Neuro physiology Flashcards
1
Q
What does the ANS regulate
A
Visceral functions such as:
arterial pressure
Gastrointestinal activity
Urinary bladder control
Sweating
Body temperature
2
Q
What is the brain stem reticular substance?
A
Control center of the ANS, located along the tractus solitarius in the medulla, pons, and mesencephalon.
Controls arterial pressure, HR, glandular secretion, gastrointestinal peristalsis, urinary bladder contraction
3
Q
The hypothalamus, a control center of the ANS, controls what?
A
Influences brain stem centers and autonomic functions
Regulates body temperature, salivation, gastrointestinal activity, bladder emptying
4
Q
Effects of brain stem transection above midpontine level
A
Basal control of arterial pressure remains, but higher modulation is lost
5
Q
Effect of brain stem transection below medulla
A
Arterial pressure drops significantly
Dead?
6
Q
ANS is activated by which areas of the brain?
A
Brain stem and hypothalamus
Cerebral cortex (especially limbic cortex) can influence autonomic control by sending signals to lower centers
7
Q
ANS operates subconscious control of ________ _________
A
Visceral organs
8
Q
Sensory signals from visceral organs can trigger ______ _________ in autonomic ganglia, brain stem, or hypothalamus
A
Reflex responses
9
Q
Subdivisions of the Autonomic nervous system
A
Sympathetic nervous system
Parasympathetic nervous system
10
Q
What does SNS do?
A
Prepares body for “fight or flight” responses
11
Q
What does parasympathetic nervous system do?
A
Controls “rest and digest” functions, promoting relaxation and conservation of energy
12
Q
Two pathways of the SNS
A
Paravertebral sympathetic chain: interconnected ganglia BESIDE the spinal column
Pre vertebral ganglia: celiac, superior mesenterio, aorticorenal, inferior mesenteric, and hypogastric ganglia.
13
Q
Sympathetic nerve origin
A
Nerve fibers originate between T1-L2 segments of spinal cord.
Enter the sympathetic chain before traveling to target organs
14
Q
Sympathetic neuron types (2)
A
Preganglionic neurons: originate in intermediolateral horn of spinal cord -> go to ganglion
Postganglionic neurons: synapse in ganglia and travel to target organ
15
Q
Pathways of preganglionic fibers (3)
A
Synapse immediately in ganglion they enter
Travel up/down the chain to synapse in another ganglion
Pass through the chain to synapse in a peripheral ganglion
16
Q
Distribution of sympathetic fibers: T1 fibers
A
To the head
17
Q
Distribution of sympathetic fibers: T2
A
To the neck
18
Q
Distribution of sympathetic fibers: T3-T6
A
To the thorax
19
Q
Distribution of sympathetic fibers: T7-T11
A
To the abdomen
20
Q
Distribution of sympathetic fibers: T12- L2
A
To the legs
21
Q
SNS:
Some preganglionic fibers travel directly to the adrenal medullae and stimulate modified neurons to release _________ & _________ into the bloodstream
A
Norepinephrine and epinephrine
22
Q
SNS vs PNS
Preganglionic axons in PNS are ________ than in the SNS
A
Longer
23
Q
All preganglionic neurons are ____________ in both SNS and PNS
A
Cholinergic
Release acetylcholine
24
Q
Cholinergic receptors:
A
Muscarinic: found on all effector cells targeted by postganglionic cholinergic neurons. USES G PROTEINS
Nicotinic: located in autonomic ganglia at synapses between preganglionic and postganglionic neurons. LIGAND-GATED ION CHANNELS
25
Adrenergic receptors
Alpha receptors:
Alpha 1 and alpha 2 - linked to different G proteins
Beta receptors: beta 1, beta 2, beta 3
(Norepinephrine excites primarily alpha receptors, epinephrine excites alpha and beta)
26
Cholinergic neurotransmitter
Acetylcholine
27
Adrenergic neurotransmitter
Norepinephrine
28
PNS postganglionic neurons
Almost all fibers are cholinergic
29
SNS postganglionic neurons
Most fibers and Adrenergic
EXCEPT, fibers to sweat glands and some blood vessels are cholinergic
30
SNS stimulation:
Stimulation of _________ ___________ lasts longer than direct sympathetic stimulation
Adrenal medulla
31
Acetylcholine synthesis and breakdown
Produced in terminal endings and varicosities
Rapid breakdown by acetylcholinesterase into acetate and choline after release
32
Norepinephrine synthesis and breakdown
Begins in axon terminal and finishes in secretory vesicles
Conversion: tyrosine -> dopa -> dopamine -> norepinephrine-> epinephrine
Breakdown: reuptake into nerve endings (50-80%)
Diffusion into surrounding fluids
Enzyme destruction (monoamine oxidase)
33
ANS receptors: acetylcholine, norepinephrine, epinephrine binding to effector cells causes __________ ____________ in receptor protein
Conformational changes
34
Conformational changes in receptor proteins can cause excitation or inhibition through which 2 mechanisms
Ion channel changes: alters membrane permeability
Enzyme activation: activates/inactivates enzymes inside the cell (adenylyl ciclase -> cAMP)
35
Neurons: A typical neuron receives signals through synapses on the _________ and soma and sends output signals via a single axon
dendrites
36
Neurons: Signals pass in a __________ across synapses, from the axon of one neuron to the dendrites of the subsequent neuron
one-way direction (unidirectional)
37
Neurons: Information is carried as nerve impulses (action potentials) through sequential neurons and impulses can be:
1.
2.
3.
