Lab 1 + 2 Test Flashcards
What does nerve depolarization involve?
An increase in membrane sodium permeability
what does nerve repolarization involve?
An increase in membrane potassium permeability
What changes are measurable in cell ion concentration during an action potential?
There are no measurable changes in any cell ion concentrations
What does the refractory period represent?
It represents a time during which a stimulus of greater than normal intensity may elicit a new action potential
What is an earthworm giant axon composed of?
It is composed of individual cells (one in each segment) linked through gap junctions to its neighbors in adjacent segments
The biphasic nature of the action potential recorded extracellularly is consequence of?
The use of two extracellular electrodes spaced some distance apart to record the potential
What is a neuron
Basic structural and functional unit of nervous system
What are a neurons properties
Excitability ( the ability to respond to stimuli )
Conduction of excitation impulse
( from dendrites through cell body of neutrite)
What are the functions of dendrites, axons and synapses
Dendrites conduct info to the cell, axons forward info and synapses transfer info to the next nerve or muscle cell
What is neuron excitability
Ability to receive and conduct impulses related to the distribution of ions on both sides of cell membrane
What is sensitivity to stimuli determined by
The presence of resting membrane potential. E.g. polarization of the neurolemma
What is the resting potential
The constant difference in electrical potential between the inside of the cell and excitable fluid
or
The unequal distribution of inorganic ions between the cytoplasm and the cell protein anions Na+, K+, Cl- and Ca2+
What is depolarization
The reduction or disappearance of membrane potential and its the result of the action of excitory stimuli
What is membrane potential
A potential difference between the inside of a cell and it’s surroundings
What is CAP vs action potential?
Compound action potential - The sum of action potentials recorded from a whole nerve
Action potential - Generated in individual axons
Name the parts of the graph and describe the action potential.
Depolarization, Repolarization, Hyperpolarization
- Intracellular channels open for Na+
- Change in membrane potential by 100mV
- A spike potential is created
- Channels for K+ open
- Repolarization
- Hyperpolarization
- Na-K pump restores initial ion distribution determining the resting potential
What is the potential on the outside of the membrane called and what number is it equal to
It’s equal to zero and called current convention
What is the voltage between both sides of the membrane
The potential inside a cell relative to its surroundings
What cells are resting potential a feature of and what kind of potential do they have
Resting potential is a feature of excitable cells and they have a constant, negative resting membrane potential
What does the inside of an excitable cell contain more of than the outside
More negative ions (electric charge difference)
Resting potential in smooth muscle, striated muscle, neurons and photoreceptors
Neuron: -60 to -70mV
Striated muscle: -95mV
Smooth muscle: -60mV
Photoreceptor: -40mV
How permeable is the cell cytoplasm for ions
Cell cytoplasm is 30x more permeable for K+ ions (140 mmol/l), 10x less for Na+ ions (14.5 mmol/l), 10x less for Cl- ions (4-20 mmol/l) and protein anions are not transported across the cell membrane
What way does K+, Na+ and Cl- travel
K+ travels out through membrane channels, Na+ can’t enter the cell so they create a layer of positive charge outside the cell and Cl- into the cell to exchange with K+ ; they travel outwards following Na+ ions
Protein anions remain inside the cell
When does the concentration of individual ions in the intracellular fluid not change
If the metabolism doesn’t change and if external stimuli do not act on the cell membrane
Under resting potential and equilibrium potential what is created between the concentration of individual ions outside and inside the cell
A balance
How many individual nerve axons does the sciatic nerve contain?
Thousands
Why does the magnitude of the CAP increase with increasing strength of stimulation?
Because different axons have different excitatory thresholds
Is the conduction velocity in the sciatic nerve varied or constant?
It is varied, it depends on the axons diameter.
What effect will each of the following have on conduction velocity in a mammalian motor nerve?
1. Blocking sodium channels with tetrodotoxin
2. Immersion in ice-cold water
3. Increase in nerve diameter
4. Loss of myelination
1,2 and 4 will decrease nerve conduction velocity, while 3 will increase the velocity
Label the graph of CAP and describe it.
Stimulus artifact, depolarization, repolarization and hyperpolarization
As a wave of depolarization travels along the nerve, external electrodes record the change in polarity of the wave as it passes underneath them. (this gives CAP its biphasic waveform)
What is a stimulus?
A change occurring in the internal or external environment causing a change in the properties of the cell membrane or intracellular metabolism.
How do nerve cells respond to stimulus?
Excitation or inhibition
Range of threshold potential
-45 to -60mV
Difference between temporal and spatial summation
Temporal- Subthreshold stimmuli are applied to cell membrane one after another raising membrane potential until one becomes the threshold stimulus
Spatial- Subliminal stiimuli act on membrane simultaneously
How do you initiate an action potential? What does stronger stimulation from neurons do?
