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Chapter 15. Neural Integration I: Sensory Pathways and the Somatic Nervous System. fig. 15-1. Sensory. Motor. General (15). Somatic (15). Special (17). Autonomic (16). Special senses. smell sight taste hearing. special “sense” organs. General senses. temperature pain touch

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Chapter 15

Neural Integration I:

Sensory Pathways and the Somatic Nervous System



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Sensory

Motor

General (15)

Somatic (15)

Special (17)

Autonomic (16)


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Special senses

smell

sight

taste

hearing

special “sense”

organs

General senses

temperature

pain

touch

pressure

vibration

proprioception

most associated with the skin


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General senses

receptors distributed throughout the body

relatively simple


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General senses

  • receptors send info to CNS

    • arriving info is calledsensation

    • our awareness of it isperception


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Sensory receptors

interface between environment

and the

body

translate stimulus into an AP

transduction


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Sensory receptors

receptors have selective sensivity

chemical

physical touch

light

heat transfer

receptors may or may not have accessory structures associated with them


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Sensory receptors

receptive field

area monitored by a receptor

size of receptive field

70 mm

1 mm

specificity

fig. 15-2


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Sensory receptors

stimulus

receptor

  • stimulus changes

  • membrane potential

    • receptor potential

(+ or -)

greater stimulus means larger receptor potential

if stimulus is large enough to get to threshold is is called generator potential ( generates an AP)

transduction


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Sensory receptors

stimulus

receptor

action potential

CNS

for processing and

interpretation

(cortical areas)


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receptor B

receptor 2

receptor A

labeled line

cortex


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a “line” carries the same “type” (modality) of information

interpretation is based on which “line” information travels on


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receptor B information

receptor 2

receptor A

labeled line

optic nerve

cortex

shut eyes and rub them gently


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When CNS receives info… information

which “line” type of stimulus

where “line” ends perception

all other attributes (strength, duration, variation) are determined by the frequency and pattern of AP’s


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receptor types: information

tonic: always “on”

phasic: only on with stimulus

some receptors combine the two

greater stimulus higher freq.

lesser stimulus lower freq.


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adaptation information

reduction in sensitivity in the presence of a constant stimulus

peripheral

central

change in receptor activity

inhibition of nuclei in pathway


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peripheral adaptation information

phasic receptors

(aka fast-adapting receptors)

example: thermoreceptors

you usually don’t notice room

temperature unless it changes


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central adaptation information

example: smell

you walk into a room and notice a new smell…

…but not for long


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adaptation reduces the amount of information reaching the cerebral cortex

about 1% of sensory information coming in reaches our awareness


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100 Keys (pg 498) cerebral cortex

“Stimulation of a receptor produces action potentials along the axon of a sensory neuron. The frequency or pattern of action potentials contains information about the strength, duration, and variation of the stimulus. Your perception of the nature of that stimulus depends on the path it takes inside the CNS.”


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General senses cerebral cortex(from chapter 12)

exteroceptors

proprioceptors

interoceptors

outside

position

inside


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General senses cerebral cortex

  • classification

    • based on nature of stimulus

pain

heat flow

physical distortion

chemical concentration

nociceptors

thermoreceptors

mechanoreceptors

chemoreceptors


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General senses cerebral cortex

nociceptors

  • common in:

    • skin

    • joint capsules

    • coverings of bones

    • around blood vessel walls

free nerve endings

large receptive fields


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nociceptors cerebral cortex

  • sensitive to:

    • extreme temperature

    • mechanical damage

    • dissolved chemicals

      • (like those release by damaged cells)

stimulation causes depolarization


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nociceptors cerebral cortex

  • two fiber types convey info

    • type A

      • fast pain (cut, etc.,)

      • easy to localize

    • type C

      • slow pain (“burning, aching”)

      • difficult to localize


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nociceptors cerebral cortex

tonic receptors

no significant peripheral adaptation

as long as the stimulus is present, it will hurt

but central adaptation can occur

(perception of pain may decrease)


