A&P Ch.7: Nervous System
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- Which systems coordinate activieties with other organ systems?
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-Nervous system
-Endocrine system -
Which system provides swift but brief responses to stimuli?
Long terms changes and adjusts metabolic operations? -
-Nervous is fast
-Endocrine is slower - What are the two anatomical divisions of the Nervous system?
- CNS and PNS
- What tissues make up the nervous system?
- neural tissue
- What organs belong to the nervous system?
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-Brain, spinal cord
-Sensory receptors of sense organs (eyes, ears, etc)
-Nerves connect nervous system with other systems - What is included in the CNS?
- The brain and the spinal cord
- What is included in the peripheral nervous system?
- all neural tissue outside the CNS (cranial and spinal nerves)
- What are the functions of the central nervous system?
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Process and coordinate:
-sensory data (inside and outside body)
-motor commands (control activities of peripheral organs)
-higher functions (intelligence, memory, learning, emotion) - What are the functions of the PNS?
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-deliver sensory information to the CNS
-Carry motor commands to peripheral tissues and systems - What are nerves?
- Bundles of axons with connective tissues and blood vessels that carry sensory information and motor commands in PNS
- What are the two functional divisions of the PNS?
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-afferent
-efferent - What is the afferent division?
- Carries sensory information from PNS sensory receptors to CNS
- What is the efferent division?
- Carries motor commands from CNS to PNS muscles and glands
- What do receptors do?
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Detect changes or respond to stimuli. Use neurons and specialized cells.
-complex sensory organs (eyes, ears) - What do effectors do?
- Respond to efferent signals from cells and organs.
- What are the divisions of the efferent division of the PNS?
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-Somatic nervous system
-Autonomic nervous system - What does the SNS do?
- Controls skeletal muscle contractions either voluntary or involuntary (reflexes)
- What does the ANS do?
- Controls subconscious actions such as contactions of smooth muscle and cardiac muscle as well as glandular secretions.
- What are the divisions of the ANS division?
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-Sympathetic (stimulating effect)
-Parasympathetic (relaxing effect) - What two cells make up neural tissue?
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1) Neuron
2) Neuroglia or glial cells - What is a neuron?
- The basic functional unit of neural tissue
- What type of cells are glial cells?
- Neuroglia which are supporting cells.
- What is the soma?
- The cell body. Have nissal bodies.
- What are nissal bodies?
- The stained portions of rough ER. Make neural tissue appear gray (gray matter).
- What are dendrites?
- Slender, sensitive processes extending from the neural cell body. Dendritic spines receive information from other neurons.
- What is the axon?
- A single, long process capable of propagating an electrical impulse. Consist of axoplasm, axolemma, axon hillock, initial segment, collaterals, telodendria, and synaptic terminals.
- What is the axoplasm of an axon?
- The cytoplasm of an axon.
- What is the axolemma of the axon?
- A specialized cell membrane of the axon.
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What are collaterals of an axon?
Telodendria?
Synaptic terminals? -
-side bransches of axon
-fine extensions of collaterals
-the end of telodendria - What is the synapse for?
- Communicating with another cell. Has a presynaptic cell and postsynaptic cell.
- Describe the presynaptic cell.
- This cell has the synaptic terminal and sends a message using synaptic vesicles that release neurotransmitters.
- Describe the postsynaptic cell.
- This cell recieves a message from the synaptic knob through either a neuromusculat or neuroglandular junction.
- Describe neurotransmitters
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-chemical messengers
-released at presynaptic membrane
-affect receptors of postsynaptic membrane
-broken down by enzymes
-reassebled at synaptic knob - What are the 4 structural classifications of neurons?
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1) anaxonic
2) bipolar
3) unipolar
4) multipolar - Describe anaxonic neurons.
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-small
-no anatomic clues to distinguish between axon and dendrites
-located in the brain and in the special sense organs
-unknown functions - Describe bipolar neurons.
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Rare: has two distinct processes
1)One dendritic process with extensive branching at its distal tip.
2)One axon with a cell body between them - Describe unipolar neurons.
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-very long axons
-fused dendrites and axon
-cell body on one side with only one connection to fused part
-most sensory neurons of the PNS are unipolar - Describe multipolar neurons.
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-very long axons
-multiple dendrites with one axon
-most common type in CNS - What are the three functional classifications of neurons?
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1) sensory
2) motor
3) interneurons -
What do sensory neurons do?
Where are their cell bodies positioned?
What are the two classifications of sensory neurons? -
-Deliver information from sensory receptors to the CNS
-Unipolar with their cell bodies located in peripheral sensory ganglia
1)somatic
2)visceral - What are ganglion?
