THE NERVOUS SYSTEM
AP BIOLOGY
MS. VITALE
THREE OVERLAPPING FUNCTIONS OF THE NERVOUS SYSTEM:
1. Sensory input- sensory receptors collect information about external and internal
environments
a. Information is sent to integration centers
2. Integration- input is interpreted and associated with appropriate response
a. Carried out in CNS = central nervous system- brain and spinal cord
3. Motor output- conduction of signals from integration centers  CNS  effector cellscarry out response (muscles or glands)
Signals are conducted by NERVES- ropelike bundles of extensions of neurons tightly wrapped in
connective tissue
PNS = peripheral nervous system- the nerves that communicate between CNS and rest of body
Neuron structure and synapses:
Neuron = nerve cell
-structural and functional unit of the nervous system
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Cell body- nucleus and other organelles
Dendrites- short, highly branched processes
o Receive information from other cells
Axons- longer
o Send messages out
Axon hillock- where axon joins cell body
Myelin sheath- insulating layer on axon
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Synaptic terminals- end of axon
o Release neurotransmitters (chemical messages)
Synapse- site where synaptic terminal contacts target cell (neuron or effector)
Presynaptic cell- transmitting cell
Postsynaptic cell- target cell
Reflex- simplest type of nerve circuit
Sensory neurons- receive information from receptor
-information is passed to a motor neuron- which signals effector cell
Interneurons- communicate with other neurons
Ganglion- cluster of nerves in PNS
Glia- supporting cells between neurons
Schwann cells- glia that form myelin sheath
Nodes of Ranvier- space between Schwann cells
 Only place on axon where signals can be transmitted
 Signals jump from node to nod, making it move faster then just traveling straight down
MS = Multiple Sclerosis- immune system destroys myelin sheath
 Loss of signal conduction, muscle control and brain function
Membrane potential- the different concentrations of ions inside and outside a cell
 Causes electrical charge difference
 Anions are more concentrated inside cell
 Cations are more concentrated outside cell
Resting potential- the membrane potential of a neuron in resting state
 Not transmitting electrical signal
 Unstimulated
 The membrane of the neuron keeps large molecule (proteins) with a (-) charge in the cell
 The membrane also uses protein pumps to pass ions through
 While resting, K+ ions are not moved out, Na+ are moved out using sodium potassium
pumps and other protein channels
 This creates a (-) charge inside the cell and a (+) charge outside the cell
stimulus- causes a nerve signal to be generated
action potential- a nerve signal
 Changes in the membrane potential can result in an electrical impulse
 Neurons have gated ion channels- that open and close in response to a stimulus
 The ion concentration changes therefore the membrane potential changes
 Different types of ion channels respond to chemicals (neurotransmitters) or voltage
(change in membrane potential)
threshold potential- the minimum change in a membrane’s voltage that must occur to
generate a nerve signal (action potential)
 Once the threshold potential is reached, a nerve signal is triggered
 Quckly, the inside of the cell becomes more (+) the the outside
 The membrane quickly repolarizes as the voltage drops back down, it goes
below resting potential and then returns to resting potential
 The quick change of the membrane potential is caused by quick movements of
ions
 The action potential only occurs at one point on the neuron’s membrane- on the
axon near the cell body
Synapse- junction between 2 neurons or between a neuron and an effector cell
Electrical synapses- action potentials directly from first to second cell
 Common in areas where steady contraction occur (ex: heart, GI tract)
 Gap junctions between first and second cell are channels that allow ions to flow from cell
to cell
Chemical synapses- synaptic cleft separates first and second cell, ions can’t be transmitted (ex:
skeletal muscles)
 The cytoplasm at tip of first cell contains sacs called synaptic vesicles- contains
thousands of molecules of neurotransmitters
 The action potential of the first cell cause synaptic vesicles to fuse with the plasma
membrane, releasing their neurotransmitters into synaptic cleft (exocytosis)
 The neurotransmitters bind to receptor molecules on second cell
 Ion channels open, ions diffuse into second cell, creating a new action potential
 Enzymes break down the neurotransmitters, closing the ion channels
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Caffeine reverses inhibiting neurotransmitters
Nicotine activates acetylcholine receptors
Alcohol increases inhibitors
TYPES OF NERVOUS SYSTEMS:
Nerve net- simplest nervous system
 Web of neurons
 No brain
 Ex: hydra
Cephalization- concentration of nervous system in head
Centralization- presence of CNS and PNS
Vertebrates are highly cephalized and centralized
Spinal cord- receives information from PNS
