chapter 9 10 nervous tissue and cns notes
TRANSCRIPT
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Chapter 9 Nervous Tissue
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Structure and Organization• Central Nervous System (CNS)• Peripheral Nervous System (PNS)• Subdivided: Somatic (SNS) & Autonomic
(ANS) nervous systems, (ENS) enteric nervous system
• Also• INPUT-Afferent or Sensory division• OUTPUT- Efferent or Motor division
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Structures of Nervous System
• Brain- Neurons enclosed in skull• Spinal cord– connects to brain &
enclosed in spinal cavity • Nerves- bundles of neuronal
axons – Cranial emerge from brain;
spinal nerves- emerge from spinal cord
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• Ganglia- groups of cell bodies outside brain & spinal cord
• Enteric plexuses- networks in digestive tract
• Sensory receptors- monitor changes in internal or external environments
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Figure 9.1
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Function• Sensory Receptors & afferent nerves
– Carry information into brain & spinal cord
• Integration- information processing– Perception = awareness of sensory input – Carry by short interneurons
• Motor activity- efferent nerves– Signals to glands and muscles (effectors)
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Figure 9.2
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Nervous System
• Neuron= nerve cell – Specialized for signal carrying & information
processing
• Neuroglia cells-support, nourish & protect neurons– Neuroglia critical for homeostasis of interstitial
fluid around neurons
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Neuronal Structure• Cell body- nucleus, cytoplasm with typical
organelles• Dendrites- highly branched input structures
emerging from cell body• Axon- conducts away from cell body toward
another neuron or effector– Emerges at cone-shaped axon hillock
• Axon terminals -at end of axon with synaptic bulbs
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Figure 9.3
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Myelination• Axons covered with a myelin sheath
– Many layered lipid & protein creating insulations
– Increases speed of nerve conduction.
• Nodes of Ranvier= gaps in the myelin– Nodes are important for signal conduction
• Some diseases destroy myelin- E.g. multiple sclerosis & Tay-Sachs
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Vocabulary Words• Central Nervous System• Peripheral Nervous
System• Somatic Nervous System
• Autonomic nervous system
• Enteric nervous system
• Ganglia
• Neuron• Cell body• Dendrites• Axon
• Nodes of Ranvier
• Myelin Sheath
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Gray and White Matter
• White matter- primarily myelinated axons
• Gray matter- cell bodies, dendrites, unmyelinated axons, axon terminals & neuroglia
• spinal cord gray matter is centrally located
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Other terms• Gray matter in brain covers surface of
cerebrum & cerebellum – cortex
• deep cluster of neuronal cell bodies = nucleus
• Bundle of white matter in CNS= Tract
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Neuroglia
• ~ half the volume of CNS
• Cells smaller than neurons
• Can multiply and divide and fill in brain areas
• Do not conduct nerve impulses
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Types of Neuroglia• Astrocytes- blood brain barrier, provides
nutrients
• Oligodendrocytes- myelin in CNS neurons
• microglia - defense
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• Ependymal cells- Cerebral Spinal Fluid production
• Schwann- PNS regeneration of axons, produce myelin sheath
• Satellite cells- in PNS ganglia
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Vocabulary Cards• White matter• Gray matter• Neuroglia• Astrocytes• microglia
• Oligodendrocytes• Schwann Cells• Satellite cells• Ependymal cells
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Action Potentials• Action potentials = nerve impulses
• Require a membrane potential– electrical charge difference across cell
membrane – like a Battery
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Ion Channels• Ion Channels- allow ions to move by diffusion =
current• Two types: leakage channels and gated
channels• Leakage channels-small steady stream of ions• Gated channels-open and close on demand• If no action potential then resting cell has
resting membrane potential
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Ion Channels• Allow specific ions to diffuse across
membrane– Move from high concentration to low– or toward area of opposite charge
• Voltage- Gated channels respond to a change in membrane potential
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Resting Membrane Potential• Leakage channels• Cytosol high in K+ & interstitial fluid high in
Na+ (sodium –potassium pumps)
• Leakage lets K+ through easily and Na+ poorly
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• Starts positive on the inside and negative on the outside, slowly changes to the opposite as ions diffuse.
