1. Anatomy and Physiology I
Chapter 12
Nervous Tissue

2. 2 Divisions Central Nervous System (CNS)
Brain and spinal cord
Peripheral Nervous System (PNS)
Everything else
Composed of nerves and ganglia
Nerves- carry signals to and from CNS
Ganglia- swelling in nerve

3. PNS Sensory Division (afferent) Signals from receptors to CNS
Informs CNS of stimuli
Somatic sensory- signals
from skin, muscle, bones, joints
Visceral sensory- signals from viscera

4. PNS Motor Division (efferent) Signals from CNS to glands or muscles
Effectors
Somatic motor- signals to skeletal muscles
voluntary cx and reflexes
Autonomic (visceral) motor- signals to glands, cardiac and smooth muscle
Involuntary actions
2 divisions

5. PNS Autonomic Motor Division Sympathetic Parasympathetic
Arouse body for action
Parasympathetic
Calming effect

6. Nervous System Electrical and chemical 3 steps Sensory CNS processes
Receives info about environment
Transmits to CNS
CNS processes
Determine response
Commands issued
Muscles, glands

7. Properties of Neurons Excitability Conductivity Secretion
Respond to stimuli
Conductivity
Produce electrical signals
Secretion
Neurotransmitter

8. Neuron Classes Sensory (afferent) Neurons Interneurons
Detect stimuli
Transmits info to CNS
Interneurons
Entirely within CNS
Receive signals, integrate signals, determine reaction
90%
Motor (efferent) Neurons
Signals to muscles or glands
Carry out response to stimuli (effectors)

10. Neuron Structure Soma- control center (cell body)
Central nucleus
Nissl bodies
Dendrites- receive signals from other neurons
Axon hillock- axon originates (mound)
Axon- rapid conduction of nerve signals
Away from soma
Nodes of Ranvier in myelinated fibers
neurilemma
Synaptic knob- swelling that forms a junction
At end of axon
Synaptic vesicles- neurotransmitters

12. Neuroglia Supportive cells Protect and help function
6 types of neuroglia
Oligodendrocytes
Ependymal cells
Microglia
Astrocytes
Schwann cells
Satellite cells

13. Oligodendrocytes Form myelin in CNS Arm-like processes
Spirals around nerve fiber
Myelin sheath- insulates nerve fiber

14. Ependymal Cells
Lines cavities of CNS
Produce and circulates CSF
Cilia

15. Microglia Phagocytize and destroy Wander through CNS
Multiple times a day
Concentrated in areas of infection, trauma, stroke

16. Astrocytes Most abundant- 90% Found everywhere in CNS
Supportive framework
Blood-brain-barrier
Nourish neurons
Promote neuron growth
Communicate with neurons
Absorb excess neurotransmitters
Form scar tissue

17. Schwann Cells Only PNS Envelop nerve fibers Myelin sheath
Regeneration of damaged fibers

18. Satellite Cells Only PNS Surround somas Electrical insulation
Regulate chemical environment

19. Myelin Myelin sheath- insulating layer around nerve fiber
Oligodendrocytes- CNS
Schwann cells- PNS
Myelination- production
Dietary fat important
Myelin sheath is segmented
Nodes of Ranvier- gaps in myelin sheath
Speeds signal conduction

20. Conduction Speed of conduction Fiber diameter
Presence or absence of myelin
Large fibers- fast
More surface area
Myelin- fast (skeletal muscles, sensory signals)
Unmyelinated- slow (secrete stomach acid, pupil dilation)

21. Nerve Fiber Regeneration
PNS- soma must be intact
1. normal nerve fiber
2. local trauma
Fiber distal to injury can’t survive
Macrophages clean up
3. Soma swells
Axon sprouts growth processes

22. Nerve Fiber Regeneration
4. Schwann cells form regeneration tube
5. Regeneration tube guides growing sprout to target cell
6. Reestablishes synapse
Soma shrinks
Not perfect
Functional deficit post-injury

23. Electrical Potentials
Difference in the concentration of charged particles b/t one point and another
Produce current- flow of charged particles
RMP- charged difference across PM
Unstimulated neuron

24. RMP Electrolytes distributed unequally b/t ICF and ECF 3 factors
Concentration gradient
Selective permeability
Electrical attraction
NaK Pump- 70% of energy requirement
Pumps 3 Na out for every 2 K it brings in
equilibrium

