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Anatomy and Physiology Chapter 12- Intro to NS
Introduction to NS
76
Anatomy
Undergraduate 2
03/19/2013

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Term
The Role Of the Nervous System
Definition
The NS detects environmental changes that impact the body, then responds to those changes. It is responsible for all our behaviors, memories, and movements.
Term
the 2 branches of the NS
Definition
The Central Nervous System (CNS), which is the brain and spinal cord (it processes environment) and the Peripheral Nervous System, which is everything else, including the spinal nerves, ganglia,enteric plexus, and sensory receptors. The PNS breaks down even more into the somatic NS, the Autonomic NS, and the Enteric NS (it senses environment)
Term
3 fundamental steps of NS
Definition
1. A sensory function detect internal and external stimuli (PNS)
2. An interpretation is made (cns)
3. A motor response occurs (PNS)
Term
Neuron
Definition
Nerve Cell-- receives, processes, and transmits info by manipulating the flow of charge across their membranes (they cant regenerate, once a neuron is lost, it will not reproduce)
They are the real functional unit of the NS, forming complex processing networks within the brain and spinal cord that bring all regions of the body under CNS
Term
Neuroglia (glial cells)
Definition
Support and provide nutrition to the brain but do not manipulate info. They maintain the internal environment so that neurons can do their job. Neuroglia can regenerate if loss. They are the glue that supports and maintains the neuronal network. They are smaller than neurons, but greatly outnumber them
Term
The peripheral NS breaks down into?
Definition
Somatic NS
Autonomic NS
Enteric NS
Term
Somatic NS (voluntary)
Definition
The SNS consists of:
1. somatic sensory (afferent-towards) neurons that convey info from sensory receptors in the head, body wall, and limbs towards the CNS
2. Somatic motor (efferent-away) neurons that conduct impulses away from the CNS towards skeletal muscles under voluntary control in the periphery
3. Interneurons that conduct impulses between afferent and efferent neurons within the CNS
Term
Interneurons
Definition
Interneurons are any neurons that conduct impulses between afferent and efferent neurons within the CNS
Term
The Autonomic NS (involuntary)
Definition
The ANS consists of:
1. Sensory neurons that convey information from autonomic sensory receptors located primarily in visceral organs like the stomach or lungs to the CNS
2. Motor Neurons under involuntary control conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands. The motor part of the ANS consists of two branches; the sympathetic and parasympathetic divisions
Term
Ganglia
Definition
small masses of neuronal cell bodies located outside the brain and spinal cord, usually closely associated with cranial and spinal nerves.
Term
Enteric NS
Definition
"the brain of the gut"; involuntary controls GI propulsion, and acid and hormonal secretions, it was once considered part of the ANS. There are over 100 million neurons in enteric plexuses
Term
Neurons Consist of?
Definition
A cell body, dentrites, axon, axon terminals, myelin sheath (some)
Term
Neuronal Cell Body
Definition
has a nucelus surrounded by cytoplasm, contains orgallelles (in neurons the rough ER is called Nissl bodies) it has a striped tiger appearance, but no miotic apparatus is present, since neurons dont undergo miosis
Term
Dentrites
Definition
Neurons gather info at dentrites and process it in the dendritic tree and cell body. Dentrites are the recieving end of the neuron. They are short, highly branched structures that conduct impulses toward the cell body. They also contain organelles
Term
Axon
Definition
Axons conduct impulses away from the body towards another neuron or effector cell. The Axon hillock is where the axon joins the cell body. The initial segemnt is the beginning of the axon. The trigger zone is the junction between the axon hillack and the initial segment
Term
Axon Terminals and Synaptic End Bulbs
Definition
The axon and its collaterals end by dividing into many fine processes called axon terminals. The tips of some azon terminals swell into the bulb-shaped structures called synaptic end bulbs
Term
Synapse
Definition
The site of communications between 2 neurons or btwn a neuron and another effector cell
Term
Synaptic Cleft
Definition
the gap between the pre and post synaptic cells
Term
Synaptic Vesicles
Definition
synaptic end bulbs and other varicosites on the axon terminals of presynaptic neurons contain many tiny membrane-enclosed sacs called synaptic vesicles that store packets of NTs
Term
Slow Axonal Transport
Definition
1. Conveys axoplasm in one direction only-- from the cell body toward to axon terminals
2. It supplies new axoplasm (the cytoplasm in axons) to developing or regenerating axons, and replenishes axoplasm in growing and mature axons
Term
Fast Axonal Transport (FAT)
Definition
1. moves materials in both directions
2. Fast axonal transport that occurs in an anterograde (forward) direction moves organelles and synaptic vesicles from the cell body to the axon terminals. FAT that moves backwards moves membrane vesicles and other cellular materials from the axon terminals to the cell body to be degraded or recycled (tropic chemcials)
Term
Multipolar Neurons
Definition
have several dendrites and only one axon and are located throughout the brain and spinal cord. Most of the neurons in the human body are mulitpolar
Term
Bipolar Neurons
Definition
have one main dentrite and one axon. they are used to convey special senses of sight, smell, hearing, and balance. As such, they are found in the retina of the eye, and the olfactory area of the brain
Term
Unipolar Neurons
Definition
contain one process which extends from the body and divides into a central branch that functions as an axon and dentritic root. Unipolar structure is often employed for sensory neurons that convey touch and streching info from the extremeties.
