Topic 2: Physiology of Nerve Cells and Synaptic Transmission Flashcards
Receive and send information communicates and controls throughout the rest of the body
Nervous System
Nervous System organs
brain, spinal cord, nerves, and ganglia
Nervous System communicate by means of
electrical signals
rapid, specific
Information processing
- Sensor
- sensory input - Integration
- motor output - Effector
Central Nervous System (CNS)
Brain & Spinal Cord
Peripheral Nervous System (PNS)
Cranial nerves
Ganglia outside CNS
Spinal nerves
Supporting Cells (GLIAL CELLS)
- Neuroglia in CNS
- Microglia
- Ependymal cells
- Oligodendrocytes
- Astrocytes
scavenger cells that resemble tissue macrophages and remove debris resulting from injury, infection, and disease
Microglia
(Glial Cells) Resemble stars. Their threadlike branches attach to neurons and to small blood vessels holding both structures together.
Astrocytes
Astrocytes branches form a 2 layer structure called the
Blood brain barrier
Separates blood tissue and nervous tissue. Protects brain from harmful chemicals that might be found in the blood.
Blood brain barrier
Supporting Cells (GLIAL CELLS)
- Neuroglia in PNS
Schwann Cells
- neurolemmocytes
- myelinate neurons
Satellite Cells
- regulate the chemical environment
Neuroglia that form the myelin sheath around axon
Oligodendrocytes and Schwann Cells
An autoimmune disease possibly triggered by a virus ingenetically susceptible individuals
- oligodendrocytes and myelin sheaths of CNS deteriorate and are replaced by hardened scar tissue
- occur especially between 20-40 years of age
- nerve fibers are severed
- myelin sheaths in CNS are gradually destroyed à short circuits; loss of impulse conduction affects mostly young adult
Multiple Sclerosis
Common symptoms of Multiple Sclerosis
Visual Problems
Muscle Weakness
Clumsiness
Eventual paralysis
A hereditary disorder seen mainly in infants of Eastern
European Jewish ancestory
- abnormal accumulation of a certain glycolipids (GM2) in myelin sheath as it accumulates it disrupts conduction of signals
- results in blindness, loss of coordination,dementia
- symptoms appear before 1 yr of age, death by 3 or
Tay-Sachs Disease
____ are the fundamental unit of the nervous system specialized to transmit information to different parts of the body
NEURONS (nerve cells)
Special Characteristics of Neurons
- Extreme longevity
- Amitotic (not mitosis)
- High metabolic rate
[Time] Brain damage
0-1 min: Cardiac irritability
0-4 minutes: Brain damage not likely
4-6 minutes: Brain damage possible
6-10 minutes: Brain damage very likely
Above 10 minutes: Irreversible brain damage
- process in which a neuron’s cell body responds to injury or stress.
- process that occurs in the peripheral nervous system (PNS) when a nerve fiber is injured or severed.
- Chromatolysis
2.Wallerian Degeneration
(Neuron)
It is the main metabolic and genetic center of the neuron.
- Region in which the neuron receives synaptic input from other neuron
Cell Body
(Neuron)
It is the main direct recipients of signals from other neurons
- May account for more than 90% of the surface area available for synaptic contact
Dendrites
(Neuron)
It conveys the output of the cell to other neuron
Axon
Three functional components of neurons
- Input region
- Conducting component
- Secretory
Sensory neurons always release _____ that excites _____
neurotransmitter; postsynaptic neuron
(Neurotransmitter)
- Increase postsynaptic membrane permeability to Na+
- Threshold is reached for message to be sent.
Excitatory neurotransmitter
(Neurotransmitter)
- Decrease permeability to Na+
- Decreases chance nerve impulse will occur
Inhibitory neurotransmitter
Structural Classification of Neurons
Unipolar cell
Bipolar cell
Pseudo-unipolar cell
Multipolar cells (Motor neuron, Pyramidal, Purkinje cell)
Functional Classification of Neurons:
1. carry impulse from the sense organs to the brain and spinal cord (CNS).
2. connect sensory and motor neurons and carry impulse between them.
