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Anatomy and Physiology I > Chapter 12: Nervous Tissue > Flashcards

Chapter 12: Nervous Tissue Flashcards

1
Q

How are the endocrine system and the nervous system different?

A

The endocrine system communicates by chemical messenger (hormones). The nervous system communicates by employing electrical and chemical means to send messages from cell to cell.

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2
Q

What is the 4 step function of the nervous system?

A
  • Sense organs receive information about changes in the body
  • They transmit messages to the brain and spinal cord (CNS)
  • CNS processes this information and relates it to past experiences and determines its response
  • CNS issues commands to muscles and gland cells to carry out a response
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3
Q

What are afferent and efferent neurons? What fibers are they made of?

A
  • Afferent neurons are sensory neurons (they lead into the CNS)
    • the somatic fibers come from skin, skeletal muscle, and joints
    • visceral fibers from internal organs
  • Efferent neurons are motor neurons (they lead out of the CNS)
    • somatic fibers to skeletal muscles (somatic NS)
    • visceral fibers to smooth muscls, cardiac muscle, or glands (Autonomic NS)
  • Remember, neurons are not the SAME
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4
Q

What are the two subdivisions of the nervous system and their basic components?

A
  • Central nervous system
    • Brain and spinal cord
  • Peripheral Nervous System
    • rest of nervous system, composed of nerves and ganglia
      • Nerve-bundle of nerve fibers (axons) wrapped in fibrous connective tissue
      • Ganglion: knotlike swelling in a nerve where neuron cell bodies are concentrated
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5
Q

Describe the motor division of the PNS

A
  • Somatic (voluntary) nervous system
    • motor neurons to skeletal muscle tissue
    • only 1 motor neuron is used
    • somatic reflexes: involuntary muscle contractions
  • Autonomic (involuntary) nervous system
    • motor neurons to smooth muscle and cardiac muscle, exocrine glands and endocrine glands
    • 2 motor neurons used
    • autonomic/visceral reflexes-involuntary responses
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6
Q

What are the 2 principal cell types of the nervous system?

A
  • Nerves
    • excitable cells that transmir electrical signals
    • functional units of the nervous system
  • Neuroglia
    • supporting cells
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7
Q

What are the universal properties of neurons?

A
  • Excitability (irritability)
    • response to environmental changes called stimuli
    • produce an electrical signal
  • Conductivity
    • conduct the electrical signal to other cells
  • Secretion
    • when an electrical signal reaches the end of nerve fiber, secretes a neurotransmitter that influences the next cell
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8
Q

What are the functional classes of neurons?

A
  • Sensory (afferent) neurons
    • detect stimuli and transmit information to CNS
  • Interneurons (association neurons)
    • connects motor and sensory pathways to CNS
    • makes decisions (integrating center)
    • about 90% of all neurons
  • Motor (efferent) neuron
    • send signals out to muscles and gland cells (the effectors)
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9
Q

What is the structure of a neuron (and the functions of its structures)?

A
  • Soma
    • control center of neuron
    • nucleus with one nucleolus
    • no centrioles
    • extreme longevity
  • Dendrites
    • branches that come off the soma
    • receives signals from other neurons
    • the more dendrites, the more info can be received
  • Axon (nerve fiber)
    • transmits signals away from soma
    • only one (or none)
    • mostly unbranched
    • may be enclosed in myelin sheath
    • axoplasm = cytoplasm
    • axolemma = cell membrane
  • Distal end has terminal arborization
  • Synaptic knob (terminal button)
    • contains synaptic vesicles full of neurotransmitters
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10
Q

What are the structural types of neurons?

A
  • Multipolar neuron
    • one axon and multiple dendrites
    • most common (most neurons in CNS)
  • Bipolar neuron
    • one axon and one dendrite
    • olfactory cells, retina, inner ear
  • Unipolar neuron
    • single process leading away from the soma
    • sensory cells from skin and organs to spinal cord
  • Anaxonic neuron
    • many dendrites but no axon
    • retina, brain, and adrenal gland
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11
Q

What is axonal transport?

A
  • A process that transports proteins to the axon or axon terminal to repair axolemma or transport organelles
  • Two way passage
    • anterograde transport: movement down the axon away from the soma
    • retrograde transport: movement up the axon toward the soma
  • Uses microtubules
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12
Q

What are the numbers and functions of neuroglia cells?

A
  • There are about 1 trillion in the nervous system
    • outnumber neurons by at least 10 to 1
  • Protect neurons and help them function
  • Bind neurons together and form framework for nervous tissue
  • In fetus, guide migrating neurons to their destination
  • If mature neuron is not in synaptic contact with another neuron, it is covered with glial cells
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13
Q

What are the 4 types of neuroglia in the CNS?

