Hey… you’re making
me nervous.
The Nervous System and Muscles
N OT E FR OM T HE N OT E -TA KE R : I R E A L LY , R E A L LY H IG HLY
R E CO M M E N D YOU R E A D T H IS S E C T I ON A N D PAY R E A L LY G O OD
AT T E N T I ON IN CL A S S . T HI S S HI T ’S T R I C K Y.
48 Overview
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Neurons: the nerve cells that transfer information within the body
o Long-distance electrical signals
o Short-distance chemical signals
o Transfer sensory info, control heart rate, coordinate hand and eye movement (what
hand-eye coordination…?), record memories, generate dreams
o Brain: groups of neurons
o Ganglia: simple clusters of neurons
48.1: Neuron organization and structure reflect function in
information transfer
Introduction to Information Processing
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Sensory neurons: transmit information form eyes and other sensors that detect external
stimuli/internal conditions
o Sent to processing centers in
the brain/ganglia
o Processing sensors interpret the
sensory input (integrate)
 Interneurons: make
only local connections,
vast majority of neurons
in the brain
 Nerves: neurons that
extend out of the
processing centers in
bundles and generate
output by triggering
muscle/gland activity,
basis of motor output
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 Motor neurons: transmit signals to muscle cells
Central Nervous System (CNS): includes brain and longitudinal nerve cord
Peripheral Nervous System (PNS): neurons that carry info in/out of the CNS
Neuron Structure and Function
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Cell body: location of the neuron’s organelles, including the nucleus
Dendrites: highly branched extensions that receive signals from other neurons
Axon: extension that transmits signals to other cells, often much longer than dendrites
Axon hillock: cone-shaped region of an axon where it joins the cell body, usually the region where
the signals travel down the axon are generate
Synapse: branched end of an axon that transmits info to another cell at a junction
Synaptic terminal: part of each axon branch that forms the junction
Neurotransmitters: chemical messengers that pass info from the transmitting neuron to the cell
Presynaptic cell: transmitting neuron
Postsynaptic cell: neuron, muscle, gland that receives that signal
Glia: supporting glial cells that insulate the axons of neurons and regulate the extracellular fluid
surrounding the neurons
48.2: Iron pumps and ion channels maintain the resti ng
potential of a neuron
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Membrane potential: difference in electric charge across their plasma membrane
Resting potential: membrane potential of a resting neuron, negative relative to the outside
Formation of the Resting Potential
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Potassium ions (K+) and sodium ions (Na+) are important, each have a concentration gradient
across the plasma membrane of the neuron
o Mammals:
 K+ = 140 mM inside, 5mM outside
 Na+ = 15mM inside, 150 mM outside
o Maintained by sodium-potassium pumps in the plasma membrane, use ATP energy to
actively transport Na+ out and K+ in
Concentrations represent potential energy
o Ion channels: pores formed by clusters of specialized proteins that span the membrane,
allow ions to diffuse back and forth – carry with them units of electric charge
 Any resulting net movement will generate a voltage across the membrane
Selective permeability: allow only certain ions to pass
o Diffusion of K+ through open potassium channels forms resting potential
 [K+] high inside cell, chemical concentration gradient favors outflow of K+
 K+ channels only allow K+ to pass, Cl- can’t accompany K+ across the membrane
 Outflow of K+ leads to an excess of negative charge inside the cell—negative
charge = membrane potential
o No backup?
 Electric potential: excess negative charges inside the cell opposes flow of
additional K+ ions out of the cell
Modeling of the Resting Potential
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Net flow of K+ out proceeds until chemical and electrical forces are in balance
Equilibrium potential (Eion): magnitude of the membrane voltage at equilibrium for a particular
ion
o Calculated using Nernst equation
o Eion = 62 mV (log [ion]outside / [ion]inside)
Because neither K+ nor Na+ is at equilibrium, each ion has a net flow across the membrane.
Resting potential remains steady—K+ and Na+ currents are equal and opposite
48.3: Action potentials are the signals conducted by axons
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What the hell does any of this mean?
