1. Nerve Tissue & The Nervous System
David L. McWhorter, Ph.D.

2. NERVOUS SYSTEM ORGANIZATION
CONSISTS OF TWO OVERLAPPING PAIRS OF SUBSYSTEMS…
CENTRAL AND PERIPHERAL NERVOUS SYSTEMS WHICH ARE DEFINED BY LOCATION:
CNS INCLUDES THE BRAIN AND SPINAL CORD
PNS INCLUDES ALL OTHER NERVE TISSUE (CRANIAL NERVES, PERIPHERAL NERVES, GANGLIA, NERVE PLEXUSES)
AUTONOMIC AND SOMATIC NERVOUS SYSTEMS WHICH ARE DEFINED BY FUNCTION & HAVE CNS AND PNS COMPONENTS:
ANS CONTROLS INVOLUNTARY VISCERAL FUNCTIONS (EG, SMOOTH MUSCLE CONTRACTION)
SOMATIC NERVOUS SYSTEM CONTROLS SOMATOSENSORY PERCEPTION (EG, TOUCH, HEAT, COLD) AND VOLUNTARY SOMATOMOTOR FUNCTIONS (EG, SKELETAL MUSCLE CONTRACTION)
The autonomic nervous system (ANS; Fig. 9‑1) and has both motor and sensory pathways, although visceral sensory pathways typically are not considered part of the ANS. Each motor pathway consists of two neurons that synapse in a peripheral autonomic ganglion (V; Fig. 9‑1). The cell body of the first (preganglionic) neuron is in the CNS; the cell body of the second (postganglionic) neuron is in the autonomic ganglion. The cell bodies of the sensory neurons are in craniospinal ganglia (V) and have processes that extend peripherally. The ANS is subdivided into the sympathetic and parasympathetic nervous systems, whose structure and functions are compared in Table 9‑2. When they innervate the same end‑organ, sympa­thetic and parasympathetic nerves usually have opposing effects. The somatic nervous system includes all nerve tissue except that of the ANS. It Acetylcholine is the most common somatic neurotransmitter.

3. There are two cell types that make up nervous tissue…
Neurons
Glial cells

4. NERVOUS SYSTEM CELLS: NEURONS
FUNDAMENTAL STRUCTURAL & FUNCTIONAL UNIT OF NERVOUS SYSTEM
> 100 MILLION
SPECIALIZED TO RECEIVE, INTEGRATE, & TRANSMIT ELECTROCHEMICAL MESSAGES
NERVE IMPULSES OR ACTION POTENTIALS
THREE MAIN PARTS:
CELL BODY
DENDRITES
AXON

5. MAIN TYPES OF NEURONS (NUMBER OF NEURITES [PROCESSES])
BIPOLAR
1 DENDRITE AND 1 AXON
UNCOMMON AND FOUND ONLY IN SPECIAL SITES: COCHLEAR & VESTIBULAR GANGLIA OF CN XIII, OLFACTORY NERVE, RETINA
MULTIPOLAR
MOST NEURONS IN BODY
MORE THAN TWO PROCESSES
EXAMPLES INCLUDE: MOTOR NEURONS AND AUTONOMIC NEURONS
PSEUDOUNIPOLAR
SINGLE PROCESS CLOSE TO CELL BODY DIVIDED INTO 2 BRANCHES
PERIPHERAL PROCESS (top)
CENTRAL PROCESS
CELL BODY NOT INVOLVED IN IMPULSE CONDUCTION
FOUND IN SPINAL DORSAL ROOT GANGLIA AND SENSORY GANGLIA OF CRANIAL NERVES V, VII, IX, AND X
Neurites – the number of processes coming off of the body
Dorsal root ganglions are collections of the cell bodies in the dorsal root

6. NEURON: CELL BODY (SOMA, PERIKARYON [G. AROUND + NUCLUEUS)
CONTAINS NUCLEUS AND SURROUNDING CYTOPLASM, EXCLUSIVE OF CELL PROCESSES
NUCLEUS IS LARGE, CENTRAL, AND EUCHROMATIC (PROMINENT NUCLEOLUS)
ABUNDANT FREE AND RER‑ASSOCIATED POLYRIBOSOMES APPEAR AS CLUMPS OF BASOPHILIC MATERIAL COLLECTIVELY CALLED NISSL BODIES
NEUROTUBULES (MICROTUBULES) AND NEUROFILAMENTS (INTERMEDIATE FILAMENTS) FOUND THROUGHOUT AND EXTEND INTO AXON AND DENDRITES
NISSL, Franz: German neurologist

