Chapter 24 Neurons and Nervous Systems

Chapter 24 Neurons and Nervous Systems

I. The Human Nervous System

receives sensory input,

performs integration, and

generates motor output to muscles and glands.

1.  The central nervous system (CNS) consists of the brain and spinal cord.

2.  The peripheral nervous system (PNS) contains the cranial and spinal nerves and ganglia.

II. Nervous Tissue

·  Nervous tissue is made up of neurons (nerve cells) and neuroglia (which support and nourish the neurons).

A. Neurons

1. The cell body contains the nucleus and other organelles.

2. Dendrites receive information and conduct impulses toward the cell body.

3. A Single axon conducts impulses away from the cell body to stimulate or inhibit a neuron, muscle, or gland.

1)  A long axon is called a nerve fiber.

2)  The long axons are covered by a white myelin sheath.

4. Types of Neurons

a.  Motor (efferent) neurons

b.  Sensory (afferent) neurons

1. Interneurons

B. Transmission of the Nerve Impulses

1. Resting Potential: Inside membrane

a.  About negative 70 mV

b.  The sodiumpotassium pump maintains this unequal distribution of Na+ and K+.

2. Action Potential

a.  The oscilloscope goes from –70 mV to +40 mV in a depolarization phase, then recovers.

b.  Due to opening of the Na+ and K+ ion gates.

3. Propagation of Action Potentials: saltatory conduction.

C. Transmission Across a Synapse

1. The minute space between the axon bulb and the cell body of the next neuron is the synapse.

2. A synapse consists of a presynaptic membrane, a synaptic cleft, and the postsynaptic membrane.

a. Synaptic vesicles store neurotransmitters that diffuse across the synapse.

b. When the action potential arrives at the presynaptic axon, synaptic vesicles merge with the presynaptic membrane.

c. When vesicles merge with the membrane, neurotransmitters are discharged into the synaptic cleft.

3. Neurotransmitters

a.  At least 100 different neurotransmitters have been identified.

b.  Acetylcholine (ACh) and norepinephrine (NE), dopamine, and serotonin (5-HT) are the major ones.

III. Central Nervous System: Brain and Spinal Cord

A. The Spinal Cord

1. The spinal cord has two main functions.

a. It is the center for many reflex actions.

b. It provides the means of communication between the brain and the spinal nerves.

2. The spinal cord is composed of white and gray matter.

B. The Brain

1. The cerebrum, also called the telencephalon, is the largest part of the brain in humans.

2. The cerebral cortex contains motor, sensory, and association areas.

1)  The human hand takes up a large proportion of the primary motor area.

2)  Sensory information from the skin and skeletal muscles arrives at a primary somatosensory area.

3)  The primary visual area in the occipital lobes.

4)  The primary auditory area in the temporal lobe receives information from our ears.

3. Basal Nuclei

1) Aside from the tracts, there are masses of gray matter located deep within the white matter.

2) These basal nuclei integrate motor commands; malfunctions cause Huntingdon and Parkinson disease.

4. The Diencephalon: contains the hypothalamus and thalamus.

5. The Brain Stem contains the medulla oblongata, pons, and midbrain. It contains vital centers for regulating heartbeat, breathing, and vasoconstriction.

IV. Peripheral Nervous System

A. Somatic System

B. The Reflex Arc

C. Autonomic System

Critical Thinking

Question 1. What keeps a nerve impulse from flowing “backward” in a neuron and across a synapse?

Question 2. How can a person be declared “brain dead” when he/she is still breathing?

Question 3. Why is it difficult to diagnose the cause of an inability to speak?

Review Qs:

1. The following pairs of terms:

Ø  Somatic nerves / Autonomous

Ø  Motor / Sensory

Ø  Sympathetic / Parasympathetic

Ø  Afferent / Efferent

Ø  Excitatory / Inhibitory

Ø  Agonist / Antagonist

Ø  Pre-synaptic / Post-synaptic

2. The Greek root word meaning "nerve" underlies the term______.

3. Anatomy of a neuron:

4. We can define a nerve impulse as______.

5. The Greek root word for "axis" underlies the term______.

6. There is a trigeminal sensory nerve that lets you feel what is happening to your face, and there is a separate facial motor nerve that allows you to control the movements of each side of your face. Also consider that the routes for these two nerves are separate but converge at the same general "facial" region in the brain.
You have no facial control but feeling is present (known as Bell palsy).The block is in ______.

7. You can neither feel one-half of your face nor control its movement; the physician is concerned about possible stroke or brain tumor.The damage is in the ______.

