1. Chapter 7: The Nervous System

2. I. Functions of the Nervous System
A. Sensory Input- gathering information to monitor changes occurring inside and outside the body
B. Integration- to process and interpret sensory input and decide if action is needed
C. Motor Output- A response to integrated stimuli, the response activates muscles or glands

3. II. Organization of the Nervous System
A. Structural Classification- Two Subdivisions:
1. Central Nervous System (CNS) - occupies the dorsal cavity,
integration and commanding
centers
a. includes the brain and
spinal cord
2. Peripheral Nervous System
(PNS) - contains mainly the
nerves that extend from the
brain and spinal cord
a. includes cranial and spinal
nerves

4. B. Functional Classification- concerned only with the PNS and has two subdivisions
1. Sensory or Afferent division- Nerve fibers that carry information to the central nervous system
2. Motor or Efferent division- Nerve fibers that carry impulses away from the central nervous system. The Two subdivisions are the somatic and autonomic nervous system.
a. Somatic nervous system = voluntary
b. Autonomic nervous system = involuntary further divided into the sympathetic and parasympathetic divisions.
i. Sympathetic division- the “fight-
or-flight” system. Its activity is
evident when we are frightened, in emergency, or threatening situations.
ii. Parasympathetic division-
sometimes called the “resting and digesting” system. It is
most active when the body is at rest and not threatened.

5. Organization of the Nervous System
Sensory neurons
Motor neurons

6. 2. Microglia- spider-like phagocytes that dispose of debris
A. Supporting Cells
1. Astrocytes- abundant star-shaped cells, brace neurons, form the boundary between capillaries and neurons, and control the chemical environment of
the brain
2. Microglia- spider-like phagocytes that dispose of debris
-mutant-type SOD1 genes activate microglial cells; in turn, the activated microglial cells release proteins that produce nitric oxide or others (cytokines) that cause inflammation, thus causing damage to motor neurons and accelerating the progress of ALS.

7. III. Nervous Tissue: Structure and Function
A. Supporting Cells
3. Ependymal cells- line cavities of brain and spinal cord, help circulate cerebrospinal fluid

8. 4.Oligodendrocytes- produce myelin sheath around nerve fibers in CNS
5. Satellite cells- protect neuron cell bodies
6. Schwann cells- form myelin sheath in PNS

9. B. Neurons- excitable little cells that make use of their potential!
1. Cells specialized to transmit messages
2. Major regions of neurons:
a. Cell body- nucleus and metabolic center
b. Processes- fibers that extend from the body
1) dendrites- convey messages towards the cell body
2) axons- conduct messages away from the cell body, axons usually end with terminals that contain vesicles (small sacs) that contain neurotransmitters
c. Synapse- the space between two neurons

10. 3. Nerve Fiber Coverings:
a. Schwann Cells- produce myelin sheaths- wrapped membranes that enclose the axon
b. Nodes of Ranvier- gaps in myelin sheaths along the axon- allows the impulse to travel quickly down the neuron

11. B. Neurons- excitable little cells that make use of their potential!
4. Functional Classification of neurons- grouped according to the direction the impulse is traveling relative to the CNS
a. Sensory or Afferent neurons- carry impulses from sensory
receptors. Examples- cutaneous nerve receptors
b. Motor or Efferent Neurons-
carry impulses from the CNS
c. Interneuron (association
neurons) - connect sensory and motor neurons
Reflex Arc Animation

12. B. Neurons- excitable little cells that make use of their potential!
5. Structural neuron classification: (determined by the number of processes extending from the cell body)
a. Unipolar-have a short process
leaving the cell body;found in
sensory neurons of PNS
b. Bipolar-one axon and one
dendrite; found in sense organs
(eye, ear)
c. Multipolar- many extensions from the cell body; most common type

13. B. Neurons- excitable little cells that make use of their potential!
C. Functional Properties of Neurons
1. Irritability- neurons have the
ability to respond to a stimulus
2. Conductivity- the ability to transmit
an impulse
3. The plasma membrane at rest is
polarized, this is called the
Resting potential (-70 mV); this
means fewer positive ions are inside the cell (K+) than outside (Na+). As long as the inside remains more negative than the outside the neuron remains inactive.
Resting Membrane Potential Animation

14. D. Action Potentials or Nerve Impulses- an electrical charge traveling down a neuron
A nerve impulse begins with a stimulus- usually this is a neurotransmitter released by other neurons, pain receptors, light excites receptors in the eye, etc.
Once the neuron is stimulated the “sodium gates” of the neuron open and sodium ions begin flowing across the cell membrane. This is called Depolarization: a decrease in membrane potential (inside less negative) increases the chances of an impulse (action potential).
If the action potential starts, it continues down the entire neuron. Action potentials are an “all or nothing” response.
Potassium ions rush out of the neuron after sodium ions rush in, which repolarizes the membrane (returns to resting). A neuron cannot conduct another impulse until repolarization occurs.
           
           
           
           
           
Action Potential Animation

16. D. Action Potentials or Nerve Impulses- an electrical charge traveling down a neuron
The propagation of a nerve impulse occurs more rapidly in cells that contain a myelin sheath. This helps the impulse jump from node to node along the length of a neuron. This is called saltatory conduction.
Action Potential Animation

17. Conductivity- How does the impulse travel to the next neuron?
Once the impulse reaches the axon endings, vesicles containing neurotransmitters fuse with the plasma membrane, which ruptures releasing the neurotransmitter (a chemical messenger).
Some neurotransmitters fit receptor sites, some return through reuptake sites and are reused, and some are destroyed by enzymes.
If enough neurotransmitter is released the action potential will continue in the next neuron.

18. Conductivity- How does the impulse travel to the next neuron?
F. Reflexes are a predictable, rapid, involuntary response to a stimulus. These responses do not carry the impulse to the brain, they take a shorter path to allow for quicker response.
Reflex Arcs- the direct route from a sensory neuron, to interneuron, to an effector.
Autonomic reflexes include regulation of: smooth muscle, blood pressure, digestive system, and glands.
Somatic reflexes involve the activation of skeletal muscles.

19. All reflex arcs have five key elements:
sensory receptor- reacts to a stimulus
effector organ- gland or muscle stimulated
afferent neurons- carry the message to the integration center
efferent neurons- carry the message away from the integration center
integration center- the connection between the afferent and efferent pathways

20. IV. Developmental Aspects of the Nervous System
A. The nervous system begins to form in the first month of embryonic development. Therefore maternal and environmental factors may impair brain development. Mothers that smoke impair the bodies ability to carry oxygen sufficiently which increased the chances of oxygen deprivation to the babies brain cells that are forming. Other severe congenital brain disorders include cerebral palsy which is thought to be caused by a temporary lack of oxygen during delivery. Furthermore, premature babies have trouble regulating their temperature because the hypothalamus is one of the last brain areas to mature prenatally.
B. The development of motor control indicates the progressive myelination and maturation of a child’s nervous system.
Cerebral refers to the affected area of the brain, the cerebrum, and palsy refers to disorder of movement. Cerebral palsy is caused by damage to the motor control centers of the young developing brain and can occur during pregnancy, during childbirth, or after birth up to about age three.

21. IV. Developmental Aspects of the Nervous System
C. Neurons continue to die throughout life and cannot be replaced. However, most healthy aged people maintain optimal intellectual functioning. Cardiovascular disease is the major cause of declining mental function with age.