Sensory Physiology Flashcards
What are peripheral neurons?
Nerves in the perphy: can be sensory (afferent) or motor (efferent)
Peripheral nerves are classified by two schemes.
- A, B C wave peripheral nerve: based on its contribution to a compound action potential from mixed nerves.
- AFFERENT FIBER characteristics: diameter, myeling thickness and conduction velocity (I, II, III and IV). Efferent fibers cannot be given these characteristics.
How is a peripheral nerves contribtion to a compound AP related to its characteristics.
• Conduction velocity determines a fiber’s contribution to the compound action potential. The compound AP and the conduction velocity are used to diagnose peripheral nerve disease.
What type of sensory (afferent) fiber types do we have?
- A: Aalpha, Abeta, Adelta
- C
SENSORY AFFERENTS
SENSORY AFFERENTS
SENSORY AFFERENTS
SENSORY AFFERENTS
SENSORY AFFERENTS
SENSORY AFFERENTS
Abeta (II); skin mechanoreceptors and secondary muscle spindles
Adelta (III); skin mechnoreceptors, thermoreceptors and nociceptors
C (IV): smallest diameter and the slowest; skin mechanoreceptors, thermoreceptors and nociceptors
Which sensory (afferent) fibers are our fastest and largest and where do they go to?
Aalpha; Ia and Ib; they go to primary muscle spindles, golgi tendon organ
Which sensory (afferent) fibers are our slowest and smallest and where do they go to?
C fibers (IV); go to skin mechanorecpetors, thermal receptors and nociceptors
Sensory receptors are will only respond to a certain modality.
Somatosensory receptors are _______
pseudounipolar
R_eceptor types vary a_cross sensory systems: they will perform the same function in different ways
But what do they all do?
They all convert the NRG that they’re sensitive to -> alter membrane potential
What is a generator potential?
A change in membrane potential that is seen when a stimulus is applied to a somatosensory receptor. When strong enough, it can cause a AP that can go t/o nervous system.
Convergence and divergence occurs where?
At receptors
Information from all sensory systems except the ______go through the ______ –> CTX.
olfactory
thalamus
How is sensory input arranged in the thalamus?
Thalamus has 1 single large nuclei for sensory input; but 2 nuclei (one for face and body) for somatosensory input. Here, the neurons that perform 1 function (touch) are separate from those that perform another function (propioception)
What is convergence?
2nd order neuron receives input from two different 1st order neurons
What is divergence?
- 1st order neurons have 2 branches that go to 2 different 2nd order neurons.
What is the difference between weak and strong stimuli?
- Weak strongly: a stimulus only activates only SOME branches of 1 sensory fiber or only activate 1 afferent neuron in a group of sensory units.
- Strong stimuli: stimulutes activates all branches of 1 sensory fiber or all afferent fibers in a group
How is the number of active receptors affected by the intensity of the stimulus?
increased intensity of the stimulus= INCREASE NUMBER OF ACTIVE RECEPTOORS
The number of active receptors increases with increased intensity of the stimulus. This allows for what?
This is how our senses can quantify small differences, allowing for very good discriminating ability
• Sensory receptors encode the intensity of the stimulus in _________
into amplitude of the receptor potential
When a stimulus persists unchanged for several minutes without a change in position or amplitude, what happens?
neural response diminishes and sensation is lost, resulting in receptor adaptation
The number of AP a stimulus produces depends on what?
strength of the stimulus
-Receptor adaptation uses two types of receptors: slowly adapting receptors and rapidly adapting receptors. What are the differences?
Slowly adapting receptors: receptors that respond to a prolonged, constant stimulation before it adapts.
Rapidly adapting receptors: receptors that respond to the begining and end of a stimulus and are only active if there is a change in intensity.
What does a slowly adapting receptor look like and give an example?
Tires fast at the begining, but continuelly fires for a prolonged period of time.
Ex. Myelinated fibers associated with smooth muscle of proximal airway
___________. are responsible for the sense of touch.
List them all
Mechanoreceptors (6) that respond to TOUCH
- Meissner corpsucles
- Pacinian corpsucles
- Ruffini endings
- Merkel cell
- Free nerve actings (tactile information)
- Hair follicle receptor
Identify the following as slowly adapting or fast adapting:
- Meissner corpsucles
- Pacinian corpsucles
- Ruffini endings
- Merkel cell
- Free nerve actings (tactile information)
- Hair follicle receptor
1. Meissner corpsucles-> RA
2. Pacinian corpsucles-> RA
3. Ruffini endings-> SA
4. Merkel cell-> SA
5. Free nerve actings (tactile information)-> SA (but these do tactile information)
6. Hair follicle receptor-> RA or SA
What type of information do the following convey?
- Meissner corpsucles
- Pacinian corpsucles
- Ruffini endings
- Merkel cell
- Free nerve actings (tactile information)
- Hair follicle receptor
- Meissner corpsucles-> tap and flutter (v sensitive- on fingers, lips)
- Pacinian corpsucles-> vibration
- Ruffini endings-> stretch of skin
- Merkel cell-> touch and pressure
- Free nerve actings (tactile information)-> tactile information
- Hair follicle receptor-> motion and direction
What is the average receptivefield size of the following?
- Meissner corpsucles
- Pacinian corpsucles
- Merkel cell
- Meisners and merkel: small (more accurate)
- Pacinian: large (less accurate)
what is a Receptive fields
Innervation of peripheral branches of ONE mechanorecptor on the skin.
REceptive fields allow us to test ______, which is what?
two point discrimination, which calculates spatial resolution for detailed structures
Does receptor adaptation = receptive field size?
no
• Tactile acuity is highest in _______________ (______receptive fields).
Tactile acuity is lowest on the___________ (______ receptive field)
• Tactile acuity is highest in lips and fingertips (smallest receptive fields).
Tactile acuity is lowest on the calf, back, thigh (largest receptive field)
how to conduct a receptive field test
put compass on two different receptive fields–> bring them close together until they can only feel 1 stimulus
Say we have a compasses (used to test 2-point discrimination) on two receptive fields on two different people.
Person A has many primary sensory neurons converging on a single secondary neuron; person B has few convergence occur. How will they differ.
- Two stimu;o compressing on two different receptive fields: if many primary sensory neurons converge on a single secondary neuron -> creates a secondary large receptive field -> thus, the brain will only sense 1 signal d/t convergence.
- In the other person, less conergence occurs, creating a smaller secondary receptor reptive field. Thus, two stimuli activate two different pathways and perceive as two different stimuli
Primary afferent neurotransmission is controlled by____________
pre and post-synpatic inhibitory mechanisms.
Primary afferent neurotransmission is controlled by pre- and postsynaptic inhibitory mechanisms.
Which exerts the most powerful form of inhibition and what is it?
Presynaptic inhibition is the strongest: causing a diminished excitatory signal.
- 1.. Presynaptic inhibition occurs when one of the 1st order neuron releases GABA
- influx of Cl- into the axon
- Results in hyperpolarization
- Less Ca2+ enters cytosol
- Leads to less total NT release
- Allows us to better localize the signal by not activating neurons located laterally
Pre-synaptic inhibition results in what?
reduced NT release from the pre-synaptic terminal, improving the brain to LOCALIZE THE SIGNAL and figure out what we are feeling because we dont want sensory overload.