Transcript Power Point - Annmarie Kotarba

Chapter 15:
Neural Integration I:
Sensory Pathways and the Somatic
Nervous System
1
Neural Integration
2
Afferent Division of
the Nervous System
• Receptors
• Sensory neurons
• Sensory pathways
3
Afferent Division
• Sensory receptors  sensory pathway

1. Somatic Sensory info
-
Sensory cortex of cerebrum
Cerebellum
2. Visceral Sensory info
-
Reflex centers in brainstem
Reflex centers in diencephalon
4
Sensory Receptors
• Specialized cells that monitor specific conditions
in the body or external environment
• General Senses:
– Temp, pain, touch, pressure, vibration,
proprioception
– Simple receptors located anywhere on body
• Special Senses:
– Are located in sense organs such as the eye or ear
– Olfaction, vision, gustation, hearing, equilibrium
– Complex receptors located in specialized sense
organs
5
Sensory Receptors
• Sensation – the sense info; action potentials
– Taste, hearing, equilibrium, and vision provided
by specialized receptor cells
– Communicate with sensory neurons across
chemical synapses
• Perception – conscious awareness of
sensation
6
Sensory Receptors
• Transduction – conversion of environmental
stimulus into action potential by sensory
receptor
– Action potential:
• When stimulated, a receptor passes information to
the CNS in the form of action potentials along the
axon of a sensory neuron
– Receptors specific for particular type of stimulus
– Specificity is due to structure of receptor
– Simplest receptors are dendrites (free nerve
endings), least specific
7
Free Nerve Endings
• Branching tips of dendrites
• Not protected by accessory structures
• Can be stimulated by many different
stimuli
8
Sensory Receptors
• Receptive field
– area monitored by single receptor (e.g. touch:
arm vs. fingertip)
– Area is monitored by a single receptor cell
– The larger the receptive field, the more
difficult it is to localize a stimulus
9
Sensory Receptors
• Labeled line
– Link between receptor and processing site in
CNS
• Stimulation anywhere on labeled line will
produce the same perception (e.g. phantom
limb)
• Stimulus -> receptor -> transduction ->
action potential -> sensation ->-> CNS
perception
10
Sensory Pathways
• Deliver somatic and visceral sensory
information to their final destinations
inside the CNS using:
– nerves
– nuclei
– tracts
11
Sensory Receptors
1. Tonic Receptors:
-
Always active
Signal at different rate when stimulated
Monitor background levels
2. Phasic Receptors:
–
-
Activated by stimulus
Become active for a short time whenever a
change occurs
Monitor intensity and rate of change of
stimulus
12
Sensory Receptors
• Adaptation
– Reduced sensitivity to a constant stimulus
1. Peripheral Adaptation:
-
Reduction in receptor activity
Phasic  fast adapting
Tonic  slow or non adapting
- Remind you of an injury long after the initial damage
has occurred
2. Central Adaptation:
-
-
Inhibition of nuclei along labeled line
Not all pathways will adapt
13
Four types of General Sensory Receptors
1.
2.
3.
4.
