KAAP309 Lecture Notes - Lecture 11: Central Nervous System, Peripheral Nervous System, Afferent Nerve Fiber
18 May 2018
School
Department
Course
Professor
Chapter 11A: Nervous System and Nervous Tissue
I. Functions of the Nervous System
A. Sensory input: information gathered by sensory receptors about internal and
external changes
B. Integration: interpretation of sensory input
C. Motor output: activation of effector organs (muscles and glands) produce a
response
II. Divisions of the Nervous System
A. Central nervous system (CNS)
1. Brain and spinal cord
2. Integration and command center
B. Peripheral nervous system (PNS)
1. Paired spinal and cranial nerves carry messages to and from the CNS
III. Peripheral Nervous System
A. Sensory (afferent) division
1. Somatic afferent fibers – convey impulses from skin, skeletal muscles,
and joints
2. Visceral afferent fibers – convey impulses from visceral organs
B. Motor (efferent) division
1. Transmits impulses from the CNS to effector organs
2. Somatic (voluntary) nervous system: conscious control of skeletal
muscles
3. Autonomic (involuntary) nervous system (ANS)
a) Visceral motor nerve fibers
b) Regulates smooth muscle, cardiac muscle, and glands
c) Two functional subdivisions:
i. Sympathetic: mobilizes body systems during activity
ii. Parasympathetic: conserves energy, promotes house-
keeping functions during rest
IV. Histology of Nervous Tissue
A. Two principal cell types
1. Neurons – excitable cells that transmit electrical signals
2. Neuroglia (glial cells) – supporting cells
a) Astrocytes (CNS)
i. Most abundant, versatile, and highly branched glial cells
ii. Cling to neurons, synaptic endings, and capillaries
iii. Support and brace neurons
iv. Help determine capillary permeability
v. Guide migration of young neurons
vi. Control the chemical environment
vii. Participate in information processing in the brain
b) Microglia (CNS)
i. Small, ovoid cells with thorny processes
ii. Migrate toward injured neurons
find more resources at oneclass.com
find more resources at oneclass.com
iii. Phagocytize microorganism and neuronal debris
c) Ependymal cells (CNS)
i. Range in shape from squamous to columnar
ii. May be ciliated
• Line the central cavities of the brain and spinal
column
• Separate the CNS interstitial fluid from the
cerebrospinal fluid in the cavities
d) Oligodendrocytes (CNS)
i. Branched cells
ii. Processes wrap CNS nerve fibers, forming insulating
myelin sheaths
e) Satellite cells (PNS): surround neuron cell bodies in the PNS
f) Schwann cells (PNS)
i. Surround peripheral nerve fibers and form myelin sheaths
ii. Vital to regeneration of damaged peripheral nerve fibers
V. Neurons (nerve cells)
A. Special characteristics
1. Long lived (100 years or more)
2. Amitotic – with few exceptions
3. High metabolic rate – depends on continuous supply of oxygen and
glucose
4. Plasma membrane functions in
a) Electrical signaling
b) Cell-to-cell interactions during development
B. Cell body (soma)
1. Biosynthetic center of a neuron
2. Spherical nucleus with nucleolus
3. Well-developed Golgi apparatus & rough ER
4. Axon hillock: cone-shaped area from which axon arises
5. Clusters of cell bodies are called nuclei in the CNS, ganglia in the PNS
C. Processes
1. Dendrites and axons
2. Bundles of processes are called
a) Tracts in the CNS
b) Nerves in the PNS
3. Short, tapering, and diffusely branched
4. Receptive (input) region of a neuron
5. Convey electrical signals toward the cell body as graded potentials
D. Axon
1. One axon per cell arising from the axon hillock
2. Long axons (nerve fibers)
3. Occasional branches (axon collaterals)
4. Numerous terminal branches (telodendria)
find more resources at oneclass.com
find more resources at oneclass.com
5. Knoblike axon terminals (synaptic knobs or boutons)
a) Secretory region of neuron
b) Release neurotransmitters to excite or inhibit other cells
6. Function:
a) Conducting region of a neuron
b) Generates and transmits nerve impulses (action potentials) away
from the cell body
c) Molecules and organelles are moved along axons by motor
molecules in two directions:
i. Anterograde—toward axonal terminal
• Examples: mitochondria, membrane
components, enzymes
ii. Retrograde—toward the cell body
• Examples: organelles to be degraded, signal
molecules, viruses, and bacterial toxins
VI. Myelin Sheath
A. Segmented protein-lipoid sheath around most long or large-diameter axons
B. Functions to
1. Protect and electrically insulate the axon
2. Increase speed of nerve impulse transmission
C. Myelin sheaths in PNS
1. Schwann cells wraps many times around the axon
a) Myelin sheath – concentric layers of Schwann cell membrane
2. Nodes of Ranvier
a) Myelin sheath gaps between adjacent Schwann cells
D. Unmyelinated Axons
1. Thin nerve fibers are unmyelinated
2. One Schwann cell may incompletely enclose 15 or more unmyelinated
axons
E. Myelin sheaths in the CNS
1. Formed by processes of oligodendrocytes, not the whole cells
2. Nodes of Ranvier are present
3. No neurilemma
4. Thinnest fibers are unmyelinated
VII. White Matter and Gray Matter
A. White matter
1. Dense collections of myelinated fibers
B. Gray matter
1. Mostly neuron cell bodies and unmyelinated fibers
VIII. Structural Classification of Neurons
A. Multipolar—1 axon and several dendrites
1. Most abundant
2. Motor neurons and interneurons
B. Bipolar—1 axon and 1 dendrite
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Chapter 11a: nervous system and nervous tissue: sensory input: information gathered by sensory receptors about internal and external changes, integration: interpretation of sensory input, motor output: activation of effector organs (muscles and glands) produce a response. Divisions of the nervous system: central nervous system (cns, brain and spinal cord, integration and command center, peripheral nervous system (pns, paired spinal and cranial nerves carry messages to and from the cns. Parasympathetic: conserves energy, promotes house- keeping functions during rest. Histology of nervous tissue: two principal cell types, neurons excitable cells that transmit electrical signals, neuroglia (glial cells) supporting cells, astrocytes (cns) Support and brace neurons: most abundant, versatile, and highly branched glial cells, help determine capillary permeability, guide migration of young neurons. Participate in information processing in the brain: microglia (cns) Small, ovoid cells with thorny processes: migrate toward injured neurons. Phagocytize microorganism and neuronal debris: ependymal cells (cns)
