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THE NERVOUS SYSTEM
DAWN V TOMY M.Pharm
Asst.Professor
Dept. Of Pharmacology
St.JOSEPH’S COLLEGE OF PHARMACY,CHERTHALA.
Part -1
2
Divisions of the Nervous System
• Central Nervous System (CNS)
• Brain.
• Spinal cord.
• Peripheral Nervous System (PNS) consists of the cranial nerves
and spinal nerves. The 3 divisions of PNS are:
1. Somatic Nervous System (SNS)
2. Autonomic Nervous System (ANS) and
3. Enteric Nervous System.
3
Divisions of Peripheral Nervous System
• Sensory Division
• Picks up sensory information and delivers it to the CNS
• Motor Division
• Carries information to muscles and glands
• Divisions of the Motor Neurons:
• Somatic Neurons – carries information to skeletal
muscle.
•Autonomic Neurons – carries information to smooth
muscle, cardiac muscle, and glands.
5
Divisions Nervous SystemCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Sensory division Sensory receptors
Motor division
Skeletal muscle
Brain
(a) (b)
Spinal
cord Spinal
nerves
Cranial
nerves
Central Nervous System
(brain and spinal cord)
Peripheral Nervous System
(cranial and spinal nerves)
Smooth muscle
Cardiac muscle
Glands
Autonomic
Nervous
System
Somatic
Nervous
System
7
Histology of Nerve cells
• Cell types in neural tissue:
• Neurons
• Neuroglial cells (also
known as neuroglia, glia,
and glial cells)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
Cell body
Axon
Nuclei of
neuroglia
© Ed Reschke
8
The Neurons
• Neurons may vary in size and shape.
• They may differ in length and size of their axons and dendrites.
• Neurons share certain features:
• Dendrites
•A cell body
•An axon
9
Neuron Structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cell body
Nucleus
Dendrites
Impulse
Nodes of Ranvier
Myelin (cut)
Axon
Axon
Chromatophilic
substance
(Nissl bodies)
Axonal
hillock
Axon collateral
Schwann
cell
Synaptic knob of
axon terminal
12
Classification of Neurons and Neuroglia
• Neurons vary in function
• They can be sensory, motor, or integrative neurons
• Neurons vary in size and shape, and in the number of axons
and dendrites that they may have
• Due to structural differences, neurons can be classified into
three (3) major groups:
• Bipolar neurons
• