4 - Sensory Physiology Flashcards
What does the somatic portion of the nervous branch do?
Transmits SENSORY signals from receptors to the brain
What are “motor functions” and “effectors?”
Motor functions are the activities which the brain controls via smooth and skeletal muscle contraction and hormone release
Effectors are the end recipients of these actions: the muscles and glands that the brain is telling to do something
the nervous system for controlling skeletal muscle contraction is called:
the skeletal motor nerve axis
What is the autonomic nervous system responsible for?
Smooth mm, glands, internal organ functions
What is facilitation?
Each time certain types of sensory signals pass through sequences of synapses, these synapses become more capable of transmitting the same type of signal the next time
Where are most subconscious functions performed?
lower areas of the brain—medulla, pons, mesencephalon, hypothalamus, thalamus, cerebellum, and basal ganglia
What are the two major types of synapses?
Chemical and Electrical
The CNS mostly relies on what type of synapses?
Chemical
Where are electrical synapses found?
Cardiac and Smooth Muscle
Most synapses in the brain are:
chemical
When are electrical synapses useful?
Since they have bidirectional conduction, they’re ideal for distributing signals for simultaneous action, like in cardiac muscle
Why are chemical synapses ideal for transmitting nervous impulses?
Transmission only flows in one direction: from the first neuron to the second neuron
What are the three parts of a motor neuron?
- Soma (main body)
- Axon (extends from soma to peripheral nerve)
- Dendrites (brances off the soma that receive sensory input from nerve endings)
What are presynaptic terminals?
80-95% attached to the dendrites
Ends of nerve fibrils that originate from other neurons
May excite or inhibit the postsynaptic neuron
What are some alternate names for presynaptic terminals?
Terminal Knobs
Boutons
End-Feet
Synaptic Knobs
How wide is the synaptic cleft usually?
200-300 angstroms
What are transmitter vesicles?
Secretory vesicles in the presynaptic neuron that contain neurotransmitters
During depolarization of a chemical synapse, what causes release of secretory vesicles into the synaptic cleft?
voltage-gated Calcium influx in the presynaptic neuron
The quantity of neurotransmitter released by the presynaptic neuron is directly proportional to:
the amount of calcium that enters the presynaptic membrane during depolarization
What are the two major parts of receptor proteins in postsynaptic neurons?
Binding Component
Intracellulary Component
Receptor activation controls the opening of ion channels in the postsynaptic cell in one of two ways:
- gating ion channels directly
- Activating Second Messengers
What are ionotropic receptors?
Receptor proteins that directly effect gated ion channels
What are metabotropic receptors?
Influence cellular activity in the postsynaptic neuron via second messenger systems
What is an excitatory transmitter?
a neurotransmitter that opens CATION channels in the postsynaptic neuron
What is an inhibitory transmitter?
neurotransmitters than open ANION channels in the postsynaptic neuron
Negative charges entering a cell =
Positive charges entering a cell =
Inhibition
Excitation
prolonged postsynaptic excitation or inhibition is always caused by:
second messenger systems
ion channel activation is rapid and short
What happens when a transmitter binds to a G protein?
- Receptor exposes a binding site for the G protein complex
- GPC binds to the receptor
- alpha subunit of GPC releases GDP and binds with GTP
- Binding with ATP separates the Alpha unit from the rest of the GPC, and it’s free to move about the cell and perform various functions
What four functions can an activated G complex perform?
- open a specific ion channel for a prolonged time
- Activate cAMP or cGMP, which can in turn activate a multitude of long term cellular changes
- Activate intracellular enzymes
- Activate gene transcription
What are the three ways postsynaptic excitation occurs?
- Opening sodium channels (making resting potential more positive, hypopolarized, easy to excite)
- Decrease conduction through Cl (decreases negative movement into the cell) and/or K gates (decreases positive movement out of the cell) making the resting potential more positive, hypopolarized, easy to excite
- Change the internal metabolism of the postsynaptic neuron to excite activity
What are three ways postsynaptic inhibition occurs?
- Opening of Cl channels, moving more negative anions into the cell and inhibiting excitation
- Increasing conductance of potassium out of the cell, moving positive anions out of the cell, hyperpolarizing and inhibiting excitation
- Activation of receptor enzymes, inhibits metabolic functions etc.
What are the two groups of synaptic neurotransmitters?
Small Molecule Rapid Acting
Neuropeptide Slow Acting or Growth Factors
Function and location of Glycine
synapses at the spinal cord
always inhibitory
Function and location of dopamine
Secreted by neurons in substantia nigra
Usually terminates in basal ganglia
Usually inhibitory
Where are small molecule transmitters synthesized?
Neuropeptides?
Cytosol
Ribosomes (large protein molecules)
When are vesicles reused? When are they not?
