Transcript File

Warm-Up
1. Name the 2 main organs of the nervous system.
2. Draw and label the parts of a neuron.
Warm-Up
• Label the parts of the neuron below.
A
D
C
B
G
E
F
Warm-Up
1. One neuron transmits a nerve impulse at 40
m/s. Another conducts at the rate of 1 m/s.
Which neuron has a myelinated axon?
2. List the following in order:
A. K+ channels open and K+ floods out of cell
B. Membrane is polarized (resting potential)
C. Neurotransmitters are released from vesicles into
synaptic cleft
D. Na+ channels open and Na+ floods into cell
E. Stimulus triggers membrane depolarization
3. What restores the resting potential of a
neuron?
The Nervous System
Chapter 9
Nervous System
• Master controlling and communicating system
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Thinking
Memory
Movement
Interpreting the world
Coordination
Homeostasis
Basic Functions
1. Sensory input – gather information
1.
Detect changes inside & outside of the body
1.
Light, sound, temperature, [oxygen], internal environment
2. Integration – process and interpret sensory input
1.
Receive impulses from sensory neurons and consciously or subconsciously act
upon them
3. Motor output – response by muscles and glands
1.
1.
Act on “decisions” made by sensory and integrative neurons and send message
to effectors
Muscle contraction or gland secretion
Organization
A. Central Nervous System (CNS)
▫ Brain & spinal cord
▫ Integrative and control centers
B. Peripheral Nervous System (PNS)
▫ Nerves (spinal nerves, cranial nerves)
▫ Communication lines between CNS and rest of body
▫ Two Divisions:
1. Sensory (afferent) Division: Sensory receptors  CNS
2. Motor (efferent) Division: CNS  effectors (muscles &
glands)
Motor Division
• Somatic nervous system (voluntary) – control skeletal muscles
• Autonomic nervous system (ANS) (involuntary) – regulate smooth
muscles, cardiac, glands
▫ Subdivisions: sympathetic & parasympathetic
Divisions of the ANS
• Sympathetic Nervous System
▫ Used when the body needs
to expend energy
▫ “Fight or Flight” response
• Parasympathetic Nervous
System
▫ Maintain homeostasis under
normal conditions
Nervous Tissue
1. Neurons (mass of nerve cells) - transmit
message
1. Three types:
1.
Sensory, motor, and interneurons
Anatomy:
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Cell body – contains nucleus; metabolic center
Dendrite – fiber that conveys messages toward
cell body
Axon – conduct nerve impulses away from the
cell body
Axon terminals – end of axon; contain
neurotransmitters & release them
Synaptic cleft/synapse – gap between neurons
Nervous Tissue
2. Neuroglia Cells (supporting cells)
CNS: astrocytes, microglia, ependymal cells, oligodendrocytes
 barrier between capillaries and neurons
 protect neurons
 immune/defense
 line brain and spinal cord cavities
 wrap nerve fibers
 produces myelin sheaths (covering)
PNS: Schwann cells, satellite cells
 surround large neurons
 protect & cushion
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Myelin: whitish, fatty material that covers nerve fibers to speed up nerve
impulses
Schwann cells: surround axons and form myelin sheath
Myelin sheath: tight coil of wrapped membranes
Nodes of Ranvier: gaps between Schwann cells
Synaptic Knob: round structure at end of axon that sends nerve impulse
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Dendrites lack Synaptic Knob, causing one-way nerve impulse
• Ganglia: collections of cell bodies
• Bundles of nerve fibers = tracts (CNS) or nerves (PNS)
• White matter: dense collections of myelinated fibers
▫ CNS myelinated; smooth/quick impulses
• Gray matter: unmyelinated fibers & cell bodies
▫ PNS unmyelinated; slow impulse (infant brain)
Classification of Neurons
1.
Functional Classification: direction nerve impulse is traveling
• Afferent (sensory)
▫ To the CNS
• Efferent (motor)
▫ Away from the CNS
• Interneurons
▫ Connect impulses
2.
Structural Classification: # processes extending from
cell body
Multipolar
Bipolar
Unipolar
1 axon, several
dendrites
1 axon, 1 dendrite
1 process
Most common
(99%)
Rare
Short with 2
branches (sensory,
CNS)
Eg. Motor
neurons,
interneurons
Eg. retina, nose,
ear
Eg. PNS ganglia
Nerve Impulses
Neuron Function
1. Irritability: ability to respond to stimulus & convert to nerve
impulse
2. Conductivity: transmit impulse to other neurons, muscles, or
glands
Exciting a Neuron:
• Cell membrane at rest = polarized
▫ Lots Na+ outside cell, lots K+ inside cell
▫ Inside is (-) compared to outside
• Stimulus  excited neuron (Na+ rushes in)  becomes depolarized
• Depolarization activates neuron to transmit an action potential
(nerve impulse)
▫ All-or-none response
▫ Impulse conducts down entire axon
• K+ diffuses out  repolarization of membrane
• Na+/K+ ion concentrations restored by sodium-potassium pump
(uses ATP)
Resting membrane potential (-70mV)
Gated Ion Channels (Na+ and K+)
Depolarization
• Saltatory conduction: electrical signal jumps from node to node
along myelinated axon (30x faster!)