Gated ion channels: Ion channels that open/close in response to stimuli- basis of almost all
electrical signaling in the nervous system – open/close alters membrane’s permeability to
particular ions, which alters membrane potential
Hyperpolarization: increase in magnitude of membrane potential, results from any stimulus that
increases either the outflow of + ions or inflow of – ions
Depolarization: reduction of magnitude of membrane potential, often involved gated sodium
channels
Graded potentials: hyperpolarization, depolarization- magnitude of change in membrane
potential varies with strength of stimulus
Production of Action Potentials
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Voltage-gated ion channels: gated ion channels that open/close in response to change in
membrane potential
Action potential: massive change in membrane voltage, result of rapid opening of all voltagegated sodium channels – nerve impulses that carry info along axon
Threshold: specific voltage at which action potentials occur – depolarization increases to this
point
o All-or-nothing: response—reflects the fact that depolarization opens voltage-gated
sodium channel – like a trigger of a gun
Generation of Action Potentials: A Closer Look (Fuck you I will not take a
closer look)
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Action potentials are extremely brief, many of them can happen a second, frequency can vary in
response to input – signal strength
Voltage-gated channels shape action potential
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1: resting potential, most voltage-gated sodium channels are closed
2: stimulus depolarizes membrane, some sodium channels open, allowing Na+ to diffuse 
further depolarization – open more channels
3: positive-feedback cycle brings membrane close to ENa—crossed threshold
4: prevent membrane potential from reaching Ena – voltage-gated sodium channels inactive soon
after opening, voltage-gated potassium channels opening (falling phase)
5: Undershoot: membrane permeability is closer to EK than resting potential—potassium gates
close—membrane potential returns to resting potential
Refractory period: downtime following action potential when a second action potential cannot
be initiated – sets limit on max freq at which action periods can be generated
Conduction of Action Potentials
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Action potential functions as long-distance signal my regenerating itself as it travels from the cell
body to synaptic terminals
Conduction Speed
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Axon diameter—wider axons conduct action potential more rapidly than narrow ones because
resistance to electrical flow is inversely proportional to cross-section already of a conductor
Myelin sheath: layer of electrical insulation that surrounds vertebrate axons, allows thinner
vertebrate axons to be just as fast
o Oligodendrocytes: in CNS
o Schwann Cells: in PNS
o Insulation- has same effect as increasing axon diameter- depolarization current
associated with action potential to spread farther along interior of axon – space
efficiency
o Nodes of Ranvier: gaps in myelin sheath, in contact with extracellular fluid – action
potentials are not generated here
o Salutatory conduction: action potential at a node travels to the next node, where it
depolarizes the membrane and regens the action potential – action potential ppears to
jump along axon from node to node
48.4: Neurons communicate with other cells at synapses
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Electrical synapses: contain gap junctions, allow electrical current to flow directly from one
neuron to another – synchronize activity of neurons responsible for rapid, unvarying behaviors
Chemical synapses: involve release of chemical neurotransmitter by presynaptic neuron
o Synaptic vesicles: membrane-bound compartments containing neurotransmitter, reaches
the terminal membrane and fuses with it
o Synaptic cleft: narrow gap that separates the presynaptic neuron from the postsynaptic
cell
o Information is more readily regulated at chemical synapses than at electrical synapses –
factors can alter responsiveness of the postsynaptic cell
1.
2.
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4.
5.
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Action potential depolarizes plasma membrane of synaptic terminal
Opens calcium channel in membrane
Elevated Ca+ concentration causes synaptic vesicles to fuse with presynaptic membrane
Vesicles release neurotransmitter into synaptic cleft
Neurotransmitter binds to receptor
Neurotransmitter released from receptors, channels close
Generation of Postsynaptic Potentials
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Ligand-gated ion channels: channels capable of binding to the neurotransmitter, clustered in
membrane of postsynaptic cell, directly opposite the synaptic terminal
Postsynaptic potential: change in membrane potential of postsynaptic cell
Excitatory postsynaptic potentials (EPSPs): depolarization that bring membrane potential closer
toward thresholds, neurotransmitter binds to channels open to both K+ and Na+
Inhibitory postsynaptic potentials (IPSPs): hyperpolarization, postsynaptic membrane
hyperpolarizes when the neurotransmitter binds to channels selectively permeable to K+ or Cl-
Summation of Postsynaptic Potentials
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Postsynaptic potentials are graded, magnitude varies with number of factors, including amount
of neurotransmitter released by postsynaptic neuron – do not regenerate as they spread along
the membrane (become smaller w/ distance from synapse)
