7 - Intro to Nervous System Flashcards
1
Q
What are the 2 principle parts of the Nervous system?
A
- Central nervous system (CNS)
- Brain & spinal cord of dorsal body cavity
- Integrating & control centre
- Peripheral nervous system (PNS)
- The portion of nervous system outside CNS
- spinal nerves and cranial nerves
2
Q
What are the 2 main cell types?
A
- neurons
- neuroglia
3
Q
What are the Neuroglia cells in the CNS?
A
- Astrocytes
- Microglia
- Ependymal cells
- Oligodendrocytes
4
Q
What are the Neuroglia cells in the PNS?
A
- Satellite cells
- Schwann cells
5
Q
What are Astrocytes?
A
- Star shaped cells found in CNS & spinal cord
- Most abundant cell of the human brain
- Guide the migration of young neurons & formation of synapses
- Help determine capillary permeability
- Control chemical environment (uptake/recycling) NTs & ions
- Have gap junctions for communication b/w astrocytes (Ca2+ pulses)
- Important in memory
6
Q
What are microglia?
A
- Small, ovoid cells w/ thorny processes
- Migrate towards injured neurons
- Phagocytize microorganisms & neuronal debris
7
Q
What are ependymal cells?
A
- Range in shape from squamous to columnar
- Circulate in & produce CSF
- Line central ventricular cavities of brain & spinal column
- Separate the CNS interstitial fluid from CSF
8
Q
What are Oligodendrocytes?
A
- One cell can produce processes that wrap up to 60 axons
- Forming insulating myelin sheaths
9
Q
What are Satellite Glial Cells?
A
- Surround neuron cell bodies in ganglia of PNS
- Control microenvmt around neuron cell body
- Similar to astrocytes of CNS
10
Q
What are Schwann cells?
A
- Most form myelin sheaths around axons
- Vital for function, maintenance & regeneration of damaged nerve fibers
11
Q
What does a Myelin Sheath do?
A
- Protect & electrically insulate axon
- Increase speed of nerve impulse transmission
12
Q
What makes up Myelin sheath in PNS?
A
- Schwann cells – wraps many times around axon
- Neurilemma – peripheral bulge of schwann cell cytoplasm
- Nodes of Ranvier – myelin sheath gaps b/w adjacent schwann cells
13
Q
What makes up Myelin sheath in CNS?
A
- Formed by processes of oligodendrocytes
- Nodes of Ranvier
- No neurilemma
- Thinnest fibers (axons) are unmyelinated
- 1 oligodendrocyte can wrap around up to 60 axons
- Give rise to white matter
14
Q
What are Neurons?
& what are their special characteristics
A
- nerve cells, are structural units of nervous system
- cells that conduct impulses
Special characteristics:
* Extreme longevity (last person’s lifetime)
* Amitotic – non-dividing, don’t regenerate
* High metabolic rate – requires continuous supply of oxygen & glucose
* All have cell body & one or more processes
15
Q
What do Neuronal Cell Bodies do?
A
- Synthesizes proteins, membranes, chemicals
- Rough ER (chromatophilic substance or nissl bodies
Clusters of cell bodies are called:
* Nuclei in CNS
* Ganglia in PNS
16
Q
Bundles of Neuron processes are called? CNS vs. PNS?
A
- Tracts in CNS
- Nerves in PNS
17
Q
What are Dendrites?
A
- Receptive (input) region of neuron
- Convey incoming messages toward cell body as graded potentials
- Contain dendritic spines – appendages w/ bulbous or spikey ends
18
Q
What are Axons? What are the 3 parts?
A
- Axon hillock, Axolemma, Axoplasm
- Each neuron has 1 axon (conducting region) that starts at axon hillock
- Long axons are called nerve fibers
- Branches are called axon collaterals
- Axons branch profusely at their end
19
Q
What are the 3 Structure types of neurons?
A
- Multipolar - 3 or more processes w/ 1 axon and rest dendrites
- Bipolar – 2 processes w/ 1 axon + 1 dendrite (rare), found in retina and olfactory mucosa
- Unipolar (pseudounipolar) - single short processes that has 2 branches
20
Q
What are the 3 Functional types of Neurons?
A
- Sensory (afferent) - transmit impulses from sensory receptors toward CNS
- Interneurons (association neurons) - shuttle signals through CNS pathways, most within CNS
- Motor (efferent) - carry impulses from CNS to effectors
21
Q
What is white matter?
A
- dense collections of myelinated fibers
22
Q
What is gray matter?
