CNS Pt2 1 Flashcards
(238 cards)
1
Q
What are the four somatic senses?
A
- Touch
- Temperature
- Proprioception
- Nociception
2
Q
What is proprioception, and can you sense it with your eyes closed?
A
- Awareness of body part position relative to each other
- Yes
- Like knowing how much your elbow is flexed
3
Q
What does proprioception allow us to do?
A
Move through the world with seamless coordination
4
Q
What does nociception detect and how is it perceived?
A
- Detects tissue damage or the threat of it
- Perceived as pain or itch
5
Q
What type of nerve endings are nociceptors, and what do they respond to?
A
- Free nerve endings that respond to noxious stimuli
- Like damaging mechanical stimuli, heat, or chemicals
6
Q
What chemicals from damaged cells and platelets can activate nociceptors?
A
- K⁺
- Histamine
- Prostaglandins (from damaged cells)
- Serotonin (from platelets)
7
Q
What system do nociceptors act as, and do they detect potential or actual harm?
A
- Act as an early warning system
- Detect both potential and actual harm
8
Q
Are nociceptors tuned to specific harmful stimuli?
A
Yes
9
Q
What type of nerve endings are thermoreceptors, and how many types are there?
A
- Free nerve endings, with two types:
1. Cold receptors
2. Warm receptors
10
Q
At what temperatures do cold and warm receptors respond maximally?
A
- Cold receptors respond maximally around 30°C
- Warm receptors around 45°C
11
Q
What is paradoxical cold and why does it occur?
A
- A hot object briefly feeling cold
- Cold fibers respond briefly to temperatures > 45°C
12
Q
Do we have more cold or warm receptors, and is precise localization crucial for temperature?
A
- More cold receptors
- Precise localization is not crucial for temperature
13
Q
What type of cells are somatosensory receptors, and where are their cell bodies located?
A
- They are neurons
- Their cell bodies for sensation below the chin are located in the dorsal root ganglia
- For sensation from the head, in the brain
14
Q
Where do these neurons transduce physical stimuli into electrical signals, and where are the nerve endings found?
A
- They transduce stimuli at their nerve endings
- Found in the tips of their fibers in the skin and viscera
15
Q
What is transduction?
A
Converting physical stimuli into electrical signals
16
Q
What do afferent fibers do?
A
Carry signals from receptors to the spinal cord
17
Q
What type of receptors are Meissner and Pacinian corpuscles, and what are encapsulated receptors sheathed in?
A
- Meissner and Pacinian corpuscles: encapsulated mechanoreceptors
- Encapsulated receptors are sheathed in connective tissue
18
Q
What do free nerve endings detect, and are they encapsulated or unencapsulated?
A
- Detect mechanical stimuli, temperature, and chemicals
- They are unencapsulated
19
Q
What are Merkel receptors also called, where are they found, and what is their shape?
A
- Also called Merkel disks
- Found at the bottom of the epidermis
- Saucer-shaped
20
Q
What kind of cells are Merkel disks in contact with?
A
- In contact with Merkel cells, which are specialized epithelial cells
21
Q
What are Merkel disks sensitive to and what type of response do they have (tonic or phasic)?
A
- Sensitive to skin deformation
- Sensitive to fine detail
- Sensitive to steady pressure
- More tonic than phasic
22
Q
What kind of message do Merkel disks send with sustained stimulation, and what do they signal?
A
- Send a sustained message with sustained stimulation
They signal:
1. Contact
2. Continuous pressure
3. Steady touch
23
Q
What is an example of something Merkel disks help you feel, and what is their primary function?
A
- Help you feel holding something in your hand
- Their primary function is signaling contact
24
Q
Where are Meissner corpuscles located, and what shape are they?
A
- At the top of the dermis in hairless skin
- Egg-shaped
25
What areas of the body have many Meissner corpuscles?
- The tongue
- Palms
- Fingertips
26
What kind of nerve endings are inside Meissner corpuscles?
Contain many looping nerve endings
27
What type of force do Meissner corpuscles detect, and what is an example of this?
- Detect sideways shearing, such as:
- Stroking a surface
- Lifting something with your fingertips
28
Are Meissner corpuscles tonic or phasic, and what do they sense?
