Physio Module 3.1 Sensory Systems

1. sensory receptors

2. neural pathways that conduct afferent information

3. parts of the brain that process information

What 3 parts does the sensory system consist of?

Photorecepters

in eye; detect light

Mechanoreceptors

in skin, joints, muscle, inner ear, etc; detect mechanical deformation such as touch or sound

thermoreceptors

detect temperature changes

chemoreceptors

detect chemicals in the internal or external environments

Nociceptors

Free axon terminals of small-diameter afterent neurons that detects painful stimuli

receptor potentials; graded

Sensory receptors transform the stimuli into ____________ which are _____________.

Graded; all-or-none

Receptor potentials are _________; action potentials are __________.

Has specialized nerve endings directly on primary afferent neurons

What is a “smell” sensory receptor arrangement like?

It has specialized receptor cells that associate with primary afferent neurons

What is a “taste” sensory receptor arrangment like?

Both

Is a receptor potential depolarizing or hyperpolarizing?

Receptor-mediated transduction

Involves the opening or closing of specific ion channels in specialized receptor membranes that results in changes in ionic current(s) moving across the membrane

Ion fluxes

Produces the receptor potential

passively

the receptor potential is propagated __________ towards the neuron’s trigger zone

Frequency

Larger receptor potentials increase action potential firing _____________.

Primary afferent neuron firing frequency

What reflects the magnitude of receptor potential, which generally reflects the magnitude of the stimulus?

1. stimulus strength

2. summation

3. receptor adaptation

What are 3 factors that affect receptor potential magnitude?

Summation

Increased stimulation activates more branches, leading to increased receptor potential and AP frequency.

Rapid adaptation

Relates to changes in AP frequency as a function of the rate of change in stimulus application/intensity

Slow adaptation

Refers to a decrease in AP frequency despite lack if change in stimulus strength

Coding

the conversion of stimuli into the Action Potentials in the CNS and the AP frequencies

Modalities (submodalities)

Ex. Temperature, sound, pressure, light, pain, taste, etc. (cold, warm, salty, sweet, etc.)

Sensory unit

A single afferent neuron with all its receptor endings or associated specialized receptor cells.

Receptive field

The area of the body where stimulation leads to activity in that afferent neuron. (Area monitored by that afferent neuron)

Localized

Stimuli can be __________.

Sensory acuity

Receptor field size, density, and pathway convergence are important factors for what?

Lateral Inhibition

neural mechanism in which an excited neuron reduces the activity of its neighboring neurons, enhancing contrast and sharpening sensory perception.

Modification

All sensory signals are subject to extensive ____________ at the various synapses along the sensory pathways before they reach higher levels of the CNS.

Specific pathways

Transmit information about a single particular sensory modality

Nonspecific pathways (polymodal)

receive input from primary afferents that detect more than one modalities

Localization

Receptive fields determine ___________.

Lateral inhibition

What improves sensory precision?

Perception

What is an active brain process?

Touch and pressure, temperature, pain, senses of posture and movement

What are types of somatic sensation are there?

skin, hair follicles, underlying tissues, skeletal muscles, bones, tendons, joints, organs of thoracic and abdominal cavities

What are locations of the receptors of the somatic sensation

Stretch-activated or Stretch-gated ion channels

open their pores in response to mechanical deformation (touch/pressure) of the plasma membrane

Meissner’s corpuscle

rapidly adapting mechanoreceptor, touch and pressure

Merkel’s corpuscle

slowly adapting mechanoreceptor, touch and pressure

Free neuron ending

slowly adapting, small-diameter, with little or no myelination, including nociceptors, thermoreceptors, and mechanoreceptors

Pacinian corpuscles

Rapidly adapting mechanoreceptor, vibration, and deep pressure

Ruffini corpuscle

slowly adapting mechanoreceptor, detects skin stretch

Muscle-spindle stretch receptors

mechanoreceptors in skeletal muscles responding both to the absolute magnitude of muscle stretch and to the rate at which the stretch occurs

Golgi tendon organs

in the fibrous tendons that connect muscles to bone, monitoring muscle tension, posture, and movement

Thermoreceptors

Specialized nerve cells that detect temperature differences. They are small neurons with free nerve endings

NO!

Does higher temperature correlate to higher action potential frequencies?

Transient receptor potential channels (TRP)

Open at various overlapping temperature ranges, and some can be opened by chemical ligands. MOLECULAR SENSORS FOR TEMPERATURE

Polymodal neuron

a type of sensory neuron that can respond to or integrate information from multiple distinct sensory modalities

closer; more sensitive

Heat receptors are ________ to the skin’s surface thus _____________ than cold receptors

1. intense mechanical deformation

2. extremes of temperature

3. many chemicals (released from damaged cells and immune system)

What are nociceptors activated by?

More sensitive

More receptors = _____________

Substance P, or glutamate

Painful stimulation releases what from afferent fibers in the dorsal horn of the spinal cord?

Endogenous opiate neurotransmitters (opiods)

Released by dorsal horn interneuron stimulation from descending inputs from the brainstem

Presynaptic and postsynaptic opiate receptors

Opioid modulations (inhibition) occurs through ____________.

Analgesia

Ex. administration of morphine and other opioids, or stimulation of opiate transmitter release

Analgesia

The selective suppression of pain without effects on consciousness or other sensations

inhibiting synaptic transmission in ascending pain pathways

How do opioids produce analgesia?

Dopamine; euphoria, addictive

Opioids stimulate __________ release, produce __________, and thus are highly _________.

It is thought to activate afferent neurons leading to the release of endogenous opioids in the descending pathways, resulting in pain relief

Why does acupuncture relieve pain?

Prostaglandins

Promotes inflammation, fever, and pain sensation

Acetaminophen, ibuprofen, and aspirin

These drugs can inhibit the synnthesis of prostaglandins…

Referred pain

The sensation of pain experienced at a site other than the injured or diseased tissue

1. increased/decreased sensitivity

2. past experiences

3. placebo effect

The level of pain felt can be altered by what?

The anterolateral system

a collection of ascending spinal pathways that transmit pain, temperature, and crude touch sensations from the body to the brain

The dorsal column system

is a major sensory pathway of the central nervous system that transmits fine touch, vibration, and proprioceptive information from the body to the brain.