Chapter 7: Structure of Nervous System
Is divided into:
Central nervous system (CNS) = brain and spinal cord
Peripheral nervous system (PNS) = cranial and spinal nerves
Consists of 2 kinds of cells:
Neurons and supporting cells (glial cells).
Neurons are ______units of NS
Glial cells maintain homeostasis. Are 5X more than neurons
Neurons:Gather and transmit information by responding to stimuli
Producing and sending electrochemical impulses. Releasing chemical messages
Have a cell body, dendrites and axon. Cell body contains the nucleus
Cell body is the ______center and makes macromolecules
Groups of cell bodies in CNS are called nuclei; in PNS are called ganglia
Dendrites receive information, convey it to cell body
Axons conduct impulses ______from cell body
Long axon length necessitates special transport systems:
Axoplasmic flow moves soluble compounds toward nerve endings
Via rhythmic contractions of axon
Axonal transport moves large and insoluble compounds ______along microtubules;very fast
Anterograde transport moves materials away from cell body
Uses the molecular motor kinesin
______transport moves materials toward cell body.
Uses the molecular motor dynein. Viruses and toxins can enter CNS this way
Functional Classification of Neurons
Sensory/Afferent neurons conduct impulses into CNS
Motor/Efferent neurons carry impulses out of CNS
Association/ Interneurons______NS activity. Located entirely inside CNS
Structural Classification of Neurons
Pseudounipolar:Cell body sits along side of single process. e.g. sensory neurons
Bipolar:Dendrite and axon arise from opposite ends of cell body (retinal neurons)
Multipolar:Have many dendrites and one axon. e.g. motor neurons
Supporting/Glial Cells
PNS has Schwann and satellite cells. Schwann cells ______PNS axons
CNS has oligodendrocytes, microglia, astrocytes and ependymal cells
Each oligodendrocyte myelinates several CNS axons
Ependymal cells appear to be neural stem cells.
Other glial cells are involved in NS ______
Myelination
In PNS each Schwann cell myelinates 1mm of 1 axon by wrapping round axon
Electrically insulates axon
Uninsulated gap between adjacent Schwann cells is called the node of Ranvier
Axon Regeneration
Occurs much more readily in PNS than CNS
Oligodendrocytes produce proteins that ______regrowth
And form glial scar tissue that blocks regrowth
Nerve Regeration
When axon in PNS is severed:Distal part of axon degenerates
Schwann cells survive; form regeneration tube
Tube releases chemicals that attract growing axon
Tube guides regrowing axon to synaptic site
Neurotrophins: Promote ______l nerve growth
Required for survival of many adult neurons. Important in regeneration
Astrocytes: Most common glial cell
Involved in:Buffering K+ levels. Recycling neurotransmitters
Regulating adult neurogenesis.
Releasing ______that regulate neuronal activity
Blood-Brain Barrier: Allows only certain compounds to enter brain
Formed by capillary specializations in brain; appear to be induced by astrocytes
Capillaries are not as ______as those in body
Gaps between adjacent cells are closed by tight junctions
Resting Membrane Potential
At rest, all cells have a negative internal charge and unequal distribution of ions:
Large cations being trapped inside cell
Na+/K+ pump and limited permeability keep Na+ high outside cell
K+ is very ______and is high inside cell
Excitability
Excitable cells can discharge their RMP quickly.
By rapid changes in permeability to ions
Neurons and muscles do this to generate and conduct impulses
Membrane Potential (MP) Changes
Measured by placing 1 electrode inside cell and 1 outside
Depolarization occurs when MP becomes more positive
Hyperpolarization: MP becomes more ______than RMP
Repolarization: MP returns to RMP
Membrane Ion Channels
MP changes occur by ion flow through membrane channels
K+ leakage channels are always open
Voltage-gated (VG) channels are opened by ______
VG K+ channels are closed in resting cells
Na+ channels are VG; closed in resting cells
The Action Potential(AP)
Is a wave of MP change that sweeps along the axon from soma to synapse
Wave is formed by rapid depolarization of the membrane by Na+ influx; followed by rapid ______by K+ efflux
Mechanism of Action Potential
Depolarization:
At threshold, VG Na+ channels open.
Na+driven inward, opens more channels
Causes a rapid change in MP from ______to +30 mV
Repolarization:
VG Na+ channels close; VG K+ channels open
Electrochemical gradient drives K+ outward. Repolarizes axon to RMP
Depolarization and repolarization occur via diffusion
After an AP, Na+/K+ pump extrudes Na+, recovers K+
APs Are All-or-None
When MP reaches threshold an AP is ______fired
Positive feedback opens more and more Na+ channels
Then Na+ channels close, inactivated until repolarization
How Stimulus Intensity is Coded
Increased stimulus intensity causes more APs to be fired.
