Sensory receptors

Are nociceptors phasic or tonic?

Tonic

Duration

How long the stimulus lasts.

slow pain

c-delta fibers are associated with slow pain and are unmyelinated. They carry non-localized sensations more slowly to the CNS and typically result in more diffuse sensations of pain.

phasic

fast adapting receptors; respond strongly at the start and at the end. Only send signals when the stimulus changes. Ex. Chemoreceptors.

Photoreceptors...

Respond to light energy

What is population coding?

When multiple receptors function together to send the CNS more information than would be possible from a single receptor.

What are the locations of the receptors?

found in the viscera and skin throughout the body. Always simple receptors.

sensory receptors

specialized cells that detect stimulus information and transmit it to sensory (afferent) nerves and the brain. Carries information towards the CNS.

What are the characteristics of a stimulus receptor?

1) All sensory receptors detect a stimulus. 2) All sensory receptors are associated with a sensory neuron that takes information about the stimulus towards the CNS. 3) Most sensory receptors will work to depolarize and produce action potential in their associated sensory neurons. 4) Sensory receptors respond best to one particular stimulus.

How is information about intensity coded for in the sensory system?

By changing the frequency of the action potential.

Fast pain.... A) Utilizes C-fibers to send messages to the CNS. B) Utilizes A-delta fibers to send messages fro the thalamus to the cerebrum. C) Travels along myelinated axons. D) Travels along unmyelinated axons.

C) Travels along myelinated axons.

Thermoreceptors

Phasic free nerve endings in the dermis, muscles, liver, and hypothalamus that respond to heat and cold.

What is lateral inhibition?

When a stimulus is in the center of one receptive field, all receptors with overlapping fields will be inhibited. This can help pinpoint the stimulus with greater accuracy.

How do muscle spindle fibers work?

When the muscle fibers stretch, the muscle spindles will increase their firing rate. When the muscle contracts, it will decrease their firing rate.

exteroreceptors

detect external stimuli: touch, pressure, pain, and temperature.

interoreceptors

detect internal stimuli: Changes in chemical concentrations, chemical stimuli, stretching of tissues, and temperature of internal organs.

simple receptors

general senses, and may be unencapsulated or encapsulated dendritic endings

Chemoreceptors

respond to chemicals

general senses

temperature, pain, touch, pressure, vibration, proprioception, chemoreceptors, and nociceptors.

Photoreceptors

respond to light

Phasic receptors....

Respond strongly to a stimulus when it changes.

complex receptors

special sense organs (vision, hearing, equilibrium, smell, taste). These include specialized receptor cells that send chemicals to a sensory neuron.

tactile receptors

touch, pressure, vibration

Pain detection... A) is accomplished by A-delta fibers and C-delta fibers. B) Is called proprioception C) Involves release of substance P at the site of damage. D) Includes only the brainstem to integrate information in the CNS.

A) Is accomplished by A-delta and C-fibers.

fast pain

A-delta fibers are associated with fast pain and are myelinated. They carry very localized, intense sensations quickly to the CNS.

Which of the following is NOT true of the general senses? A) Most first order neurons originate in the periphery of the body and synapse in the spinal cord. B) The general senses include primarily complex receptors. C) Proprioception tells the brain how the body is positioned in space. D) The general senses include touch, pain and proprioception.

B) The general senses include primarily complex receptors.

What is a sensory homunculus?

Body map for the general senses that is based on the density of the somatic receptors.

What are receptor potentials?

Complex receptors; no action potential is formed; depolarization will signal a release of neurotransmitter that will bind to the sensory neuron.

Which of the following is not true of sensory receptors? A) Some receptors respond to a stimulus as long it is present. B) Sensory receptors can be classified by the stimulus type they respond to. C) Some sensory receptors respond to change in the internal environments. D) Each sensory receptor can only respond to one type or stimulus.

D) Each sensory receptor can only respond to one type of stimulus.

What is a primary neuron?

Dendrites are receiving messages and generating an action potential in that neuron. It synapses in the brain stem or spinal cord.

free nerve endings

Naked dendrites of sensory neurons that are located throughout the epithelium and associated connective tissue. Ex: Hair follicle receptors, thermoreceptors, nociceptors, chemoreceptors, and some mechanoreceptors.

Mechanoreceptors

Phasic or tonic; respond to touch, pressure, vibration, stretch, and itch

Golgi tendon organs

Receptors sensitive to change in tension of the muscle and the rate of that change. They will increase their firing rate when the tendon is stretched and decrease when it contracts.

What are generator potentials?

Simple receptors; usually depolarizations which generate action potentials.

muscle spindles

Specialized muscle cells located inside skeletal muscle near joints.

What is a tertiary neuron?

Takes information from the thalamus out to the primary somatic sensory cortex and from there it is sent to other parts of the cerebrum.

What is a secondary neuron?

Takes information to the thalamus. It crosses the midbrain and results in contralateral projection.

contralateral projection

The left hemisphere is sensing things on the right and vice versa.

Nociceptors

Tonic; Respond to pain.

What are intrafusal fibers?

Tonic; They send messages regarding muscle stretch and contraction. Typically run parallel to contractile muscle fibers.

Proprioceptors

Tonic; monitor the position and movement of skeletal muscles and joints. Monitor the degree of stretch and movement at joints to inform the CNS about body's position in space.

What is convergence?

When two or more neurons synapse onto an interneuron. If a message is coming into the brain, there's no way to know which sensory neuron is sending the signal. We end up with a less localized accuracy.

Tonic

Very slow to adapt to a stimulus and will continue to respond to the stimulus as long as it is present. Ex: nociceptors.

Transduction

When a sensory receptor converts energy from one form into another form.

receptive field

an area of space that each receptor monitors. Many times they overlap.

encapsulated nerve endings

dendrites enclosed in connective tissue capsule for pressure, vibration, and some touch sensations. Ex: Tactile corpuscles, Lamellated corpuscles, proprioceptors.

Baroreceptors

detect changes in blood pressure