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nociceptors cerebral cortex

sensory neurons bringing in pain info use glutamate and/or substance P as their neurotransmitter

these nts can cause facilitation (?)

pain may be disproportional

(feels worse than it should)

pain can be reduced by endorphins and enkephalins (inhibit activity in pathway) [neuromodulators chpt. 12]


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nociceptors cerebral cortex

endorphins

pain centers use substance P

as nt.

endorphins bind to presynaptic membrane and inhibit substance P release, reducing perception of pain


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to here 3/9 cerebral cortex

lec # 24


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thermoreceptors cerebral cortex

free nerve endings in the dermis

skeletal m.

hypothalamus

liver

warm receptors

or

cold receptors


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thermoreceptors cerebral cortex

  • phasic receptors

    • active when temperature is changing, quickly adapting to stable temperature

  • detect transfer of heat

    • heat loss from skin cool

    • heat gain to skin warm


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mechanoreceptors cerebral cortex

contain mechanically regulated ion channels (chapter 12)


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c. mechanically regulated channels cerebral cortex

closed

mechanical

stimulus-

opens

remove

stimulus-

closed

fig. 12-10c


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mechanoreceptors cerebral cortex

three classes

tactile receptors

baroreceptors

proprioceptors

touch, pressure, vibration

pressure changes

(gut, genitourinary)

position of joints/muscles


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mechanoreceptors cerebral cortex

tactile receptors

fine touch/pressure

crude touch/pressure

small (narrow) receptive field

detailed information

sensitive

wide receptive field

poor localization


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fig. 15-3 cerebral cortex


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tactile receptors cerebral cortex

range of complexity

free nerve endings

root hair plexus

tactile discs

tactile corpuscles (Meissner’s)

lamellated corpuscles (pacinian)

Ruffini corpuscles


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tactile receptors cerebral cortex

free nerve endings

in epidermis of skin

cornea of eye

sensitive to touch and pressure

tonic receptors

small receptive field


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tactile receptors cerebral cortex

root hair plexus

around each hair follicle

sense movement of hair

adapt quickly


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tactile receptors cerebral cortex

tactile discs

  • sensitive, tonic receptors

    • in epidermis

  • fine touch and pressure


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    tactile receptors cerebral cortex

    tactile corpuscles (Meissner’s)

    fine touch, pressure , vibration

    adapt quickly

    surrounded by Schwann cells

    in dermis of skin

    eyelids, fingertips (sensitive areas)


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    tactile receptors cerebral cortex

    lamellated corpuscles (pacinian)

    • sensitive to deep pressure

      • high-frequency vibrations

    • adapt quickly

    • nerve ending is encapsulated

    • by layers of supporting cells

      • (onion)

      • dermis, pancreas, fingers…


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    tactile receptors cerebral cortex

    Ruffini corpuscles

    pressure and skin distortion

    located deep in the dermis

    tonic, little if any adaptation


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    fig. 15-3 cerebral cortex


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    sensivitity can be altered cerebral cortex

    infection

    disease

    damage to pathway

    e.g., damage to a spinal nerve

    would affect an entire dermatome


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    tickle and itch cerebral cortex

    closely related to touch and pain


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    baroreceptors cerebral cortex

    • free nerve endings in the walls of organs that stretch

      • e.g., blood vessels

    when pressure changes they expand or contract

    changes activity of receptors


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    proprioceptors cerebral cortex

    muscle spindles

    Golgi tendon organs

    receptors in joint capsules

    stretch reflex

    monitor tendon tension

    free nerve endings in joints


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    proprioceptors cerebral cortex

    no adaptation

    continuously send info to CNS

    most processed at subconscious level


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    chemoreceptors cerebral cortex

    respond to chemicals dissolved in the surrounding fluids

    • respiratory centers in brain

      • pH, CO2 levels in blood

  • carotid bodies and aortic bodies

    • pH, CO2, O2 levels in blood


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    Pathways in the CNS cerebral cortex

    spinothalamic tract

    spine to thalamus

    =sensory

    corticospinal tract

    cortex to spine

    =motor


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    Pathways in the CNS cerebral cortex

