CHAPTER 11 - FUNCTIONAL ORGANIZATION OF NERVOUS TISSUE
I. FUNCTIONS - "CHIMES" (p. 370)
A. CONTROL of muscles & glands
B. HOMEOSTASIS - regulation & coordination
C. INTEGRATION - process input, initiate responses
D. MENTAL ACTIVITY - thinking, memory, emotions, etc.
E. SENSORY INPUT - from all senses
II. DIVISIONS - 1 SYSTEM (Fig. 11.1, p. 370 & Fig.11.3, p. 372)
A. C.N.S. - in dorsal body cavity
1. BRAIN - cranium
2. SPINAL CORD - vertebral canal
B. P.N.S. - everything else!, Cranial & Spinal nerves
1. AFFERENT/SENSORY
a. Flow TOWARDS C.N.S. from P.N.S. P.N.S. è C.N.S.
b. RECEPTORS
2. EFFERENT
a. Flow FROM C.N.S. to P.N.S. C.N.S. è P.N.S.
b. 2 subdivisions
i. SOMATIC MOTOR/VOLUNTARY - to skeletal muscles
ii. AUTONOMIC/INVOLUNTARY - to smooth & cardiac,
& glands
1. SYMPATHETIC - excitatory, speeds up
2. PARASYMPATHETIC - inhib., slows down
III. CELLS OF THE NERVOUS SYSTEM
A. NEURON = FIBER = STRUCTURAL UNIT OF N.S. (Fig. 11.4, p. 373)
- Receive stimuli, transmit action potentials
1. BODY/SOMA
a. Nucleus w/ nucleolus
b. NISSL substance – rough E.R. è protein synthesis
2. DENDRITES - AFFERENT processes, impulses TO body
3. AXONS - EFFERENT processes, impulses AWAY from body
a. HILLOCK - base of axon
b. PRESYNAPTIC TERMINALS or TELODENDRIA - distal terminals
of axon/synapses
B. NEURON CLASSES/TYPES - shapes (Fig. 11.5, p. 374)
1. MULTIPOLAR - more than 1 dendrite, most CNS & motor n.
2. BIPOLAR - 1 dendrite, 1 axon; rods & cones, olfactory neur.
3. PSEUDO-UNIPOLAR - axon only; most other sensory neurons
C. NON-NEURAL CELLS = GLIA = NEUROGLIA = nerve glue
- Non-conductive cells, no A.P.
- SUPPORTIVE: Mechanical, nourishment, phagocytic
- All but #3 derived from ECTODERM
1. ASTROCYTES (p. 375)
a. Many processes
b. BLOOD/BRAIN BARRIER = Astrocytes + endothelium
c. Encircle all vessels in C.N.S.
2. EPENDYMA (p. 375)
a. Lines VENTRICLES & central canal of cord, ciliated
b. CHOROID PLEXUS - C.S.F. secretion
3. MICROGLIA (p. 375)
a. Modified Macrophages-Phagocytose debris/infection
b. From Mesoderm
4. OLIGODENDROCYTES (p. 376)
a. MYELIN SHEATHS around axons in C.N.S. neurons
b. 1 cell may wrap several axons
5. SCHWANN CELLS/NEUROLEMMOCYTES (p. 376)
a. MYELIN SHEATHS around axons in P.N.S. neurons
b. Only wraps 1 axon
c. Concentric layers 40-100/axon
d. Gaps = NODES OF RANVIER
e. SATELLITE CELLS - surround neuron bodies
D. AXON SHEATHS (Fig. 11.11, p. 376)
1. MYELINATED (Fig. 11.22, p. 389)
a. SALTATORY CONDUCTION - A.P. “leaps” from node-node
b. Fastest conduction
c. Type A - large diameter, myelinated.
SENSORY & MOTOR neurons
d. Type B & C - medium/small, lightly myelinated/unmyelinated
AUTONOMIC N.S.
2. UNMYELINATED (Fig. 11.21, p. 388)
a. P.N.S - Invagination in Schwann cell
b. C.N.S. - Invagination in Oligodendrocyte
c. A.P. propagated along membrane
d. AUTONOMIC N.S.