-
Pain: nociceptor
Temperature: thermoreceptor
Physical: mechanoreceptor
Chemicals: chemoreceptors
All can be found in both somatic
(exteroceptors) and visceral (interoceptors)
locations except:
-
Proprioceptors (a mechanoreceptor) are
somatic only
-
report the positions of skeletal muscles and joints
14
1. Pain Receptors: Nociceptors
• Detect Pain
• Are common in the:
– superficial portions of the
skin
– joint capsules
– within the periosteum of
bones
– around the walls of blood
vessels
• Rare in deep tissue and visceral
organs
• Consist of free nerve endings
with large receptor fields
15
Figure 15–2
1. Pain Receptors: Nociceptors
• Mode of Action:
1. Injured cells release arachidonic acid
2. Arachidonic acid is converted into
prostaglandins by the interstitial enzyme
cyclo-oxygenase
3. Prostaglandins activate nociceptors
-
Many pain medications like aspirin function to
inhibit cyclo-oxygenase
16
1. Pain Receptors: Nociceptors
• Once transduced pain sensations are carried
on either type A and type C fibers/axons:
– Type A:
• Fast pain; stab or cut; triggers defensive reflexes
– Type C:
• Slow pain; aching pain
• Tonic receptors with no peripheral
adaptation
• Pain levels are modulated by endorphins
which inhibit CNS function
17
2. Thermoreceptors
• Detect temperature
• Found in skin, skeletal muscle, liver,
and hypothalamus
• Consist of free nerve endings
• Phasic receptors that adapt easily
18
3. Mechanoreceptors
**Detect membrane distortion
Three receptor types:
• Tactile Receptors
• Proprioceptors
• Baroreceptors
19
3. Mechanoreceptors
1. Tactile Receptors
- Detect touch, pressure and vibration on skin
A. Free nerve endings
-
Detect touch on skin
Tonic receptors with small receptor fields
B. Root hair plexus nerve endings
-
Detect hair movement
Phasic receptors, adapt rapidly
C. Tactile discs/Merkel’s discs
-
Detect fine touch
Extremely sensitive
Whole cell tonic receptors
20
3. Mechanoreceptors
1. Tactile Receptors
D. Tactile corpuscles/Meissner’s corpuscles
-
Detect fine touch and vibration
Larger receptor structure
Phasic receptors, adapt rapidly
E. Lamellated corpuscles/Pacinian corpuscles
-
Detect deep pressure
Larger multi-layer receptors
Phasic receptor, adapt rapidly
F. Ruffini corpuscles
-
Detect pressure and distortion
Large tonic receptors, no adaptation
21
22
3. Mechanoreceptors
2. Proprioceptors:
- Detect positions of joints and muscles
- Tonic receptors, do not adapt, complex
A. Muscle spindles
-
Modified skeletal muscle cell
Monitor skeletal muscle length
B. Golgi tendon organs
-
-
Dendrites around collagen fibers at the muscletendon junction
Monitor skeletal muscle tension
C. Joint capsule receptors
-
Monitor pressure, tension and movement in the
23
joint
24
3. Mechanoreceptors
3. Baroreceptors
-
-
Detect pressure changes
Found in elastic tissue of blood vessels and
organs of digestive, reproductive and urinary
tracts
Consists of free nerve endings
Phasic receptors, adapt rapidly
25
26
4. Chemoreceptors
• Detect change in concentration of
specific chemicals or compounds
– E.g. pH, CO2
• Found in respiratory centers of the brain
and in large arteries
• Phasic receptors, adapt rapidly
27
28
KEY CONCEPT
• Stimulation of a receptor produces action
potentials along the axon of a sensory
neuron
• The frequency and 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
29
Somatic Sensory Pathways
• Carry sensory information from the
skin and musculature of the body wall,
head, neck, and limbs
30
Somatic Sensory Pathways
• Consist of two or three neurons:
1. First Order Neuron:
-
Sensory neuron
Connects from receptor to CNS
Cell body is in dorsal root ganglion/cranial nerve
ganglion
2. Second Order Neuron:
-
Interneuron (stimulated by first order)
Located in spinal cord or brain stem
Subconscious processing of info
3. Third Order Neuron:
-
Located in thalamus
Relays info to primary somatosensory cortex of
cerebrum for conscious awareness (perception)
31
• Only ~1% of somatic sensory info reaches
cerebrum (major changes only,
“background” in filtered)
– LSD interferes with sensory damping/filtering =
sensory overload
• All sensory info undergoes decussation in
spine before reaching target in CNS
32
3 Major Somatic
Sensory Pathways
33
Figure 15–4
Posterior Column
Pathway
• Carries sensations
of highly localized
(“fine”) touch,
pressure, vibration,
and proprioception
34
Figure 15–5a