A
  • Ogliodendrocytes
    • form myelin sheaths in CNS
  • Ependymal Cells
    • line internal cavities of the brain
    • secrete and circulate cerebrospinal fluid
  • Microglia
    • WBCs that wander through CNS looking for debris and damage
  • Astrocytes
    • most abundant glial cell in CNS
    • covers brain surface and most nonsynaptic regions of neurons in the gray matter (framework)
    • forms blood/brain barrier
    • convert glucose to lactate for neurons
    • secrete nerve growth factors
    • communicate electrically with neurons
    • absorb excess neurotransmitters and ions
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14
Q

What is astrocytosis/ sclerosis?

A

When neuron is damaged, astrocytes form hardened scar tissues and fill in space.

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15
Q

What are the two types of neuroglia cells in the PNS?

A
  • Schwann cells
    • produce a myelin sheath around axons in PNS
    • Assist in regeneration of damaged fibers
      • axon ONLY can regenerate
  • Satellite cells
    • surround / protect the neurosomas in ganglia of the PNS
    • provide electrical insulation around the soma
    • regulate the chemical environment of the neurons
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16
Q

What is myelin sheath / myelination?

A
  • Insulation around a nerve fiber (axon)
    • formed by ogliodendrocytes in CNS and Schwann cells in PNS
    • Consists of the plasma membrane of glial cells
      • 20% protein and 80% lipid
  • Myelination: the production of myelin sheath
    • begins at 14 weeks of fetal development
    • proceeds rapidly during infancy
    • completed in late adolesence
    • dietary fat is important to CNS development
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17
Q

What is myelin sheath in the PNS v. CNS?

A
  • In the PNS
    • entire schwann cells spirals repeatedly around single nerve fiber
      • one hundred layers of membrane
      • no cytoplasm between membranes
    • Neurilemma: outermost coil of myelin sheath
      • contains nucleus and most of its cytoplasm
      • external to neurilemma is basal lamina and endoneurium
  • In the CNS
    • an ogliodendrocyte myelinates several nerve fibers in its immediate vicinity
      • does not migrate around like Schwann cells
      • must push new layers of myelin under older ones, so spirals in toward nerve fiber
      • no neurilemma or endoneurium
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18
Q

What is the structure of myelin?

A
  • Myelin sheath is segmented
    • Nodes of ranvier: gaps between segments
    • Internodes: myelin covered segments
    • Initial segment: section between the axon hillock and the first glial cell
    • Trigger zone: the axon hillock and the initial segment
      • important in initating nerve signal
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19
Q

What are brain tumors in relation to glial cells?

A
  • Tumors are masses of rapidly dividing cells
    • in the nervous sytem, come from meninges, metastasis from other tumors (e.g. melanoma), and glial cells
  • Gliomas grow rapidly and are highly malignant
    • Blood brain barrier decreases effectiveness of chemotherapy
    • treatment consists of radiation or surgery
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20
Q

How do nerve fibers regenerate?

A
  • Only the peripheral nerve fiber can regenerate and only if the soma is intact
  • Steps:
    • fiber distal to injury degenerates
    • soma swells, ER breaks up
    • Axon stump spouts multiple growth processes
    • Schwann cells, basal lamina, and neurilemma spout regeneration tube
    • Once contact is reestablished, soma shrinks
      • nucleus returns to normal shape
      • atrophied muscle fibers grow
21
Q

What are the diseases of myelin sheath?

A
  • Multiple sclerosis
    • ogliodendrocytes and myelin sheath in CNS deteriorate
    • Myelin replaced by hardened scar tissue (“sclerosis”)
    • Nerve conduction disrupted
      • (double vision, tremors, numbness, speech defects)
    • Onset between 20 and 40 years
    • Cause my be autoimmune
  • Tay-Sachs disease
    • Hereditary disorder of Easter European infants
    • Abnormal accumulation of ganglioside disrupts conduction of nerve signals
      • blindness, loss of coordination, and dementia
    • fatal before age 4
22
Q

What is the conduction speed of nerve fibers?

A
  • Speed at which a nerve signal travels along the surface of a nerve fiber
  • Depends on two factors:
    • Diameter of fiber
      • larger fibers = more surface area = conduct signals faster
    • Presence or absence of myelin
      • myelin further speeds signal conduction
  • Examples: slow signals are sent to gastrointestinal tract where speed is less of an issue
  • Fast signals sent to skeletal muscles where speed improves balance and coordinated body movement
23
Q

What are the problems with nerve fiber generation?