- Phasic
- Sense changes in shear
29
Where are Pacinian corpuscles found, and what is their distinctive shape?
- Found deep in the dermis or subcutaneous tissue
- Have an onion-shaped structure
30
What are Pacinian corpuscle nerve endings sheathed in?
Many layers of connective tissue
31
What kind of displacements can Pacinian corpuscles sense if the motion is quick?
Sense tiny displacements
32
Are Pacinian corpuscles tonic or phasic, and what does being phasic mean for their response?
- Phasic
- Meaning they respond strongly to rapid changes
33
What type of stimuli do Pacinian corpuscles respond strongly to, and what makes them ideal for detecting these?
- Respond strongly to vibration and other fast-changing stimuli
- Making them ideal due to their sensitivity to fast transient changes
34
What type of mechanoreceptors are most common, and how do phasic receptors respond to sustained stimuli?
- Phasic mechanoreceptors are most common
- Depolarize but quickly return to baseline when the stimulus is sustained
35
Approximately how fast do phasic receptors return to baseline?
About ~3 milliseconds
36
What do phasic receptors register, and when do you perceive more from them?
- Changes in stimulation
- You perceive more when the stimulation is changing
37
What happens to sensation when your hand stops moving on a surface, and why do you rarely notice constant pressure like clothes on your skin?
- You sense far less
- Because phasic receptors adapt quickly
38
What does the phasic response help the nervous system focus on?
- Helps focus on what's new
39
Are somatosensory receptors distributed evenly across the body?
No
40
Which body areas have more densely packed receptors, and what are these areas called?
- Palms
- Fingertips,
- Lips
- Called the foveas
41
What does a higher density of receptors lead to, and what test measures somatosensory acuity?
- Higher receptor density = higher acuity
- The two-point discrimination test measures this acuity
42
How far apart can fingertips distinguish two points, and how far apart do points need to be on the calves to be distinguished?
- Fingertips: Two points 2–4 mm apart,
- Calves: About 40 mm apart
43
What does the result of the two-point discrimination test depend on?
Depends on the density of sensory receptors in the area
44
What carries signals from receptors to the CNS, and how many groups do somatosensory afferents fall into?
- Somatosensory afferent fibers carry signals
- Fall into two groups:
1. Small fibers
2. Large fibers
45
What are the two types of small fibers, and are they myelinated?
1. C fibers (unmyelinated)
2. Aδ (A-delta) fibers (myelinated)
46
What are the conduction speeds of C fibers and Aδ fibers?
1. C fibers: up to 2 m/s
2. Aδ fibers: up to 30 m/s
47
What types of stimuli do small fibers respond to, and what kinds of responses do they evoke?
- Mechanical stimuli
- Chemicals
- Temperature
- Evoke simple responses to specific stimuli
48
Give examples of responses evoked by small fibers.
- Withdrawing from pain
- Brushing away a bug
- Thermoregulatory and sexual responses
49
Do small fiber responses require immediate input from the brain?
- No
- Many responses are processed in the spinal cord
50
What does the anatomy of small fibers reflect?
- Quick
- Localized
- Often protective responses
51
What are the large fibers called, and are they myelinated?
- Aβ (A-beta) fibers
- Myelinated
52
What is the conduction speed of Aβ fibers?
Up to 70 m/s
53
Where do Aβ fibers originate from?
- Merkel disks
- Or encapsulated mechanoreceptors like Meissner or Pacinian corpuscles
54
What is the primary function of Aβ fibers, and why must they conduct signals quickly?
- Provide rapid feedback to the brain, especially for object manipulation
- Must conduct quickly because their signals travel long distances to reach the brain promptly
55
Are large fibers associated with rapid or slow feedback?
Rapid feedback
56
Where do large fibers travel upon reaching the spinal cord, and where do they synapse and cross the midline?
- Large fibers ascend ipsilaterally in the dorsal columns
- They synapse and cross the midline in the medulla
57
Where do small fibers synapse in the spinal cord, where do they cross the midline, and what tracts do they ascend in after crossing?
- Synapse in the dorsal horn
- Cross the midline immediately in the spinal cord
- Ascend in the spinothalamic tracts
58
Where are the spinothalamic tracts located?