• Actual value depends on the relative leakage channel numbers
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Figure 9.4
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Action Potential (AP)• Series of active events
• Channels actively open & close
• Some initial event is required to reach a voltage threshold (~ = - 55 mv)
• Stimulus = any event bringing membrane to threshold
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Action Potential• Then
• Depolarizing phase- – membrane potential rises and becomes
positive
• Repolarizing phase- – potential restored to resting value– May overshoot =hyperpolarizing phase– Then recovery to rest.
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Active Events• Stimulus to reach threshold
• Na+ channel opens=>
• Na+ ions enter=>
• positive potential=>
• Causes K+ channel opening =>
• repolarization
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All- or -None• This sequence is always the same
• If threshold is met, then the same size of changes occur, no larger or smaller APs
• Stimulus must reach threshold to start, if it’s too small, NO AP!
• After one AP there is a short period before next can be triggered= refractory period
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Figure 9.5
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Conduction of Nerve Impulses• Each section triggers next locally• Refractory period keeps it going the right
direction• unmyelinated fiber- continuous conduction• With myelin- saltatory conduction
– Can only be triggered at Nodes of Ranvier
• Myelinated fibers faster & larger neurons faster
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Figure 9.6a
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Figure 9.6b
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Vocabulary Words
• Membrane potential• Resting membrane
potential• Action potential
• Depolarizing phase• Repolarizing phase• conduction
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Synaptic Transmission• Sequence of events at synapse • Triggered by voltage change of the
Action Potential• Sending neuron = presynaptic• Receiving neuron = postsynaptic• Space between = synaptic cleft• Neurotransmitter carries signal across
cleft
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Events at Synapse• AP arrives at presynaptic end bulb=>
• Opens voltage gated Ca2+ channels=>– Ca2+ flows into cell
• increased Ca2+ concentration =>
• exocytosis of synaptic vesicles=>
• Neurotransmitter released into cleft
• Diffuse across and bind to receptors in postsynaptic cell membrane
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Synaptic Transmission• Binding at receptors • Chemical trigger of ion channels• May depolarize or hyperpolarize
postsynaptic cell membrane• If threshold reached at axon hillock then
postsynaptic cell action potential results
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Synaptic Transmission
• Finally the neurotransmitter must be removed from the cleft-
• Diffusion away
• Destroyed by enzymes in cleft
• Transport back into presynaptic cell
• Neuroglia destruction
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Figure 9.7
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Neurotransmitters• AcetylCholine (Ach)- common in PNS
– May be stimulatory or inhibitory
• Amino Acids- – Glutamate, Aspartate, gamma aminobutyric
acid (GABA), glycine
• Modified amino acids- – Norepinephrine (NE), Dopamine (DA),
serotonin
• Neuropeptides – endorphins• Nitric oxide (NO)
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Vocabulary Words
• Synapse• Neurotransmitter
• Leakage channels• Gated channels
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Chapter 10 Central Nervous System
• The CNS includes the brain and spinal chord.
• The meninges are three layers of connective tissue that extend around the spinal chord and brain.
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3 Layers• Dura mater- tough, dense irregular tissue
for protection.
• Arachnoid mater- collagen and elastic fibers resemble a spider’s web
• Pia mater- transparent inner layer of collagen and elastin that adhere to the surface of spinal chord and brain.
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Spinal Chord• The interior of the spinal chord resembles
a butterfly and contains gray matter.
• The outer of the spinal chord is white matter.
• The spinal chord is protected by the vertebrae in the spine although the chord doesn’t extend fully throughout the back.
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Reflex ArcA reflex is a fast, involuntary sequence of actions that occurs in response to a particular stimulus.
Some reflexes are inborn such as withdrawal reflex (take your hand from a hot surface.)
