatosensory system (sense external environment)
   - mechanoreceptors (MR) in skin detect touch, stretch, and vibration; in muscles, tendon and joints (referred to as proprioceptors) detect the position of limbs and body
   - Thermoreceptors in skin detect temperature
   - Nociceptors in skin detect tissue-damaging mechanical thermal or chemical stimuli
2. Visceral sensory system (sense internal environment)
   - MR detect blood pressure
   - Chemoreceptors detect pH & O2 in blood
   - Nociceptors also present
3. Special sensory system (sense external environment_
   - photoreception (vision)
   - mechanoreception (hearing, balance and equilibrium)
   - Chemoreception (taste and smell)

Question 3

Explain “modality” and “adequate stimulus”.

Answer 3

Modality:
• Each type of sensory receptor responds only to specific form of energy or modality
E.g. eyes has photoreceptors - normally detect only light)

Adequate stimulus:
• Modality to which receptor responds best is called the adequate stimulus

• Modalities other than the adequate stimulus may activate receptor, but only at high energy levels (e.g. person receiving blow to eye sees light)

Question 4

List the specific types of mechanoreceptors, thermoreceptors, and nociceptors that are present in human skin. For each type of receptor, give the modality.

Answer 4

Sensory receptor on skin: (refer to P7 on PPT)
• Mechanoreceptors detect various forms of mechanical energy, include pressure, vibration, touch and stretch
• Thermoreceptors detect temperature
• Nociceptors detect tissue-damaging (noxious) mechanical, thermal and chemical stimuli
• Signals from these receptors conveyed (via thalamus) to cerebral cortex, where the particular sensation is perceived

Question 5

Explain how the type, location, intensity and duration of a stimulus are identified (or “coded”) by the nervous system.

Answer 5

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Question 6

Explain the general sequence of events that occur in a spinal reflex

Answer 6

Information from somatosensory receptors travels to spinal cord (acts as integrating center). Initiate reflex response without input from the brain. However, signals from somatosensory receptors also travel to brain, where conscious perception occurs

Question 7

Explain how tapping the patellar tendon with a rubber hammer evokes extension of the lower leg 膝跳反应

Answer 7

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