Receptor cells

a. Molecule that can bind to hormones, drugs, and antigens. b. Receptor cells can sense some stimuli, but not others. Specialized. c. Converts energy into a change in the electrical potential across its membrane. d. They sort of act as filters, ignoring background noise and converting the stimuli into electrical signals.

Stimulus

a. A physical event that triggers a sensory response.

Labeled lines

a. A concept that says the brain recognizes distinct senses because action potentials travel along separate nerve tracts.

b. We have very distinct labeled lines, and each sensory receptor has its own pathway up to the brain.

Mechanoreceptors a. Tiny receptors all over the body, how the body senses touch. b. Sends signals to the brain about what kind of touch is being felt. Found on the end of some neurons. c. Called “mechano” because they detect mechanical sensations: differences in pressure.

Pacinian corpuscles a. Skin receptors that respond to vibration and pressure. b. Located deep in the skin, in the hypodermis layer. c. Since it's deeper, it needs stronger stimuli like a push or poke.

Maisner's corpuscles a. Perceives the form of objects that we touch. b. More sensitive, on the top layer of skin. c. Responsible for light touch, aware when you brush lightly against something or when you put on a light t-shirt. d. They need constantly changing stimuli to make you aware of sensations.

Merkel’s discs

a. More sensitive to touch, at the base of the epidermis but still near the top layer of skin.

b. Specialized skin cells, respond to indentations of the skin like poking.

c. Adapts slowly to pressure, record sustained pressure, aka stimuli that are present for longer.

Ruffini’s corpuscles a. Perceive stretching of the skin when we move. b. Near the bottom layer of the skin.

Free nerve endings

a. 2 different types, thermoreceptors and nociceptors.

b. Thermoreceptors have 2 different types for perceiving hot and cold.

c. Cold receptors kick in when the temp is under 95, most stimulated at 77 degrees and turn off once skin is under 41, this is why skin goes numb in extreme cold. d. Hot receptors perceive above 86 degrees, most stimulated at 113 degrees but beyond that pain receptors will take over in order for damage to be avoided to skin. When you’re sunburnt, pain receptors will communicate but thermoreceptors weren’t aware due to slow introduction to heat.

Receptive Fields

a. The receptive fields are the regions in which a stimulus will alter a sensory neuron's fighting rate.

b. The location of a stimulus is determined based on a map-like representation of the position of the activated receptors.

c. We stimulate a receptor and scan where the brain is fired up to see what's going on. d. In order to get specificity in a receptive field, outside of the field are inhibited and don't fire so that you know exactly where a stimulus was touching you. When you squeeze on a papercut, you’re confusing the receptors. When poking close spots together without looking, it feels like one poke; when they go farther apart, we notice them as two spots.

Sensory adaptation a. Stimulus intensity can be encoded by the number and threshold of activated cells. If there are a lot, you’re aware of them. b. With higher intensities, other sensory neurons are recruited. c. We can't perceive everything that we are sensing all the time. d. Adaptation is desensitization, the process by which receptors show a progressive decrease in sensitivity.

Phasic Receptors a. The stimuli are still there, but we stop firing because it is not important. b. Let us know when there are changes in sensory stimuli, gives us the ability to stop paying attention to constant stimuli like temperature or smells. c. Decreases the frequency of action potentials firing.

Tonic Receptors

a. Don't slow down or decline firing in the presence of continued stimulation.

b. Meissner and Pacinian corpuscles are phasic receptors; they respond immediately but stop responding unless there is a change in the stimulus.

c. Keeps constant the frequency of action potentials firing.

Accuracy

a. Sensory systems often shift away from accurate portrayals of reality in order to function; otherwise, you’re overloaded.

b. Noting changes can be more important than exactness.

c. Our perception is suppressed by removing the stimulus. Our brain tells us to close our eyes, plug our ears, take clothes off, anything to remove a stimulus.

Central modulation of sensory modulation a. When your brain is actively focusing on certain inputs and ignoring others. b. The cortex and the thalamus are involved in this. VI. Somatosensory System

Somatosensory system a. We have distinct pathways from sensory receptors that leads from the periphery to the central nervous system.

Dorsal column system

a. Responsible for delivering touch information.

b. Receptors send axons via the dorsal spinal cord to synapse onto neurons in the brainstem.

c. Once in the brainstem, they cross the midline and go to the thalamus.

Primary sensory cortex a. One primary sensory cortex exists for each modality

Nonprimary sensory cortex a. Receives direct projections from the primary sensory cortex for that modality.

Primary somatosensory cortex (S1)

a. In the postcentral gyrus.

b. On each hemisphere of the brain that processes touch information from the opposite side of the body.

c. S1 cells are arranged as a map of the body; a sensory homunculus.

d. We have receptors that help us perceive information, but one type is almost never activated alone; things work in tandem.

Sensory brain regions a. Highly plastic and change as a result of experience. They can influence each other. Changes can occur after weeks/months of no use.

Association areas a. Process a mixture of sensory inputs from different modalities. b. They hold polymodal neurons that hold different neurons and allows them to interact.