Temporal summation: EPSPs occur at single synapse before the membrane potential returns to
resting potential– EPSPs add together
Spatial summation: EPSPs produced nearly simultaneously by different synapses and add
together
EPSPs can depolarize the membrane at the axon hillock to the threshold, causing postsynaptic
neuron to produce action potential
o Also applies to IPSPs
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Whenever membrane potential at axon hillock reaches threshold, action potential is generated
and travels along axon to synaptic terminals – refractory period, neuron may produce another
membrane potential
Modulated Synaptic Transmission (I have no idea what’s going on right now)
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There are synapses in which the receptor for the neurotransmitter is not part of an ion channel –
binding of neurotransmitter to its receptor in postsynaptic cell activates signal transduction
pathway involving second messenger
o Slower onset, but last longer
o Second messenger modulate responsiveness of postsynaptic neurons to inputs in diverse
ways, altering number of open K+ channels
o cAMP as second messenger – binding of neurotransmitter molecule to a single receptor
can open/close many channels
Neurotransmitters
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Over 100 neurotransmitters
Acetylcholine
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Most common in vertebrates/invertebrates
Except in heart, vertebrate neurons that form a synapse with muscle cells release acetylcholine as
an excitatory transmitter
Binds to receptors on ligand-gated channels on muscle cell, producing EPSP
Nicotine binds to the same receptors – physiological/psychological stimulate result from affinity
to acetylcholine receptors
Inhibit presynaptic release of acetylcholine – botulism: muscles required from breathing fail to
contract because acetylcholine release is blocked
o Botox- minimize wrinkles by immobilizing facial muscles
Regulation of heart: inhibitory effects
Biogenic Amines
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Neurotransmitters derived from amino acids
o Serotonin- synthesized from tryptophan
o Dopamine, epinephrine and norepinephrine (both neurotransmitters and hormones)
Involved in modulating synaptic transmission
o Dopamine and serotonin – sleep, mood, attention, learning
Parkinson’s = lack of dopamine, depression – lack of biogenic amines (Prozac)
Amino Acids
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Gamma-aminobutyric Acid (GABA) glutamate
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GABA – inhibitory synapses in brain, produces IPSP by increasing permeability of
postsynaptic membrane
Glutamate – always excitatory
Glycine – acts at inhibitory synapses, lie outside the brain
Neuropeptides
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Relatively short chains of amino acids, operate via signal transduction pathways – produced by
cleavage of much larger protein precursors
Substance P : excitatory neurotransmitter = pain
Endorphins: natural pain decreaser
Gases
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NO (ED) - Not stored in cytoplasmic vesicles, but is synthesized on demand
49.1: Nervous systems consist of circuits of neurons and
supporting cells
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Cnidarians – nerve net: series of interconnected nerve cells which controls the contraction and
expansion of the Gastrovascular cavity
More complex animals- nerves: axons of multiple nerve cells bundled together, channel and
organize information flow along specific routes through the nervous system
Bilaterally symmetrical bodies – even more specialized nervous systems – cephalization
o Clustering of sensory neurons and interneurons at anterior end
o Nerve cords extending toward posterior end connect structures with nerves elsewhere
o Behavior of segmented worms regulated by more complicated brains and by ventral
nerve cords containing ganglia
Nervous system organization correlates with lifestyle (cephalization = more specialized =
complete tasks)
Vertebrates: brain and spinal cord form CNS, nerves and ganglia comprise PNS
Organization of the Vertebrate Nervous System
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Brain: integrative power that underlies complex behavior of vertebrates
o Gray matter: consists of neuron cell bodies, dendrites and unmyelinated axons
o White matter: consists of bundled axons that have myelin sheaths, give axons a whitish
appearance
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Spinal cord: conveys info to and from brain,
generates basic patterns of locomotion
o Runs dorsal side of body
o Has ganglia just outside the spinal cord
o Derived from dorsal embryonic nerve
cord (hollow)
 Central canal – hollow cavity of
embryonic nerve cord is
transformed into this and the
ventricles of the brain
 Cerebrospinal fluid: four
ventricles and central canal fills
with this, formed by filtration of
arterial blood in the brain –
circulates slowly through the
central canal and ventricles,
then drains into veins –
cushions the brain/spinal cord
o Acts independently of brain, produces
reflexes- body’s automatic responses to
certain stimuli
Reflexes
o Protect body by triggering rapid, involuntary response to particular stimulus
Sensory neurons
convey info to
spinal cord
1. Reflex is
initiated by
tapping the
tendon
connected to
quads
Sensors detect a
sudden stretch in
quads
Motor neurons
convey signals to
quads, leg jerks
forward
Sensory neurons
communicate with
interneurons
Interneurons inhibit
motor neurons that
lead to hamstring
muscle- prevents
