1. Introduction to Nervous System

2. Nervous Tissue
Controls and integrates all body activities within limits that maintain life
Three basic functions
sensing changes with sensory receptors
interpreting and remembering those changes
reacting to those changes with effectors (motor function)
Controls and integrates all body activities within limits that maintain life
Three basic functions
sensing changes with sensory receptors
fullness of stomach or sun on your face
transport sensory information from skin, muscles, joints, sense organs & viscera to CNS
interpreting and remembering those changes
connect sensory to motor neurons
90% of neurons in the body
reacting to those changes with effectors
muscular contractions
glandular secretions
Lecutre 8: Nervous System

4. The PNS is divided into :
1- a somatic nervous system (SNS)
2- an autonomic nervous system (ANS)

5. CNS CNS Sensory (Afferent) vs. Motor (Efferent)
sensory (afferent) nerve
CNS
e.g., skin
(pseudo-) unipolar neurons conducting impulses
from sensory organs to the CNS
motor (efferent) nerve
CNS
e.g., muscle
multipolar neurons conducting impulses
from the CNS to effector organs (muscles & glands)
Gray’s Anatomy

6. Organization Sensory Integration Motor SNS (Sensory) Brain Spinal cord
ANS
(Motor)
ANS
(Sensory)

7. Neuron has three parts:
(1) a cell body: perikaryon or soma
(2) dendrites
(3) an axon

8. Neurons • Dendrites: carry nerve impulses toward cell body
• Axon: carries impulses away from cell body
• Synapses: site of communication between neurons using chemical neurotransmitters
• Myelin & myelin sheath: lipoprotein covering produced by glial cells (e.g., Schwann cells in PNS) that increases axonal conduction velocity
dendrites
cell
body
axon with
myelin sheath
Schwann
cell
synapses
Moore’s COA5 2006

9. Notice that action potential propagation is unidirectional

10. Neurons Cell body Nissl bodies Golgi apparatus Neurofilaments (IFs)
Microtubules
Lipofuscin pigment clumps
Cell processes
Dendrites
Axons
Functional unit of nervous system
Have capacity to produce action potentials
electrical excitability
Cell body
single nucleus with prominent nucleolus
Nissl bodies (chromatophilic substance)
rough ER & free ribosomes for protein synthesis
neurofilaments give cell shape and support
microtubules move material inside cell
lipofuscin pigment clumps (harmless aging)
Cell processes = dendrites & axons
Lecutre 8: Nervous System

11. Structure of neurons Axoplasm: cytoplasm of axon
Axolemma: cell membrane of axon
Axon hillock: where axon originates from soma
Synaptic boutons: swelling of axon terminal
Synapse: junction axon makes with cell acting upon
Synaptic vesicles

12. Axon Dendrite Becomes much thinner (tapering) short Branches profusely
The cytoplasm of its base is similar to cell body
Dendtric spines (points of synapse with other neurons)
Always unmyelinated
Nearly constant diameter
Much Longer
Branches less profusely
Distal end forms terminal arborization and terminal boutons
Mostly myelinated, could be unmyelinated
Axoplasm contains mitochondria, microtubules, neurofilaments and SER but not RER and ribosomes
Bidirectional transport along the axon

13. presynaptic neuron
Synaptic vesicles
contain the neurotransmitter
synaptic cleft
postsynaptic neuron

15. Axonal transport
Anterograde: movement away from soma
Retrograde: movement up toward soma

17. Neurons:
Sensing, thinking, remembering, controlling muscle activity, and regulating glandular secretions
Do not divide (no centriols!!!)
Long lived
High metabolic activity
Electrically excitable
Neuroglia :
Support, nourish, and protect neurons
Divide
Smaller cells but they greatly outnumber neurons

18. Parts of a Neuron Neuroglial cells Nucleus with Nucleolus
Axon or Dendrites
Cell body

19. Multipolar neurons
usually have several dendrites and one axon
motor neurons
2. Bipolar neurons
have one main dendrite and one axon
the retina of the eye
3. Unipolar neurons (pseudounipolar neurons)
sensory neurons
Structural classification of neurons

20. Don’t produce action potential Regulatory function
Figure 9–4 Structural classes of neurons.
Shown are the three main types of neurons, with short descriptions. (a) Most neurons, including all motor neurons and CNS interneurons, are multipolar. (b) Bipolar neurons include sensory neurons of the retina, olfactory mucosa, and inner ear. (c) All other sensory neurons are unipolar or pseudounipolar. (d) Anaxonic neurons of the CNS lack true axons and do not produce action potentials, but regulate local electrical changes of adjacent neurons.
4- Anaxonic neuron:
CNS
Lack true axon
Don’t produce action potential
Regulatory function
Figure 9-4

21. 1. Tissues: neurons vs. glia 2. Position: CNS vs. PNS
3. Function 1: sensory vs. motor
4. Function 2: somatic vs. visceral
glial cell
Gray’s Anatomy

22. Continuous versus Saltatory Conduction
Continuous conduction (unmyelinated fibers)
Saltatory conduction (myelinated fibers)
A.P. Na Na Na Na Na Na Na
Continuous conduction (unmyelinated fibers)
step-by-step depolarization of each portion of the length of the axolemma
Saltatory conduction
depolarization only at nodes of Ranvier where there is a high density of voltage-gated ion channels
current carried by ions flows through extracellular fluid from node to node Na Na Na
Lecutre 8: Nervous System

23. Saltatory Conduction
Nerve impulse conduction in which the impulse jumps (Salta) from node to node Na
A.P. Na Na Na Na
Local anesthetics!!!!!!

24. Types of synapses

25. Clusters of Neuronal Cell Bodies
a ganglion (plural is ganglia) a cluster of neuronal cell bodies located in the PNS.
a nucleus: a cluster of neuronal cell bodies located in the CNS.

26. Bundles of Axons
A nerve: is a bundle of axons that is located in the PNS.
Cranial nerves connect the brain to the periphery
spinal nerves connect the spinal cord to the periphery
A tract: is a bundle of axons located in the CNS.
Tracts interconnect neurons in the spinal cord and brain.

28. Figure 9–26 Peripheral nerve connective tissue: Epi-, peri-, and endoneurium.
(a) The diagram shows the relationship among these three connective tissue layers in large peripheral nerves. The epineurium (E) consists of a dense superficial region and a looser deep region that contains the larger blood vessels. (b) The micrograph shows a small vein (V) and artery (A) in the deep epineurium (E). Nerve fibers (N) are bundled in fascicles. Each fascicle is surrounded by the perineurium (P), consisting of a few layers of unusual squamous fibroblastic cells that are all joined at the peripheries by tight junctions. The resulting blood-nerve barrier helps regulate the microenvironment inside the fascicle. Axons and Schwann cells are in turn surrounded by a thin layer of endoneurium. X140. H&E.
(c) As shown here and in the diagram, septa (S) of connective tissue often extend from the perineurium into larger fascicles. The endoneurium (En) and lamellar nature of the perineurium (P) are also shown at this magnification, along with some adjacent epineurium (E). X200. PT.
(d) SEM of transverse sections of a large peripheral nerve showing several fascicles, each surrounded by perineurium and packed with endoneurium around the individual myelin sheaths. Each fascicle contains at least one capillary. Endothelial cells of these capillaries are tightly joined as part of the blood-nerve barrier and regulate the kinds of plasma substances released to the endoneurium. Larger blood vessels course through the deep epineurium that fills the space around the perineurium and fascicles. X450.
Figure 9-26