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Flashcards in 2.5 Sensory systems Deck (74):
1

Sensory homonculus

What the male body would look like if each part grew in proportion to the area of the cerebral cortex of the brain concerned with its sensory perception

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Frontal lobe

Anterior half of cortex, motor functions

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Parietal lobe

Posterior half of cortex, sensory functions

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Stimulus

Change in the external or internal environment that causes a reaction-specifically potentials- in peripheral NS receptors

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Examples of stimuli

Light, sound, touch, chemical odor, chemical taste

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Sensation (Perception)

Conscious awareness, in the cerebral cortex, of stimuli received by peripheral sensory receptors

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1st step of afferent sensory circuit

Stimulation and transduction (peripheral sensory receptor neuron transforms stimulus into electrical signals--> graded potentials)

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2nd step of afferent sensory circuit

Generation of action potentials in the 1st order sensory neuron (may be separate cell from sensory receptor)
-Triggers at threshold stimulus level

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AP frequency dictated by...

Strength of stimulus and graded potentials

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Sensation

APs transmission to the thalamus, then to cerebral cortex where selective attention yields conscious perception of a stimulus

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What is the thalamus' role in sensation

Filters "noise," decides whether or not it's worth it to perceive incoming information

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Types of peripheral sensory receptors

Exteroreceptors
Interoreceptors
Propioreceptors

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Exteroreceptors

Monitor external environment; associated with skin (somatic sensory receptors) or special sense organs of the head

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Interoreceptors

AKA visceral sensory receptors
Monitor internal environment
Associated with internal organs and tissues (ex: blood vessels, visceral organs)

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3 types of interoreceptors

Chemoreceptors
Thermoreceptors
Stretch receptors

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Propioceptors

Monitor body position and movements, muscle length / tension, joint positions
Associated with joints, tendons , muscles and vestibular organ

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Receptors classified by modes of stimuli

Chemoreceptors
Thermoreceptors
Mechanoreceptors
Photoreceptors
Baroreceptors
Nociceptors

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Chemoreceptors

Detect chemicals detected in fluid-liquid or airborne
Ex: blood gases, salts, scents in the air, flavors in foods)

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Thermoreceptors

Respond to changes in temperature

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Mechanoreceptors

Respond to touch, external pressure, vibration and stretch (mostly skin but also gut and bladder)

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Photoreceptors

Respond to photons (light)

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Baroreceptors

Sense pressure by 'reading' deformation of a body structure
Ex: blood vessel stretch for blood pressure regulation

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Nociceptors

React to painful, noxious stimuli, can be both extero and intero (but fewer intero)

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Stimulation of a sensory receptor causes...

A local dendritic depolarization

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Transduction

Transforming physical or chemical stimulus into electrical signal

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Generator potential

The first order neuron itself has has the graded potential and will itself fire the the action potential towards the central nervous system

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What do generator potentials apply to?

Common, applies to all tactile (mechano) receptors in the skin and visceral organs

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Receptor potentials

A dedicated receptor experiences a graded potential response that varies with stimulus intensity--> Stimulates action potentials in adjacent first order neuron

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What are receptor potentials used by?

Relatively rare, used by gustatory and photoreceptors

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Tactile (touch) receptors

Where generator potentials can start
Often "free nerve endings" (i.e. dendrites) that transduce mechanical stimuli

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What do deep pressure receptors sense?

Vibration

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What do slowly adapting touch receptors sense?

Rough?

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Skin averages ~ ___ tactile receptors/ square inch

400

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Where are afferent tactile signals processed / perceived?

Primary somatic sensory cortex

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Small receptive fields

Surface area of skin occupied by a single receptor

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Small receptive fields

Has many MORE neurons in the primary cortex
(surface area of skin occupied by a single receptor)
-appears larger on "map"
ex: fingers

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Large receptive fields

Represented by fewer neurons in the cortex, appear smaller
ex: trunk

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Smaller receptive fields allow for what?

Very fine spatial resolution of sensations.. impacts two-point discrimination

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If receptors are numerous and close together, leads to

Small receptor fields

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For generator potentials in a tactile receptor, transduction leads to this type of membrane potential in the dendrite of the first order sensory neuron

Graded potential
THERE ARE NOT ACTION POTENTIALS IN DENDRITES

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What are nociceptors stimulated by?

Thermal, mechanical or noxious (potentially damaging) stimuli

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Chemical stimuli of nociceptors

Injuries locally release prostaglandins and other substances that stimulate nociceptors

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Mechanical stimuli of nociceptors

Severe distention (gut, joints), skeletal muscle spasms or a "charlie horse"

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What do the stimuli of nociceptors initiate?

Generator potentials in free nerve endings in skin and visceral organs

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What happens after there is a generator potential in nociceptors?

AP delivered to peripheral NS nerves, ultimately to CNS tracts in DORSAL HORN and GANGLION of the spinal cord

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The more painful the stimulus...

The faster the action potentials fire from nociceptors

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What do nociceptors express that facilitate Ca2+ release at their presynaptic junctions?

μ-opioid receptors

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Ca2+ release in nociceptors (presynaptic junction) is essential for...

Substance P neurotransmitter release

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What does morphine do in pre-synaptic neuron?

It blocks the Ca2+ release in nociceptors in presynaptic junction which stops AP propogation

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POSTsynaptic sensory neurons in the dorsal horn also express...

μ-opioid receptors

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What do μ-opioid receptors normally do in the post-synaptic sensory neurons?

Depolarize the cell..

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What does morphine do in the post-synaptic neuron?

Blocks the μ-opioid receptors and hyper polarizes the post-synaptic dendrite

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What natural substance can work in a similar fashion to morphine?

Endogenous endorphins
(enkephalins and dynorphins)

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Propioreceptors provide information about...

-The position and rate of movement of body parts
-The weight of held objects (golgi tendon organs)
-The range of movement of a joint

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Propioreceptors are located in

-Deep skin, joints and muscles (muscle spindles and Golgi tendon organs)
-Vestibular organ (ears)

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Where is propioreceptive info typically processed?

-First in the cerebellum (balance, coordination)
-Ultimately perceived as your body sense in the cerebral cortex

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Propioreceptors are (tonic / phasic)

Tonic
Never fatigue

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Nociceptors are (tonic / phasic)

Phasic
Fatigue

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Trigenimothalamic tract

Conveys pain, tickle itch and temperature from face to contralateral cortex (neck up)

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The Trigenimothalamic is a _____ neuron system

3

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Trigenimothalamic tract: primary

Trigeminal (fifth) nerve from face, nose, mouth to brainstem

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Trigenimothalamic tract: secondary

Crosses to opposite side (decussates) in brainstem, enters trigenimothalamic tract, ascends to thalamus

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Trigenimothalamic tract: tertiary

Thalamus to somatosensory cortex

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Spinothalamic tract

Conveys pain, tickle, itch and temperature (from body to contralateral cortex)
Neck down

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The spinothalamic tract is a ____ neuron system

3

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Spinothalamic tract: primary (1st order)

From body periphery to posterior (dorsal) horn of spinal cord

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Spinothalamic tract: secondary (2nd order)

Crosses to opposite side (decussates) in spinal cord, enters spinothalamic tract, ascends to thalamus

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Spinothalamic tract: tertiary (3rd order)

Thalamus to somatosensory cortex

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Spinocerebellar system

-Carries tonic propioreceptive information to cerebellum (unconscious)
-Coordinates movement of major motor units (cerebrum) effecting major muscle groups

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The spinocerebellar is a ____ neuron pathway

2

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Spinocerebellar system: steps

-Primary neuron to spinal cord
-Secondary neuron to ipsilateral cerebellum

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Does the spinocerebellar system decussate?

NO

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: The vestibular organs in your inner ear contain numerous ___________ that communicate information about body position & balance to the
___________

Proprioceptors / cerebellum

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Where are tactile inputs processed?

Primary somatic sensory cortex