1. Intro to Neurons and the CNS
Medgar Evers College
Anatomy and Physiology II lab
Fall 2017
Dr. Santos

2. Nervous system Central nervous system (CNS)
Brain
Spinal cord
Peripheral nervous system (PNS)
Nerve outside the brain and spinal cord

3. Nervous Tissue Comprise of 2 types of cells
Neuroglial = supporting cells
The insulators, adhesive, protectors and nourishers
Neurons = nerve cells that transmit impulses or neuronal action potentials or action potentials

4. 6 types of neuroglial cells

5. Nervous Tissue: Support Cells (Neuroglia)
Astrocytes
Most abundant, star-shaped cells
Anchor neurons and
blood vessels in place
Form barrier between capillaries and neurons
Control the chemical environment of the brain
Figure 7.3a

6. Nervous Tissue: Support Cells
Microglia
Spider-like phagocytes
Dispose of debris
Ependymal cells
Line cavities of the brain and spinal cord
Circulate cerebrospinal fluid
Figure 7.3b–c

7. Nervous Tissue: Support Cells
Oligodendrocytes
Produce myelin sheath around nerve fibers in the central nervous system
Figure 7.3d

8. Nervous Tissue: Support Cells
Satellite cells
Protect neuron cell bodies
Schwann cells
Form myelin sheath in the peripheral nervous system
Figure 7.3e

9. Nervous Tissue: Neurons
Neurons = nerve cells
Cells specialized to transmit messages
Major regions of neurons
Cell body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell body

10. Neuron Anatomy Cell body (cyton)
Nissl bodies – densely packed microtubules and filaments that compartmentalize the rough endoplasmic reticulum

11. Neuron Anatomy
Cell body
Nucleus
Large nucleolus
Figure 7.4a–b

12. Location of Neuron Cell Body
Most are found in the central nervous system
Gray matter – cell bodies and unmylenated fibers
Nuclei – clusters of cell bodies within the white matter of the central nervous system
Ganglia – collections of cell bodies outside the central nervous system

13. Neuron Anatomy Extensions outside the cell body
Dendrites – conduct impulses toward the cell body, receive message from other neurons
Axons – conduct impulses away from the cell body
Figure 7.4a

14. Axons and Nerve Impulses
A single axon exits the cell body to transmit messages in the form of action potentials to other neurons, muscles, and glands.
An axon generates action potentials across its axolemma, at the axon hillock.
The action potential propagates the length of the axon and down its many terminal branches, called telodendria. The end of each is called axon terminal.

15. Axons end in axonal terminals
Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from the next neuron by a gap
Synaptic cleft – gap between adjacent neurons.

16. Nerve Fiber Coverings
Schwann cells – produce myelin sheaths in jelly-roll like fashion
Nodes of Ranvier – gaps in myelin sheath along the axon
Internode- part of axon covered

17. Functional Classification of Neurons
Sensory (afferent) neurons
Carry impulses from the sensory receptors
Cutaneous sense organs
Motor (efferent) neurons
Carry impulses from the central nervous system

18. Functional Classification of Neurons
Interneurons (association neurons)
Found in neural pathways in the central nervous system
Connect sensory and motor neurons

19. Structural Classification of Neurons
Multipolar neurons- one axon and 2 or more dendrites
Figure 7.8a

20. Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite, found on retina, roof of nasal cavity and inner ear.
Figure 7.8b

21. Structural Classification of Neurons
Pseudo-unipolar neurons – have a short single process leaving the cell body.
Found in the skin
Figure 7.8c

22. Starting a Nerve Impulse
Depolarization – a stimulus depolarizes the neuron’s membrane
A depolarized membrane allows sodium (Na+) to flow inside the membrane
The exchange of ions initiates an action potential in the neuron

23. The Action Potential
If the action potential (nerve impulse) starts, it is propagated over the entire axon
Gated sodium ion channels open, and sodium ions rush in, causing depolarization.
Then they close and gated potassium ion channels open and potassium rushes out repolarizing the membrane.

24. Once it reaches the axon terminal, calcium channels open, allowing calcium to enter the axon terminal.
The influx of calcium causes the neuronal vesicles to leave via exocytosis.
They diffuse across the synaptic cleft and bind to receptors in the post synaptic membrane. The action potential continues.

