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A&P Ch.7: Nervous System


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Which systems coordinate activieties with other organ systems?
-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?
What tissues make up the nervous system?
neural tissue
What organs belong to the nervous system?
-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?
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?
-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?
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?
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?
-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?
-Sympathetic (stimulating effect)
-Parasympathetic (relaxing effect)
What two cells make up neural tissue?
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.
What are collaterals of an axon?
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
-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?
1) anaxonic
2) bipolar
3) unipolar
4) multipolar
Describe anaxonic neurons.
-no anatomic clues to distinguish between axon and dendrites
-located in the brain and in the special sense organs
-unknown functions
Describe bipolar neurons.
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.
-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.
-very long axons
-multiple dendrites with one axon
-most common type in CNS
What are the three functional classifications of neurons?
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
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
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?
The processes of specialized sensory neurons or cells monitored by sensory neurons.
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?
Somatic: innervate skeletal muscles
visceral: innervate all peripheral effectors other than skeletal muscles
What are the two groups of efferent axons.
-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?
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?
1) ependymal cells
2) astrocytes
3) oligodendrocytes
4) microglia
Where are ependymal cells and what do they do?
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?
-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?
1) Satellite cells
2) Schwann cells
What do satellite cells do?
Surround the neuron cell bodies in ganglia.
What are Schwann cells?
-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.
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?
-response to temporary changes in membrane permeability
-resulting from opening or closing specific membrane channels.
What are passive channels?
Always open and leaky
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?
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?
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.
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?
1) continuous propagation
2) saltatory propagation
List 5 characteristics of continuous propagation.
-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.
-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?
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?
1) electrical
2) chemical
Describe a chemical synapse.
-Cells not in direct contact
-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?
-amount of neurotransmitter released
-sensitivity of postsynaptic cell
What are two types of neurotransmitters and what does each cause?
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?
-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?
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?
ACh triggers Ca+ channels open
Exocytosis occurs allowing transmission of neurotransmitters.
What are some other important neurotransmitters?
-norepinephrine (NE)
-gamma aminobutyric acid (GABA)
At the simplest level, how does information processing occur?
-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?
1) excitatory
2) inhibitory
Describe each type of postsynaptice potentials.
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?
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?
1) divergence
2) convergence
3) serial processing
4) parallel processing
5) reverberation
What are the small components of the CNS?
-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.
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?
-posterior horns
-anterior horns
-lateral horns
-gray commissures
Describe posterior gray horns.
-contain somatic and visceral sensory nuclei
-contain somatic motor nuclei
Describe lateral gray horns and gray commissures.
-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?
-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?
-dorsal ramus
-ventral ramus
-white ramus and gray ramus
What are the functions of the spinal cord?
-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?
-ascending tracts
-descending tracts
-bundles of axons compose all tracts
How are structural tracts organized?
-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?
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?
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.
-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.
-Complements withdrawal reflexes
-The motor response occurs on the side opposite the stimulus (contralateral reflex arc).

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