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Chapter 9 Nervous Tissue
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
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
• Ganglia- groups of cell bodies outside brain & spinal cord
• Enteric plexuses- networks in digestive tract
• Sensory receptors- monitor changes in internal or external environments
Figure 9.1
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)
Figure 9.2
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
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
Figure 9.3
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
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
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
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
Neuroglia
• ~ half the volume of CNS
• Cells smaller than neurons
• Can multiply and divide and fill in brain areas
• Do not conduct nerve impulses
Types of Neuroglia• Astrocytes- blood brain barrier, provides
nutrients
• Oligodendrocytes- myelin in CNS neurons
• microglia - defense
• Ependymal cells- Cerebral Spinal Fluid production
• Schwann- PNS regeneration of axons, produce myelin sheath
• Satellite cells- in PNS ganglia
Vocabulary Cards• White matter• Gray matter• Neuroglia• Astrocytes• microglia
• Oligodendrocytes• Schwann Cells• Satellite cells• Ependymal cells
Action Potentials• Action potentials = nerve impulses
• Require a membrane potential– electrical charge difference across cell
membrane – like a Battery
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
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
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
• 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
Figure 9.4
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
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.
Active Events• Stimulus to reach threshold
• Na+ channel opens=>
• Na+ ions enter=>
• positive potential=>
• Causes K+ channel opening =>
• repolarization
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
Figure 9.5
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
Figure 9.6a
Figure 9.6b
Vocabulary Words
• Membrane potential• Resting membrane
potential• Action potential
• Depolarizing phase• Repolarizing phase• conduction
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
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
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
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
Figure 9.7
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)
Vocabulary Words
• Synapse• Neurotransmitter
• Leakage channels• Gated channels
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.
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.
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.
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.)
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.
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
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.
Vocabulary Words
• Dura mater
• Arachnoid mater
• Pia mater
• Blood-Brain Barrier (BBB)
• Cerebrospinal Fluid (CSF)
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
Brain Stem• The brain stem consists of three regions:
– Medulla oblongata
– Pons– midbrain
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.
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.
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.
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.
Midbrain• Contain several reflex arcs including:
– Scanning and tracking movements of the eyes
– Pupillary reflex (pupil size)– Accommodation reflex (shape of lens)– Startle reflex
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.
Diencephalon
• The major regions include:– Thalamus– Hypothalamus– Pineal gland
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.
Hypothalamus• 1. Control of ANS-regulate gland
secretion, heart rate, digestion and contraction of urinary bladder
• 2. Control the pituitary gland- release of hormones
Hypothalamus• 3. Regulation of emotional and behavioral
patterns- together with limbic system, regulates feelings of rage, aggression, pain, pleasure and arousal
Hypothalamus• 4. Regulation of eating and drinking- thirst
center- detects changes in osmotic pressure in cells and initiates the sensation of thirst.
Hypothalamus• 5. Control of body temperature- directs
ANS to promote heat loss or heat production depending on stimuli.
Hypothalamus• 6. Regulation of circadian rhythms and
states of consciousness- establish patterns of sleep and waking.
Pineal Gland
• Size of a small pea.
• Secretes melatonin that promotes sleepiness and setting the body’s internal clock.
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.
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.
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.
BRAIN GAMES
• Right/Left Brain Controversey
• Optical Illusions
Vocabulary Cards
• Brain stem-medulla, pons, midbrain
• Diencephalon- thalamus, hypothalamus, pineal gland
• Limbic system• Cerebrum• cerebellum
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.
• 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.
• 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.
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.
Parasympathetic Division
• This division emphasizes rest and digest activities.
• SLUDD- salivation, lacrimation, urination, digestion, and defecation.
• Decreases heart rate, decreased breathing, decreased blood pressure.
Vocabulary Words• Sympathetic nervous system
• Parasympathetic nervous system
• Acteylcholine
• Norepinephrine
• Pre-ganglionic neuron
• Post-ganglionic neuron
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.
• 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.
• 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.
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.
• 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.
• 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.
• 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.