A
- mostly neuronal cell bodies & unmyelinated fibers
23
Q
Neurons & membrane potentials
A
- Like all cells, neurons have a resting membrane potential
- Unlike most other cells, neurons can rapidly change resting membrane potential
- Neurons are highly excitable
24
Q
What is Ohm’s law
A
- (I) = V/R
- current directly proportional to voltage
- Resistance inversely proportional to voltage
25
Q
2 Main types of ion channels
A
- Leakage (nongated) channels - always open
- Gated channels - in which part of the protein changes shape to open/close channel
26
Q
What are the 3 types of Gated channels
A
- chemically gated, voltage-gated, mechanically gated
27
Q
What Factors influence Resting Membrane Potential
A
- Impermeable to negatively charged proteins
- Slightly permeable to Na+ (Na+ leakage channels)
- 25-100 times more permeable to K+ (K+ leakage channels)
- Freely permeable to Cl-
- Differences in ionic composition of ICF & ECF
- Differences in plasma membrane permeability
28
Q
What generates the Resting Membrane Potential?
A
- Na/K pumps more cations out
- [ ] gradient of K
- higher permeability of K
- membrane impermeable to anionic proteins
- chemical gradient + electrical gradient
29
Q
Membrane potential changes when…
A
- [ ] s of ions across membrane change
- Membrane permeability to ions changes
30
Q
What are the 2 types of signals produced by changes in membrane potential?
A
- Graded potentials
- Incoming signals operating over short distances
- Action potentials
- Long-distance signals of axons
31
Q
What is Depolarization?
A
- Reduction in membrane potential
- Going more +ve
- Inside of membrane becomes less negative than resting potential
- Increase probability of producing a nerve impulse
32
Q
What is Hyperpolarization?
A
- Increase in membrane potential
- Going more –ve
- Inside of membrane becomes more negative than resting potential
- Decrease probability of producing a nerve impulse
33
Q
What are graded potentials?
A
- Short-lived localized changes in membrane potential
- stronger the stimulus, the more voltage changes & farther current flows
- Triggered by stimulus that opens gated ion channels
- Results in depolarization or hyperpolarization
34
Q
What are the types of graded potentials?
according to location & function
A
- Receptor potential (generator potential) - graded potentials in receptors of sensory neurons excited by some form of energy (heat, light or other)
- Postsynaptic potential - neuron graded potential
35
Q
What are Action Potentials?
A
- Principal way neurons send signals
- long-distance neural communication
- primarily in muscle cells & axons of neurons
- Action potentials (APs) do not decay over distance
- AKA nerve impulse
36
Q
Describe Voltage gated Na+ channels
A
- have 2 gates, alternate b/w 3 different states
- Activation gates - closed at rest, open w/ depol, allowing Na+ to enter cell
- Inactivation gates - open at rest, block channel once it is open, prevent more Na+ from entering cell
- closed - at rest
- open - opened by depol
- inactivated - blocked by inactivation gates soon after they open
37
Q
Describe Voltage gated K+ channels
A
- have 1 gate & 2 states
- Closed at rest
- Opens slowly w/ depol
38
Q
What is the absolute refractory period?
A
- Time from opening of voltage-gates Na+ channels until resetting of channels (involved opening the inactivation gate)
- Time where you can’t generate any APs
- Ensures that each AP is an all-or-none
- Enforces 1-way transmission of nerve impulses
39
Q
What is the Relative refractory period?
A
- Most voltage-gated Na+ channels have returned to resting state
- Some voltage-gate K+ channels are still open
- During hyperpolarization
- Threshold required for initiating an AP generation is elevated
- Need higher potential to initiate AP during relative refractory period
40
Q
Explain Threshold & all-or-none response
A
- Not all depolarization events produce APs
- depolarization must reach threshold voltage to trigger AP
- All-or-none – an AP either happens completely or does not happen at all
- Size of AP doesn’t change depending on strength of stimulus
41
Q
Describe the Propagation of an AP
A
- AP to be transmitted from origin down entire axon length toward terminals
- local currents that cause opening of Na+ voltage gates in adjacent membrane areas
- Once initiated, an AP is self-propagating
- AP occurs only in forward direction
42
Q
How does stimulus intensity affect APs?
A
- All APs are alike & are independent of stimulus intensity
- Strong stimuli - can generate APs more often than weaker stimuli
43
Q
What increase Conduction Velocity of neurons?
A
- larger diameter fibers - less resistance to current flow, faster impulse conduction
- myelination - insulate & prevent leakage of charge
44
Q
What is Saltatory Conduction?
A
- Voltage-gates Na+ channels located at nodes of Ranvier
- APs jump rapidly from node to node (30X faster than non-myelinated)
45
Q
What are the 3 nerve fiber classifications?
