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DCCC BIO150 (Spring 2021) > Unit 4: Ch 12 (Nervous Tissue) > Flashcards

Unit 4: Ch 12 (Nervous Tissue) Flashcards

1
Q

Action potential conduction types

A
  • Continuous
  • Saltatory
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2
Q

Action potentials

  • Characteristics
  • Effects
A
  • Characteristics
    • All or none: occurs at the same intensity. Occurs or does not occur
    • Irreversible: goes to completion once it begins
    • Nondecremental: signal maintains same strength regardless of distance
  • Effects
    • Depolarization
    • Repolarization
    • Hyperpolarization
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3
Q

Anatomical classes of neurons

A
  • Unipolar neurons
    • Have only a single process leading away from the soma
    • Examples: carry signals to the spinal cord for touch and pain
  • Bipolar neurons (related to the head)
    • 1 axon and 1 dendrite
    • Examples: cells of nose, eyes, & ear
  • Multipolar neurons (most common)
    • 1 axon and multiple dendrites
    • Examples: most neurons of the brain and spinal cord
  • Anaxonic neurons (rare)
    • Multiple dendrites but no axon
    • Communicate locally through their dendrites and do NOT produce action potentials
    • Examples: brain, retina, and adrenal medulla
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4
Q

Anatomical subdivisions of the NS

A
  • Central Nervous System (CNS)
    • Brain & spinal cord
  • Peripheral Nervous System (PNS)
    • Cranial & spinal nerves
    • Sends & receives information to/from the CNS
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5
Q

CNS-specific components

A
  • Astrocytes: maintain the chemical environment of neurons
  • Ependymal cells: secrete and circulate cerebrospinal fluid; line cavities of brain and spinal cord
  • Microglia: phagocytize and destroy foreign matter; helps with immunity
  • Nucleus
  • Oligodendrocytes: form myelin
  • Tract: axon
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6
Q

Continuous conduction

A
  • Second way of nerve impulse transmission
  • Occurs in unmyelinated axons
  • Action potential is generated along the entire length of the axon. Hence, it takes time to generate and transmit action potential
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7
Q

Depolarization

A
  • Any voltage shift to a less negative value
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8
Q

Excitatory adrenergic synapse

  • Description
  • Steps
A
  • Description
    • Neurotransmitter is norepinephrine (NE) & monoamines, and neuropeptides
    • Acts through second-messenger systems
    • Receptor is associated with a G protein on the inner face of the membrane
  • Steps
    • Unstimulated NE receptor is bound to a G protein
    • Binding of NE to the receptor causes the G protein to dissociate from it
    • G protein binds to adenylate cyclase, converting ATP to cAMP
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9
Q

Excitatory cholinergic synapse

  • Description
  • Steps
A
  • Description
    • Ligand specific
    • Neurotransmitter is ACh
  • Steps
    • Voltage-gated Ca channels open with nerve signal
    • Ca enters the terminal and triggers exocytosis of the synaptic vesicles, releasing ACh
    • Empty vesicles drop back into the cytoplasm to be refilled with ACh, while synaptic vesicles in the reserve pool move to the active sites and release their ACh
    • ACh diffuses across the synaptic cleft and binds to ligand-gated channels on the postsynaptic neuron
    • As Na enters, it spreads out along the inside of the plasma membrane and depolarizes it, producing a local voltage shift called the post-synaptic potential
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10
Q

Key structures of a neuron

A
  • Axon
    • Axon hillock: A mound on one side of the neurosoma
    • Axoplasm: cytoplasm
    • Axolemma: phospholipid bilayer (membrane)
    • 2 forms
      • Myelin sheath
      • Synaptic knobs
  • Dendrites
    • Primary site for receiving signals from neurons
  • Soma/cell center/neurosoma/perikayron/cell body
    • Central nucleus with large nucleolus
    • Cytoplasm: mitochondria, lysosomes, Golgi complex, inclusions, rER, & cytoskeleton
    • Cytoskeleton: microtubules & neurofibrils
    • Lacks centrioles
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11
Q

Local potentials

  • Characteristics
  • Effects
A
  • Characteristics
    • Graded: proportional to stimulus strength
    • Decremental: signal grows weaker with distance
    • Reversible: returns to RMP if stimulation ceases before the threshold is reached
  • Effects
    • Excitation: cause a more positive or less negative change in charge on the cell membrane (depolarizing)
    • Inhibition: cause a more negative voltage change (hyperpolarizing)
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12
Q

