A&P Chapter 11 Flashcards
What is the nervous system?
Master controlling and communicating system of the body
What are the three overlapping functions of the nervous system?
Sensory input, integration, and motor output
What is sensory input?
Information gathered by sensory receptors about internal and external changes
What is integration?
Processing and interpretation of sensory input
What is motor output?
Activation of effector organs (muscles and glands) produces a response
What are the parts of the central nervous system (CNS)?
Brain and spinal cord
What are the parts of the peripheral nervous system (PNS)?
Cranial nerves, spinal nerves, and ganglia
What is the brain?
Receives and processes sensory information, initiates responses, stores memories, generates thoughts and emotions
What is the spinal cord?
Conducts signals to and from the brain, controls reflex activities
Where does the impulse go in motor neurons?
CNS to muscles and glands
Where does the impulse go in sensory neurons?
Sensory organs to CNS
What is the somatic nervous system?
Controls voluntary movements
What is the autonomic nervous system?
Controls involuntary responses
What is the sympathetic division?
Fight or flight
What is the parasympathetic division?
Rest or digest
How is the peripheral nervous system broken down?
Motor neurons and sensory neurons
How are motor neurons broken down?
Somatic nervous system and autonomic nervous system
How is the autonomic nervous system broken down?
Sympathetic division and parasympathetic division
What are the two cell types in nervous tissue?
Neuroglia (glial cells) and neurons (nerve cells)
What are neuroglia (glial cells)?
Small cells that surround and wrap delicate neurons
What are neurons (nerve cells)?
Excitable cells that transmit electrical signals
What are the functions of a oligodendrocyte?
- Myelinates and insulates CNS axons
- Allows faster action potential propagation along axons in the CNS
What are the functions of an astrocyte?
- Helps form the blood-brain barrier
- Regulates interstitial fluid composition
- Provides structural support and organization to the CNS
- Assists with neuronal development
- Replicates to occupy space of dying neurons
What are the functions of an ependymal cell?
- Lines ventricles of brain and central canal of spinal cord
- Assists in production and circulation of cerebrospinal fluid
What are the functions of a microglial cell?
- Phagocytic cells that move through the CNS
- Protects the CNS by engulfing infections and other potential harmful substances
What are the neuroglia of the CNS?
Astrocyte, ependymal cell, microglial cell, and oligodendrocyte
What are the neuroglia of the PNS?
Satellite cells and Schwann cells
What do satellite cells and Schwann cells do in the PNS?
Surround neurons
What do Schwann cells form?
Myelin sheaths
What are the general characteristics of neurons?
- Excitability
- Conductivity
- Extreme longevity (lasts a person’s lifetime)
- Antimitotic (few exceptions)
- High metabolic rate
What do neurons need a continuous supply of?
Oxygen and glucose
What is the cell body?
Biosynthetic center and receptive region that synthesizes proteins, membranes, and chemicals
What are the 2 alternate names of the cell body?
Perikaryon or soma
What is the rough ER in the cell body called?
Nissl bodies
What are dendrites?
Receptive (input) region of the neuron
What does each neuron contain?
One axon that starts at a cone-shaped area called the axon hillock
What shapes can an axon have?
Short, long, or absent
What are long axons called?
Nerve fibers
Axons have occasional branches, what are they called?
Axon collaterals
What are the distal endings of the neuron called?
Axon terminals or terminal boutons
What is the function of the axon?
Generates nerve impulses and transmits them along the axolemma to the axon terminal
What is the axolemma?
Neuron cell membrane
What is the axon terminal?
Region that secretes neurotransmitters
What are neurotransmitters?
Chemical messengers
The axon can _____ or _____ neurons that it contacts
Excite or inhibit
What two directions does transport occur in the axon?
Anterograde and retrograde
What does anterograde mean?
Away from the cell body
What are some examples of anterograde transport?
Mitochondria, cytoskeletal elements, membrane components, enzymes
What does retrograde mean?
Toward cell body
What are some examples of retrograde transport?
Organelles to be degraded, signal molecules, viruses, and bacterial toxins
What do certain viruses and bacterial toxins damage, and how?
They damage neural tissues by using retrograde axonal transport
What are some examples of viruses and bacterial toxins that use retrograde axonal transport?
Polio, rabies, herpes simplex viruses, and the tetanus toxin
Most neuron cell bodies are located in which NS?
CNS
What are nuclei?
Clusters of neuron cell bodies in the CNS
What are ganglia?
Clusters of neuron cell bodies in the PMS
The CNS contains what in the armlike processes that extend from the cell body?
