Download Neurons - Jordan High School

Neurons vs. neuroglia
Anatomical Divisions of Nervous System
Central nervous system (CNS)
Spinal cord & brain
Integrate, process, coordinate data
Peripheral nervous system (PNS)
Neural tissue outside CNS
Delivers sensory info, carries motor commands
Nerves vs. cranial nerves vs. spinal nerves
Functional Divisions of PNS
Afferent division
Brings sensory info to CNS from receptors
Efferent division
Carries motor commands from CNS to target organs
(effectors)
Somatic nervous system vs. autonomic nervous
system
Structure of Neurons
Cell body
Perikaryon contains organelles & neurotransmitters
Dendrites vs. axons
Axon: axon hillock  telodendria  synaptic
terminals
Synapse
Presynaptic cell  synaptic cleft  postsynaptic
cell
Presynaptic cell releases neurotransmitters
Classification of Neurons
Anaxonic vs. bipolar vs. unipolar vs. multipolar
neurons
Sensory vs. motor vs. interneurons
Sensory = afferent, motor = efferent
Intero-, extero- & proprioceptors
Interneurons most abundant
Neuroglia of CNS
Ependymal cells
Line passages for cerebrospinal fluid
Astrocytes
Maintain blood-brain barrier
Oligodendrocytes
From myelin sheaths around axon
Microglia
Remove cell debris
Neuroglia of PNS
Satellite cells
Surround cell bodies
Schwann cells
Form sheath around axons
Resting Potential
↑Na+ & Cl- in extracellular fluid (ECF), ↑ K+ in
intracellular fluid (ICF)
Neuron interior negative compared to outside
Electrochemical gradient for K+
ICF conc. ↑, ECF conc. ↓ (chemical gradient)
Electrical gradient opposes K+ movement; small
amounts of K+ move into ECF
Electrochemical gradient for Na+
ICF conc. ↓, ECF conc. ↑
Electrical gradient draws Na+ into cell
Read Table 12-1!!
Na+ & K+ channels
Passive channels always open
Chemically gated channels need specific chemicals
Voltage-gated channels respond to changes in
transmembrane potential
At resting potential, most gated channels closed
Graded Potentials
Na+ enters cell, transmembrane potential
becomes more positive (depolarization)
More open channels = more Na+ = more
depolarization
Repolarization vs. hyperpolarization
Action Potential (Nerve Impulse)
All-or-none principle
Action potential begins between -60 & -55 mV
(threshold)
Stimulus triggers action potential, or not at all if
doesn’t meet threshold
Examine Figure 12-14 (pg 396-397) for steps of
action potential
Saltatory propagation—impulse jumps from
node to node, impulse travels quicker
Larger axon diameter = lower resistance
Type A fibers—largest myelinated, fastest
impulse speed
Type B fibers—smaller myelinated, medium
impulse speed
Type C fibers—smallest & unmyelinated,
slowest impulse speed
Electrical vs. chemical synapses
Most synapses are chemical
Excitatory neurotransmitters vs. inhibitory
neurotransmitters
Cholinergic synapses release ACh
ACh releases into synaptic cleft
ACh causes depolarization of postsynaptic
membrane
Postsynaptic Potentials
Excitatory postsynaptic potential (EPSP)
Depolarization of postsynaptic membrane
Inhibitory postsynaptic potential (IPSP)
Hyperpolarization of postsynaptic membrane
Temporal vs. spatial summation
EPSPs & IPSPs balance polarization