1. Major Structures of the Nervous System
Brain, cranial nerves, spinal cord, spinal nerves, ganglia, enteric plexuses and sensory receptors

2. Nervous System Divisions
Central Nervous System (CNS)
consists of the brain and spinal cord
Peripheral Nervous System (PNS)
consists of cranial and spinal nerves that contain both sensory and motor fibers
connects CNS to muscles, glands & all sensory receptors

3. Nerve – a bundle of hundreds to thousands of axons plus associated connective tissue and blood vessels that lies outside the brain and spinal cord.  
Cranial Nerve – nerves that emerge from the brain & follows a defined path
Spinal Nerves – nerves that emerge from the spinal cord & follows a defined path
Ganglia – small masses of nervous tissue, consisting primarily of neuron cell bodies and are located outside of the brain and spinal cord. They are associated with the brain and spinal nerves.

4. Enteric plexuses – networks of neurons located in the walls of organs of the gastrointestinal tract that help regulate the digestive system
Sensory receptor – a structure of the nervous system that monitors changes in the external or internal environment.

6. PERIPHERAL NERVOUS SYSTEM
CENTRAL
NERVOUS
SYSTEM
brain
spinal cord
sensory
nerves
axons of
motor nerves
somatic
subdivision
(motor functions)
These nerves carry
signals to and from
skeletal muscles,
tendons, and skin.
autonomic
subdivision
(visceral functions)
These nerves carry
signals to and from
internal organs (gut,
heart, glands, etc.).
Sensory
Motor
parasympathetic
nerves
sympathetic
nerves
PERIPHERAL NERVOUS SYSTEM

7. Controls and integrates all body activities within limits that maintain life
Three basic functions
1. Sensing changes with sensory receptors
- internally & externally
2. Integration (interpreting, remembering) of those changes in the internal & external environment
3. Motor- reacting to those changes with effectors; by muscular contractions (smooth, cardiac & skeletal) & glandular secretions

8. Neuroglial Cells Do not produce action potentials(AP)
Half of the volume of the CNS
Smaller cells than neurons
25 times more numerous than neurons
Cells can divide
rapid mitosis in tumor formation (gliomas)
4 Neuroglial Cell types in CNS
astrocytes, oligodendrocytes, microglia & ependymal
2 Neuroglial Cell types in PNS
Schwann and satellite cells

9. Neurons Functional unit of nervous system
Most do not divide & are limited in number
Have capacity to produce action potentials
Cell body
single nucleus with prominent nucleolus
Nissl bodies (will stain dark)
rough ER & free ribosomes for protein synthesis
Nerve fiber – general term for any neuronal process that emerges from the cell body of a neuron.
Dendrites- the receiving on input portions of a neuron.

10. Neuroglial cells
Nucleus with Nucleolus
Axons or Dendrites
Cell body

11. Axon Conduct impulses away from cell body
Long, thin cylindrical process of cell
Arises at axon hillock
Impulses arise from trigger zone
Side branches (collaterals) end in fine processes called axon terminals
Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters

13. Neurotransmitters
a molecule released from a synaptic vesicle that excites or inhibits another neuron, muscle fiber or gland cell.

15. Classifying Neurons
Structural classification is based on the number of processes (axons or dendrites) extending from the cell body.
Structural or Anatomic Classification: Anaxonic, bipolar, unipolar (pseudounipolar) , or multipolar.
Functional Classification: Sensory afferents, interneurons, motor efferents.

16. Classifying Neurons
Multipolar neurons have several dendrites and only one axon and are located throughout
the brain and spinal cord.
The vast majority of the
neurons in the human body
are multipolar.

17. Classifying Neurons
Bipolar neurons have one main dendrite and one axon.
They are used to convey the special senses of sight, smell, hearing and balance.
Found in the retina of the eye, theinner ear, and the olfactory (olfact = to smell) area of the brain.

18. Classifying Neurons
Unipolar neurons contain one process which extends from the body and divides into a central branch that functions as an axon and as a dendritic root.
Unipolar structure is often employed for sensory neurons that convey touch, pressure and pain.

