ch 16: sensory, motor and integrative systems Flashcards
sensation vs perception
Perception is the conscious awareness & interpretation of a sensation
◦ Perception of a sensation involves the cortex
◦ precise localization & identification
◦ memories of sensations are stored in cortex
Sensation is any stimuli the body is aware of (consciously or not)
◦ Chemoreceptors, thermoreceptors, nociceptors, baroreceptors
◦ What are we not aware of?
◦ X-rays, ultra high frequency sound waves, UV light
◦ We have no sensory receptors for those stimuli
what is sensory modalities? What are the two classes?
Sensory Modality is a type of sensation
◦ a given sensory neuron carries information for only one sensory modality
◦ touch, pain, temperature, hearing, vision, are all different sensory
modalities
Two classes of sensory modalities
◦ general senses (somatic and visceral senses)
◦ special senses (smell, taste, vision, hearing, and equilibrium)
what are the 4 steps in the process of sensation
- Stimulation of sensory receptors - Each receptor only responds to one type of stimulus
- Transduction of the stimulus = conversion into a graded potential
Graded potentials vary in amplitude depending on the strength of the
stimulus and are not propagated - Generation of nerve impulses when the graded potential reaches threshold,
an action potential is triggered neurons that conduct nerve impulses from PNS
directly to CNS are called first-order neurons - Integration of sensory information A specific part of CNS receives and integrates the
sensory nerve impulses
what are free nerve endings? what are they useful for?
Free nerve endings are the dendrites of first-order neurons
For the sensations of pain, temperature, tickle, itch &
light touch, and smell
The graded potential triggered in a neuron with free nerve endings is
called a generator potential
describe encapsulated nerve endings
Receptors for pain, temperature, tickle, itch, and some touch sensations are free nerve endings. Receptors for other somatic and visceral sensations, such as pressure, vibration, and some touch sensations, are encapsulated nerve endings.
what are separate sensory cells
what does the graded potential trigger?
What does the receptor potential trigger
used for vision (photoreceptors), taste (gustatory receptor cells), hearing and equilibrium (hair cells)
these cells synapse with fist-order neurons
the graded potential triggered in a sensory cell is called a receptor potential
the receptor potential triggers the release of neurotransmitters onto the first-order neuron
generator vs receptor potential
true or false they are both graded?
Generator potential
◦ Triggers an AP in the 1st order neuron
◦ E.g., Free nerve endings, encapsulated nerve endings & olfactory receptors
Receptor potential
◦ Receptor cells release neurotransmitter molecules on first-order neurons
producing postsynaptic potentials → PSP may trigger a nerve impulse
◦ E.g. Vision, hearing, equilibrium and taste receptors produce receptor
potentials
Both are GRADED → Amplitude of potentials vary with stimulus intensity
A generator potential produces action
potentials and a receptor potential causes
release of neurotransmitters.
a) True
b) False
true
Separate sensory cells are different from other
sensory receptors in that
a) Separate sensory cells are part of the first-order neuron
b) Separate sensory cells are part of the dendrites of first-order
neurons
c) When separate sensory cells are involved, first-order neurons are
not required
d) Separate sensory cells synapse onto first-order neurons
D
where are exteroceptors located? what do they do
(outside)
◦ Located near surface of body
◦ receive external stimuli
◦ hearing, vision, smell, taste, touch, pressure, pain, vibration & temperature
where are interoceptors located? what do they do?
(inside)
Located in and monitor internal environment (BV, viscera, muscles, nervous
system)
◦ not consciously perceived except for pain or pressure
where are proprioceptors found and what do they do?
Located in muscles, tendons, joints & inner ear
◦ sense body position & movement
what do mechanoreceptors detect?
◦ detect mechanical stimuli (eg. deformation, stretching, bending)
◦ touch, pressure, blood pressure, vibration, proprioception, hearing and equilibrium
what do thermoreceptors detect
changes in temperature
what do nociceptors detect
damage to tissue = pain
what do photoreceptors detect?
light
what do chemoreceptors detect
molecules
taste, smell and changes in body fluid chemistry
what do osmoreceptors detect?
detect osmotic pressure in fluids
how do most sensory receptors exhibit adaptation
the tendency for the generator or receptor potential to decrease in amplitude
during a maintained constant stimulus
◦ because of adaptation, the perception of a sensation may fade or disappear
even though the stimulus persists
what are the different types of variability in the tendency to adapt?