______of APs remains constant
Refractory Periods
Absolute refractory period:
Membrane cannot produce another AP because Na+ channels are inactivated
Relative refractory period occurs when VG K+ channels are ______, making it harder to depolarize to threshold
Cable Properties
Axon’s properties affect its ability to conduct current
High resistance of cytoplasm decreases as axon diameter increases
Conduction in an Unmyelinated Axon
Axon ______fires AP, its Na+ influx depolarizes adjacent regions to threshold
Generating a new AP. Process repeats all along axon.
So AP amplitude is always same. Conduction is slow
Conduction in Myelinated
Ions can't flow across myelinated membrane. Thus no APs occur under myelin
and no current leaks. This ______current spread
Gaps in myelin are called Nodes of Ranvier
APs occur only at nodes. VG Na+ channels are present only at nodes
Current from AP at 1 node can depolarize next node to threshold
Fast because APs skip from node to node.
Called ______conduction
Synaptic Transmission: Synapse
Is a functional connection between a neuron (presynaptic) and another cell (postsynaptic)
There are chemical and electrical synapses
Synaptic transmission at ______synapses is via neurotransmitters (NT)
Electrical synapses are rare in NS
Electrical Synapse
Depolarization flows from presynaptic into postsynaptic cell through channels called ______
Found in smooth and cardiac muscles, brain, and glial cells
Chemical Synapse
Synaptic cleft separates terminal bouton of presynaptic from postsynaptic cell
______are in synaptic vesicles
Vesicles fuse with bouton membrane; release NT by exocytosis
Amount of NT released depends upon frequency of APs
NT (ligand) diffuses across cleft
Binds to receptor proteins on postsynaptic membrane
______chemically-regulated ion channels
Depolarizing channels cause EPSPs (excitatory postsynaptic potentials)
Hyperpolarizing channels cause IPSPs (inhibitory postsynaptic potentials)
These affect VG channels in postsynaptic cell
EPSPs and IPSPs summate
If MP in postsynaptic cell reaches ______at the axon hillock, a new AP is generated
Acetylcholine (ACh): Most widely used NT.
Used in brain and ANS; used at all neuromuscular junctions
Has nicotinic and muscarinic receptor subtypes
These can be excitatory or ______
Nicotinic ACh Channel
2 subunits contain ACh binding sites. Opens when 2 AChs bind.
Moves Na+ into and K+ out of postsynaptic cell. Produces EPSPs
Muscarinic ACh Channel
Binding of 1 ACh activates ______which
Opens some gated K+ channels, causing hyperpolarization
Closes others, causing depolarization
Acetylcholinesterase (AChE)
______ACh, terminating its action; located in cleft
Acetylcholine in the PNS
Cholinergic neurons use acetylcholine as NT
The large synapses on skeletal muscle are termed end plates or neuromuscular junctions (NMJ)
Produce large EPSPs called end-plate potentials.
Open VG channels beneath end plate. Cause muscle contraction
Curare ______ACh action at NMJ
Monoamine NTs
Include serotonin, norepinephrine and dopamine
Serotonin is derived from tryptophan
Norepinephrine and dopamine are derived from tyrosine. Called ______
Serotonin
Involved in regulation of mood, behavior, appetite and cerebral circulation
LSD is structurally similar
Dopamine: is involved in motor control
______of this system causes Parkinson's disease
is involved in behavior and emotional reward
Most addictions activate this system
Overactivity contributes to schizophrenia
Norepinephrine (NE)
Used in PNS and CNS. In PNS is a ______NT
In CNS affects general level of arousal
Amino Acids NTs
Glutamic acid and aspartic acid are major CNS excitatory NTs
Glycine is an inhibitory NT
GABA (gamma-aminobutyric acid) is most common NT in brain
______
Polypeptide NTs (neuropeptides): Cause wide range of effects
Involved in learning and neural plasticity
Neuropeptide Y is most common neuropeptide
Powerful stimulator of appetite
Gaseous NTs: NO and CO are gaseous NTs
NO causes smooth muscle relaxation. ______increases NO
Synaptic Integration: EPSPs
Graded in magnitude. Have no threshold. Cause depolarization
Summate. Have no refractory period
Spatial Summation
Cable properties cause EPSPs to ______quickly over time and distance
Spatial summation takes place when EPSPs from different synapses occur in postsynaptic cell at ______time
Temporal Summation
Temporal summation occurs because EPSPs that occur closely in time can sum before they fade
Synaptic Plasticity
Repeated use of a synapse can increase or decrease its ease of transmission
= synaptic facilitation or synaptic depression
High frequency stimulation often causes enhanced excitability
Called ______
Believed to underlie learning
Synaptic Inhibition