IV. ORGANIZATION OF NERVOUS TISSUE
A. WHITE MATTER
1. MYELINATED axons
2. RAPID A.P. CONDUCTION
3. C.N.S. - NERVE TRACTS
4. P.N.S. – NERVES
B. GRAY MATTER
1. UNMYELINATED neuron cell bodies & dendrites
2. SYNAPSES & INTEGRATION
3. C.N.S. - NUCLEI = group of neuron bodies
a. CEREBRUM - cortex
b. CEREBELLUM
4. P.N.S. – GANGLIA
V. ELECTRICAL SIGNALS
A. SPECIALIZED/EXCITABLE TISSUES
1. MUSCLE & NERVOUS
2. RESPOND TO STIMULUS - CHEMICAL & ELECTRICAL
a. DETECTABLE CHANGE IN ENVT.
b. DEPENDS ON CELL & RECEPTORS
3. POLARIZED MEMBRANES
a. SEPARATION OF (+) & (-) charges across MEMBRANE
b. LOCALIZED @ SURFACE in & out of cells
c. DEPENDS ON [ION] differences across membrane
d. CHANGES IN [ION] differences è ELECTRICAL SIGNALS
e. ACTION POTENTIALS = electrical signals being passed
B. CONCENTRATION DIFFERENCES (Tab 11.1, p. 378)
1. EXTRACELLULAR - HI [Na+], HI [Cl-]
2. INTRACELLULAR - HI [K+], HI [P- = anionic proteins-]
a. ANIONIC PROTEINS syn. in cell, can’t get out of cell
-ATTRACT K+ , REPELS Cl-
3. INTRA & EXTRACELL FLUIDS ELEC. NEUTRAL
4. [ ] DIFF. DUE TO 2 MAJOR FACTORS:
a. Na+/K+ EXCHANGE PUMP (Fig. 3.21, p. 73)
i. Pumps 3 Na+ out, against [ ] gradient
ii. Pumps 2 K+ in, against [ ] gradient
b. PERMEABILITY CHARACTER. OF MEMB. (Fig. 11.12 p. 379)
i. Non-gated ion, “LEAK” channels – K+, always open
ii. Gated ion channels
1. LIGAND-SENSITIVE - respond to CHEMICAL
ex. [Ca2+] - Hi EXTRACELL. [Ca2+] closes Na+ gates
- Lo EXTRACELL. [Ca2+] opens Na+ gates
2. VOLTAGE-SENSITIVE - respond to A.P.
C. RESTING MEMBRANE POTENTIAL - RMP. (Fig. 11.13, p. 379)
1. MEASURE OF CHARGE DIFF. ACROSS MEMBRANE @ REST
RMP = neg. charge inside cell @ equilibrium
a. VOLTMETER/OSCILLOSCOPE
b. INSIDE is -85 mV (-70 è -90mV range)
c. SEPARATION OF CHARGES è POTENTIAL ENERGY (BATTERY)
2. ESTABLISHING RMP (Fig. 11.14, p. 380)
a. 100X greater diffusion of K+ out results in LOCALIZED
HI [K+] or (+) “coating” OUTSIDE p.m. surface
b. ANIONIC PROTEINS can’t diffuse out, remain inside &
results in LOCALIZED (-) “lining” INSIDE p.m.
c. RMP = equilibrium when no further K+ diffuse out due to
attraction to anionic proteins lining inside membrane
3. Tab. 11.2, p. 381
4. CHANGING RMP (Fig. 11.15, p. 381)
a. é Extracellular K+ è DEPOLARIZATION
b. ê Extracellular K+ è HYPERPOLARIZATION
D. ELECTRICALLY EXCITABLE CELLS
1. LOCAL POTENTIAL (Fig 11.16, p. 383 & Tab. 11.3 p. 383)
a. LOCAL DEPOLARIZATION - é permeability to Na+
b. DUE TO SUBTHRESHOLD STIMULUS
c. SMALL DEPOLARIZATION as Na+ rushes/floods in
d. GRADED - STRONGEST EFFECT @ POINT OF STIMULATION
- SMALL STIM. è SMALL DEPOLARIZATION
- GREATER STIM. è GREATER DEPOLARIZATION
- DIMINISHES FURTHER AWAY FROM PT. OF STIM.
