Processes

1
Processes

• Armlike projections from the cell body.
• Bundles of processes in the CNS are called
  Tracts.
• Bundles of processes in the PNS are called
  Nerves.
• There are 2 types of processes
• 1. Dendrites- are short, tapered, and branch.
• Responsible for sensory input and impulse
  transmissions.
• 2. Axons- can be extremely long (3-4 ft)
• Generate and transmit impulses.

2
Myelin Sheath

• This is a protein-lipoid that covers, protects,
  and insulates nerve fibers from one another.
• It also increases the speed of nerve impulses.
• Dense collections of myelinated fibers are
  called white matter and are mostly fiber
  tracts.
• Dense collections of nerve bodies (unmyelinated)
  are called gray matter.

3
Neurons are Classified Structurally and
Functionally

• Structurally
• Multipolar-
• Have three or more processes.
• Most common type (gt99 ).
• Bipolar-
• Have two processes (one axon and one dendrite).
• Found in special sense organs.
• Unipolar-
• Have one process that branches into an axon and a
  dendrite.
• Found in the ganglia of PNS.

4
Neurons are Classified Structurally and
Functionally (cont.)

• Functionally This is based on the direction
  impulses travel in relationship to the CNS.
• Sensory- transmits from receptors to CNS.
• Nearly all of these are unipolar.
• Motor- Transmits from CNS to effector organs.
• Most are multipolar.
• Interneurons- are found between motor and sensory
  neurons and transmit signals through the CNS.
• Most are multipolar.

5
Nerve Impulse Transmission

• The operation of the nervous system depends on
  the flow of information through chains of
  neurons.
• This occurs at synapses (junctions between
  neurons or neurons and effector cells).
• Most synapses occur between axonal endings of one
  neuron and the dendrites of another.
• Impulses conducted toward the synapse are called
  the Presynaptic Neurons and away from the synapse
  is the Postsynaptic Neuron.

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There are Two Type of Synapses

• 1. Electrical-
• Is the least common type.
• Is very fast (100m/s)
• Have protein channels that interconnect the
  cytoplasm of neighboring neurons.
• Current-carrying ions flow directly from one
  neuron to the next.
• Responsible for stereotyped movement (ex. Jerky
  movement of eyes).
• Most of these synapses are replaced by chemical
  synapses by adulthood.

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There are Two Type of Synapses(cont.)

• 2. Chemical-
• Is the most common.
• Have slower impulses (.3-5m/s)
• Designed to release and receive
  neurotransmitters.
• Neurotransmitters cause the opening and closing
  of ion channels in cell membranes.
• Consist of two main parts
• 1. Axonal Terminal- knob-like end of axon with
  synaptic vesicles.
• 2. Receptor Region- possesses neurotransmitter
  receptors.
• The space between the two is the synaptic cleft.

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Steps to Impulse Transmission Across a Chemical
Synapse

• A depolarization wave (nerve impulse) causes Ca
  ions gates to open in the axonal terminal.
• Ca ions promote fusion of synaptic vesicles to
  the terminal membrane causing a release of
  neurotransmitter by exocytosis.
• The neurotransmitter diffuses across the synaptic
  cleft and bind to the receptors of the
  postsynaptic membrane.

9
Steps to Impulse Transmission Across a Chemical
Synapse

• 4.The binding of the neurotransmitter causes the
  postsynaptic membrane to open ion channels
  (depolarization).
• 5. The neurotransmitter is broken down quickly by
  enzymes allowing for repolarization.

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The Central Nervous System

• Made up of the brain and spinal cord.
• Parts of the brain
• Ventricles
• These are hollow chambers filled with
  cerebralspinal fluid.
• There are 4 interconnected and they are found
  deep within the brain.
• Cerebral Hemisphere
• Make up about 83 of the brains mass.
• Form the superior part of the brain.
• Surface is covered with ridges (gyri) and grooves
  (sulci).
• Deep grooves are called Fissures.
• Longitudinal fissure- separates the right and
  left hemispheres.
• Transverse fissure-separates the cerebral
  hemispheres from cerebellum.