3. convey impulses (motor output) from the CNS to the effector cells (muscles and glands)
- Sensory Neurons
- Interneurons
- Motor neurons
Neurons are highly ___
irritable
(Operation of gated channels
- Plasma membranes are peppered with a variety of _____
- Passive or leakage channels are _____
- The Active or gated channels (2)
- ion channels
- always open
- Chemically gated channels & Voltage gated channels
- potential difference is measured
- resting cells potential difference
- muscle and nerve cells avergae
- voltage
- -50 to -200 mV
- average: - 70 mV
T or F
1. There are more negative ions inside cell
2. Negative ions (esp proteins) generally can cross membrane
- T
- F
small to large changes in membrane potential
due to opening and closing of chemical
- local phenomenon, signal over short distances
Graded potential
(Graded potential)
1. membrane potential decreases
2. membrane potential increases
- Depolarization
- Hyperpolarization
Depolarization occurs and response stimulatory
- Depolarization might reach threshold producing an action potential and cell response
Excitatory postsynaptic potential (EPSP)
Hyperpolarization and response inhibitory
- Decrease action potentials by moving membrane potential farther from threshold
Inhibitory Postsynaptic Potential (IPSP)
summation of EPSP’s or IPSP’s due to repeated stimulation by one neuro
Temporal Summation:
summation of EPSP’s or IPSP’s due to stimulation by more than one neuron simultaneously
Spatial Summation
a rapid, long-distance signals, all-or-none change in the membrane potential, followed by a return to the resting membrane potential
Action Potential
In a neuron, a transmitted action potential is called
nerve impulse
Only axons are capable of generating
action potentials (________)
axon hillock
3 phases of Action Potential
- depolarization
- repolarization
- undershoot
If a neuron has received a threshold stimulus and
is undergoing depolarization and repolarization,
how much time must pass before a second
stimulus can produce an action potential?
In the interval from the onset of the action potential
until repolarization is about one-third complete, no
stimulus can elicit another response; the dead
phase ( absolute refractory period)
(Action potential)
To generate a ction potential an axon requires a stimulus of a certain minimum strength
Threshold
Means each action potential has the same amplitude independently from the strength of the stimulus
All-or-none
A second action potential cannot occur during this period
Refractory period
Refractory Period (2)
- Absolute Refractory Period
- Relative Refractory Period
Conduction velocities of Axon
- Myelinated axon (node of Ranvier - action potential - myelin sheath - spread of depolarization)
- Unmyelinated axon (- action potential)
Cellular junctions where signals are transmitted from neurons
Synapses
The Synapses Target cells
- Other neurons (Axodendritic synapse, Axoaxonic synapse Axosomatic)
- Muscle cell (Neuromuscular junctions)
- Gland Cells (neuroglandular junctions)
Two types of communicating junctions or synapses:
- Electrical synapses (via gap junctions)
- Chemical synapses (involving neurotransmitters)
(Synapse)
This allows current to flow directly from one cell to another. It also allows the exchange of small molecules between cells.
- A patch where cells are separated by a narrow gap of 2- 4 nm
Electrical synapses (Gap junctions)
Gap junctions are formed where hexameric pores called _____ connect with one between cells.
connexons
Allows the flow of ions between neuron and are
specialized for the release and reception of
chemical neurotransmitters.
- Unidirectional
Chemical Synapses
(Chemical synapse)
An actual gap or space between nerve cells;
separated by the
Synaptic cleft (30 to 5m nm wide)
Chemical Synapses: Two Parts
- Axon terminals: Synaptic vesicles
- Receptor Region of the postsynaptic neuron
Criteria that define a neurotransmitter
- Must be present at presynaptic terminal
- Must be released by depolarization, Ca++-dependent
- Specific receptors must be present
Synaptic vesicle release consists of three principal steps:
Docking
Priming
Fusion
____lie close to plasma membrane (within 30 nm)
(Docking) Docked vesicles
can be induced to fuse with the plasma membrane by sustained depolarization, high K+, elevated Ca++, hypertonic sucrose treatment
(Priming) Primed vesicles
is the site of physiological release, and can sometimes be recognized as an electron-dense structure
The ‘active zone’
Events of signal transmission at a chemical synapse
- Action potentials arrive at axon terminal.
- Voltage-gated Ca2+ channels open
- Ca2+ enters the cell
- Ca2+ signals to vesicles
- Vesicles move to the membrane
- Docked vesicles release neurotransmitter by exocytosis.
- Neurotransmitter diffuses across the synaptic cleft and binds to receptors.
Chemical Synapse:
- According to how they affect the membrane potential of the postsynaptic neuron
- Excitatory Synapes- Excitatory postsynaptic potentials (EPSPs)
- Inhibitory Synaspes- Inhibitory postsynaptic potentials (IPSPs)
What determines whether a stimulus will be strong
enough to produce an action potential in a nerve cell
The resting membrane potential is about -70mV. A threshold stimulus will sufficiently increase the membrane’s permeability to sodium ions to raise the membrane potential to about -55mV.
Once this threshold potential has been reached , complete depolarization and reporalarization occur and an action potential is generated
Is the size of the action potential related to the strength of the stimulus? Why?
No. Nerve and muscles obey the all-or-none law,
which states that a threshold stimulus evokes a
maximum response and that a subthreshold stimulus
evokes no response
What factors influence the speed at which impulses are conducted along the excitable cell membrane.
- Diameter of the conducting fiber
- Temperature of the cell
- Presence or absence of the myelin sheath
- Saltatory conduction