7. CNS CELL BODIES
(POLYGONAL SHAPE)
PNS CELL BODIES
(ROUND SHAPE)

8. NEURON: DENDRITES (G., TREE)
USUALLY SHORT AND DIVIDE LIKE BRANCHES OF A TREE
PRINCIPAL SIGNAL RECEPTION AND PROCESSING SITES ON NEURONS
MOST SYNAPSES BETWEEN NEURONS OCCUR AT DENDRITIC SPINES
SMALL "DOOR KNOB" SHAPED EXTENSIONS FROM THE SURFACES OF THE DENDRITIC PROCESSES
INVOLVED IN PLASTIC CHANGES THAT UNDERLIE ADAPTATION, LEARNING, AND MEMORY

9. NEURON: AXON (G., AXIS)
USUALLY VERY LONG, SINGLE PROCESS WITH A CONSTANT DIAMETER
SPECIALIZED TO CONDUCT NERVE IMPULSES TO OTHER CELLS
MAY ALSO RECEIVE INFORMATION FROM OTHER NEURONS…MAINLY MODIFIES TRANSMISSION OF ACTION POTENTIALS TO OTHER NEURONS
ORIGIN HAS A SHORT PYRAMID-SHAPED REGION CALLED THE AXON HILLOCK
DISTAL PORTION USUALLY BRANCHED (COLLATERAL BRANCHES) AND ITS TERMINAL PORTIONS ARE CALLED END BULBS OR BOUTONS
FORM INTERACTIONS WITH OTHER NEURONS OR NON-NERVE CELLS CALLED SYNAPSES
PLASMA MEMBRANE AND CYTOPLASM OF AN AXON ARE CALLED AXOLEMMA AND AXOPLASM, RESPECTIVELY
Axon hillock is the beginning part
ABSENCE OF NISSEL BODIES
The main long component of a neuron is the axon (nerve fibers)

10. DENDRITE VERSUS AXON HISTOLOGY
ENTIRE AXON USUALLY NOT VISIBLE IN SECTIONED MATERIAL
ABSENCE OF NISSL‑RELATED BASOPHILIA AT ORIGIN DISTINGUISHES AXON FROM DENDRITES
Does not contain the clumps of Nissel Bodies

11. NERVOUS SYSTEM CELLS: NEUROGLIA (GLIAL CELLS OR SUPPORTING CELLS)
CNS NEUROGLIA:
ASTROCYTES
MOST POPULOUS GLIAL CELL
PART OF BLOOD- BRAIN BARRIER
OLIGODENDROCYTES
FORM MYELIN IN CNS
MICROGLIA
PHAGOCYTIC CELLS
EPENDYMAL CELLS
HELP MAKE UP CHOROID PLEXUS
PNS NEUROGLIA:
SCHWANN CELLS
FORM MYELIN IN PNS
GLIAL: G., GLUE
GLIAL CELLS ARE 10 TIMES MORE ABUNDANT THAN NEURONS.
ONE SCHWANN CELL FORMS MYELIN AROUND A SEGMENT OF ONE AXON, WHEREAS AN OLIGODENDROCYTE MAY BRANCH AND SERVE MORE THAN ONE NEURON.
ASTROCYTES ARE STAR-SHAPED CELLS; MOST NUMEROUS GLIAL CELL
*salutatory conduction (leaping signals)
Microglia are like the macrophages of the neuro system
Ependymal cells are what produce the CSF

12. CNS TERMS
NUCLEUS IS A GROUP OF CELL BODIES INVOLVED IN A COMMON FUNCTION
LOCATED IN THE GRAY MATTER
TRACT: (PATHWAY)
COLLECTIONS OF MYELINATED AXONS CONNECTING NEIGHBORING OR DISTANT NUCLEI
LOCATED IN THE WHITE MATTER
MENINGES:
C.T. LAYERS BETWEEN CNS AND SKULL & VERTEBRAL CANAL
Central Nervous system:
White matter - myelinated axons in tracts (bundles of axons originating & ending in CNS)
Gray matter -neuronal cell bodies (nuclei), dendrites, glia, unmyelinated axons
Tracts in the CNS and neurofibers in the PNS