A
  • It takes up to 2 years
  • some nerve fiber connect with wrong muscle fibers and some die
  • Regeneration of damaged fibers in CNS does NOT happen
24
Q

Define the following: electric potential and electric current

A
  • Electric potential: a difference in concentration of charged particles between one point and another
  • Electrical current: a flow of charged particles from one point and another
    • in the body, currents are movements of ions
    • gated channels are opened or closed by various stimuli
    • enables cells to turn electrical currents on and off
25
Q

What is Resting Membrane Potential?

A
  • Cell is positive outside the membrane and negative inside the membrane
    • potential energy difference at rest is -70 mV
    • cell is polarized
    • Unequal distribution of electrolytes between ECF and ICF
      • High concentration of Na outside and K inside
        • potassium has the greatest influence on RMP
26
Q

How do potassium and sodium affect RMP?

A
  • Potassium has the greatest influence on RMP
    • highly permeable
    • leaks out until electrical charge of cytoplasmic ions attract it back in and equilibrium is reached
    • more concentrated in ICF
  • Sodium has some influence on RMP
    • not very permeable
    • more concentrated in ECF
    • some sodium leaks into cell (diffusion)
    • Sodium leakage makes RMP slightly less negative
  • Na+/K+ pump moves out 3 sodium for every 2 potassium
    • this exchange contributes about -3mV to RMP of -70 mV
27
Q

What are the 3 steps of changes in membrane potential?

A
  • Depolarization (less negative)
  • Repolarization (returns to RMP)
  • Hyperpolarization (more negative)
    • will inhibit electrical impulse
28
Q

What are local (graded) potentials?

A
  • short distances (die out quickly)
  • on dendrites and cell bodies
  • sodium gates open in response to chemicals, light, heat, or mechanical stimulation
  • size of signal depends on stimulus strength
  • membrane will either:
    • depolarize (leads to action potential)
    • hyperpolarize (prevents an action potential)
      • keeps you from twitching all the time
29
Q

What are the steps of an action potential?

A
  • An action potential is a rapid up and down shift in the membrane voltage involving a sequence of steps
  • arrival of an axon hillock depolarizes membrane
  • depoloarization much reach threshold: critical voltage (-55 mV) to open voltage regulated gates
  • voltage gated sodium channels open
  • sodium enters and depolarizes cell
  • opens more channels (positive feedback)
  • as membrane potential rises above 0mV, sodium channels are inactivated and close
    • voltage peaks at +35mV
  • slow potassium channels open and outflow of K polarizes cell
  • Cell hyperpolarizes
  • RMP is restored as sodium leaks in and potassium is removed by astrocytes
    *
30
Q

What are the characteristics of an action potential?

A
  • often called a “spike” (happens so fast)
  • only a think layer of cytoplasm next to cell membrane is affected
    • small amount of ions involved
  • follows an all-or-none law
    • threshold is or is not reached
  • Nondecremental (do not get weaker with distance)
  • Irreversible (cannot be stopped one started)
31
Q

What is the refractory period?

A
  • The period of resistance to stimulation
  • During an action potential and for a few milliseconds after it is impossible to stimulate that region of a neuron to fire again
  • Absolute refractory period: cannot produce another AP
  • Relative refractory: can produce another AP but only with a superstimulus
32
Q

How do local anesthetics work?

A
  • Novocaine and lidocaine
  • Nerve impulses cannot pass the anesthetized region
    • prevent voltage-gated sodium channels from opening
33
Q

What causes intesity of sensation with action potential?

A
  • frequency of stimulus
  • number of neurons
34
Q

Compare action potentials in the nerve v. the muscle

A
  • Location
    • nerve: only on the axon
    • muscle: entire sarcolemma
  • Resting Membrane Potential
    • nerve: -70 mV
    • muscle: close to -90mV
  • Duration
    • nerve impulse: 1/2 to 2 msec
    • skeletal musle: 1-5 sec
    • Cardiac and smooth muscle: 10-300 msec
  • Speed
    • fastest nerve impulse is 18 times faster than a muscle fiber
35
Q

What is continuous conduction in nerve tissue?

A
  • Unmyelinated fibers have voltage gated channels along their entire length
    • Produce action potential along entire length of axon
      • baby steps v. giant steps
    • chain reaction continues until the nerve signal reaches the end of the axon
  • Myelinated fibers generate an action potenital in each Node of Ranvier
    • very fast
    • ‘Saltatory Conduction’
36
Q

What are synapses?

A
  • A presynaptic neuron may synapse with a dendrite, soma, or axon of postsynaptic neuron to form axodendritic, axosomatic, or axoaxonic synapses
  • A neuron can have an enormous number of synapses
    • spinal motor neurons covered by about 10,000 synaptic knobs
    • In the cerebellum of the brain, one neuron can have as many as 100,000 synapses
37
Q

What are the types of synapses?

