Anatomy and Physiology

1
Anatomy and Physiology

• 9.3 Central Nervous System

2
Warm Up 01.25.07

• Explain what a reflex arc is.

3
Nerve Impulses

• A nerve impulse is a self-propagating wave of
  electrical disturbance that travels along the
  surface of the neurons plasma membrane
• They are initiated by a stimulus a change in
  temperature, pressure, etc
• See Figure 9.8 page 271

4
Nerve Impulses (contd)

• The membrane of a resting neuron has a slightly
  charge on the outside and a negative charge on
  the inside.
• Because there are lots of Na on the outside
• When the membrane is stimulated, the Na flows
  into the cell and the inside of the membrane
  becomes suddenly and the outside becomes
  negative

5
Nerve Impulses (contd)

• Even though the section of membrane that was
  stimulated immediately recovers, the electrical
  disturbance opens other Na channels and the
  electrical wave continues to travel down the
  membrane in one direction

6
Saltatory Conduction

• If the impulse encounters a section of membrane
  that is covered with myelin, it jumps through
  the myelin.
• This is called saltatory conduction and is much
  faster than conduction through nonmyelinated
  sections
• Figure 9-8, Page 271

7
The Synapse

• A synapse is a place where impulses are
  transmitted from one neuron (the presynaptic
  neuron) to another neuron (the postsynaptic
  neuron)
• A synapse has three structures a synaptic knob,
  a synaptic cleft and that plasma membrane of the
  postsynaptic neuron

8
Parts of a Synapse

• The synaptic knob is a tiny bulge at the end of a
  terminal branch of a presynaptic neurons axon
• Each contains many small sacs or vesicles
• Each vesicle contains a very small quantity of a
  chemical compound called a neurotransmitter
• When the nerve impulse arrives at the synaptic
  knob, neurotransmitter molecules are released
  from the vesicles into the synaptic cleft a
  space between the synaptic knob and the PM.

9
Synaptic Cleft

• The synaptic cleft is an incredibly narrow space
  only about two-millionths of a centimeter in
  width
• The plasma membrane of a postsynaptic neuron has
  protein molecules embedded in it which serve as
  receptors to which neurotransmitter molecules
  bind
• This binding can initiate an impulse by opening
  ion channels

10
Neurotransmitters

• They are chemicals by which neurons communicate
• They assist, stimulate or inhibit postsynaptic
  neurons
• At least 30 different compounds have been
  identified as neurotransmitters
• Not distributed randomly through the spinal cord
  and brain they are localized in discrete groups
  of neurons and released in specific pathways

11
Examples of Neurotransmitters

• Acetylcholine, Norepinephrine, Dopamine,
  Serotonin
• Each belong to a group called catecholamines
  which play a role in sleep, motor function, mood
  and pleasure recognition
• Endorphins, Enkaphalins
• They inhibit conduction of pain impulses
  natural pain killers

12
Neurotransmitters (contd)

• Nitric Oxide (NO)
• Diffuses across the plasma membrane of neurons
  instead of being released from vesicles
• NO is the neurotransmitter that leads to the male
  arousal response
• Sildenafil (Viagra) treats ED by promoting the
  same response as NO naturally creates

13
Parkinson Disease

• Chronic nervous disorder deficient levels of
  dopamine in the brain
• Symptoms rigidity and trembling of the head and
  extremities, a forward tilt of the trunk and a
  shuffling manner of walking
• Famous people with it Mohammed Ali, Michael J.
  Fox

14
Central Nervous System

• Obviously, it is centrally located
• 2 Major Structures Brain spinal cord
• The brain is protected in the cranial cavity of
  the skull and the spinal cord is protected by the
  spinal cavity of the vertebral column
• The brain and spinal cord are also covered by
  protective membranes -- meninges

15
Divisions of the Brain Fig 9-12 (page 276)

• Brainstem
• Medulla oblongata
• Pons
• Midbrain
• Cerebellum
• Diencephalon
• Hypothalamus
• Thalamus
• Cerebrum

16
Brainstem

• The lowest part of the brainstem is the medulla
  oblongata, above that is the pons and above that
  is the midbrain
• The medulla oblongata is an enlarged extension of
  the spinal cord, just inside the cranial cavity
• It lies directly above the foramen magnum
• Consists of gray and white matter but in a
  different arrangement than the spinal cord

17
Brainstem (Contd)

• The pons and the midbrain consist of the same
  pattern of white and gray matter as the medulla
  oblongata
• A reticular formation of gray and white (netlike)
  and scattered
• They all function as two-way conduction paths
• Sensory fibers conduct impulses up from the cord
  to other parts of the brain

18
The Vital Centers

• The cardiac, respiratory and vasomotor (the vital
  centers) are all located in the medulla
• Impulses from these centers control heartbeat,
  respirations and blood vessel diameter