- Blocked between neurons
- Transformed into repetitive impulses
- Integrated with other impulses for complex patterns
38
Synapses
Junction between neurons, allows signal transfer and controls direction of signal flow (Some synapses transmit signals readily, while others offer resistance)
39
Synapses: Facilitatory vs. Inhibitory
Facilitatory signals can enhance transmission
Inhibitory signals can reduce or block transmission
40
What is an axon?
Extends from soma to subsequent nerves, carrying output signals
41
What is the soma?
Cell body of a neuron
42
Synaptic transmission: Calcium Channels & Neurotransmitter Release:
Depolarization opens voltage-gated calcium channels
Calcium influx triggers neurotransmitter release from vesicles
43
What are dendrites?
: Branch out from the soma with up to 200,000 presynaptic terminals
44
Synaptic transmission: What are presynaptic terminals?
Form synapses with other neurons
Can be excitatory (stimulating) or inhibitory (blocking)
45
What is the difference between inotropic receptors and metabotropic receptors?
Ionotropic Receptors: Directly open ion channels
Metabotropic Receptors: Activate second messengers to alter cell functions
46
Second Messanger Systems: (G-Proteins)
Activation Process: G protein binds GTP, and separates into active components
Functions:
Open ion channels for prolonged effects
Activate cAMP or cGMP to alter cell activity
Activate enzymes for specific cellular functions
Trigger gene transcription, leading to long-term changes
47
Types of ion channels:
Cation Channels: Allow sodium (Na+), sometimes potassium (K+) or calcium (Ca2+) influx; excitatory
Anion Channels: Primarily allow chloride (Cl-) ions influx; inhibitory
Channel Selectivity: Determined by size, shape, and charge of the channel
48
Mechanism of Excitation:
1. Opening Sodium Channels: Allows positive ions to enter, increasing membrane potential toward threshold
2. Reduced Chloride or Potassium Conductance:
Chloride: Less negative ions enter
Potassium: Fewer positive ions leave
Both actions make the inside of the cell more positive
3. Metabolic Changes:
Increase excitatory receptors or decrease inhibitory receptors on the membrane
49
Chemical Synapses:
(Predominant in the brain and CNS)
Mechanism: Presynaptic neuron releases neurotransmitters to excite, inhibit, or modify the postsynaptic neuron
One-Way Conduction: unidirectional supporting actions like sensation and motor control
Ex: Acetylcholine, norepinephrine, GABA, serotonin, glutamate
50
Mechanisms of Inhibition:
1. Opening Chloride Channels: Negative ions flow in, making the cell interior more negative
2. Increased Potassium Conductance: Positive ions exit, further increasing negativity inside
3. Enzyme Activation: Alters cellular functions to boost inhibition and reduce excitation
51
Electrical Synapses:
(Cytoplasms of adjacent cells connected by gap junctions)
Mechanism: Gap junctions allow free movement of ions and, therefore, electrical charge
Bidirectional Transmission: Allows coordinated activity across interconnected neuron groups
Common in cardiac and smooth muscle
52
Small-Molecule, Rapidly Acting Transmitters:
Trigger acute responses like sensory and motor signals
Synthesized in the cytosol of presynaptic terminals and stored in recycled vesicles
Example: Acetylcholine (synthesized from acetyl CoA and choline, broken down by cholinesterase in the synaptic cleft)
53
RMP: ___mV
-65
54
Neuropeptides, Slowly Acting Transmitters:
Induce prolonged effects (e.g., receptor number changes, long-term synapse modifications)
Synthesized in the cell body and transported to nerve terminals
Released vesicles are not recycled; neuropeptides are more potent but released in smaller quantities
55
Co-Transmission:
Some neurons store both types in the same or separate vesicles, releasing them simultaneously or in sequence
(Small-molecule and neuropetides)
56
Ion Concentrations:
(Na, K, Cl)
High Na+ outside, low inside
High K+ inside, low outside
Cl- high outside, low inside due to the negative membrane potential
57
Does EPSP raise or decrease membrane potential?
Na+ Influx raises membrane potential (e.g., -65 mV to -45 mV)
Threshold for action potential ~ -45 mV
58
Neuronal Excitation: Spatial Summation
Multiple presynaptic terminals fire simultaneously
59
Neuronal Excitation: Temporal Summation
Repeated firing of one terminal over time
60
Neuronal Excitation: Dendritic Transmission
Primarily by electronic conduction; no action potentials
Closer synapses to soma have a greater effect
61
GABA opens ______ channels in the terminal, reducing the excitatory effect by counteracting Na+ influx
Cl-
62
What are two ways for IPSP to occur?
1. Chloride Channels: Open to allow Cl- influx, making the interior more negative
2. Potassium Channels: Open for K+ efflux, also increasing intracellular negativity
63
Summation of IPSP and EPSP:
IPSPs counteract EPSPs; they can partially or fully cancel each other
If excitatory potential nears but doesn’t reach threshold, the neuron is facilitated, making it more responsive to future excitatory inputs
64
What is hyperpolarization
moving membrane potential further from threshold (towards -70 mV)
65
What is post synaptic fatigue?
Repetitive stimulation of excitatory synapses leads to a decrease in postsynaptic neuron firing over time
Mechanism: Depletion of neurotransmitter stores, receptor inactivation, and abnormal ion concentrations
Prevents overexcitation, such as in epileptic seizures
66
What is synaptic delay and how many milliseconds is it?
Time taken for neurotransmitter release, diffusion, receptor binding, and initiation of an action potential
Approximately 0.5 milliseconds
67
What are the three factors affecting neuronal excitability?