Myelin description

A
  • Segmented (discontinuous)
    • Myelin-covered segments from each node to the next are internodal segments
    • Each gap between segments is a myelin sheath gap or node of Ranvier
  • ​Myelin is found in the internodes
  • Myelination is the production of the myelin sheath
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13
Q

Nerve fibers conduction speed

  • Description
  • Factors impacting speed
  • Fiber classifications
A
  • Description
    • The speed at which a nerve signal travels along a nerve fiber
  • Factors
    • Diameter of nerve fiber (larger is faster)
    • Presence or absence of myelin
    • Temperature
  • Classification system
    • A fibers: fastest, largest diameter, myelinated
    • B fibers: intermediate, myelinated
    • C fibers: slowest, smallest diameter, unmyelinated
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14
Q

Neural circuits

  • Description
  • Intensity variables
  • Types
A
  • Neural circuits interconnect to one another to form large-scale brain networks
  • Intensity variables
    • Population
    • Frequency
  • Types
    • Converging circuit: many neurons condensed into 1 output
    • Diverging circuit: 1 neuron provides instruction to multiple neurons
    • Parallel after-discharge circuit: neurons run in parallel. They do not synapse with each other
    • Reverberating circuit: allows for the signal to multiple neurons that returns a signal to the original neuron
    • Simple circuit: contains presynaptic neuron that provides to 1 postsynaptic neuron
  • Notes
    • Important for regulation of the heart and regions of the respiratory system
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15
Q

Neuroglia

A
  • Helps to maintain homeostasis of the NS
  • Unable to create instructions
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16
Q

Neuron

A
  • Functional cell of the NS
  • Provide electrical and chemical signals to other cells to be able to produce a response
17
Q

Neuron classes

A
  • Sensory (afferent) neurons
    • The receptor
    • Detect stimuli such as light, heat, pressure, & chemicals
    • Transmit info to the CNS
  • Interneurons
    • The integrating center
    • Limited to the CNS
    • Process, store, and retrieve information and “make decisions” that determine how the body responds to stimuli
  • Motor (efferent) neurons
    • The effector
    • Send signals to muscle and gland cells
    • Called motor neurons because most of them lead to muscle cells
18
Q

Neurotransmitter classifications

  • Classification name
  • Categories
A
  • Acetylcholine
    • Formed from acetate & choline
  • Amino acids
    • Aspartate
    • GABA (inhibitory)
    • Glutamate (excitatory)
    • Glycine
  • Monoamines
    • Catecholamines
    • Histamine
    • Serotonin
  • Neuropeptides (Help with pain)
    • Endorphin
    • Enkephalin
    • Cholecystokinin
    • SO4
    • Substance P
19
Q

Neurotransmitters

  • Function
  • Effects
A
  • Function
    • Transmit a message in the NS
    • Excitatory & inhibitory
  • Effects
    • Ionotropic: receptors/quick response; only 1 effect (ligand-regulated ion gates)
    • Metabotropic: receptors/longer response; can create multiple effects (2nd messenger system)
20
Q

NS functions

A
  • Receive information about changes in the body and the external environment and transmit messages to the CNS
  • CNS processes this information and determines what response, if any, is appropriate
  • CNS issues instruction, carried out by the motor neurons
21
Q

Peripheral NS (PNS) divisions

A
  • Sensory (afferent) division
    • Visceral sensory division: viscera/organs (ie stretch)
    • Somatic sensory division: general senses (ie touch, pain)
  • Motor (efferent) division
    • Effectors
    • Visceral motor division (ANS)
      • Autonomic reflexes
      • Sympathetic division
      • Parasympathetic division
    • Somatic motor division
      • Somatic reflexes
22
Q

Physiological subdivisions of the NS

A
  • Enteric NS (ENS)
    • System of the gut
  • Somatic NS (SNS)
    • Neuromuscular junction
    • Deals with skeletal muscle control
  • Autonomic NS (ANS)
    • Sympathetic NS: fight or flight
    • Parasympathetic NS: rest & digest
23
Q

PNS-specific components

A
  • Ganglion: The cell body of peripheral neurons
  • Nerve: a bundle of nerve fibers; axon
  • Satellite cells: electrical insulation and maintain the chemical environment of PNS
  • Schwann cells: creates myelin
24
Q

Postsynaptic potentials

  • Description
  • Methods
A
  • Potentials with the function to initiate or inhibit action potentials
  • 2 methods
    • EPSP
      • Help produce depolarization (less negative)
      • Closer to threshold
      • Helps to produce an action potential
    • IPSP
      • Induces hyperpolarization
      • Less likely to produce an action potential
      • Important for pain & anesthesia
25
Q

