Download Nervous System

Nervous System
B. Supporting cells of the CNS
Oligodendrocytes
Astrocytes: protoplasmic
fibrous
Microglia
Ependymal cells
① oligodendrocytes
One oligodendrocyte may
myelinate one axon or
several nearby axons
② Astrocytes
＋
Protoplasmic astrocyte
Fibrous
③ Ependymal cells
Line the brain ventricles and central canal of the spinal
cord
Some are ciliated to facilitate the movement of
cerebrospinal fluid
④ Microglia
Derived from bone marrow, phagocyte in nerve
tissue
Involved with inflammation and repair in the
CNS
Summary 2



Supporting cells in the PNS
Myelin sheath
neuroglia
I. The peripheral nervous system
Nerve fibers
Ganglia
Nerve ending
1. Nerve fibers
A peripheral
nerve is a
bundle of
nerve
fibers
held
together
by
connectiv
e tissue
Unmyelinated nerve fiber
2. Ganglia


Ovoid structures containing neuronal
cell bodies and glial cells supported
by connective tissue
The direction of the nerve impulse
determines whether sensory or
autonomic ganglia.

Sensory ganglia: receive afferent
impulses that go to the CNS
Cranial ganglia: cranial nerves
Spinal ganglia: dorsal root of spinal
nerves

Autonomic ganglia:
Sympathetic: paravertebrate,
preveterbrate
Parasympathetic: close to organs or in
organs
3. Nerve ending

Sensory nerve ending
Free: pain, temperature
Tactile corpuscle: sense of touch
encapsulate Lamellar corpuscle: pressure, vibration
Muscle spindle: limbs position

Motor nerve ending
Motor end plate
Visceral motor
Tactile corpuscle
Lamellar corpuscle
Muscle spindle
Motor end plate
Autonomic nervous system
The ANS consists of motor neurons that:
Innervate smooth and cardiac muscle
and glands (most of the effectors are
viscera)
Three major differences in the ANS and SNS

Effectors

Efferent pathways

Target organ responses
Effectors
The effectors of the SNS are skeletal muscles
The effectors of the ANS are cardiac muscle,
smooth muscle, and glands
Efferent Pathways
Myelinated axons of the somatic motor neurons extend
from the CNS to the effector (lacks ganglia)
Pathways in the ANS are a two-neuron chain
The preganglionic (first) neuron has a lightly myelinated
axon. The ganglionic (second) unmyelinated neuron
extends to an effector organ via the postganglionic axon
Neurotransmitter Effects
All somatic motor neurons release Acetylcholine at
their synapses, Ach always has an excitatory effect
In the ANS:
Preganglionic fibers release ACh
Postganglionic fibers release norepinephrine
(most s.) or ACh (p.) and the effect is either
stimulatory or inhibitory
The nuclei of the Sym. are located in the thoracic and
lumbar segments of the spinal cord.
The 2nd neuron is located in sensory ganglia.
The nuclei of the Para. are located in the medulla and
midbrain and in the sacral portion of the spinal cord.
The 2nd neuron is in ganglia located near or within the
effector organs
II. The central nervous system
Cerebrum
 Cerebellum
 Spinal cord
CNS has almost no connective tissue,
A relatively soft gel-like tissue.


White matter
Myelinated nervous fibers and
oligodendrocytes

Gray matter
Neuronal cell bodies
dendrites
Initial segment
Glial cells
1. Cerebrum


The gray matter forms cortex, the
white matter forms medulla.
Cerebral cortex has six layers of cells
Sensory inputs first
activate neurons in layer
4, which propagate the
excitement up to layer
2,3, and down to layer 5,6
2. Cerebellar cortex has 3 layers
Out molecular
layer
Purkinje cells
layer
Inner
granular
Purkinje
cells are
the
efferent
layer
neurons
Mossy and
climbing fibers are
afferent fibers
3. Spinal cord
DH: sensory fibers
form dorsal root
VH: motor neurons
4. Connective tissue of the CNS

Meninges
Connective tissue
encase the skull and
the vertebral column
Dura mater
Arachnoid
Pia mater
The region between
the arachnoid and
pia mater is filled
with CSF
5. Blood-brain barrier (BBB)
Prevents the passage of
some substances, such as
chemical and bacterial toxin
matter, from the blood to
nerve tissue
Response of neurons to injury
Summary
The PNS
Nerve fibers, ganglia, nerve ending
Autonomic nerve system
 The CNS
Spinal cord
Cerebrum
Cerebellum
Meninges
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Questions


List differences between the Central
and Peripheral nervous systems.
List difference between the somatic
and autonomic nervous systems