contraction of
hamstring
Glia in the CNS
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Glia present throughout vertebrate and spinal cord fall into many categories
o Ependymal cells line ventricles and have cilia that promote circulation of the
cerebrospinal fluid
o Microglia protect nervous system from invading microorganisms
o Oligodendrocytes function in axon myelination
o Astrocytes: diverse set of functions
 Provide structural support for neurons
 Regulate extracellular concentrations of ions/neurotransmitters
 Respond to activity in neighboring neurons by facilitating info transfer at
synapses, release neurotransmitters
 Cause nearby blood vessels to dilate, increasing blood flow to area
 Blood-brain barrier: restricts passage of most substances into CNS – permits
tight junctions – tight control of EC chemical environment of brain/SC
o Radial glia: development of nervous system- form tracks along newly formed neurons
that migrate from neural tube – ac at stem cells
Peripheral Nervous System
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Afferent – toward; efferent – away
Cranial nerves: connect brain with locations mostly in organs of the head and upper body
o Afferent only: olfactory nerves
Spinal nerves: run between spinal cord and parts of the body below the head
Both types contain both efferent and afferent neurons
Motor system: neurons that carry signals to skeletal muscles in response to external stimuli
Autonomic nervous system: regulates internal environment by controlling smooth and cardiac
muscles and organs of the digestive, cardiovascular, excretory and endocrine systems –
involuntary
o Sympathetic division: corresponds to arousal/energy generation – fight/flight response
o Parasympathetic division: promote calming and return to self-maintenance functions –
rest/digest response (lowers heart rate, enhances digestion)
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Enteric division: consists of networks of neurons in digestive tract, pancreas and
gallbladder – control secretion, control smooth muscles that produce peristalsis
Motor system and autonomic nervous systems cooperate in maintaining homeostasis
50.5: Physical interaction of
protein filaments is required for
muscle function
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Muscle cell function relies on microfilaments, actin
components of the cytoskeleton
o Powered by chemical energy, brings
about contraction (muscle extension
occurs only passively
Vertebrate Skeletal Muscle
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Skeletal muscle: attached to and responsible for
movement of bones, characterized by hierarchy of
smaller and smaller units
o Most consist of bundle of long fiber that
run || to length of the muscle
o Each fiber is a single cell w/ multiple nuclei
o Formed by fusion of many embryonic cells
o Fiber contains bundle of smaller
myofibrils, arranged longitudinally
o Myofibrils composed of thin filaments
and thick filaments
 Thin: two strands of actin and two
strands of regulatory protein
coiled around each other
 Thick: staggered arrays of myosin
molecules
o Skeletal muscle is striated muscle
because the regular arrangement of
filaments creates a pattern of light/dark
bands
 Repeating unit = sarcomere –
basic contractile unit of muscle
 Arrangement of sarcomere is
responsible for how the muscle
contracts
The Sliding-Filament Model of Muscle Contraction
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Sliding-filament model: neither
thin/thick filaments change in length
when sarcomere shortens – the two
slide past each other longitudinally,
increasing overlap of thin/thick
filaments
o Based on interaction
between myosin and actin
molecules
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Myosin has a long tail region and a globular head region, tail adheres to the tails
of other myosin molecules that form the thick filament – head is center of of
bioenergetics reactions (ATP hydrolysis)
Energy needed for repetitive contractions is stored in creatine phosphate and
glycogen
 Creatine phosphate can transfer phosphate group to ADP to synthesize
additional ATP
 Glycogen is broken down to glucose, which can be used to generate ATP
by aerobic respiration/glycolysis
The Role of Calcium and Regulatory Proteins
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Tropomyosin: regulatory protein
Troponin complex: set of addition regulatory proteins
Both are bound to actin strands of thin filaments
At rest, tropomyosin covers myosin-biding sites along thin filaments, preventing actin/myosin
from interaction
Presence of Ca2+ causes myosin-binding sites to be exposed
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This is caused by motor neurons triggering
release of Ca2+
o Transverse (T) tubules: infoldings of the
plasma membrane, make contact with the
sarcoplasmic reticulum (SR), specialized ER
– spread of action potential along T tubules
triggers change in SR, opening Ca2+
channels
o When motor neuron input stops, muscle cell
relaxes – filaments slide back into starting
position, Ca2+ pumped back into the cytosol
Diseases that fuck with this process: Lou Gehrig’s
disease, Myasthenia gravis
Nervous Control of Muscle Tension
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2 mechanisms by which nervous system produces graded contractions: varying # muscle fibers
that contract, varying rate at which muscle fibers are stimulated
Motor unit: consists of single motor neuron and all the muscle fibers it controls
o When motor neuron produces an action potential, all the muscle fibers in its motor unit
contracts as a group
