- 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

- Crainial Nerves - Spinal Nerves

Fundamentals of the Nervous System Flashcards by Sarah Beddingfield

The master controlling and communicating system of the body

Nervous System

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Functions of the nervous system:

Sensory Input
Integration
Motor Output

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The two principle cell types of the nervous system are:

Neurons

2. Supporting Cells (Neuroglial Cells)

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Smaller cells that work with/ support neurons

Neuroglial

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Part of neuron that receives information:

Dendrite

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List the sequence of the nervous system

Sensory input–> Integration–> Motor Output

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Has myelinated axons

White matter

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Has unmyelinated axons or structures

-Includes cell body and dendrites

Gray Matter

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Structural units of the nervous system

composed of body, axon, and dendrites

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Characteristics of Neurons:

long-lived
amniotic
Have a high metabolic rate

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Function in:

Electrical Signaling
Cell-to-cell signaling during development

Neural Plasma Membrane

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Nerve cell body is also known as:

Perikaryon or soma

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Characteristics of nerve cell body:

Has no centrioles (thus amniotic)
Has well-developed Nissl Bodies
Contains an axon hillock

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Rough ER

-Appears to make the neurotransmitters of the neuron

Nissl Bodies

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Slender processes branching form the hillock

Axon

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Long axons are called:

Nerve Fibers

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Secretory component of neuron

end of axon tail

Axon Terminal

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Usually ___ unbranched axon per neuron

One

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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

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A neural impulse in the next neuron or excite a particular muscle or gland

Neurotransmitters

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CNS

Brain

- Spinal Cord

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PNS

Crainial Nerves

- Spinal Nerves

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The supporting cells (neuroglia) have:

Many different types with specific functions

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Produce myelin on peripheral myelinated neurons
Increase neurotransmission

*Not found in brain or spinal cord

Schwann Cells

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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