Transcript Nervous System

Nervous System
Objectives:
1. Identify structures of the nervous system.
2. Explain differences in the function of the
peripheral nervous system and the central
nervous system.
D. Nervous Tissue
• Nervous tissue is
– found in the brain, spinal cord, and nerves.
– made up of:
1. Neurons: nerve cells (bundles of axons)
2. Neuroglial cells: helper cells
– “glia” = glue
– Support and bind components of nervous tissue to each
other and to blood vessels
– Function similarly to connective tissue in other organ
systems
• Sketch neuron
andof
label
parts.
Parts
a Neuron
Nervous System
• Organs of this system are divided into 2
groups:
1. Central Nervous System (CNS)
•
•
Brain
Spinal cord
2. Peripheral Nervous System (PNS)
•
Composed of the nerves (peripheral nerves) that
connect the CNS to other body parts
• Functions of the nervous system:
1. Sensory
2. Integrative
3. Motor
1. Sensory Function
• Sensory receptors at the ends of peripheral
neurons:
– Gather info by detecting changes inside and
outside the body.
• Inside: temperature and oxygen concentration
• Outside: light and sound intensities
– Convert info into nerve impulses
(electrochemical changes) which are transmitted
along peripheral nerves to the CNS
2. Integrative Function
• Nerve impulses are integrated (brought
together) in the CNS.
• Allows us to make conscious or subconscious
decisions.
3. Motor Function
• Peripheral nerves carry impulses from the
CNS to effectors (responsive structures).
• Effectors are NOT part of the nervous system,
but include muscles and glands.
Motor Function
• Motor functions can be divided into 2 groups:
– Somatic nervous system
• Consciously controlled (voluntary)
• Controls skeletal muscle
– Autonomic nervous system:
• Involuntary
• Includes heart, smooth muscle, and various glands
Nervous System Function Recap
1. Detects changes inside and outside the
body,
2. Makes decisions based on the information
received, and
3. Stimulates muscles or glands to respond.
• What is the purpose of this process?????
Neuroglial Cells
• Functions:
– Fill spaces
– Provide structural frameworks
– Produce myelin
– Carry on phagocytosis
• Vary from CNS to PNS
• Table: Type of Cell, Location, Function, Other
specific info
CNS Neuroglial Cells
• Greatly outnumber neurons in the CNS
(think worker ants vs. Queen ant)
1. Microglial cells
– Scattered throughout CNS
– Support neurons and phagocytize bacterial cells
and cellular debris
2. Oligodendrocytes
– Occur in rows along nerve fibers
– Provide layers of myelin around axons within
brain and spinal cord
CNS Neuroglial Cells, continued….
3. Astrocytes
– Found between neurons and blood vessels
– Provide structural support, help regulate
nutrients and ions in tissues
– Form scar tissue to fill spaces after CNS injuries
4. Ependymal cells
– Form epithelial-like membrane in parts of the
brain (choroid plexuses)
– Form inner linings that enclose ventricles in the
brain and central canal in the spinal cord
CNS Neuroglial Cells
PNS Neuroglial cells
1. Schwann cells: form myelin sheath around
axons
Neurons
•
Vary in size and structure, but have
common features:
1. Cell Body
2. Dendrites
3. Axon
•
Mature neurons do not divide, but neural
stem cells can divide and form neurons or
neuroglial cells.
1. Cell Body
• Contains normal cellular structures (golgi
apparatus, mitochondria, cytoplasm, cell
membrane, etc.)
• Neurofibrils – fine threads that extend into
the axon
• Nissl bodies (chromatophilic substances)
– Membranous sacs in the cytoplasm
– Similar to rough ER
– Ribosomes on Nissl bodies synthesize ______
2. Dendrites
• Usually short and highly branched (dendr = ?)
• The main receptive surfaces for receiving
communication from axons of other neurons
3. Axons
• Arise from a slight elevation of the cell body,
called the axonal hillock.
• Conduct nerve impulses away from the cell
body
• Contains many mitochondria, microtubules,
and neurofibrils
• Originates as a single structure, but may have
branches, especially at the end to interact
with receptive surfaces of other cells
PNS Axons
• Enclosed in myelin sheaths composed of
many Schwann cells
• Myelin is a lipoprotein.
• Neurilemma sheath surrounds the myelin
sheath
• Nodes of Ranvier – narrow gaps in the myelin
sheath between the Schwann cells
Classification of Neurons
• Classification based on Structural differences:
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
• Classification based on Functional differences:
• Sensory neurons (afferent neurons)
• Interneurons (association or internuncial neurons)
• Motor neurons (efferent neurons)
Structural Differences
• Sketch the neurons below. Notes on the next
3 slides:
Structural Differences, cont…..
1. Bipolar:
– 2 processes
•
•
Axon
Dendrite
– Found in specialized parts of the eyes, nose, and
ears
Structural Differences, cont…..
2. Unipolar:
– 1 process divides into 2 branches, which
function as a single axon
•
•
1 branch (peripheral process) associated with
dendrites
Other branch (central process) enters brain or spinal
cord
Structural Differences, cont…..
3. Multipolar:
– Many processes arising from cell body:
•
•
1 axon
Many dendrites
– Most neurons whose cell bodies lie in the brain
or spinal cord are multipolar.
• Direction of impulse is ALWAYS from
dendrites to axon.
Functional Differences
1. Sensory (afferent) neurons
– From peripheral body parts to the brain or spinal
cord
– Have specialized receptor ends at the tips of their
dendrites OR
– Dendrites closely associated with receptor cells
in the skin or sensory organs.
– Most are unipolar, but some are bipolar.
Functional Differences, cont…..
2. Interneurons (association or internuncial
neurons)
– Lie entirely in the brain or spinal cord
– Multipolar and link other neurons
– Transmit impulses from one part of the brain or
spinal cord to another
3. Motor (efferent) neurons
– Multipolar
– Carry nerve impulses from brain or spinal cord to
effectors
– Stimulate muscles or glands
Copy Diagram on Whiteboard
1.
2.
3.
4.
Identify the direction of nerve impulse.
How can you tell the direction?
Label all dendrites, cell bodies, and axons.
Label each nerve as either sensory neuron,
interneuron, or motor neuron.
5. Color code the CNS and PNS portions of the
pathway.