Unit 7: Sensory System Flashcards
Sensory systems allow for…
-the body to detect changes + maintain homeostasis.
Five Sensory Systems
- somatosensory
- visual
- auditory + vestibular
- olfactory
- gustatory
Sensory system General Function
Events in the outside world are detected and converted into APs, sent to the brain, and are consciously perceived.
Transduction of Environmental Information
how the information from the external environment is turned into language the brain understands, APs.
Environmental Stimuli
- Heat; light; touch or sound
- are all detected by sensory receptors which convert the info into APs
- different sensory receptors detect different stimuli and convert them into APs
Mechanical Stimulus
- touching; vibrating the skin
- stretches sensory receptors in the skin
- opens ion gated channels causing a depolarization of the sensory neuron producing an action potential
Chemical Stimulus
- Sour taste; odor in the nose
- binds with a receptor causing a depolarization + then an AP
Light Energy
Absorbed by photoreceptors in the eye (rods and cones in the retina) and then eventually produces action potentials
Gravity + Motion
Detected by hair cells in the vestibular system, which converts this form of external stimulus into APs
Adequate Stimulus for the receptor
The particular form of environmental stimulus to which the sensory receptor is most sensitive.
each receptor has a corresponding stimulus but the receptor can detect more than one type of stimulus
-but not necessarily in an optimal way.
Receptor/Generator Potential
- sensory receptor is stimulated by an environmental stimulus causes a change in ion permeability leading to a local depolarization
- local depolarization
- generator/receptor potential
Receptor/Generator Potentials (2)
- since the receptor does not have the voltage gated channels necessary to fire an AP, the receptor potential must spread to an area on the sensory neuron that does contain these channels
- receptor potential needs to be strong enough
- usually at the first node of Ranvier
- the AP will then be generated + propagated along the axon and into the spinal cord
Receptors with no axons has the depolarization spread to…
(hair cells in the inner ear), has the depolarization spread to the synapse to result in the release of a neurotransmitter.
Receptor Potential + Neural Coding
- weight of an object is coded into APs (the heavier an object the more APs per second)
- the heavier weight will trigger the receptor to produce a larger receptor potential, larger receptor potentials will trigger many APs on the axon of the sensory neuron.
- longer duration + travel
- Burst of high-frequency APs will eventually reach the brain when you become consciously aware of the heavier weight in your hands.
The Somatosensory System
- detects + processes the sensation of touch, vibration, temperature, and pain
- these originate in the skin
- detecting each sensation requires several different sensory receptors w/ in the skin each developed to detect its adequate stimulus
- collectively referred to as cutaneous receptors
cutaneous receptors
- Hair follicle receptors
- sensitive to fine touch + vibration
- Meissner’s corpuscles
- detect low-frequency vibrations (between 30-40 cycles/sec) and touch
- Ruffini’s corpuscules
- detect touch
- Pacinian corspuscules
- detect high-frequency vibration (250-350 cycles/sec) and touch
Receptive Field
- Each receptor will only respond to a stimulus w/in a certain region of the skin.
- area on the surface of the skin where an adequate stimulus will activate a particular receptor to fire an AP in the neuron
- any stimulus applied outside the receptor field will not generate an AP
- AP must be propagated to a specific area of the brain so that the individual becomes consciously aware of the stimulus
Spinothalamic (Anterolateral) Tract
- spinothalamic tract transmits information dealing with the very basic sensation like pain, temperature + crude touch
- information from the first sensory neuron (first-order neuron) enters the spinal cord where it synapses w/ a second-order neuron
- this neuron crosses to the contralateral side of the spinal cord + ascends to the thalamus
- thalamus acts as a relay station for almost all sensory information (except for smell)
- A second synapse with a third-order neuron occurs there (at the thalamus) and then travels to the somatosensory cortex
Dorsal Column: Medial lemnisical system
- The dorsal column, medial lemniscal system transmits information associated with the more advanced sensation of fine detailed touch, proprioception (muscle sens) and vibration
- info from the sensory neuron (first-order neuron) enters the spinal cord + immediately travels up the spinal cord
- in the upper spinal cord the sensory neuron synapses with a second-order neuron which crosses to the opposite side of the spinal cord
- it continues to the thalamus where it synapses again onto third-order neuron that travels to the somatosensory cortex
The Somatosensory Cortex
Information that has reached the brain travels to the primary somatosensory cortex located in the parietal lobe on the postcentral gyrus behind the central sulcus.
The somatosensor Homonoculus
- the sensory information arriving at this cortex is not randomly scattered around on the surface, it is “geographically preserved”
- all sensory information for the foot is located in one area that of the leg just next to it and the hip next to the leg, so on and so forth for the entire body.
- somatosensory homunculus
- topographical representation of the body on the surface of the cortex
- some area on the cortex like the areas dealing with the hand, tongue, lips receive more sensory information and require more of the brain to process that information
some area on the cortex like the areas dealing with the _____, ______, ______ receive more sensory information
hands, tongue, lips