A
Group A fibers = 150 m/s fastest
* Large diameter, myelinated
* somatic sensory & motor fibers
Group B fibers = 15 m/s
* Intermediate diameter, lightly myelinated
* ANS motor fibers serving visceral organs & smaller somatic sensory fibers from skin (pain & touch)
Group C fibers = 1 m/s slowest
* Smallest diameter, unmyelinated
* some ANS motor fibers serving visceral organs & smaller somatic sensory fibers from skin (pain & touch)
46
Q
What is Multiple Sclerosis?
A
- autoimmune disease that affects primarily young adults
- immune system attacks myelin - Myelin sheaths in CNS are destroyed
- Turns myelin into hardened lesions called scleroses
- Impulse conduction slows & eventually ceases
- Demyelinated axons increase Na+ channels, causing cycles of relapse & remission
47
Q
What is a synapse?
A
- A junction that mediates info transfer from 1 neuron to another neuron or an effector cell
- Presynaptic neuron - conducts impulses toward synapse
- Postsynaptic neuron - transmit impulses away from synapse
48
Q
What are Chemical synapses?
A
- most common
- release & reception of chemical neurotransmitters
- Axon terminal of presynaptic neuron – contains synaptic vesicles filled w/ NTs
- Receptor region on postsynaptic neuron’s membrane – receives NT’s
- Electrical (synapse) -> chemical (synaptic cleft) -> electrical (synapse)
49
Q
What is synaptic delay?
A
- NT must be released, diffuse across synapse, & bind to receptors
- Synaptic delay (0.3-0.5 ms)
- synaptic delay is rate-limiting step of neural transmission
50
Q
What are Electrical Synapses?
A
- Less common than chemical synapses
- In embryonic development
- Neurons are electrically coupled (gap junctions)
- Communication is very rapid
- May be unidirectional or bidirectional
- Are important in stereotyped movements
51
Q
Postsynaptic potential strengths are determined by?
A
- amount of NT released
- Time NT is in area
52
Q
2 types of postsynaptic potentials
A
- EPSP – excitatory postsynaptic potential
- IPSP – inhibitory postsynaptic potentials
53
Q
Excitatory synapses & EPSP
A
- NT binds chemically gated channels that allow simultaneous flow of Na+ & K+ in opposite directions
- Na+ influx > K+ efflux (causes net depolarization)
- EPSP helps trigger AP at axon hillock
54
Q
Inhibitory synapses & IPSPs
A
- NT opens chemical gated channels for either K+ or Cl-
- Causes hyperpolarization
- Reduces postsynaptic neuron’s ability to produce an AP
55
Q
What is synaptic potentiation?
A
- Repeated use increases efficiency of neurotransmission (long-term potentiation)
- Ca2+ concentration increases in presynaptic terminal & postsynaptic neuron
56
Q
What is Presynaptic inhibition?
A
- Release of excitatory NT by one neuron may be inhibited by activity of another neuron via an axoaxonic synapse
- Block axon from releasing NTs before even getting response into synaptic cleft -> presynaptic inhibition
- Less NT is released & smaller EPSPs are formed
57
Q
What are the NT classes?
A
- Acetylcholine
- Biogenic Amines (aka monoamines)
- Amino acids
- Peptides (neuropeptides)
- Purines
- Gases & liquids
58
Q
What is Acetylcholine?
A
- Synthesized from choline & acetyl CoA by choline acetyltransferase (ChAT) & degraded by acetylcholinesterase
- Released at neuromuscular junctions, some ANS neurons, and some CNS neurons
- Nicotinic receptors (N) excitatory - on skeletal muscle, ANS ganglia & CNS
- Muscarinic receptors (M) can be inhibitory or excitatory – on visceral effectors & in CNS
59
Q
What are Biogenic Amines?
A
- Aka monoamines
- Drug class: monoamine oxidase inhibitor (MOAI)
- Derived from single amino acids
- Play roles in emotional behaviors & biological clock
3 classes:
* Catecholamines (dopamine, norepinephrine, epinephrine)
* Indolamines (serotonin or 5HT)
* Imidazoleamine (histamine)
60
Q
Dopamine
A
- inhibitory or excitator
- Released by substantia nigra & hypothalamus
- Important for motor pathways, motivation, reward & reinforcement
- Tyrosine precursor
60
Q
NE & Epinephrine
A
- inhibitory or excitatory
- Released from locus coeruleus, limbic system, cerebral corte, postganglionic neurons in SNS & adrenal Medulla
- Involved in mood, sleep, wakefulness, attention, feeding behaviour & SNS
- Tyrosine -> dopamine -> NE -> E precuror
61
Q
Serotonin
A
- mainly inhibitory
- Brain & spinal cord
- Role in sleep, appetite, nausea, migraine headaches, mood & digestion
- Tryptophan precursor
62
Q
Histamine
A
- Hypothalamus
- Involved in wakefulness, appetite control, learning & memory, gastric secretions, in CT mediates inflammation & vasodilation
- Histidine precursor
63
Q
What are Amino acids?
