CONTROL

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CONTROL AND COORDINATION
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NERVOUS SYSTEM

• The nervous system is composed of
  specialized cells called neuron, which exercise
  control by sending electrical signals called
  nerve impulses. Nerve cells are the structural
  and functional unit of nervous system.

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STRUCTURE OF NEURON

• A neuron consists of three prominent parts-
• 1.Cell body- The cell body of neuron is also
  called cyton or soma. It receives
  nerve impulses from dendrites and transmit them
  to axon.
• 2.Dendrites- dendrites are the parts of neuron
  where sensation acquired. The information then
  travels as an electric impulse towards the cell
  body.

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• Axon-It is a single, cylindrical protoplasmic
  nerve fibre. At its terminal axon is highly
  branched. The axon conducts nerve impulses away
  from the cell body.

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ARRANGEMENT OF NEURON

• The neurons lie end to end in chains to
  transmit nerve impulses in the animal body. The
  neurons are not connected. There occurs a very
  minute gap between terminal portion of axon of
  one neuron and the dendron of other neuron. This
  minute gap is called synapse.
• Axon terminal expand to form presynaptic
  knob and dendrite forms post synaptic depression.
  In between the two lies a fluid filled space
  called synaptic cleft.

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• As the nerve impulses reaches the pre-synaptic
  knob, the synaptic vesicles get stimulated to
  release a chemical called neurotransmitter in the
  synaptic cleft. The neurotransmitter molecules
  diffuse across the gap to come in contact with
  the chemoreceptor site in the nerve impulses
  passes from one neuron to other.

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REFLEX ACTIONS

• A Reflex actions may be defined as a
  spontaneous, automatic and mechanical response to
  a stimulus , acting on a specific receptor ,
  without the will of an animal . In certain
  situation , sensation requires immediate response
  as time used for processing may cause harm to the
  body. In such situation reflex action occur.
• Example-blinking of eyes ,withdraw of hand
  suddenly pinched or touched by a hot object.

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HUMAN NERVOUS SYSTEM

• Human nervous system is the most complex.
  It is divided into two main parts-
• Central nervous system
• Peripheral nervous system

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CENTRAL NERVOUS SYSTEM

• It is hollow and lies on the mid-dorsal
  part along the main axis of the body. It is
  covered by a part of axial skeleton. The CNS in
  turn consists of two parts-
• 1. Brain or Encephalon situated in the head.
• 2. Spinal cord or Myelon located in the neck and
  trunk.

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BRAIN

• The brain is the widest and the uppermost part
  of the central nervous system . It is the highest
  coordinating centre in the body. Brain is
  situated in the cranial cavity of the skull. The
  brain is soft, whitish organ. It weighs 1.2 to
  1.4 kg and forms about 98 of the weight of the
  whole nervous system. It has about 100 bilion
  neurons. Brain is surrounded by three membranes
  called meninges which provide protection to it.
  The space between the meninges is filled with the
  cerebro- spinal fluid .

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• Brain is divisible into three main region
• FOREBRAIN- It forms the greater part of the
  brain. It consists of three parts olfactory
  lobes, cerebral hemisphere and diencephalon.
• i) Olfactory lobes- A pair of widely
  separated club- shaped small structure . Each
  olfactory lobe consist of an anterior olfactory
  bulb and a posterior narrow olfactory stalk.
  These lobes receive impulses from
  olfactoreceptors and relay sense of smell to the
  temporal region of the cerebrum.

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• (ii) Cerebral hemisphere- It is the largest part
  of the brain . The two cerebral hemisphere lie
  side by side separated by deep cerebral fissure.
  The cerebral hemisphere divided into four lobes
  
• a. Frontal lobe is the region for speech
  ,facial, muscular activities and mental
  activities.
• b. Temporal lobe is the region for auditory
  reception (hearing ) .
• c. Occipital lobe is the region for visual
  reception (sight )
• d. Parietal lobe is the region for touch ,taste
  ,smell, temperature and conscious association.