- a collection of neuron cell bodies in teh PNS.
- What type of fibers make up the processes of sensory neurons?
- -afferent fibers
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What do somatic sensory neurons monitor?
Visceral sensory neurons? -
-They monitor the effects of external environment
-Monitor internal environment - What are sensory receptors and what types are there?
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The processes of specialized sensory neurons or cells monitored by sensory neurons.
-exteroceptors
-proprioceptors
-interoceptors - What do exteroceptors do?
- Sense external environment (touch, temperature, pressure, sight, smell, and hearing).
- What do proprioceptors do?
- Sense the position and movement of skeletal muscles and joints.
- What to interoceptors do?
- Monitor inside organ systems and sense tastes, depp pressure and pain.
- What do motor neurons do?
- -Carry instructions from the CNS to peripheral effectors via efferent fibers.
- What are the two classes of motor neurons and what does each do?
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Somatic: innervate skeletal muscles
visceral: innervate all peripheral effectors other than skeletal muscles - What are the two groups of efferent axons.
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-preganglionic fibers
-postganglionic fibers - What are interneurons?
- -Responsible for analyzing sensory information and coordinating motor outputs. Also involved in memory, planning, and learning in humans.
- Where are interneurons and how many are in humans?
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Most located in brain and spinal cord (some in autonomic ganglia). One or more between sensory neurons and motor neurons.
-about 20 billion in a human - What are the four (4) types of neuroglia?
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1) ependymal cells
2) astrocytes
3) oligodendrocytes
4) microglia - Where are ependymal cells and what do they do?
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They line the central canal of the spinal cord and ventricles of brain.
-secrete cerebrospinal fluid
-monitor CSF
-contain stem cells for repair - What are astrocytes?
- The largest and most numerous neuroglia in CNS. They maintain teh blood-brain barrier: lining CNS capillaries, so blood does not freely access CSF.
- What are microglia?
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-Act as wandering police force: engulfing cellular debris, waste products and pathogens.
-Least numerous and smallest
-Many fine branches from the cytoplasmic processes. - What are oligodendrocytes?
- Similar to Schwann cells, they cheath the axons of the CNS.
- What forms the gray matter of the CNS?
- Unmyelinated axons and densely packed neuron cell bodies with the concentration of Nissel bodies.
- What forms white matter in teh CNS?
- Regions dominated by myelinated axons.
- What are the neuroglia of the PNS?
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1) Satellite cells
2) Schwann cells - What do satellite cells do?
- Surround the neuron cell bodies in ganglia.
- What are Schwann cells?
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-Form a sheath around every peripheral axon
-Can only myelinate one segment of a single axon, however it can enclose segments of several unmyelinated axons. - What are neurilemma?
- The outer surface of the schwann cell covering an axon.
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How is the resting membrane potential determined?
What controls this? -
-Membrane permiability to Na+ and K+ ions.
-The sodium potassium exchange pump stabilizes this - What is the Equilibrium potential?
- The transmembrane potential at which there is no net movement of a prticular ion across the cell membrane.
- What causes transmembrane potential to rise or fall?
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-response to temporary changes in membrane permeability
-resulting from opening or closing specific membrane channels. - What are passive channels?
- Always open and leaky
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What are active channels?
What are the three states of these? -
Gated channels that open or close in response to specific stimuli.
1) closed but capable of opening
2) Open (activated)
3) Closed an inactivated - What are the three classes of active channels?
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1) chemically regulated
2) voltage-regulated
3) mechanically regulated - How do chemically regulated channels work and where are they?
- In the presence of specific chemicals at a binding site, channel opens. They are found on neuron cell body and on dendrites.
- How do voltage-regulated channels work and where are they found?
- Respond to changes in transmembrane potential and have activation and inactivation gates. These are found in neural axons, skeletal muscle sarcolemma, and cardiac muscles.
- How do mechanically regulated channels work and where are they found?
- Respond to membrane distortion and found in sensory receptors (touch, pressure, vibration).
- What are graded potentials?
- Magnitude is proportional to magnitude of stimulus (more channels open). Changes in transmembrane potential can't spread far from stimulation site.
- What are the stages of a graded potentials?
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-exitiation
-inhibition
-repolarization - What is excitation in a graded potential?
- When a stimulus triggers the opening of additional Na+ channels, allowing membrane potential to move toward zero (depolarization). The effect spreads passively owing to local currents and decreases with distance.
- What is the inhibition part of a graded potential?
- When a stimulus triggers the openin gof addition K+ channels, increasing the membrane potential (hyperpolarization).