Stimulus of sufficient intensity is required to depolarize the neuron
Increase in frequency of potential production by the neuron as all action potentials reach the same amplitude
Difference between Absolute and relative refraction
Absolute refraction- Cell is unable to respond to any stimulus (Na+ channels)
Relative refraction- Stronger stimulus needed to trigger another action potential
Graded potential vs Action potential
Graded potential- important in signaling over shorter distances and are local limmited changes in membrane potential
Amplitude of potential changes is different and depends on strength of stimulus. Contribute to the initiation of action potentials
Action potential- Created in axon membrane and carry information of longer distances
Show the same amplitude and shape along the entire length of the axon,
Limitation of action potentials
Subject to all or nothing law
Limited by relative and absolute refraction
Characteristics depend on stimulation recieved by neuron, structure of axon and degree of its myelination
how is CAP recorded
The CAP electrical activity is recorded by two external electrodes on the peripheral nerve
What are the 5 steps that contribute to reflex time?
1.Converting the energy of a stimulus into a nerve impulse
2.Conducting the impulse to the center
3. Pulse transmission through the center’s synapses
4.Conduction in the efferent nerves
5.Latent effector excitation
What is the objective and the tools used in checking reflex?
Objective: Precise localisation of the disease process. making a diagnosis and prognosis or used in causative therapy
Tools: Neurological hammer, haemostatic forceps, a source of strong spotlight
What is the shape and amplitude of a CAP determined by?
The stimulus voltage and the diameter of axons in the nerve
What is the jendraasik maneuver?
Patient is occupied clenching teeth,flexes all fingers in a hook like shape and interlocks the fingers to illicit a greater response when hit with a reflex hammer
Pupillary light reflex, sphincter. What dialates and constricts the pupil
Multisynaptic, unconditional, autonomous, foreign reflex
Sphincter: Parasympathetic innervation (midbrain), the pupil dilator and sympathetic innervation (Th1-2)
Dilator: Looking at distant objects, poor lighting, pain, emotions, shortness of breath
Constrictor: Strong lighting, looking at objects close by, sleep
At what stimulus voltage do large diameter axons reach the threshold for firing? And why?
At a lower stimulus voltage compared to small diameter axons. Because their membrane resistance to current flow is lower
True or false: At low stimulus voltages, a CAP may be smaller in amplitude because only a few axons are firing
True
How high can the amplitude of CAP rise?
Until it reaches a maximum value and when all axons in the nerve are firing
How did we investigate CAP in lab 1?
By delivering external electrical stimulation to the median nerve at the elbow and recording the time of the muscle contractions with electrodes on the skin (recording is refered to as evoked potential or evoked CAP
What technique did we use in lab 1?
Electromyography (EMG)
What muscle did we stimulate in the first lab?
Abductor pollicis brevis
What is a reflex?
It’s an automatic reaction of the executive organ to an external or internal stimulus that occurs and is directed by the nervous system
What are the parts of the reflex arc?
- Receptor
- Afferent fiber (sensory, ascending
- Center
- Efferent fiber (motor, descending)
- Effector organ
What are receptors capable of?
- Specific recognition of stimulation (physiochemical nature)
- Triggering a response to stimulation (directly or through other structures)
- Convert stimuli into nerve Impulses
what is equilibrium potential of na+ and k+
for na+=+65
for k+=-90
what is membrane potential a result of
result of equilibrium potential of many ions and the value of this potential is closest to the equilibrium potential of the ion for which the membrane is currently the most permeable
what is the resting membrane potential for most nerve cells
-70->-90mV
what is the potential difference due to
- presence of sodium potassium pump
- selective permeability of the membrane towards these ions
- differences in ionic concentrations, mainly the na+ and k+ ions on the sides of the cell membrane
- diffusion of these ions through the membrane according to their concentration gradient ( so called diffusion potential)
What does pump action require
- constant supply of glucose and oxygen
- continuous ATP synthesis
- maintaining a constant temperature of 37 degrees celsius
- co2 removal appropriate concentration of mg2+ ions appropriate concentration of na+ and k+ ions
Stop the pump leads to
- loss of specific properties by cells
- Lack of cell response to stimuli their insexcitability
- Changes in the composition of intracellular fluid changes in the composition of extracellular fluid, in which the na+ ion concentration decreases and k+ ion concentration increases
factors that inhibit pump action include
- hypoxia
- temperature drop
- cellular respiration inhibitors
- selective pump inhibition
Afferent pathway, what neurons does it have and what does it do?
- Sensory neuron
- conducts the stimulation produced in the receptor to the center
- Sensory information (encoded in the form of the frequency of nerve impulses)
- Creates synapse with other nerve cell
Efferent pathway, what neurons does it have and what does it do?
- Somatic and autonomic motor neurons
- transmit stimulation in the form of a nerve impulse to the efferent organs
Recall the different receptor types
Stimulus localisation - Stimulus type
1. Exteroreceptors - Mechanoreceptors
2. Proprio receptors - Presoreceptors
3. Interoreceptors - Thermoreceptors
4. Telereceptors - Nociceptors (pain receptors)
5. [Nociceptors] - Electromagnetic receptors
Where are simple reflexes located?
Spinal cord
Where are complex reflexes located?
Main part + disseminated part in CNS (Central Nervous System)
What are the different roles of the reflex center?
