Download Chapter 3 Notes (part 1) 1. Basic Elements of the Nervous System (a

Chapter 3 Notes (part 1)
1. Basic Elements of the Nervous System
(a) The Neuron
i. Functional Cells of the Nervous System
A. exchange of information via electrochemical transmission
B. electrical signals travel from axon hillock to axon terminal
C. secretion of chemical neurotransmitters either excites or inhibits other neurons
ii. Key Parts
A. Cell Body/Soma
 includes the nucleus, organelles, and other structures in the cytoplasm (interior
of the cell)
B. Cell Membrane/Cytoplasmic Membrane
 selectively-permeable membrane which separates the cytoplasm from the
extracellular matrix
 contains ion channels and protein pumps which manage the flow of ions
(charged particles) into and out of the cell
C. Axon
 The part of the cell which carries the electrical signal (action potential); in some
cases, the axon is wrapped in fatty glial cells collectively called myelin
 begins at axon hillock and ends at axon terminal, where there are vesicles
containing neurotransmitters
D. Dendrites
 location of the receptor sites; neurons may have hundreds or even thousands of
dendrites, but relatively few axons
E. Synapse
 the gap between the pre-synaptic neuron and the post-synaptic neuron where the
axon terminal nearly meets the receptor sites, separated by a gap called the
synaptic cleft
iii. Types of Neurons
A. Motor (efferent) neurons
 Carry motor signals from the brain to the body
B. Sensory (afferent) neurons
 Carry sensory information from sensory receptors in the body to the brain
C. Inter-neurons
 Carry information within the neural network; for example, the corpus callosum
(b) Glial Cells
i. Supportive cells of the nervous system
ii. augment the function of neurons as myelin (speeding up transmission)
iii. areas of greater glial cell density appear as “white” matter
(c) Action Potentials (electrical)
i. Caused by changes in the relative voltage difference between the cytoplasm and the
extracellular matrix
ii. Polarization
A. In the resting state (the Resting Potential) the cytoplasm is negatively charged due to
high levels of NEGATIVELY charged Chloride ions (Cl-) and relatively low levels
of positively charged sodium (Na+) and potassium (K+). The relative charge is 70mv.
B. DIFFUSION of Na+ from the more densely populated extracellular matrix is
balanced by protein pumps removing positively charged ions from the cytoplasm. If
nothing else happens, the cell will maintain its negative charge
C. BINDING of excitatory neurotransmitters to the receptor sites will cause some Na+
channels to open, beginning the process of depolarization
iii. Depolarization
A. Increasing bindings raise the relative charge from -70mv to -55mv
B. at -55mv (the stimulus threshold) Na+ channels all open, causing a rapid increase in
the positivity of the cytoplasm.
C. The charge rises to +35 or +40mv, at which point this “extra” charge propagates
down the axon toward the axon terminal (this is the action potential)
D. The “all or nothing” principle states that neurons are either active or inactive.
EITHER the charge reaches the stimulus threshold, causing an action potential, or it
fails to reach that level, in which case the cell repolarizes without firing.
iv. Repolarization
A. When the “wave” of the action potential passes a point on the axon, the Na+
channels close, and K+ ions are pumped out of the cell, causing the cell to repolarize
B. For a brief “refractory” period, the cell is unable to fire.
(d) Synaptic Transmission (chemical)
i. neurotransmitters
A. chemical compounds which are either excitatory (opening Na+ channels) or
inhibitory (closing Na+ channels)
B. released from terminal vesicles when stimulated by an action potential
ii. other important parts of the synapse
A. receptor sites
 chemically matched to specific neurotransmitters
B. autoreceptors
 receptor sites on the pre-synaptic neuron which track how much neurotransmitter
is in the synapse and initiate reuptake
C. transporters
 responsible for “corralling” neurotransmitters from one location to the next
iii. Factors that influence Neurotransmitter Action
A. Agonists
 substances that increase the effectiveness of neurotransmitters
B. Antagonists
 substances which decrease the effectiveness of neurotransmitters
C. Reuptake
 re-absorption of neurotransmitters initiated by autoreceptors
D. Enzyme Deactivation
 metabolic deactivation of neurotransmitters by substances such as monoamine
oxidase or acetylcholinesterase.
2. The Structure of the Nervous System
(a) Nervous System Organization
i. Central Nervous System
A. The “executive” responsible for decision making
 Brain
 Spinal Cord
ii. Peripheral Nervous System
A. All nerves radiating out from the brain or spinal cord
B. Somatic Nervous System – voluntary, conscious
 Sensory nerves
 Motor nerves
C. Autonomic Nervous System
 sympathetic division
 responsible for activation of the body as part of “fight or flight” response
 parasympathetic division
 responsible for non-fight/flight functions such as peristalsis and release of
digestive enzymes
(b) Brain Anatomy and Localization of Function
i. Neuroplasticity and Neurogenesis
A. neurogenesis – the growth of new neurons and neural connections
 primarily occurs in utero, but some continues until the late 20s or early 30s
 “maturation” refers to the cessation of neurogenesis (for the most part)
B. Neuroplasticity – the brain’s ability to adjust, recover, and heal after an injury
 tied with neurogenesis; the “younger” that part of the brain is, the more easily it
can restore function
ii. Hindbrain
A. matures first, therefore it has the least plasticity
B. responsible for critical organ functions and involuntary motor functions
C. Medulla
 responsible for autonomic responses, peristalsis, respiration, regulation of
consciousness
 ascending reticular activating system/reticular formation – consciousness
 area postrema – vomit reflex
D. Cerebellum
 muscle memory, implicit learning, balance and coordination
E. Pons
 contra-lateral organization
iii. Midbrain
A. Tectum
 sensory orienting reflexes
B. Tegmentum
 motor impulse generation
iv. Forebrain
A. Cortex
 divided into two hemispheres, joined together by corpus callossum
 each hemisphere divided into four lobes
 occipital – contains primary visual cortex and visual association areas
 temporal – contains primary auditory cortex; left side responsible for naming
objects and verbal auditory processing
 parietal – somatosensory corext; sensory processing
 frontal – primary motor cortex, pre-frontal cortex (decision making,
inhibition, behavioral and emotional regulation)
 last portion of the brain to mature
B. Sub-Cortices
 Limbic System
 hippocampus (memory)
 amygdala (emotional impulses)
 basal ganglia (motor impulses)
 Thalamus – sensory relay center
 Hypothalamus – “thermostat” responsible for regulating hormone release by
glands
 Pituitary gland – releases HGH and other hormones
 Pineal gland – releases Serotonin and Melatonin as part of sleep/wake cycling