Reused with small molecule. Autolyzed with neuropeptides.
How is electrical potential distributed within the soma of a neuron?
Uniformly
any change in potential in any part of the intrasomal fluid causes an almost exactly equal change in potential at all other points inside the soma, as long as the neuron is not transmitting an action potential
What is an EPSP?
Excitatory Postsynaptic Potential
Positive increase in voltage above the normal resting membrane potential
Increased Na movement in. Hypopolarizes. Excites.
What size EPSP is required to elicit an actional potential in the soma?
In the axon initial segment?
+30 to +40 mV
Only +10 to +20 mV
The is why action potentials generally begin in the axon initial segment and not the soma
What is the resting membrane of a neuron?
Threshold for excitement of a neuron?
- 65 mV
- 45 mV
What is an IPSP?
Inhibitory Postsynaptic Potential
An increase in the negativity of the resting membrane potential.
Usually reduces from -65mV to -70mV
Hyperpolarization of a neuron is caused by _____ moving out and _______ moving in
Potassium
Chloride
In most cases, which inhibitory transmitter causes presynaptic inhibition?
GABA
How does GABA cause presynaptic inhibition?
Opens chloride channels on the presynaptic neuron, causing hyperpolarization
How long does inhibitory or excitatory effect on ion channels last if they don’t elicit an action potential?
15 mseconds
What is temporal summation?
successive discharges from a single presynaptic terminal
What does it mean if a neuron is facilitated?
its membrane potential is nearer the threshold for firing than normal but is not yet at the firing level
What is electrotonic current?
Dendrites have almost no sodium channels, so they don’t transmit action potentials.
Instead they spread electronic conduction directly through ions in the cell cytoplasm to the soma
what is decremental conduction?
Most of the membrane potential generated at the ends of the dendrites is lost before it reaches the soma, because the dendrites are very leaky to sodium
What is synaptic transmission fatigue?
What causes it?
repetitive stimulation at a high rate results in decreased excitation. prtective mechanism against excess neuronal activity (why seizures are usually self limited)
- exhausted stores of neurotransmitters
- inactivation of postsynaptic membrane receptors
- abnormal ion concentration in the postsynaptic cell
Alkalosis ________ neuronal activity.
Acidosis ________ neuronal activity.
Increases
Depresses
Why is hyperventilation dangerous in epileptic patients?
pH going from 7.4 to 7.8 to 8.0 often causes cerebral epileptic seizures
Even a short period of hyperventilation, which blows off carbon dioxide and elevates the pH, may precipitate an epileptic attack.
The excitatory terminals on many neurons can store enough excitatory transmitter to cause _______ action potentials
about 10,000
Which three excitatory drugs are found in coffee?
caffeine
theophylline
theobromine
What does strychnine do?
Excitatory
Inhibits the inhibitory transmitter substances, especially glycine, resulting in severe seizures
What is the minimum synaptic delay?
0.5 milliseconds
Since each nerve only sends action potentials, how do different nerve fibers transmit different modalities of sensitivity?
the type of sensation felt when a nerve fiber is stimulated is determined by the point in the nervous system to which the fiber leads
What is the labeled line principle?
specificity of nerve fibers for transmitting only one modality of sensation
What is the receptor potential?
a change in the membrane electrical potential of the receptor
Four mechanisms of generating receptor potential
(1) Mechanical deformation stretches the receptor membrane and opens ion channels
(2) application of a chemical to the membrane opens ion channels
(3) change of membrane temp alters permeability of the membrane
(4) effects of electromagnetic radiation, such as light on a retinal visual receptor, which either directly or indirectly changes the receptor membrane characteristics and allows ions to flow through membrane channels.
What are tonic receptors?
Slowly adapting receptors that continuously detect stimulus strength
Pain receptors, baroreceptors, chemoreceptors
Rapidly adapting receptors are also called:
Rate Receptors
Movement Receptors
Phasic Receptors
What do rapid adapting receptors transmit?
Changes in stimulus strength
The large the diameter of a nerve fiber, the greater the ____
conducting velocity
Describe Type C nerve fibers
small unmyelinated nerve fibers that conduct impulses at low velocities
Describe Type A Nerve Fibers
large and medium-sized myelinated fibers of spinal nerves
What’s the difference between spacial and temporal summation
different gradations of intensity transmitted by using increasing numbers of parallel fibers
different gradations of intensity transmitted bysending more action potentials along a single fiber
Describe A beta fibers
Heavily myelinated
Large Diameter
transduce innocuous or low-threshold mechanical stimulation
Describe A delta fibers
lightly myelinated
medium-diameter
rapidly conduct first pain
Describe C fibers
unmyelinated
small fibers
slow conducting
second pain
What are somatic senses?