◦ Rapidly adapting receptors (eg. smell, pressure, touch)
◦ specialized for detecting changes in a stimulus
◦ Slowly adapting receptors (eg. pain, body position)
◦ nerve impulses continue as long as the stimulus persists – Pain is not easily
ignored
Which of the following primarily consists of
slowly adapting sensory receptors?
a) Body position
b) Touch
c) Pressure
d) Smell
A) body position
Which of the following somatic sensations
has an encapsulated nerve ending as its
sensory receptor?
a) tickle
b) pain
c) heat or cold
d) pressure
e) itch
d) pressure
what are the different types of somatic sensations
- TACTILE SENSATIONS
- THERMAL SENSATIONS
- PAIN SENSATIONS
- PROPRIOCEPTIVE SENSATIONS
describe the corpuscle of touch (Meissner corpuscle)
what doe they detect
Corpuscle of touch (Meissner corpuscle) are
encapsulated nerve endings located in the dermal
papilla of hairless skin (fingertips, hands, eyelids,
tip of tongue, lips, nipples, soles, clitoris and tip of
penis). They are sensitive and rapidly adapting
Detect: pressure, lower-frequency vibrations
describe the hair root plexuses
what do they detect?
Hair root plexuses are rapidly adapting free
nerve endings wrapped around hair follicles
(dermis).
They detect hair movements, itch, tickle sensations
Type I cutaneous mechanoreceptors (Merkel tactile discs)
what do they detect?
Type I cutaneous mechanoreceptors (Merkel
tactile discs) are slowly adapting free nerve
endings located in the dermal papilla (fingertips,
hands, lips, external genitalia). They make contact
with Merkel cells from the stratum basale
Detect: pressure, itch, tickle
type II cutaneous mechanoreceptors (Ruffini corpuscles)
Type II cutaneous mechanoreceptors (Ruffini
corpuscles) are slowly adapting
encapsulated nerve endings located deep in
the dermis, ligaments and tendons. Sensitive
to stretching as digits and limbs move.
define pressure
involves sustained deformation in deep tissues felt over larger area than touch
describe lamellated (Pacinian) corpuscles
what do they detect?
Lamellated (Pacinian) corpuscles are encapsulated
nerve endings widely distributed in the body (deep in
the dermis and subQ layer; mucous and serous
membranes; joints, tendons, muscles; periosteum;
mammary glands, external genitalia and some viscera
Detect: higher-frequency vibrations
define vibration
involves rapidly repetitive sensory signals from tactile receptors
define itch
stimulation of free nerve endings by certain chemicals (often released during an
inflammatory response)
define tickle
stimulatikon of free nerve endings that occurs only when someone else touches you
what is phantom limb sensations
When sensations (often pain) are coming from an amputated limb (which,
obviously, isn’t there)
Could be due to sectioned neurons remaining in the stump, which get activated
Could be due to rewiring of the brain, leading to stimulations from other parts of
the body being perceived as coming from the amputated limb
Traditional pain medicine ineffective
Alternative therapies more promising (mirror therapy, electrical nerve
stimulation, acupuncture, biofeedback)
Which somatic sensory receptor is rapidly
adapting and responsible for fine touch?
a) type I cutaneous mechanoreceptor
b) lamellated corpuscle
c) nociceptor
d) corpuscle of touch
e) type II cutaneous mechanoreceptor
d) corpuscle of touch
describe thermal sensations and where receptors are found
Free nerve ending receptors on the skin surface
◦ Cold receptors in the stratum basale (100C to 400C)
◦ Warm receptors in the dermis (320C to 480C)
Both adapt rapidly at first, but continue to generate impulses at a low frequency
Pain receptors rather than thermoreceptors are activated below 100C and over
480C
describe pain sensations. Which ones are the pain receptors?
