Download Nervous System Lecture

Nervous System
All behavior ultimately has its roots
in the biology of the nervous system
Cells in the Nervous System
The Neuron - Microanatomy
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Neurons are the building blocks of the nervous system
There are approximately 100 billion of them in the nervous system
All neurons have the same basic structures
– Cell body (contains all of the DNA and controls cellular functions)
– Axon (take information away from the cell body)
• Some neurons can be up to 3 or 4 feet long
• Myelin sheathing around fiber helps to increase speed of conduction
(up to 10X the speed, protects the fiber, is found in vertebrate animals,
and is a fat that is critical in the health of the nervous system
– Dendrites (take information to the cell body – about 10000 connections per
neuron!)
– Synapse is the end point of the neuron and is where one neuron
communicates with another
We are born with all of the neurons we will ever have
There is a thinning of neurons some time during adolescence
Sometimes functions lost by some neurons are taken over by other neurons,
this is called plasticity
Typical Neuron
Typical Neurons
Microphysiology – The Action Potential
• Neurons are filled with and surrounded by fluids
• Fluids contain ions (electrolytes) which are Na+, K+, and Cl –
• There are relatively more Na+ outside than inside the neuron
giving the inside a negative charge (-70mv). This is called the
resting potential.
• The charge within the neuron changes when it is stimulated to fire.
This occurs because the membrane opens up.
• The inside of the neuron is momentarily more positive than the
outside (1/1000 second) and it goes up to +40mv. This is called
depolarization.
• The membrane closes quickly and this is followed by a period
when the neuron cannot fire called the refractory period when K+
is being pumped out of the neuron.
• Eventually, the Na+/K+ pump re-establishes the resting potential.
It is said that this process is all or none.
• The process of the action potential is the same in all neurons in
the body and occurs between 200 and 1000 times per second!
• Levels of electrolytes in the body can affect the functioning of the
nervous system.
Action Potential - Exchange of Ions
The Action Potential
Propagation of Action Potential
Macrophysiology – Communications between
neurons in the synapse
• When the impulse of the action potential reaches the
synapse on the pre-synaptic side, the membrane in the
synapse opens and neurotransmitters are released which
stimulate the adjacent membrane, the post-synaptic
membrane, to open and another action potential to occur.
• Neurotransmitters are amino acids or proteins that are
much bigger than the ions within the cells and find specific
receptor sites on the post-synaptic membrane.
• Neurotransmitters can either excite or inhibit the postsynaptic membrane.
• Diet can affect the amount of neurotransmitters in the
nervous system.
The Synapse
Neurotransmitters
Acetylcholine
• Memory (Alzheimer’s Disease)
• Neuromuscular Junction
• Poisoning
– Black Widow Spiders – excess production
– Botulism/Curare – blocks release
Norepinephrine
• Arousal/anxiety
• Depression
Dopamine
• Mood
• Movement/Parkinson’s Disease/tremors (too much)
Serotonin
• Mood
• Schizophrenic symptoms
Endorphins
• Pain mediation
• Natural mechanism within the body
More Neurotransmitters
Ananamide
• Marijuana like neurotransmitter
• Runner’s high
GABA (Gamma Amino Butyric Acid)
• Most abundant inhibitory neurotransmitter
Glutamine
• Most abundant excitatory neurotransmitter
Vasopressin
• Regulates levels of fluids in the body
Oxytocin
• Regulates the production/release of milk
NMDA (n-methyl, d-aspartate)
• Secondary release causes structural and functional changes in the
synapse
Neurotransmitters
The Big Picture of the Nervous System
The Big Picture
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Central Nervous System
– Brain
• Hind Brain (vegetative functions)
• Mid Brain (homeostatic functions)
• Forebrain (higher mental functions)
– Spinal Cord
• Transmission of impulses up/down the spinal cord
• Reflex arc
Peripheral Nervous System
– Autonomic Nervous System
• Fight/Flight Response
– Sympathetic arousal (+)
– Parasympathetic arousal (-)
• Endocrine System
– Production and release of hormones (like NT) into the blood
stream
– Somatic Nervous System
• Sensory (afferent) transmission
• Motor (efferent) transmission
Autonomic Nervous System
Endocrine Glands
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Hypothalamus (Stimulates release of hormones by pituitary gland)
Pituitary Gland (anterior and posterior pituitary)
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Thyroid Gland
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Production of Insulin (absorption of glucose into cells) and glucagon (storage of glucose
as glycogen)
Gonads
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Production of adrenaline/epinephrine during stress
Immune system response
Production of sex hormones
Pancreas
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Use of calcium and potassium in body
Adrenal Glands
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Thyroxin regulates the rate of oxygen consumption
Hyperthyroidism/hypothyroidism
Parathyroid
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Master gland (controls other endocrine glands)
Growth Hormone
Regulates water retention in kidneys
Release of milk after childbirth
Testosterone in men (secondary sex characteristics)
Estrogen/Progesterone in women (secondary sex characteristics)
Pineal Gland
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Melatonin which regulates sleep
The Endocrine System
Anabolic Steroids
Spinal Cord
• Hidden within the spinal column for protection
• Allows for the transmission of impulses to and from the brain
• Sensory impulses leave the spinal column on the back (dorsal) area
of the spinal cord
• Motor impulses return on the front (ventral) area of the spinal cord
• Gray area in the center (butterfly shaped area) are the cell bodies
while the white areas are myelin on axons
• Damage to the spinal cord can affect function from the point of injury
downward called paralysis
– Damage to lower areas of the spinal cord cause paraplegia
– Damage to higher areas of the spinal cord cause quadriplegia
– Damage to one side (front, back, or side) of the spinal cord cause a
hemiplegia
• Spinal reflexes
– The connection of sensory and motor roots by an interneuron allows for
the quick response of the nervous system to avoid further damage to the
body.
