General Principles Of Sensory Systems (Theme C)

Question 1

What do interneurones do?

Answer 1

Form connections between other neurones

They are neither motor nor sensory

Question 2

What is a sensory system?

Answer 2

Sensory system ⇒ a system that receives information from the environment through receptors at the periphery, and transmits this information to the CNS

Question 3

Sensory systems encode 4 basic attributes of a stimulus. What are they?

Answer 3

1. Modality (type)
2. Intensity
3. Duration
4. Location

Question 4

What are the (7) sensory modalities?

Answer 4

Vision
Hearing
Touch
Taste
Smell
Balance
Proprioception

Question 5

What is the role of sensory receptors?

Answer 5

To transduce (convert) stimulus energy into neural activity (APs)

Question 6

What does sensory adaptation involve?
How is this represented in a trace?

Answer 6

• Adaptation involves a decline in the amplitude of the transduction current or receptor potential in receptor cell
• This is reflected as a reduction in the frequency of APs in a sensory neurone
• This is seen in a trace as a decline in the firing rate of the neurone

Question 7

Why is sensory adaptation important?

Answer 7

• Adaptation allows sensory systems to signal a wide range of intensities
• It enables the system to adapt to a new set point, making it responsive to different levels of stimuli

Question 8

Why does sensory adaptation often result in / involve a desensitisation of ion channels involved in transduction?

Answer 8

• Helps sensory systems to adapt to prolonged / constant stimuli - ensuring that they remain sensitive to dynamic changes in the environment
• Prevents the continuous signalling of the same level of stimulation

Question 9

What are the different types of sensory adaptation?

Answer 9

• Slowly (or non)-adapting neurones are referred to as TONIC and signal prolonged stimuli
  
  • E.g., Muscle spindles, nociceptors
• Rapidly adapting neurones are referred to as PHASIC and signal brief changes in stimuli
  
  • E.g., Hair cells, olfactory receptors, Meissner’s corpuscles (touch)
• There can also be MIXED phasic-tonic responses
  
  • E.g., some Retinal Ganglion Cells

Question 10

What underlies the receptor potential?

Answer 10

1. Transduction process generates a change in conductance (resistance of the membrane)
2. Causes opening / closing of transduction channels (ion channels)
3. Generating a membrane potential (Vm)
4. Generating a graded receptor potential

Question 11

Describe rate / frequency coding in sensory transduction

Answer 11

• The intensity of a stimulus determines the magnitude / amplitude of the receptor potential
• The amplitude of the receptor potential determines the number of APs per unit of time (firing rate)
• Therefore, the intensity of a stimulus determines the rate of discharge of APs = Rate / Frequency coding

Question 12

What are the different types of sensory receptors? (4)

Answer 12

1. Chemoreceptors (taste / smell / CO2 / pO2)
2. Mechanoreceptors (hearing / balance / touch / proprioception) - e.g., muscle spindles
3. Photoreceptors (vision) - i.e., rods & cones
4. Nociceptors (touch - painful (noxious) stimuli)

Question 13

Which structures control what aspects of our sense of balance?

Answer 13

1. Rotational acceleration → 3 semicircular canals
2. Linear acceleration → otolith organs
3. Gravity → otolith organs

Question 14

What are the 2 otolith organs and what do they sense?

Answer 14

• Utricle - horizontal movement, moving head back & forth
• Saccule - vertical movement, senses gravity

Question 15

What is the vestibular labyrinth (made up of 3 semi-circular canals) responsible for?

Answer 15

Responsible for our sense of head rotational acceleration in 3 different planes

Question 16

What are the key properties of a receptor potential?

Answer 16

• Propagates electrotonically (passive spread of charge)
• Restricted to the sensory receptor’s cell membrane
• GRADED potential - i.e., the bigger the stimulus, the bigger the RP