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Reflexes• Reflexes that take place in the spinal
chord gray matter are called a spinal reflex. These bypass the brain.
• If the integration or connection occurs in the brain, it’s called a cranial reflex.
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Blood-Brain Barrier• The blood-brain barrier protects brain cells
from harmful substances and pathogens by preventing passage of many substances from the blood to brain tissue.
• However, the BBB doesn’t prevent all substances from getting through.– Examples: oxygen, carbon dioxide, alcohol,
anesthesia
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Cerebrospinal Fluid• The spinal chord and brain are further
protected against chemical and physical injury by CSF.
• This is a clear, colorless liquid that carries oxygen, glucose and other nutrients from the blood to neurons and neuroglia.
• The CSF also removes wastes and toxic substances.
• CSF circulates in the subarachnoid space in the spinal chord.
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Vocabulary Words
• Dura mater
• Arachnoid mater
• Pia mater
• Blood-Brain Barrier (BBB)
• Cerebrospinal Fluid (CSF)
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The Brain• The brain is one of largest organs in the
body with 100 billion neurons and 10-50 trillion neuroglia cells.
• The four major parts of the brain are:Brain stem
Diencephalon
Cerebrum
cerebellum
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Brain Stem• The brain stem consists of three regions:
– Medulla oblongata
– Pons– midbrain
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Medulla Oblongata• Contain all sensory and motor neurons
ascending and descending between the brain and spinal chord.
• Contain cardiovascular center which controls heart rate, force of beat and diameter of blood vessels.
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Medulla Oblongata• Contain medullary rhythmicity area which
adjusts the rhythm of breathing.
• Control reflexes for swallowing, vomiting, coughing, and sneezing
• Receive sensory input from or provides motor output to cranial nerves.
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Pons• This is a bridge that connects parts of the
brain with one another.
• Voluntary movements are relayed to the cerebellum.
• Contain sensory and motor tracts.
• Help control breathing.
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Midbrain• The midbrain connects the pons to the
diencephalon.
• Contains neurons that conduct impulses from the cerebrum to the spinal chord. Medulla, and pons.
• Loss of these neurons is associated with Parkinson’s disease.
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Midbrain• Contain several reflex arcs including:
– Scanning and tracking movements of the eyes
– Pupillary reflex (pupil size)– Accommodation reflex (shape of lens)– Startle reflex
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More about the Brainstem• Also contains an area called the reticular
activating system (RAS)
• When RAS is stimulated, the result is consciousness.
• The RAS maintains wakefulness.
• Inactivation of RAS produces sleep.
• RAS also maintains muscle tone.
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Diencephalon
• The major regions include:– Thalamus– Hypothalamus– Pineal gland
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Thalamus• They are a paired oval shaped area.
• Important relay station for sensory impulses for all parts of the brain.
• Plays an essential role in awareness and acquisition of knowledge, which is called cognition.
• Maintains consciousness and regulation of involuntary activities.
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Hypothalamus• 1. Control of ANS-regulate gland
secretion, heart rate, digestion and contraction of urinary bladder
• 2. Control the pituitary gland- release of hormones
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Hypothalamus• 3. Regulation of emotional and behavioral
patterns- together with limbic system, regulates feelings of rage, aggression, pain, pleasure and arousal
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Hypothalamus• 4. Regulation of eating and drinking- thirst
center- detects changes in osmotic pressure in cells and initiates the sensation of thirst.
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Hypothalamus• 5. Control of body temperature- directs
ANS to promote heat loss or heat production depending on stimuli.
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Hypothalamus• 6. Regulation of circadian rhythms and
states of consciousness- establish patterns of sleep and waking.
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Pineal Gland
• Size of a small pea.
• Secretes melatonin that promotes sleepiness and setting the body’s internal clock.
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Cerebellum• Consists of two hemispheres.
• Surface consists of gray matter.
• The cerebellum compares intended movements with what is actually happening.
• Regulates posture and balance and coordinate muscle contractions.