Lateral part of the spinal cord
59
Where do somatosensory signals go after the spinal cord, and what is the function of this structure?
- Signals pass through the thalamus
- Acts as a relay station for signals to the cortex
60
Which thalamic nucleus receives signals from below the chin, and which from the head?
- The ventroposterolateral (VPL) nucleus receives signals from below the chin
- The ventroposteromedial (VPM) nucleus receives signals from the head
61
Where do signals from the VPL and VPM nuclei go next?
To the primary somatosensory cortex (S1)
62
Where is the primary somatosensory cortex (S1) located, and what is its role?
- In the postcentral gyrus of the parietal lobe, just behind the central sulcus
- Its role is to integrate inputs from various receptors and create a cohesive sense of touch, proprioception, etc
63
Does S1 receive direct input from receptors?
- No
- Receives relayed input from the thalamus
64
What does S1 help create, and is this representation perfect?
- A mapped representation of the body surface called a somatotopic map
- The map is distorted based on receptor density and sensitivity
65
Which areas are overrepresented in the somatosensory cortex and why?
- Areas with high receptor density (the hands and lips)
- They transmit more detailed sensory information
66
How do neighboring skin areas project in the cortex?
Neighboring skin areas project to neighboring neurons in the cortex
67
What does lateral inhibition enhance in the somatosensory system, and how does it work?
- Enhances spatial contrast (edges and boundaries) by amplifying differences between adjacent areas
- Done through inhibition of neighboring neurons
68
What is a real-life example of lateral inhibition?
Sharp feeling at the edge of a hot bath’s waterline
69
What visual illusion is similar to lateral inhibition in somatosensation?
Chevreul illusion
70
What type of ion channels do many nociceptors and thermoreceptors have, and are these channels found in both?
- Many have transient receptor potential (TRP) channels
- Found in both nociceptors and thermoreceptors
71
What are TRPV1 channels also called, what do they respond to, and what chemical activates them?
- Vanilloid receptors
- Respond to damaging heat and chemicals like capsaicin
- The chemical in chili peppers that causes a burning sensation in the mouth
72
Do TRPV1 channels act as an alarm for dangerously high temperatures?
Yes
73
What do TRPM8 channels respond to, what ingredient activates them, and can they cause a sensation without an actual temperature change?
- Respond to cold and menthol
- Menthol activates them
- Yes, menthol can cause a cool sensation without an actual temperature decrease
74
What do nociceptive signals report and what sensations do they evoke?
- Damage or danger to the body
- Evoke pain or itch
75
What is congenital analgesia and why do people with it often die young?
- Rare condition where people cannot feel pain
- Leading to early death due to injury and infection
76
How many types of pain do we have, and what are they called?
1. Fast pain
2. Slow pain
77
Which type of pain is sharp and localized, which fibers carry it, and what response does it evoke?
- Fast pain is sharp and localized
- Carried by Aδ fibers
- Evokes quick withdrawal
78
Which type of pain is dull and more diffuse, which fibers carry it, and what response does it promote?
- Slow pain is dull and diffuse
- Carried by C fibers
- Promotes prolonged immobilization for healing
79
What is one immediate response triggered by nociceptive signals?
Withdrawal reflex
80
Is the withdrawal reflex a spinal reflex, does it require immediate input from the brain, and where is it processed locally?
- Yes, it is a spinal reflex
- Does not require immediate brain input
- Processed in the spinal cord
81
Which brain areas do nociceptive signals reach that cause emotional distress, and what other responses can they cause via these areas?
- Reach the limbic system and hypothalamus
- Causing emotional distress
- Nausea
- Vomiting
- Sweating
82
Can descending pathways modulate pain, and where do they originate from?
- Yes, descending pathways can modulate pain
- They originate from the brain stem
83
Through which structure can descending pathways block nociceptive cells in the spinal cord, and what is their purpose?
- The thalamus
- Their purpose is to block or reduce pain signals
84
When might descending pathways override pain perception?
- In emergencies where survival depends on ignoring pain
85
What is referred pain, and what causes it at the neural level?
- Pain in an internal organ that is felt on the body surface
- It occurs because nociceptors from different locations converge on a single ascending tract
86
Where do the converging nociceptors synapse, and what does the brain know about the pain source?