13. CNS TERMS: BLOOD-BRAIN BARRIER
CNS TISSUE RECEIVES OXYGEN AND NUTRIENTS FROM CAPILLARIES IN PIA MATER
STRUCTURAL AND FUNCTIONAL BARRIER THAT PROTECTS CNS NEURONS FROM MANY EXTRANEOUS INFLUENCES: (i>o)
NON-FENESTRATED ENDOTHELIAL CELLS JOINED BY TIGHT JUNCTIONS
Basement membrane (basolamina)
CYTOPLASMIC PROCESSES OF ASTROCYTES
Blood‑Brain Barrier: CNS tissue receives oxygen and nutrients from capillaries in the pia mater. These capillaries are relatively impermeable because (1) their endothelial cells lack fen­estrations and are joined at their borders by tight junctions, and (2) they are partly surrounded by the cytoplasmic processes of neuroglia called astrocytes (III.A.1). These features contribute to a structural and functional barrier that protects CNS neurons from many extraneous influ­ences and prevents certain antibiotics and chemotherapeutic agents from reaching the CNS.

14. PNS COMPONENTS PERIPHERAL (SPINAL) NERVES (31 PAIRS):
8-CERVICAL
12-THORACIC
5-LUMBAR
5-SACRAL
1-COCCYGEAL
CRANIAL NERVES (12 PAIRS)
EMERGE FROM FORAMINA IN SKULL & COVERED BY MENINGES
NUMBERED I THROUGH XII FROM ANTERIOR TO POSTERIOR
11 OF 12 PAIRS ARISE FROM BRAIN
11TH PAIR ARISES MOSTLY FROM SUPERIOR PART OF SPINAL CORD
GANGLIA:
CLUSTERS OF NEURON CELL BODIES
TWO MAJOR TYPES
CRANIOSPINAL
AUTONOMIC
NERVE PLEXUSES:
NETWORK OF PERIPHERAL NERVES
THREE MAJOR NERVE PLEXUSES…
Peripheral Nervous System
nerves, ganglia (cell bodies) and nerve endings
Cranial nerves - 12 pair
Spinal nerves - 31 pair

15. PERIPHERAL (SPINAL) NERVE (31 PAIRS)
NEURONS BETWEEN SENSORY AND MOTOR NEURONS THAT GOVERN COORDINATED ACTIVITY
ARISES FROM SPINAL CORD VIA NERVE ROOTLETS
CONVERGE TO FORM TWO NERVE ROOTS:
VENTRAL ROOT
DORSAL ROOT
VENTRAL AND DORAL ROOTS UNITE TO FORM PERIPHERAL NERVE
PERIPHERAL NERVE DIVIDES INTO TWO RAMI:
ANTERIOR RAMUS
POSTERIOR RAMUS
PERIPHERAL NERVES CONSISTS OF:
BUNDLES OF NERVE FIBERS (AXONS) HELD TOGETHER BY C.T. SHEATHS
SENSORY NEURONS THAT CONVEY INFORMATION FROM THE SKIN, MUSCLES, AND JOINTS OF THE LIMBS AND TRUNK TO THE SPINAL CORD ARE PSEUDOUNIPOLAR NEURONS THAT HAVE A BIFURCATED AXON WITH CENTRAL AND PERIPHERAL BRANCHES. THE PERIPHERAL BRANCH TERMINATES IN SKIN, MUSCLE, OR OTHER TISSUE AS A FREE NERVE ENDING OR IN ASSOCIATION WITH SPECIALIZED RECEPTORS. THE CENTRAL BRANCH ENTERS THE SPINAL CORD CLOSE TO THE TIP OF THE DORSAL HORN.
Afferent – going to CNS
Efferent – leaving CNS
Peripheral nerves contain myelinated and unmyelinated axons, Schwann cells, and fibroblasts, but lack neuron cell bodies. Nuclei seen in peripheral nerve cross‑sections belong to Schwann cells (large, pale‑staining) or to fibrocytes (mature fibroblasts; small, dark‑staining). Each peripheral nerve (Fig. 9‑3) is surrounded by a dense connective tissue sheath, or epineurium, branches of which penetrate the nerve, dividing the nerve fibers into bundles, or fascicles. The sheath surrounding each fascicle is called the perineurium. Fine slips of reticular connective tissue from the perineurium penetrate the fascicles to surround each nerve fiber, forming the endoneurium. Branches of blood vessels in the epineurium. penetrate the nerve along with the connective tissue. The three main fiber types in peripheral nerves (A, B, and Q are compared in Table 9‑5.

18. PERIPHERAL (SPINAL) NERVE: FOUR TYPES OF NERVE FIBERS
SOMATIC SENSORY AND MOTOR FIBERS:
GENERAL SOMATIC AFFERENT (GSA) FIBERS
TRANSMIT SENSATIONS FROM BODY TO SPINAL CORD (EG., PAIN, TEMPERATURE, TOUCH, & PRESSURE)
GENERAL SOMATIC EFFERENT (GSE) FIBERS
TRANSMIT IMPULSES TO SKELETAL MUSCLES
VISCERAL SENSORY AND MOTOR FIBERS:
GENERAL VISCERAL AFFERENT (GVA) FIBERS
TRANSMIT REFLEX OR PAIN FROM MUCOUS MEMBRANES, GLANDS, AND BLOOD VESSELS BACK TO CNS
GENERAL VISCERAL EFFERENT (GVE) FIBERS
TRANSMIT IMPULSES TO SMOOTH AND CARDIAC MUSCLE AND GLANDULAR TISSUES

19. PERIPHERAL (SPINAL) NERVE: HISTOLOGY
LONGITUDINAL OR OBLIQUE SECTION:
“WAVINESS” OF BUNDLES
LIGHTER STAINING THAN CONNECTIVE TISSUE
DUE TO MYELIN
CROSS-SECTION:
BUNDLES OF DARK-STAINING AXONS SURROUNDED BY LIGHT/ABSENT MYELIN SHEATH
PRESENCE OF DARK-STAINING CT SHEATHS
ENDONEURIUM
PERINEURIUM
EPINEURIUM
Dark dots are axons and the white is myelin and the dark area surrounding them is the endoneuruim, separating the sections is the perineurium, and surrounding the WHOLE thing is the epineurium

20. PNS: CRANIOSPINAL GANGLIA
DORSAL ROOT GANGLIA (SPINAL GANGLIA)
CRANIAL NERVE GANGLIA
GANGLIA
Peripheral clusters of neuron cell bodies, called ganglia, are of two major types: and. Each ganglion contains large ganglion (neuron) cell bodies surrounded by satellite cells. Cell processes are supported by Schwann cells with smaller, elongated, pale‑staining nuclei. Condensed fibroblast nuclei occur in the capsule and are scattered throughout the ganglion it­self. Table 9‑4 compares the key structural and functional features of t~e two main ganglion types.
Outside the brain are these collections of cell bodies (ganglia)

21. GANGLIA HISTOLOGY CELL BODIES ARE USUALLY ROUND
WHAT ARE THE “YELLOW-BROWN PATCHES?”
The yellow stuff is lipofuschin (junk that cannot be digested)

22. PNS: AUTONOMIC GANGLIA (3)
SYMPATHETIC GANGLIA:
PARAVERTEBRAL (CHAIN) GANGLIA
PREVERTEBRAL GANGLIA
PARASYMPATHETIC GANGLIA:
WITHIN WALL OF ORGAN THEY SUPPLY
GANGLIA
Peripheral clusters of neuron cell bodies, called ganglia, are of two major types: and. Each ganglion contains large ganglion (neuron) cell bodies surrounded by satellite cells. Cell processes are supported by Schwann cells with smaller, elongated, pale‑staining nuclei. Condensed fibroblast nuclei occur in the capsule and are scattered throughout the ganglion it­self. Table 9‑4 compares the key structural and functional features of t~e two main ganglion types.
2 neuron system – preganglionic and postganglionic parts
Parasympathetic preganglionic nerve fibers are longer than sympathetic and the PS ganglion is actually associated with the wall of the organ itself
-the sympathetic preganglionic axon is shorter and the ganglion is outside of the organ wall and has a long postganglionic fiber

