TIS

Chapter 3

CNS vs PNS

I. ORGANIZATION

A. Central vs. Peripheral Nervous System

1. Central Nervous System (CNS): brain and spinal cord

2. Peripheral Nervous System (PNS): cranial and spinal nerves

B. Somatic vs. Autonomic Nervous System

1. Somatic Nervous System: innervates skeletal muscle, receives sensory info from the senses

2. Autonomic Nervous System: innervates the viscera (organs)

II. NERVOUS TISSUE CELLS

A. Neurons: respond to stimuli and conduct impulses

B. Neuroglia: support and protect neurons

III. NEURON COMPOSITION

A. Cell Body:

* function: responsible for nutrition, growth and repair of neuron

B. Nucleus:

* contains nucleolus

C. Nissl Bodies (Chromatophilic substances): rough ER

D. Dendrites:

* conduct nerve impulses toward cell body

E. Axon:

* conducts nerve impulses away from cell body

F. Axon Hillock: portion of cell body where axon originates

* DEVOID of Nissl bodies

IV. NEURON CLASSIFICATION

A. By Function:

1. Sensory (afferent) Neurons: brings information TO the CNS

2. Motor (efferent) Neurons: takes information FROM CNS to other parts of the body

3. Association Neurons (Interneurons): help coordinate and integrate info between sensory and motor components

B. By Structure:

1. Multipolar Neuron: one axon and many dendrites

2. Bipolar Neuron: two processes: one axon and one dendrite

3. Pseudounipolar Neuron: single process divides into two branches (a dendrite and an axon)

V. TYPES OF NEUROGLIA

-- in PNS:

A. Satellite Cells: surround neuron cell bodies in spinal ganglia

* (Ganglion=group of neuron cell bodies located outside CNS)

B. Schwann Cells (Neurolemmocytes): myelinate axons in PNS

-- in CNS:

C. Oligodendrocytes: myelinate axons in CNS

D. Microglia: phagocytize damaged neurons

E. Astrocytes: helps form the "blood-brain barrier"

F. Ependymal Cells: line the central canal and ventricles - help circulate cerebrospinal fluid (CSF)

VI. MYELINATION OF AXONS

-- Myelination = process of wrapping an axon with myelin

-- myelination procedure in PNS:

1. Schwann cells wrap around a portion of an axon successively

2. cytoplasm and nucleus of Schwann cell get "squeezed" to the outside

3. inner layers of cell membrane make up the myelin sheath

-- Schwann cells separated by nodes of Ranvier

-- In CNS, one oligodendrocyte myelinates portions of many axons

 

SYNAPSES

A. Definition: functional connection between a neuron and a second cell

* nerve impulses (action potentials) conducted here

B. Types of synapses

1. Electrical Synapse: impulse transmitted between two electrically coupled cells

*cells joined by gap junctions

* in areas of LOW electrical resistance

2. Chemical Synapse: nerve impulse transmitted with assistance of a chemical neurotransmitter

* how a chemical synapse works:

1) nerve impulse (action potential) travels in presynaptic neuron to the axon terminal

2) Action potential causes Ca++ to enter axon terminal

3) Ca++ cause storage vesicles to release neurotransmitter into synaptic cleft

4) Neurotransmitter binds to receptor protein sites on next cell

5) Receptor sites open, allow exchange of ions to generate an action potential in next cell

II. DEVELOPMENT OF NERVOUS SYSTEM

-- beginning of 3rd week: cells differentiate: develop into disc w/ 3 primary germ layers:

1. Ectoderm:

2. Mesoderm:

3. Endoderm:

* primary germ layers: earliest structures from which all human body cells develop

-- nervous system derived from ectoderm

-- 3rd week:

* formation of neural plate

* neural plate develops neural groove

* on either side of groove are neural folds

-- end of 3rd week - 4th week: neural folds fuse, forming a neural tube

* forms CNS

-- as neural tube is forming, some ectodermal cells detach

* neural crest cells

** forms PNS

III. DEVELOPMENT OF THE BRAIN

-- 4th week: cranial part of neural tube will develop into 3 primary vesicles:

1. Prosencephalon: forebrain

2. Mesencephalon: midbrain

3. Rhombencephalon: hindbrain

-- 5th week: 3 primary vesicles differentiate into 5 secondary vesicles:

* prosencephelon differentiates into:

1. Telencephalon: cerebrum

2. Diencephalon: thalamus & hypothalamus

* 3. mesencephalon

* rhombencephalon differentiates into:

4. Metencephalon: cerebellum and pons

5. Myelencephalon: medulla oblongata

-- hollow inside of neural tube becomes:

* ventricles

* cerebral aqueduct

* central canal

IV. DEVELOPMENT OF SPINAL CORD

-- uneven thickening of neural tube walls produces sulcus limitans

* separates posterior thickening (alar plates) from anterior thickening (basal plates)

-- basal plates --->anterior (ventral) horns, lateral horns, and gray commissure

* horns contain cell bodies of motor neurons

-- alar plates ---->posterior (dorsal) horns

* fibers from sensory nerve cells

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