Lecture 13: The Nervous System

Nervous System Functions: Communication and control

1. Collect information from the environment

2. Process the information and coordinate an integrated response

3. Respond to the information and DO SOMETHING

Organization of the nervous system: Structural categories

1. Central nervous system (CNS): Processes and integrates a response to sensory info

A. Brain

B. Spinal cord

C. Tracts (bundles of axons that run completely within the CNS...as opposed to nerves, which are running in the PNS)

D. Nuclei (groups of neuron cell bodies found in the CNS...as opposed to ganglia found in the PNS)

2. Peripheral nervous system (PNS): Receives sensory info and carries out response

A. Spinal nerves- 31 pairs (bundles of axons that originate in the spinal cord)

B. Cranial nerves- 12 pairs (bundles of axons that originate in the brain)

C. Ganglia (groups of neuron cell bodies found outside the brain and spinal cord)

Functional categories

1. Sensory (Afferent)

A. Receives information

B. 2 categories that differ in WHERE the information comes from (and some of this is based on embryological development):

i. Somatic sensory (info comes from places you can FEEL through general and special senses)

ii. Visceral sensory (info comes from places you aren’t consciously aware of, like guts...though it can cause pain...)

2. Motor (Efferent)

A. Carries out ACTION

B. 2 categories that differ in WHO carries out the action.

i. Somatic motor (effectors are voluntary; skeletal muscle)

ii. Visceral motor (effectors are involuntary, including cardiac muscle, smooth muscle, and glands)

a. This category of the nervous system is called the autonomic nervous system (ANS). There are 2 categories of the

ANS, and both categories innervate all visceral effectors!

b. Sympathetic nervous system: Oh shit response (fight or flight)

c. Parasympathetic nervous system: Life is good (feed and breed)

Functional unit: Neuron

Draw a neuron, and label the following parts:

• Cell body (soma), Nucleus, Axon, Dendrites (sometimes have spines that increase the number of synapses they can create, Synaptic knobs, Synapse (to label this, you need an “effector”)

Anatomy of a nerve

Bundles of axons all running together in the PNS are considered a nerve. A nerve has a hierarchical organization, just like muscles!

1. Neurons and their Schwann cells (neurolemmocytes) are surrounded by the endoneurium (areolar CT)

2. Bundles of axons are called fascicles, and are surrounded by the perineurium (dense irregular CT)

3. All fascicles in a single nerve are surrounded by the epineurium (dense irregular CT)

Other cells of the nervous system

Glial cells support neurons and outnumber neurons 9 to 1. There are 4 types of glial cells found in the CNS and 2 found in the PNS.

1. Astrocytes (CNS)

A. Most abundant glial cell

B. Play a role in forming the blood brain barrier and can form scar tissue in the brain following an injury

C. Found primarily in gray matter because they are associated with the cell bodies of neurons.

D. They are the neuron Mamas...they remove NT from synapses, help form new synapses, help maintain ionic balance in ECF

2. Oligodendrocytes (CNS)

A. Produce myelin sheaths that surround some axons...

B. Found primarily in white matter.

C. Can be attacked by the immune system in diseases like multiple sclerosis, leading to inefficient transmission of info down axon.

D. Multiple cells create the myelin sheath, but there are spaces between the different cells (Nodes of Ranvier)

3. Microglia (CNS)

A. Specialized macrophages that enter the brain tissue during development.

B. They can be dormant or activated. When activated, they can secrete chemical signals to initiate local inflammatory responses.

C. Wander around eating debris...

4. Ependymal cells (CNS)

A. Specialize epithelium that lines spaces in the brain and spinal cord.

B. Produce and circulate cerebrospinal fluid.

5. Satellite cells (PNS)

A. The mama cells in ganglia, surrounding and protecting the cell bodies

6. Schwann cells (neurolemmocytes) (PNS)

A. The myelin makers, surrounding axons, but found in the PNS

Anatomy of the Spinal Cord

Part 1: Nervous system histology

1. Nerve, Ox Spinal Cord (H 4.11)

A. Neuron

B. cell body

C. nucleus

D. cell processes (axons, dendrites)

E. Neuroglia

2. Nerve/ Nerve Roots (H 3594)

A. nerve fibers (axons)

B. nerve fiber bundles

C. Schwann cell

D. myelin sheath (often lost in tissue processing - only a space remains)

E. nucleus

F. node of Ranvier

G. endoneurium

H. perineurium

I. epineurium

3. Motor Nerve Endings (H 1684)

A. axons

B. motor end plates

C. muscle fibers

Part 2: Spinal cord histology

1. Spinal cord ganglion AND Spinal cord XS (H 1572 and H 1560 and HE 2-21)

A. spinal cord

i. central canal

B. white matter (organized in “columns”, or funiculi)

i. posterior funiculus

ii. lateral funiculus

iii. anterior funiculus

C. gray matter

i. anterior horn

ii. cell bodies of somatic motor neurons

iii. lateral horn (may not be present)

iv. cell bodes of visceral motor neurons

v. posterior horn

D. posterior root

E. posterior root ganglion

i. ganglion cell bodies (somatic sensory neurons)

ii. satellite cells

iii. nerve fibers

F. anterior root

G. spinal nerve

H. meninges

i. pia mater

ii. arachnoid mater

iii. dura mater

Describe the major functions of the nervous system

Your Task

1. Draw a cross section of the spinal cord. Include all the required structures in your drawing.

2. What direction does information travel through a neuron?

3. What form does the information take?

4. Draw a single neuron, labeling all of the required parts.

5. Draw a nerve, labeling all required connective tissue layers. Indicate what kind of connective tissue each layer is made of.

6. List and describe all the glial cells found in the nervous system. Indicate where you would expect to FIND these different types

of cells.

7. Can you tell axons from dendrites in your slides? Why or why not?

8. What is a motor unit?

9. What is the functional significance of motor unit size?

10. How is the organization of a nerve similar to the organization of a muscle organ?

11. What is the functional significance of myelination? Of nodes of Ranvier?

Attribution: Wendy Riggs