Transcript The Nervous System

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
Nervous System
• Master controlling and communicating system
Basic Functions
1. Sensory input – gather information
2. Integration – process and interpret sensory input
3. Motor output – response by muscles and glands
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
Nervous Tissue
1. Neurons (nerve cells) - transmit message
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. Supporting cells (Neuroglia)
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
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Ganglia: collections of cell bodies
Bundles of nerve fibers = tracts (CNS) or nerves (PNS)
White matter: dense collections of myelinated fibers
Gray matter: unmyelinated fibers & cell bodies
It’s a Mad, Mad, Mad Neuron
Classification of Neurons
1.
Functional Classification: direction nerve
impulse is traveling
Sensory
neurons
Motor
neurons
Interneurons
carry impulses
from sensory
receptors to CNS
carry impulses
from CNS to
muscles & glands
connect sensory &
motor neurons
Vision, hearing,
equilibrium, taste,
smell, pain,
pressure, heat
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
▫ Na+ outside cell, 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 sodiumpotassium 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!)
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
Neuron Talk
Neurotransmitters
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50+ identified
Excitatory: cause depolarization
Inhibitory: reduce ability to cause action potential
Eg. acetylcholine, serotonin, endorphins
Mouse Party
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
Reflexes
• Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
▫
Eg. jerking away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles,
heart, glands
▫
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 Activities
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
Patellar (Knee-jerk)
Reflex
• Stretch reflex
• Tapping patellar ligament
causes quadriceps to
contract  knee extends
• Help maintain muscle
tone, posture, & balance
Pupillary Reflex
• Optic nerve  brain stem
 muscles constrict pupil
• Useful for checking brain
stem function and drug
use
Flexor (withdrawal) reflex:
painful stimulus  withdrawal of
threatened body part
▫ Pin prick
Plantar reflex:
draw object down sole of foot 
curling of toes
▫ Babinski’s sign: check to see if
motor cortex or corticospinal tract
is damaged
Voluntary Reactions
• More neurons and synapses are involved 
longer response times
Reflex = Involuntary Reaction
Voluntary Reaction
Warm-Up
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?
Human Brain
4 Major Regions
1. Cerebral
Hemispheres
2. Diencephalon
3. Brain stem
4. Cerebellum
1.
Cerebral Hemispheres (Cerebrum)
 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
• Grey matterCortex
Cerebral
• “Executive suite”  conscious mind
Functions of the Major Lobes
2.main
Diencephalon
3
structures: (interbrain)
1. Thalamus: relay station for incoming info
2. Hypothalamus:
A.
B.
C.
D.
E.
F.
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
3. Epithalamus: pineal gland (sleep-wake cycle)
Diencephalon
3. Brain Stem
• 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
Brain Stem
4. Cerebellum
• Balance, equilibrium, timing of skeletal muscle
activity
Protection of CNS
• 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
Meningitis
Symptoms of Meningitis
Treatment
for Meningitis
• Bacterial  antibiotics
• Herpes meningitis  antiviral meds
• IV fluids
• Prevention: vaccines for bacterial infections
(HiB)
Blood-Brain Barrier: endothelial cells in
capillaries prevent substances from crossing
into brain
NO:
YES:
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Urea
Toxins
Proteins
White blood cells
Bacteria
Most drugs
Water
Glucose
Amino acids
Gases
Fat-soluble
substances
• Some drugs:
anesthetics, alcohol,
nicotine
The Senses
Special senses
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Smell
Taste
Sight
Hearing
“Touch” = temperature + pressure +
pain of skin, muscles, & joints
• Equilibrium (in the ear)
• Large complex
organs (eyes, ears)
Sensory
Receptors
• Localized clusters of receptors (taste
buds, olfactory epithelium)
Vision Tests
Are the squares inside the blue and
yellow squares all the same color?
Bezold effect
The smaller squares inside the blue and
yellow squares are all the same color.
They seem different (magenta and orange)
because a color is perceived differently
depending on its relation to adjacent
colors (here blue or yellow depending on
the outer square).
Are the horizontal lines straight or
crooked?
Café Wall Illusion
The horizontal lines are straight, even
though they do not seem straight. In this
illusion, the vertical zigzag patterns
disrupt our horizontal perception.
Does Lincoln’s face look
normal?
Some neurons in the brain seem specialized in
processing faces. Faces are usually seen upright.
When presented upside down, the brain no longer
recognizes a picture of a face as a face but rather as an
object. Neurons processing objects are different from
those processing faces and not as specialized. As a
consequence these neurons do not respond to face
distortions as well. This explains why we miss the
weird eyes when the face is inverted.
Can you see a baby?
Illusory Contour
The baby’s head is on the left, the baby’s feet
are against the trunk of the tree on the right.
Illusory Contour: a form of visual
illusion where contours are perceived
without a luminance or color change across
the contour
How quickly can you say the
color of the words below?
Taste Tests
Jellybean Test
Flavor = taste + smell
5 Types of Taste Receptors
Aging
• After age 50, ability to smell and taste
decrease
• Membranes lining nose become thinner &
drier  olfactory nerve deteriorate
• # taste buds decrease with age  more
difficult to detect sweet/salty  foods taste
more bitter
• As people age, their food tastes more bland
 eat less  possible malnutrition
Genetics of Taste
PTC =
phenylthiocarbamide
• Discovered in 1931 by when a DuPont
chemist named Arthur Fox accidentally
released a cloud of fine crystalline PTC in the
lab.
• A nearby colleague complained of the bitter
taste, while Dr. Fox tasted nothing.
• Fox continued to test the taste buds of family
and friends, setting the groundwork for
future genetic studies.
of PTC
PTC(Tas2r38)
Tastingis
•Genetics
Gene for tasting
located on Chromosome 7.
• PAV = taster (T), AVI =
nontaster (t), AAV = another
allele
▫ PAV-PAV = TT = very bitter
▫ PAV-AVI = Tt = somewhat
bitter
TAS2R38
▫ AVI-AVI = tt = nontaster
• General Population: 70% Tasters,
30% Nontasters
Bitter tastes = Result of selection
pressures?
• Thiocynate Compounds (bitter taste)
found in broccoli, cauliflower, mustard
family
▫ Tasters: avoid these foods in diet
▫ Nontasters: more varied diet, include
green leafy veggies
• Thiocynates might inhibit thyroid function
 tasters may have protection against
thyroid diseases
Bitter tastes = Result of selection
pressures?
• Poisons = bitter taste
▫ Tasters: part of hunter-gatherer societies?
• Genetic Drift
▫ Europeans: all 3 alleles (PAV, AVI, AAV)
▫ Asians: AAV allele rare
▫ Native Americans: 98% have PAV allele
only
Denver Museum of Nature and
Science
• Expedition Health: Genetics of Taste
Study
• Purpose of Study:
▫ Is ability to taste bitter compounds related
to what foods you eat, your % body fat, and
BMI?
▫ Is your ability to taste bitter compounds
related to your genetic ancestry?
Substances related to PTC
• Thiourea (thiocarbamide) – very bitter!!!
• Sodium benzoate – sweet, salty, bitter, no taste
▫ Food preservative
Family Pedigree
• Tasters:
▫ Supertasters (TT)
▫ Tasters (Tt)
• Non-tasters (tt)