LECTURE 13 - SENSATION PART A

what region of the brain is responsible for processing information generated via general sensory receptors

general senses include: touch, temperature, pressure, vibration, stretch

do not require specialized sensory organs

information is sent to the somatic sensory cortex in the parietal lobe

what regions of the brain are responsible for processing information generated via each of the special sensory receptors

includes:

• hearing and balance —→ processed by the temporal lobe

• taste —→ processed by the gustatory association area

• smell/olfaction —→ process by the olfactory association area

• vision —→ processed by the visual cortex in the occipital lobe

what are the sensory systems comprised of?

comprised of:

• sensory receptors that detect external or internal stimuli

• afferent neurons carrying information to the CNS

• regions of the brain or spinal cord that process the information

what is sensation? how does sensation differ from perception?

sensation: occurs when the stimulus “reaches consciousness” (when we become aware of the stimulus)

perception: consists of the awareness of sensation and how the sensation is perceived (how you are going to perceive the stimulus)

know the general structure of receptor neurons.

• what types of “information” do they carry?

peripheral end of the neuron contains a receptor membrane that detects stimuli

• receptors in membrane allow for the depolarization of the neuron

  • if the threshold potential is reached then an action potential will be produced and will travel back toward the CNS

typically are somatic sensory neurons

• carry sensory information from skeletal muscle, skin, tendons, ligaments, and other joint structures

*they act as the receptor as well as the afferent neuron

know the general structure of receptor cells.

• where are receptor cells typically found?

separate cell acts as the sensory receptor

• contains receptors in membrane that detect the stimulus allowing for depolarization of the receptor cell

  • if the threshold potential is reached an action potential is produced and neurotransmitters are released from opposing side of the membrane

    • neurotransmitters bind to afferent neuron

afferent neurons are visceral sensory neurons

• cell receptors are typically found in viscera

how are we able to detect stimuli of varying strengths?

stronger stimuli result in an increase in action potential frequency

• note: action potentials are all or none

increased frequency of action potential —→ increase neurotransmitter released at the axon terminal

• increased neurotransmitter concentration at synapse in CNS

* higher frequency of action potentials means stronger stimulus. Lower frequency of action potentials means weaker stimulus.

how do tonic vs phasic receptors differ?

rapid/phasic receptors

-action potentials are produced at the onset of the stimulus and when changes occur to the intensity of the stimulus (or removal)

• ex. pressure receptors in the gluteal region

slow adapting/tonic receptors

-constant firing of action potential until the stimulus ends

• ex. hands when you are griping onto something

what is a receptive field?

area of the body that leads to activity in a particular afferent neuron when stimulated

• contains the peripheral ends of the receptors

(space in which it can detect stimulus)

in terms of sensation, what is a modality? be able to provide several examples.

modality: type of sensory stimulus

• ex: temperature, pressure, pain, sound, smell, etc.

sub-modality: includes the range of stimuli (ex: hot or cold)

how can the chances of a receptive field firing an action potential be increased?

multiple peripheral endings can be activated simultaneously or only one may be activated

• increased number of activated peripheral endings result in an increased chance of teaching threshold potential

how do narrow vs broad receptive fields differ? where would each be found? why?

NARROW RECEPTIVE FIELDS

• detect stimuli from only a small/narrow area —→ allow for more precise location detection of stimulus

• found in area where precise detection is necessary

  • ex. lips, face in general

BROAD RECEPTIVE FIELDS

• receptive fields that carry information from a larger/broader region

  • may be less precise

• found in areas where less precise detection occurs

  • ex: back, shoulders, etc.

what is localizaiton?

receptive field may overlap

• receptive field where stimulus primarily occurs will fire the highest frequency of action potentials allowing for more precise location detection

  • called localization

what is lateral inhibition?

afferent neurons can inhibit other afferent neurons that are carrying information from adjacent overlapping receptive fields

• allows for more precise detection of the location of the stimulus

how do localization and lateral inhibition allow us to detect a precise location of a stimulus?

LOCALIZATION

• receptive field may overlap

  • receptive field where stimulus primarily occurs will fire the highest frequency of action potentials allowing for more precise location detection

LATERAL INHIBITION

• afferent neurons can inhibit other afferent neurons that are carrying information from adjacent overlapping receptive fields

  • allows for more precise detection of the location of the stimulus

know the following information for Meisner corpuscles, Merkel corpuscles, free nerve endings, Pacinian corpuscles, and Ruffini corpuscles?

• are they slow or rapid adapting?

• what type of stimulus/modality is being detected?

• where are they found?

MEISNER CORPUSCLE

• rapid adapting (phasic) receptors

• found in dermal papilla

• responsible for detecting pressure (in skin)

MERKEL CORPUSCLE

• slow adapting (tonic) receptors

• found where the epidermis and the dermis meet

• responsible for detecting pressure and stretch

FREE NERVE ENDINGS

• slow adapting (tonic) receptors

• carry information from the epidermis

• responsible for thermo-reception, nociception (pain/itching), and pressure

PACINIAN CORPUSCLE

• rapid adapting (phasic) receptors

• located deep within the dermis

• detect vibrations

RUFFINI CORPUSCLE

• slow adapting (tonic) receptors

• found within the dermis

• responsible for detecting “stretch”

what are nociceptors? what types of stimulus do they detect?

detect extreme temperatures, mechanical deformation, and specific chemicals/molecules.

• (all stimuli perceived is painful) perception = pain

• different membrane receptors detect different stimuli

  • ex. different membrane receptors for temp, pressure (deformation like child birth), etc.

contain little to no myelination

• result is slow processing

what is decussation?

all somatic sensory information travels to the spinal cord, to the thalamus, and then to the somatic sensory cortex

different types of information decussates at different locations

-decussation: information crossing from right to left side and vise versa (so left side to right side) (locations can be like the hindbrain specifically medulla oblongata or spinal cord)