- Synapse on the same secondary neuron
- The brain doesn’t know exactly where the stimulus came from
87
Why does the brain interpret the pain as coming from the skin, and does the secondary neuron specify the exact location?
- Pain is more common in the skin than in internal organs
- No, the secondary neuron won’t specify the exact location
88
Is referred pain common, and what does the brain use to interpret the source?
- Yes, it is commonly discussed in medical contexts
- The brain makes an educated guess based on probability
89
What kind of signals are carried by the ascending tract involved in referred pain?
Nociceptive signals
90
Where is pain from the appendix typically felt?
- Rght side of the abdomen
91
What kind of pain is associated with kidney stones, and where can it radiate?
Flushing or radiating pain that can go down to the groin area
92
Where can pain from the liver and gallbladder be felt, and what nerve is involved in shoulder referral?
- The upper right quadrant of the abdomen
- Referred to the right shoulder via the phrenic nerve
93
What spinal segments are associated with the phrenic nerve and shoulder innervation?
C3 to C5
94
What is a well-known example of referred pain from the heart, and where is it typically felt?
- Myocardial infarction (heart attack)
- Typically felt as squeezing chest pain
95
Where else can heart attack pain be referred?
- The left arm
- Jaw/neck
96
What kind of nerve fibers from the heart converge with somatic fibers, and what spinal segments are involved?
- Visceral afferent fibers
- T1 to T5
97
Can referred pain from the heart sometimes only be felt in the jaw?
- Yes
- Make diagnosis challenging
98
What is pain gating, and what theory is it associated with?
- Pain can be gated or reduced by Aβ activity
- Associated with the gate control theory of pain
99
What types of fibers carry touch and injury signals?
- Aβ fibers carry touch signals
- C fibers carry injury signals
100
Where do C fibers contact secondary neurons, and what inhibits those neurons?
- In the dorsal horn
- Aβ fibers inhibit them via interneurons
101
What do Aβ fibers activate to inhibit C fibers, and what sensation do they help prevent?
- Activate an interneuron
- They help prevent oozing pain
102
What is an example of Aβ activity dampening pain?
Rubbing a sore shoulder
103
What is TNS, and how are non-painful stimuli perceived in chronic pain?
- TNS (transformed nociceptive system) is the dysregulation of pain modulation
- In chronic pain, non-painful stimuli are perceived as painful
104
What are analgesics, and how does Acetylsalicylic acid (aspirin) work?
- Drugs that relieve pain
- Aspirin inhibits prostaglandins and inflammation, which slows down pain signal transmission
105
What are examples of opioids, and how do they work at the neural level?
- Morphine and codeine
- They decrease transmitter release from primary sensory neurons and postsynaptically inhibit secondary neurons
106
What are examples of natural painkillers the body produces, and where are they made?
- Endorphins
- Enkephalins
- Dynorphins
- Produced in the brain and spinal cord
107
What are smell and taste both forms of, and is this a fundamental survival mechanism?
- Both forms of chemoreception
- A fundamental survival mechanism
108
Is chemoreception evolutionarily old or new, and which organisms use it?
- Old
- Organisms from bacteria to complex animals use chemoreception
109
What is hypothesized to have evolved from chemoreception?
Chemical synaptic communication
110
Where is the olfactory epithelium located and how large is it?
- At the top of the nasal cavity
- About 3 cm² on each side
111
How many receptor cells does the olfactory epithelium contain, and is it pigmented?
- Around 10 million receptor cells
- Yes, it is pigmented
112
What does the depth of the epithelium’s color correlate with, and what colors are seen in humans vs. cats?
- Correlates with olfactory sensitivity
- In humans, it is pale yellow
- In cats, dark mustard brown
113
What type of neurons are olfactory receptor cells, and how many dendrites do they have?
- Ciliated neurons
- One dendrite
114
Where does the dendrite extend, and what does it branch into?
- Into the olfactory epithelium
- It branches into non-motile cilia
115
What is the function of the nonmotile cilia, and do they move?
- Increase surface area to catch odorant molecules
- No, they do not move
116
What type of receptor molecules are in the membrane of these cells, and how many does each express?