A
  • Electrical
    • spreads through gap junctions
    • faster
    • two-way transmission
    • can’t make decisions
    • wake up in AM, some emotions
  • Chemical
    • one way transmission
      • from pre-synaptic to post-synaptic neuron
    • uses neurotransmitters
    • most thinking
38
Q

What is the structure of a chemical synapse (pre-synaptic v. post-synaptic)?

A
  • Synaptic knob of presynaptic neuron contains synaptic vesicles containing neurotransmitter
  • Postsynaptic neuron membrane contains proteins that function as receptors and ligand-regulated ion gates
39
Q

How do chemical synapses work?

A
  • nerve impulses reach the axonal terminal of a presynaptic neuron and open calcium channels
  • neurotransmitter is released into synaptic cleft via exocytosis
  • neurostransmitter crosses synaptic cleft and binds to receptors on postsynaptic neuron
  • Postsynaptic brain permeability changes
    • causes excitatory (E-PSP)
      • post synpatic potential
    • or inhibitory (IPSP) effect
40
Q

What are the categories of neurotransmitters?

A
  • More than 100 identified
  • Four major categories:
    • acetylcholine
      • in a class by itself
      • formed by acetic acid and choline
      • broken down by Acetylcholine Esterase (AChE)
    • amino acids
    • monoamines
      • synthesized from amino acids
      • broken down by Monoamineoxydase (MAD)
      • Include the catecholamines
        • epinephrine
        • norepinephrine
        • dopamine
        • histamine
        • ATP
        • serotonin
    • neuropeptides
      • chains of 2 to 40 amino acids
41
Q

How are neurotransmitters removed?

A
  • Diffusion
    • move down concentration gradient away from synapse
  • Enzymatic degradation
    • E.g. AChE or MAD
  • Uptake by neuron or glial cells
    • neurotransmitter transporters
42
Q

What is neural integration?

A
  • The ability to process, store, and recall information and use it to make decisions
  • Chemical synapses allow for decision making
    • brain cells are very well connected allowing for complex integration
    • trade off: chemical transmission involves synaptic delay that makes info slower than it would be with no synapse
43
Q

What are post synaptic potentials?

A
  • Different neurotransmitters cause different types of postsynaptic potentials in the cells they bind to
  • A neurotransmitter might excite some cells and inhibit others, depending on the type of receptors the postsynaptic cells hae
    • ACh and norepinephrine work this way
    • ACh excites skeletal muscle but inhibits cardiac muscle because of different ACh receptors
44
Q

Define the following: summation (temporal and spatial)

A
  • Summation: the process of adding up postsynaptic potentials and responding to their net effect
    • one neuron can receive input from thousands of other neurons
    • some produce ESPs and some ISPs
    • neuron’s response depends on whether the net input is excitatory or inhibitory
    • occurs in trigger zone
  • Temporal summation: occurs when a single synapse generates ESPS so quickly that each is generated before the previous one fades
  • Spatial summation: occurs when ESPS from several different synapses add up to threshold at an axon hillock
45
Q
A
46
Q

Define the following: facilitation and inhibition

A
  • Facilitation: a process in which one neuron enhances the effect of another
  • Presynaptic inhibition: process in which one presynaptic neuron suppresses another one
    • opposite of faciliation
47
Q

What is strychnine poisoning?

A
  • In spinal cord, Renshaw cells normally release an inhibitory transmitter (glycine) onto motor neurons preventing excessive muscle contraction
  • Strychnine binds to and blocks glycine receptors in the spinal cord
  • Causes a tetanus
48
Q

What is Alzheimer’s disease?

A
  • A disease that causes 100,000 deaths a year
    • affects 11% of population over 65 and 45% by age 85
  • memory loss for recent evets, moody, combative, lose ability to talk/walk/ear
  • show deficiencies of acetylcholine and nerve growth factor (NGF)
  • Diagnosis confirmed at autopsy
    • atrophy of gyri folds in cerebral cortex
    • Neurofibrilliary tangles and senile plaques
    • formation of B-amyloid protein (from breakdown of plasma membrane)
  • Treatment
    • block AChE or NGF (inhibitors)
    • clear B-amyloid or halt its production (caused serious side effects)
49
Q

What is Parkinson’s disease?

A
  • Progressive loss of motor function beginning in 50s or 60s
    • no recovery
    • Degeneration of dopamine releasing neurons
      • Dopamine normally prevents excessive activity in motor centers (basal nuclei)
    • Involuntary muscle contractions
      • facial rigidity, slurred speech, pill rolling motion, illegible handwriting, slow gait
  • Treatment: drugs and physical therapy
    • dopamine precursor (L-dopa) crosses brain barrier
      • bad side effects on heart and liver
    • MAO inhibitor slows neural degeneration
    • surgical technique to relieve tremors

Anatomy and Physiology I (19 decks)

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