8. The inside of the neuron membrane at rest isnegatively / positively charged.

9. How fast a person can type or play the piano keys depends upon the ultimate limitation to the number of nerve impulses she or he can send to a muscle per second. This is determined by

A.primarily the type of muscle.
B.whether the signal is pain, sound, motor, etc.
C.the magnitude or strength of the nerve signal.
D.the number of neurons and synapses involved.
E.the speed with which sodium ions can be pumped back outside the neuron membrane.

10. Which statement is NOT true about the neuron cell membrane?

A.The resting potential of a typical neuron is -70 mV within the neuron.

B.There is a difference in electrical potential between the sides of the cell membrane.
C.There is a voltage difference between the inside and the outside of the cell membrane.
D.The resting potential is the difference in electrical potential between the sides of the cell membrane when the cell is at rest.
E.The action potential is a rapid change in the electrical potential, making it more negative inside the cell than it was before.

11. In the axon, the nerve impulses travelaway / towards the cell body.

12. Which is NOT a correct association of structure and function?

A.axons--outgoing signals
B.sensory neuron--delivers signals to control sensory organs such as eye movement
C.cell body--nucleus and organelles
D.dendrites--incoming signals
E.interneuron—conveys signals to other parts of the CNS

13. When a finger or other appendage is severed in an accident, it is possible to surgically rejoin most tissues (bone, skin, etc.) and most will grow back together. However, in a cut through an appendage nerve, it is currently very difficult to reconnect what are primarily severed______.

14. Which statement is NOT true about the development of an action potential?

A.It can be produced by an electric shock or a sudden pH change.
B.There is a rapid change in polarity from about -70 mV to about +40 mV.
C.The action potential ends when the polarity across the membrane reaches +40 mV.
D.Depolarization occurs when sodium gates open and allow sodium ions to enter the cell.
E.Potassium gates open after the sodium gates and allow potassium ions to leave the cell.

15.Which statement is NOT true about the action potential of the neuron?

A.Large fibers in neurons of some invertebrates carry very rapid nerve impulses.
B.The action potential travels the length of the axon in a self-propagating fashion.
C.Repolarization occurs as movement of potassium ions occurs across the cell membrane.
D.The action potential moves more slowly along a myelinated nerve fiber than along one with no myelin sheath.
E.Saltatory conduction occurs from one neurilemmal node to another along a myelinated neuron.

16. What keeps a nerve impulse from flowing "backward" in a neuron?

17. The connection space between the dendrite of one cell and the axon of another cell is called
______.

18.At a synapse,

A.synaptic vesicles fuse with the postsynaptic membrane.
B.synaptic vesicles fuse with the pre-synaptic membrane.
C.neurotransmitters diffuse across the synaptic cleft.
D.neurotransmitters are actively transported across the synaptic cleft.
E.synaptic vesicles fuse with the pre-synaptic membrane, and neurotransmitters diffuse across the synaptic cleft.

19.The likely effect on a neuron of two excitatory signals and twenty inhibitory signals is

A.transmission of a nerve impulse.
B.transmission of a nerve impulse releasing inhibitory neurotransmitters at the next synapse.
C.prohibiting the axon from firing at all.
D.confused integration.

20.Which of the following is NOT true about the myelin sheath?

A.It is composed of layers of cellular membrane containing myelin around nerve fibers.
B.It gives nerve fibers their white glistening appearance.
C.It is surrounded by the neurilemma.
D.It decreases the speed of nerve impulse conduction.
E.It is formed from Schwann cells.

21. The sodium/potassium pump is primarily responsible for the______.

22. Neurotransmitters are molecules that cross the synaptic cleft andinhibit / excite / both the post synaptic neuron.

23. You spray an insect with a common insecticide that destroys the ability of acetylcholinesterase to recycle acetylcholine. What then happens?

A.This kills the neuron directly.
B.The lack of recycled acetylcholine brings cell metabolism to a halt.
C.The insect loses control of body functions as nerve impulses flow continuously.
D.This prevents the synapse from restoring its ability to "reset" itself for the next impulse.
E.The synapse is prevented from restoring its ability to "reset" itself for the next impulse, therefore, the insect loses control of body functions due to a continuous flow of impulses.

24.Carpal tunnel syndrome is due to damage to one nerve and results in lack of control to the wrist and also numbness. This indicates that the

A.nerve contained sensory neurons.
B.nerve contained motor neurons.
C.nerve contained both sensory and motor neurons.
D.damage was to a central body in a ganglion.
E.damage was to the spinal cord interneuron.

25. The peripheral nervous system consists of the______and ______.

26. Spinal nerves contain______and ______fibers.

27. The primary functions of the spinal cord involve______and ______.

28. A reflex action

A.is an automatic, involuntary response.
B.does not require the central nervous system.
C.is normally controlled consciously.
D.has no protective value.
E.is only found in humans.

29. The Greek root word for "membranes covering the brain" underlies the term______.