Unit 3a - Sensory Systems Flashcards
What is proprioception?
sensory information from skin and muscle/joint receptors
What are simple receptors?
neurons with free nerve endings, and may have myelinated or unmyelinated axons
What are complex neural receptors?
have nerve endings enclosed in connective tissue capsules
What are special sense receptors?
cells that release neurotransmitter onto sensory neurons, initiating an action potential, eg. hair cell
What are chemoreceptors?
respond to chemical ligands that bind to the receptor
What are mechanoreceptors?
respond to various forms of mechanical energy
What are photoreceptors?
respond of light
What are thermoreceptors?
respond to temperature
What does each sensory receptor have?
an adequate stimulus (type of energy to which it responds best)
although sensors are specific for one form of energy, they respond to most other forms if the intensity is high enough
What does the stimulus do to receptors?
stimulus opens or closes ion channels in receptor cell membrane (directly or via second membrane systems)
they mostly open cation channels which results in influx of Na or Ca (depolarization)
sometimes there is an efflux of K (hyperpolarization)
What is receptor potential?
change in sensory receptor membrane potential (graded potential)
What is a receptive field?
a certain physical area which stimuli must full on to activate somatosensory and visual neurons
eg. photoreceptors - light falling on area of retina
are often defined by neurons further up the pathway (sensory input can then be gathered from more than one primary sensory neuron)
What are the two afferent neurons pathways to the brain?
- first order (primary) sensory neuron which directly associates with stimuli
- second order (secondary) neuron which relays information from first neuron
What do many primary neurons converge onto?
a secondary neuron, so the secondary receptive field is very large
- convergence allows summation of multiple stimuli
Does convergence (large receptive fields) have two-point discrimination?
no, the two stimuli fall within same secondary receptive field so only one signal goes to brain and is perceived as a single point
Does smaller receptive fields have better two-point discrimination?
yes, the two stimuli activate separate pathway to the brain, so the two points are perceived as distinct stimuli
Where is sensory information integrated in?
the CNS
1. olfactory pathways from the nose project through the olfactory bulb to the olfactory cortex
2. most sensory pathways project to the thalamus. the thalamus modifies/processes and relays information to appropriate cortex
3. equilibrium pathways project primarily to the cerebellum
summary: smell smth, goes to the bulb, then the thalamus, then the cortex
What are the sensory pathways for visceral sensory information? (neurons that monitor the internal environment and organ systems)
are mostly integrated in brain stem and spinal cord
does not usually reach conscious perception
eg. completely subconscious (blood pressure)
How are sensations decoded and processed in the CNS if all stimuli converted to graded potentials to APs are all identical?
CNS must be able to distinguish 4 properties of a stimulus: type of stimulus (modality), location, intensity, and duration