special senses
1. Sensation
There are different modalities (forms) of sensation Sound, pain, pressure, touch, stretch, vibration, heat, cold, vision, taste, smell, proprioreception, hearing, equilibrium, gustation, etc.
Each modality has a specific receptor
Each modality is conducted by sensory (afferent) neurons to the CNS and is the result of different neural pathways and synaptic connections
2. Sensory Pathways
3. Law of Specific Nerve Energy
Each sensory neuron carries information about only one sensation: they usually respond best to one form of stimulus energy (but other stimuli can evoke a response)
It ISN’T THE NEURON, it’s WHERE IT GOES IN THE CNS
Normal or Adequate stimulus Allows receptors to function as filters Requires the least amount of energy to start an AP Under normal conditions (no tissue injury) correct CNS interpretation of receptors
4. Nerves
Nerves carry both afferent and efferent axons (mixed nerve)
The axons are all of different sizes
Remember that thicker axons have a faster conduction velocity Decrease in K+ and Cl- leaks through ungated channels Less resistance to current flow
Myelination allows a decrease in axon diameter with increased conduction velocities Rapid flow through reflex arcs Increase the number of axons in neural tissue : “miniaturization” of nervous system Fewer APs required so less ion flow: less Na+/K+ ATPase used so the neurons conserve energy
5. Nerve Conduction
Three types of fibers are generally recognized in the sensory subclass: A-beta fibers
▪Largest fibers
▪Mediate touch and mild pressure, as well as vibration and the position of joints
▪Conduction velocity above 30 m/sec. A-delta fibers
▪Smaller than A-beta fibers
▪Mediate cold and the first components of pain
▪Conduction velocity between 2 and 30 m/sec. C fibers
▪Slowest and smallest, serve most of autonomic peripheral functions
▪Mediate the sensation of
There are different modalities (forms) of sensation Sound, pain, pressure, touch, stretch, vibration, heat, cold, vision, taste, smell, proprioreception, hearing, equilibrium, gustation, etc.
Each modality has a specific receptor
Each modality is conducted by sensory (afferent) neurons to the CNS and is the result of different neural pathways and synaptic connections
2. Sensory Pathways
3. Law of Specific Nerve Energy
Each sensory neuron carries information about only one sensation: they usually respond best to one form of stimulus energy (but other stimuli can evoke a response)
It ISN’T THE NEURON, it’s WHERE IT GOES IN THE CNS
Normal or Adequate stimulus Allows receptors to function as filters Requires the least amount of energy to start an AP Under normal conditions (no tissue injury) correct CNS interpretation of receptors
4. Nerves
Nerves carry both afferent and efferent axons (mixed nerve)
The axons are all of different sizes
Remember that thicker axons have a faster conduction velocity Decrease in K+ and Cl- leaks through ungated channels Less resistance to current flow
Myelination allows a decrease in axon diameter with increased conduction velocities Rapid flow through reflex arcs Increase the number of axons in neural tissue : “miniaturization” of nervous system Fewer APs required so less ion flow: less Na+/K+ ATPase used so the neurons conserve energy
5. Nerve Conduction
Three types of fibers are generally recognized in the sensory subclass: A-beta fibers
▪Largest fibers
▪Mediate touch and mild pressure, as well as vibration and the position of joints
▪Conduction velocity above 30 m/sec. A-delta fibers
▪Smaller than A-beta fibers
▪Mediate cold and the first components of pain
▪Conduction velocity between 2 and 30 m/sec. C fibers
▪Slowest and smallest, serve most of autonomic peripheral functions
▪Mediate the sensation of