Pain is a sensation necessary for survival – signals the presence of tissuedamaging conditions
◦ stretching, prolonged muscular contractions, muscle spasms, ischemia
Pain receptors (nociceptors) are free endings that are located in nearly every
body tissue (except brain)
◦ adaptation is slight if it occurs at all
what happens when tissue injury occurs
Tissue injury releases chemicals that stimulate nociceptors
◦ e.g. prostaglandins, kinins, potassium
◦ pain may remain even after stimulus is removed because chemicals are still
present
what is fast pain
◦ sharp, acute, pricking pain (needle puncture or cut)
◦ occurs rapidly after stimulus (.1 second)
◦ not felt in deeper tissues
◦ travels through large, fast-conducting nerve fibers
what is slow pain
◦ chronic, aching, burning or throbbing pain (eg. toothache)
◦ begins more slowly (1 sec) & increases in intensity
◦ in both superficial and deeper tissues
◦ travels through small, slow-conducting nerve fibers
what is superficial somatic pain
◦ Involves the stimulation of pain receptors in the skin
what is deep somatic pain
◦ Involves the stimulation of receptors in skeletal muscles, joints, and tendons
what is visceral pain
◦ Involves the stimulation of pain receptors in visceral organs; if stimulation is
diffuse (involves large areas), visceral pain can be severe. Can be due to
pressure, tears, ischemia, stretching, rubbing…
describe referred pain
Visceral pain is usually felt in specific skin or surface areas; skin area and organ
are usually served by the same spinal cord segment
e.g., heart attack can be felt in skin along left arm since both
are supplied by spinal cord segment T1-T5
a) Shoulder pain while throwing a baseball
b) Pain still present several minutes after stubbing your toe
c) “Brain freeze” (sharp headache upon eating or drinking
something cold)
d) Pain down your leg from a pinched nerve in your back
c) “Brain freeze” (sharp headache upon eating or drinking
something cold)
what are the different ways we can get pain relief
▪can block formation of chemicals that stimulate nociceptors (aspirin and
ibuprofen)
▪can block conduction of nerve impulses along pain fibers (Novocaine = local
anesthetic)
▪can lessen the perception of pain in the brain – pain is still sensed, but is not
perceived as noxious (Morphine)
what is proprioception
Awareness of body position & movement
◦ walking or getting dressed without looking
◦ estimate weight of objects (so can adjust necessary force)
Proprioceptors adapt only slightly
where is info about [roprioceptions sent to? What are the receptors?
Sensory information is continuously sent to cerebellum & cerebral cortex
◦ Receptors located in muscle, tendon, joint capsules & hair cells in the
vestibular apparatus
◦ Receptors include
1. Muscle spindles,
2. Tendon organs (Golgi tendon organs),
3. Joint kinesthetic receptors
describe proprioceptors: muscle spindles
Muscle spindles are proprioceptors
in skeletal muscles that monitor the
length of muscle fibers (participate
in stretch reflex)
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1. Stretching
stimulates
muscle spindle EFFECTOR (same
muscle) contracts
and relieves the
stretching
2. MOTOR NEURON excited
SENSORY
NEURON
excited
Within
3. INTEGRATING CENTER (spinal
cord)
Based on the input from muscle spindles, the brain
also sets muscle tone
what are the different components of a muscle spindle
- Sensory nerve endings
wrap around 3-10
specialized muscle fibers
(intrafusal fibers) - Alpha motor neurons innervate
extrafusal muscle fibers to cause
contraction of the muscle in
response to stretching - Gamma motor neurons
innervate intrafusal fibers to
keep tension and maintain
sensitivity of the muscle spindle
even when muscle is contracted
muscle spindle capsule (connective tissue)
how a muscle spindle works
- Sensory neurons monitor
the degree of stretching - Impulses are sent to the cerebral cortex (primary somatosensory
area) for conscious perception of position and movement; impulses
also sent to cerebellum for movement coordination - Motor neurons cause same muscle
to contract in response to stretching
(remember stretch reflex)
Muscle spindles
a) Are found in tendons
b) Are responsible for the stretch reflex
c) When stretched, lead to relaxation of the muscle
d) A and B
e) A, B and C
b) are responsible for the stretch reflex
proprioceptors: tendon organs
Tendon organs are
proprioceptors located at
the junction of tendons and
muscles (involved in tendon
reflex)
what are the components of a tendon organ
Tendon fascicles
(bundles of collagen
fibers) laced with
sensory nerve endings
Capsule of
connective tissue
how does a tendon organ work
- Sensory nerve endings detect
overstretching in the tendon (too
much tension in muscle) - Impulses are sent to the cerebral
cortex for conscious perception of
position and movement; impulses
also sent to cerebellum for
movement coordination - Motor neuron is
inhibited so muscle
can relax (remember
tendon reflex)
proprioceptors: joint kinesthetic receptors
Type II cutaneous mechanoreceptors (Ruffini corpuscles)
◦ found in joint capsule
◦ respond to pressure
Small lamellated (Pacinian) corpuscles
◦ found in connective tissue around the joint
◦ respond to acceleration & deceleration of joints
what are the sensory, motor and integrative pathways
In general, pathways are:
1. Paired - located bilaterally
2. Axons are grouped based on body region innervated (recall nerves)
3. All tracts involve the Brain and the Spinal cord
4. The name of a pathway indicates its origin and its destination:
e.g. spinothalamic
e.g. vestibulospinal
sensory information ______
motor information ________
pathways are made of ______ and nuclei
synapses are the site at which ________ of information will occur
ascends, descends, tracts, transfer / integration
true or flase: how many synapses a pathway has will depend on the type of pathway
How many synapses a pathway has will depend on the type of pathway
◦ Examples:
◦ Sensory pathways that end in the cortex have three neurons
◦ Sensory pathways that end in the cerebellum have two
what are somatic sensory pathways and what do they consist of?
