Unit 4: Ch 12 (Nervous Tissue)

Question 1

Action potential conduction types

Answer 1

• Continuous
• Saltatory

Question 2

Action potentials

• Characteristics
• Effects

Answer 2

• 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

Question 3

Anatomical classes of neurons

Answer 3

• 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

Question 4

Anatomical subdivisions of the NS

Answer 4

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

Question 5

CNS-specific components

Answer 5

• 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

Question 6

Continuous conduction

Answer 6

• 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

Question 7

Depolarization

Answer 7

• Any voltage shift to a less negative value

Question 8

Excitatory adrenergic synapse

• Description
• Steps

Answer 8

• 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

Question 9

Excitatory cholinergic synapse

• Description
• Steps

Answer 9

• 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

Question 10

Key structures of a neuron

Answer 10

• 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

Question 11

Local potentials

• Characteristics
• Effects

Answer 11

• 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)

Question 12

Myelin description

Answer 12

• 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

Question 13

Nerve fibers conduction speed

• Description
• Factors impacting speed
• Fiber classifications

Answer 13

• 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

Question 14

Neural circuits

• Description
• Intensity variables
• Types

Answer 14

• 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

Question 15

Neuroglia

Answer 15

• Helps to maintain homeostasis of the NS
• Unable to create instructions

Question 16

Neuron

Answer 16

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

Question 17

Neuron classes

Answer 17

• 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

Question 18

Neurotransmitter classifications

• Classification name
• Categories

Answer 18

• 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

Question 19

Neurotransmitters

• Function
• Effects

Answer 19

• 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)

Question 20

NS functions

Answer 20

• 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

Question 21

Peripheral NS (PNS) divisions

Answer 21

• 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

Question 22

Physiological subdivisions of the NS

Answer 22

• 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

Question 23

PNS-specific components

Answer 23

• 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

Question 24

Postsynaptic potentials

• Description
• Methods

Answer 24

• 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

Question 25

Potential

Answer 25

* Indicates an electrical change or a different gradient between the sides of a cell

Question 26

Refractory period * Description * Periods

Answer 26

* **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

Question 27

Resting Membrane Potential (RMP)

Answer 27

* 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

Question 28

Reuptake

Answer 28

* Reabsorption of a neurotransmitter

Question 29

Saltatory conduction

Answer 29

* 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

Question 30

Sensory (afferent) division

Answer 30

* 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

Question 31

Action potential cessation

Answer 31

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

Question 32

Na⁺ & K⁺ channel process during an action potential

Answer 32

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

Question 33

Spatial summation

Answer 33

* 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

Question 34

Summation

Answer 34

* 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_

Question 35

Synapses * Description * Parts to every synapse * Types

Answer 35

* **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

Question 36

Temporal summation

Answer 36

* 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)

Question 37

Universal properties of neurons

Answer 37

* **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