1. The Nervous System: The Spinal Cord and Spinal Nerves
Chapter 8
The Nervous System: The Spinal Cord and Spinal Nerves

2. Role of the Nervous System
Nervous system coordinates all body systems
Detects and responds to stimuli
Brain and spinal cord act as switching centers
Nerves carry messages to and from centers

3. Structural Divisions Central nervous system (CNS) Brain Spinal cord
Peripheral nervous system (PNS)
Cranial nerves
Spinal nerves

4. Anatomic divisions of the nervous
system.

5. Functional Divisions Somatic nervous system Controlled voluntarily
Effectors are skeletal muscles
No further subdivisions
Autonomic (or visceral) nervous system (ANS)
Controlled involuntarily
Effectors are smooth muscle, cardiac muscle, and glands
Subdivided into
Sympathetic nervous system
Parasympathetic nervous system

6. Checkpoint 8-1: What are the two divisions of the nervous system based on structure?
Central nervous system
Autonomic nervous system
Checkpoint 8-2: The nervous system can be divided functionally into two divisions based on type of control and effectors. What division is voluntary and controls skeletal muscle, and what division is involuntary and controls involuntary muscles and glands?
The somatic system is voluntary and controls skeletal muscle
The autonomic system is involuntary and controls involuntary muscles and glands

7. Neurons and Their Functions
Functional cells of nervous system
Highly specialized
Unique structure

8. Structure of a Neuron Cell body Nucleus Other organelles Cell fibers
Dendrites
Axons
Some are protected by myelin sheath

9. Diagram of a motor neuron.
ZOOMING IN • Is the neuron shown
here a sensory or a motor neuron?
Motor neuron

10. A typical neuron as seen under the microscope.

11. Formation of a myelin
sheath.

12. Checkpoint 8-3: The neuron, the functional unit of the nervous system, has long fibers extending from the cell body. What is the name of the fiber that carries impulses toward the cell body and what is the name of the fiber that carries impulses away from the cell body?
The dendrite carries impulses toward the cell body and the axon carries impulses away from the cell body. Try to remember it this way – DCBA
D – dendrite > CB – cell body > A - axon

13. Checkpoint 8-4: Myelin is a substance that covers and protects some axons. What color describes myelinated fibers, and what color describes unmyelinated tissue of the nervous system?
Myelinated fibers are white
Unmyelinated tissue is gray matter

14. Types of Neurons Sensory neurons (afferent neurons)
Conduct impulses to spinal cord, brain
Motor neurons (efferent neurons)
Conduct impulses to muscles, glands
Interneurons (central or association neurons)
Conduct information within CNS

15. Nerves and Tracts Nerve: fiber bundle within PNS
Tract: fiber bundle within CNS
Organized into fascicles
Connective tissue layers
Endoneurium
Perineurium
Epineurium

16. Cross section of a nerve as seen under the microscope (x132).

17. Checkpoint 8-5: Nerves are bundles of neuron fibers in the PNS
Checkpoint 8-5: Nerves are bundles of neuron fibers in the PNS. These nerves may be carrying impulses either toward or away from the CNS. What name is given to nerves that convey impulses toward the CNS, and what name is given to nerves that transport away from the CNS?
Nerves that convey impulses toward the CNS are sensory or afferent.
Nerves that carry impulses away from the CNS are motor or efferent.

18. Neuroglia Neuroglia (glial cells) Protect nervous tissue
Support nervous tissue
Aid in cell repair
Remove pathogens and impurities
Regulation composition of fluids around and between cells

19. Examples of neuroglia.

20. Checkpoint 8-6: The nonconducting cells of the nervous system serve in protection and support. What are these cells called?
Neuroglia

21. The Nervous System at Work
Electrical impulses are sent along neuron fibers and transmitted between cells at junctions

22. The Nerve Impulse
Plasma membrane carries electrical charge (potential)
Plasma membrane is polarized (negative charge)
Membrane potential reverses, generates electrical charge (action potential)
Resting state
Depolarization
Repolarization
Myelin sheath speeds conduction

23. The action potential.

24. A nerve impulse.

25. Checkpoint 8-7: An action potential occurs in two stages
Checkpoint 8-7: An action potential occurs in two stages. In the first stage, the charge on the membrane reverses, and in the second stage, it returns to the resting state. What are the names of these two stages?
The first stage is depolarization and the second stage is repolarization
Checkpoint 8-8: What ions are involved in generating an action potential?
Sodium (Na+) and potassium (K-)

