The%20Nervous%20system

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The Nervous system

• The nerve cell is the basic unit of communication
  in the vertebrate nervous system

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Three Classes of neurons

• The Neural circuit consists of
• Sensory neurons
• receptor for stimulus
• Interneuron
• integrate signals
• Motor neuron
• transfer signal to effector (muscle)

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Anatomy of a Neuron

• Cell body functional portion
• Dendrites short extensions that receive signals
• Axon long extension that transmits impulses

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How does a neuron hold and move info?

• A neuron at rest has a voltage difference across
  the plasma membrane called a resting voltage
  potential
• An action potential is when this charge across
  the membrane is briefly switched
• The action potential moves down the membrane at a
  rapid pace.
• Ap can move faster over mylenated portions is
  called saltatory conduction

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How does a signal move from one neuron to another?

• A synaptic cleft divides 2 neurons
• The AP will not move across the synaptic cleft
• Neuro transmitters are released by the signal
  cell to the receiver cell
• Move by diffusion

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Types of chemical synapse

• Acetylcholine neuromuscular junctions, glands,
  brain and spinal cord
• Norepinepherine affects brain regions concerned
  with emotions, dreaming

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Paths of information flow

• Signals between the brain and spinal cord move to
  the body regions by nerves

• Sensory nerves move a signal towards the brain
  and spinal cord
• Motor neurons move a signal from the brain or
  spinal cord to the body

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Divisions of the nervous System

• Central nervous system
• CNS
• Is the brain and spinal cord

• Peripheral nervous system
• PNS
• all nerves that carry signals to and from the CNS

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Parts of the PNS

• Sensory Division carries info to the brain and
  spinal cord.
• Motor Division carries info from the brain to
  the bodies effectors (things that do the work)

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The Motor division of the PNS has 2 divisions

• Somatic nerves relay commands to and from
  skeletal muscle
• Voluntary control

• Autonomic nerves send signals to and from smooth
  muscles
• Involuntary control
• Sympathetic
• Parasympathetic

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The autonomic divisions

• Parasympathetic
• slow down the body activity when the body is not
  under stress
• Rest and digest

• Sympathetic
• increase overall body activity during times of
  stress, excitement or danger
• fight or flight response
• hormone epinephrine

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Sympathetic and Parasympathetic

• Are Antagonistic
• Work towards the automatic, subconscious
  maintenance of homeostasis.

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Components of the CNS

• Spinal cord
• 31 pair of spinal nerves
• Grey matter
• White matter
• Controls some reflex actions like bladder emptying

• Brain parts
• Hindbrain
• medulla oblongata
• cerebellum
• pons
• Midbrain
• Forebrain
• cerebrum
• thalamus
• hypothalamus

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Other parts of the CNS

• The two cerebral hemispheres communicate through
  the corpus collosum
• left verbal skills
• right nonverbal skills such as music math,
  abstract
• Brain cavities and Canals
• cerebrospinal fluid surrounds and fills in
  cavities in the brain
• Blood Brain barrier- controls what moves into the
  brain. Will prevent infections.

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Our state of consciousness

• The CNS governs sleeping, dozing, daydreaming and
  full alertness
• neurons of the reticular activating system
  control the changing levels of consciousness by
  releasing serotonin.

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Limbic system

• Involved in both memory and emotion.
• Is involved with behavior.
• Odors pass through this system and may influence
  or behavior and emotions.

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Memory

• Association is the linkage of information to
  structural and chemical changes
• short term- few bits lasts a couple of hours
• Long term- permanent and limitless

• The most important info goes rapidly into long
  term storage
• memory is stored in a form resistant to
  degradation
• Possibly caused by changes in synapses.

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Tips on studying

• Concentrate on what you study.
• Minimize interference.
• Study takes time.
• Break material into smaller portions.
• Rephrase materials in your own words.
• Test yourself to see what you know.

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Disorders of the nervous system

• Trauma
• Infections
• Transmission and synaptic defects.
• Abnormal growth

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Sensory Reception

• If a tree falls in the woods with no one to
  listen does it make a sound?

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Receptors

• Are the actual structures that respond to our
  environment.
• Each receptor will respond to a different signal.
• Essentially translators, they translate an energy
  into one that can be perceived by the brain.

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Sensory systems consist of

• Each system has 3 parts
• 1) sensory receptors.
• 2) pathway to the brain.
• 3) region of the brain that recognizes this
  section.

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Types of sensory Receptors

• Chemoreceptors
• Mechanoreceptors
• Thermoreceptors
• Nociceptors
• Photoreceptors

• olfaction and taste
• touch, stretch, hearing, equilibrium
• radiant energy, infared
• pain receptors
• light

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Sensory Pathways

• If a receptor is stimulated enough it results in
  an action potential.
• The action potential reaches the brain.
• The stronger the stimulus the greater number of
  action potentials reach the brain.
• Sensory adaptation is when the action potentials
  are reduced by a constant stimulus.
• Certain receptors will not adapt.