Both neuron cell bodies and their processess
The PNS contains what in the armlike processes that extends from the cell body?
Neuron processes
What are tracts?
Bundles of neuron processes (axons) in the CNS
What are nerves?
Bundles of neuron processes (axons) in the PNS
What is the myelin sheath?
Whitish, protein-lipid substance that protects and insulates the axon and increases the speed of nerve impulses
Nonmyelinated fibers do not contain what?
Myelin sheath
Nonmyelinated fibers conduct impulses more _______ when compared to myelinated fibers
Slowly
Myelination in the PNS is formed by what?
Schwann cells
One cell forms ___ segment of myelin sheath (PNS)
One
What is the outer collar of perinuclear cytoplasm? (PNS)
Peripheral bulge containing nucleus and most of the cytoplasm
What was the previous name of the outer collar of perinuclear cytoplasm? (PNS)
Neurilemma
How do Schwann cells wrap around the axon? (PNS)
“Jelly roll” fashion
What are myelin sheath gaps/Nodes of Ranvier? (PNS)
Gaps between adjacent Schwann cells
Axon collaterals can emerge from where? (PNS)
Axon collaterals
What are nonmyelinated fibers? (PNS)
Thin fibers not wrapped in myelin. They are surrounded by Schwann cells but no coiling. One cell may surround 15 fibers
Myelination in the CNS is formed by what?
Oligodendrocytes, not whole cells
Each oligodendrocyte cell can wrap how many axons at once? (CNS)
60
The myelin sheath gap is present in which NS?
CNS
There is no outer collar of perinuclear cytoplasm in which NS?
CNS
What is white matter? (CNS)
Regions of the brain and spinal cord with myelinated fibers
What is gray matter? (CNS)
Neuron cell bodies and nonmyelinated fibers
What are the structural classes of neurons?
Multipolar, bipolar, and unipolar (psuedounipolar)
What is a multipolar neuron?
Many processes extend from the cell body. All are dendrites except for a single axon
What is a bipolar neuron?
Two processes extend from the cell body. One is a fused dendrite and the other is an axon
What is a unipolar (psuedounipolar) neuron?
One process extends from the cell body and forms central and peripheral processes, which together comprise an axon
Many bipolar neurons do not generate what?
Action potentials
In bipolar neurons, the ones that generates an action potential has the location of the trigger zone that is not ________
Universal
Multipolar neurons have what two types of neurons?
Motor and interneurons
Bipolar neurons have what type of neurons?
Special sensory (Retina)
Unipolar neurons have what type of neurons?
Sensory
What is the receptive region of a neuron?
Receives stimulus
What is the conducting region of a neuron?
Generates/transmits action potential
What is the secretory region of a neuron?
Axon terminals release neurotransmitters
What is the most abundant neuron type?
Multipolar
What is the major neuron type in the CNS?
Multipolar
How often are bipolar neurons found?
Rarely
Where are bipolar neurons found?
Some special sensory organs (olfactory mucosa, eye, ear)
Where are unipolar neurons found?
Mainly in the PNS
Where are unipolar neurons commonly found within the PNS?
Dorsal rot ganglia of the spinal cord and sensory ganglia of the cranial nerves
What is multiple sclerosis?
Progressive demyelination of neurons in the CNS
What type of disorder is multiple sclerosis considered and why?
Autoimmune because oligodendrocytes are attacked by immune cells
What is the physiology of multiple sclerosis?
Repeated inflammatory events cause scarring and permanent loss of function
What is Guillain-Barrè syndorme?
Loss of myelin from peripheral nerves due to inflammation
How does muscle weakness progress in Guillain-Barrè syndrome?
Begins in distal limbs, then advances to proximal muscles
What is the prognosis for Guillain-Barrè syndrome?
Most function is recovered with little medical intervention
Neurons have a resting membrane potential, what is a RMP?
A charge across the cell membrane due to ion distribution
What is the resting membrane potential of a neuron at rest?
-70 mV, but can rapidly change as ions are redistributed
Extracellular fluid has a higher concentration of ______ than intracellular fluid
Na+, balanced by Chloride ions (Cl-)
Intracellular fluid has a higher concentration of _____ than extracellular fluid
K+, balanced by negatively charged proteins
Which ion has the most important role in membrane potential?
K+
The membrane potential is (number) times more permeable to (which ion) than (which ion)
25 times more permeable to K+ than sodium
K+ diffuses out _____ the concentration gradient (more than sodium diffuses in)
Along
Because K+ diffuses out along the gradient more than sodium diffuses in, the inside is more ______
Negative (-)
What are the two main types of ion channels?
