Neurons Flashcards
(120 cards)
1
Q
The nervous system
A
receives information, processes information, and sends signals to the muscles and glands to deliver the appropriate response.
Intergrates and controls the other systems
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Q
Nervous tissue
A
is responsible for the communication between the cells of the body by forming a system of electrical impulses that communicate very rapidly.
Wiring of the body
3
Q
What are the two main divisions of the central nervous system?
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Central nervous system (CNS) and peripheral nervous system (CNS)
4
Q
Central nervous system
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includes the brain and spinal cord
The skull protects the brain and the vertebrae protect the spinal cord
Sends signals and impulses to and receives impulses from the peripheral nervous system
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Q
nuclei
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collection of cell bodies inside the CNS.
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Q
tracts
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collection of nerve axons in the central nervous system
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Q
peripheral nervous system
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includes all nerves not in the brain or spinal cord
Includes cranial and spinal nerves
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Brainstem
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regions include the midbrain, pons, and medulla
9
Q
Where do cranial nerves and peripheral nerves project from
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CN project from the brainstem and PN project from the either side of the vertebrae.
10
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What do CN and PN innervate?
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CN- the face, head, and neck f
PN- the rest of the body including the trunk and extremities
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Q
Ganglia
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collection of cell bodies inside the PNS
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Q
Nerves
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collection of nerve axons in the PNS
13
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Two divisions of the PNS
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Sensory or Afferent division and Motor or Efferent division
The peripheral system connects all parts of the body to the CNS
14
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Sensory organs
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The peripheral nervous system receives impulses from the sensory organs via afferent division and then relays signals or impulses from the CNS to muscles and glands
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Glands
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receives information from the CNS via motor or efferent division.
16
Q
Two divisions of the Efferent system
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Somatic and automatic systems
somatic system nerves - under conscious (voluntary) control
controls movement if the skeletal muscles, skin, and joints
automatic system nerves- controls the glands and smooth muscles of the internal organs.
Not under voluntary/conscious control
17
Q
Two divisions of the automatic nervous system
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sympathetic and parasympathetic system
sympathetic - prepares body for vigorous musclular activity, stress, and emergencies
parasympathetic system generality operates during normal situations, permits digestion, and conserves energy.
18
Q
Nuerons
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nerve cells that conduct electrical impulses and relay information throughout the body.
19
Q
Three parts of a neuron
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dendrites, cell body, and axons
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Neuron facts
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They do not undergo mitosis/cell division
Can survive an entire person’s lifetime, which is why brain and spinal cord damage are so serious.
Any neurons that die due to brain damage can not be replaced
neurons can survive just minutes without oxygen
21
Q
Neuron cell body
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synthesizes all nerve cell products
consists of large nucleus with surrounding cytoplasm containing normal organelles
information is sent and received in the same direction within a neuron.
22
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dendrites
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are the receiving end of a neuron
these are numerous short extensions that emanate from the cell body, which receive information from the neurons and conduct those nerve impulses toward the cell body
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Q
axon
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the single axon conducts nerve impulses away from the cell body to its axon terminals
vary in length -being very short or very long (up to 3 feet)
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Q
What are axons composed of?
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cell components like the cell body but lack rough endoplasmic reticulum
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What do axons depend on
the neuron's cell body to send the necessary proteins down the length of the axon
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What does the cell body of a neuron cell contain?
nucleus and other organelles typically found in other cells, except for centrioles, which are not capable of mitosis
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Main function of the cell body
to manufacture neurotransmitters
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Neurotransmitters
are chemicals stored inside secretory vesicles (axon terminal vesicles) at the end of axon terminals
when neurotransmitters are released by the axon vesicles, they carry the transmission of the nerve impulse from one neuron to another
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synapse
neurotransmitters are emitted across a synapse to the dendrite of another neuron
a synapse is a gap between two neurons as neurons do not physically touch one another
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presynaptic neuron
means before the synapse
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postsynaptic neuron
a neuron found after the synapse
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How are neurotransmitters sent?
from the presynaptic neuron through the synapse to the postsynaptic neuron.
the message continues in the same manner from one neuron to the next
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How are neurons classified?
according to the number of extension from their cell body as multipolar, bipolar and unipolar
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Multipolar neurons
have three or more extensions from their cell body
they have one axon and many dendrites
can be called motor neurons
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bipolar neurons
have a central body with two extensions
these are found within in the body, as special receptor cells in the visual and olfactory systems.
