Fundamentals of the Nervous System Flashcards
The master controlling and communicating system of the body
Nervous System
Functions of the nervous system:
- Sensory Input
- Integration
- Motor Output
The two principle cell types of the nervous system are:
- Neurons
2. Supporting Cells (Neuroglial Cells)
Smaller cells that work with/ support neurons
Neuroglial
Part of neuron that receives information:
Dendrite
List the sequence of the nervous system
Sensory input–> Integration–> Motor Output
Has myelinated axons
White matter
Has unmyelinated axons or structures
-Includes cell body and dendrites
Gray Matter
Structural units of the nervous system
composed of body, axon, and dendrites
Characteristics of Neurons:
- long-lived
- amniotic
- Have a high metabolic rate
Function in:
- Electrical Signaling
- Cell-to-cell signaling during development
Neural Plasma Membrane
Nerve cell body is also known as:
Perikaryon or soma
Characteristics of nerve cell body:
- Has no centrioles (thus amniotic)
- Has well-developed Nissl Bodies
- Contains an axon hillock
Rough ER
-Appears to make the neurotransmitters of the neuron
Nissl Bodies
Slender processes branching form the hillock
Axon
Long axons are called:
Nerve Fibers
Secretory component of neuron
end of axon tail
Axon Terminal
Usually ___ unbranched axon per neuron
One
Functions of axons:
- Generate and transmit action potential
- Secrete neurotransmitters from the axonal terminals
- Neurotransmitters initiate a neural impulse in the next neuron to excite particular muscles or glands
A neural impulse in the next neuron or excite a particular muscle or gland
Neurotransmitters
CNS
- Brain
- Spinal Cord
PNS
- Crainial Nerves
- Spinal Nerves
The supporting cells (neuroglia) have:
Many different types with specific functions
- Produce myelin on peripheral myelinated neurons
- Increase neurotransmission
*Not found in brain or spinal cord
Schwann Cells
Support clusters of neuron cell bodies (ganglia)
Satellite Cells
- Most abundant, versatile, and highly branched glial cells
- Mop up excess ions
- Induce synapse formation
- Connect neurons to blood vessels
*Found in CNS
Astrocyte
*Starburst
- Found in CNS
- Are myelin-forming cells
Oligodendrocytes
- Small, ovid cells with spiny processes
- Phagocytic cells of the CNS
Microglia
- Range in shape from squamous to columnar
- Ciliated cells of CNS
- Line the central canal of the spinal cord and ventricles of the brian
Ependyma
Einstein has more ____ in his brain
More neuroglial (not more neurons)
- Whitish, fatty (protein-lipoid), segmented sheath around most long axons
- It functions to insulate the axon of a neuron
- Make sure the neuron impulses run down the axon and stimulates the next cell
Myelin Sheath
___ is formed by Schwann cells in the PNS
Myelin
Remaining nucleus and cytoplasm of a Schwann Cell
Neurilemma
- Gaps in the myelin sheath between adjacent Schwann cells
- They are sites where axon collaterals can emerge
Nodes of Ranvier (Neuorfibral Nodes)
In _____, there is no regeneration if you cut the axon
in spinal cord
*B/c oligodendrocytes do not divide
Both myelinated and unmyelinated fibers are present
Axons of the CNS
When myelin sheaths are formed in the CNS, they are formed by:
Oligodendrocytes
Two divisions of the Nervous System:
- Sensory (afferent) division
- Motor (efferent) division
Two main systems in the Motor Division:
- Somatic Nervous System
- Automatic Nervous System
Picks up sensory information and delivers it to CNS
Sensory (afferent division)
Carries info to skeletal muscle
Motor (efferent) division
Carries info to smooth muscle, cardiac muscle, and glands
Autonomic nervous system
Sensory Functions:
Sensory receptors gather info and info is carried to the CNS
Integrative Functions:
Sensory information used to create:
- Sensations
- Memories
- Thoughts
- Decisions
Motor Functions:
- Decisions are acted upon
- Impulses are carried to effectors
What are effectors?
Muscles or glands
Structural differences of neurons:
- Bipolar
- Unipolar
- Multipolar
- Two processes
- In eyes, nose, and ears
Bipolar
- One process
- Neural Ganglia
Unipolar
- Many processes
- Significant component of the CNS
Multipolar
Functional differences of neurons:
- Sensory Neurons
- Interneurons
- Motor neurons
- Afferent neurons
- Carry impulses to the CNS
- Most are unipolar (some bipolar)
Sensory Neurons
- Link neurons
- Multipolar
- Park of CNS (brain and spinal cord)
Interneurons
- Multipolar
- Carry impulses away from the CNS to effectors (muscles and glands)
Motor Neurons
Neurons are highly _____
irritable
Action potentials, or nerve impulses, are generated from:
neurotransmitters
Neurotransmitters are released from:
synaptic bulb when stimulated by a neural impulse
Measure of electrical potential difference in energy
Voltage (V)
Voltage measured between two points
Potential Difference
The flow of electrical change between two points
Current (I)
Hinderance to charge flow
Resistance (R)
Electrical current in the body reflects the flow of ____ rather than electrons
ions
There is a potential on either side of membranes when:
- The number of ions is different across the membrane
- The membrane provides a resistance to ion flow
What is resting membrane potential?