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Cerebrum• Consists of gray matter on the outside and white
matter inside.• Consists of two hemispheres connected by the
corpus callosum.
• Provides us with the ability for higher cognitive functions such as writing, speaking, reading, calculating, planning, and creating.
• Contains many folds called gyri to increase surface area.
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Limbic system• Sometimes called the emotional brain.
• Produces a variety of emotions including: pain, pleasure, docility, affection and anger.
• Control patterns of behavior and may be linked to animal instinct for survival.
• Together with parts of the cerebrum, it functions in memory.
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BRAIN GAMES
• Right/Left Brain Controversey
• Optical Illusions
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Vocabulary Cards
• Brain stem-medulla, pons, midbrain
• Diencephalon- thalamus, hypothalamus, pineal gland
• Limbic system• Cerebrum• cerebellum
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Chapter 11 Autonomic Nervous System
• Autonomic motor neurons regular the ongoing activities in their effector tissues such as cardiac, smooth and glands.
• All of these are involuntary unlike somatic neurons which are voluntary.
• Autonomic motor pathways contain two motor neurons unlike other pathways.
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• The two neurons are called the preganglionic neuron and the postganglionic neuron.
• The preganglionic neuron in in the CNS, either in the gray matter of the spinal cord or the nucleus of the brainstrem.
• The postganglionic neuron lies entirely in the PNS.
• Somatic neurons only have one neuron and effect tissues directly.
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• Somatic motor neurons (voluntary) release ACh (actetylcholine) as their neurotransmitter.
• Autonomic motor neurons release ACh and norepinephrine. (NE)
• The motor part of the autonomic nervous system has two parts: the sympathetic and the parasymphatic divisions.
• Some organs have dual innervation and receive impulses from both divisions.
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Sympathetic Division• The sympathetic division usually excitesor
stimulates a neuron or pathway.
• Examples could be increased heart rate, increased breathing, sweating, pupil dilation…etc
• “E” situations- exercise, emergency, excitement, embarrassment
• Produces fight or flight responses.
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Parasympathetic Division
• This division emphasizes rest and digest activities.
• SLUDD- salivation, lacrimation, urination, digestion, and defecation.
• Decreases heart rate, decreased breathing, decreased blood pressure.
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Vocabulary Words• Sympathetic nervous system
• Parasympathetic nervous system
• Acteylcholine
• Norepinephrine
• Pre-ganglionic neuron
• Post-ganglionic neuron
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Chapter 12 Special Senses• Sensation is the conscious or
subconscious awareness of external and internal conditions of the body.
• For a sensation to occur, four conditions must be achieved.
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• 1. A stimulus or change in the environment capable to activating sensory neurons must occur.
• 2. A sensory receptor must convert the stimulus to an electrical signal.
• 3. The nerve impulses must be conducted along a neural pathway to the brain.
• 4. A region of the brain must receive and integrate the nerve impulses into a sensation.
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• Adaptation of receptors can occur so that the sensation is no longer perceived or the sensation decreases in intensity.
• Example are clothes or temperature.
• Many special senses protrude into the limbic system which invokes emotions and memories associated with that sense.
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Focus: The Eye• Cornea-covers the eye and helps focus
the light
• Sclera- dense connective tissue, the “white” of the eye, protects and gives shape.
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• Ciliary bodies- muscle- alter the shape the lens for distance or near viewing. Processes- secrete aqueous humor.
• Lens-transparent structure that focuses light on the retina- elastic protein.
• iris- colored part, contains smooth muscle.
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• Pupil-hole in the center that lets light in
• Retina- inner coat of the eyeball and where light focuses for sight.– Contains rods that detect light and cones that
detect color.
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• Aqueous humor- (front of eye)fluid filled cavity, maintains shape of eyeball
• Vitreous humor (body) (back of eye)-jelly like fluid keeps eyeball from collapsing.
• Optic nerve-sends messages from the photoreceptor cells to the brain to be processed.
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