Download notes - Mrs. Blackmon`s Science Blackboard

The
Nervous
System
Overview
sensory input -
monitors changes
outside and inside
the body
integration -
processes and
interprets input and
makes decision
motor output -
effects a response
from either a
muscle or a gland
Basic Functions:
• sensory input - monitors changes outside and
inside the body
• integration - processes and interprets input
and makes decision
• motor output - effects a response from
either a muscle or a gland
Divisions of the Nervous System
• Central (CNS) brain and spinal
cord
integrating and
command centers
• Peripheral (PNS) nerves outside of
CNS
Histology of
Nervous
Tissue
Nervous Tissue: Support Cells
• collectively called
neuroglia (nerve glue)
• supporting cells
• assist, segregate, and
insulate neurons
• 9 times more
numerous than neurons
1. astrocytes
• control ionic environment
• attach neurons to capillaries
(nutrients)
2. microglia
• type of macrophage
• engulf microorganisms
3. ependymal
• form cerebrospinal fluid (CSF)
4. oligodendrocytes
• form myelin sheath
• insulates nerve fibers
5. Schwann cells
• form myelin sheath
• act as phagocytes
• insulates
6. satellite cells
• control chemical
environment
Types of Glia Cells
1. astrocytes - control ionic environment, attach
neurons to caps. (nutrients)
2. microglia - type of macrophage, engulf
microorganisms
3. ependymal - form cerebrospinal fluid (CSF)
4. oligodendrocytes - form myelin sheath, insulates
nerve fibers
5. Schwann cells - form myelin sheath, act as
phagocytes, insulates
6. satellite cells - controlling chemical environment
The
Neuron
Neuron Structure
• able to generate and conduct nerve impulse
• can live and function for a lifetime amitotic
• cell body - large nucleus and nucleolus
– rough ER in form of Nissl bodies
• processes - cytoplasmic
extensions (extend from cell
body)
1. dendrites - short, branched
– conduct impulses toward
cell body
2. axon - only 1
may have side branches
ends in terminals or synaptic
bulbs which release
neurotransmitters
conduct impulses away from
cell body
• insulated by myelin
sheath
• made of Schwann
cells (wrap around)
• adjacent Schwann cells don’t
touch
– gaps are Nodes of Ranvier
• increase speed of transmission
Node of
Ranvier
Myelin sheath
Schwann Cell
Formation of
Myelin Sheath
• As the Schwann cells
wrap around the axon,
the myelin sheath
forms.
• The neurilemma is the
outer most part of the
myelin sheath with the
majority of the
cytoplasm and nuclei.
– innermost is called
the myelin sheath
• White matter is a collection of myelinated fibers.
• Gray matter is unmyelinated with only a single layer
of Schwann cells. Gray matter is slow and found
where distances are short.
Neuron
Classification
According To
Structure
number of processes extending
from the cell body
1. Multipolar
•
•
•
•
many dendrites
1 axon
1 cell body
most common
2. Bipolar
•
•
•
•
•
1 axon
1 dendrite
1 cell body
rare
ex: olfactory and retina
3. Unipolar
• single process that merges
with cell body
• sensory neurons
• ex: skin
Neuron
Classification
According To
Function
direction of impulse conduction
1. sensory / afferent –
toward CNS, from skin or internal organs
2. motor / efferent –
away from CNS, to muscle or glands, most
multipolar
3. association neurons / interneurons –
lie between sensory and motor neurons,
shuttle signals
Nerves
• Nerves are cord like
bundles of nerve
fibers wrapped by
connective tissue.
• Blood and lymph
vessels are also
found inside.
• Nerves are only
found in the PNS.
Types of Nerves
1. sensory nerves (afferent) toward CNS
2. motor nerves - (efferent)
away from CNS
3. mixed nerves –
both sensory (afferent)
and motor (efferent)
nerves, to and from CNS
** most nerves
Regeneration of Nervous Tissue
• mature neurons do not undergo mitosis
• if damage is severe or close to cell body,
neuron may die
• however, cut or compressed axons can
regenerate in the PNS
Regeneration of Nervous Tissue
1. Damage area is reabsorbed
2. Neurilemma of Schwann cells form a tunnel
to guide axonal “sprouts” to their original
contacts. Schwann cells also releases
growth factor.
–
–
–
The grater the distance, the less chance of
nerve recovery.
Neurosurgeons align cut nerve endings
surgically to enhance regeneration.
Post trauma regrowth is never exactly the
same.
Regeneration of Nervous Tissue
• CNS cells never regenerate (lack
neurilemma)
• supporting neuroglial cells provide no
guiding tunnel and scaring blocks axon
sprouts