e. NON-PROPAGATED - local, not passed on
f. HYPERPOLARIZATION è éperm. to K+ or Cl- (more negative)
2. ACTION POTENTIAL - transmission of stim. via wave of depol/repol.
a. THRESHOLD - local potentials reach this point
- ALL OR NONE reaction
- PULLING TRIGGER ON A GUN
b. PROCESS (Tab. 11.4, p. 384; Fig. 11.17, p. 383, STEPS - p. 385)
- STIMULUS è THRESHOLD
- Na+ gates open è Na+ floods in è DEPOLARIZATION
- Na+ gates close; K+ gates open è K+ floods out è
REPOLARIZATION back to normal RMP
-. PROPAGATED = PASSED p. 388 & 389)
c. OVER 1,000 A.P./SECOND !
d. A.P. TAKES ONLY 1-2 MILLISECONDS
e. REFRACTORY PERIOD - membrane won’t react to another stim (386)
i. ABSOLUTE - COMPLETELY INSENSITIVE to stim.
ii. RELATIVE - near end of repolarization
- If stim. é than threshold è another A.P.
E. ACTION POTENTIAL FREQUENCY = # of A.P. per unit of time (Fig. 11.20, p. 387)
1. SUBTHRESHOLD – local, no A.P.
2. THRESHOLD – A.P.
3. MAXIMAL – greater/stronger stimulusè é frequency of A.P./unit time
a. SUBMAXIMAL – between threshold & maximal
b. SUPRAMAXIMAL – greater than maximal
4. ACCOMMODATION
a. Decreased frequency of A.P. even w/ constant stimulus
b. Clothing on skin, certain sounds & smells
VI. SYNAPSE
- PLACE WHERE 2 EXCITABLE CELLS MEET
- A. P. PASSED FROM 1 CELL TO ANOTHER
A. ELECTRICAL (Fig. 11.23, p. 392)
1. DIRECT
2. GAP JUNCTION – 2 cells fused together
3. DUE TO IONS – Na+/K+
B. CHEMICAL (Fig. 11.24, p. 393)
1. INDIRECT
2. CLEFT
3. NEUROTRANSMITTERS (see Tab. 11.5, p. 395-398)
4. PRESYNAPTIC CELL = NEURON
5. POSTSYNAPTIC CELL = NEURON, MUSCLE or GLAND
C. AXOAXONIC = EPSP & IPSP (Fig. 11.26, p. 399)
1. EXCITATORY POST-SYNAPTIC POTENTIAL
a. é permeability to Na+ in
b. Local depolarization è A.P. passed
2. INHIBITORY POST-SYNAPTIC POTENTIAL
a. é permeability to Cl- in or K+ out
b. Hyperpolarization è No A.P. passed
3. PRESYNAPTIC REGULATION (Fig. 11.27, p. 399) In C.N.S.
a. INHIBITION - ê neurotransmitter
b. FACILITATION - é neurotransmitter
D. INTEGRATION (Fig. 11.28, p. 400)
1. SUMMATION - many local potentials èthreshold èA.P.
a. SPATIAL - A.P. from 2 presynaptic axons to 1 postsyn.
b. TEMPORAL - many stimuli from 1 presynaptic axon
c. COMBINED - overall effect of all presynaptic axons
VII. NEURONAL PATHWAYS & CIRCUITS
A. SIMPLE èCOMPLEX
1. TRILLIONS of cells in N.S.
2. Up to 1,000 connections w/other neurons/cells
B. 3 TYPES
1. CONVERGENT - many axons è1 synapse (Fig. 11.29a, p. 402)
a. Spatial summation
2. DIVERGENT - 1 axon è many neurons (Fig. 11.29b, p. 402)
3. OSCILLATORY/REVERBERATING (Fig. 11.29c, p. 402)
a. Sets up a continuous, rhythmic stimulation
b. After discharge - prolongs response to a stimulus
c. Continues until “stop” or fatigue
d. Respiration, wake/sleep cycle