Nervous System

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Nervous System

• By the end of the lesson you should be able to
• Describe the transmission of impulses from senses
  to central nervous system and back to muscles.
• Describe the reflex action and the pathway of the
  reflex arc.
• Describe the function of reflex response.
• Describe the role of the central nervous system.

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nervous system
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Cells of the Nervous System

• Neuron- transmit impulses, amitotic( Lack
  centrioles)
• Neuroglia/ Glial- hold the functioning neurons

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Basic nerve cell structure
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Cross section of myelin sheaths that surround
axons
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3 main types of nerve cells
sensory neuron
relay neuron
motor neuron
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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
Carries impulses from sensory nerves to motor
nerves.
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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 e.g ADH
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Types of Glial Cells

• Astrocytes- hold neurons and blood vessels
• Microglia- capable of phagocytosis, Police force
  and janitorial service
• Oligodendroglia- hold nerve fibers together,
  produce myelin sheath

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Transmission of signals
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The Synapse
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Neurotransmitters

• small molecules, some are even hormones.
• The time for neurotransmitter action is between
  0,5 and 1 millisecond.
• Neurotransmitters are either destroyed by
  specific enzymes in the synaptic cleft, diffuse
  out of the cleft, or are reabsorbed by the cell.
• More than 30 organic molecules are thought to act
  as neurotransmitters. The neurotransmitters cross
  the cleft, binding to receptor molecules on the
  next cell, prompting transmission of the message
  along that cell's membrane.
• neurotransmitters are active for only a short
  time. Enzymes in the cleft inactivate the
  neurotransmitters. Inactivated neurotransmitters
  are taken back into the axon and recycled.

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Main parts of the Brain

• cerebrum (seat of consciousness),
• cerebellum, and the medulla oblongata (these
  latter two are "part of the unconscious brain").

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The major brain areas and lobes

• The occipital lobe (back of the head) receives
  and processes visual information.
• The temporal lobe receives auditory signals,
  processing language and the meaning of words.
• The parietal lobe is associated with the sensory
  cortex and processes information about touch,
  taste, pressure, pain, and heat and cold.
• The frontal lobe conducts three functions
• -motor activity and integration of muscle
  activity
• -speech
• -thought processes

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Cerebrum

• Cerebral hemispheres are divided by the corpus
  callosum .
• . governs intelligence and reasoning, learning
  and memory.

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Cerebellum

• The cerebellum is the third part of the
  hindbrain, but it is not considered part of the
  brain stem.
• Functions of the cerebellum include fine motor
  coordination and body movement, posture, and
  balance.

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Midbrain and pons

• The midbrain and pons are also part of the
  unconscious brain.

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Thalamus

• The thalamus serves as a central relay point for
  incoming nervous messages.

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Hypothalamus

• regulates homeostasis
• It has regulatory areas for thirst, hunger, body
  temperature, water balance, and blood pressure,
  and links the Nervous System to the Endocrine
  System.

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The Spinal Cord

• The gray matter of the spinal cord consists
  mostly of cell bodies and dendrites.
• The surrounding white matter is made up of
  bundles of interneuronal axons (tracts). Some
  tracts are ascending (carrying messages to the
  brain), others are descending (carrying messages
  from the brain).
• The spinal cord is also involved in reflexes that
  do not immediately involve the brain.

• 1Spinal Nerve
• 5Central Canal
• 2Dorsal Root Ganglion
• 6Grey Matter3Dorsal Root (Sensory)
• 7White Matter
• 4Ventral Root (Motor)  

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Protective membranes of the Spinal Cord

• Dura Mater- tough tube that encases the two inner
  membranes
• (arachnoid and pia mater)
• spinal fluid, commonly called cerebrospinal fluid
  (CSF).
• cushions, protects and nourishes the spinal cord
  and nerve roots.