A
- GABA – inhibitory
- Principle inhibitory NTs in brain
- Important for axoaxonal presynaptic inhibition
- Glycine – inhibitory
- Principal inhibitory NT in spinal cord
- Glutamate – excitatory
- Principal excitatory NT
- Important in learning & memory
- Aspartate – excitatory NT in some brain regions
64
Q
What are Neuropeptides?
A
- Tachykinins – excitatory
- Substance P, neurokinin A
- PNS = mediator of pain signals
- CNS = respirator & cardiovascular controls & mood
- Also released by enteric neurons
- Endorphins – inhibitory
- Act as natural opiates
- Reduce pain perception
- Inhibits substance P
- Cholecystokinin (CCK) - excitatory
- Found in CNS & released by small intestines to encourage digestion
- Involved in anxiety, pain, memory inhibit appetite
- Somatostatin – inhibitory
- Found in CNS & released by pancreas, stomach & intestines to slow down/inhibit digestion
65
Q
What are Gastrotransmitters?
A
- Synthesized on demand
- Diffuse out of cells that make them (lipid soluble)
- Travel into target cell to bind to intracellular receptors
- Nitric oxide (NO) - inhibitory or excitatory
- Involved in learning & memory
- Smooth muscle relaxation
- Carbon monoxide (CO) - inhibitory or excitatory
65
Q
What are purines?
A
- Act in both CNS & PNS to produce fast or slow response
- ATP – inhibitory or excitatory
- Released by sensory neurons
- Provokes pain sensation
- Adenosine – inhibitory
- Potent inhibitor in brain
- Caffeine stimulates by blocking brain adenosine receptors
- Also cause vasodilation to increase blood flow to heart & other tissues as needed
66
Q
What are lipids?
A
- Endocannabinoids – inhibitory
- Synthesized on demand from membrane lipids
- Receptors also activate by THC
- Involved in memory as a retrograde messenger to decrease NT release
- Involved in controlling appetite, suppressing nausea & vomitting & neuronal development
67
Q
What are Channel-linked receptors
A
- Ligand-gated ion channels
- Actions is immediate & brief (direct action)
- Excitatory receptors – channels for small cations (Na+ influx contributes most to depolarization)
- Inhibitory receptors – allow Cl- influx or K+ efflux that causes hyperpolarization
- Ex. Ach & AAs
68
Q
What are G Protein-linked recpetors?
A
- Have indirect action
- NT binds to G protein-linked receptor & acts through intracellular 2nd messenger
- Responses are indirect, slow, complex & often prolonged/widespread
- Ex. Biogenic amines, neuropeptides, cannabinoids, & gases
69
Q
What are neuronal pools?
A
- Neuronal pools – functional groups of neurons that:
- Integrate incoming info
- Forward processed info to other destinations
70
Q
What is a Diverging circuit?
A
- 1 input, many outputs
- Amplifying circuit
- Ex. single neuron can activate 100 or more motor neurons in spinal cord, & thousands of muscle fibers
71
Q
What is a converging circuit?
A
- Many inputs, 1 output
- Concentrating circuit
- Common in sensory & motor systems
- Ex. Diff stimuli can elicit same memory
72
Q
What is a reverberating/oscillating circuit?
A
- Chain of neurons containing collateral synapses w/ previous neurons
- Sleep-wake cycles, breathing, repetitive motor patterns
73
Q
What is Parellel after discharge circuit?
A
- Signal stimulates neurons arranged in parallel arrays that eventually converge on single output
- Impulses reach output cell at diff times causes a burst of impulses
- Involved in complex types of mental processing
- Ex. Mathematics
74
Q
What is Serial processing?
A
- Input travels along one pathway to specific destination
- Works in all or none manner to produce specific response
- Ex. Simple spinal reflexes
75
Q
What is Parallel processing?
A
- Input travels along several pathways
- 1 stimulus promotes numerous responses
- Important for higher-level mental functioning
- Ex. Step on sharp object – serial processed to withdraw foot, parallel processing of higher order (rub foot & seek help)