- G protein-coupled receptors (GPCRs)
- Each cell expresses one type
117
How many kinds of olfactory receptor cells do humans have, and what are these called?
- About 400 kinds
- Called primary odors
118
How sensitive can one olfactory receptor cell be?
Ccan detect a single molecule of its preferred chemical
119
What is notable about the olfactory receptor gene family in vertebrates?
The largest known gene family
120
How many olfactory receptor genes exist in the vertebrate genome, and what percent of the human genome do they represent?
- Around 1000 genes
- Making up about 3–5% of the human genome
121
How many of these genes are actually expressed in humans?
About 400
122
What is the lifespan of an olfactory receptor cell, and how are they replaced?
- About 1–2 months
- New receptor cells grow from below
123
Is this kind of neuron regeneration in olfaction common in the nervous system, and what does it suggest?
- No, it's unusual
- Suggests potential for healing other injuries in the nervous system
124
What happens when an odorant binds to its receptor, and what G protein is activated?
- G_olf is activated
- Which increases local cAMP concentration
125
What opens in response to increased cAMP, and what does this cause?
- cAMP-gated cation channels open
- Causing depolarization of the receptor neuron
126
What does depolarization trigger, and where does it go?
- Triggers an action potential
- Travels along the axon to the olfactory bulb
127
What unusual property do olfactory receptor cells have involving fluid?
- Pinocytotic
- They continuously sip fluid
128
Where is this fluid sent, and do we know why they sip it?
- Sent along nerves into the brain
- The purpose is unknown
129
Are these receptor molecules found only in the nose?
No, some are also expressed in the skin
130
Through what structure do olfactory axons enter the brain?
The cribriform plate
131
What is the cribriform plate, and what bone is it part of?
- The bone at the base of the cranial cavity with tiny holes
- Olfactory axons pass through it
132
What can damage to the cribriform plate and nerve fibers lead to?
Anosmia — loss of the sense of smell
133
What is the projection from receptors to the bulb called, and which cranial nerve is it?
- The olfactory nerve
- Cranial Nerve I
134
Is the olfactory nerve part of the Peripheral or Central Nervous System?
PNS
135
What is the olfactory nerve considered in terms of brain-environment connection?
A peripheral link
136
Where do the axons from olfactory receptor cells project, and what happens there?
- Project to the olfactory bulb
- They synapse with secondary neurons
137
Where is the olfactory bulb located, and what is it an extension of?
- The underside of the frontal lobes
- An extension of the cerebrum
138
Where do the secondary neurons carry information, and what path does it follow?
- Deeper into the brain
- Specifically, to the olfactory cortex
139
What is unique about the olfactory pathway compared to other sensory systems?
- It bypasses the thalamus
- Goes directly to the cortex
140
Where is the olfactory cortex located?
In the frontal and temporal lobes — between them
141
What happens with many receptor cells in the olfactory bulb, and what is the consequence?
- Converge on each bulb neuron
- Enhances sensitivity but sacrifices spatial information
142
What does this convergence prioritize, and what does it make difficult?
- Prioritizes detecting faint smells
- Makes pinpointing the exact location of a smell difficult
143
Are humans skilled at localizing smell, and can they track scents?
- No, not particularly skilled
- Can track scents under the right condition
144
What other brain system does the olfactory bulb project to, and what is it involved in?
- The limbic system
- Involved in motivation and emotion
145
What areas of the limbic system receive olfactory input?
- The cingulate gyrus
- The hippocampus
- The amygdala
146
What does the connection to the limbic system explain about smells?
Why odors can evoke strong emotional memories
147
How does olfaction adapt, and why is this useful?
- Slowly but completely
- Filters out background odors so we can focus on new ones
148
What kind of odors does adaptation help us focus on, and what’s an example?
- New odors
- Like smoke signaling danger
149
What are pheromones?
Chemicals released by an animal that affect others of the same species
150
What organ in rodents detects pheromones and what does it do?
- The vomeronasal organ (VNO)
- Involved in behavioral responses to sex pheromones
151
Is the VNO functional in adult humans?
- No
- Disappears during fetal development
152
Do humans still respond to airborne chemical signals?
- Yes
- Though responses are weaker and less specialized than true pheromone responses
153
Where are most taste receptor cells clustered, and how many do humans have?