Postsynaptic inhibition
GABA and glycine produce IPSPs
IPSPs dampen EPSPs
Making it ______to reach threshold
Presynaptic inhibition:
Occurs when 1 neuron synapses onto axon or bouton of another neuron, inhibiting release of its NT
Chapter 8: The Central Nervous System
Consists of brain and spinal cord
Receives input from sensory neurons
Directs activity of motor neurons
______neurons integrate sensory and motor activity
Perform learning and memory
CNS composed of gray and white matter
Gray matter consists of neuron bodies and dendrites
White matter (myelin) consists of axon tracts
Adult brain weighs 1.5kg. Contains 100 billion neurons
Receives ______of blood flow to body
Embryonic Development
Neural tube forms from groove in ectoderm by 20th day. Becomes the CNS
Neural crest cells develop where tube fuses. Become ______of PNS
During 4th week, 3 swellings form on neural tube
These will become forebrain, midbrain and hindbrain
During 5th week: Forebrain elaborates into telencephalon and diencephalon
______does not subdivide
Hindbrain forms metencephalon and myelencephalon
Telencephalon grows disproportionately forming hemispheres of cerebrum
Ventricles and central canal are remnants of hollow part of neural tube
Contain ______
Cerebrum
Is largest part of brain (80% of mass). Is responsible for higher mental functions
Its right and left hemispheres are interconnected by tract of the corpus callosum
Cerebral Cortex
Is highly ______
An elevated fold is called a gyrus.A depressed groove is called a sulcus
Each hemisphere has 5 lobes: frontal, parietal, temporal, occipital and insula
Frontal lobe is separated from parietal by central sulcus
Precentral gyrus of frontal lobe is involved in motor control
Postcentral gyrus of parietal lobe receives ______info from areas controlled by precentral gyrus
Temporal lobe contains auditory centers; receives sensory info from cochlea
Also links and processes auditory and visual info
Occipital lobe is responsible for vision and coordination of eye movements
Insula plays role in ______encoding
Integrates sensory info with visceral responses
Coordinates cardiovascular response to stress
Visualizing the Brain
X-ray computed tomography (CT) visualizes soft tissues
Positron-emission tomography (PET) examines brain metabolism and blood flow, drug distribution
Magnetic resonance imaging (MRI) shows brain ______
Functional MRI (fMRI) shows areas with increased neural activity by tracking blood flow
Electroencephalogram
Measures ______l activity of cerebral cortex
Used to diagnose epilepsy and brain death
EEG Waves
Alpha waves are recorded from parietal and occipital lobes with person awake, relaxed, eyes closed
______are strongest from frontal lobes; evoked by visual stimuli and mental activity
Theta waves come from temporal and occipital lobes
Common in newborns. In adults indicates severe emotional stress
Delta waves are from cerebral cortex
Common during adult sleep and in awake infants
In awake adult indicates brain ______
Sleep: 2 types of sleep are recognized
REM - rapid eye movement
EEGs are similar to awake ones. Type when dreaming occurs
Non-REM has delta waves
For consolidation of short- into long-term memory
Basal Nuclei (basal ganglia)
Are distinct masses of cell bodies located deep inside cerebrum
Function in control of ______movement
Cerebral Lateralization
Specialization of each hemisphere for certain functions
Each cerebral hemisphere controls movement on ______side of body
And receives sensory info from opposite side of body
Hemispheres communicate thru the corpus callosum
Left hemisphere possesses language and ______abilities
Right hemisphere is best at visuospatial tasks
Language
Language areas of brain are known mostly from aphasias
(speech and language disorders due to brain damage)
Broca’s area is necessary for speech
Wernicke’s area is involved in ______comprehension
Limbic System and Emotion
The hypothalamus and limbic system are crucial for emotions
Including aggression, fear, feeding, sex and goal-directed behaviors
Memory
Includes ______- and long-term memory. Involves a number of regions in brain
There are two types of long-term memory
Non-declarative (explicit) includes memories of simple skills and conditioning
Declarative (implicit) includes verbal memories
______have impaired declarative memory
Hippocampus is critical for acquiring new memories
And consolidating short- into long-term memory
Amygdala is crucial for fear memories
Storage of memory is in cerebral hemispheres
Higher order processing and planning occur in ______
Long-Term Potentiation (LTP)
Is the increased excitability of a synapse after high frequency stimulation
LTP is thought to be a form of synaptic learning
