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
2 Main types of ion channels
* Leakage (nongated) channels - always open
* Gated channels - in which part of the protein changes shape to open/close channel
26
What are the 3 types of Gated channels
* chemically gated, voltage-gated, mechanically gated
27
What Factors influence Resting Membrane Potential
* 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
What generates the Resting Membrane Potential?
* Na/K pumps more cations out
* [ ] gradient of K
* higher permeability of K
* membrane impermeable to anionic proteins
* **chemical gradient + electrical gradient**
29
Membrane potential changes when...
* [ ] s of ions across membrane change
* Membrane permeability to ions changes
30
What are the 2 types of signals produced by changes in membrane potential?
* Graded potentials
- Incoming signals operating over short distances
* Action potentials
- Long-distance signals of axons
31
What is Depolarization?
* Reduction in membrane potential
* Going more +ve
* Inside of membrane becomes less negative than resting potential
* Increase probability of producing a nerve impulse
32
What is Hyperpolarization?
* Increase in membrane potential
* Going more –ve
* Inside of membrane becomes more negative than resting potential
* Decrease probability of producing a nerve impulse
33
What are graded potentials?
* 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
What are the types of graded potentials?
| according to location & function
* 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
What are Action Potentials?
* 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
Describe Voltage gated Na+ channels
* 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
Describe Voltage gated K+ channels
* have 1 gate & 2 states
* Closed at rest
* Opens slowly w/ depol
38
What is the absolute refractory period?
* 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
What is the Relative refractory period?
* 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
Explain Threshold & all-or-none response
* 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
Describe the Propagation of an AP
* 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
How does stimulus intensity affect APs?
* All APs are alike & are independent of stimulus intensity
* Strong stimuli - can generate APs more often than weaker stimuli
43
What increase Conduction Velocity of neurons?
* larger diameter fibers - less resistance to current flow, faster impulse conduction
* myelination - insulate & prevent leakage of charge
44
What is Saltatory Conduction?
* Voltage-gates Na+ channels located at nodes of Ranvier
* APs jump rapidly from node to node (30X faster than non-myelinated)
45
What are the 3 nerve fiber classifications?
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
What is Multiple Sclerosis?
* 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
What is a synapse?
* 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
What are Chemical synapses?
* 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
What is synaptic delay?
* 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
What are Electrical Synapses?
* 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
Postsynaptic potential strengths are determined by?
* amount of NT released
* Time NT is in area
52
2 types of postsynaptic potentials
* EPSP – excitatory postsynaptic potential
* IPSP – inhibitory postsynaptic potentials
53
Excitatory synapses & EPSP
* 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
Inhibitory synapses & IPSPs
* NT opens chemical gated channels for either K+ or Cl-
* Causes hyperpolarization
* Reduces postsynaptic neuron's ability to produce an AP
55
What is synaptic potentiation?
* Repeated use increases efficiency of neurotransmission (long-term potentiation)
* Ca2+ concentration increases in presynaptic terminal & postsynaptic neuron
56
What is Presynaptic inhibition?
* 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
What are the NT classes?
* Acetylcholine
* Biogenic Amines (aka monoamines)
* Amino acids
* Peptides (neuropeptides)
* Purines
* Gases & liquids
58
What is Acetylcholine?
* 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
What are Biogenic Amines?
* 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
Dopamine
* inhibitory or excitator
* Released by substantia nigra & hypothalamus
* Important for motor pathways, motivation, reward & reinforcement
* Tyrosine precursor
60
NE & Epinephrine
* 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
Serotonin
* mainly inhibitory
* Brain & spinal cord
* Role in sleep, appetite, nausea, migraine headaches, mood & digestion
* Tryptophan precursor
62
Histamine
* Hypothalamus
* Involved in wakefulness, appetite control, learning & memory, gastric secretions, in CT mediates inflammation & vasodilation
* Histidine precursor
63
What are Amino acids?
* 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
What are Neuropeptides?
* 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
What are Gastrotransmitters?
* 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
What are purines?
* 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
What are lipids?
* 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
What are Channel-linked receptors
* 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
What are G Protein-linked recpetors?
* 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
What are neuronal pools?
* Neuronal pools – functional groups of neurons that:
* Integrate incoming info
* Forward processed info to other destinations
70
What is a Diverging circuit?
* 1 input, many outputs
* Amplifying circuit
* Ex. single neuron can activate 100 or more motor neurons in spinal cord, & thousands of muscle fibers
71
What is a converging circuit?
* Many inputs, 1 output
* Concentrating circuit
* Common in sensory & motor systems
* Ex. Diff stimuli can elicit same memory
72
What is a reverberating/oscillating circuit?
* Chain of neurons containing collateral synapses w/ previous neurons
* Sleep-wake cycles, breathing, repetitive motor patterns
73
What is Parellel after discharge circuit?
* 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
What is Serial processing?
* Input travels along one pathway to specific destination
* Works in all or none manner to produce specific response
* Ex. Simple spinal reflexes
75
What is Parallel processing?
* 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)