- In taste buds
- About 5,000 in humans
154
Where are taste buds located?
- Mostly on the top of the tongue
- Also on:
- The soft palate
- The epiglottis
- The upper esophagus
155
What is the lifespan of a taste bud, and how many receptor cells does each have?
- About 10 days
- Each has around 100 receptor cells
156
Are taste receptor cells neurons, and how are they arranged?
- No
- Specialized epithelial cells
- Arranged like petals
157
What is the taste pore?
A small opening through which receptor cells contact the oral cavity
158
How many kinds of receptor cells are in a typical taste bud, and what do they detect?
- At least five
- Each detecting one basic flavor
159
What are the five basic flavors and what do they detect?
1. Sweet: Sugar (energy)
2. Umami: Glutamate (protein)
3. Bitter: Poisons
4. Salty: Na⁺
5. Sour: H⁺
160
Might the tongue also have receptors for fatty acids?
- Yes
- Important for nutrients and survival
161
Are all five taste receptors found all over the tongue?
Yes
162
How many major types of taste receptor cells are there, and what does each do?
1. Type I: Likely sense salt
2. Type II: Sense sweet, bitter, and umami
3. Type III: Sense sour
163
Which type of taste cell forms synapses with sensory neurons and what neurotransmitter does it use?
- Only Type III cells form synapses
- They use serotonin
164
What do Type II cells release, and what does it act on?
- Release ATP
- Acts on neurons and Type III cells
165
What receptors do sweet, umami, and bitter taste cells use, and what G protein is involved?
- Use G protein-coupled receptors (GPCRs)
- The G protein gustducin
166
What happens when gustducin is activated?
- Intracellular Ca²⁺ increases
- Triggering ATP release
167
How are salty and sour tastes detected, and do these receptors involve G proteins?
- Detected by ion channels
- Do not involve G proteins
- These channels allow for a rapid, direct response
168
Do different receptor cells use different mechanisms for taste detection?
- Yes—GPCRs are used for sweet, umami, and bitter
- Ion channels are used for salty and sour
169
Which cranial nerves carry taste information, and where do taste signals first synapse?
Cranial nerves VII (facial - 7)
- IX (glossopharyngeal - 9)
- X (vagus - 10) carry taste info
- Signals first synapse in the medulla
170
Where do taste signals go after the medulla, and what is the final processing area?
- Signals go to the thalamus
- Then to the gustatory cortex, which processes and interprets taste
171
Which cranial nerve detects texture, spice, and coolness in the mouth?
Cranial nerve V (trigeminal nerve - 5)
172
What other senses affect taste perception?
- Smell
- Texture
- Temperature
- Pain
- Crunch
- Appearance
- Cognition
173
What role does smell play in taste perception?
aroma strongly influences flavor perception
174
What channels detect temperature and chemicals in the mouth, and what do specific types detect?
TRP channels:
- Vanilloid receptors detect heat and capsaicin (from chili peppers)
- TRPM8 channels detect cold and menthol
175
Are chemoreceptors only found in the mouth?
Also found in the stomach and intestine
176
What do gut chemoreceptors monitor, and do some resemble taste receptors?
- Monitor stomach and intestinal contents
- Some resemble taste receptors, including those for sweet and umami
177
Does sensory input from food continue after swallowing?
- Yes
- Gut receptors continue to influence perception
178
Where are the hypothalamus and pituitary gland located in the brain?
Diencephalon region
179
What gland lies directly beneath the hypothalamus, and is it above or below the hypothalamus?
- Pituitary gland
- Below the hypothalamus
180
What structure near the hypothalamus and pituitary is involved in vision?
The optic chiasm
181
What vital connection does the hypothalamus form, and what is the core of its regulation?
- Connects the brain and endocrine system
- With negative feedback at its core
182
What does negative feedback process and why?
- Chemical and neural signals
- Monitor internal functions and detect disturbances
183
What happens when the hypothalamus detects a disturbance?
Initiates corrective action to restore balance
184
What is the goal of homeostasis, and what’s an example of a regulated factor?
To keep internal conditions roughly constant (e.g., plasma osmolality)
185
Do all hypothalamic systems maintain constant states?
