Week 7 - Nervous System

Question 1

define the three specific functions of the nervous system

Answer 1

1. sensory input - gathering information
   - sensory receptors monitor changes, called “stimuli” occurring inside and outside the body
2. integration
   - nervous system processes and interprets sensory input and decides whether action is needed
3. motor output
   - a response, or effect, activates muscles or glands

Question 2

describe the organization of the nervous system, including the structural and functional classifications

Answer 2

• structure (structural classification)

- activities (functional classification)

Question 3

what is the central nervous system (CNS)?

Answer 3

Organs

• brain
• spinal cord

Question 4

what are the functions of the central nervous system (CNS)?

Answer 4

• integration; command center
• interprets incoming sensory information
• issues outgoing instructions

Question 5

what is the peripheral nervous system (PNS)?

Answer 5

• nerves extending from the brain and spinal cord
• spinal nerves: carry impulses to an from the spinal cord
• cranial nerves: carry impulses to and from the brain

Question 6

what are the functions of the peripheral nervous system (PNS)?

Answer 6

serves as communication lines among sensory organs, the brain and spinal cord, and glands or muscles

Question 7

what are the functional classifications?

Answer 7

• sensory (afferent) division

- motor (efferent) division

Question 8

what is the sensory (afferent) division?

Answer 8

nerve fibers that carry information to the central nervous system

• somatic sensory (afferent) fibers carry information from the skin, skeletal muscles, and joints
• visceral sensory (afferent) fibers carry information from visceral organs

Question 9

what is the motor (efferent) division?

Answer 9

nerve fibers that carry impulses away from the central nervous system organs to effector organs (muscles and glands)

Question 10

what are the two subdivisions of the motor (efferent) division?

Answer 10

somatic nervous system = voluntary
- consciously (voluntarily) controls skeletal muscles

autonomic nervous system = involuntary

• automatically controls smooth and cardiac muscles and glands
• further divided into the sympathetic and parasympathetic nervous systems

Question 11

what are the basic structures and functions of neuroglia types?

Answer 11

• support cells in the CNS are grouped together as neuroglia

general functions:

• support
• insulate
• protect neurons

Question 12

what are the two principal cells types that the nervous tissue is made of? (structure and function)

Answer 12

1) supporting cells (called “neuroglia, “glial cells” “glia”)
- resemble neurons
- unable to conduct nerve impulses
- never lose the ability to divide

2) neurons

Question 13

Describe the CNS glial cells: astrocytes

Answer 13

• abundant, star-shaped cells
• brace and anchor neurons to blood capillaries
• determine permeability and exchanges between blood and capillaries and neurons
• protects neurons from harmful substances in the blood
• control the chemical environment of the brain

Question 14

Describe CNS glial cells: microglia

Answer 14

• spiderlike phagocytes
• monitor health of nearby neurons
• dispose of debris

Question 15

describe CNS glial cells: ependymal cells

Answer 15

• line cavities of the brain and spinal cord

- cilia assist with circulation of cerebrospinal fluid

Question 16

describe CNS glial cells: oligodendrocytes

Answer 16

• wrap around nerve fibers in the central nervous system

- produce myelin sheaths

Question 17

What are the PNS glial cells?

Answer 17

Schwann cells
- form myelin sheath around nerve fibers in the PNS

Satellite cells
- protect and cushion neuron cell bodies

Question 18

what are neurons?

Answer 18

• neurons = nerve cells

- cells specialized to transmit messages (nerve impulses)

Question 19

what are the major regions of all neurons?

Answer 19

cell body - nucleus and metabolic center of the cell

processes - fibers that extend from the cell body

Question 20

what is the cell body of the neuron?

Answer 20

• cell body is the metabolic center of the neuron
• nucleus with lark nucleolus
• nissl bodies: rough endoplasmic reticulum
• neurofibrils: intermediate filments that maintain cell shape

Question 21

what are the processes (fibers)?