Leakage (non-gated) channels = Always open
Gated channels = Protein changes shape to open/close the channel
How does the Na+/K+ pump maintain the membrane potential?
By pumping 3 Na+ out for 2 K+ in (3 out, 2 in)
What is the concentration of Na+ on the outside of the cell?
140 mM
What is the concentration of K+ on the outside of the cell?
5 mM
What is the concentration of K+ on the inside of the cell?
140 mM
What is the concentration of Na+ on the inside of the cell?
15 mM
The entire neuron has what three channels/pumps?
Na+/K+ pump, Na+ leak channel, and K+ leak channel
What is the receptive segment of a neuron?
From cell body to dendrites
What channels does the receptive segment have?
Chemically gated cation channel, chemically gated K+ channel, and chemically gated Cl- channel
Where is the initial segment of a neuron?
Axon hillock
What channels does the initial segment have?
Voltage-gated Na+ channel and voltage-gated K+ channel
Where is the conductive segment of the neuron?
Axon
What channels does the conductive segment have?
Voltage-gated Na+ channel and Voltage-gated K+ channel
Where is the transmissive segment of the neuron?
Axon terminal
What channels/pumps does the transmissive segment have?
Voltage-gated Ca2+ channel and Ca2+pump
What two types of signals are produced by changes in ion concentrations?
Graded potentials and action potentials
What are graded potentials?
Cause the inside of the cell to become either more negative or less negative
What are action potentials?
All-or-nothing nerve impulse
What is depolarization?
Inside of membrane becomes less negative than the resting membrane potential
What is hyperpolarization?
Inside of membrane becomes more negative than the resting membrane potential
What is the principal way neurons send signals?
Action potentials
What are the only two things do action potentials occur in?
Muscle cells and axons of neurons
Actions do not _____ over distance as graded potentials do
Decay
Actions potentials are ____ - _____ - ______
All or none
Action potentials involves the opening of what?
Specific voltage-gated channels
What are the steps of action potential?
- Unstimulated/at rest
- Graded potentials reach the initial segment
- Depolarization
- Repolarization
- Hyperpolarization
- Returns to rest
What is step 1 of an action potential?
The unstimulated axon has a resting membrane potential of -70 mV
What is step 2 of an action potential?
Graded potentials reach the initial segment are added together
What does the voltage go to in step 2 of an action potential?
-70 mV + -55 mV
What happens every time the voltage reaches -55 mV?
The whole thing always occurs, All-or-None
What is step 3 of an action potential?
Depolarization occurs when the threshold (-55 mV) is reached; voltage-gated Na+ channels open and Na+ enters rapidly, reversive the polarity from negative to positive
What is the “threshold” of an action potential?
-55 mV
What does the voltage go to during step 3 of an action potential?
-55 mV –> +30 mV
What is step 4 of an action potential?
Repolarization occurs due to the closure of voltage-gated Na+ channels (inactivation state) and opening of voltage-gated K+ channels. K+ moves out of the cell and polarity is reversed from positive to negative
What happens to the voltage during step 4 of an action potential?
+30 mV –> 70 mV
What is step 5 of an action potential?
Hyperpolarization occurs when voltage-gated K+ channels stay open longer than the time needed to reach the resting membrane potential. During this time, the membrane potential is less than the resting membrane potential
What happens to the voltage during step 5 of an action potential?
-70 mV –> -80 mV
What is step 6 of an action potential?
Voltage-gated K+ channels are closed, and the plasma membrane has returned to resting conditions by activity of Na+/k+ pumps
What happens to the voltage during step 6 of an action potential?
-80 mV –> -70 mV
Voltage-gated Na+ channels have ____ gates and alternate between ____ different states
2 gates, 3 different states
What are the 3 different states of voltage-gated Na+ channels?
- Closed (no Na+ enters the cell)
- Opened (by depolarization, allows Na+ to enter the cell)
- Inactivated (blocked by inactivation gates soon after they open)
Voltage-gated K+ channels have ____ gate and ____ states
1 gate, 2 states
What are the two states of voltage-gated K+ channels?
- Closed (no K+ exits)
- Opened (by depolarization, allows K+ to exit the cell)
Repolarization resets ____ conditions but not _____ conditions
Resets electrical conditions, not ionic conditions
After repolarization, Na+/K+ pumps restore ______ conditions
Ionic
What is propagation?
Allows the action potential to be transmitted down the entire axon towards the terminals