Visceral Sensory Pathways
• Interoceptors transmit info to solitary
nucleus of medulla oblongata for relay to
visceral centers in brainstem and
diencephalon
– No perception
• Two neurons: 1st and 2nd order
35
Efferent Division
• Conscious and subconscious motor
centers in brain -> motor pathways ->
1. Somatic Nervous System  skeletal muscle
2. Autonomic Nervous System  visceral
effectors
-
Smooth and cardiac muscle, glands, and adipose
36
Somatic Nervous System
• Motor control of skeletal muscle
• Consists of two neurons:
1. Upper motor neuron
- Has soma in CNS processing center:
A. Primary motor cortex of cerebrum
- voluntary control
B. Cerebrum, diencephalon, and brain stem
- subconscious control:reflex
C. Basal nuclei of cerebrum and cerebellum
- coordination, balance, fine tuning
2. Lower motor neuron
-
Soma in brain stem or spinal cord
Links to skeletal muscle motor unit
37
Motor Homunculus
38
Sensory Homunculus
Functional map of the primary sensory cortex
39
Figure 15–5a, b
Processing in the Thalamus
• Determines whether you perceive a
given sensation as fine touch, as
pressure, or as vibration
40
Motor Related Disorder
1. Parkinson’s Disease
-
Jittery movements: lack of fine tuning of motor
Results from degeneration of dopamine neurons
of substantia nigra
-
-
Inhibits basal nuclei
Overactive basal nuclei = “ticks”
2. Amylotrophic Lateral Sclerosis
-
Degeneration of motor neurons in CNS
Causes muscle atrophy and death
41
Motor Related Disorder
3. Epilepsy
-
1/25 people
Wide range in condition:
-
-
Absence seizures (blank) to grand mal
seizures (convulsions, unconscious)
Uncontrolled/chaotic neuron activity in
brain: blocks normal messages
42
When the nociceptors in your hand are
stimulated, what sensation do you
perceive?
1.
2.
3.
4.
pain
heat
vibration
pressure
43
What would happen to you if the information
from proprioceptors in your legs were
blocked from reaching the CNS?
1. no pain sensations from the legs
2. uncontrolled blood pressure in
the legs
3. uncoordinated movements and
inability to walk
4. no tactile sensations in the legs
44
Chapter 16:
Neural Integration II:
The Autonomic Nervous System
and Higher-Order Functions
45
46
Autonomic Nervous System (ANS)
• Operates without conscious instruction
• Coordinates systems functions:
–
–
–
–
–
cardiovascular
respiratory
digestive
urinary
reproductive
47
Autonomic Nervous System
• Motor control of visceral effectors
• Involves three neurons:
1. Visceral motor nuclei in hypothalamus to
autonomic nuclei in CNS
2. Autonomic nuclei to autonomic ganglia in PNS
3. Autonomic ganglia to visceral effector
**Nuclei = in CNS, a center with a visible boundary
**Ganglia = in PNS, collection of somas together in
one place
48
Autonomic Nervous System
49
•
1.
2.
-
Two subdivisions
Sympathetic: “fight or flight”
Parasympathetic: “rest and digest”
Typically oppose each other on same
effector
Some effectors innervated by only one:
-
Blood vessels/sweat glands –> sympathetic only
Smooth muscle of eye –> parasympathetic only50
Sympathetic Division
• Prepares body for heightened somatic
activity
• Ganglia:
1. Located near spinal cord
2. Adrenal Medulla
-
Center of adrenal gland (above kidney)
Releases epinephrine and norepinephrine as
hormones into blood to control effectors body
wide at one (endocrine function)
51
Sympathetic Division
• Sympathetic Activation Results
–
–
–
–
–
Increased alertness
Insensitivity to pain
Elevation in blood pressure, respiratory rate
Elevation in muscle tone
Mobilization of energy reserves
52
Sympathetic Division:
Neurotransmitter
1. Preganglionic Neurons release acetycholine
(cholinergic synapse)  EPSP on ganglionic
neuron
- directly open ion channel
- fast acting, short lived
53
Sympathetic Division:
Neurotransmitter
2. Ganglionic neurons/postganglionic fibers
release norepinephine at effectors
(adrenergic synapse)
-
NE and E from adrenal medulla: hormones
Result depends on type of receptor:
1. Alpha1 and beta1 receptors:
- excititory/stimulatory to effector
2. Alpha2 and beta2 receptors:
-
Inhibitory
**beta-blockers: block beta1 receptors
-
G protein  second messengers
Slow acting but long lasting
54
Parasympathetic Division
•
•
•
•
Stimulates visceral activity
Maintains homeostasis
Ganglia located in or near effector
Vagus nerve carries 75% of
parasympathetic innervations
55
Parasympathetic Division
• Parasympathetic activations results:
1.