– Patellar and ulnar reflexes are examples of spinal reflexes
– Developmental reflexes
Spinal Column
Spinal Cord
The Reflex Arc
Hindbrain (lower center)
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Vegetative functions like breathing, heart rate, blood pressure, and some
auditory & visual reflexes
The brain stem is composed of the
– Medulla Oblongata which is involved in involuntary reflexes including
tongue and eye movements, swallowing, heart rate, respiration,
swallowing, startle response, ability to sleep, sense of balance (vestibular
function)
• Cross laterality exists within the medulla oblongata
– Pons is the relay station for messages going to and from the brain
• Responsible for rapid eye movement during sleep
– Cerebellum smoothes and coordinates body movements
• Especially responsible for complex, repetitive movements
• Balance and equilibrium
• Damage results in jerky tremors, involuntary trembling, walking,
vertigo, slurred speech (scanning speech), dyspraxia
– Reticular Activating System (RAS) is at the top of the brain stem and is
responsible for activation and arousal
• Acts as a valve for sensory messages from lower to higher centers of
the brain
Midbrain
– Limbic System controls instinctive, complex behaviors
• Involved in the display of emotion
– Amygdala produces reactions of rage and aggression when
stimulated
– Septum reduces the intensive of emotional reactions when
stimulated
– Hippocampus is involved in the formation of long term
memories
– Hypothalamus mediates motivational and emotional behaviors and
homeostatic functions like eating, thirst, warming of the body, and
sexual behavior.
– Basal Ganglia is a collection of structures that controls slow body
movements
– Thalamus is a relay station between the cerebral cortex and the lower
areas of the brain.
• Integrates sensory messages and sends them to the cerebral
cortex and is involved in wake-sleep patterns.
The Core of the Brain
Limbic System
More Limbic System – Another view
Emotions and Memory
Forebrain (cerebral cortex)
• Large outer covering of the brain involved in higher
mental functions and voluntary action
• Two hemispheres (right/left)
– Each hemisphere is connected by the corpus
callosum
• Four Lobes with one in each hemisphere
– Frontal
– Temporal
– Occipital
– Parietal
The Cerebrum
Cerebral Layers
Cerebral Complexity
The Cerebral Cortex
Frontal Lobes
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Consciousness
Initiating activity
Judgment
Inhibition of emotional responses
Expressive language
– Broca’s Aphasia (expressive aphasia)
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Assigns meaning to words
Word associations
Motor strip (motor homunculus)
Personality
Speech Centers
The Homunculus – Motor and Sensory Strips
Gateway to Consciousness
Frontal Lobe Problems
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Paralysis
Sequential movement
Loss of spontaneity
Loss of flexibility of thinking
Perseveration
Inattention
Change in social behavior
Changes in personality
Difficulties with problem solving
Broca’s Aphasia
Temporal Lobes
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Hearing ability
Memory (short & long term)
Musical ability
Some visual perception
Categorizing objects
Temporal Lobe Epilepsy
Temporal Lobe Problems
• Difficulty with faces (prosopagnosia)
• Difficulty understanding spoken words (Wernicke’s
Aphasia)
• Disturbance with selective attention to what we see
and hear
• Difficulty with identification of and verbalization about
objects
• Loss of short term memory
• Increase or decrease in sexual behavior
– Kluver-Bucy Syndrome
• Inability to categorize things
• Persistent talking with right lobe damage
• Increase in aggressive behavior
– Kluver-Bucy Syndrome
Occipital Lobes
• Vision
– Primary association area (direct response to visual
stimuli)
– Secondary association area (gives meaning to
those visual stimuli)
Visual Pathways
Occipital Lobe Problems
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Defects in vision (visual field cuts)
Difficulty locating objects
Difficulty identifying colors (color agnosia)
Visual hallucinations
Visual illusions
Word blindness (difficulty recognizing words)
Difficulty recognizing drawn objects
Difficulty identifying movements (movement
agnosia)
• Difficulty reading and writing
Parietal Lobes
• Visual attention
• Touch perception (somatosensory
homunculus)
• Goal directed voluntary movements
• Manipulation of objects
• Integration of different senses that allows for
understanding a single concept (association
cortex)
The Homunculus – Motor and Sensory Strips
Parietal Lobe Problems
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Problems attending to more than one thing at a time
Difficulty naming objects (dysnomia)
Difficulty locating words for writing (dysgraphia)
Difficulty reading (dyslexia)
Difficulty with drawing objects (constructional
dyspraxia)
Difficulty distinguishing left from right
Difficulty doing math (dyscalculia)
Lack of awareness of certain body parts and/or
surrounding space (dyspraxia) that lead to difficulty in
self-care (right side neglect)
Difficulty focusing visual attention
Difficulty with eye/hand coordination
Hemisphere Differences
• Each hemisphere has specific functions
– Left – usually dominant and is involved in speech &
language
– Right – usually involved in expression and
interpretation of emotion and processing visualspatial (artistic) information
Hemisphere Differences
Imaging Techniques
• The last three decades has seen a tremendous advance in noninvasive diagnostic techniques
• EEG was used since the 1940’s but has limited use and limited
advantages
• X-ray techniques are also limited to examination of bony
structures of the skull
• CAT (computerized axial tomography) allows for the investigation
of brain in two dimensions
• MRI (magnetic resonance imaging) utilizes large external magnets
to provide a rich three dimensional image of the brain
• fMRI (functional magnetic resonance imaging) allows for the
investigation of the brain while engaged in activity
• PET (positron emission tomography) uses irradiated glucose to
investigate the metabolism of brain tissue under specific
conditions
MRI
PET Scan