Potential

A
  • Indicates an electrical change or a different gradient between the sides of a cell
26
Q

Refractory period

  • Description
  • Periods
A
  • Description
    • The time immediately following a stimulus and when a muscle is contracting
    • A period when it cannot respond to a second stimulus
    • Since this is occurring at the same time as the contraction, it does not appear on the myogram as a separate event
  • Periods
    1. Absolute refractory period
      • ​occurs during the depolarization phase of action potential
      • cannot recreate an action potential during this time due to K channels needing to be closed and reset before being reopened
    2. Relative refractory period
      • ​lasts until hyperpolarization ends
      • possible to create an action potential; available if a suprathreshold stimulus is available
      • needs suprathreshold stimulus to reopen
27
Q

Resting Membrane Potential (RMP)

A
  • RMP exists because electrolytes are unequally distributed between the ECF & ICF
  • Combined effect of 3 factors:
    • Diffusion of ions down their concentration gradients through the membrane
    • Selective permeability of the membrane, allowing some ions to pass more easily than others
    • The electrical attraction of cations and anions to each other
  • Net intracellular charge that is negative due to
    • K-Na pump moving in unequal numbers (net -1 charge)
    • Large anions in the cell that cannot escape
    • Leaky channels; more K channels that are leaky inside the cell membrane, therefore K is more permeable to the cell
28
Q

Reuptake

A
  • Reabsorption of a neurotransmitter
29
Q

Saltatory conduction

A
  • Occur on myelinated fibers/axons
  • Faster than unmyelinated action potentials
  • Steps
    1. Na inflow at node generates an action potential
    2. Positive charge flows rapidly along the axon and depolarizes membrane; signal grows weaker with distance
    3. Depolarization of membrane at next node opens Na channels, triggering a new action potential
30
Q

Sensory (afferent) division

A
  • Carries signals away from various receptors to the CNS
  • Informs CNS of stimuli within and around the body
  • Subdivisions
    • Somatic sensory division: carries signals from receptors in the skin, muscles, bones, & joints
    • Visceral sensory division: carries signals from the viscera of the thoracic and abdominal cavities, such as the heart, lungs, stomach, and bladder
31
Q

Action potential cessation

A
  • Methods to prevent continual instructions/signals
    1. Diffusion
    2. Reuptake
    3. Degradation in the synaptic cleft (via enzyme)
      • AChE
      • COMT & MAO
32
Q

Na+ & K+ channel process during an action potential

A
  1. Resting membrane potential
    • Na+ and K+ channels closed
  2. Depolarization begins
    • Na+ channels open
    • Na+ enters cell
    • K+ channels beginning to open
  3. Depolarization ends, hyperpolarization begins
    • Na+ channels closed
    • K+ channels fully open
    • K+ leaves cell
  4. Repolarization complete
    • Na+ channels closed
    • K+ channels closing

Notes

  • Na opens at a faster rate than K, so Na move down the concentration gradient faster than K
33
Q

Spatial summation

A
  • Occurs when EPSPs from several synapses add up to threshold at the axon hillock
  • Any one synapse may generate only a weak signal, but several synapses acting together can bring the hillock to the threshold
  • The presynaptic neurons collaborate to induce the postsynaptic neuron to fire
34
Q

Summation

A
  • The process of adding up postsynaptic potentials and responding to their net effect
  • A balance between EPSPs and IPSPs
  • 2 ways in which EPSPs can add do this; may occur simultaneously
    • Temporal summation
    • Spatial summation
35
Q

Synapses

  • Description
  • Parts to every synapse
  • Types
A
  • Description
    • Physical space that separates a cell
    • Stimulates neurons
  • Parts
    • Presynapse: before the cleft; releases the chemical
    • Postsynapse: after the cleft; receives the chemical
  • Types
    • Axosyomatic
    • Axoaconic
    • Axodendritic
36
Q

Temporal summation

A
  • Occurs when a single synapse generates EPSPs so quickly that each is generated before the previous one fades
  • Deals with the variable of time or frequency (1:1 ratio)
37
Q

Universal properties of neurons

A
  • Secretion
    • When the signal reaches the end of a nerve fiber, the neuron secretes a neurotransmitter that crosses the gap and stimulates the next cell
  • Excitability (irritability)
    • Respond to environment changes/stimuli
  • Conductivity
    • Neurons respond to stimuli by producing electrical signals that are conducted to other cells at distant locations

DCCC BIO150 (Spring 2021) (9 decks)

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