- What is repolarization in graded potentials?
- Restore of normal RMP after depolarization by channels and ion pumps.
- What is the initial stimulus for action potentials?
- A graded depolarization of axon hillock large enough to change resting membrane to threshold level of voltage-regulated sodium channels (-60 - -55mV).
- What is the all-or-none principal?
- If a stimulus exceeds threshold amount, the action potential remains the same no matter how large the stimulus.
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What are the 4 steps in generation of action potentials?
*See video for indepth explanation. -
1) depolarization to threshold (-60mV)
2) Activation of voltage-regulated Na+ channels
3) Inactivation of Na+ channels, activation of K+ channels
4) Return to normal permeability. - What is the absolute refractory period?
- The brief period during which a local area of a neurons membrane resists restimulation and will not respond to a stimulus, no matter how strong.
- What is the relative refractory period?
- Time during which the membrane is repolarized and restoing the resting membrane potential; will respond only to a very strong stimulus.
- What is propagation of action potentials?
- Moving of action potentials generated in axon hillock along entire length of axon in a series of repeated actions, not passive flow.
- What are the two methods of propagating action potentials?
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1) continuous propagation
2) saltatory propagation - List 5 characteristics of continuous propagation.
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-local current depolarizes next segment and cycle repeats
-cell body lacks coltage-regulated channels, no repsonse to action potential
-action potential only moves foward becuase of absolute refractory period
Slow speed ~1m/s - What is the saltatory potential propagation? List 4 points.
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-action potential appears to leap from node to node, skipping intervening membrane surface
-occurs on myelinated axons
-carries imulses much faster than continuous propagation
-use proportionately less energy - What are the three groups of axons?
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Type A fibers
Type B fibers
Type C fibers
*Information transfer in the nervous system reflects a compromise between time and space. - Describe type A fibers
- They are 4-20um, are myelinated, and move 140m/s
- Describe type B fibers
- They are 2-4um, myelinated, and move 18m/s
- Describe type C fibers
- They are less then 2um, unmyelinated, and move 1m/s
- What are the two types of synapses?
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1) electrical
2) chemical - Describe a chemical synapse.
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-Cells not in direct contact
-unidirectional
-action potential may or may not continue to postsynaptic cell
-more dynamic (tune-up to grade or action potentials) - What determines if action potentials are passed to postsynaptic cells in a chemical synapse?
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-amount of neurotransmitter released
-sensitivity of postsynaptic cell - What are two types of neurotransmitters and what does each cause?
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1) excitatory: depolarization of postsynaptic membrane to promote action potentials
2) inhibitory: cause hyperpolarization of postsynaptic membranes to supress action potentials - What effect on a postsynaptic membrane does a neurotransmitter have?
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-Depends of receptor not on neurotansmitter
-Usually promotes action potentials, but inhibits cardiac neuromuscular junctions. - What is a synaptic knob?
- A tiny bulge at the end of a terminal branch of presynaptic neurons axon that contains vesicles housing neurotransmitters.
- What is the synaptic cleft?
- The space between a synaptic knob and the plasma membrane of a postsynaptic neuron.
- What does the plasma membrane in a postsynaptic neuron have?
- Has protein molecules that serve as receptors for the neurotansmitters.
- What chemical does a Cholinergic synapses use and where?
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ACh released at:
-all neuromuscular junctions incolcing skeletal muscle fibers
-many synapses in CNS
-All neuron-to-neuron synapses in PNS
-All junction sof the parasympathetic division of ANS. - What is synaptic fatigue?
- The synapse remains inactive until ACh has been replenished.
- What does ACh cuase to move and what does this do?
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ACh triggers Ca+ channels open
Exocytosis occurs allowing transmission of neurotransmitters. - What are some other important neurotransmitters?
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-norepinephrine (NE)
-dopamine
-serotonin
-gamma aminobutyric acid (GABA) - At the simplest level, how does information processing occur?
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-Graded potentials developed in a postsynaptic cell in response the neurotransmitters
-many dendrites receive neurotransmitter messages simultaneously
-some excitatory, some inhibitroy
-net effect on axon hillock determines if action potential is produced - What are 2 types of postsynaptic potentials?
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1) excitatory
2) inhibitory - Describe each type of postsynaptice potentials.
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EPSP: a graded depolarization caused by the arrival of a neurotransmitter at the postsynaptic membrane
IPSP: a transient hyperpolarization of the postsynaptic membrane - What is inhibition?
- When a neuron recieves many IPSP's, it is inhibited from producing an action potential becuase of the stimulation needed to reach threshold is increased.