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26. Action Potentials Rapid up and down shift in membrane voltage
Resting neuron- polarized
1. Sodium enters cell
Depolarization of the membrane
2. Must meet the threshold
Minimum needed to open gates
3. Neuron produces action potential
Further depolarizes membrane

27. Action Potentials 4. Voltage peaks
Positive inside
Negative outside
5. Potassium leaves cell and repolarization occurs
6. Potassium gates stay open longer
Membrane potential drops slightly more negative than original RMP- hyperpolarization

28. Action Potential

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30. Action Potential All-or-None Law Nondecremental Irreversible
If threshold reached- neuron fires at max voltage
If threshold not reached- neuron doesn’t fire
Stronger stimulus does not produce stronger action potentials
Nondecremental
Do not get weaker with distance
Irreversible
Threshold reached- action potential completes
Can’t be stopped

31. Refractory Period Period of resistance to restimulation Absolute
Impossible or difficult to stimulate same region
Absolute
No stimulus will trigger new action potential
Lasts from start of AP until membrane returns to resting potential
Relative
Unusually strong stimulus will trigger potential
Lasts until hyperpolarization ends

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33. Signal Conduction Unmyelinated fibers
Voltage-regulated gates along entire length
Action potentials triggers new action potential distally
Continues until reaches axon end
Stimulates next one
Can’t go backwards
Slower
Nondecremental

34. Signal Conduction Myelinated fibers Saltatory Conduction-
Voltage-regulated gates are
scarce
Conduction is decremental
Recharges at nodes of Ranvier
Creates new
action potential
Saltatory Conduction-
propagation of nerve signal
that jumps from node to node
Fast

35. Synapses Presynaptic neuron- releases neurotransmitter
Postsynaptic neuron- responds to neurotransmitter
Synaptic cleft- gap b/t neurons

36. Neurotransmitters 1. Synthesized by presynaptic neuron
2. Released in response to stimulation
3. Bind to specific receptors on postsynaptic cell
4. Alter physiology of that cell
Excitatory/ Inhibitory

37. Excitatory Cholinergic Synapse
Acetylcholine (ACh)
1. nerve signal arrives at synaptic knob
Opens Ca gates
2. Ca enter knob- triggers vesicles
Ach released
3. Ach diffuses across synaptic cleft
Bind to gates on postsynaptic neuron
Gates open: Na enter, K leave
4. Na enters cell, depolarizes it, triggers postsynaptic potential

39. Cessation of Signal Turn off stimulus
Prevents postsynaptic cell from firing indefinitely
1. Stop new neurotransmitters
Cessation of signal
2. Get rid of old
Diffusion- astrocytes absorb
Reuptake- synaptic knob reabsorbs, breaks down
Degradation in synaptic cleft- AChE breaks down ACh

40. Neural Integration
Ability of neurons to process information, store and recall it, and make decisions
Based on postsynaptic potentials
Excitatory postsynaptic potential (EPSP)- voltage change that makes neuron more likely to fire
Inhibitory postsynaptic potential (IPSP)- makes neuron less likely to fire
Summation- process of adding up postsynaptic potentials and responding to their net effect

41. Postsynaptic Potentials
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–20 mV
–40
Threshold
–60
EPSP
Resting membrane
potential
Repolarization
–80
Depolarization
(a)
Stimulus
Time
–20 mV
–40
Threshold
–60
Resting membrane
potential
IPSP
Figure 12.24
–80
Hyperpolarization
(b)
Stimulus
Time

42. Summation Temporal summation Spatial summation
ESPSs generated so quickly that a new one is generated before the old one fades
Spatial summation
EPSPs from several synapses add up to threshold

43. Summation of EPSPs +40 +20 Action potential mV –20 –40 Threshold –60
Action potential mV
–20
–40
Threshold
–60
EPSPs
Resting
membrane
potential
–80
Stimuli
Time

44. Memory Physical basis of memory 3 kinds
Memory trace- pathway through the brain
Synapses formed to make transmission easier
Added, taken away, modified
3 kinds
Immediate memory
Short-term memory
Long- term memory

45. Immediate Memory
Few seconds
Flow of events and sense of present
Read

46. Short-term Memory Few seconds to few hours
Quickly forgotten if stop mentally reciting it, distracted, or new

47. Long-term Memory Lifetime
Declarative memory- retention of events and facts
Procedural memory- retention of motor skills