1. pH levels:
Alkalosis (7.8-8.0) increases excitability (may trigger seizures)
Acidosis (<7.0)- decreases excitability (induce coma)
2. O2 supply: Lack of oxygen for a few seconds leads to neuron in-excitability, causing unconsciousness
3. Drugs: Stimulants (e.g., caffeine) lower excitation thresholds, increasing excitability
Anesthetics raise excitation thresholds, decreasing excitability
68
Sensation: Sensory Information Pathway:
Sensory data from receptors is transmitted through peripheral nerves to the CNS
69
Sensation: Initiation of Nervous System Activities:
Most activities are triggered by sensory experiences
Sensory input can lead to immediate responses or be stored as memories for future reactions
70
Sensation: what five areas is information relayed to?
1. Spinal Cord: Initial processing and reflexes
2. Reticular Substance: Located in the medulla, pons, and midbrain
3. Cerebellum: Coordinates fine motor control
4. Thalamus: Acts as a sensory relay station
5. Cerebral Cortex: Integrates sensory information for perception and decision-making
71
Motor function: Primary role of the nervous system is to control bodily functions by regulating:
Skeletal Muscle Contraction: Enables movement
Smooth Muscle Contraction: Manages internal organ function
Secretion of Substances: Activates exocrine and endocrine glands
72
Motor function: What are the effectors in the nervous system?
Muscles and glands are the effectors, carrying out responses based on nerve signals
73
What are the five levels of control for skeletal muscles?
1. Spinal Cord: Manages reflexive, automatic responses
2. Reticular Substance: Controls arousal and involuntary motor functions
3. Basal Ganglia: Facilitates smooth voluntary movements
4. Cerebellum: Refines coordination and balance
5. Motor Cortex: Plans and initiates complex voluntary movements
74
What are the three main divisions of the CNS?
Spinal cord, subcortical (lower brain level), cortical (higher brain level)
75
What is the spinal cord level responsible for?
Functions independently for many reflexes and movements
Ex:
Walking movements, withdrawal reflexes (from painful stimuli), postural reflexes (supporting body against gravity), autonomic reflexes (control of blood vessels, digestion, and excretion)
76
What is the subcortical level responsible for?
Manages subconscious and autonomic functions
Includes medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia
Controls emotional responses (e.g., anger, pleasure) and basic life functions
77
What is the higher brain responsible for?
Acts as a large memory storehouse
Essential for thought processes and precise control over lower brain functions
Works in association with lower centers, which initiate wakefulness and access to memories
78
What percent of sensory information is discarded as irrelevant or unimportant?
99%
79
What is integrative function?
The process of filtering, channeling, and directing sensory information to evoke targeted responses
80
Where is most sensory information stored for future use?
Cerebral cortex
81
What do mechanoreceptors detect?
Detect mechanical compression or stretching in tissues
82
What is synaptic facilitation?
Repeated signal transmission strengthens synapses, making them more capable of transmitting similar signals in the future
It enables memories to be recalled even without sensory input
83
What are thermoreceptors?
Sense temperature changes, with distinct receptors for cold and warmth
84
What are nociceptors?
Pain receptors that detect physical or chemical damage in tissues
85
What are electromagnetic receptors?
Respond to light on the retina, enabling vision
86
What are chemoreceptors?
Detect chemical changes:
1. Taste (mouth)
2. Smell (nose)
3. O2 and CO2 levels (blood)
4. Osmolality and other chemical factors in body fluids
87
Normal SNS and PNS tone, both systems are continuously active.
What does normal SNS and PNS tone do?
SNS: keeps systemic arterioles constricted to about 1/2 their maximum diameter. Can increase constriction with heightened stimulation or dilate with decreased stimulation.
PNS: background tone in GI tract
Cutting vagus nerve can lead to serious and prolonged gastric and intestinal atony
88
Denervation hypersensitivity
Loss of tone occurs immediately, but intrinsic compensation occurs over time, returning the function of the organ to almost normal level. Tissue may become hypersensitive to neurotransmitter.
89
Mass discharge of SNS
Fight or flight reaction:
Increased arterial BP
Increased blood flow to active muscles (decreased flow to non-essential organs)
Increased cellular metabolism
Increased blood glucose concentration
Increased glycolysis
Increased muscle strength
Increased blood coagulation
90
Autonomic reflexes
Baroreceptors: stretch receptors in large vessels -> inhibit SNS & excite PNS
GI reflexes: food stimuli initiates signals to vagus, glossopharyngeal, salivatory nuclei -> secretion of gastric juices before food even enters mouth
Urinary bladder functions: stretch of bladder sends impulse to sacral cord -> contraction of bladder -> promotes relaxation of urinary sphincters
91
Adrenal medulla when stimulated by sympathetic nerves releases….
Epinephrine and norepinephrine into blood stream
92
Physiologic effects of norepinephrine
Vasoconstriction
Increased Heart activity
Inhibit GI activity
Dilates pupils
93
Physiologic effects of epinephrine
Similar to norepinephrine but,
Greater cardiac stimulation d/t beta receptor activation
Weak vasoconstriction
Increases metabolic rate 5-10 times more than norepinephrine
94
Why is the adrenal medulla stimulated in addition to direct innervation?
Safety mechanism, one mechanism compensates for the other if needed. Also stimulates structures not DIRECTLY innervated by sympathetic fibers.
95
Cerebral blood flow
4 large arteries: 2 carotid, 2 vertebral
Merge to form the circle of Willis.