• IMPULSE TRAVELS IN ONE-WAY DIRECTION
Multiple Sclerosis (MS)
• Autoimmune disease
• Myelin sheaths destroyed  reduced to hardened lesions
(scleroses)
• Blindness, muscle weakness, speech disturbance, urinary
incontinence
• Treatment: interferons, glatiramer (hold off attacks)
Nerve Conduction
• Action potential reaches axon
terminal  vesicles release
neurotransmitters (NT) into
synaptic cleft
• NT diffuse across synapse  bind
to receptors of next neuron
• Transmission of a nerve impulse
= electrochemical event
Neurotransmitters
• 50+ identified
• Excitatory: cause depolarization
▫ Ex. Acetylcholine, norepinephrine
• Inhibitory: reduce ability to cause action potential
▫ Ex. Dopamine and glycine
Neurotransmitters
Neurotransmitter
Action
Affected by:
Acetylcholine
muscle contraction
botulism, curare
(paralytic), nicotine
Dopamine
“feeling good”
cocaine,
amphetamines
Serotonin
sleep, appetite, nausea,
mood, migraines
Prozac, LSD,
ecstasy
Endorphins
inhibit pain
morphine, heroin,
methadone
GABA
main inhibitory NT
alcohol, Valium,
barbiturates
Epilepsy
• Abnormal & excessive
discharge of impulses to
skeletal muscles
• Neurotransmitters depleted
• Dilantin
▫ stabilizes Na+ so impulses
aren’t over used
• Anesthetics
▫ block permeability of Na+
so pain can’t be sensed
▫ http://www.youtube.com/
watch?v=MNQlq004FkE
Types of Nerves
• Sensory Nerves
▫ conduct impulses to the brain
• Motor Nerves
▫ carry impulses to the effectors
• Mixed Nerves
▫ both sensory and motor functions
▫ most typical type found
Spinal Cord
• Slender column of nerve cells that pass downward from the brain
into the vertebral canal
• “Begins” at the Foramen magnum
• Ends at the intervertebral disc between L1 and L2 vertebrae
Structure of the Spinal Cord
• 31 segments – each has a pair of spinal nerves
▫ Cervical Enlargement
 Thickening in the neck region; supplies nerves to the upper limbs
▫ Lumbar Enlargement
 Thickening in the lower back region; supplies nerves to the lower
limbs
▫ Nerve Tracts
 Bundles of myelinated nerve fibers; make up major nerve pathways
▫ Central Canal
 contains cerebrospinal fluid
 Fluid in the ventricles of the brain, meninges and the central
canal of the spinal cord
Functions of the Spinal Cord
• Two major functions:
▫ Conducting nerve impulses
▫ Center for spinal reflexes
• Axons supply 2-way communication between brain and body
▫ Ascending tracts
 Relay message to the brain
▫ Descending tracts
 Relay motor impulses from the brain to muscles and glands
• Center for spinal reflexes  reflex arcs pass through spinal cord
▫ Knee jerk
▫ Withdrawal
Reflexes
• Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
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Eg. jerking away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles, heart,
glands
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Eg. salivation, digestion, blood pressure, sweating
Reflex Arc (neural pathway)
Five elements:
1. Receptor – reacts to stimulus
2. Sensory neuron
3. CNS integration center
4. Motor neuron
5. Effector organ – muscle or gland
Reflex Lab
• Patellar Tendon Reflex (knee jerk)
▫ Sit on lab bench and tap lightly on
partners leg right below the patella
• Achilles Tendon Reflex (ankle-jerk)
▫ Hold partners foot in a relaxed
manner
▫ Using the palm of your hand, tap
the Achilles tendon and record
response
Babinski sign (Plantar Reflex)
• Rub a pencil eraser from heel to toe on the outer
edge of the sole of partners foot
▫ Normal response – foot curls
▫ Abnormal response – toes extend
 Normal under 2 years of age b/c the nervous
system is not completely developed
 Later in life, it is a sign of a CNS problem
Babinski Reflex
Static Equilibrium
• Stand with arms at side, feet square,
shoulders level
▫ Eyes open
▫ Eyes closed
▫ After twirling
Spatial Orientation
• Take index fingers and press tips together with
arms straight out
▫ Eyes open
▫ Eyes closed
▫ After twirling
Ciliospinal Reflex
• Rub one side of your partners neck lightly with a
cotton swab
▫ Look for a change in pupil size on that side
Convergence Reflex
• Sit off the side of your partner and have them focus
on distant object for 20 seconds
• Then quickly focus on an object 10-12 inches in
front of face
▫ Look for a change in pupil size
Voluntary Reactions
• More neurons and synapses are involved  longer response times
Reflex = Involuntary Reaction
Voluntary Reaction
1.