- Analysis and selection of sensory impulses
- Decision on reaction strength (excitation transformation)
- Information integration
- Feedback and antagonistic inhibition
What are the effectors of the reflex center?
- Muscle cell
- Glandular cell
- Reacts with stimulation to the descending impulse
- The effectors enable the animal’s body to respond to stimulation from the nervous system
The unconditional (innate) vs conditioned (acquired) reflexes :
The unconditional:
- Direct reaction to stimulus
- Always same reaction to the same stimulus
The conditional:
- Learned and shows great variability in response to stimuli
- Can dissapear and re-emerge
Own reflexes vs Foreign reflexes
Own
- Receptor within the effector (e.g. knee reflex)
Foreign
- Receptor outside the effector (most often in skin or mucosa (e.g. withdrawal reflex)
What are superficial reflexes triggered by? Example of reflex.
- Irritation of the skin or mucous membrane
- E.g. Blinking of irritated eyes
What are deep reflexes triggered by? Example of reflex.
- Irritation of the proprioreceptors
- Contractions of streched muscle
- E.g. Contraction of biceps
What are Visceral reflexes triggered by? Example of reflex.
- Reactions of ANS (autonomic nervous system) to external stimuli
- E.g. Constriction of pupils under the influence of light
From the pretectal nucleus (thalamus) where do the fibers travel to
The oculomotor nucleus (midbrain)
what happens during a nervous system/ neurological examination
- Defining awareness, behaviour, the animals posture and manner of walking
- Examination of posture and postural reactions (proprioceptive reactions)
- Examination of cranial nerves
- Examination of spinal reflexes
- Testing the sensory part, sensitivity and muscularity of the animal
what happens during a cranial nerve examination
- Smell (NC 1) - observation of the animal in the office and the owner’s account of the animal’s behavior at home or on a walk (the animal does not sniff if it does not encounter an interesting object)
2.Sight (NC II) - several tests, incl. placing obstacles (e.g. chairs, boxes) in the room that the animal does not know
- Sneezing reflex (NC V II r.) - irritate the nasal mucosa with a brush, bird’s feather or a rod
What happens during a pupil examination
(NC II, III parasympathetic fibers, Th1-3 sympathetic n.)
Both pupils, their size, symmetry and reaction to light should be compared.
Perform the test in a darkened room using a strong light source.
Results:
uneven pupills (anisokoria),
narrowing of both pupils (miosis)
dilatation of both pupils (mydriasis).
Mydriasis indicates damage to the parasympathetic innervation of the pupil, miosis indicates
damage to the sympathetic innervation.
What happens during an examination of the spinal reflex
Examination of spinal reflexes allows the assessment of the lower motor neuron (LMN)
and the upper motor neuron (UMN).
What happens during an examination of the patellar reflex
The patellar reflex (L4-L6 segments, femoral nerve) is performed by hitting the flat side
of the neurological hammer against the patellar straight ligament. The extension of the
lower leg is then observed
What happens during an examination of the flexor reflex
The flexor reflex (withdrawal reflex) (L7-S1 segments, sciatic nerve). The examiner
should use his fingers or hemostatic forceps to press against the interdigital fold. The
correct reaction is to withdraw the limb. This reflex also allows the assessment of limb
strength, in a neurological examination.
How to examine the reflex of the extensor carpii radialis and what is the reaction for it
The reflex of the extensor carpii radialis (segments C7-T2) is performed by hitting with the top of the
neurological hammer on this muscle.
Reaction: straightening of the front paw at the wrist.
How is the examination of the flexor reflex performed
The flexor reflex (segments C6-T2) is performed similarly to the pelvic limb.
Is it possible to perform on the biceps and triceps reflexes, where are they located
It is also possible to perform the biceps and triceps reflexes in the shoulder limb, but their clinical
significance is small.
How many segments and what reflexes and nerves work for The perineal, vulvar, bulbocavernous reflexes
S2-3 segments, vulvar nerve
What should you pinch with a hemostatic forceps
The area of the perineum,
vulva, foreskin or the area around the anus
What reaction do you get from pinching The area of the perineum,
vulva, foreskin or the area around the anus
symmetrical tightening of the anal sphincter
What is the cns (central nervous system) sensitive to
Hypoxia and ischemia
After how many minutes of interruption in the supply of oxygen and blood irreversible changes in brain cells occur
5 minutes
After how many minutes does nervous activity disappear
0.5 to 1.5 minutes
What structures are most sensitive to hypoxia
the cortex, hippocampus, cerebellum and subcortical nuclei
What are less sensitive to a lack of oxygen
Nerve fibers and muscle cells
The centers of the spinal cord show greater resistance to …
Hypoxia
Stenson’s experiment shows how sensitive the CNS is to … and what is the definition of …
cardiac arrest (lack of oxygen and nutrients)
How do you execute stensons experiment
Execution:
By pressing abdominal wall of the rabbit compress the abdominal aorta, inhibiting the blood supply to the lumbosacral part of the spinal cord:
20-30 sec. the tonus of the tail muscles is lost
30-40 sec. the tonus of the hind limbs disappears (inertia)
1min. The feeling of pain fades (needle stick to the skin of the hind limbs)
