Chapter 12, 13

Nervous Tissue, Spinal Cord

Divisions of NS1. CNS-central nervous system

A. Brain

B. Spinal Cord

2. PNS-peripheral nervous system- primarily nerves of body

A. Spinal nerves- 31 pairs

B. Cranial nerves- 12 pairs

Divisions of PNS

a. Somatic- controls skeletal muscle, skin

b. Autonomic-controls smooth, cardiac muscle

1. Sympathetic- fight/flight, emergencies

2. Parasympathetic-relaxation, “vegetative”

reflexes

3 Basic Functions

1. Sensory (afferent)

Receptors send impulses to CNS

2. Motor (efferent)

CNS sends impulses to effectors (muscles or glands)

3. Integrated Functions- intelligence, creativity, personality, etc.

Organelles in a neuron

1. Nucleus

2. Granular ER(Nissl bodies)

3. Mitochondria

4. Neurofibrils(microtubules)

5. No centrioles

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Classification of Neurons

• P365

1. Anaxonic- located in brain, special sense organs

2. Bipolar-special sense organs

3. Unipolar-sensory neurons of PNS

4. Multipolar- most common

Neuroglia

2. Neuroglia in PNS

A. Satellite Cells- similar to astrocytes

B. Schwann Cells- similar to oligodenedrocytes, produce myelin sheath in PNS

Neuroglia

1.Neuroglia in CNS A. Astrocyte- function in creating blood-brain barrier, provide structureB. Oligodendocyte- produce myelin sheathC. Microglia- immune cells of CNS, similar to macrophagesD. Ependymal- found in ventricles of brain, produce cerebrospinal fluid

Synapse

• A specialized site where neurons communicate with one another

• http://faculty.washington.edu/chudler/synapse.html

Myelin

• Acts like electrical insulation• Nodes of ranvier-gaps between schwann

cells on axon; allows nerve impulse to jump between nodes; leads to high conduction speeds= 100m/s

• Locations-A. All motor neuronsB. All spinal nervesC. 99% of brain

Unmyelinated

• Slow conductions speed, .5 m/s

• Located

A. In autonomic nervous system

Spinal Cord- Chapter 13• Length= 18”, width=.5”• Extends from

base(foramen magnum) of skull to 2nd lumbar vertebra

• “carrot shaped”• Ends @ conus

medullaris- many nerves exit and form cauda equina

• 2 enlargements=cervical and lumbar- where more nerves enter and leave the cord

# of spinal nerves-31

• Cervical- 8

• Thoracic-12

• Lumbar-6

• Sacral-5

Organization

1. White matter- myelinated sections on outermost parts

• can be ascending- going to brain

-carry sensory info

-called afferent

• Can be descending- coming from brain - carry motor info

- called efferent

• Root- where nerve enters or exits cord

dorsal root=sensory/afferent

ventral root= motor/efferent

** In back door out front door**

Organization

1. Gray matter- unmyelinated sections forming H pattern in the interior

• posterior horns- contain afferent neurons

• anterior horns- contain efferent neurons

• “cross bar”=commissure

Plexuses

• Plexus- interwoven network of nerves

1. Cervical plexus

2. Brachial plexus

3. Lumbar plexus

4. Sacral plexus

Reflexes• Rapid automatic response to a specific

stimuli

• Work through a reflex arc- a simple neural

pathway

1. reception

2. transmission via sensory neuron

3. integration

4. transmission via motor neuron

5. response

Classifying Reflexes p 424

1. By response

A. Somatic reflex- involves skin, skeletal muscle, function in protection

B. Visceral reflex- involves cardiac, smooth muscle, glands, bl.v, function in homeostasis

2. By development

A. Innate- w/drwal fr. pain, suckling, tracking objects w/ eye

B. Acquired- driving, sports

3. By processing siteA. Spinal- patellar reflexB. Cranial- sudden noise, bright light,

respiration

4.Complexity of circuitA. Monosynaptic-B. Polysynaptic