- What are the two types of summation?
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Both formed from individual EPSP's combining
1) temporal
2) spatial - What is temporal summation?
- Summation of repeated stimulation by a single synapse.
- What is spatial summation?
- Adds together the effects of several knobs being activated simultaneously (multiple synapses, simultaneously).
- What is divergence?
- The spread of information from on eneuron or neuronal pool to several neurons or pools.
- What is convergence?
- Several neurons synapse on the same postsynaptic neuron.
- What is serial processing?
- Neurons or pools work in sequence.
- What is parallel processing?
- Several neurons or neuronal pools process the same information at one time.
- What is reverberation?
- Collateral axons establish a circuit that further stimulates presynaptic neurons. Positive feedback.
- What are the 5 higher levels of orgnaization and processing?
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1) divergence
2) convergence
3) serial processing
4) parallel processing
5) reverberation - What are the small components of the CNS?
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-cerebrospinal fluid (CSF)
-spinal cord
-the brain
-cranial nerves
-bone and meningers (covering of brain and spinal cord) - How many segments of the spine are there and what "pair" are they associated with?
- 31 segments each with a pair of dorsal roots and a pair of ventral roots.
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Describe a ventral root?
Dorsal root? -
ventral: contains axons of motor neurons and carry motor information out of the spinal cord
dorsal: contains axons of sensory neurons and carry sensory information into the spinal canal. -
What is a spinal nerve?
Dorsal root ganglia? -
-A single mixed nerve on each side where the dorsal and ventral nerve roots join together.
-contain cell bodies of sensory neurons - What is white matter in the spinal cord?
- Myelinated and unmyelinated axons.
- What is gray matter in the spinal cord?
- Cell bodies of neurons and neuroglia and unmyelinated axons.
- What are the different parts of the gray horns?
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-posterior horns
-anterior horns
-lateral horns
-gray commissures -
Describe posterior gray horns.
Anterior? -
-contain somatic and visceral sensory nuclei
-contain somatic motor nuclei - Describe lateral gray horns and gray commissures.
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-Laterals are located in thoracic and lumbar segments and contain visceral motor nuclei.
-Commissures are axons that cross from one side to the other. - How is white matter organized?
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-into six columns
-each column has tracts
-ascending and descending tracts carry information from the brain to the spinal cord. - What is dorsal ramus (of peripheral distribution of spinal nerves).
- Sensory and motor innervation to skin and muscles of the back.
- What is the ventral ramus (of peripheral distribution of spinal nerves)?
- Sensory and motor innervation to muscles and glands in the body wall, and the limbs.
- What is the white ramus and gray ramus (of peripheral distribution of spinal nerves)?
- Innervate glands and smooth muscles in the visceral organs (sympathetic nerves).
- How are spinal nerves distributed peripherally?
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-dorsal ramus
-ventral ramus
-white ramus and gray ramus - What are the functions of the spinal cord?
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-provides conduction routes to and from the brain
-services as the integrator (or reflex center) for all spinal reflexes - What are conduction routes composed of?
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-ascending tracts
-descending tracts
-bundles of axons compose all tracts -
How are structural tracts organized?
Functional? -
-all acons of any one tract originate in the same structure and terminate in the same structure
-all axons that compose one tracts serve one general function. - What are reflexes?
- Rapid, automatic responses to stimuli showing very little variability (monosynaptic and polysynaptic).
- What is the purpose of neural reflexes?
- Being an involuntary motor response by the nervous system, it helps maintain homeostasis by rapidly adjusting the functions of organs or organ systems.
- What is a reflex arc and what are it's five steps?
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The neural "wiring" of a single reflex.
1) the arrival of a stimulus and activation of a receptor
2) The activation of a sensory neuron
3) Information processing
4) The activation of a motor neuron
5) A response by an effector - What are monosynaptic reflexes?
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Stretch reflexes: automatically regulates skeletal muscle length and muscle tone (such as patellar reflex)
-Many stretch reflexes are postural reflexes (reflexes that maintain normal upright posture
-The sensory stimulus and motor response occur on the same side of the body (ipsilateral reflex arcs). - What are two types of polysynaptic reflexes?
- Withdrawal and crossed extensor reflexes.
- Describe withdrawal polysynaptic reflexes.
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-Move affected portions of the body away from a source of stimulation
-interneurons in spinal cord coordinate muscular contractions and reduce resistance to movement
*The flexor reflex is a withdrawal reflex affecting the muscles of a limb - Describe a crossed extensor reflex.
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-Complements withdrawal reflexes
-The motor response occurs on the side opposite the stimulus (contralateral reflex arc).