Chapter 6 Peripheral Nervous system: Afferent Flashcards by Emily Twomey

Sensory Input

Can be external or internal

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External stimuli

Light, touch, taste, sound, etc

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Internal stimuli

Proprioception, detection of O2 content of blood, detection of changes in solute concentration in ECF

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Sensory transduction

The process of transforming stimulus energy into an electrical signal in peripheral sensory receptors

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Receptor Potential

Activation by stimulus causes a graded potential

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Sensory Receptors

-found at the peripheral ends of afferent neurons
-if receptor potential large enough, triggers an action potential to travel towards CNS

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6 types of sensory receptors

Photoreceptors, mechanoreceptors, thermoreceptors, osmoreceptors, chemoreceptors, nociceptors

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Photoreceptors

Visible light

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Mechanoreceptors

Mechanical energy such as stretch or pressure

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Thermoreceptors

Heat or cold

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Osmoreceptors

Changes in ECF solute concentration and resultant change in osmotic activity

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Chemoreceptors

Specific chemicals, such as odorants, tastants, O2 or CO2 concentration, or digestive chemicals

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Nociceptors

Tissue damage, such as cutting or burning

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How does sensory transduction happen

Stimulus either directly or indirectly leads to opening of cation channels

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Cation channels

Positive ions
Channels that allow passing of sodium or potassium

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Receptor Potential

A stimulus causes the opening of a cation channel and sodium floods in and depolarizes the membrane

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2 versions of sensory receptors

Receptor as part of the afferent neuron
Receptor separate from the afferent neuron

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Why are afferent neurons unique?

Action potential initiated adjacent to sensory receptor, not at axon hillock
Cell body hangs off side of axon

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Property of sensory receptors

Strength of the stimulus ultimately encoded in the rate of action potentials of the afferent neuron

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T/F action potentials always have the same amplitude

True

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Action potentials are always of a ___ magnitude (all or none)

Fixed

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Tactile sensation is transduced by

Mechanoreceptors

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Receptive Field

The sensory receptor surface area that activates one afferent

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Somatosensory

Tactile sensation

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Acuity

The ability to discriminate between two stimuli

Smaller receptive fields have greater or lesser acuity

Greater

Larger receptive fields have greater or lesser acuity

Lesser

Pain

A protective mechanism that indicates tissue damage about to occur or has occured

What are painful stimuli transduced by?

Nociceptors

3 types of nociceptors

Mechanical Thermal Polymodal

Mechanical Nociceptors

Respond to intense mechanical stimulation (ex. Cutting, crushing, pinching)

Thermal nociceptors

Respond to intense heat or cold

Polymodal Nociceptors

Respond to chemicals released from injured tissue -> therefore respond to all damaging stimuli

How is bradykinin activated

By damaged cells that release enzymes to activate it

What does bradykinin activate?

Polymodal nociceptors

T/F Axons of mechanical and thermal nociceptors are small and not myelinated

False

Equilibrium

sense of body orientation and motion

three parts of the vestibular apparatus

Semicircular Canal Utricle Saccule

Semicircular Canal

detection of rotation of the head (all 3 planes)

Utricle

Detects horizontal linear acceleration

Saccule

Detects vertical linear acceleration

Gustation

taste

Tastants

Taste stimuli

Tastants are transducer by

Chemoreceptors (taste receptor cells)

Taste receptor cells cluster into ___

Taste buds

Microvilli extend up into an opening called

Taste pore

5 Primary tastes

Salty, Sour, Sweet, Bitter, Umami

Olfaction

Smell

T/F axons of Polymodal nociceptors are small and unmyelinated making them slower

True

Perception of pain for a fast pain pathway

Sharp and localized

Perception of pain from a slow pain pathway

Dull and long lasting

What do inhibitory interneurons in the spinal cord release?

Enkephalin- an opioid produced by the body that acts as a neurotransmitter

What activates the inhibitory interneuron?

Neurons in the brain to silence the pain signal

Analgesics- pain killers

Opioids produced outside of the body can activate the opioid receptors

The retina contains what

Photoreceptors

The iris contains what 2 muscles

Sphincter muscle and radial muscle

Is constriction of the eye sympathetic or parasympathetic? What muscle is used?

Parasympathetic Sphincter muscle

Is dilation of the eye sympathetic or parasympathetic? What muscle is used?

Sympathetic Radial muscle

Refraction

The path of light bends when passing from one medium to another

What do convex surfaces do to light?

The converged light rays from one point in visual field into a focal point

What does the cornea do?

The cornea helps your eye to focus light so you can see clearly.

What is the pathway of electrical activity through cell types in the retina?

Photoreceptor-> Bipolar cell -> Ganglion cell -> brain

Accommodation

the ability to adjust the strength (roundness) of the lens in order to focus light sources on the retina

Rods

for night vision

Cones

for daytime vision and color vision

Do photoreceptors have more synaptic activity in the dark or in the light?

In the dark

What are the steps of the phototransduction 2nd messenger signal cascade?

1. Retinal absorbs photon of light and activates the opsin 2. Opsin activates the G-protein transduction 3. Transduction activates effector protein phosphodiesterase, which degrades 2nd messenger cGMP in the intracellular fluid 4. Less cGMP which leads to less activation of cGMP- gated channels 5. less influx of Na+-> hyper polarization of photoreceptor 6. Less synaptic transmission

What is sound?

a wave of altering high and low air pressure

Sound pathway

air pressure wave rattles the tympanic membrane moving the ossicles which pushes back and forth into a fluid-filled cochlea into the oval window. The fluid moves all throughout the cochlea and out of the round window.

What is the purpose of the tympanic membrane and ossicles?

They act to increase force on the oval window

Cochlear duct

separates top and bottom fluid filled compartments in the cochlea and is flexible.

What is important about the tip links that connect stereocilia?

tension in tip leads to opening of mechanotransduction channel