topic 10

Two categories of senses:

– Special senses—vision, hearing, taste, smell,

equilibrium

– Somatic senses—touch, temperature, pain,

itch, proprioception (proprioceptors)

Stimulus as physical energy →

sensory receptor

– Receptor acts as a transducer

Transduce (=change) environmental info into Apps that affect ion channels how?

Ion channels or second messengers initiate membrane

potential change

Intracellular signal →

usually change in membrane potential

Modality

Each receptor type responds to particular info

Different modalities are perceived differently because of CNS

pathways stimulated

differently because of CNS pathways stimulated

Sensory system directions

Stimulus →threshold → action potential to CNS

Integration in CNS →

cerebral cortex or acted on subconsciously

identify

Identify

Neural receptors can be

• Naked (“free”) nerves

▪ Complex neural receptors encased in connective

tissue capsules

Neural receptors sheath or no sheath

Can be myelinated or unmyelineated

Nonneural receptors for four special senses

– Olfaction

– Gustation

– Vision

– Hearing and Balance

Nonneural receptors for four special senses structures are

Highly specialized cells

– Associated with sensory neurons

Sensory Transduction Converts

Stimuli into Graded Potentials

Adequate stimulus:

Form of energy to which a receptor is most responsive

Receptor potential (graded potential)

Change in sensory receptor membrane potential

Threshold

Minimum stimulus

Receptors Respond to

to Particular Forms of Energy

Four major groups of receptors

Chemo, mechanical,thermo, and photo

Chemoreceptors respond to chemical ligands:

Taste and smell

Mechano receptors

Mechanical energy pressure and sound

Thermoreceptors

Temperature

Photoreceptors

Light

Sensory receptive field

Physical area where stimuli activates neuron

– Primary sensory neuron =

– Secondary sensory neuron =

• transduces stimulus

• typically in CNS

Sensory neuron receptive field frequently

Overlap and neighboring fields may converge

Receptive field size determines sensitivity with

Two-point discrimination test

Two-point discrimination test:

Smaller receptive field vs larger

▪ Smaller receptive fields = more sensitive areas

▪ Larger receptive fields = less sensitive areas

CNS integrates sensory information through

– Spinal cord to brain by ascending pathways

– Directly to brain stem via cranial nerves

No conscious perception (usually) of

• Stimulus level to be aware of sensation =

• Decreased perception through inhibitory modulation =

=Visceral reflexes

=Perceptual threshold

=Habituation

What distinguishes stimulus properties

Coding and processes

Sensory modality

– Which sensory neurons activated

-Where neurons terminate in brain

• Location of the stimulus

– Which receptive fields activated

– Lateral inhibition

Intensity of the stimulus

– Number of receptors activated

– Frequency coding

Duration of the stimulus

– Duration of action potentials

– Receptors adapt

Somatic senses receptors located in

Skin and viscera

Somatic Primary sensory neurons synapses

Synapse in CNS with secondary sensory neurons

Somatic Secondary sensory neurons

– Interneurons in CNS

– Synapse with tertiary sensory neurons in thalamus

Tertiary sensory neurons

– Project to Somatosensory cortex

Nociceltors initiate protective responses

Nociceptors- not found in cns

– Neurons with free nerve ending

– Found in:

▪ Skin

▪ Joints

▪ Muscles

▪ Bones

▪ Viscera

Nociceptors Initiate Protective Responses: Pain is

is subjective perception

Acute pain:

Sharp and localized pain transmitted rapidly by myelinated 𝐴𝛿 fibers

Chronic pain:

Duller, aching, and more diffuse pain transmitted more slowly by unmyelinated C fibers

Nociceptors initiate protective responses by responding to __ like __.

Respond to intense stimuli:

– Mechanical (e.g., pinching, cutting)

– Thermal (e.g., extreme heat or cold)

– Chemical (e.g., acids, capsaicin

Local chemicals mediate inflammatory response at site of injury through

histamine, prostaglandins, serotonin, substance P

Inflammatory pain

Increased sensitivity to pain at sites of injury

Ascending pathways to cortex

become conscious sensation

Chronic pain: Pathological (neuropathic) pain reflects

reflects damage to or long-term changes to nervous system

Nociceptors Referred pain are

Poorly localized pain perceptions from:

▪ Visceral pain

▪ Somatic pain

– Converge on single ascending tract

Olfactions

One of the oldest senses that allows us to discriminate among millions of different odors

Olfactory pathways

– Ascending pathways to amygdala and hypothalamus

▪ Link between smell, memory, and emotion

Olfactory epithelium

Embedded with olfactory sensory neurons (primary sensory neurons

Olfactory signal transduction

– Odorants bind to odorantmreceptors

5 sensations that make up taste

– Sweet, bitter, umami, sour, and salty tastes

Gustation is the

sense of taste that is closely linked to olfaction

Nontraditional taste sensations

– Specific hunger

– salt appetite

Hearing is

Perception of energy carried by sound waves

Hearing Signal transduction is a multistep

process

Sensory (receptor) cells are hair cells in the cochlea

Vision is

Light reflected from objects in the environment are translated into a mental image

3 steps of vision

1. Light enters the eye, and the lens focuses the light on the retina

2. Photoreceptors of the retina transduce light energy into an electrical signal

3. Neural pathways from retina to brain process electrical signals into visual images

Rods

function well in low light and are used in night vision

Cones

are responsible for high-acuity vision and color vision during the daytime