Nervous mechanisms that collect sense from all over the body
NOT special sense
What are the special senses?
Vision
Hearing
Taste
Smell
Equilibrium
What are the three types of somatic senses?
Mechanoreceptors
Thermoreceptors
Pain
Visceral sensation generally refers to:
sensation from the deep organs of the body
What are the six tactile receptors?
- Free Nerve Endings
- Meissner’s Corpuscle
- Merkel Discs
- Hair End Organ
- Ruffini Endings
- Pacinian Corpuscles
Meissner’s Corpuscle
Highly sensitive touch receptor
Non-hairy Skin
Menkel’s Discs
responsible for giving out steady-state signals to determine continuous touch of objects against the skin
Form touch domes
Ruffini’s Endings
deeper layers of the skin and deeper internal tissues
adapt very slowly
heavy prolonged touch and pressure signals
Found in joints to detect degree of rotation
Pacinian Corpucles
Rapidly adapt
immediately beneath the skin and deep in the fascial tissues of the body
tissue vibration or other rapid changes in the mechanical state of the tissues
Almost all specialized sensory receptors transmit signals via ________ nerve fibers
A beta
Except free nerve endings, which transmit over A delta and type C
From the dorsal root of the spinal cord, sensory signals follow which two pathways to the brain:
- Dorsal column - medial lemniscal
- anterolateral
How does the dorsal column - medial lemniscal travel to the brain?
Up via Dorsal Columns
Medulla - crosses over
to thalamus via medial lemniscus
How does the anterolateral tract travel to the brain?
Dorsal nerve roots
Synapse in the Dorsal Horns
Immediately crosses over and then ascends through the anterior and lateral tracts
Travels up to the thalamus
Sensory information that must be transmitted rapidly with temporal and spatial fidelity is transmitted via:
Why?
Dorsal Column - Medial Lemniscal
Has a high degree of spatial orientation
Sensory information that does not need to be transmitted rapidly or with great spatial fidelity is transmitted via:
Anterolateral
What can the anterolateral tract do which the dorsal medial cannot?
transmit a broad spectrum of sensory modalities, such as pain, warmth, cold, and crude tactile sensations
What sensations are transmitted via Dorsal Column - Medial Lemniscal Tract?
- Touch sensations requiring high degree of localization
- Touch sensations requiring transmission of fine gradations of intensity
- Phasic sensations, such as vibratory sensations
- Sensations that signal movement against the skin
- Position sensations from the joints
- Pressure sensations related to fine degrees of judgment of pressure intensity
What sensation are transmitted via the anterolateral system?
- Pain
- Thermal sensations, including both warm and cold sensations
- Crude touch and pressure sensations capable only of crude localizing ability on the surface of the body
- Tickle and itch sensations
- Sexual sensations
The medial lemniscus is located in the ______
pons
How does the dorsal column - medial lemniscal tract transmit with such specific spacial orientation?
dorsal columns: fibers from the lower parts of the body lie toward the center of the cord, progressively higher segmental levels form successive layers laterally
In the thalamus: tail end of the body represented by the most lateral portions of the ventrobasal complex, head and face represented by the medial areas of the complex
What are brodmann’s areas?
A map of the human cerebral cortex
In general, where do sensory signals from all modalities of sensation terminate in the brain?
in the cerebral cortex immediately posterior to the central fissure
Visual signals terminate in the ______
Auditory signals terminate in the _______
Occipital Lobe
Temporal Lobe
Where is the motor cortex?
Sensory cortex?
Frontal Lobe: Anterior to central fissure
Parietal Lobe: Posterior to central fissure
What divides the frontal lobe from the parietal lobe
central sulcus
Which has a higher degree of localization:
Somatosensory I or II
I
II has very little localization
If somatosensory area I is removed/destroyed, will the person still feel pain?
Yes! But the pain will not be well localized
What is the role of the somatosensory association area?
Allows interpretation of sensation, like knowing you’re holding a knife or a ball from the way it feels
How does lateral inhibition work?
Whenever there is excitation, the sensory pathway also produces inhibition of the lateral sides of the pathway and prevents spread to adjacent neurons
It blocks spread, which allows greater distinction and interpretation. The brain knows exactly where that sensation is coming from, because spread is inhibited
Which pathway exhibits the most lateral inhibition?
Dorsal. This is part of its precise localization.
What is the Weber-Fechner Principle?
a change will only be detected if it’s delta ratio is greater than 1:30
So if you are holding 30g, the body can only detect the addition of more weight if the added amount is greater than 1g
Which sensors help determine joint angulation?
Normal range: Muscle Spindles
Extreme Range: pascinian, ruffini, golgi tendon receptors
What is the function of the thalamus in somatosensory perception?
discrimination of pain and temperatue
crude discrimination of tactile senses
What are some chemicals that incite pain?
