BIOL 1201 Lecture 2: Chapter 49 Notes
CHAPTER 49 BIOLOGY FINAL NOTES – NERVOUS SYSTEMS
• Brain cell circuits complex; brainbows; powerful imaging techniques;
• Brain activity makes info storage and organization possible
• Nervous systems consist of circuits of neurons and supporting cells
• Hydras, jellies, cnidarians – simplest animals with nervous systems
o Radially symmetrical bodies organized around central digestive
compartment (gastrovascular cavity)
o Interconnect neurons form nerve net – controls the contraction and
expansion of Gast. Cav and lacks clusters of neurons that perform
specialized functions
• Complex animals – axons of multiple nerve cells bundled together→nerves
o Nerves (fibrous structures) channel and organize info flow along
specific routes of NS; Sea star with sensory input and muscle contract
• Animals with elongated, bilaterally symmetrical bodies
o Even more specialized NS
o Exhibit cephalization
▪ Evolutionary trend towards a clustering of sensory neurons
and interneurons at anterior (front) of body
o Non-segmented worms with small brain and longitudinal nerve cords
is simplest clearly defined CNS; planarian
▪ Nematode worm is simple – only 302 neurons
o Segmented worms – more complex invertebrates
▪ Annelids
o Arthropods have many more neurons than simple
▪ Regulated by more complicated brains and ventral nerve cords
with ganglia, also applies to annelids
• NS organization often correlates with lifestyle
o Mollusk example: Clam vs. Squid and Octopus
• Vertebrates – Brain (provides integrative power for complex behaviors) +
Spinal Cord (conveys info to and from brain and generates basic locomotion
patterns) = Central Nervous System
o Nerves + Ganglia = Peripheral Nervous System
o Both systems contain regionalized specialization
• Spinal Cord is closely connected with brain in CNS, but can also act
independently of brain as part of simple nerve circuits that produce reflexes
– body’s automatic responses to stimuli; protects body through rapid
involuntary response
• Nerve Cord
o Invertebrates – ventrally
o Vertebrates – Dorsally
• Cavity of the nerve good on hollow dorsal side during embryonic develop
gives rise to the narrow central canal of the spinal cord as well as ventricles
of brain; cerebrospinal fluid = canal + ventricles; formed in brain by filtration
of arterial blood
• Cerebrospinal fluid circulates slowly through canal and ventricles, then
drains into the veins→this circulation provides brain with nutrients and
hormones to carry away wastes
o Mammals – also cushions brain and sp cord by circulation btw layers
of connective tissue around the CNS
• Brain and Spinal Cord contain:
o Gray matter –neuron cell bodies, dendrites, unmyelinated axons
o White matter – bundled axons w/ myelin sheathswhite appearance
▪ Lies on outside in spinal cord consistent with linking CNS to
sensory and motor neurons of PNS
▪ In brain – on inside, consistent with signaling role between
neurons of brain in learning, feeling emotions, processing
sensory info, and generating commands
• Glia in brain and spinal cord – nourish, support, regulation neuron functions
o Ependymal cells line ventricles; have cilia that promote circulation of
CBS fluid
o Astrocytes – facilitate info transfer at synapses and sometimes release
NTMs; when next to active neurons, cause nearby blood vessels to
dilate, increasing blood flow, enabling neurons to obtain O2 and
glucose more quickly; also regulate extracellular concentrations of
ions and NTMs
o Oligodendrocytes – myelinate axons in CNS→ increases conduction
speed of action potential
o Schwann cells – myelinate axons in PNS
o Microglia – immune cells that protect against pathogens
• Glia – essential role in development of NS – in embryos, radial glia form tracts
along which newly formed neurons migrate from neural tube, the structure
that gives rise to the CNS →later, astrocytes induce cells that line the caps in
CNS to form tight junctions = result of blood-brain barrier, which controls
extracellular environment of the CNS by restricting entry of most substances
from blood
• Radial glia and astrocytes act as stem cells = generating new ones; replace
• PNS transmits info to and from CNS; regulates movement and internal
environment; afferent (carry forward)
• After info processing in CNS, instructions travel to muscles, glands, and
endocrine cells along PNS neurons as efferent (to carry away)
• Most neurons are afferent and efferent except olfactory nerve; only conveys
sensory info from nose to brain
• PNS has two different components:
o Motor System – neurons that carry sigs to skeletal muscles; can be
voluntary or involuntary
o Autonomic Nervous System – regulation of smooth and cardiac
muscles; involuntary; sympathetic and parasympathetic are
antagonistic in organ function regulation, except compliment each
other in regulating reproductive activity
▪ Sympathetic – postganglionic neurons (PNS cell bodies);
activation of sympathetic division is arousal and energy
generation (“fight-or-flight”)
• Dilates pupil
• Inhibits salivary gland secretion
• Relaxes bronchi in lungs
• Accelerates heart
• Inhibits activity of stomach and intestines
• Inhibits activity of pancreas
• Stimulates glucose release by liver; inhibits
gallbladder
• Stimulates adrenal medulla
• Inhibits emptying of bladder
• Promotes ejaculation and vaginal contractions
▪ Parasympathetic – preganglionic neurons (CNS cell bodies);
activation of parasympathetic division generally promotes
calming and a return to self-maintenance (rest and digest)
• Constricts pupil of eye
• Stimulates salivary gland secretion
• Constricts bronchi in lungs
• Slows heart
• Stimulates activity of stomach and intestines
• Stimulates activity of pancreas
• Stimulates gallbladder
• Promotes emptying of bladder
• Promotes erection of genitalia
▪ Enteric – networks of neurons active in digestive tract,
pancreas, gallbladder; normally regulated by sympathetic and
parasympathetic, but capable of independent activity
• Regulates secretion and peristalsis
▪ 3 together control organs of the digestive, cardiovascular
excretory, and endocrine systems
• Homeostasis relies on cooperation btw motor & autonomic nervous systems
o Example: when body temp drops, hypothalamus sigs motor system to
cause shivering (increasing heat prod) and sigs ANS to constrict
surface blood vessels (reducing heat loss)
• The vertebrate brain (most complex organ) is regionally specialized; brain
organization relates to brain function
• Cerebrum – part of brain whose surface lies just beneath skull
o Calculation
o Contemplation
o Memory
• Rapid transitions are regulated by brainstem and cerebrum