96
Map the branching of arteries in the cerebrum
Arteries from the circle of Willis travels along brain surface -> plial arteries -> penetrating arterioles-> capillaries
97
Virchow-Robin space
Space that separates the brain tissues from the penetrating vessels, an extension of the subarachnoid space.
98
Normal Cerebral blood flow
Avg. 50-65ml/100g of brain tissue
Total 750-900ml/min for entire brain
99
Key metabolic factors influencing cerebral blood flow
CO2 concentration
Hydrogen ion concentration
O2 concentration
Substances released from astrocytes
100
Increased CO2 causes __________ in the brain.
Vasodilation
70% increase in arterial CO2 = double cerebral blood flow
CO2 -> carbonic acid -> dissociating into H+ ions -> vasodilation
101
O2 utilization in the brain
3.5ml O2/100g of brain tissue/min
Insufficient O2 supply -> vasodilation to restore blood flow
102
Astrocyte influence on brain regarding blood flow
Releases vasoactive metabolites that mediate local vasodilation in response to neuronal activity
103
Cerebral microcirculation:
Capillary density
Greatest density where highest metabolic needs are greatest
104
Capillary structure in brain
Capillaries are much less ‘leaky’ compared to other tissues
Supported by glial feet, providing physical support & preventing overstretching
105
Brain capillary response to high BP
Arterioles leading to capillaries thicken in response to high BP, maintaining constriction to protect capillaries from high BP.
Breakdown of this protective mechanisms can lead to brain edema -> coma -> death
106
Normal Autoregulation of cerebral blood flow
Autoregulated between 60-150 mmHg
107
Hypertension effect on cerebral blood flow
Chronic HTN —> hypertrophic remodeling of cerebral blood vessels —> shifts auto regulatory curve to right
Partially protects against high BP but increases vulnerability to ischemia if pressures drop too rapidly (think 20% rule)
108
Impairment of autoregulation of cerebral blood flow makes blood flow more dependent on _________
Arterial pressure
109
Conditions that can disrupt autoregulation of cerebral blood flow?
Preeclampsia: can cause pressure-dependent increases in cerebral blood flow —> edema —> seizures
Old age, atherosclerosis, varios brain disorders: autoregulation impairment increases risk of brain injury 2/2 blood pressure fluctuations
110
Entire cerebral vault capacity
1600 -1700ml
111
Normal Cerebrospinal fluid (CSF) capacity
150ml
112
Location of CSF in brain
Present in:
Ventricles
Cisterns
Subarachnoid space surrounding brain and spinal cord
113
Pressure of the CSF is maintained at a ________ ______
Constant level
All chambers containing CSF are interconnected
114
Function of CSF
Cushions the brain
Allows brain to float in the fluid
115
CSF is formed at a rate of ___________ /day
500ml
116
2/3 of CSF originates from the ________ _______ in the ventricles
Choroid plexus
(Ependymal cells)
117
What is the choroid plexus?
Cauliflower-like growth of blood vessels covered by epithelial cells. Responsible for CSF creation. Active transport of Na+ drives fluid secretion into ventricles
118
Osmotic/ionic Characteristics of CSF
Osmotic pressure = to plasma
Na concentration similar to plasma
Cl concentration 15% > than plasma
K concentration 40% < than plasma
Glucose 30% < than plasma
119
CSF flow pathway
Lateral ventricles —> 3rd ventricle —> aqueduct of Sylvius ->
4th ventricle —> exits 4th ventricle through cisterna magna —> subarachnoid space
120
What are arachnoidal villi?
Microscopic projections that allow CSF to flow into venous sinuses
121
Normal pressure of CSF
Average: 130 mm of H2O (10 mm Hg)
Ranges from 65 - 195 mm of H2O
122
CSF pressure is regulated by
Arachnoidal villa: function as valves for CSF flow
(CSF pressure must be 1.5 mmHg greater than venous blood pressure for flow to occur)
123
Blood brain barrier
Barrier between blood vessels and brain parenchyma
Facilitates transport of certain hormones into the hypothalamus
124
Blood brain barrier is highly permeable to
Glucose, hormones, CO2, O2, most lipid-solvable substances (alcohol)
125
BBB is mostly impermeable to
Plasma proteins and most non-lipid soluble large organic molecules
126
Blood-CSF barrier
Tight junctions between endothelial cells limit permeability
Similar permeability as BBB
127
Resting brain metabolism
15% of total body metabolism, but only 2% of total body mass
Metabolism per unit mass: 7.5 times than of non-nervous tissues
128
Most brain metabolism occurs in the _______
Neurons
(Pumping ions across membranes)
High activity can increase metabolism 100-150%
129
Brain relies on continuous O2 supply, therefore it cannot participate in
Anaerobic metabolism
130
Cessation in cerebral blood flow can cause unconsciousness within __________
5-10 seconds
131
Energy source of the brain
Glucose
132
Glucose transport into neurons is insulin _________
Independent
Diabetic pt’s with low BG —> mental function impairment/possible coma
133
Modalities of Sensation
Types of sensory experiences (sound, touch, pain, sight etc.)
134
Sensory nerve fibers only transmit _______ regardless of sensation type
Sensory nerve fibers only transmit **impulses** regardless of sensation type
135
Each sensory receptor type is highly sensitive to a specific ______
Each sensory receptor type is highly sensitive to a specific **stimulus**
136
# Labeled Line Principle
The type of sensation perceived depends on
the ________ of the nerve fibers in the CNS
The type of sensation perceived depends on
the **destination** of the nerve fibers in the CNS
137
________ in neural pathways ensures each fiber
transmits only one modality of sensation
**Specificity** in neural pathways ensures each fiber
Specificity
138
All sensory stimuli induce a
change in the membrane
_________ ________ of
receptors, called
a _______ _________
All sensory stimuli induce a
change in the membrane
**electrical potential** of
receptors, called
a **receptor potential**
139
Receptor potentials trigger
action potentials when .....