Brain- master control center
Blood vessels in brain have a blood-brain barrier- very
what goes in brain tissue
Ventricles-space in center of brain
 Filled with fluid
 Drain into central canal of spinal cord
selective as to
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Capillaries secrete cerebrospinal fluid which cushions CNS, supplies nutrients, hormone,
and WBCs
Meninges- connective tissue layers surround and protect brain and spinal cord
 Cerebrospinal fluid between 2 layers creates cushion
White matter- outer part of spinal cord
 Mainly axons
 White due to myelin
Gray matter- inside spinal cord
 Cell bodies and dendrites
Crainal nerves- to and from brain
Spinal nerves- to and from spinal cord
Both are part of Peripheral Nervous System
PERIPHERAL NERVOUS SYSTEM
 Sensory (afferent) division- incoming nerves
o From sensory receptors of external and
internal environment
 Motor (efferent) division- outgoing nerves
CNS and effector cells
o Somatic nervous system
 Carries signals to skeletal
muscles in response to external stimuli
 Voluntary, conscious control
o Autonomic nervous system
 Carries signals that regulate internal environment
 Muscles of cardiac, digestive, excretory, and endocrine systems
 Sympathetic division- arousal and energy generation
 Occurring during fight or flight and strenuous exercise
 Increase heart rate and respiration
 Liver converts glycogen to glucose
 Adrenaline is released
 Digestion slows
 Parasympathetic division- calming, maintenance, resting
 Decrease heart rate
 Increase in digestion
 Energy is stored
from
Three hollow bulges at anterior end of neural tube in embryo form the brain
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Forebrain- cerebrum is outgrowth of forebrain
o Cerebrum evolved in complex vertebrates
o Cerebrum is largest in virds and mammale
Midbrain
Hindbrain
Brainstem- anterior of spinal cord
 Medulla oblongata
o Contains centers that control visceral functions (breathing, heart rate, swallowing,
digestion)
 Pons
o Also controls visceral activities
 Midbrain
o Auditory data
o Visual reflexes
o Sends sensory data to higher brain centers
Sleep and arousal are controlled by several centers in the brainstem and cerebrum
EEG- electroencephalogram
- measures brain waves (electrical activity of brain)
Cerebellum- coordination and error checking during motor,
cognitive performances
- learning and remembering
- eye-hand coordination
Thalamus- main input center for sensory information going to cerebrum
and main output center for information leaving cerebrum
- sorts incoming information and sends to appropriate higher
centers
- receives information that regulates emotion and arousal
perceptual, and
brain
Hypothalamus- regulates homeostasis
- makes 2 hormones
o posterior pituitary and releasing hormones
o contains thermostat
o regulates hunger, thirst, basic survival mechanisms
o sex and mating behavior
o flight or fight
o pleasure
Rhythmic behavior (daily rhythms)
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When we eat, sleep, peak
Circadian rhythm
 24 hour cycle
 persists even in absence of external
clues
 strong internal component called
biological clock
o SCN = suprachiasmatic nuclei
 In mammals biological
clock in hypothalamus
 Pair of structures whose
cells produce proteins in
response to dark and
light
Cerebrum-most highly evolved structure of mammalian brain
- Divided into right and left hemispheres
- Each hemisphere has an outer covering
gray matter called the cerebral cortexo gray matter
o largest and most complex part of
brain
o has evolved the most
- Each hemisphere also has white matter
basal nucleio A cluster of nuclei deep within white
matter
o Important for movement
o Damage can cause Parkinson’s or
Huntington’s disease
- Neocortex-
of
the
and
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o
o
o
o
Additional outer layer of cortex
Only in mammals
Associated with greater cognitive abilities and more sophisticated behavior
 Relative to size and presence of convolutions which increase surface
area
Human neocortex = .5m 2 surface area = 80% total brain mass
 Porpoise is 2nd largest
 Left cerebral cortex is responsible for right side of body and visa-versa
Corpus callosum- thick band of fibers communicates between right and left sides
Cerebral cortex has 4 lobes:
Motor cortex- sends commands to skeletal muscles
Somatosensory cortex- touch, pain, pressure, temperature
Language and speech- Broca’ s areas for speaking, in frontal lobe of motor cortex
- Wernicke’s area for speech comprehension, in posterior of temporal lobe
Limbic system- ring around brainstem
- Sections of thalamus and hypothalamus with
hippocampus and olfactory cortex
- Central to behavior
o Ex: nurturing of infants and bonding which
distinguishes mammals from other animals
o Laughing and crying
o Feelings
Memory and learning- Short-term memory in frontal lobe
- Long-term memory in hippocampus
Consciousness- experiencing ourselves as sensing, acting, feeling, and thinking about the past
and the future
- How many of these capabilities extend to other animals is a big debate