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• (iii) Diencephalon-It lies on the side of
  cerebrum It roof is called epithalamus, sides are
  called thalami and its floor is called
  hypothalamus. Diencephalon has a narrow cavity
  called third ventricle.
• 2. MID BRAIN-It is significantly small region.
  It consists of two fibre tracts called crura
  cerebri and a pair of two swellings called
  superior and infeior colliculi on each side. the
  two superior colliculi have centres for sight
  reflexes and the two inferior colliculi have
  centre for sight reflexes. It controls the
  movement of head, neck, eye muscles changes in
  pupil size as well as shape of eye lens.

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• 3. HIND BRAIN- The hind brain consists of three
  parts- cerebellum, pons varolii and medulla
  oblongata. The cerbellum is the second largest
  part of the brain , constituting nearly 12 of
  it. It has two large, lateral cerebellar
  hemispheres and a central vermis. Cerebellum
  maintains the posture, equilibrium and muscles
  tone. Pons varolii controls some aspects of
  respiration. Medulla oblongata is the posterior
  part of the brain. It controls rate of heartbeat,
  breathing movements etc.

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SPINAL CORD

• Spinal cord is a cylindrical structure and is
  about 45cm long . It begins in continuation with
  the medulla oblongata of brain extend downward
  up to early part of the lumber region . It then
  extend to the end of vertebral column as fibrous
  connective called filum terminale. Internally the
  spinal cord possess a narrow, fluid filled cavity
  called central canal. Spinal cord is enclosed in
  the vertebral column or backbone which protect
  it. It conducts sensory and motor impulses to and
  from the brain. It act as center for the reflex
  action

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PERIPHERAL NERVOUS SYSTEM

• It connects CNS with different part of the
  body . It has two component, voluntary and
  Autonomic nervous system. These are-
• 1. Voluntary peripheral nervous system is under
  the control of will. It consist of nerves that
  arise directly from CNS connecting different body
  parts for voluntary control of the brain.

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• 2. Autonomic nervous system (involuntary
  nervous system), on other hand, is not under the
  control of human will. It developed branches of
  some cranial and some spinal nerves called
  visceral nerves. It is subdivided into two parts
• (i) sympathetic nervous system
• (ii) parasympathetic nervous system

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The Organization of the Sympathetic Division of
the ANS
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Sympathetic ganglia

• Sympathetic chain ganglia (paravertebral ganglia)
  preganglionic fibers of the sympathetic NS that
  carry motor impulses to the body wall or thoracic
  cavity synapses in chain ganglia
• Collateral ganglia (prevertebral ganglia)
  group of second order neurons that innervate
  organs in the abdominopelvic region

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Sympathetic Pathways
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Sympathetic Pathways
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Sympathetic Pathways
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The Distribution of Sympathetic Innervation
Animation The sympathetic division (see tutorial)
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Postganglionic fibers

• Rejoin spinal nerves and reach their destination
  by way of the dorsal and ventral rami
• Those targeting structures in the thoracic cavity
  form sympathetic nerves
• Go directly to their destination

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Abdominopelvic viscera

• Sympathetic innervation via preganglionic fibers
  that synapse within collateral ganglia
• Splanchic nerves carry fibers that synapse in
  collatheral ganglia

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Abdominopelvic viscera

• Celiac ganglion
• Innervates stomach, liver, gall bladder,
  pancreas, spleen
• Superior mesenteric ganglion
• Innervates small intestine and initial portion of
  large intestine
• Inferior mesenteric ganglion
• Innervates kidney, urinary bladder, sex organs,
  and final portion of large intestine

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Sympathetic activation

• Sympathetic activation is controlled by
  sypathetic centers in the hypothalamus.
• In crises, the entire sympathetic division
  responds
• Sympathetic activation
• Affects include increased alertness, energy and
  euphoria, increased cardiovascular and
  respiratory activities, elevation in muscle tone,
  mobilization of energy resources

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Neurotransmitters and sympathetic function