Somatic sensory pathways relay information from somatic receptors to the
primary somatosensory area in the cerebral cortex.
The pathways consist of three neurons
◦ first-order neuron – from somatic receptor to spinal cord or brain stem
◦ second-order neuron – from spinal cord or brain stem to thalamus (opposite
side because of decussation)
◦ third-order neuron – from thalamus to primary somatosensory area of cortex
(on same side as thalamus)
In the posterior column medial lemniscus
pathway, first-order neurons…
a) synapse with second-order neurons in the thalamus
b) synapse with third-order neurons in the thalamus
c) synapse with second-order neurons in the pons
d) synapse with second-order neurons in the medulla
D
Which sensation is not carried by the posterior
column-medial lemniscus pathway?
a) Proprioception
b) Vibration
c) Temperature
d) Fine touch
c) temperature
describe the anterolateral (spinothalamic) pathway to the cortex
info is sent to primary somatosensory area of cortex
second-order neurons and third-order neurons synapse in the thalamus
first-ord3er neurons and second order neurons synapse in the posterior gray horn of the spinal cord
second order-neurons deccusate to the other side of the spinal cord
(at the bottom) receptors for pain, cold, warmth, tickle and itch
describe the trigemino-thalamic pathway to cortex (think how info would travel when the sun is on you face)
inform,ation is sent to the primary somatosensory area of cortex
second-order neurons and third-order neurons synapse in the thalamus
first-order neurons and second-order neurons synapse in the pons of medulla
(in trigeminal nerve) receptors for touch, pressure, vibration, pain, cold, warmth, itch and tickle in the face, nasal cavity and teeth
second order neurons deccusate to the other side of the brain stem
describe the sensory pathways to the cerebellum
(in the posterior spinocerebellar tract) axon collaterals of proprioceptive sensory neuros use the posterior and anterior spinocerebellar tracts to carry singlas into the cerebellum (not consciously perceived)
(these are essential for posture, balance and coordination of skilled movements)
describe the two neuron pathway of the sensory pathways to the cerebellum (where are the receptors)
Receptor → 1
st order neuron →
poterior grey horn → 2
nd order neuron
Signal travels up to same side of body
(no decussation)
receptors are: muscle spindle and Golgi tendon organ
In sensory pathways to the cortex…
a) the second-order neuron is always the one that decussates
b) decussation always takes place in the medulla
c) decussation always takes place in the thalamus
d) A and B
e) A, B and C
A
describe somatic motor pathways. What 2 motor neurons are always involved?
what is the final common pathways
Always involve 2 motor neurons in series
* Upper Motor Neuron (UMN): cell body in the CNS motor area (80% in cortex;
20% in brainstem)
* Lower Motor Neuron (LMN): extends from the brain stem or spinal cord to
innervate skeletal muscles
FINAL COMMON PATHWAY
* From brainstem through cranial nerves to innervate muscles of face and
head
* From spinal cord through spinal nerves to innervate muscles of limbs
and trunk
where to lower motor neurons extend directly to
Lower Motor Neurons (LMN)
extend directly from the CNS
(where their cell bodies are)
to skeletal muscles
for somatic motor pathways what does contol of body movement involve?