Receptor potentials trigger
action potentials when **they
rise above the threshold**
140
List 4 mechanisms of sensory receptor excitation:
1. Mechanical Deformation:
2. Chemical Application
3. Temperature Change
4. Electromagnetic
Radiation
141
Mechanical Deformation:
Stretches membrane causing opening of ion channels
142
Chemical Application:
Opens ion channels via chemical signals
143
Temperature Change:
Alters membrane permeability
144
Electromagnetic
Radiation:
Changes
membrane characteristics
(e.g., light on retinal
receptors)
145
Higher stimulus
strength increases.....
receptor potential amplitude
146
Higher receptor potential
results in
increased....
frequency of
action potential
147
Degree of Adaptation varies
among receptors:
* Pacinian Corpuscles:
Pacinian Corpuscles: Rapid
adaptation within milliseconds
148
Degree of Adaptation varies
among receptors:
* Baroreceptors:
* Baroreceptors: Slow
adaptation, taking up to 2 days
149
List the 2 mechanisms of adaptation:
**Viscoelastic Properties:** Fluid
redistribution in structures like
Pacinian corpuscles reduces
receptor potential
**Accommodation:** Gradual
inactivation of Na+ channels in
the nerve fiber
150
# Type of Adaptation?
Transmit impulses
continuously as long as the
stimulus is present
* Examples: Muscle spindles,
pain receptors, baroreceptors,
chemoreceptors
Tonic (slowly-adapting) receptors
151
Respond only to changes in
stimulus strength; cease firing
when stimulus remains
constant
* Examples: Semicircular canals
for detecting movement and
rate of change
Phasic (Rapidly Adapting)
Receptors:
152
Large to medium myelinated fibers with high
conduction velocity
Type A Fibers:
* Subtypes: Aα, Aβ, Aγ, Aδ
153
Small, unmyelinated fibers with low conduction velocity
* Constitute most sensory fibers in peripheral nerves and all
postganglionic autonomic fiber
Type C Fibers:
154
Function and Conduction Velocity of Type A Fibers:
Fast conduction for functions requiring quick response
(e.g., motor control)
155
Function and Conduction Velocity of Type C Fibers:
Slower conduction, used for signals that can tolerate
delay (e.g., chronic pain)
156
List the 2 Mechanisms for Transmitting
Intensity:
1. Spatial Summation:
2. Temporal Summation:
157
Spatial Summation
* Involves activating increasing numbers of
parallel fibers
* Stronger signals recruit additional fibers,
broadening the response area
* Example: Pain fibers covering a large area of
skin, with each fiber branching into many nerve
endings
158
Temporal Summation:
Temporal Summation:
* Increases the frequency of action
potentials within a single fiber
* Higher stimulus intensity results in more frequent
impulses along the same fiber
159
The area within a pool influenced by an incoming fiber, with
the strongest influence on nearby neuron
Stimulatory field
160
Signal spreads to an increasing number of neurons in
successive orders (e.g., corticospinal pathway)
Amplifying Divergence
161
Signal splits and travels to different areas
(e.g., dorsal columns to cerebellum and thalamus)
Divergence into multiple tracts
162
Multiple terminals from a single input fiber unite
on one neuron, enabling spatial summation
Single source convergence
163
Inputs from multiple sources (e.g., peripheral
nerves, corticospinal tract) combine on a single neuron, allowing summation of
diverse signals
Multiple source convergence
164
A single excitatory input ____ causes an action potential
A single excitatory input **rarely** causes an action potential - Summation of inputs (either simultaneously or in rapid succession)
is needed to excite the neuron
165
Neurons are strongly
stimulated and reach threshold for activation
Discharge Zone (Excited/Liminal Zone)
166
Neurons are
influenced but do not reach threshold; they are more excitable for
future signals
Facilitated Zone (Subthreshold/Subliminal Zone):
167
Inhibitory input dampens neuron activity, with the
strongest inhibition at the center of the field
Inhibitory Zone
168
Reciprocal Inhibition Circuit:
* Enables coordination of _________ muscle pairs
* Input fiber excites one pathway and activates an inhibitory
interneuron to inhibit the opposing pathway
Reciprocal Inhibition Circuit:
* Enables coordination of **antagonistic** muscle pairs
* Input fiber excites one pathway and activates an inhibitory
interneuron to inhibit the opposing pathway
169
* A prolonged output discharge from a neuron that continues after the initial
signal ends
* Duration ranges from milliseconds to several minutes, depending on the
mechanism
Afterdischarge:
170
* Mechanism of Afterdischarge:
* Postsynaptic Potential: Excitatory synapses create an electrical potential
that can persist for milliseconds, especially with _____-acting
neurotransmitters
* Sustained potential causes the neuron to continue firing a _______ of
impulses, even after the initial input signal has ceased
Mechanism of Afterdischarge:
* Postsynaptic Potential: Excitatory synapses create an electrical potential
that can persist for milliseconds, especially with **long-acting**
neurotransmitters
* Sustained potential causes the neuron to continue firing a **train** of
impulses, even after the initial input signal has ceased
171
Significance of Afterdischarge:
* Allows a single brief input to produce a _______ effect, enabling sustained
output without continuous input
* Important for processes requiring extended responses, such as maintaining
_______ ______ or continuous signal output
Significance of Afterdischarge:
* Allows a single brief input to produce a **prolonged** effect, enabling sustained
output without continuous input
* Important for processes requiring extended responses, such as maintaining
**muscle tone** or continuous signal output
172
Continuous Output:
Intrinsic Neuronal Discharge:
* Some neurons have a high enough membrane potential to emit
