Nervous System

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Nervous System
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Introduction

• perform the three overlapping functions of
  sensory input, integration, and motor output
• 2 Main Divisions Central Nervous System include
  the brain and spinal cord
• Peripheral Nervous System made up of peripheral
  nerves, cranial nerves, and spinal nerves
• 2 Divisions of Peripheral
• Sensory Division picks up sensory information and
  delivers it to the CNS
• Motor Division carries information to muscles and
  glands
• Divisions of the Motor Somatic carries
  information to skeletal muscle Autonomic
  carries information to smooth muscle, cardiac
  muscle, and glands

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How it Works
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Nerves

• signals of the nervous system are conducted by
  nerves.
• neuron is the structural and functional unit of
  the nervous system. Specialized to transmit
  messages
• impulses are conducted along a neuron.
• Dentrite ? cell body ? axon hillock ? axon
• Some axons are insulated by a myelin sheath
• Dendrites conduct impulses toward the cell body
• Axons conduct impulses away from the cell body
• Axonal terminals contain vesicles with
  neurotransmitters
• Axonal terminals are separated from by a gap
• Synaptic cleft gap between adjacent neurons
• Synapse junction between nerves

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Types of Neurons

• Sensory Neurons are afferent carry impulse to
  CNS
• Interneurons link neurons in the CNS
• Motor Neurons carry impulses away from CNS to
  effectors, muscle
• SUPPORT CELLS Of Nervous System
• Schwann Cells peripheral nervous systemproduce
  myelin sheath
• Oligodendrocytes CNS myelinating cell
• Microglia CNS phagocytic cell
• Astrocytes CNS form scar tissue, mop up excess
  ions, etc, induce synapse formation, connect
  neurons to blood vessels
• Ependymal CNS ciliated line central canal of
  spinal cord line ventricles of brain

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Simple Nerve Path
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2 Main Paths Convergence and Divergence
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Generating and Impulse

• polarized membrane inside is negative relative
  to the outside under resting conditions due to
  distribution of ions controlled by Na/K pump
  that require ATP
• Nerve impulse starts when the membrane of the
  nerve depolarizes due to some stimulus, chemical,
  temp. changes, mechanical ect.
• Depolarization is caused by the influx of Na
  which causes the membrane to become more
  positive. This starts an action potential, or
  nerve impulse. They follow the all or none law!!!
• The membrane will repolarize when K leaves the
  cell setting the membrane back to resting
  potential or polarized
• This de and repolarization continues down the
  nerve until it reaches another nerve to pass on
  the impulse or until it reaches an effector.

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Saltatory Conduction
Appear the jump from node to node. Speed of
impulses is much faster on myelinated nerves then
unmyelinated ones. Speed also increases with
increase in diameter. Ex.) 120m/s skeletal muscle
.5m/s skin
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Neuron Communication
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2 Divisions

• Central nervous system (CNS)-Brain and spinal
  cord.
• contain fluid-filled spaces which contain
  cerebrospinal fluid (CSF).
• The central canal of the spinal cord is
  continuous with the ventricles of the brain.
• White matter is composed of bundles of myelinated
  axons
• Gray matter consists of unmyelinated axons,
  nuclei, and dendrites.
• Peripheral nervous system.
• Everything outside the CNS.

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PNS

• Helps to maintain homeostasis
• Made of cranial nerves that originate in the
  brain and innervate the head and upper body
  and----Paired spinal nerves that originate in the
  spinal cord and innervate the entire body.
• There are efferent and afferent nerves in the
  PNS---efferent carry impulses to effectors like
  muscles or glands these are also called motor
  neurons.
• Afferent carry impulses back to the CNS and are
  called sensory neurons

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Fight or Flight parasympathetic and sympathetic
are the 2 divisions of the Autonomic nervous
system which functions without conscious effort
controls visceral activities regulates smooth
muscle, cardiac muscle, and glands
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Classifying PNS Nerves

• General somatic efferent fiber- carry motor
  impulses from CNS to skeletal muscles
• General visceral efferent fibers- carry motor
  impulses away from CNS to smooth muscles and
  glands
• General somatic afferent fibers- carry sensory
  impulses to CNS from skin and skeletal muscles
• General visceral afferent fibers- carry sensory
  impulses to CNS from blood vessels and internal
  organs
• Special somatic efferent fibers- carry motor
  impulses from brain to muscles used in chewing,
  swallowing, speaking, and forming facial
  expressions
• Special visceral afferent fibers- carry sensory
  impulses to brain from olfactory and taste
  receptors
• Special somatic afferent fibers- carry sensory
  impulses to brain from receptors of sight,
  hearing, and equilibrium

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Cranial Nerves
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Spinal Nerves31 pairs 8 cervical (C1 to C8) 12
thoracic (T1 to T12) 5 lumbar (L1 to L5) 5
sacral (S1 to S5) 1 coccygeal (Co)
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CNSThe Brain and Spinal Cord