26. The Synapse Junction point for transmitting nerve impulse
Axon (presynaptic cell)
Dendrite (postsynaptic cell)
Synaptic cleft
Neurotransmitter
Epinephrine (adrenaline)
Norepinephrine (noradrenaline)
Acetylcholine
Receptors

27. A synapse.

28. Checkpoint 8-9: Chemicals are needed to carry information across the synaptic cleft at a synapse. As a group, what are all these chemicals called?
Neurotransmitters

29. The Spinal Cord Links PNS and brain
Helps coordinate impulses within CNS
Contained in and protected by vertebrae

30. Spinal cord and spinal
nerves.
ZOOMING IN • Is the
spinal cord the same
length as the spinal
column? How does the
number of cervical
vertebrae compare with
the number of cervical
spinal nerves?
No, it isn’t. There are 7 cervical vertebrae but 8 cervical spinal nerves

31. Structure of the Spinal Cord
Unmyelinated tissue (gray matter)
Dorsal horn
Ventral horn
Gray commissure
Central canal
Myelinated axons (white matter)
Posterior median sulcus
Anterior median fissure
Ascending and descending tracts

32. The spinal cord.

33. Checkpoint 8-10: The spinal cord contains both gray and white matter
Checkpoint 8-10: The spinal cord contains both gray and white matter. How is this tissue arranged in the spinal cord?
The gray matter is in the central portion and the white matter on the outside
Checkpoint 8-11: What is the purpose of the tracts in the white matter of the spinal cord?
Sensory (afferent) impulses to the brain are transmitted in the ascending tracts and motor (efferent) impulses are transmitted in the descending tracts to the peripheral nervous system.

34. The Reflex Arc Receptor detects stimulus
Sensory neuron transmits impulses to CNS
CNS coordinates impulses and organizes response
Motor neuron carries impulses away from CNS
Effector carries out response

35. Typical reflex arc.
ZOOMING IN • Is this a
somatic or an autonomic reflex
arc? What type of neuron is
located between the sensory
and motor neuron in the CNS?
This is a somatic reflex arc. Interneurons are located between the sensory and motor neuron.

36. Checkpoint 8-12: What name is given to a pathway through the nervous system from a stimulus to an effector?
Reflex arc

37. Reflex Activities
Simple reflex
Rapid
Uncomplicated
Automatic
Spinal reflex
Coordinated in spinal cord
Stretch reflex is example

38. The patellar (knee-jerk) reflex
ZOOMING IN • How many total neurons are involved in this spinal reflex? What
neurotransmitter is released at the synapse shown by number 5?
2 neurons are involved. Acetylcholine is the neurotransmitter

39. The Spinal Nerves 31 pairs
Each nerve attached to spinal cord by two roots
Dorsal root
Dorsal root ganglion
Ventral root
Mixed nerves

40. Branches of the Spinal Nerves
Plexus (network)
Cervical plexus
Phrenic nerve
Brachial plexus
Radial nerve
Lumbosacral plexus
Sciatic nerve
Dermatomes

41. Dermatomes.
ZOOMING IN • Which spinal nerves
carry impulses from the skin of the
toes? From the anterior hand and
fingers?
Toes - Ist sacral, anterior hand and feet – 8th cervical

42. Checkpoint 8-13: How many pairs of spinal nerves are there?

43. The Autonomic Nervous System (ANS)
Regulates the action of glands, smooth muscles of hollow organs and vessels, and heart muscle
Preganglionic neuron connects spinal cord to ganglion
Postganglionic neuron connects ganglion to effector

44. Checkpoint 8-14: How many neurons are there in each motor pathway of the ANS?
All autonomic pathways contain 2 motor neurons connecting the spinal cord with the effector organ.

45. Divisions of the Autonomic Nervous System
Sympathetic nervous system
Thoracolumbar area
Collateral ganglia
Adrenergic
Parasympathetic
Craniosacral
Terminal ganglia
Cholinergic

46. Autonomic nervous system.
ZOOMING IN • Which division
of the autonomic nervous system
has ganglia closer to the effector
organ?
Parasympathetic

47. Functions of the Autonomic Nervous System
Sympathetic nervous system
Fight-or-flight response
Parasympathetic nervous system
Returns body to normal
Systems generally have opposite effects on organ

48. Checkpoint 8-15: Which division of the ANS stimulates a stress response, and which division reverses the stress response?
The sympathetic division stimulates a stress response and the autonomic division reverses it.