impulses __________
* Common in neurons of the ________; output rate can be
adjusted by excitatory or inhibitory inputs
Continuous Output:
Intrinsic Neuronal Discharge:
* Some neurons have a high enough membrane potential to emit
impulses **continuously**
* Common in neurons of the **cerebellum**; output rate can be
adjusted by excitatory or inhibitory inputs
173
Reverberatory Circuits:
* Self-sustaining reverberating circuits generate ________
impulses
* ______ signals can increase or decrease the output; inhibition can
___________ the signal
Reverberatory Circuits:
* Self-sustaining reverberating circuits generate **continuous**
impulses
* **Input** signals can increase or decrease the output; inhibition can
**extinguish** the signal
174
Rhythmical Output:
* Rhythmical Signals: Produced by _________ circuits that create
________ patterns
Rhythmical Output:
* Rhythmical Signals: Produced by **reverberating** circuits that create
**cyclical patterns**
* Examples: Respiratory rhythm (medulla and pons), heart rate,
vascular tone, and digestive activity
175
Give an example of a reverberating circuit and its location
* Examples: **Respiratory rhythm (medulla and pons)**, heart rate,
vascular tone, and digestive activity
176
Inhibitory Feedback Circuits:
* Feedback from pathway ______ inhibits excitatory neurons at the input or intermediate stages.
* Common in ________ pathways to prevent ________
Inhibitory Feedback Circuits:
* Feedback from pathway **termini** inhibits excitatory neurons at the input or intermediate stages.
* Common in **sensory pathways** to prevent **overexcitation**
177
Inhibitory Neuronal Pools:
* Certain pools, like the _______ ________, exert broad inhibitory control, stabilizing functions such as
muscle control
Inhibitory Neuronal Pools:
* Certain pools, like the basal ganglia, exert broad inhibitory control, stabilizing functions such as
muscle control
178
Synaptic Fatigue:
* Progressive Weakening: Synaptic transmission decreases with _________ excitation
* Moderates the sensitivity of ______ pathways (fatigue) and increases sensitivity in _______
pathways (recovery)
Synaptic Fatigue:
* Progressive Weakening: Synaptic transmission decreases with **prolonged excitation**
* Moderates the sensitivity of **overused** pathways **(fatigue)** and increases sensitivity in **underused**
pathways **(recovery)**
179
Long-term Regulation:
* Downregulation of receptors with ________
* Upregulation of receptors with _________
Long-term Regulation:
* Downregulation of receptors with **overactivity**
* Upregulation of receptors with **underactivity**
180
Physiological Types of Somatic Senses:
* Mechanoreceptive Senses: Includes ______ and _______ senses; Activated by ________ displacement in body tissues
* Thermoreceptive Senses: Detects ______ and _____
* Pain Sense: Triggered by factors that cause _____ _______
Physiological Types of Somatic Senses:
* Mechanoreceptive Senses: Includes **tactile and position** senses; Activated by **mechanical displacement** in body tissues
* Thermoreceptive Senses: Detects **heat and cold**
* Pain Sense: Triggered by factors that cause **tissue damage**
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Other Classifications of Senses:
* Exteroreceptive Sensations: From the body ______
* Proprioceptive Sensations: Related to body’s ______ state (e.g.,
position, muscle tension, balance)
* Visceral Sensations: Arising from _____ ________ (viscera)
* Deep Sensations: From ____ ______, including fasciae, muscles, and
bones; includes deep pressure, pain, and vibration
Other Classifications of Senses:
* Exteroreceptive Sensations: From the **body surface**
* Proprioceptive Sensations: Related to body’s **physical state** (e.g.,
position, muscle tension, balance)
* Visceral Sensations: Arising from _____ ________ (viscera)
* Deep Sensations: From **deep tissues,** including fasciae, muscles, and
bones; includes deep pressure, pain, and vibration
182
* Touch: Detected by _____ receptors near the ____ surface
* Pressure: Result of ________ in deeper tissues
* Vibration: Detected through rapidly ______ signals
* Touch: Detected by **tactile receptors** near the **skin **surface
* Pressure: Result of **deformation** in deeper tissues
* Vibration: Detected through **rapidly repetitive** signals
183
Types of Tactile Receptors:
* Free Nerve Endings: Found throughout skin; detect _____ and _______
* Meissner’s Corpuscles: ______ sensitive, _____-adapting; abundant in fingertips and lips
* Merkel’s Discs: _______-adapting, grouped in touch domes; localize _____ and _____
* Hair End-Organs: Detect ______ and initial ______; adapt _____
* Ruffini’s Endings: ____-adapting; detect _______ deformation, found in skin and joint
capsules
* Pacinian Corpuscles: _____-adapting; detect _____ and ______ changes in pressure
Types of Tactile Receptors:
* Free Nerve Endings: Found throughout skin; **detect touch and pressure**
* Meissner’s Corpuscles: **Highly sensitive, rapid-adapting**; abundant in fingertips and lips
* Merkel’s Discs: **Slow-adapting**, grouped in touch domes; localize **touch and texture**
* Hair End-Organs: Detect **movement and initial contact**; adapt **quickly**
* Ruffini’s Endings: **Slow-adapting**; detect **continuous deformation**, found in skin and joint
capsules
* Pacinian Corpuscles:** Rapid-adapting**; detect **vibration ** and **quick** changes in pressure
184
Nerve Fiber Types:
* Type Aβ: _______ transmission (30-70 m/s), used by most ________ receptors
* Type Aδ and Type C: _______ transmission for _____ nerve endings; carry ____ critical signals
Nerve Fiber Types:
* Type Aβ: **Rapid transmission** (30-70 m/s), used by most **specialized receptors**
* Type Aδ and Type C: **Slower transmission** for **free** nerve endings; carry **less critical signals**
185
T or F?