-70mV Millivolts
At -70mV, there is a ____ concentration of Sodium outside the membrane
outside
Types of plasma membrane ion channels:
- Passive, or leakage, channels
- Chemically gated channels
- Voltage-gated channels
- Mechanically gated channels
Type of ion channel that is always open:
Passive, or leakage, channels
Open with binding of a specific neurotransmitter
Chemically gated channels
Open and close with response to membrane potential
Voltage-gated channels
Open and close with response to physical deformation of receptors
Mechanically gated channels
Operation of a Gated Channel
- Example: Na+-K+ pump (gated channel)
- Closed when a neurotransmitter is not bound to the extracellular receptor (Na+ cannot enter the cell and K+ cannot exit the cell)
- Open when a neurotransmitter is attached to the receptor (Na+ enters the cell and K+ cannot exit the cell)
Operation of a Voltage-Gated Channel
- Example: Na+ channel
- Closed when the intracellular environment is negative (Na+ cannot enter the cell)
- Open when the intracellular environment is positive (Na+ can enter the cell)
When gated channels are open:
- Ions move quickly across the membrane
- Movement is along their electrochemical gradients
- An electrical current is created
- Voltage changes across the membrane
When gated channels open, and ions move across the membrane, they move along their ____
electrochemical gradient
In gated channels, ions flow from an area of ___ to an area of _____
high concentration to an area of low concentration
The potential difference (-70mV) across the membrane of a resting neuron is generated by different concentrations of:
Na+, K+, Cl-, and protein anions (A-)
Ionic differences are the consequence of:
- Differential permeability of the neurolemma to Na+ and K+
- Operation of the sodium-potassium pump
Changes in membrane potential are created by three events:
- Depolarization
- Repolarization
- Hyperpolarization
The inside of the membrane becomes less negative
Depolarization
the membrane returns to its resting membrane potential
Repolarization
The inside of the membrane becomes more negative than the resting potential
Hyperpolarization
Before you open gated channels, the inside is ___
more negative
A ____ might not generate an action potential
weak stimulus
Short-lived, local changes in membrane potential (cover a short distance)
Graded Potentials
Graded potentials decrease in:
intensity with distance
Graded potentials’ magnitude varies directly with:
the strength of the stimulus
Sufficiently strong graded potentials can initiate:
action potentials
*ex: pebbles in a pond
A brief reversal of membrane potential with a total amplitude of 100 mV
Action Potential (APs)
Action potentials are only generated by:
muscle cells and neurons
____ do not decrease in strength over distance
Action Potentials
They are principle means of neural communication
Action Potentials
An action potential in the axon of a neuron:
nerve impulse
Na+ and K+ channels are closed
Action Potentials: Resting State
In the resting state, ____ are closed and ____ are open
Activation gates are closed and inactivation gates are open
In the Depolarization Phase, ____ gates are open, ____ gates are closed
Na+ gates are opened, K+ gates are closed
A critical level of depolarization (-55 to -50 mV)
Threshold
At threshold, depolarization becomes:
self-generating
*Dendrite= more +, so they want to get to a negative area, so they automatically flow down axon
- Sodium inactivation gates close
- Membrane permeability to Na+ declines to resting levels
- As sodium gates close, voltage-sensitive K+ gates open
- K+ exits the cell and internal negativity is restored
Repolorization Phase
- Potassium gates remain open, causing an excessive efflux of K+
- This efflux causes hyperpolorization of the membrane
- The neuron is insensitive to stimulus and depolarization
Hyperpolorization
- Restores the resting electrical conditions of the neuron
- Does not restore the resting ionic conditions
Repolorization
Restores resting ionic conditions
Sodium-Potassium Pump
Describe sequence of events:
- When open up chemically gated channel, sodium will move in
- Sodium voltage gated channels open up (more sodium comes in)
- We need to change membrane potential
- to +30 in order to open up K+ voltage gated channel
- K+ opens up, voltage gated channels form b/c APs form
- When K+ opens, depolarization (potassium moving out) bc K+ is sensitive to 30+ mV
- Sodium still in axon and continues to move down
- Keeps occuring segmentally down length of axon at different voltage gates
- Stimulate release of neurotransmitters
Ions of the extracellular fluid move toward the area of greatest negative charge
