Nervous System Structure

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Nervous System Structure

• Biology 12

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The Miracle of Mind

• Imagine you are on a beach. What do you feel?
  What do you see? Smell?
• You can recreate the experience of being at the
  beach without any external stimuli.
• How is this possible?

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• What is pain? What is pleasure? What are
  thoughts?
• We know the brain is made up of cells but how
  does the miracle of the mind emerge from this
  mass of cells?
• The human Nervous System is a whole that is far
  greater than the sum of its parts.

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• ...from the brain, and from the brain only,
  arise our pleasures, joys, laughter and jests, as
  well as our sorrows, pains griefs and tears.
  Through it, in particular, we think, see, hear...
  Eyes, ears,
• tongue, hands and feet act in accordance with
  the discernment of the brain.
• Hippocrates

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Mystery of the Mind

• Much of what we know about the brain is drawn
  from inferences.
• There remain many unanswered questions... This
  makes neuroscience so fascinating!

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The NS must accomplish the following

1. Receive sensory messages that provide information
   about the external environment
2. Organize that information and integrate it with
   other, already stored information in useful ways.
3. Use the integrated information to send out
   messages to the muscles and glands to produce
   organized movements and adaptive secretions

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• 4. Provide the basis for what we call conscious
  experience the stream of perceptions, thoughts
  and feelings that make up our mental life!

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Divisions of the Nervous System
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Central Nervous System

• The brain the spinal cord
• The center of
• integration and control

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Peripheral Nervous System

• The nervous system outside of the brain and
  spinal cord
• Consists of
• 31 Spinal nerves
• Carry info to and from the spinal cord
• 12 Cranial nerves
• Carry info to and from the brain

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Autonomic Nervous System

• Can be divided into
• Sympathetic Nervous System
• Fight or Flight
• Parasympathetic Nervous System
• Rest and Digest

These 2 systems are antagonistic. Typically,
we balance these 2 to keep ourselves in a state
of dynamic balance - homeostasis.
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ANS

• organs of our body, such as the heart, stomach
  and intestines, are regulated by the autonomic
  nervous system (ANS).
• part of the peripheral nervous system
• controls many organs and muscles within the body.
  
• functions in an involuntary, reflexive manner.
  For example, we do not notice when blood vessels
  change size or when our heart beats faster.

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The ANS is most important in two situations

• 1. In emergencies that cause stress and require
  us to "fight" or take "flight" (run away)
• 2. In non-emergencies that allow us to "rest"
  and "digest."

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What does the ANS regulate?

• Muscles
• in the skin (around hair follicles smooth
  muscle)
• around blood vessels (smooth muscle)
• in the eye (the iris smooth muscle)
• in the stomach, intestines and bladder (smooth
  muscle)
• of the heart (cardiac muscle)
• Glands

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Sympathetic Nervous System

• It is a nice, sunny day...you are taking a nice
  walk in the park.
• Suddenly, an angry bear appears in your path.

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• Do you stay and fight OR do you turn and run
  away?
• These are "Fight or Flight" responses.
• In these types of situations, your sympathetic
  nervous system is called into action - it uses
  energy - your blood pressure increases, your
  heart beats faster, and digestion slows down.

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• The sympathetic nervous system originates in the
  spinal cord. Neurons lead to the "target" -
  either a muscle or a gland.
• Adrenalin is involved in the activation of this
  system.
• So

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• This is why you may pee when you are surprised by
  a bear?
• This tid-bit will impress your friends!

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Parasympathetic Nervous System

• You fight off the bear and the danger is over.
• This calls for "Rest and Digest" responses. Now
  is the time for the parasympathetic nervous to
  work to save energy - your blood pressure
  decreases, your heart beats slower, and digestion
  can start.

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• Sympathetic changes are detected by polygraphs to
  help determine when someone is lying!
• These two systems are antagonists they are
  opposites of each other.

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ANS fun animation

• http//itc.gsw.edu/faculty/gfisk/anim/autonomicns.
  swf

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The Neuron

• The neuron is the basic functional unit of the
  nervous system.
• Function Send impulses to and from the CNS and
  PNS and the effectors (muscles/glands)

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Neuron Structure
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• Dendrite ? Fine hair-like extensions on the end
  of a neuron.
• Function receive incoming stimuli.
• Cell Body or Soma ? The control center of the
  neuron.
• Function Directs impulses from the dendrites to
  the axon.
• Nucleus ? Control center of the Soma.
• Function Tells the soma what to do.

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• Axon? Pathway for the nerve impulse (electrical
  message) from the soma to the opposite end of the
  neuron.
• Myelin Sheath ? An insulating layer around an
  axon. Made up of Schwann cells.
• Nodes of Ranvier ? Gaps between schwann cells.
• Function Saltatory Conduction (Situation where
  speed of an impulse is greatly increased by the
  message jumping the gaps in an axon).

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Impulses Along a Neuron

• Dendrites receive the nerve impulse and carry it
  toward the cell body, which contains the nucleus.
• The axon carries the impulse from the cell body
  toward the synaptic knobs/terminals where it will
  be transferred to other neurons.

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Myelinated Vs. Unmyelinated

• Myelinated neurons carry nerve impulses faster
  than unmyelinated ones because the impulse jumps
  from one node of Ranvier to the next, instead of
  traveling along the whole length of the axon.
• This is called saltatory conduction

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3 Types of Neurons

• There are 3 types of neurons.
• Sensory Neurons ? Neurons located near receptor
  organs (skin, eyes, ears).
• Function receive incoming stimuli from the
  environment.
• Motor Neurons ? Neurons located near effectors
  (muscles and glands)
• Function Carry impules to effectors to initiate
  a response.
• Interneurons ? Neurons that relay messages
  between other neurons such as sensory and motor
  neurons. (found most often in Brain and Spinal
  chord).

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Sensory Neurons

• Carries impulses from receptors e.g pain
  receptors in skin to the CNS( brain or spinal
  cord)

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Relay Neuron/Interneuron

• Carries impulses from sensory nerves to motor
  nerves.
• Responsible for integration

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Motor Neuron

• Carries impulses from CNS to effector e.g. muscle
  to bring about movement or gland to bring about
  secretion of hormone

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Nerves

• Nerves ? Collections of neurons that are joined
  together by connective tissue.
• Responsible for transferring impulses from
  receptors to CNS and back to effectors.
• http//www.youtube.com/watch?featureplayer_embedd
  edvxRkPNwqm0mM

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Impulses from PNS to CNS

• Specialized receptors (light, sound, taste,
  touch) react to a stimulus and generate nerve
  impulses in the sensory neurons near them.
• The sensory neurons carry the impulse to the
  spinal cord and then to the brain where
  interneurons interpret the sensory information
• The interneurons send out impulses to motor
  neurons which elicit a response by an effector
  (muscle or gland)

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Reflexes

• The simplest neural pathway is called a reflex
  arc and it does NOT involve the brain
• The pathway is receptor, sensory neuron,
  interneuron in spinal cord, motor neuron, effector

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Reflex Arcs Contd...

• The fact that the decision is made in the
  spinal cord saves the time that it would take the
  nerve impulse to travel through the many circuits
  of the brain.
• Reflexes are often so fast they are involuntary
• Reflexes are important mechanisms that are
  important in maintaining homeostasis

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Reflex Arc Animationshttp//msjensen.cehd.umn.edu
/1135/Links/Animations/Flash/0016-swf_reflex_arc.s
wf
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• http//www.sumanasinc.com/webcontent/animations/co
  ntent/reflexarcs.html

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Structure of a Spinal Nerve

• Label the handout placing the components of the
  reflex arc in the spinal nerve.