CNS Lecture 2 Flashcards
What is de-afferentiation
Loss of sensory inputs = severely affects control
What does modality of a sensory input refer to?
The type of sensory information that is transmitted (eg vision, touch, hearing, movement etc)
ie what is perceived after stimulus (eg temperature modality is perceived after heat or cold stimulate a receptor)
Light, sound, taste, temperature, sound, pressure etc
What component of a sensory receptor determines which modality of stimulus it responds to?
The structure of a sensory receptor determines which modality of stimulus it responds to
The modality activity a given receptor is called:
The adequate stimulus of that receptor
Different modality’s are processed in different _____ _____. Provide an example
Different modality’s are processed in different brain regions. Provide an example
eg Somatosensory cortex processes sensory input from skin and muscles; input from retina/eyes is processed in the visual cortex
Specific types of mechanosensory stimulation are transduced by specific types of:
Receptor Cells
Such as:
- Tactile (meissner’s) corpuscle = A
- Tactile (merkels) corpuscle = B
- Free nerve endings = C
- Lamellated (Pacinian) corpuscle = D
- Ruffini corpuscle = E
Label A-E in the image:
Provide what each receptor senses.
-
A Tactile (meissner’s) corpuscle
- Light touch
-
B Tactile (merkels) corpuscle
- Touch
-
C Free nerve endings
- Pain
-
D Lamellated (Pacinian) corpuscle
- Vibration and Deep Pressure
-
E Ruffini corpuscle (two types)
- Warmth - type one - increases firing rate as temperature rises
- Cold - Type Two - increases firing rate as temperature falls
Describe the Meissner’s Corpuscle:
- bulbous receptor in which the sensory terminal of the nerve axon is spiralled inside a capsule
- Respond to light touch of the skin
A in the image
Describe the Merkel’s Corpuscle:
Less complex than Meissner’s corpuscle
Separate branch
Respond to touch - require more pressure than Meissner’s corpuscles
What do free nerve endings respond to?
Respond to tissue damage (sensory modality is pain)
What are Pacinian corpuscles?
What feature do they have to combat pressure increase?
D in the diagram
Sensory receptor that responds to vibration (eg vibration at 500hz = 500 axon potentials)
- Have slippery layers called Lammellae that slide over each other as pressure around corpuscle rises
What are the two types of Ruffini corpuscle and what triggers firing of each type?
1: Warm Receptors: increases firing rate as temperature increases
2: Cold Receptors: Increases firing rate as temperature falls
E in the image
What are the two types of sensory receptors (a and b) show in the image:
a) Specialized endings of afferent axons: eg Skin/muscle receptors = axons project directly to the spinal cord
b) Separate cells that respond to the stimulus and transmit signals via synapses with the afferent neurons:
- comprised of 1st order receptor cells respond to stimuli = synapse on 2nd order cells which transmit the info to the nervous system
- eg: cochlear hair cells, retinal photoreceptor cells
What happens to the membrane potential at the initial segment of a sensory receptor’s afferent axon as stimulus intensity increases?
The Membrane potential at the initial segment of the sensory receptor’s afferent axon increases until action potentials are generated
What causes sensory receptor recruitment? What is recruitment?
An increase in stimulus intensity causes increases in action potential rate and an increase in the number of sensory receptors that are active: this is recruitment
How does an increase in stimulus intensity effect the release of neurotransmitters within the CNS?
An increase in intensity of stimulus causes an increased release of NT within the CNS
What happens in the case of mechanoreceptors when a stimulus (such as a poke on the arm) is encountered?
- The membrane is distorted
- Causes tiny pores in membrane to open
- Na+ ions enter cell
- reduces voltage difference between intracellular and extracellular environment (inside of cell becomes less negative)
What is the receptor potential?
Change in voltage at the initial segment (ie at the sensory receptor) caused by deformation of the receptor
What is the relationship between the intensity of a stimulus and the change in voltage across the membrane?
The larger the intensity of the stimulus = larger change in voltage
What are three mechanisms of intensity coding?
- Frequency coding
- Population code
- Temporal pattern code
What is Frequency coding?
The bigger the stimulus, the more the membrane channels in the sensory ending are distorted, the greater the number of action potentials/sec (AP/s)
What is Population coding?
The bigger the stimulus, the more sensory neurons are recruited into activity = more AP’s
What is Temporal Pattern Coding?
Variability of firing rate (bursts vs steady firing) may mediate certain types of sensation
Slowly adapting receptors are called:
Tonic Receptors
What is the difference between slowly-adapting receptors (tonic) and Rapidly-Adapting Receptors?
- Slowly adapting receptors generate action potentials throughout the duration of the stimulus
- Rapidly-adapting receptors respond only briefly each time the stimulus changes
What two sensory receptors are examples of Rapidly-Adapting receptors?
Pacinian corpuscles and Meissner’s corpuscles
What are three examples of Slow-Adapting Receptors?
- Merkel’s corpuscles
- free neuron endings
- Ruffini Corpuscles
Define adaptation in terms of action potentials
Reduction in response (number of AP/s) in the continuous presence of a stimulus