23. AUTONOMIC NERVOUS SYSTEM
DESCRIBED AS “VISCERAL MOTOR (EFFERENT) SYSTEM” THAT SUPPLIES:
SMOOTH MUSCLE
CONDUCTION SYSTEM OF HEART
GLANDS
CONSISTS OF TWO NEURONS THAT SYNAPSE IN AN AUTONOMIC GANGLION
CELL BODY OF FIRST NEURON IS IN CNS
PREGANGLIONIC FIBER
CELL BODY OF SECOND NEURON IS IN PNS (AUTONOMIC GANGLION)
POSTGANGLIONIC FIBER
ANS SUBDIVIDED INTO:
SYMPATHETIC NERVOUS SYSTEM
PARASYMPATHETIC NERVOUS SYSTEM
The autonomic nervous system (ANS; Fig. 9‑1) and has both motor and sensory pathways, although visceral sensory pathways typically The somatic nervous system includes all nerve tissue except that of the ANS. It Acetylcholine is the most common somatic neurotransmitter.
Sensory/afferent neurons; visceral receptors within internal organs to CNS
General Visceral Afferent (GVA)
Motor/efferent neurons carry impulses from the CNS to the visceral effector organs
(Smooth & cardiac muscle, glands); General visceral efferent (GVE)
Sympathetic - GVE signals for “fight or flight” behavior
Cell bodies of neurons found in T1-L2 lateral gray
“Thoracolumbar” division
Parasympathetic - GVE signals necessary for vegetative functions
cell bodies found in brain (CN III, VII, IX, X) and sacral regions (S2-4)
“Craniosacral” division

24. ANS: SYMPATHETIC NERVOUS SYSTEM
PREGANGLIONIC CELL BODIES:
SPINAL CORD GRAY MATTER (T1-L3 SPINAL SEGMENTS)
POSTGANGLIONIC CELL BODIES:
PARAVERTEBRAL & PREVERTEBRAL GANGLIA

25. ANS: PARASYMPATHETIC NERVOUS SYSTEM
PREGANGLIONIC CELL BODIES:
BRAINSTEM GRAY MATTER
CRANIAL DIVISION
GRAY MATTER OF SPINAL SEGMENTS S2-S4
SACRAL DIVISION
POSTGANGLIONIC CELL BODIES:
CRANIAL GANGLIA
TARGET ORGANS

26. ANS SUMMARY

27. SOMATIC NERVOUS SYSTEM
CONTROLS SOMATOSENSORY PERCEPTION
TOUCH, HEAT, COLD
TAKES 3 neurons
CONTROLS SOMATOMOTOR (VOLUNTARY) FUNCTIONS
SKELETAL MUSCLE CONTRACTION
Takes 2 neurons
ACETYLCHOLINE IS MOST COMMON SOMATIC NEUROTRANSMITTER

28. CONCLUSION: IMPORTANT POINTS OF LECTURE (SLIDE 1 OF 2)
WHAT DO BRAIN AND SPINAL CORD COMPRISE?
WHAT DO CRANIAL NERVES, PERIPHERAL NERVES, GANGLIA, NERVE PLEXUSES COMPRISE?
WHAT ARE COLLECTIONS OF CELL BODIES CALLED IN THE CNS? PNS?
WHAT ARE COLLECTIONS OF AXONS IN THE CNS? PNS?
WHAT ARE THE TWO CHIEF COMPONENTS OF THE BLOOD BRAIN BARRIER?
WHAT ARE A NETWORK OF PERIPHERAL NERVES? LIST THE FIRST TWO YOU WILL ENCOUNTER?
WHAT IS THE CHIEF COMPONENT OF A PERIPHERAL NERVE?
WHICH CELL(S) MAKE MYELIN IN THE CNS AND PNS?
WHICH STRUCTURE CONTAINS ONLY SENSORY FIBERS? MOTOR FIBERS? BOTH SENSORY AND MOTOR?
WHERE ARE SENSORY CELL BODIES LOCATED?

29. CONCLUSION: IMPORTANT POINTS OF LECTURE (SLIDE 2 OF 2)
WHAT IS LOCATED IN THE SPINAL CORD GRAY MATTER (T1-L3 SPINAL SEGMENTS)?
WHAT IS THE SECOND NEURON OF THE MOTOR COMPONENT OF THE ANS CALLED AND WHERE IS IT LOCATED?
WHERE ARE THE POSTGANGLIONIC SYMPATHETIC CELL BODIES LOCATED?
WHAT IS LOCATED IN THE MEDULLA AND MIDBRAIN NUCLEI (CNS GRAY MATTER) AND GRAY MATTER OF SPINAL SEGMENTS S2-S4?
WHERE ARE POSTGANGLIONIC PARASYMPATHETIC CELL BODIES LOCATED?
WHICH AUTONOMIC FIBER TYPE HAS A SHORT PREGANGLIONIC AXON AND A LONG POSTGANGLIONIC AXON THAT SECRETES NOREPINEPHRINE?