    sensory pathways

    neurons involved

    first order neuron

    second order neuron

    third order neuron

    sensory neuron (DRG)

    in CNS (crosses over)

    in thalamus


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    Pathways in the CNS cerebral cortex

    sensory pathways

    Somatic sensory pathways

    carry sensory info

    from skin and muscles of

    body wall, head, neck, limbs


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    Pathways in the CNS cerebral cortex

    sensory pathways

    Somatic sensory pathways

    posterior column pathway

    anterolateral column pathway

    spinocerebellar pathway


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    fig. 15-4 cerebral cortex


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    The Posterior Column Pathway cerebral cortex

    fine touch

    pressure

    vibrations

    proprioception


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    The Posterior Column Pathway cerebral cortex

    • inferior half of body

      • first order neuron in DRG

        • up the fasciculus gracilis to the

          • nucleus gracilis of med. oblong.

    • superior half of body

      • first order neuron in DRG

        • up the fasciculus cuneatus to the

          • nucleus cuneatus of med. oblong.


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    The Posterior Column Pathway cerebral cortex

    • second order neuron in nucleus ?

      • cross to other side and ascend to

        • the ventral nucleus of thalamus

    • third order neuron in thalamus

      • project to the primary sensory cortex


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    fig. 15-4 cerebral cortex

    fig. 15-5a


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    The Anterolateral Pathway cerebral cortex

    “crude” touch

    pressure

    pain

    temperature


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    The Anterolateral Pathway cerebral cortex

    • first order neuron in DRG

      • synapses on 2nd order neuron

        • in dorsal horn of spinal cord

    • second order neuron

      • cross to opposite side and ascend


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    The Anterolateral Pathway cerebral cortex

    • second order neuron

      • cross to opposite side and ascend

    anterior spinothalamictract

    lateral spinothalamic tract

    crude touch and pressure

    to ventral nucleus of thalamus

    pain and temperature

    to ventral nucleus of thalamus


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    The Anterolateral Pathway cerebral cortex

    • second order neuron in spinal cord

      • cross to other side and ascend to

        • the ventral nucleus of thalamus

    • third order neuron in ventral thalamus

      • project to the primary sensory cortex


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    fig. 15-4 cerebral cortex

    fig. 15-5b


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    The Anterolateral Pathway cerebral cortex

    phantom pain ?

    activity along pathway, even if “limb” is not there

    referred pain?

    viceral pains sensations may stimulate neurons of AL pathway


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    fig. 15-6 cerebral cortex


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    The Spinocerebellar Pathway cerebral cortex

    posterior s.c. tracts

    axons from same side to cerebellum

    anterior s.c. tracts

    axons cross over and

    ascend to cerebellum

    information goes to Purkinjie cells

    in the cerebellum (proprioception)


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    fig. 15-4 cerebral cortex

    fig. 15-7


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    100 Keys cerebral cortex(pg. 507)

    Most somatic sensory information

    is relayed to the thalamus for processing. A small fraction of the arriving information is projected to the cerebral cortex and reaches our awareness.


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    to here 3/12 cerebral cortex

    lec # 25


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    Pathways in the CNS cerebral cortex

    sensory pathways

    Somatic sensory pathways

    posterior column pathway

    anterolateral column pathway

    spinocerebellar pathway


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    fig. 15-4 cerebral cortex


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    Pathways in the CNS cerebral cortex

    sensory pathways

    Somatic sensory pathways

    posterior column pathway

    anterolateral column pathway

    spinocerebellar pathway


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    Pathways in the CNS cerebral cortex

    sensory pathways

    Somatic sensory pathways

    Visceral sensory pathways

    • info from interoceptors

      • (internal organs)


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    Pathways in the CNS cerebral cortex

    Somatic sensory pathways

    Visceral sensory pathways

    nociceptors, thermoreceptors,

    tactile receptors, baroreceptors, chemoreceptors


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    Pathways in the CNS cerebral cortex