- No
- Some, like circadian rhythms, vary through time
186
Do hypothalamic nuclei only send signals outside the brain?
- No
- Send neural signals to each other
187
Does the hypothalamus have bidirectional communication?
Yes
188
Which neurons send axons to the posterior pituitary?
- Magnocellular neurons from the paraventricular and supraoptic nuclei
189
What are Herring bodies?
Bulges along axons that store neurosecretory materials
190
What does the hypothalamus release to control the anterior pituitary, and how do these hormones reach it?
- Releases releasing hormones
- Travel to the anterior pituitary via the hypophyseal portal system, a specialized network of capillaries
191
What do releasing hormones trigger, and where are anterior pituitary hormones made?
- Trigger the anterior pituitary to release its own hormones
- Which are made in the anterior pituitary itself
192
What do parvocellular neurons signal to, and what is the benefit of this vascular route?
- The medial capillary complex in the median eminence
- The two-step vascular route allows for precise control using small amounts of releasing hormones
193
How do mice regulate calorie intake with varying nutrient concentrations?
- Adjust food intake to maintain consistent caloric intake
194
What happens to mice with ventromedial hypothalamus (VMH) lesions versus lateral hypothalamus (LH) lesions?
- VMH lesions → overeating and obesity (“Very Much Hungry when lesioned.”)
- LH lesions → reduced eating and thinness (“Lacks Hunger when lesioned.”)
195
Which hypothalamic nucleus controls the VMH and LH, and where are they located?
The arcuate nucleus (ARC) controls both
- VMH is located ventral and medial to the ARC
- LH is located laterally, along the outer edges of the hypothalamus
196
What is the function of the arcuate nucleus (ARC), and what are its two main neuron types?
The ARC integrates hunger and satiety signals as a first-order sensor
- It contains:
1. NPY/AgRP neurons (promote hunger)
2. POMC neurons (promote satiety)
197
What is the function of NPY/AgRP neurons, and what is a mnemonic to remember it?
- Drive hunger (orexigenic)
- Mnemonic: “Need Plenty of Yummies!”
198
When is the arcuate NPY system active, and what does it encourage?
- Active during fasting, and it encourages feeding
199
What neurotransmitters and peptides do NPY neurons release, and what kind of molecule is GABA?
- Release neuropeptide Y (NPY), GABA
- Some release Agouti-related peptide (AgRP)
- GABA is a classic inhibitory neurotransmitter
200
Where do arcuate NPY neurons project, and which nucleus do they inhibit?
- Project to the paraventricular nucleus (PVN) and lateral hypothalamus (LH)
- They inhibit the PVN
201
What is the PVN, what mnemonic is used, and what signals do NPY neurons send to it?
- A satiety or anorexigenic center
- “Pasta – Very No, thank you!”
- NPY neurons send it inhibitory signals
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What happens when PVN activity is inhibited?
- It reduces sympathetic nervous system activity
- Disinhibits feeding
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What system does the PVN normally excite, and what is the result of decreased PVN activity?
- Excites the sympathetic nervous system
- Decreased activity → less sympathetic tone → more feeding
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Which nucleus is excited by NPY neurons, and what does it do?
- Lateral hypothalamus (LH)
- A feeding/motivation center
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What kind of signals do NPY neurons send to the LH, and what does the LH release?
- Excitatory signals
- LH releases orexin (hypocretin)
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What are the effects of orexin, and what else does it regulate?
- Inhibits the PVN and stimulates feeding
- Also regulates sleep, wakefulness, and appetite
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Where is orexin produced, and what kind of molecule is it?
- Produced in the hypothalamus
- A neuropeptide hormone
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What is the overall effect of arcuate NPY neurons on feeding?
Promote feeding by inhibiting satiety signals and stimulating hunger pathway
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How do NPY neurons promote hunger indirectly?
- By dampening PVN-mediated sympathetic activity
- Which normally inhibits feeding
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What is the brain’s general strategy during arcuate NPY activation?
- Quiet calorie-burning systems (like the sympathetic system)
- Ramp up food-seeking systems
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What is the function of POMC neurons, and what is a mnemonic to remember it?
- Promote satiety (anorexigenic)
- Mnemonic: “Prevents Overeating with Much Control.”
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When are POMC neurons active, and what is their function?