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unipolar neurons (pseudounipolar)
have one extension off the cell body that branches into two: one central process running to the CNS.and another peripheral process running to the sensory receptor
these neurons are sensory neurons in the peripheral nervous system
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How are neurons classified functionally?
sensory, motor, and interneurons
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sensory neurons
afferent
unipolar
function to carry information from the peripheral to the central nervous system
most sensory neurons carry impulses from the skin or internal organs to the CNS
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Interneurons
called association neurons are found only in the CNS
typically multipolar neurons
transmit impulses within different parts of the CNS
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Motor neurons
efferent
multipolar neurons which send messages form the CNS to the peripheral
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nerve
consists of hundreds of thousands of axons wrapped together in connective tissue.
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ganglia
in the PNS the cell bodies of neurons are grouped together in masses called ganglia, which is part of a single nerve
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neuroglial cells
highly important for neuron function
support cells for neurons
neurons require a highly specific environment to survive and conduct electrical impulses efficiently
help to support neurons to enable them to thrive in their needed environment
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Schwann cells
the peripheral nerve axon is coated in short sections called schwann cells
a special type of neuroglial cell found in the PNS and composed of a white fatty layer called myelin sheath
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myelin sheath
rolled around the axon, insulating the nerve fiber from others and increasing the speed of nerve impulses
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unmyelinated fibers
common in gray matter of the brain and spinal cord in which schwann cells do not wrap around the axon but are loosely associated with the axon
the schwann cells insulating sections are not continuous, having gaps between them called nodes of ranvier
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Nodes of ranveir
The Schwann cells insulating sections are not continuous having gaps between them called nodes of ranveir
at these exposed nodes, the nerve impulse is forced to jump to the next node in a manor called saltatory conduction.
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satellite cells
surround the cell bodies of peripheral neurons helping to regulate the cell body environment
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saltatory condunction
at exposed nodes (nodes of ranveir), the nerve impulse is forced to jump to the next node in a manor called saltatory conduction - greatly increasing the nerve impulse transmission along the axon
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axonal regeneration
Neurons can not regrow, but axons in the PNS can under certain circumstances.
If peripheral nerves are servered in an injury, the schwann cells grow ahead of the axon creating a path for the axon to follow
it is possible for axons to regrow after injury to peripheral nerve, although growth is very slow
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Neuroglial cells of the CNS
ependymal cells, oligodendrocytes, astrocytes, microglial cells
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ependymal cells
circulate cerebrospinal fluid
allow fluid exchange between brain and spinal cord and cerebrtospinal fluid.
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cerebrospinal fluid CSF)
a clear fluid that only circulates in the brain and spinal cord
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Oligodendrocytes
act as insulation of the CNS axons
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Astrocytes
control the chemical environment of neurons by wrapping around blood capillaries
this physical barrier is called the blood brain barrier
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Blood brain barrier
a physical barrier made by astrocytes
allows the passage of only certain substances into the CNS
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microglial cells
protect the CNS by scavenging dead cells and infectious microorganisms
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polarized
at rest, the plasma membrane is said to be polarized
one side has a different charge than the other
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resting potential
when an axon is not conducting an impulse this difference in electrical charge is called resting potential or resting state of neuron
equal to -70 mV (milivolts)
charge is negative because the inside of the axon's cell membrane is 70mV less than the outside of the membrane
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sodium potassium pump
uses active transport to carry ions across the plasma membrane.
the pump uses an integral carrier protein that for ever 3 sodium ions (Na+) pumped out, two potassium ions (K+) are pumped in.
pump must be in constant operation because Na+ and K+ will naturally diffuse back to where they originated
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Why is there a positive change on the outside of the cell membrane?
The plasma membrane is more permeable to K+ diffusing outward and because more Na+ ions are being pumped outward than K+ pumped inward, a relative positive charge develops and is maintained on the outside of the membrane
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action potential
if the axon is stimulated to conduct a nerve impulse, there is a rapid change in the polarity called an action potential
the resting potential becomes an action potential if the membrane becomes depolarized
once an action potential occurs it travels it continues it continues through the entire length of the axon
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depolarization
first the membrane potential becomes more positive (depolarization)
indicating that the inside of the membrane is now more positive than the outside
then it returns to normal (re-polarization)
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re-polarization
the potential returns to normal after being depolarized, indicating that the inside of the axon is negative again.
