Transcript Document

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)
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
our awareness of it is
sensation
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. 15-2
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
receptor 2
cortex
a “line” carries the same “type”
(modality) of information
interpretation is based on which “line”
information travels on
receptor A
receptor B
receptor 2
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”
greater stimulus
lesser stimulus
higher freq.
lower freq.
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
(aka fast-adapting receptors)
example:
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
to here 3/9
lec # 24
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
stimulusopens
remove
stimulusclosed
fig. 12-10c
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. 15-3
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
high-frequency 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. 15-3
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
receptors in 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. 15-4
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.
superior half of body
first order neuron in DRG
up the fasciculus cuneatus to the
nucleus cuneatus of med. oblong.
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. 15-4
fig. 15-5a
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. 15-4
fig. 15-5b
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. 15-6
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. 15-4
fig. 15-7
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.
to here 3/12
lec # 25
Pathways in the CNS
sensory pathways
Somatic sensory pathways
posterior column pathway
anterolateral column pathway
spinocerebellar pathway
fig. 15-4
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 system
(ANS)
involuntary
motor pathways in the CNS
the somatic nervous system (SNS)
always involve at least two neurons
upper motor neuron
inside CNS (+ or -)
lower motor neuron
stimulates a motor unit
motor pathways in the CNS
motor information follows
one of three main pathways:
corticospinal pathway
medial pathway
lateral pathway
motor pathways in the CNS
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
motor pathways in the CNS
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…
motor pathways in the CNS
corticospinal pathway
three pairs of tracts:
corticobulbar tracts
lateral corticospinal tracts
anterior corticospinal tracts
fig. 15-9
Pathways in the CNS
motor pathways
motor information follows
one of three main pathways:
corticospinal pathway
medial pathway
lateral pathway
fig. 15-8
Pathways in the CNS
motor pathways
corticospinal pathway
medial pathway
muscle tone
gross movement
neck
trunk
proximal
limbs
Pathways in the CNS
motor pathways
medial pathway
UMN in:
vestibular nuclei
posture &
balance
(hind)
superior colliculus
(mid)
reticular formation
(brain stem)
reflexive
head position
various
Pathways in the CNS
motor pathways
lateral pathway
control of muscle tone
precise movement of distal limbs
UMN in red nucleus (mid)
descend down rubrospinal tract
Basal Nuclei
background patterns of movement
(walking, running, etc.)
adjust activities of UMN in cortex
normally:
two populations:
ACh
stimulatory
GABA
inhibitory
inactive
inhibited
active
Cerebellum
monitors (sensory):
proprioception
visual
vestibular (balance)
spinocerebellar tract
superior colliculus
vestibular nucleus
output
continually adjusts UMN activity
Several conditions
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
100 Keys (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”