Answer 21

dendrites: conduct impulses toward the cell body
- neurons may have hundreds of dendrites

axons: conduct impulses away from the cell body
- neurons have only one axon arising from the cell body at the axon hillock
- end in axon terminals, which contain vesicles with neurotransmitters
- axon terminals are separated from the next neuron by a gap

synaptic cleft: gap between axon terminals and the next neuron
synapse: functional junction between nerves where a nerve impulse is transmitted

Question 22

describe myelin

Answer 22

• white, fatty material covering axons
• protects and insulates fibers
• speeds nerve impulse transmission

Question 23

describe myelin sheaths

Answer 23

1) schwann cells - wrap axons in a jelly roll-like fasion (PNS) to form the myelin sheath
- neurilemma - part of the Schwann cecll external to the myelin sheath
- nodes of Ranvier - gaps in myelin sheath along the axon

2) Oligodendrocytes - produce myelin sheaths around axons of the CNS
- lack a neurilemma

Question 24

Functional Classification - Describe Sensory (afferent) neurons

Answer 24

• carry impulses from the sensory receptors to the CNS
  receptors:
• cutaneous sense organs (skin)
• proprioceptors (muscles and tendons)

Question 25

Functional Classification - Describe Motor (efferent) neurons

Answer 25

carry impulses from the central nervous system to viscera and/or muscles and glands

Question 26

Functional Classification - Describe Interneurons (association neurons)

Answer 26

- cell bodies located in the CNS | - connect sensory and motor neurons

Question 27

What is structural classification?

Answer 27

based on number of processes extending from the cell body

Question 28

Describe structural classification - Multipolar Neurons

Answer 28

many extensions from the cell body - all motor and interneurons are multipolar - most common structural type

Question 29

Describe structural classification - Bipolar neurons

Answer 29

one axon and one dendrite - located: special sense organs (nose and eyes) - rare in adults

Question 30

Describe structural classification - Unipolar neurons

Answer 30

have a short single process leaving the cell body - sensory neurons found in PNS ganglia - conduct impulses both toward AND away from the cell body

Question 31

what are the functional properties of neurons?

Answer 31

1) irritability - ability to respond to a stimulus and convert it to a nerve impulse 2) conductivity - ability to transmit the impulse to other neurons, muscles, or glands

Question 32

what are the types of sensory receptors?

Answer 32

1) free nerve endings (pain and temperature receptors) 2) Meissner's corpuscle (touch receptor) 3) Lamellar corpuscle (deep pressure receptor) 4) Golgi tendon organ (proprioceptor) 5) Muscle spindle (proprioceptor)

Question 33

What is the electrical conditions of a resting neuron's membrane?

Answer 33

- the plasma membrane at rest is inactive (polarized) - fewer positive ions are inside the neuron's plasma membrane than outside - ---- K is the major positive ion inside the cell - ---- Na is the major positive ion outside the cell - as long as the inside of the membrane is negative (fewer positive ions) than the outside, the cell remains inactive

Question 34

What are the steps of the nerve impulse?

Answer 34

1. resting membrane is polarized 2. stimulus initiates local depolarization 3. depolarization and generation of an action potential 4. propagation of the action potential 5. repolarization 6. initial ionic conditions restored

Question 35

Describe action potential initiation and generation

Answer 35

- a stimulus changes the permeability of the neuron's membrane to sodium ions - sodium channels now open, and sodium (Na+) diffuses into the neuron - the inward rush of sodium ions changes the polarity at that site and is called "depolarization" - a graded potential (localized depolarization) exists where the inside of the membrane is more positive and the outside is less positive - if the stimulus is strong enough and sodium influx great enough, local depolarization activates the neuron to conduct an action potential (nerve impulse)

Question 36

Describe propagation of the action potential

Answer 36

- if enough sodium enters the cell, the action potential (nerve impulse) starts and is propagated over the entire axon - "all-or-none response" means the nerve impulse either is propagated or is not - fibers with myelin sheaths conduct nerve impulses more quickly

Question 37

Describe repolarization

Answer 37

- membrane permeability changes again --- becoming impermeable to sodium ions and permeable to potassium ions - potassium ions rapidly diffuse out of the neuron, repolarizing the membrane - repolarization involved restoring the inside of the membrane to a negative charge and the outer surface to a positive charge - initial conditions of the sodium and potassium ions are restored using the sodium-potassium pump - this pump, using ATP, restores the original configuration - 3 sodium ions are ejected from the cell - 2 potassium ions are returned to the cell - until repolarization is complete, a neuron cannot conduct another nerve impulse