CNS 2 Flashcards
The structure of a sensory receptor determines which
modality of stimulus it responds to.
The modality activating a given receptor is called that receptor’s
adequate stimulus.
Different modalities are processed in different
brain regions ( eg. Sensory cortex, visual cortex).
Specific types of mechanosensory stimulation are transduced by specific types of receptor cells
A: Tactile (Meissner’s) corpuscle (Light touch)
B: Tactile (Merkel’s) corpuscle (Touch)
C: Free nerve ending (Pain)
D: Lamellated (Pacinian) corpuscle (Vibration and deep pressure)
E: Ruffini corpuscle (Warmth)
Sensory receptors are either:
a. Specialized endings of afferent axons ( eg. Skin and muscle receptors)
b. Separate cells that respond to the stimulus and transmit signals via synapses with the afferent neurons (eg. Cochlear hair cells, retinal photoreceptor cells)
Several million neurons from body to CNS, signaling:
1) mechanoreceptors
2) thermoreceptors
3) nocireceptors (pain)
4) proprioceptors
5) vestibular receptors
Ve s t i b u l a r receptors
Head acceleration and tilt
Proprioceptors
Movement & force in muscles & joints
Nociceptors
Pain (tissue damage) in skin, viscera, muscle
Thermoreceptors
Temperature in skin & brain
Mechanoreceptors
Local tissue deformation in skin & viscera
Sensory receptors signal stimuli with action potentials in widely
ranging species (Invertebrates, vertebrates including humans).
The coding mechanism of information transfer in nervous systems (Pulse rate modulation) must have evolved before
Invertebrates and vertebrates diverged
How many types of sensory axons types
- la (myelin): muscle spindle primary ending
- lb (myelin)
- lll (thin myelin)
- IV (none): nocirecpetors (ache) and warmth thermoreceptors
Motor axon types
- a : (myelin): extrafusul ,muscle fibres
- y : (myelin): intrafusal muscle fibres
Autonomic axon types
- Preganglionic fibres (Myelin) thick
- Postganglionic fibers (myelin) thin
As stimulus intensity increases, the membrane potential at the initial segment of the sensory receptor’s afferent axon
increases until action potentials are generated.
Further increases cause increases in
action potential rate and the recruitment of more sensory receptors.
Changes in regularity of firing rates may also encode
stimulus properties.
Frequency code:
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)
Population code:
the bigger the stimulus, the more sensory neurons are recruited into activity, so the more AP/s
Temporal pattern code:
variability of firing rate (bursts vs steady firing) may mediate certain types of sensation
Duration
Slowly adapting (tonic) receptors respond the entire time a stimulus is applied.
Adaptation:
reduction in response (number of
action potentials/sec) in continuous presence of a stimulus
Different sensory receptors vary in
their
speed of adaptation to stimuli