◦ Control of body movement involves:
◦ Motor portions of cerebral cortex
◦ Initiate & control precise movements
Basal nuclei help establish muscle tone & integrate semi-voluntary automatic
movements
Cerebellum helps make movements smooth & helps maintain posture &
balance
what are basal nuclei
The basal nuclei are 3
nuclei deep within each
hemisphere:
Caudate
nucleus
Putamen
Globus
pallidus
what are the 4 distinct neural circuits (somatic motor pathways - they always tell each other what to do) participate in control of movements by providing input to lower and upper motor neurons
- Local circuit neurons are located close to lower motor neuron cell bodies
in the brain stem and spinal cord. - Local circuit neurons and lower motor neurons receive input from upper
motor neurons. - Neurons of the basal ganglia provide input to upper motor neurons.
- Cerebellar neurons also control activity of upper motor neurons.
In somatic motor pathways…
a) all pathways ultimately lead to the activation of the basal nuclei
b) all pathways ultimately lead to the activation of the cerebellum
c) all pathways ultimately lead to the activation of lower motor
neurons
c) all pathways ultimately lead to the activation of lower motor neurons
where are local circuit neurons located and what do they do?
Local circuit neurons are located close
to LMN cell bodies (in spinal cord or
brain stem); they coordinate rhythmic
activities (like alternating flexion and
extension of lower limb muscles when
walking). They receive input from
sensory neurons as well as from
higher centers in the brain.
Local circuit neurons…
a) are neurons located in the basal nuclei
b) are neurons located in the cerebral cortex
c) are neurons located near lower motor neurons
c) are neurons located near lower motor neurons
describe upper motor neurons
UMN from cortex are
involved in planning,
initiating and
directing movements.
Most UMN synapse onto
local circuit neurons, and
some of them synapse
directly onto LMN. They
receive input from the
basal nuclei and the
cerebellum.
UMN from brain
stem regulate muscle tone,
posture, orientation of head and body
Upper motor neurons…
a) can descend from the brainstem or from the cerebral cortex
b) can synapse onto local circuit neurons or onto lower motor
neurons
c) a and b
C
describe basal nuclei neurons
Basal nuclei neurons provide
input to UMN (in cortex or
brain stem); neural circuits
interconnect the basal nuclei,
the cerebral cortex and the
brainstem. Help initiate and
terminate movements,
suppress unwanted
movements and set normal
level of muscle tone
The basal nuclei…
a) influence upper motor neurons in the cortex or brain stem
b) communicate directly with lower motor neurons
c) a and b
a) influence upper motor neurons in the cortex or brain stem
what is the difference between the upper motor neurons from direct motor pathways and UMN from indirect motor pathways
UMN from direct motor pathways extend directly from the cerebral cortex to LMN
UMN from indirect motor pathways extend from various nuclei of the brainstem and will use various tracts before they connect with LMN
in both direct and indirect motor pathways, the basal nuclei and the cerebellum influences the UMN
direct motor pathways: describe the lateral corticospinal pathway
for movements of hands and feet (highly skilled movements) from cortex, through cerebral peduncles, 90% of UMN deccusate in the pyramids of medulla
the lateral corticospinal tract forms in the lateral part of the SC
UMN synapse either with local circuit neurons
or with LMN in anterior gray horn of SC
LMN exit through anterior root of spinal nerve
direct motor pathways: describe the anterior corticospinal pathway
The anterior corticospinal pathway is
for movements of the trunk and
proximal parts of limbs
The remaining 10% of UMN that
do NOT decussate in the
pyramids use this tract
Decussation occurs in the spinal cord, just
before synapsing with local circuit neurons
or LMN in anterior gray horn of SC
direct motor pathways: corticobulbar pathway
The corticobulbar pathway is for
movements of skeletal muscles
in head: eyes, tongue, neck,
chewing, expression & speech
from cortex to nuclei in brain stem,
then cranial nerves: all but I, II and VIII
(because these are sensory nerves)
Some decussate,
others don’t
Most motor neurons from direct motor
pathways are dedicated to…
a) Movements of hands and feet
b) Movements of facial muscles
c) Movements of trunk and proximal part of limbs
d) a and b
a) movements of hands and feet
describe indirect pathways
All motor pathways other than the
corticospinal and corticobulbar tracts
Axons from UMNs descend from various
nuclei in brainstem into 5 major tracts of
spinal cord
synapse w/ local circuit neurons or LMNs
describe the different basal nuclei connections
- Basal nuclei influence movements through
their effect on UMN
◦ Input from cortex (sensory, motor,
association) and substantia nigra (midbrain)
◦ Output to cortex via thalamus
◦ Cortex to basal nuclei to thalamus to cortex
– involved in initiating and terminating
movements - Basal nuclei reduce muscle tone
– damage causes a generalized increase in muscle tone - Basal nuclei suppress unwanted movements
describe how the cerebellum modulates movement
The cerebellum is active in both learning and performing rapid, coordinated,
highly skilled movements and in maintaining proper posture and equilibrium.