List and describe the 5 elements of a reflex arc.
2.
List an example of a reflex.
3.
What is the difference between a reflex and a voluntary
reaction?
1.
2.
3.
4.
Cerebral
Hemispheres
Diencephalon
Brain stem
Cerebellum
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L & R hemispheres
Corpus callosum: large fiber tract; connects 2 hemispheres
Lobes: major regions (named for cranial bones)
 Parietal, frontal, occipital, temporal
Gyri (gyrus) = elevated ridges of tissue
Sulci (sulcus) = shallow grooves
Fissures = deeper grooves, separate large regions of brain
Motor & sensory function: opposite hemispheres
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Hemisphere Dominance
 Dominant Hemisphere
▪ speech, writing, reading
▪ verbal, analytical, computational skills
 Non-dominant hemisphere
▪ motor tasks, interpreting music, nonverbal visuals
▪ emotional and intuitive thinking
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Outermost layer; grey matter
“Executive suite”  conscious mind
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Ventricles
 Reservoirs of cerebrospinal
fluid
▪ Helps protect and cushion
the brain
▪ Responsible for
transporting nutrients and
removing waste from the
brain and spinal cord
3 main structures:
1. Thalamus: relay station for incoming info
2. Hypothalamus:
A.
B.
C.
D.
E.
F.
3.
Autonomic control center (heart rate, BP, digestion)
Emotional response (limbic system)
Body temperature regulation
Regulate food intake
Sleep-wake cycles
Control endocrine system  pituitary gland at base
Epithalamus: pineal gland (sleep-wake cycle)
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Programmed, automatic behaviors
for survival
3 regions:
1. Midbrain: vision, hearing, reflex
2. Pons: breathing
3. Medulla oblongata: heart rate, BP,
breathing, swallowing, vomiting,
coughing, sneezing
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Balance, equilibrium, timing of skeletal muscle activity
Meninges: connective tissue covering CNS structures
 Dura mater (leathery outer), arachnoid mater (web-like middle), pia
mater (surface of brain)
 Meningitis: inflammation of meninges; bacterial or viral infection
 Cerebrospinal fluid (CSF): watery cushion to protect NS from trauma
 Lumbar (spinal) tap – test for infection, tumors, multiple sclerosis
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Bacterial  antibiotics
Herpes meningitis  anti-viral meds
IV fluids
Prevention: vaccines for bacterial infections (HiB)
NO:
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Urea
Toxins
Proteins
White blood cells
Bacteria
Most drugs
YES:
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Water
Glucose
Amino acids
Gases
Fat-soluble substances
Some drugs:
anesthetics, alcohol,
nicotine
12 pairs of cranial nerves that originate from brainstem (all except one pair)
 I
Olfactory
Smell
 II Optic
Vision
 III Oculomotor
Eyelid movement, lens focus, pupil dilation
 IV Trochlear
Eyeball movement
 V Trigeminal (3)
Eye, mouth, jaw muscle movement
 VI Abducens
Eyeball movement
 VII Facial
Facial expression; taste; tear secretion
 VIII Vestibulocohlear (2) Equilibrium; hearing
 IX Glossopharyngeal
Swallowing and saliva secretion
 X Vagus
Speech, swallowing, heart and smooth muscle impulse
 XI Accessory (2)
Soft palate, pharynx, larynx; neck and back
 XII Hypoglossal
Tongue movement
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31 pairs originate from spinal cord
Cervical Plexuses
 Deep in neck; supply muscles and skin of neck
Brachial Plexuses
 Located deep within shoulders between neck and armpits
 Supply muscles and skin of arm, forearm, and hand
Lumbosacral Plexuses
 Located from lumbar region of back into pelvic cavity
 Supply muscles and skin of lower ab wall, external genitalia, buttocks, legs,
and feet
▪ Major nerve braches include:
▪ Obturator, femoral, and sciatic nerves
Parkinson’s
 Less dopamine released
 Overactive inhibitory movement
 Dopamine can’t pass the blood brain barrier – use L-dopa
Huntington’s
 Dominant gene; late acting
 Neurons deteriorate; unrestrained movement
 Whiplash
 Damage to cervical nerves
 CVA
 Stroke
 Hemorrhage/cessation of blood
flow to the brain
 Cerebral palsy
 Damage to brain tissue at birth
 Permanent, non-progressive
damage to motor control area
Varicella zoster virus
 Must have had chicken pox to develop shingles
 Inflammation of nerves
 No treatment
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Alzheimer’s
 Lesions develop in cortex
 Short term memory loss
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Hydrocephalus
 CSF accumulates in the brain
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Drug tolerance
 physiological response to a particular dose of a drug
becoming less intense over time
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CNS depressants
 Barbiturates
 Opiates
 Cannabinoids
 Hallucinogens