• Spinal Cord Carries impulses to and from the
  brain as well as playing a major role in reflexes
  both somatic and autonomic
• extends foramen magnum to 2nd lumbar vertebra
• 31 segments each with a pair of nerves
• Central canal carries CSF
• CSF- Cerebrospinal fluid--Forms a watery cushion
  to protect the brain, Similar to blood plasma
  composition, Circulated in arachnoid space,
  ventricles, and central canal of the spinal cord
• Ventricles- interconnected cavities within
  cerebral hemispheres and brain stem continuous
  with central canal of spinal cord filled with
  cerebrospinal fluid (csf)

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Ventricles
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Spinal Cord Reflex
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The Brain

• Functions interprets sensations, determines
  perception, stores memory, reasoning, makes
  decisions, coordinates muscular movements,
  regulates visceral activities, and determines
  personality

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Development
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Structure and Function

• Brain stem--Consists of the medulla oblongata,
  pons, and midbrain.
• Functions in homeostasis, coordination of
  movement, conduction of impulses to higher brain
  centers
• Medulla Oblongata- Breathing, heart and blood
  vessel activity, swallowing, vomiting, digestion,
  and Relays information to and from higher brain
  centers
• Pons- involved in the regulation of visceral
  activities such as breathing and relays info. to
  higher brain
• Midbrain-integration of sensory information, in
  the regulation of visual and auditory reflexes,
  and relays as well

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Cont

• Reticular Formation- network of nerve fibers
  scattered throughout the brain stem connects to
  centers of hypothalamus, basal nuclei,
  cerebellum, and cerebrum
• filters incoming sensory information
• arouses cerebral cortex into state of
  wakefulness so controls sleep. Involved in motor
  control of visceral organs
• Cerebellum- develops from the metencephalon.
• Functions to error-check and coordinate motor
  activities, and perceptual and cognitive factors.
  Relays sensory information about joints, muscles,
  sight, and sound to the cerebrum. Coordinates
  motor commands issued by the cerebrum. Maintains
  posture

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Cont

• Epithalamus, thalamus, and hypothalamus are
  derived from the embryonic diencephalon
• Thalamus- gateway for sensory impulses heading to
  cerebral cortex, receives all sensory impulses
  (except smell), and channels impulses to
  appropriate part of cerebral cortex for
  interpretation
• Hypothalamus- Regulates autonomic activity
  involved in thermoregulation, hunger, thirst,
  sexual and mating behavior, etc part of the
  limbic system (emotions)
• The pituitary gland is attached to the
  hypothalamus
• Epithalamus- contains the pineal gland which is
  involved in hormone release

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Cont

• Cerebrum is derived from the embryonic
  telencephalon it is the most highly evolved
  structure in the mammalian brain.
• divided into left and right cerebral hemispheres.
• corpus callosum is the major connection between
  the two hemispheres.
• The left hemisphere is responsible for the right
  side of the body. The right hemisphere is
  responsible for the left side of the body.
• Functions interpretation, initiating voluntary
  movements, storing memory, retrieving memory,
  reasoning, center for intelligence and
  personality

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Cont

• Frontal Lobe Association Areas concentrating,
  planning, problem solving, judging
• Parietal Lobe Association Areas understanding
  speech, using words to express thought
• Temporal Lobe Association Areas remember visual
  scenes, remember music, remember complex patterns
• Occipital Lobe Association Areas combine visual
  images with other sensory experiences
• Fact- 90 of population, left hemisphere is
  dominant, some are right dominant, and others are
  equal

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Memory

• Short-term memory stored in the frontal lobes.
• The establishment of long-term memory involves
  the hippocampus. changes structure and function
  of neurons when you make a new connection.
• 60 trillion possible connections so there is
  plenty of free space.
• The transfer of information from short-term to
  long-term memory.
• Is enhanced by repetition (remember that when you
  are preparing for an exam).
• Influenced by emotional states mediated by the
  amygdala.
• Influenced by association with previously stored
  information.

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Emotions

• limbic system is composed of the hippocampus,
  olfactory cortex, inner portions of the cortexs
  lobes, and parts of the thalamus and
  hypothalamus.
• Mediates basic emotions (fear, anger), involved
  in emotional bonding, establishes emotional
  memory
• For example, the amygdala is involved in
  recognizing the emotional content of facial
  expression

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References

• Jack Brown M.S. Biology
• Shier,David, Jackie Butler, Ricki Lewis Holes
  Human Anatomy and Physiology 10th edition 2004
  McGraw-Hill
• Marieb, Elaine Essentials of Human Anatomy and
  Physiology 7th edition. 2003 Pearson Education
  Inc Benjamin Cummings pub.
• Microsoft Encarta Encyclopedia 2004
• Starr and Taggart The Unity and Diversity of
  Life 10th edition 2004 Thomson Brookes/Cole
• Campbell and Reece Biology 6th edition 2002
  Benjamin Cummings.
• Raven and Johnson Holt Biology 2004 Holt,
  Rinehart and Winston.