66 - Sensory Systems Flashcards
Define proprioceptor
• Proprioceptors provide information about joint angles, muscle length and muscle tension. This information can be integrated by the brain (with vestibular input) to give you a perception of the position of your body in space and the relative position of your limbs.
Define adequate stimulus
Adequate Stimulus Under normal circumstances a specific receptor is affected by only one stimulus modality – this is the adequate stimulus.
Define nociceptor
pain receptors
Define sensory modality
Sensory modalities include five classical senses: vision, hearing, taste, smell and touch; and also pain, temperature, itch, proprioception and vestibular sense
Define receptive field
In the somatosensory system the receptive field of a neuron is the region of tissue (e.g. skin) within which a stimulus can evoke a change in the firing rate of the neuron.
Define graphesthesia
the sense through which figures or numbers drawn on the skin can be recognized
Define agraphesthesia
Loss of graphesthesia is called agraphesthesia
Define stereognosis
ability to recognize objects through touch alone
Define asterognosis
loss of stereognosis is called astereognosis
Be able to compare and contrast a receptor potential and an action potential. What is the relationship of the receptor potential to the action potential?
The receptor potential is a change in the membrane potential produced by a transducer mechanism. It is a local graded potential.
- Most receptor potentials are depolarizations
- If depolarization reaches threshold, generate action potentials
- Rate at which action potentials are generated increases as receptor potential rises higher above threshold.
- If the receptor potential is a hyperpolarization it does not generate an action potential.
How does the brain code for “what” the stimulus is?
The labeled line principle – tells you the sensory modality since there is a chain of connected neurons from the sensory receptor which responds to the stimulus to the brain area that perceives the stimulus
(think sensory modalities)
How do we know “where” the stimulus is coming from?
In the somatosensory system the receptive field of a neuron is the region of tissue (e.g. skin) within which a stimulus can evoke a change in the firing rate of the neuron.
How do we know “duration” of the stimulus?
Maintain continuous signal during stimulus
Have on-signal and off-signal
How does the nervous system code for stimulus strength (intensity)?
Signal increasing stimulus strength by increasing frequency of nerve impulses - frequency code.
Signal increasing stimulus strength by increasing the number of fibers activated - population code.
Describe adaptation of a receptor
Adaptation - When a maintained stimulus of constant strength is applied to a receptor, the frequency of the action potentials in the receptor’s sensory nerve decreases over time.
- adaptation is a general property of sensory receptors
- different receptors can have different mechanisms of adaptation
Phasic receptors
Rapidly adapting receptors
AKA rate receptors
Describe phasic receptors
- disadvantage - cannot give continuous signal in response to continuous stimulus
- useful for signaling beginning and end of stimulus
- can signal change in stimulus intensity
- number of action potentials transmitted related to rate at which change is taking place
- extract dynamic information e.g. velocity and acceleration
- knowing rate of change enables the nervous system to make prediction
Example of phasic receptors
Pacinian corpuscles
Meissner’s corpuscles
Tonic receptors
Slowly adapting receptors
Describe tonic receptors
- useful for giving continuous information about stimulus strength and signaling stimulus duration
- not as useful for signaling stimulus duration at low stimulus intensities
- when stimulus intensity low, firing rate low, difficult to decide when stimulus began or ended
Example of tonic receptors
Merkel cell ending or Merkel’s disks
Which category of receptors is often categorized with slowly adapting receptors?
Non-adapting receptors (never completely adapt)
Nociceptors
There are two different classification systems of nerve fibers. What are they?
- Roman number classification system
- Letter classification scheme
Describe the Roman system
Types I, II and III are myelinated, type IV is not.
If we exclude the A gamma fiber to the muscle spindles from the I to IV scheme, we can assign an “average” conduction velocity to each fiber type and the average conduction velocity