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Somatic sensations

• Mechanoreceptors that respond to changes or
  constant pressure
• Increase in temperature causes and increase in AP
• Respond to intense stimulus on other receptors,
  cannot be ignored
• Mechanoreceptors give measurement as to the
  location of all the muscles and bones in a given
  moment.

• Touch Pressure
• Temperature
• Pain
• Muscle sense

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Limb position, length and tension

• How do we know where we are at?

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Referred pain
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Taste and Smell

• Gustation Taste
• Receptors located on tongue, roof of mouth,
  throat and palate
• Four tastes
• sweet
• sour
• bitter
• salty

• Olfaction smell
• detect chemicals
• olfactory bulbs in brain interpret smell
• smell is often combined with emotion

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Taste

• Taste Bud 25 cells
• Taste hairs project into mouth
• Hairs contain receptors
• Categories
• Sweet
• Sour
• Salty
• bitter

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Hearing

• Acoustical receptors detect vibrations
• The ear
• In the organ of corti loudness is determined by
  The total number of cells that are stimulated
• Pitch depends on frequency of vibration

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Balance

• Vestibular apparatus
• Closed system of fluid filled sacs
• Contain otoliths that detect changes in
  orientation as well as acceleration

• Overstimulation of the hair cells of the
  vestibular apparatus results in motion sickness

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Vestibular apparatus
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The Eye
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Structure of the eye

• Outer sclera (white) (is all the way around)
• Cornea (clear)
• Pupil (opening to the back)
• Lens (transparent)
• Retina (back side has photoreceptors and support
  material)
• Fovea has highest concentration of photoreceptors.

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Regulating light amount

• The iris adjusts to amount of light entering the
  eye.
• The lens goes through accommodation to adjust
  lens curvature (as we age the lens cannot buldge
  enough to focus on a close object)

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Light must reach the sensors by going through
neurons.

• Outermost layer is pigmented to absorb light not
  absorbed by the sensors
• Photoreceptors are in middle layer
• Translucent neurons and ganglions are on top of
  the photoreceptors.

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Production of Action Potentials by Rods and Cones

• Within these cells flattened disks contain
  photopigment
• When this protein absorbs light it changes
  conformation, if enough are activated they cause
  an action potential.
• Rods contain rhodopsin and are most sensitive to
  dim light
• Cones contain different pigments

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Rods and Cones

• Bright light tends to use more cones, 300x more
  sensitive
• Dim light uses Rods and Rhodopsin, it is broken
  apart by light and must be remade (hence the 5-10
  minute wait to see in darker areas)

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Signaling to visual perception

• Photoreceptors are in the retina
• When rods or cones are stimulated they send a
  signal to the brains visual cortex.
• In the brain the final interpretation makes sense
  of sight

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Problems with the Eyes

• Retinal detachment retina separates form choroid
• Cataracts lens becomes opaque
• Color blindness Inability to distinguish
  colors, is a genetic disease, lacks specific
  types of cones

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The Endocrine system

• The oldest method of control is using a signal
  molecule that moves from one part of the body to
  the other

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The Endocrine System Regulates

• Salt and water balance
• Blood pressure
• Stress responses
• Digestion
• Cellular metabolism
• Production of RBCs
• Growth and development

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Location of Endocrine Glands
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Hormones and other signal molecules

• Hormones molecules secreted by glands into the
  blood that move to a nonadjacent target
• Neurotransmitters act on a directly adjacent
  cell
• Local signaling molecule act quickly and degrade
  quickly
• Pheromones secreted by glands and target cells
  in other organisms

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Signaling Mechanisms

• Requirements
• Cells that secrete the signal molecule are either
  within a gland or nervous tissue
• The signal molecule
• Steroid hormone (fat soluble will move through
  the plasma membrane)
• Non steroid hormone (peptides and other molecules
  must bind to a receptor on the cell)
• Target cell

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Target cell activities

• Different hormones activate different cellular
  response mechanisms
• No all cells have receptors for all hormones

Three possible hormones
A cell with a single receptor on it
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Characteristics of the Endocrine system

• Each hormone acts only on certain cells
• Cells respond only when they have receptors
• Is slower than nervous system control
• Endocrine and nervous system to interact with one
  another.

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Interaction of Endocrine System and Nervous System
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Negative Control using Hormones
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The pancrease an endocrine and an exocrine gland

• Glucagon raises blood sugars, release of stores
  and AA metabolism
• Insulin lowers blood sugars opposes glucagon
• Somatostatin inhibits secretion of the above
  enzymes

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Bracketing using hormones
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Regulation of Blood Calcium concentration

• Increase Calcium
• Parathyroid Hormone removes calcium and
  phosphate from bone, increase absorption,
  retention of calcium in kidneys
• Decrease of Calcium
• Calcitonin

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Oxytocin and nursing, a cascade of events

• At the end of pregnancy, Estrogen rise.
• Uterus produces more oxytocin receptors
• Fetus produces oxytocin, starts a cycle of
  material production of oxytocin
• Oxytocin is a part of the neuroendocrine reflexes
  and will help in the smooth muscle contractions
  which cause the release of milk.

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