1. The Nerve Impulse

2. The Nerve Impulse
The plasma membrane contains a variety of ion channels.
Some are open –
passive or leakage channels
Some are active or gated allowing certain molecules to change the shape and pass through. (open when neurotransmitter binds)

3. An electrochemical gradient creates an electrical current when ion channels open and ions diffuse across the plasma membrane.

4. chemical gradients –
passive, ions move from areas of high concentration to areas of lower concentration

5. 2. electrical gradients –
ions move towards areas of opposite charge

6. Polarized Membrane + + + + + + + + + + - - - - - - - - - - - - -
A neuron is at its resting potential when it is inactive.
The plasma membrane is positive on the outside compared to the inside.
The membrane is said to be polarized.
Positive outside
axon
Negative inside
Positive outside
Polarized Membrane

7. This resting potential is due to:
active transport of Na+ ions to the exterior of the cell - sodium pump

8. 2. reciprocal transfer of K+ ions to the interior - potassium pump

9. “leaking” of K+ ions to the exterior
(membrane more permeable to K+)
this creates a deficit of positive charge in interior

10. The electrochemical change that occurs across the membrane surface of a neuron is dependent upon an unequal distribution of ions between the outside and the inside of the plasma membrane.

12. When a stimulus occurs, a rapid inflow of Na+ changes the interior locally - negative to positive.
The membrane becomes depolarized.

13. A halt of the inflow of Na+ and a rapid outflow of K+ return the interior negative - repolarization.
This “action potential” or nerve impulse sweeps along a nerve fiber.

15. Absolute Refractory Period
during the time of one impulse traveling down the neuron (depolarization), a second impulse cannot be sent

16. All or Nothing Phenomenon
Stimulus is strong enough to produce an action potential - threshold stimulus produces an “all the way” action potential
No such thing as a little stimulus producing a weak response.

17. When the nervous system perceives a strong stimulus, the nerve impulses are generated often.
Two impulses cannot travel down a neuron.
The absolute refractory period is the time between the completion of one sweep and the beginning of another.

18. What Factors Can Affect the Nerve Impulse?

19. Axons of large diameter carry impulses faster.
Myelinated axons carry impulses faster.

20. Impulse is able to jump from node to node = faster impulse

21. Alcohol, sedatives, and anesthetics block nerve impulses by reducing the membrane’s permeability to Na+.

22. Cold or pressure that cuts off circulation will reduce nutrients and oxygen and impair impulses. (cold causes vessels to narrow)

23. The Synapse

24. The Synapse
Synapses are junctions between neurons or nervous and muscle cells (or other effectors).
* Most occur between an axon and a dendrite.

25. presynaptic neurons are “senders” postsynaptic neurons are “receivers”
postsynaptic cell either a neuron or an effector cell (muscle or gland cell)
Postsynaptic Neuron
Presynaptic Neuron

26. Two Kinds of Synapses 1. electrical synapses -
allow flow of ions between neurons
found in:
fetal tissue
cardiac muscle
smooth muscle
allows sequential
and rhythmic excitations

27. 2. chemical synapses -
release and receive chemical neurotransmitters which open and close ion channels

28. Neurotransmitters regulate many body activities
ex: sleep, hunger, memory, anger, joy
over 100 have been identified

30. Neuron Circuits

31. Circuits
Different patterns of synaptic connections are called circuits.
1. divergent –
amplify impulse

32. 2. convergent –
concentrates impulse

33. Neural Processing
The Reflex Arc

34. Neural Processing - The Reflex Arc
Reflexes are rapid, automatic responses to stimuli.
ex: pull away from pain
gag
blink
cough
sneeze

35. The reflex arc is a serial processing pattern consisting of:

36. 1. receptor - site of stimulus action
Stimulus at distal end of neuron
Skin
Receptor
(a)

37. 2. sensory neuron - transmits to CNS
Stimulus at distal end of neuron
Skin
Receptor
Sensory neuron
(a)

38. 3. integration center - within CNS connects sensory neuron to motor neuron
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Integration center
(a)

39. 4. motor neuron - transmits to effector organ
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Sensory neuron
Motor neuron
Integration center
(a)

40. 5. effector - muscle fiber or gland cell that responds to impulse
Stimulus at distal end of neuron
Skin
Spinal cord
(in cross section)
Interneuron
Receptor
Effector
Sensory neuron
Motor neuron
Integration center
(a)

41. The reflex arc is a serial processing pattern consisting of:
receptor - site of stimulus action
sensory neuron - transmits to CNS
integration center - within CNS; connects sensory neuron to motor neuron
motor neuron - transmits to effector organ
effector - muscle fiber or gland cell that responds to impulse