1. The Nervous System (Pgs. 167-176)

2. The Nervous System Organs of the nervous system are divided into
Central Nervous System (CNS)
Peripheral Nervous System (PNS)

3. Functions of the Nervous System
Sensory
Integrative
Motor

4. Functions of the Nervous System
Sensory functions detect changes
Sensory receptors at the end of peripheral nerves detect changes inside/outside of the body
External – light, sound touch Internal – pH levels, oxygen/carbon dioxide concentrations
Information gathered is converted to nerve impulses of the PNS which sends the information to the CNS

5. Functions of the Nervous System
Integrative functions bring sensory information together and makes decisions that are acted upon by using motor function

6. Functions of the Nervous System
Motor functions are responses to sensory information
Employ peripheral nerves that carry impulses from CNS to responsive parts called effectors
Effectors are outside the NS and include
a. Muscles – contract when stimulated
b. Glands – secrete hormones when stimulated (glandular epithelial tissue)

7. Glandular Epithelium

8. Functional Organization

9. Anatomical and Functional Organizaton

10. Nervous Tissue Neurons (nerve cells) are the functional unit;
Specialized to react to physical & chemical changes in their surroundings and conduct nerve impulses
Neuroglia support the physiological needs of neurons
Fig. 8-2, 8-3, 3-21 pg. 70

11. Anatomy of a Neuron

12. Anatomy of a Neuron
dendrite – provide receptive surfaces to carry impulses toward cell body; relatively short & highly branched
cell body – contains various organelles
axon – a single axon arises from cell body; transmit impulses away from the cell body; some are surrounded by specialized glia cells called Schwann cells that form myelin sheath

13. Functional Differences of Neurons
motor neurons – transmit impulses form brain to an effector (efferent neurons) (multipolar)
sensory neurons – transmit impulses to spinal cord & brain (afferent neurons) (most unipolar, some bipolar)
interneurons – carry impulses from sensor neurons to motor neurons (multipolar)

14. Refex Arc

15. Structural Differences of Neurons
bipoloar – only 2 nerve fibers, one arising from either end; found in specialized parts of the eyes, nose, & ears

16. Structural Differences of Neurons
unipolar/monopolar – single nerve fiber extending from its cell body; found in ganglia outside the brain or spinal cord

17. Structural Differences of Neurons
multipolar – many nerve fibers arising from their cell bodies; most common type of neuron in the brain & spinal cord (ganglia – a mass of neuron cell bodies, usually outside the CNS)

18. Neuroglia Cells
Accessory cells – Schwann cells, astrocytes, microglia, oligodendrocytes, ependymal (We will discuss the functions of each of these types of cell during the lab.)
Fill spaces, support neurons, hold nervous tissue together; play a role in the metabolism of glucose, help regulate K+ concentration, produce myelin, and carry on phagocytosis
Fig. 8-3

19. Types of Neuroglia Cells

20. Regeneration of Nerve Fibers
If a neuron cell body is injured, the neuron is likely to die
If the axon of a peripheral nerve fiber is severed, its distal portion will die, but the proximal portion may regenerate & re-establish its former connections
Significant regeneration is unlikely to take place in the CNS

21.   Structure of Peripheral Nerves – consists of bundles of nerve fibers surrounded by connective tissue – Fig. 8-4
Epineurium – outermost layer; dense and include many collagenous fibers
Fasicicle – a bundle of nerve fibers
Perineurium – less dense connective tissue surrounding fascicle
Endoneurium – small amount of loose connective tissue that surrounds individual nerve fibers

22. Cell Membrane Potential and Nerve Impulses – Fig. 8-6 & 8-7

23. Resting Potential

24.   A cell membrane is usually electrically charges or polarized so that outside is + and inside is -
Resting Potential (-70 mvolts)
Nerve cell is not conducting impulses
[Na+] is greater on the outside of the cell and [K+] is greater on the inside of the cell
There is a large number of negatively charged ions inside the cell which can’t diffuse out
At rest inside stays negative because K+ can diffuse easily out of the cell through open channels; Na+ can’t diffuse as easily into cells through “their” protein channels
Na+ /K+ pump (active transport) – maintains system so equilibrium is not reached; therefore, Na+ is always being pumped back out and K+ is being pumped back in

25. Local Potential Changes

26. Local Potential Changes
Stimulation of a membrane affects its resting potential in a local region (light, temp., other neurons
Membrane starts to become depolarized (moves toward zero)
Threshold potential is reached which causes an action potential

27. Action Potential

28. Action Potential 1/1000 sec. or less
At threshold, Na+ channels open and Na+ diffuse inward causing depolarization
About the same time K+ channels open and K+ diffuses outward, causing repolarization
This rapid change in potential is an action potential
Many action potentials can occur before an active transport mechanism re-establishes the original resting potential
The propagation of actions potentials along a nerve fiber is an impulse

29. Refractory Period Refractory Period
A brief time (10-30 m/sec.) following the passage of a nerve impulse when the membrane is unresponsive to ordinary stimuli
Membrane must return to resting potential before it can be stimulated again
All – or – None Response
If a nerve fiber responds at all, it responds completely
All impulses carried on that fiber will be of the same strength

30. Coding & Interpretation of Messages
Frequency of action potentials – a weak stimulus initiates only a few action potentials/sec., a strong stimulus initiates many (upper limit because of refractory period)
Duration of a burst of action potentials – a weak stimulus may give rise to a short burst of pulses in the neuron, a strong stimulus a longer burst
Number & kinds of neurons firing – The threshold needed to initiate a nerve impulse varies from one neuron to another. Thus a weak stimulus will cause only a few neurons to fire, strong will fire all of these neurons, plus others with higher thresholds.

31. Impulse Conduction Myelinated vs Unmyelinated

32. Impulse Conduction
Unmyelinated fibers conduct impulses that travel over their entire surface
Myelinated – impulses travel from node to node
Impulse conduction is more rapid on myelinated fibers with large diameters

33. The Synapse – The junction between 2 neurons
The Synapse – The junction between 2 neurons. A synaptic cleft is the gap between parts of two neurons at a synapse. Fig. 8-7
Impulses usually travel from a dendrite or cell body, then along the axon to a synapse
Axons have synaptic knobs at their distal ends that secrete neurotransmitters
The neurotransmitter is released when a nerve impulse reaches the end of an axon and the neurotransmitter diffuses across the synaptic cleft.
When the neurotransmitter reaches the nerve fiber on the distal side of the cleft, a nerve impulse is triggered.

34. The Synapse

35. Nerve Pathways – the route followed by an impulse as it travels through the nervous system, Fig. 8-5
Reflex Arc – simplest nerve pathway
A reflex arc usually includes a sensory neuron, a reflex center composed of interneurons, and a motor neuron
Reflex arc is the behavioral unit of the nervous system
Reflex Behavior
Reflexes are automatic unconscious responses to changes
Help maintain homeostasis
Knee jerk – 2 neurons
Withdrawal reflexes are protective actions

36. Reflex Arc