15
Sensory Chapter Pathways and the Somatic Nervous System
Neural Integration I:
fig. 151
Sensory General (15) Special (17)
Motor Somatic (15) Autonomic (16)
General senses temperature pain touch pressure vibration proprioception most associated with the skin
Special senses smell sight taste hearing special "sense" organs
General senses receptors distributed throughout the body relatively simple
General senses receptors send info to CNS
arriving info is called sensation our awareness of it is perception
Sensory receptors interface between environment and the body translate stimulus into an AP transduction
Sensory receptors receptors have selective sensivity chemical physical touch light heat transfer receptors may or may not have accessory structures associated with them
Sensory receptors receptive field area monitored by a receptor size of receptive field
70 mm 1 mm
fig. 152
specificity
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
Sensory receptors stimulus receptor action potential
CNS for processing and interpretation (cortical areas)
receptor A receptor B lab
receptor 2
ele d lin
e
cortex
a "line" carries the same "type" (modality) of information
interpretation is based on which "line" information travels on
receptor 2 receptor A receptor B lab ele op tic d lin n er e ve cortex
shut eyes and rub them gently
When CNS receives info...
which "line" where "line" ends type of stimulus perception
all other attributes (strength, duration, variation) are determined by the frequency and pattern of AP's
receptor types: tonic: always "on" higher freq. lower freq.
greater stimulus lesser stimulus
phasic: only on with stimulus some receptors combine the two
adaptation reduction in sensitivity in the presence of a constant stimulus
peripheral change in receptor activity central inhibition of nuclei in pathway
peripheral adaptation phasic receptors example:
(aka fastadapting receptors)
thermoreceptors
you usually don't notice room temperature unless it changes
central adaptation example: smell
you walk into a room and notice a new smell... ...but not for long
adaptation reduces the amount of information reaching the cerebral cortex about 1% of sensory information coming in reaches our awareness
100 Keys (pg 498) "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."
General senses (from chapter 12) exteroceptors outside proprioceptors position interoceptors inside
General senses classification based on nature of stimulus
nociceptors thermoreceptors mechanoreceptors chemoreceptors
pain heat flow physical distortion chemical concentration
General senses nociceptors
common in: skin joint capsules coverings of bones around blood vessel walls free nerve endings large receptive fields
nociceptors sensitive to: extreme temperature mechanical damage dissolved chemicals
(like those release by damaged cells)
stimulation causes depolarization
nociceptors
two fiber types convey info type A fast pain (cut, etc.,) easy to localize type C slow pain ("burning, aching") difficult to localize
nociceptors
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)
nociceptors
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]
nociceptors 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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thermoreceptors free nerve endings in the dermis skeletal m. hypothalamus liver warm receptors or cold receptors
thermoreceptors phasic receptors active when temperature is changing, quickly adapting to stable temperature detect transfer of heat heat loss from skin heat gain to skin cool warm
mechanoreceptors contain mechanically regulated ion channels (chapter 12)
c.
mechanically regulated channels
closed mechanical stimulus opens remove stimulus closed
fig. 1210c
mechanoreceptors three classes tactile receptors touch, pressure, vibration baroreceptors pressure changes (gut, genitourinary) proprioceptors position of joints/muscles
mechanoreceptors tactile receptors fine touch/pressure small (narrow) receptive field detailed information sensitive crude touch/pressure wide receptive field poor localization
fig. 153
tactile receptors range of complexity free nerve endings root hair plexus tactile discs tactile corpuscles (Meissner's) lamellated corpuscles (pacinian) Ruffini corpuscles
tactile receptors free nerve endings in epidermis of skin cornea of eye sensitive to touch and pressure tonic receptors small receptive field
tactile receptors root hair plexus around each hair follicle sense movement of hair adapt quickly
tactile receptors tactile discs sensitive, tonic receptors in epidermis fine touch and pressure
tactile receptors tactile corpuscles (Meissner's) fine touch, pressure , vibration adapt quickly surrounded by Schwann cells in dermis of skin eyelids, fingertips (sensitive areas)
tactile receptors lamellated corpuscles (pacinian) sensitive to deep pressure highfrequency vibrations adapt quickly nerve ending is encapsulated by layers of supporting cells (onion) dermis, pancreas, fingers...
tactile receptors Ruffini corpuscles pressure and skin distortion located deep in the dermis tonic, little if any adaptation
fig. 153
sensivitity can be altered infection disease damage to pathway e.g., damage to a spinal nerve would affect an entire dermatome
tickle and itch closely related to touch and pain
baroreceptors 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
proprioceptors muscle spindles stretch reflex Golgi tendon organs monitor tendon tension in receptors joint capsules free nerve endings in joints
proprioceptors no adaptation continuously send info to CNS most processed at subconscious level
chemoreceptors 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
Pathways in the CNS spinothalamic tract
spine to thalamus =sensory
corticospinal tract
cortex to spine =motor
Pathways in the CNS sensory pathways neurons involved first order neuron sensory neuron (DRG) second order neuron in CNS (crosses over) third order neuron in thalamus
Pathways in the CNS sensory pathways Somatic sensory pathways carry sensory info from skin and muscles of body wall, head, neck, limbs
Pathways in the CNS sensory pathways Somatic sensory pathways posterior column pathway anterolateral column pathway spinocerebellar pathway
fig. 154
The Posterior Column Pathway fine touch pressure vibrations proprioception
The Posterior Column Pathway inferior half of body
first order neuron in DRG up the fasciculus gracilis to the nucleus gracilis of med. oblong. first order neuron in DRG up the fasciculus cuneatus to the nucleus cuneatus of med. oblong.
superior half of body
The Posterior Column Pathway
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
fig. 154 fig. 155a
The Anterolateral Pathway "crude" touch pressure pain temperature
The Anterolateral Pathway 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
The Anterolateral Pathway second order neuron
cross to opposite side and ascend
anterior spinothalamic tract crude touch and pressure to ventral nucleus of thalamus lateral spinothalamic tract pain and temperature to ventral nucleus of thalamus
The Anterolateral Pathway
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
fig. 154 fig. 155b
The Anterolateral Pathway
phantom pain ? activity along pathway, even if "limb" is not there referred pain? viceral pains sensations may stimulate neurons of AL pathway
fig. 156
The Spinocerebellar Pathway
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)
fig. 154 fig. 157
100 Keys (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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Pathways in the CNS sensory pathways Somatic sensory pathways posterior column pathway anterolateral column pathway spinocerebellar pathway
fig. 154
Pathways in the CNS sensory pathways Somatic sensory pathways posterior column pathway anterolateral column pathway spinocerebellar pathway
Pathways in the CNS sensory pathways Somatic sensory pathways Visceral sensory pathways info from interoceptors (internal organs)
Pathways in the CNS Somatic sensory pathways Visceral sensory pathways nociceptors, thermoreceptors, tactile receptors, baroreceptors, chemoreceptors
Pathways in the CNS 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)
Pathways in the CNS 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
Pathways in the CNS sensory pathways motor pathways
the somatic nervous system (SNS) voluntary autonomic nervous ...