Reflex Arcs

1
Reflex Arcs

• By
• Mr.G.Burgess Oct.2003.

2
Reflex Arc

• A reflex arc is the transmission of a stimulus
  from a sensory cell to the spinal cord to a
  muscle.

Fig.1 http//web.ukonline.co.uk/webwise/spinneret/
humans/recodr.htm, October 2003.
3
Types of Neurons

• Three types of neurons are used for the reflex
• Sensory neuron (afferent pathway) taste, touch,
  see, hear
• interneuron relays messages from sensory to
  motor neurons.
• Motor Neurons (efferent pathway) sends messages
  to muscles so that they contract.

4
Sending Messages

• Messages are electrochemical impulses that are
  send through neurons by depolarizing them and
  making an action potential.
• Neurons that are not sending messages are
  polarized they have a greater concentration of
  Na outside the cell and a greater concentration
  of K inside the cell.

5
Working a Reflex

• First, the sensory neuron is stimulated enough to
  send an immediate impulse to the spine.
• The stimulus causes the cell to depolarize and
  creates an action potential.
• This action potential travels from the dendrites
  of the sensory neuron through the cell body to
  the end brush.

6

• While the impulse travels the cell is repolarized
  behind it and readies for another impulse.
• Repolarization of the neuron is accomplished
  through the reversal of concentration gradients
  of Na and K.
• When the impulse reaches the synapse it causes
  Ca2 to enter the endbrush forcing the vessicles
  containing neurotransmitters to open into the
  synapse.

7

• The dendrites on the interneuron are stimulated
  by the neurotransmitters and a new impulse is
  formed.
• The interneuron splits the message sending part
  to the brain for processing and the other to a
  muscle cell via a motor neuron so that the part
  of the body in peril may be removed.

8

• Each type of neuron requires that the impulse
  begin anew as it stimulates the dendrites of the
  next neuron, and creates an action potential.
• When the action potential reaches the endbrush of
  the motor neuron, the neurotramsmittier released
  from the vessicles is acetylcholine.
• Muscles are stimulated to contract when this
  neurotransmitter reacts with the receptor sites
  on the muscle tissues.

9
(No Transcript)
10
Bibliography

• NERVOUS RESPONSE and COORDINATION,
  http//web.ukonline.co.uk/webwise/spinneret/humans
  /recodr.ht, Dr. Richard G. Steane1999 Reflex
  image Fig 1.
• Biology of Living Systems, Glencoe, 1996.

Other useful Weblinks UC Irvine Psychology 9A
Index http//webs.wofford.edu/pittmandw/misc/02PSY
104A.pdf Great notes