**All** tactile receptors can detect vibration
TRUE:
Each receptor type responds to different vibration frequencies based on its
**adaptation rate and sensitivity**
186
Tickle and Itch sensation:
* Detected by ________ adapting ___________ ____ nerve endings in the
superficial skin layers
* Exclusively found in the ____ and respond primarily to light stimuli on the skin
surface
Tickle and Itch sensation:
* Detected by **rapidly adapting mechanoreceptive free nerve endings** in the
superficial skin layers
* Exclusively found in the **skin** and respond primarily to light stimuli on the skin
surface
187
Itch and Tickle Transmission: Carried by _____, _________ type ____ fibers, similar to those
that transmit slow, aching pain
Itch and Tickle Transmission: Carried by s**mall, unmyelinated type C fibers,** similar to those
that transmit slow, aching pain
188
Types of Position Senses:
* Static Position Sense:
* _________ perception of body orientation and position of body parts
relative to each other
* Dynamic Position Sense (Kinesthesia):
* Awareness of the ____ and _______ of movement
Types of Position Senses:
* Static Position Sense: **Conscious** perception of body orientation and position of body parts
relative to each other
Dynamic Position Sense (Kinesthesia): Awareness of the **speed and direction** of movement
189
Mechanisms of Position Sensing:
* ______ Angulation: Determined by multiple receptors that provide
information on the angle and movement of joints
Joint
190
Proprioceptive Receptor Types:
* Muscle Spindles: Key for sensing ______ joint angles and changes
in _______ ________
* Deep Receptors (e.g., Pacinian Corpuscles, Ruffini’s Endings):
Important at ______ joint angles, detect stretch in ligaments and deep
tissues
* Golgi Tendon-Like Receptors: Provide information on _______ ________
tension
Proprioceptive Receptor Types:
* Muscle Spindles: Key for sensing **midrange** joint angles and changes
in **muscle stretch**
* Deep Receptors (e.g., Pacinian Corpuscles, Ruffini’s Endings):
Important at **extreme** joint angles, detect stretch in ligaments and deep
tissues
* Golgi Tendon-Like Receptors: Provide information on **muscle tendon
tension**
191
Cerebral Cortex Layers:
Six Layers of Neurons:
* Layer _____: Primary **entry point** for sensory signals
* Layers ___ & ____: Receive diffuse input for excitability control
* Layers ___ & ____: Send signals across hemispheres via the corpus callosum
* Layers ____ & ____: Project to deeper brain areas, controlling signal
transmission and influencing thalamic activity
Cerebral Cortex Layers:
Six Layers of Neurons:
* **Layer IV**: Primary **entry point** for sensory signals
* **Layers I & II:** Receive **diffuse input** for excitability control
* **Layers II & III**: Send signals **across hemispheres** via the **corpus callosum**
* **Layers V & VI**: Project to **deeper brain areas,** controlling signal
transmission and influencing thalamic activity
192
Vertical Columns:
* Each column specializes in a _____ sensory modality (e.g., touch,
pressure)
* Located in ____________ _______ __ (postcentral gyrus), organized by ____
region
* Vertical Columns:
* Each column specializes in a **single sensory modality** (e.g., touch,
pressure)
* Located in **somatosensory area I (postcentral gyrus)**, organized by **body
region**
* Somatosensory Areas:
* Somatosensory Area I:
* High degree of localization; different parts of the body are represented
proportionally to receptor density (e.g., large areas for lips, fingertips)
* Key for precise tactile information (located in Brodmann’s areas 3, 1, and 2)
* Somatosensory Area II:
* Less precise localization
193
* Somatosensory Area I: _______ degree of localization; different parts of the body are represented
proportionally to receptor ______ (e.g., large areas for lips, fingertips); Key for precise tactile information (located in Brodmann’s areas ___, ___, and ___)
* Somatosensory Area II: _____ precise localization
* Somatosensory Area I:
* **High degree of localization**; different parts of the body are represented
proportionally to **receptor density** (e.g., large areas for lips, fingertips)
* Key for precise tactile information (located in **Brodmann’s areas 3, 1, and 2**)
* Somatosensory Area II: **Less precise** localization
194
Somatosensory Association Areas:
Location:
* Brodmann’s Areas ___ and ____ in the parietal cortex, located behind
somatosensory area __
Function:
* Combines and interprets sensory information from _______ ______ _
* Effects of Damage: __________
Location:
* **Brodmann’s Areas 5 and 7** in the parietal cortex, located behind
**somatosensory area I**
* Function: Combines and interprets sensory information from **somatosensory
area I**
* Effects of Damage: Amorphosynthesis:
195
Amorphosynthesis:
* Loss of ability to recognize ______ objects or forms by touch on
the _______ side of the body
* Reduced ________ of the _______ side of the body and body
parts
* Leads to a lack of ____ and _____ perception on the affected side
Amorphosynthesis:
* Loss of ability to recognize **complex objects or forms** by touch on
the opposite side of the body
* Reduced **awareness of the opposite side** of the body and body
parts
* Leads to a lack of **spatial and form perception** on the affected side
196
Sensory Information Entry:
* Sensory signals enter the spinal cord through the _____
roots of spinal nerves
Sensory Information Entry:
* Sensory signals enter the spinal cord through the dorsal
roots** of spinal nerves
197
Two Main Sensory Pathways:
1. Dorsal Column-Medial Lemniscal System: ___ spatial orientation of nerve fibers; Transmits information ____ with high temporal and
spatial fidelity
*Ideal for _______, _______ sensations
2. Anterolateral System:
* ______ spatial orientation
* Transmits information that does not require high speed or
precision
* Suitable for __________ sensations
Two Main Sensory Pathways:
1. Dorsal Column-Medial Lemniscal System: **High spatial **orientation of nerve fibers
* Transmits information **rapidly** with high temporal and
spatial fidelity
* Ideal for **precise, localized** sensations
2. Anterolateral System:
* **Less **spatial orientation
* Transmits information that **does not **require high speed or
precision
* Suitable for **generalized** sensations
198
Functional Differences:
* Dorsal Column: For sensory information that needs ______,
accurate transmission
* Anterolateral System: For sensory signals that can tolerate
_____, _____ precise transmission
Functional Differences:
* Dorsal Column: For sensory information that needs **rapid,
accurate** transmission
* Anterolateral System: For sensory signals that can tolerate
**slower, less precise** transmission
199
Dorsal Medial Lemniscal Pathway:
**Anatomy:** Composed of ______ _________ fibers
* Fibers ascend in the _____ columns of the spinal cord
* Synapse in the _______ column nuclei (______ and
_______ nuclei) of the medulla
* Cross to the opposite side and ascend via the medial
lemniscus to the thalamus
Dorsal Medial Lemniscal Pathway:
**Anatomy:** Composed of **large myelinated fibers**
* Fibers ascend in the **dorsal columns** of the spinal cord
* Synapse in the **dorsal column nuclei (cuneate and
gracile nuclei)** of the medulla
* Cross to the opposite side and ascend via the **medial
lemniscus** to the thalamus
200
Dorsal Medial Lemniscal Pathway:
Function:
* Transmits ______ touch, ________,
and _____________ information
* Provides high spatial resolution for tactile _______
Dorsal Medial Lemniscal Pathway:
Function:
* Transmits **fine touch, vibration,
and proprioceptive information**
* Provides high spatial resolution for tactile **localization**
201
Dorsal Medial Lemniscal Pathway:
Key Characteristics
* ______ conduction velocities (____-_____ m/sec)
* Essential for discerning precise ____ and ____
position
Dorsal Medial Lemniscal Pathway:
Key Characteristics:
* Fast conduction velocities **(30-110 m/sec)**
* Essential for discerning **precise touch and joint
position**
202
Initial Division of the Dorsal Medial Lemniscal Pathway:
* Large myelinated fibers divide into ______ and ______ branches upon
entering the spinal cord
* Medial Branch: Travels upward through the _______ columns to the
______
Initial Division of the Dorsal Medial Lemniscal Pathway:
* Large myelinated fibers divide into **medial and lateral branches** upon
entering the spinal cord
* Medial Branch: Travels upward through the **dorsal columns** to the
**spinal cord**
* Lateral Branch: Synapses **locally** in the **dorsal horn** and serves three
functions.
203
* Lateral Branch: serves three
functions:
* Sends fibers to the _____ columns for upward travel
* Terminates locally to mediate ______ reflexes
* Contributes to the ______________ tracts
* Lateral Branch: serves three
functions:
* Sends fibers to the **dorsal columns** for upward travel
* Terminates locally to mediate **spinal reflexes**
* Contributes to the **spinocerebellar tracts**
204
Dorsal Medial Lemniscal Path to the Brain:
* Fibers ascend through the dorsal columns to the dorsal medulla and
synapse in the ________ and ______ nuclei
* Second-order neurons cross to the opposite side in the ______ and ascend
via the _______ _________ to the ______
* Third-order neurons project to somatosensory area ___ in the postcentral
gyrus
Dorsal Medial Lemniscal Path to the Brain:
* Fibers ascend through the dorsal columns to the dorsal medulla and
synapse in the **cuneate and gracile nuclei**
* Second-order neurons cross to the opposite side in the **medulla** and ascend
via the **medial lemnisci** to the thalamus
* Thalamic Relay and Cerebral Cortex Projection:
* In the thalamus, fibers terminate in the ventrobasal complex
* Third-order neurons project to **somatosensory area I** in the postcentral
gyrus
205
Dorsal Medial Lemniscal Pathway:
Thalamic Relay and Cerebral Cortex Projection:
* In the thalamus, fibers terminate in the ________ complex
Dorsal Medial Lemniscal Pathway:
Thalamic Relay and Cerebral Cortex Projection:
* In the thalamus, fibers terminate in the **ventrobasal complex**
206
**Spatial Orientation of the Dorsal Medial Lemniscal Pathway:**
* Maintained throughout the pathway, with ______ body fibers central and _______
body fibers more lateral in the dorsal columns
* Medial lemniscal crossing results in _________ representation in the
________
**Spatial Orientation of the Dorsal Medial Lemniscal Pathway:**
* Maintained throughout the pathway, with l**ower body fibers central and higher
body fibers more lateral** in the dorsal columns
* Medial lemniscal crossing results in **contralateral representation in the
thalamus**