19. Functional Classification of Neurons
Sensory / Afferent Neurons
transport sensory information from skin, muscles, joints, sense organs & viscera to CNS
Motor / Efferent Neurons
send motor nerve impulses to muscles & glands & other neurons
Interneurons / Association Neurons
connect sensory to motor neurons
90% of neurons in the body

20. Neurons and Neuroglia
As the “thinking” cells of the brain, each neuron does, in miniature, what the entire nervous system does as an organ: Receive, process and transmit information by manipulating the flow of charge across their membranes.
Neuroglia (glial cells) play a major role in support and nutrition of the brain, but they do not manipulate information.
They maintain the internal environment so that neurons can do their jobs.

21. Astrocytes – In CNS Star-shaped cells
Help form blood-brain barrier by covering blood capillaries
Metabolize neurotransmitters
Regulate K+ balance
Provide structural support

22. Oligodendrocytes – In CNS
Most common Glial cell type
Each cell forms myelin sheath around more than one axon in CNS

23. Microglia Cells – In CNS
Small cells found near blood vessels
Phagocytic role -- clear away dead cells

24. Ependymal cells – In CNS
Form epithelial membrane lining cerebral cavities & central canal
Produce & circulate cerebrospinal fluid (CSF)

25. Schwann Cells – In PNS The Schwann cells encircle PNS axons
Each cell produces part of the myelin sheath surrounding an axon in the PNS

26. Satellite Cells – In PNS
Flat cells surrounding neuronal cell bodies in peripheral ganglia
Support neurons in the PNS ganglia

27. Neuroglia

28. Neuroglia
Myelination is the process of forming a myelin sheath which insulates and increases nerve impulse speed.
Myelin is formed by
Oligodendrocytes
in the CNS and by
Schwann cells in
the PNS.

29. Axon Coverings in PNS
All axons surrounded by a lipid & protein covering (myelin sheath) produced by Schwann cells
Neurolemma is cytoplasm & nucleus of Schwann cell / Myelin Sheath is plasma
membrane of Schwann Cell
gaps called nodes of Ranvier
Myelinated fibers appear white
jelly-roll like wrappings made of lipoprotein = myelin
acts as “ion insulator”
speeds conduction of nerve impulses
Unmyelinated fibers
slow, small diameter fibers
only surrounded by neurolemma but no myelin sheath wrapping

30. Myelination in PNS In PNS
Schwann cells myelinate (wrap around) individual axons in the PNS during fetal development
Schwann cell cytoplasm & nucleus forms outermost layer of neurolemma with inner portion being the myelin sheath
Tube guides growing axons that are repairing themselves

31. The group of cells bodies in the peripheral nervous system are known as ganglia.
The axons leaving these cells are called nerves.
Most ganglial cells are sensory neurons which gather nerve information from sensory systems and motor neurons and transfer processed information to muscles, glands and internal organs.

32. Gray and White Matter
White matter = myelinated processes (white in color)
Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color)
In the spinal cord = gray matter forms an H-shaped inner core surrounded by white matter
In the brain = a thin outer shell of gray matter covers the surface & is found in clusters called nuclei inside the CNS

33. Resting Membrane Potential
More negative ions along inside of cell membrane & more positive ions along outside of membrane at REST
potential energy difference at rest is -70 mV
cell is “POLARIZED”
Resting Membrane Potential exists because;
1. Concentration of ions different inside & outside
extracellular fluid rich in Na+ and Cl-
cytosol full of K+, organic phosphate & amino acids
2. Membrane permeability differs for Na+ and K+
greater permeability for K+
inward flow of Na+ can’t keep up with outward flow of K+
3. Na+/K+ pump removes Na+ as fast as it leaks in
3 Na+ out of the cell & 2 K+ into the cell

34. Continuous versus Saltatory Conduction
Continuous conduction (unmyelinated fibers)
step-by-step depolarization of each portion of the length of the neuron
Saltatory conduction - over myelinated axons in PNS
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 / much faster

35. Saltatory Conduction
Nerve impulse conduction in which the impulse jumps from node to node

36. Chemical Synapses
Action potential reaches end bulb and voltage-gated Ca+2 channels open
Ca+2 flows inward triggering release of neurotransmitter
Neurotransmitter crosses synaptic cleft & binding to ligand-gated receptors
the more neurotransmitter released the greater the change in potential of the postsynaptic cell
One-way information transfer

37. Removal of Neurotransmitter
Diffusion
move down concentration gradient into the blood stream
Enzymatic degradation
acetylcholinesterase brakes it down
Uptake by neurons or glia cells
neurotransmitter transporters