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sodium gates and potassium gates
the action potential is due to special protein lined channels in the membrane, which can open to allow either sodium or potassium ions to pass through
these channels and their gated are voltage activated
as proteins respond to changes in voltage with changes in shapes
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resting potential
during resting phase, both sodium and potassium gates are closed
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depolarization
the sodium gates are open
sodium rushes into the axon during the depolarization phase of action potential.
voltage travels to zero and then on up to +40mV
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after polarization
also called hyper polarization.
Poatssium gates are slow to close and there is an undershoot of the action potential
the voltage drops below -70mV and then returns to -70 mV as the resting state begins
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repolarization
the sodium gates close, and potassium gated open allowing potassium to rush out of the axon
this returns a negative voltage to the inside of the axon
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self propagating
because the ion channels are prompted to open whenever the membrane potential decreases (depolarizes) in an adjacent area
The action potential travels along the axon like a wave
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all-or-nothing
an action potential is an all or nothing response, either occurring or not.
No variation exists in the strength of a single impulse
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How can intensity of a sensation vary if there is only a single strength in an action potential?
intensity of a sensation (minor or major pain) is distinquished
by the numbers of neurons stimulated and the frequency with which the neurons are stimulated
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synapse
a minute fluid-filled space between an axon terminal of the sending (presynaptic) neuron and the dendrite of the receiving (postsynaptic) neuron
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electrochemical
a transmission of nerve impulses are electricalchemical in nature as chemicals called neurotransmitters allow to the signal to jump the synaptic gap.
signal moves from electrical (through the neuron) to chemical (in the synapse) to electrical again once the signal reaches the next neuron.
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Depolarization
when a nerve impulse reaches the end of an axon, voltage gated calcium ions open.
As Ca+ rushes in, it causes vesicles containing the neurotransmitters to fuse with the plasma membrane and release the neurotransmitter in the synapse
When neurotransmitter released binds with a receptor on the next neuron, sodium ion (Na+) channels in the receiving dendrites open.
Depolarization occurs in the next neuron, and the impulse is propagated forward to another neuron or to a target organ **ALWAYS in one direction.
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acetylcholinesterase (cholinesterase)
breaks down the neurotransmitter acytelcholine
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What happens once a neurotransmitter is released into the synapse?
it only has a short time to act.
some synapses contain enzymes that rapidly inactivate the neurotransmitter
ex. acetylcholinesterase
in others the synaptic ending rapidly reabsorbs the neurotransmitters.
some neurons repackage the neurotransmitters into synaptic vesicles while others chemically breakdown the neurotransmitters
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Why do neurontransmitters have a short existence?
the short existence of neurotransmitters in the synapse is to prevent continuous stimulation of postsynaptic membranes.
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Inhibition
Neurotransmitters are short lived in the synapse to prevent continuous stimulation of postsynaptic membranes.
Prevention of continuous stimulation is called inhibition
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Norepinephrine and epinephrine
neurotranmitters produced by the adrenal glands
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dopamine
is a specialized brain neurotransmitter that regulate emotional responses and muscle tone
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acetylcholine
Neurotransmitter found at neuromuscular junctions (NMJ) in the peripheral nervous system.
The NMJ is located where a motor neuron ends on a muscle instead of another neuron.
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What happens for a muscle to contract
The nervous system must work together with the muscular system.
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NMJ (neuromuscular junction)
the nervous system interacts with the muscular system at NMJ to enable a muscular contraction.
nerve impulse must be sent to muscle by presynaptic motor neuron.
NMJ is a special type of synapse formed between a motor neuron and motor tissue
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What happens when a nerve impulse reaches the muscle fiber?
acetylcholine is released into the synapse.
acetylcholine binds to receptors on the muscle fiber that cause sodium channels to open.
sodium rushes into the muscle cell, triggering an action potential which releases into the sacroplasmic reticulum (special type of smooth ER found in striated muscle tissue.
Calcium is then released from the sarcoplasmic reticulum that causes the muscle to contract.
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reflexes
nearly instantaneous, automatic, and involuntary responses within the nervous system.
start from stimulus inside or outside the body.
come in a variety of forms
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Subconscious reflexes
occur within the body such as regulation of blood sugar by hormones
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Different reflexes
some include shivering in response to body temperature dropping.
when touching a hot surface, the reflux to remove your hand
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reflexes that involve the brainstem
blinking the eye
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brainstem
midbrain, pons, and medulla
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reflex arc
some reflexes only require spinal nerves and spinal cord in an action know as reflex arc
this refers to a neural pathway that nerve impulses travel.
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how can some reflexes be tested?
some reflexes can be tested to examine the function of the nervous system because the arc system passes through the CNS
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dorsal root
sensory informations travels into the spinal cord via the dorsal root
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ventral root
motor information travels out the ventral root of the spinal cord
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gray matter
the gray matter of the spinal cord contains cell bodies of neurons
also where neurons synapse with other neurons (such as interneurons)
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white matter
the white matter of the spinal cord contains the axons and neurons
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how are the white and gray matter arranged?
The spinal cord is located centrally with the white matter surrounding the gray matter.
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interneurons
located within the CNS and connect neurons to each other
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dorsal root ganglion
contains cell bodies of sensory neurons
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what does the dorsal root contain
axons and sensory neurons
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posterior horn
sensory nuerons synapse on cells within the posterior horn of the spinal cord in the gray matter
sensory neurons synapse on interneurons within the gray matter of the spinal cord
interneurons than synapse on motor neurons.
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anterior horn
Motor neuron cell bodies are located in the anterior horn of the gray matter
motor neurons (axons) leave the spinal cord via ventral root
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spinal nerve
contains both sensory and motor neurons from ventral and dorsal roots
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spinal reflexes
this are faster than a conscious decision to move coming from the brain.
they are faster because they involve fewer neurons, but because the electrical signal does not have to travel to the brain and back
spinal reflexes only travel to the spinal cord and back ** which is a much shorter distance
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examples of stretch reflexes
flexor reflex -withdraw your hand from a hot object
stretch reflex- on an opposing muscle to prevent overstretching of its antagonist.
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How does the reflex arc prevent harm to an organism.
a reflex arc provides immediate withdrawal from dangerous stimuli
while all sensory information reaches the brain the advantage of of the reflex arc is production of a response by way of the spinal cord without the need for waiting for the processing by the brain.
in this way, a response occurs in the body even before it is consciously perceived by the brain
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5 components of a reflex arc
the neural pathway that a nerve travels:
1. the receptor at the end of a sensory neuron reacts to a stimulus.
2.The sensory (afferent) neuron conducts nerve impulses along the afferent pathway towards the CNS
3. The integration center consists of one or more synapses in the CNS
4. a motor (efferent) neuron conducts a nerve impulse along the efferent pathway from the integration center to the effector
5. An effector repsonds to the efferent impulses by contracting (a muscle) or secreting a product (a gland)
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stretch reflexes
are a special type of muscle that protect a muscle against increases in length that may tear or damage the muscle fibers
these are very important in maintaining upright posture
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muscle spindles
are specialized muscle cells that are constantly monitoring the amount of stretch in a muscle
if a muscle becomes overstretched, it triggers a reflex to occur, which contracts the muscle back to its appropriate length
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patellar reflex
one example of a stretch reflex
the patellar reflex is also called a knee jerk reflex used in the physicians office
the patellar reflex tests the stretch reflex of the quadriceps femoris muscle in the thigh.
the primary purpose of this reflex is to prevent the overstretcching of the quadriceps
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patellar tendon
attaches the quadricep muscle to the tibia bone of the lower leg.
quadricep muscle is an extensor muscle of the knee
it raises the lower leg as it contracts, thereby extending the angle of the knee joint.
tapping the patellar tendon when the leg is lower is suspended off a table stretches the tendon which also stretches the quadricep muscle.
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flexor withdrawal reflex
if a very hot object is touched, a pain receptor in the skin generates nerve impulses, which move along the dendrite of a sensory neuron toward the cell body and the CNS.
From the cell body, impulses travel along the axon of a sensory nerve and synapse on many interneurons with the gray matter of the spinal cord
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excitatory interneurons
send excitatory signals to motor neurons, causing muscular contraction.
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inhibitory interneurons
send inhibitory signals to prevent muscle contraction
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why do cell bodies in neurons lack centrioles?
because they do not undergo mitosis so they do not need them
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why do axons lack rough ER?
because they are relying on the cell body to send the proteins they need
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sensory neurons
carry information from PNS to CNS
many found in skin or internal organs to the CNS
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Interneurons
found only in the CNS
typically multipolar
transmit info within a different part of CNS
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Motor neurons
multipolar
send messages from CNS to PNS
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