    Somatic sensory pathways

    Visceral sensory pathways

    CN V, VII, IX, X carry info from

    pharynx, mouth, palate, larynx, trachea and esophagus

    • project to solitary nucleus

      • (medulla oblongata)


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    Pathways in the CNS cerebral cortex

    Somatic sensory pathways

    Visceral sensory pathways

    T1 to L2 abdominal organs

    S2 to S4 pelvic organs

    first order neurons project to interneurons which travel up the anterolateral pathway to sol. nuc.

    usually subconscious


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    Pathways in the CNS cerebral cortex

    sensory pathways

    motor pathways

    the somatic nervous system (SNS)

    autonomic nervous system (ANS)

    voluntary

    involuntary


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    motor pathways in the CNS cerebral cortex

    the somatic nervous system (SNS)

    always involve at least two neurons

    upper motor neuron

    lower motor neuron

    inside CNS (+ or -)

    stimulates a motor unit


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    motor pathways in the CNS cerebral cortex

    motor information follows

    one of three main pathways:

    corticospinal pathway

    medial pathway

    lateral pathway


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    motor pathways in the CNS cerebral cortex

    corticospinal pathway

    (aka., pyramidal system)

    upper motor neurons are

    pyramidal cells in primary motor cortex

    • synapse on lower motor neurons

      • (ventral horn of spinal cord)

  • also project to other control centers


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    motor pathways in the CNS cerebral cortex

    corticospinal pathway

    three pairs of tracts:

    corticobulbar tracts

    to motor nuclei of

    CN III, IV, V, VI, VII, IX, XI, XII

    conscious control of eye, jaw and face muscles…


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    motor pathways in the CNS cerebral cortex

    corticospinal pathway

    three pairs of tracts:

    corticobulbar tracts

    lateral corticospinal tracts

    anterior corticospinal tracts


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    fig. 15-9 cerebral cortex


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    Pathways in the CNS cerebral cortex

    motor pathways

    motor information follows

    one of three main pathways:

    corticospinal pathway

    medial pathway

    lateral pathway


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    fig. 15-8 cerebral cortex


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    Pathways in the CNS cerebral cortex

    motor pathways

    corticospinal pathway

    medial pathway

    • neck

    • trunk

    • proximal

      • limbs

    muscle tone

    gross movement


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    Pathways in the CNS cerebral cortex

    motor pathways

    medial pathway

    • UMN in:

      • vestibular nuclei

      • (hind)

      • superior colliculus

      • (mid)

      • reticular formation

      • (brain stem)

    posture &

    balance

    reflexive head position

    various


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    Pathways in the CNS cerebral cortex

    motor pathways

    lateral pathway

    control of muscle tone

    precise movement of distal limbs

    UMN in red nucleus (mid)

    descend down rubrospinal tract


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    Basal Nuclei cerebral cortex

    • background patterns of movement

      • (walking, running, etc.)

    • adjust activities of UMN in cortex

    normally:

    inactive

    active

    two populations:

    ACh stimulatory

    GABA inhibitory

    inhibited


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    Cerebellum cerebral cortex

    monitors (sensory):

    spinocerebellar tract

    superior colliculus

    vestibular nucleus

    proprioception

    visual

    vestibular (balance)

    output

    continually adjusts UMN activity


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    Several conditions cerebral cortex

    • ALS

      • amyotrophic lateral sclerosis

      • (aka Lou Gerhig’s disease)

      • degeneration of UMN’s and/or LMN’s

        • atrophy of muscle

    • cerebral palsy

      • affect voluntary muscle performance

      • trauma, exposure to drugs etc., genetics

        • cerebrum, cerebellum, basal nuclei, hippocampus, thalamus

      • abnormal motor skills, posture, speech…

    • anencephaly

      • lack of higher brain development


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    100 Keys cerebral cortex(pg. 513)

    “Neurons of the primary motor cortex (UMN) innervate motor neurons in the brain and spinal cord (LMN) responsible for stimulating skeletal muscles. Higher centers in the brain can suppress or facilitate reflex responses; reflexes can complement or increase the complexity of voluntary movements”