2.
3.
4.
5.
6.
7.
8.
Constriction of pupils
Secretion by digestive glands
Secretion of hormones for nutrient uptake
Sexual arousal
Activation of digestive tract
Defecation and urination
Constriction of respiratory pathways
Reduction in heart rate
56
Parasympathetic Division:
Neurotransmitters
• All release Ach: all cholinergic synapses
• Effects quick, localized, short-lived
• Type of effect depends on receptor:
1. Nicotonic receptor
-
Excititory effect on target
2. Muscarinic receptor
-
Inhibitory or excititory, depends on target cell
57
How many motor neurons are required
to conduct an action potential from the
spinal cord to smooth muscles in the
wall of the intestine?
1.
2.
3.
4.
one
two
four
six
58
While out for a brisk walk, Julie is suddenly
confronted by an angry dog. Which division of
the autonomic nervous system is responsible for
the physiological changes that occur in Julie as
she turns and runs?
1.
2.
3.
4.
parasympathetic division
somatic nervous system
enteric nervous system
sympathetic division
59
On the basis of anatomy, how could you
distinguish the sympathetic division from
the parasympathetic division of the
autonomic nervous system?
1.
2.
3.
4.
origin of preganglionic fibers
number of preganglionic fibers
placement of ganglia
both 1 and 3 are correct
60
How would a drug that stimulates
acetylcholine receptors affect the
sympathetic nervous system?
1. complete shut-down of
sympathetic activity
2. decreased sympathetic activity
3. uncontrolled sympathetic
activity
4. increased sympathetic activity
61
An individual with high blood pressure is
given a medication that blocks beta
receptors. How could this medication help
correct that person’s condition?
1.
2.
3.
4.
aids sympathetic stimulation
decreases blood volume
prevents sympathetic stimulation
none of the above
62
Which nerve is responsible for the
parasympathetic innervation of the lungs,
heart, stomach, liver, pancreas, and parts of
the small and large intestines?
1.
2.
3.
4.
cranial nerve IX
splanchic nerve
vagus nerve
pelvic nerve
63
What effect would the loss of sympathetic
tone have on blood flow to a tissue?
1. Blood flow would decrease.
2. Blood flow would be redirected
to heart, lungs and brain.
3. Blood flow would increase.
4. Blood flow would become erratic.
64
What physiological changes would you
expect in a patient who is about to
undergo a root canal and is quite
anxious about the procedure?
1. change in motility of digestive
tract
2. increased heart rate
3. increased breathing rate
4. all of the above
65
Harry has a brain tumor that is interfering with the
function of his hypothalamus. Would you expect this
tumor to interfere with autonomic function? Why or
why not?
1. Yes; hypothalamus regulates ANS.
2. Yes; all brain tumors affect ANS
functioning.
3. No; ANS has no connection to the
hypothalamus.
4. No; ANS function is regulated by
thalamus.