- Active after a meal (postprandial)
- Inhibit feeding and promote satiety
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What peptide do POMC neurons contain, and what do they cleave it into?
- Contain pro-opiomelanocortin (POMC)
- Cleave it into α-melanocyte-stimulating hormone (α-MSH)
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Where is α-MSH released, and what does it do?
- Released at POMC neuron synapses
- Inhibits feeding behaviors
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What is the purpose and ultimate goal of POMC activity?
- Suppress feeding
- Prevent overeating
- Maintain energy balance
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Where do Arc-POMC neurons mainly project, and what neurotransmitter do they release?
- Project to other hypothalamic nuclei
- Release α-MSH
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Which nuclei are affected by α-MSH from Arc-POMC neurons, and how?
- Excite the PVN and VMH (satiety centers)
- Inhibit the DMH (which drives hunger and inhibits sympathetic activity)
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What is the result of inhibiting the DMH, and how does this relate to the postprandial state?
- Increases sympathetic activity
- Which reduces feeding and supports energy expenditure in the postprandial state
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What does the DMH do, and how is it affected by Arc-POMC neurons?
- Drives hunger ("Drives Me Hungry.")
- Inhibits sympathetic nervous system activity
- Arc-POMC neurons inhibit it, disinhibiting sympathetic activity
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What kind of effect does the sympathetic nervous system have on feeding?
Inhibits feeding behavior
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What excites and inhibits Arc-POMC neurons?
Excited by:
- Sympathetic activity
- Blood glucose
- Gut hormones (CCK, PYY, GLP-1)
- Leptin
Inhibited by:
- Arc-NPY neurons
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What feedback loop is formed when sympathetic activity excites Arc-POMC neurons?
- A positive feedback loop
- Amplifies sympathetic inhibition of feeding
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What does leptin do to Arc-POMC neurons, Arc-NPY neurons, LH, PVN, VMH, and DMH?
Excites:
- Arc-POMC
- PVN
- VMH
Inhibits:
- Arc-NPY
- LH
- DMH
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What is leptin's overall effect on feeding and sympathetic activity?
- Suppresses feeding
- Promotes sympathetic activity
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What is leptin’s role in energy balance, and why is it not the main signal to end a meal?
- Acts as a slow signal to conserve energy when fat stores are sufficient
- Not fast enough to end a meal immediately
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What fast signals help terminate a meal, and how do they act?
- Rising blood glucose and gut hormone release
- They excite Arc-POMC, PVN, VMH, inhibit DMH, and stimulate the vagus nerve
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How does rising blood glucose affect feeding?
- Excites Arc-POMC neurons
- Inhibits LH
- Promotes satiety
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What do gut sensors detect and release in response to food?
- Stretch
- Sugar
- Protein
- Release CCK, PYY, and GLP-1
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How do gut hormones affect the brain and nervous system?
- Excite Arc-POMC, PVN, VMH
- Inhibit DMH
- Stimulate the vagus nerve
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Where does the vagus nerve send signals, and what’s the overall effect of gut hormones?
- To the NTS in the brainstem
- Which relays them to the hypothalamus
- Overall effect is inhibition of feeding and amplification of satiety
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What is ghrelin, and when is it released?
- The "hunger hormone"
- Released when the stomach is empty
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What stops ghrelin release, and how does ghrelin act?
- Stomach stretch stops it
- Ghrelin excites Arc-NPY and LH
- Inhibits PVN
- Promotes feeding
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Are many appetite suppressants safe, and what are some examples?
- No, many have serious side effects
- Amphetamines and fenfluramine were used but had risks
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What receptor does Rimonabant block, and what are its side effects?
- CB1 endocannabinoid receptor
- Causes nausea, major depression, and suicide
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Why is leptin ineffective in many obese individuals?
Most are leptin resistant, not deficient
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What is liraglutide, and why is it promising?
- GLP-1 agonist
- Promotes satiety and delays gastric emptying
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How does feeding control generally work, and what do feedback signals tell the brain?
- Through negative feedback signaling
- Tells the brain how close the system is to the body weight set point
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What happens to the set point with VMH and LH lesions?
- VMH lesions raise it (obesity)
- LH lesions lower it (weight loss)