Term
Sensory or Afferent Neurons
Definition
Convey action potentials into the CNs via cranial and spinal nerves. Most are unipolar
Term
Motor or Efferent Neurons
Definition
Convey action potentials away from the CNS to effectors (muscle and glands) in the periphery through cranial and spinal nerves. Most are multipolar.
Term
Neuroglia
Definition
they do not generate or conduct nerve impulses. they support neutrons by forming the blood brain barrier, forming the mylein sheath, making the CSF, and participating in phagocytosis
Term
Neuroglia CNS
Definition
Astrocytes, oligodendrocytes,microglia, and ependymal cells
Term
astrocytes
Definition
support neurons in the CNS and maintain the chemical environment (sodium and potassium) They are the most common
Term
oligodendrocytes
Definition
produce myelin in CNS
Term
microglia
Definition
participate in phagocytosis, and protect brain cells from toxins
Term
ependymal cells
Definition
Form and circulate CSF
Term
Neuroglia PNS
Definition
Satellite Cells and Schwann Cells
Term
Satellite Cells
Definition
Support neurons in the PNS
Term
Schwann Cells
Definition
Produce myelin in PNS, the outer nucleated cytoplasmic later of the schwann cell, which encloses the myelin sheath is the neurolemma. When an axon is injured, the neurolemma aids regeneration by forming a regeneration tube that guides and stimulates regrowth of the axon
Term
Myelination
Definition
process of forming a myelin sheath, which insulates and increases nerve impulse speed. Oligodendrocytes in CNS form it, Schwann cells in PNS form it. MS is a disease where the body attacks myelin sheath
Term
Nodes of Ranvier
Definition
the gaps in the myselin sheath
Term
White Matter
Definition
White matter of the brain and spinal cord is formed from aggregations of myelinated axons from many neurons
Term
Gray Matter
Definition
(gray because it lacks myelin) of the brain and spinal cord is formed from neuronal cell bodies and dentrites.
Term
Graded Potentials
Definition
are used for short distance communication only. Graded potentials have different names depending on the type of stimulus and where they occur. They are voltage variable aptitudes that can be added together (summate) or cancel each other out-- the net result is a larger or smaller graded potential. Graded Potentials occur mainly on dendrites and cell body of a neuron--they do not travel down the axon
Term
Action potentials
Definition
allow communcations over long distances within the body. It is a signal which travels the length of the neuron. During an AP, the membrane potential reverses and then eventually is restored to its resting state. If a neuron receives a threshold stimulus, a full strength nerve impulse is produced and spreads down the axon of the neuron to the axon terminals. If a stimulus is not strong enough, no nerve impulse will result
Term
Ligand-Gated channels
Definition
respond to a NT and are mainly concentrated at the synapse (produce graded potentials)
Term
Voltage Gated Channels
Definition
respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon. (Produce APS)
Term
Mechanically Gated Channels
Definition
respond to mechanical deformation (applying pressure to a receptor)(produce graded potentials)
Term
"leakage" channels
Definition
They are also gated, but they are not active, and they open and close randomly
Term
The RMP in a neuron is
Definition
-70 mv.A cell that exhibits RMP is said to be polarized. in this state the cell is primed, and is ready to produce an action potential, but it must first produce graded potentials to depolarize the cell to threshold.
Term
Depolarizing
Definition
Increase in mv, sodium rushes into the cell
Term
hyperpolarizing
Definition
decrease in mv
Term
An Action Potential
Definition
Term
2 main phases of AP
Definition
1. Depolarizing Phase
2. Repolarizing Phase
(-70 is RMP, -55 is threshold. =30 is peak of AP
Term
Depolarization
Definition
Graded potentials that result in depolarization of the neuron from -70 mV to threshold (about -55mv) will cause a sequence of events to rapidly unfold. Voltage gated NA+ channels open during the steep depolarization phase allowing sodium to rush into the cell making it more positive.
Term
Repolarization
Definition
Potassium channels open and potassium rushes out of the cell, the process of k leaving overshoots the RMP but eventually the RMP of -70 is restored. If the K+ channels remain open, hyperpolarization can occur, (-90mv)
Term
All or Nothing Principle
Definition
If a stimulus reaches threshold, the action potential will always be the same.A stronger stimulus will not cause a larger impulse
Term
Absolute Refractory Period
Definition
A time which a cell cannot generate another AP, no matter how strong the stimulus is. This period coincides with the period of sodium channel activation and inactivation.(depolarization and repolarization)
Term
Relative Refractory Period
Definition
a period in time during which a second action potential can be generated, but only by a larger-than-normal stimulus. It coincides with the period when the voltage gated potassium channels are open after inactivated sodium channels have returned to their resting state. (hyperpolarization)Graded potentials do not exhibit a refractory period.