• Stimulation of sympathetic division has two
  distinct results
• Release of ACh or NE at specific locations
• Secretion of E and NE into general circulation
• Most postganglionic fibers are adrenergic, a few
  are cholinergic or nitroxidergic

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Sympathetic Variosities
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Parasympathetic division

• Preganglionic neurons in the brainstem and sacral
  segments of spinal cord
• Ganglionic neurons in peripheral ganglia located
  within or near target organs

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The Organization of the Parasympathetic Division
of the ANS
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Organization and anatomy of the parasympathetic
division

• Preganglionic fibers of parasympathetic neurons
  can be found in cranial nerves III, VI, IX, X
• Sacral neurons form the pelvic nerves
• Almost 75 of all parasympathetic outflow travels
  along the vagus nerve (cranial nerve X)

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The Distribution of Parasympathetic Innervation
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Parasympathetic activation

• Effects produced by the parasympathetic division
• relaxation
• food processing
• energy absorption

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Neurotransmitters and parasympathetic functions

• All parasympathetic fibers release ACh
• Short-lived response as ACH is broken down by
  AChE and tissue cholinesterase

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Sympathetic and parasympathetic divisions

• Sympathetic
• Widespread influence on visceral and somatic
  structures
• Parasympathetic
• Innervates only visceral structures serviced by
  cranial nerves or lying within the abdominopelvic
  cavity
• Effects produced by the parasympathetic branch
  include increased secretion by digestive glands
• Dual innervation organs that receive input from
  both systems

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Anatomy of dual innervation

• Sympathetic and parasympathetic systems
  intermingle to form autonomic plexuses
• Cardiac plexus sympathetic and parasympathetic
  fibers bound for the heart and kungs pass through
  the cardiac plexus
• Pulmonary plexus
• Esophageal plexus
• Celiac plexus
• Inferior mesenteric plexus
• Hypogastric plexus

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The Autonomic Plexuses
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Comparison of the two divisions

• Important physiological and functional
  differences exist

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Summary The Anatomical Differences between the
Sympathetic and Parasympathetic Divisions
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A Comparison of Somatic and Autonomic Function
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Higher levels of autonomic control

• Activity in the ANS is controlled by centers in
  the brainstem that deal with visceral functioning

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Levels of Autonomic Control
Example of higher-level of autonomic function
would be increased heart rate when you see a
person that you dislike.
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Higher order functions

• Are performed by the cerebral cortex and involve
  complex interactions
• Involve conscious and unconscious information
  processing
• Are subject to modification and adjustment over
  time

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Memory

• Short term or long term
• Memory consolidation is moving from short term to
  long term
• Hippocampus is essential for memory consolidation
• Mechanisms involved in memory formation and
  storage are
• Increased release of neurotransmitter
• Formation of additional synaptic connection
• Formation of memory engrams (single circuit that
  correspond to single memory)
• Amnesia is the loss of memory due to disease or
  trauma

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Memory

• Memory that can be voluntarily retrieved and
  verbally expressed are called declarative
  memories
• Conversion of a short term memory to a long term
  memory is called memory consolidation

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Memory Storage
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Consciousness

• Deep sleep, the body relaxes and cerebral cortex
  activity is low
• The reticular activating system (RAS) is
  important to arousal and maintenance of
  consciousness
• RAS is located in the mesencephalon

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The Reticular Activating System
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Age-related changes

• Reduction in brain size and weight
• Reduction in the number of neurons
• Decrease in blood flow to the brain
• Changes in synaptic organization of the brain
• Intracellular and extracellular changes in CNS
  neurons

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You should now be familiar with

• The organization of the autonomic nervous system.
• The structures and functions of the sympathetic
  and parasympathetic divisions of the ANS.
• The mechanisms of neurotransmitter release in the
  sympathetic and parasympathetic divisions.
• The effects of sympathetic and parasympathetic
  neurotransmitters on target organs and tissues.
• The hierarchy of interacting levels of control in
  the ANS.
• How memories are created, stored and recalled.
• The effects of aging on the nervous system.