66
Higher Order Functions
1. Involve cerebral cortex
2. Involve both conscious and
subconscious processing
3. Are not part of genetic wiring
(reflex): can be modified
e.g. memory and consciousness
67
Memory
•
•
•
•
Memory – storage and retrieval of info
Fact memories – specific bits of info
Skill memories – learned motor behaviors
Short term memory (STM)
–
–
–
–
primary/working memory
Rapid recall but short retention
Store 7-8 bits of info at one time
STM can be converted to long term memory for
more permanent storage
68
Memory
• Memory consolidation: STMLTM
–
–
Performed by hippocampus
Depends on:
1. Emotional State
2. Rehearsal
3. Association
4. Automatic memory
69
Memory
• Long term memory (LTM)
– Infinite info
– Can be stored for lifetime
– Secondary memories:
• fade with time, can be difficult to recall much later
– Tertiary memories:
• part of one’s consciousness (e.g. name)
– LTMs are broken into component parts to store in
appropriate cerebral cortex
• E.g. visual, olfactory, etc.
70
Memory
• Mechanism of memory storage not clearly
understood but involves:
1. New mRNA and protein synthesis in neurons
involved
2. Change of shape of dendritic spines
3. Change in size and number of synaptic
terminals
4. Release of more neurotransmitter
71
Memory
• Amnesia = loss of memory, due to disease
or trama of hippocampus and amygdala
1. Retrograde Amnesia:
-
Lose memories of past events,
Remember now  forward
2. Anterograde Amnesia
-
Unable to store new memories
Only remember past
72
Consciousness
• Conscious: aware of external stimuli
• Unconscious: range of unawareness
– Drowsy  coma  brain dead
73
Sleep
•
Sleep = partial unconsciousness from which a
person can be aroused with stimuli
1. Deep Sleep
-
Relaxed state
Heart and respiratory rate decreased
Minimal activity in cerebral cortex
2. REM (rapid eye movement): sleep
-
active, dreaming state
Cerebral cortex as active/more active than in conscious
state
But little reaction to outside stimuli
Skeletal muscles inhibited
74
Activity in Cerebral Cortex
75
• Alternate between deep and REM sleep
throughout sleep period
• Sleep required for life, but not clear why
• Lack of sleep leads to serious disturbance in
mental function
• During sleep protein synthesis in neurons
increases: sleep may be used to repair and
recharge neural tissue
76
Sleep Disorders
1. Narcolepsy
-
Condition where person lapses abruptly into
sleep for ~ 15 min
Usually follows pleasant event
Cause unknown
Sufferers show reduced levels of REM sleep
at night
2. Sleep apnea
-
Person stops breathing until hypoxia (lack of
O2) wakes them
Hypoxic wake response ability declines with
77
age or respiratory illness
Arousal
• Requires Reticular Activating System (RAS)
• RAS located in brainstem, provides
consciousness
• Mechanism:
– Stimulation of RAS  activation of cerebral
cortex
– Positive feedback (reverberation) on RAS
maintains consciousness after initial stimulus
– Over time RAS becomes less responsive = sleep
feeling
• Internal clock in suprashiasmatic nucleus of
hypothalamus
– sets normal sleep-wake cycle
78
Which of the following is not a
characteristic of higher order functions?
1. require cerebral cortex
2. involve conscious and
unconscious processing
3. part of the programmed wiring of
the brain
4. subject to modification over time
79
After suffering a head injury in an automobile
accident, David has difficulty comprehending
what he hears or reads. This symptom might
indicate damage to which portion of his brain?
1. right temporal lobe of the
cerebrum
2. left temporal lobe of the cerebrum
3. frontal lobe of the cerebrum
4. left parietal lobe of the cerebrum
80
As you recall facts while you take your
A&P test, which type of memory are you
using?
1.
2.
3.
4.
long term memory
skill memory
memory consolidation
short term memory
81
You are asleep. What would happen to you
if your reticular activating system were
suddenly stimulated?
1. You would wake up.
2. You would experience a pleasant
dream.
3. You would experience a
nightmare.
4. You would experience muscular
contraction and cramping.