Thalamus and Epithalamus
Are located at base of cerebral hemispheres
Thalamus is a ______center thru which all sensory info (except olfactory) passes to cerebrum
And plays role in level of arousal
Epithalamus contains the choroid plexus which secretes CSF
Also contains ______which secretes melatonin
Involved in sleep cycle and seasonal reproduction
Hypothalamus
Is most important structure for homeostasis
Contains neural centers for hunger, thirst, body temperature
Regulates sleep, emotions, sexual arousal, anger, fear, ______
Controls hormone release from anterior pituitary
Produces ADH and oxytocin
Coordinates sympathetic and parasympathetic actions
Pituitary Gland
Is divided into anterior and posterior lobes
______pituitary stores and releases ADH (vasopressin) and oxytocin
Both made in hypothalamus and transported to pituitary
Hypothalamus produces releasing and inhibitinghormones that control anteriorpituitary hormones
Circadian Rhythms
Are body's daily rhythms
Regulated by SCN (suprachiasmatic nucleus) of hypothalamus
SCN is the ______clock. Adjusted daily by light from eyes
Controls pineal gland secretion of melatonin which regulates circadian rhythms
Midbrain contains:
Superiorcolliculi -- involved in visual reflexes
Inferiorcolliculi -- relay ______information
Rednucleus and substantianigra -- involved in motor coordination
S. nigra dopamine neurons degenerate in Parkinson’s
Hindbrain
Contains pons, cerebellum and medulla
Pons
Contains several nuclei of cranial nerves. And 2 ______control centers: Apneustic and pneumotaxiccenters
Cerebellum
2nd largest structure in brain
Receives input from ______(joint, tendon and muscle receptors)
Involved in coordinatng movements and motor learning
Medulla
Contains all tracts that pass between brain and spinal cord
And several crucial centers for breathing and cardiovascular systems
Reticular Activating System (RAS)
Is an ascending arousal system from the pons, midbrain reticular formation, hypothalamus and basal forebrain
These project to the cerebral cortex and control its level of ______
Activation of the RAS promotes wakefulness; inhibition promotes sleep
Spinal Cord Tracts
Sensory info from body travels to brain in ______spinal tracts
Motor activity from brains travels to body in descending tracts
Ascending Spinal Tracts
Ascending sensory tracts ______(cross) so that brain hemispheres receive info from opposite side of body
Same for most descending motor tracts from brain
Descending Spinal Tracts: Are divided into 2 major groups:
Pyramidal (or corticospinal) tracts descend from cerebral cortex to spinal cord without synapsing
Originate in ______.Function in control of fine movements
Extrapyramidal (or Reticulospinal) tracts descend with many synapses
Influence movement indirectly
Peripheral System (PNS)
Consists of nerves that exit from CNS and spinal cord, and their ganglia (collection of cell bodies ______CNS)
Cranial Nerves: Consists of 12 pairs of nerves
2 pairs arise from neurons in forebrain
10 pairs arise from midbrain and hindbrain neurons
Most are ______nerves containing both sensory and motor fibers
Spinal Nerves
Are mixed nerves that separate next to spinal cord into dorsal and ventral roots
Dorsal root composed of sensory fibers.
Ventral root composed of motor fibers
There are 31 pairs: ______cervical, 12 thoracic, 5 lumbar,1 coccygeal
Reflex Arc
Is a simple sensory input, motor output circuit involving only peripheral nerves and spinal cord
Sometimes arc has an association neuron between sensory and motor neuron.
Chapter 9: TheAutonomic Nervous System
Autonomic nervous system (ANS) manages our physiology
Regulates organs and organ systems, and their smooth muscles and glands
Smooth muscle maintains a ______in absence of nerve stimulation
Smooth becomes more sensitive when ANS input is cut (denervation hypersensitivity)
Many smooth are spontaneously active and contract rhythmically without ANS input. ANS input simply increases or decreases intrinsic activity
Autonomic Neurons
ANS has 2 neurons in its efferent pathway
1st neuron (______neuron) has cell body in brain or spinal cord
Synapses with 2nd neuron (postganglionic neuron) in an autonomic ganglion
Postganglionic axon extends from autonomic ganglion to target tissue
Divisions of the ANS
ANS has sympathetic and parasympathetic divisions
Which usually have ______effects
These coordinate physiology with what’s going on in person's life
Sympathetic mediates "fight, flight, and stress" reactions
Parasympathetic mediates "rest and digest" reactions
Sympathetic Division
Is also called thoracolumbar division because its preganglionics exit spinal cord from T1 to L2
Most then synapse on postganglionics in the ______ganglia