Download Nervous Tissue (Ch

NERVOUS TISSUE (Ch. 13)
Human Anatomy lecture
I. Overview of nervous system
A. Organization (compare w/Fig. 13.2)
Central Nervous System (CNS)
(brain & spinal cord)
Peripheral Nervous System (PNS)
Somatic NS
(SNS)
-voluntary-
sensory
(conscious)
Autonomic NS
(ANS)
motor
(skeletal
muscle)
sensory
motor
(unconscious)
sympathetic
Enteric NS
(ENS)
-involuntary-
“entero”=small
intestine
sensory
motor
(unconscious)
parasympathetic
gut
(cardiac muscle, smooth muscle
& glands)
NOTE: Your text classifies the ANS as “visceral motor”, excluding any sensory component
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B. 2 major cell types
- neurons -- conduct action potentials
- neuroglia -- nervous connective tissue
“glue”
II. Neurons
A. Properties
1. excitability (irritability) – respond to stimuli
2. conductivity – produce traveling electrical signals
3. secretion – release chemical signals, neurotransmitters
B. Structure KNOW: 13.4a (*review sketch in Histology lecture notes)
1. soma (cell body)
- contains typical organelles
* Nissl bodies – dense networks of rough endoplasmic reticulum,
compartmentalized by
* neurofibrils - intermediate filaments (actin) of cytoskeleton
2. dendrites - receive
- short, highly branched
- not usually myelinated
3. axon - sends
- long, few branches (except for axon collaterals)
- no Nissl bodies
- originates at axon hillock
- cytoplasm = axoplasm; plasma membrane = axolemma
- terminal arborization:
 “tree”
 synapses with another neuron, muscle, or gland cell
 synaptic knobs contain neurotransmitters (chemical
messengers)
Ex: NMJ seen in Lab 1
C. Classification of neurons
1. structural - by the number of processes KNOW Fig. 13.5
- multipolar - many dendrites, 1 axon
- most CNS neurons
- bipolar - 1 dendrite and 1 axon
- retina, inner ear, olfactory
- unipolar - 1 process which branches
- always sensory: dorsal root ganglion near spinal cord
-anaxonic – no axon
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2. functional - by the direction the impulse travels  KNOW Fig. 13.3
- sensory (afferent) - receptor — CNS
- motor (efferent) - CNS --- effector
- association (interneurons) - connect sensory to motor and to each other
- 90% of all neurons
III. Neuroglia -- Table 13.1
- support cells, also interact metabolically
- can divide and multiply  source of most “brain tumors”
- outnumber neurons ~5 to 50:1, makeup over ½ CNS volume
A. CNS neuroglia  KNOW Fig. 13.6
1. astrocytes - many processes
“star”
- largest & most common glial cell (90% of some brain areas)
- cover brain surface & nonsynaptic areas in gray matter
- form supportive network, link neurons to blood vessels
- contribute to blood-brain barrier
2. oligodendrocytes - few processes
“few”
“tree”
- form supporting network
- form myelin sheath in CNS
3. microglia
“small”
- derived from WBCs
- phagocytes
“eat”
4. ependymal cells
- epithelial cells
- line ventricles (brain) and central canal (spinal cord)
- produce cerebrospinal fluid (CSF)
B. PNS neuroglia
1. neurilemmocytes (Schwann cells)
“sheath”
- form myelin sheath in PNS
- enclose unmyelinated axons – Fig. 13.8
2. satellite cells
- small
- support cells in ganglia
- surround neuron cell bodies
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IV. Myelin sheath – Fig. 13.4 & 13.7
- electrically insulates axons
- increase speed, decrease energy of conduction
A. formed by Schwann cells in PNS
- myelin sheath = compacted membranes
- neurilemma = outer layer of cytoplasm + nucleus
- node of Ranvier = bare axolemma
 Schwann cell can also protect nerve fibers without forming myelin sheath
(Fig. 13.8)
B. formed by oligodendrocytes in CNS
- one oligodendrocyte can wrap multiple axons
- no neurilemma
V. Terminology
- nerve fiber - axon (usually) or dendrite
- nerve - bundle of fibers in PNS with c.t. coats- Fig. 14.7
1. epineurium - surrounds entire nerve
2. perineurium - surrounds bundle of fibers (fascicle)
3. endoneurium - surrounds single fiber
 Be able to sequence path of a needle inserted into a peripheral nerve that pierces the
axoplasm
4. neurilemma
5. myelin sheath
6. axolemma
- tract - bundle of fibers in CNS (no c.t.)
- ganglion - collection of neuron cell bodies in the PNS
- nucleus - collection of neuron cell bodies in the CNS
- white matter = myelinated axons (tracts in CNS)
- gray matter = cell bodies (nuclei in CNS)
+ unmyelinated axons, neuroglia
 I extend this distinction into the PNS
Rule #1? Functional differences
 White matter = information pathways
 Gray matter = integration centers (decision-making)
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