- A current is created that depolorizes the adjacent membrane in a foreword direction
- The impulse propagates away from its point of origin
Propogation of an Action Potential
The action potential moves:
away from the stimulus
When sodium gates are closing, potassium gates:
are open and create current flow
15 to 20 mV
Threshold
Action potentials either happen completely or not at all (not stronger or weaker)
All-or-none phenomenon
- Established by the total amount of current flowing through the membrane
- Weak (subthreshold) stimuli
- Strong (threshold) stimuli
Threshold
Not released into action potentials
Weak (subthreshold) stimuli
Released into action potentials
Strong (threshold) stimuli
All action potentials are alike and are:
independent of stimulus intensity
Strong stimuli can generate an action potential more often than
weaker stimuli
The CNS determines stimulus intensity by:
the frequency of impulse transmission
Time from the opening of the Na+ activation gates until the closing of inactivation gates
Absolute Refractory Period
- Prevents the neuron from generating an action potential (while still generating first)
- Ensures that each action potential is separate
- Enforces one-way transmission of nerve impulses
Absolute Refractory Period
The interval following the absolute refractory period when:
- Sodium gates are closed
- Potassium gates are open
- Repolorization is occuring
- The threshold level is elevated, allowing: strong stimuli to cause action potentials
Relative Refractory Period
Extends from depolarization through hyperpolorization
Relative Refractory Period
Rate of impulse propagation is determined by:
- Axon diameter–> the greater the diameter, the faster the impulse
- Presence of a myelin sheath–> myelination dramatically increases impulse speed
Fluid-filled space separating the presynaptic and postsynaptic neurons
Synaptic Cleft
Prevents nerve impulses from directly passing from one neuron to the next
Synaptic Cleft
Transmission across the synaptic cleft:
- Is a chemical event (as opposed to an electrical one)
- Ensures unidirectional communication between neurons
Nerve impulses reach the axonal terminal of the presynaptic neuron and open ___ channels
Ca2+
*Bringing in Ca+ will stimulate vesticles to release neurotransmitters
____ is
- released into the synaptic cleft via exocytosis
- Crosses the synaptic cleft
- binds to receptors on the postsynaptic neuron
Neurotransmitter
Neurotransmitter bound to a postsynaptic neuron:
- Produces a continuous postsynaptic effect
- Blocks reception of additional “messages”
- Must be removed from its receptor
Removal of neurotransmitters occurs when they:
- Are degraded by enzymes
- Are reabsorbed by astrocytes or the presynaptic terminals
- Diffuse from the synaptic cleft
The two types of graded postsynaptic potentials are:
- EPSP
- IPSP
A single EPSP _____ induce an action potential
cannot
EPSPs must summate:
temporally or spacially
An ____ depolarizes the membrane of postsynaptic neuron
EPSP
Hyperpolorizes membrane of post synaptic neuron
IPSP
Action potential of postsynaptic neuron becomes LESS likely
IPSP
Action potential of postsynaptic neuron becomes MORE likely
EPSP
EPSPs and IPSPs are added together in a process called
Summation
More EPSPs lead to:
greater probability of action potential
Chemicals used for neuronal communication with the body and the brain
Neurotransmitters
*classified chemically and functionally
- Acetylcholine (ACh)
- Peptides
- Novel Messengers
Chemical Neurotransmitters
- Degraded by the enzyme acetylcholinesterase
- Biogenic Amines
- Amino Acid
Acetylcholine
ATP and dissolved gasses NO and CO
Novel Messengers
Glycine, GABA, Glutamate
Amino Acids
Dopamine, Serotonin, Epi
Biogenic Amine
Encephaline (Endorphins)
Peptides (IPSP)
Groups of interneurons that make synaptic connections with one another
Neuronal Pools
Interneurons work together to perform:
A common function
- Neuron receives input from sensory neurons
- incoming impulses represent information from difference types of sensory receptors
- Allows nervous system to collect, process, and respond to info
- Makes it possible for a neuron to sum impulses from different sources
Convergence
- One neuron sends impulses to several neurons
- Impulse from a single neuron in CNS may be amplified to activate enough motor units for a single muscle contraction
Divergence
Membrane surrounding CNS
Meninges
Three layers of meninges:
- dura matter
- arachnoid matter
- pia matter
- Interconnected cavities
- within cerebral hemispheres and brain stem
- continuous with central canal of spinal cord
- filled with cerebrospinal fluid (CSF)
Ventricles