The four aspects of cerebellar function
◦ Monitoring intention for movement
◦ Monitoring actual movement
◦ Comparing intention with actual performance
◦ Sending out corrective feedback
what are the integrative functions of the cerebrum
SLEEP & WAKEFULNESS
LEARNING AND MEMORY
sleep vs wakefullness
Sleep - a state of altered consciousness or partial
unconsciousness from which an individual can be
aroused by different stimuli
During wakefulness, the cerebral cortex is very active
During most stages of sleep, less activity is seen in the
cerebral cortex
what does the reticular activating system (RAS) do?
Sleep and wakefulness are
controlled by the reticular
activating system (RAS), found
in the reticular formation
RAS has numerous connections to
the cortex; Arousal involves
increased activity in the RAS, which
increases activity in the cortex
Many types of inputs can activate
the RAS: pain, light, noise, muscle
activity, touch (but not smell)
describe sleep
During sleep, activity in the RAS is very low
◦ Adenosine is a sleep-inducing chemical in the brain that inhibits activity in RAS
◦ caffeine binds to adenosine receptors, thereby preventing adenosine from
binding and inducing sleep
Normal sleep consists of two types:
◦ non-rapid eye movement sleep (NREM)
◦ inactive brain, active body
◦ rapid eye movement sleep (REM)
◦ active brain, inactive body
describe REM sleep
Most dreams occur during REM sleep
3-5 episodes of REM in a 7-8 hour sleep, increasing in length (first ~10min, last ~50min)
◦ total REM sleep = 90 to 120 minutes
Total REM & dreaming time decreases with age
◦ ~80% REM in newborns
◦ ~50% REM in infants
◦ ~35% REM in 2yo
◦ ~25% REM in adults
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* Neuronal activity & oxygen use is highest in REM sleep
(higher than during intense mental or physical activity!)
* Motor neurons are inhibited (except for breathing and
eye movements) = paralysis of skeletal muscles
* REM thought to be important for proper brain
development and function
learning vs memory
Learning is the ability to acquire new information or skills
through instruction or experience
Memory is the process by which that information is stored and
retrieved
For an experience to become part of memory, it must produce
persistent structural and functional changes that represent the
experience in the brain
◦ The capability for change with learning is called PLASTICITY
what are the different types of memory
Declarative memory vs Procedural memory
Short-term memory lasts only seconds or minutes and is the ability to recall
bits of information; changes in synapses
Long-term memory lasts from hours, days to years and is related; anatomical
and biochemical changes at synapses
◦ Long-term memory for information that can be verbalized is stored in
cerebral cortex
◦ Long-term memory for motor functions stored in basal ganglia, cerebellum
and cortex
what are the different stages of sleep (not super important)
Stage 1
◦ person is drifting off with eyes closed (first few minutes)
Stage 2
◦ person becomes increasingly harder to awaken
Stage 3
◦ relaxed, deep sleep, body temperature & BP drop, reflexes and muscle tone
are intact
◦ bed-wetting & sleep walking occur in this phase
Note: stages 3 used to be separated into stages 3 and 4
Sleepwalking occurs in which stage of nonrapid eye movement (NREM) sleep?
a) stage 1
b) stage 2
c) stage 3
d) None of these – it occurs during REM sleep
C
when do you get the greatest amount of deep sleep
Cycles of N1 → N2 → N3 → N2 → REM. There is a greater amount of
deep sleep (stage N3) earlier in the night, while the proportion of REM
sleep increases later in the night, in the cycles before natural awakening