82
Age Related Changes
• Decrease
–
–
–
–
–
Brain size and weight (cerebrum)
Number of neurons
Blood flow to brain (incr. chance of stroke)
Number of synapses
Neurotransmitter production
83
Age Related Changes
• Accumulation of deposits:
A. Inside Cells
-
lipofuscin: granular pigment
Neurofibrillary tangles: packed neurofibrils
B. Extracellular
-
plaques: collections of fibrillar proteins entangling
abnormal cell processes
- Amyloid proteins: normal proteins misfolding become
sticky
* All forms of deposits affect processing and
memory ability, motor speed, and sensory
sensitivity
84
Age Related Changes
• Increased disease:
1. Alzheimer’s Disease
-
Loss of higher order functions
Occurs in 15% over 65 years
Progressive, untreatable
Due to reduction of Ach levels and
accumulation of beta amyloid peptide
-
-
Plaques and tangles
Current treatments block Ach breakdown
85
Age Related Changes
2. Huntington’s Disease
-
-
genetic, middle age onset
Accumulation of huntington’s protein kills
neurons of basal ganglia and cerebral cortex
 ticks, cognitive dysfunction
Progressive and fatal
-
On set  death in ~ 15 years
86
One of the problems associated with aging is
difficulty in recalling things or even a total
loss of memory. What are some possible
reasons for these changes?
1. decreased blood flow to brain
2. formation of neurofibrillary
tangles
3. reduction in brain weight
4. all of the above
87
88
SUMMARY
• Brain, spinal cord, and peripheral nerves
continuously communicate with each other and
with internal and external environments
• Information arrives via sensory receptors and
ascends within afferent division, while motor
commands descend and are distributed by
efferent division
• Sensory receptor is a specialized cell or cell
process that monitors specific conditions within
body or in external environment:
– arriving information is called a sensation
– awareness of a sensation is a perception
89
SUMMARY
• General senses are pain, temperature, physical
distortion, and chemical detection:
– receptors for these senses are distributed throughout
the body
• Special senses, located in specific sense organs,
are structurally more complex
• Each receptor cell monitors a specific receptive
field
• Transduction begins when a large enough
stimulus changes the receptor potential reaching
generator potential
90
SUMMARY
• Tonic receptors are always active
• Phasic receptors provide information about intensity
and rate of change of a stimulus
• Adaptation is a reduction in sensitivity in presence
of a constant stimulus
• Tonic receptors are slow-adapting receptors, while
phasic receptors are fast-adapting receptors
• 3 types of nociceptor found in the body provide
information on extremes of pain:
– temperature
– mechanical damage
– dissolved chemicals
• myelinated Type A fibers carry fast pain
• Type C fibers carry slow pain
91
SUMMARY
• Thermoreceptors are found in the dermis
• Mechanoreceptors are sensitive to distortion of their
membranes and include:
– tactile receptors, baroreceptors, proprioceptors
• 6 types of tactile receptors in the skin
• 3 types of proprioceptors
• Chemoreceptors include carotid bodies and aortic
bodies
• Sensory neurons that deliver sensations to CNS are
referred to as first-order neurons:
– synapse on second-order neurons in brain stem or spinal
cord
– next neuron in this chain is a third-order neuron, found in
the thalamus
92
SUMMARY
• Functions of the autonomic nervous system
(ANS)
• Functions of CNS preganglionic neurons
• The sympathetic division
• Sympathetic activation
• Function of neurotransmitters:
– acetylcholine (ACh)
– norepinephrine (NE)
– epinephrine (E)
93
SUMMARY
• Sympathetic ganglionic neurons
• Two types of sympathetic receptors:
– alpha receptors
– beta receptors
• The parasympathetic division (food
processing and energy absorption)
• Muscarinic and nicotinic receptors
94
SUMMARY
• Memory:
– short–term or long–term
• Memory consolidation
• Consciousness, unconsciousness, and
sleep
• Age-related changes in the nervous
system
95