o Strength of contraction depends on how many muscle fibers the motor neuron controls
o Recruitment: of motor neurons, control of more muscle when more motor neurons are
activated
 tetanus: smooth, sustained contraction –
when muscle fiber can’t relax between stimuli
(twitches)
Types of Skeletal Muscle Fibers
Oxidative and Glycolytic Fibers
 Oxidative: Rely mostly on aerobic
respiration, have many mitochondria, rich blood
supply, large amount of myoglobin (stores
oxygen)
 Glycolytic: rely on glycolysis, fatigue much
more readily
Fast/Slow-Twitch Fibers
 Fast-Twitch: develop tension 2-3 times
faster, used for brief-rapid-powerful contractions
 Slow-twitch: found in muscles that
maintain posture, sustain long contractions – less
SR and pumps Ca2+ more slowly
 Slow-twitch are all oxidative, Fast-twitch
can be either
 Most skeletal muscles contain both types
Other Types of Muscle
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Cardiac muscle: found only in the heart – have ion channels in plasma membrane that causes
rhythmic depolarization – electrical and membrane properties are different
o Intercalated disks: plasma membranes of adjacent cardiac muscle cells interlock here,
where gap junctions provide direct electric coupling between the cells
Smooth muscle: walls of hollow organs – lack striations because actin/myosin are not regularly
arrayed along the length of the cell –thick filaments scattered throughout cytoplasm, thin
filaments attached to structures called dense bodies – contract and relax more slowly than
striated muscles
49.2: The vertebrate brain is regionally specialized
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Embryonic: Forebrain, midbrain and hindbrain
Adult: cerebrum, cerebellum, diencephalon, midbrain, pons, medulla
Brainstem
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Functions in homeostasis, coordination of movement, conduction of info to/from higher brain
centers
Sometimes called lower brain, forms a stalk with cap-like swellings at anterior end of spinal cord
Includes pons, medulla oblongata, midbrain
Transfer of info between PNS and midbrain/forebrain = one of the most important functions of
the medulla and pons
o All axons carrying sensory info to/motor functions from high brain regions pass through
the brain stem
o Coordinate large-scale body movements
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Midbrain – contains centers for receiving and integrating sensory info, sends coded sensory info
to forebrain
Arousal and Sleep (or I mean, just talk about sleep, that’s cool too)
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Reticular formation: diffuse network of neurons in the core of the brainstem, determines which
incoming info reaches cerebral cortex = regulated by melatonin
Please tell me what sleep is
Cerebellum
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Coordinates movement and balance
Diencephalon
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Thalamus, hypothalamus, epithalamus
Thalamus, hypothalamus act as relay stations for info flow in the body
Thalamus – main input center for sensory information going to the cerebrum
Hypothalamus: controls homeostasis – body’s thermostat, regulates thirst, hunger- source of
posterior pituitary hormones, release of hormones
Biological clock and regulation by hypothalamus
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Biological clock: molecular mechanism that directs periodic gene expression and cellular activity
– synchronized to light and dark- lol sleep
Suprachiasmatic nucleus (SCN): group of neurons that coordinate circadian rhythms
Cerebrum
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Divided into left/right cerebral hemispheres- covered in gray matter and internal white matter
Extensive in mammals, controls perception, voluntary movement and learning
Corpus callosum: thick band of axons that enables right/left cerebral cortices to communicate
Evolution of Cognition in Vertebrates
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Insert Your Inner Fish
49.3: The cerebral cortex controls voluntary movement and
cognitive functions
Information Processing in the Cerebral Cortex
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Somatosensory receptors: provide info about touch/pain/temperature/position
Path of information: comes into cortex-> thalamus->primary sensory areas within brain lobes
o Thalamus directs different types of input to distinct locations
Integrated sensory info passes to the frontal association area, which helps plan actions and
movements
Language and Speech
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Linked to a large network of brain regions: visual + listening+ hearing + meaning + words with
concepts + what?!
Lateralization of Cortical Function
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Lateralization: establishes in differences in hemisphere function in humans
o Relates to handedness
o Usually two hemispheres work together all peachy-like, sometimes things get mixed up
and only one half of the brain works
Emotions (I just have a lot of feelings.)
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Involves many regions of the brain
o Limbic system- amygdala, hippocampus, thalamus
o Emotions stored as memories = amygdala – temporal lobe
o Prefrontal cortex = emotional experience = temperament and decision making
Consciousness
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Neuronal activity correlates with conscious experiences
Emergent property of brain = recruits activities in many areas of the cerebral cortex – scanning
mechanism = integrating widespread activity into a unified conscious movement
OH MY GOD I’M DONE THANK GOD