Term
Continuous Conduction
Definition
propagation of An AP down an unmyelinated axon (slow)
Term
Saltatory Conduction
Definition
propagation of an AP down a myelinated axon (fast)
Term
Speed of an Action potential is affected by?
Definition
1. Myelination
2. Axon diameter
3. Temperature
4. Frequency of AP
5. # of neurons recruited
Term
A fibers
Definition
large, fast, myelinated neurons that carry touch and pressure sensations, many motor neurons are also this type
Term
B fibers
Definition
are of medium sized and speed (15m/sec) and comprise myelinated visceral sensory and autonomic preganglionic neurons
Term
C fibers
Definition
are the smallest and slowest and comprise unmyelinated sensory and autonomic motor neurons (pain)
Term
Neurotransmitters
Definition
Both excitatory and inhibitory neurotransmitters are present in the CNS and PNS.
The same neurotransmitter may be excitatory in some locations and inhibitory in others.
For example, acetylcholine (ACh) is a common neurotransmitter released by many PNS neurons (and some in the CNS). Ach is excitatory at the NMJ but inhibitory at other synapses.
Many amino acids act as neurotransmitters:
Glutamate is released by nearly all excitatory neurons in the brain.
GABA is an inhibitory neuro-
transmitter for 1/3 of all brain synapses.
Valium is a GABA agonist that enhances GABA’s depressive effects (causes sedation).
Other important small-molecule neurotransmitters are listed
Term
Signal transmission at the synapse
Definition
a one-way transfer from a presynaptic neuron to a postsynaptic neuron.
When an AP reaches the end bulb of axon terminals, voltage-gated Ca2+ channels open and Ca2+ flows inward, triggering release of the neurotransmitter.
The neurotransmitter crosses the synaptic cleft and binds to ligand-gated receptors on the postsynaptic membrane.
The more neurotransmitter released, the greater the number and intensity of graded potentials in the postsynaptic cell.
In this way, the presynaptic neuron converts an electrical signal (nerve impulse) into a chemical signal (released neurotransmitter). The postsynaptic neuron receives the chemical signal and in turn generates an
electrical signal (postsynaptic
potential).
The time required for these
processes at a chemical synapse
produces a synaptic delay of
about 0.5 msec.
Term
Neurotransmitter effects
Definition
Synthesis can be stimulated or inhibited.
Release can be blocked or enhanced.
Removal can be stimulated or blocked.
The receptor site can be blocked or activated.
An agonist is any chemical that enhances or stimulates the effects at a given receptor.
An antagonist is a chemical that blocks or diminishes the effects at a given receptor.
Term
Excitatory postsynaptic potential (EPSP)
Definition
causes a depolarization of the postsynaptic cell, bringing it closer to threshold. Although a single EPSP normally does not initiate a nerve impulse, the postsynaptic cell does become more excitable.
Term
Inhibitory postsynaptic potential (IPSP)
Definition
) hyperpolarizes the postsynaptic cell taking it farther from threshold
Term
Spatial summation
Definition
occurs when postsynaptic potentials arrive near the same location
Term
Temporal summation
Definition
occurs when postsynaptic potentials arrive close to the same time
Whether or not the
postsynaptic cell
reaches threshold
depends on the
net effect after
Summation of all
the postsynaptic
potentials.
Term
NT Clearance
Definition
If a neurotransmitter could linger in the synaptic cleft, it would influence the postsynaptic neuron, muscle fiber, or gland cell indefinitely – removal of the neurotransmitter is essential for normal function.
Removal is accomplished by diffusion out of the synaptic cleft, enzymatic degradation, and re-uptake by cells.
An example of a common neurotransmitter inactivated through enzymatic degradation is acetylcholine. The enzyme acetylcholinesterase breaks down acetylcholine in the synaptic cleft.
Term
Neural Circuits
Definition
Neurons process info when changes occur at the trigger zone through spatial and temporal summations of IPSPs and EPSPs. An average neuron receives 10,000 synaptic inputs
Term
Integration
Definition
is the process accomplished by the postsynaptic neuron when it combines all excitatory and inhibitory inputs and responds accordingly. This process occurs over and over again as interneurons are activated in higher parts of the brain
Term
Neuronal Network
Definition
A neuronal network may contain thousands or even millions of neurons. Types of circuits include diverging, converging, reverberating, and parallel after discharge
Term
Diverging Circuit and Converging circuit
Definition
a small # of neurons in the brain stimulate a much larger number of neurons in the spinal cord A converging circuit is the opposite.
Term
Reverberating Circuit
Definition
impulses are sent back through the circuit time and time again--used in breathing, coordinated muscular activites, waking up, and short-term memory
Term
Parallel after--discharge circuits
Definition
involve a single presynaptic cell that stimulates a group of neurons, which then synapse with a common postsynaptic cell--used in precise activites such as mathematical calculations
Term
Converging Circuit
Definition
A large # of neurons in the brain stimulate a much smaller # of neurons in the spinal cord
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