Bradykinin
Serotonin
Histamine
Potassium
Acids
Acetylcholine
What substances enhance the sensitivity of pain endings, but do not directly excite them?
Prostaglandins
Substance P
How adaptable are pain receptors?
Very little if at all
Makes them different from almost all other sensory receptors
Pain resulting from heat is closely correlated with:
the rate of damage,
not the amount of damage that has occurred
Velocity of A delta
C
6-30 m/sec
0.5-2 m/sec
What neurotransmitter is secreted at A delta fiber endings in the spinal cord?
glutamate
A delta fibers travel to the brain via the ______ tract
C fibers travel to the brain via the _______ tract
Neospinothalamic
Paleospinothalamic
Where does the neospinothalamic tract terminate?
Some in reticular areas
Most directly to the thalamus to ventrobasal complex (same as dorsal column - medial lemniscal)
Type C pain fiber terminal release _____ and ______
glutamate
substance P
Glutamate involves _____ pain
Substance P involves _____ pain
acute/fast
chronic/slow
Where does the paleospinothalamic tract terminate?
Reticular Nuclei
Periaqueductal Gray
Tectal Mesencephalon
Why is it almost impossible to sleep well with chronic pain?
The paleospinothalamic tract primarily terminates in the reticular area, which is responsible for wakefulness
Which neurotransmitters are involved in efferent dorsal inhibition?
serotonin
enkephalin
The brains opiate system is made up of ______ and _____
endorphins
enkephalins
Why does accupuncture relieve pain?
The inhibitory effect of simultaneous tactile stimulations
AND
psychogenic activation of the central analgesia system
Why is internal visceral pain often associated with referred pain?
In the spinal cord, visceral and skin nerve fibers synapse on the same second order neurons
When visceral pain fibers are stimulated, pain signals from the viscera are conducted through at least some of the same neurons that conduct pain signals from the skin, and the person has the feeling that the sensations originate in the skin.
Why does an incision to the bowel produce no pain, but necrosis or ischemia in the bowel produces extreme pain?
Highly localized damage almost never causes pain
diffuse stimulation does
Why is all visceral pain dull, diffuse, and aching?
Virtually all of the nerve fibers that supply the gut are C Fibers
Which areas of organs are completely insensitive to pain?
The alveoli in the lungs
The parenchyma of the liver (NOT the liver capsule, which is exquisitely sensitive)
What is the difference between true visceral pain and parietal pain?
True visceral pain is transmitted via pain sensory fibers in the autonomic bundles and is often referred
Parietal pain is conducted directly into local spinal nerves from the parietal peritoneum, pleura, or pericardium, and is localized directly over the painful area.
Why is visceral pain often felt in two places simultaneously?
From referred pain via the visceral pathway and direct pain via the parietal pathway
Appendix pain occurs in which two places?
Parietal: irritation of the parietal wall causes pain in the abdominal wall directly over the area
Visceral: appendix transmission through sympathetic fibers enters the spinal cord at T10 and therefore causes referred pain in the umbilical area
What causes primary and secondary hyperalgesia?
Primary: excessive sensitivity of the receptors
Secondary: increased facilitation of sensory transmission
What’s an example of primary hyperalgesia?
Sunburn (everything that touches the burned skin hurts, even if it’s just your sheets)
What causes secondary hyperalgesia?
usually lesions in the spinal cord or thalamus
Shingles results when:
herpesvirus infects a dorsal root ganglion
The rash and pain occur within the dermatome and on the side of that nerve root
What is Tic Douloureaux?
lancinating or stabbing type of pain over one side of the face in the sensory area of the fifth or ninth nerves
Usually stimulated initially by a mechanoreceptor (food bolus passing a tonsil)
Requires surgical excision of nerve
What is Brown-Sequard Syndrome?
Spinal cord transected only on one side
sensations of pain, heat, and cold—sensations served by the spinothalamic pathway—are lost on the opposite side of the body
the sensations that are transmitted only in the dorsal and dorsolateral columns—kinesthetic and position sensations, vibration sensation, discrete localization, and two-point discrimination—are lost on the side of the transection
Does the body have more cold spots or warm spots?
3-10x as many cold spots
Warmth receptors have ____ receptors and are transmitted over ______ fibers
free nerve ending
C
Cold sensation is transmitted via ______ fibers
A delta
Do warmth and cold receptors primarily detect:
changes in temperature, not necessarily degree of temperature
If you’re constantly in 100 degree weather it will be more tolerable than walking from 70 degrees into 100 degree weather
rapid changes in temperature as little as 0.01°C can be detected if:
temperature changes 100 times as great often will not be detected when:
this change affects the entire surface of the body
the affected skin area is only 1 square centimeter in size.