26. Continuation of the Nerve Impulse between Neurons
Impulses are able to cross the synapse to another nerve
Neurotransmitter is released from a nerve’s axon terminal
The dendrite of the next neuron has receptors that are stimulated by the neurotransmitter
An action potential is started in the dendrite

27. Central Nervous System (CNS)
CNS develops from the embryonic neural tube
The neural tube becomes the brain and spinal cord
The opening of the neural tube becomes the ventricles
Four chambers within the brain
Filled with cerebrospinal fluid

28. brain
Hollow organ consisting of 4 fluid filled ventricles.

29. Choroid plexus
Collection of blood vessels found within each of the 4 ventricles.
As blood flows through the ventricles, fluid filters out into the ventricles, at this point called cerebrospinal fluid.

30. Regions of the Brain Cerebral hemispheres Diencephalon Brain stem
Cerebellum
Figure 7.12b

31. Cerebrum
Cognitive functions such as learning, language, conscious interpretation of sensory info, conscious planning of movement and personality.

32. Cerebral Hemispheres (Cerebrum)
Paired (left and right) superior parts of the brain
Include more than half of the brain mass
The surface is made of ridges (gyri) and grooves (sulci)
Figure 7.13a

33. Lobes of the Cerebrum
Fissures (deep grooves) divide the cerebrum into lobes
Surface lobes of the cerebrum
Frontal lobe
Parietal lobe
Occipital lobe
Temporal lobe
Deep lobe (insula)

34. Lobes of the Cerebrum

35. Layers of the Cerebrum Gray matter White matter Basal nuclei
Outer layer
Composed mostly of neuron cell bodies
White matter
Fiber tracts inside the gray matter
Example: corpus callosum connects hemispheres
Basal nuclei
– internal islands of gray matter

36. Diencephalon
Deep in the cerebral hemispheres in the central core. Made of three parts
Thalamus “gateway into the cerebrum”
Hypothalamus regulates endocrine function, monitors sleep wake cycle, thirst, hunger, body temp. The pituitary gland is connected to the hypothalamus via the infundibulum.
Epithalamus, contains the pineal gland that secretes melatonin, which helps to regulate sleep wake cycle.

37. Diencephalon
Figure 7.15

38. Brain Stem Attaches to the spinal cord Parts of the brain stem
Midbrain
Pons
Medulla oblongata

39. Midbrain Mostly composed of tracts of nerve fibers
Has two bulging fiber tracts – cerebral peduncles
Has four rounded protrusions – corpora quadrigemina
Reflex centers for vision and hearing

40. Pons The bulging center part of the brain stem
Mostly composed of fiber tracts
Includes nuclei involved in the control of breathing

41. Medulla Oblongata The lowest part of the brain stem
Merges into the spinal cord
Includes important fiber tracts
Contains important control centers
Heart rate control
Blood pressure regulation
Breathing
Swallowing
Vomiting

42. cerebellum
Coordinates and plans ongoing motor activities and its responsible for balance.

43. meninges
Set of three membranes that surround and protect the brain and spinal cord. They are the dura, arachnoid and pia mater.

44. Spinal cord

45. Spinal cord The medulla oblongata becomes the spinal cord.
Vertebral column and the meninges provides protection and provide physical stability.
Ends between the 1st and 2nd lumbar vertebra, the end is called the conus medullaris.

46. The conus medullaris gives off a tuft of nerve roots called cauda equina, which fills the remainder of the vertebral column.

49. Gray matter- shape of a butterfly and divided into anterior (ventral) and posterior (dorsal) horns, and lateral horns.
Anterior horn (ventral horn)- contains cell bodies of motor neurons.
Axons of the anterior (ventral) horns exit and form the ventral root.

50. Dorsal horn( posterior horn)- composed of sensory neurons.
Axons of the posterior (dorsal) horns exit and form the dorsal nerve root.
The cell bodies of the dorsal root are found in an enlarged area called dorsal root ganglion.

51. Lateral horns- contain cell bodies of autonomic neurons

52. The ventral and dorsal nerve root merge to form the spinal nerve!

53. White matter Surrounds the gray matter!
Divided into three columns; posterior, anterior and lateral funiculus.
Each funiculus contains bundles of myelinated axons called tracts.
Ascending tract- carry info from sensory neurons to brain
Descending tract- carry info from the brain to motor neurons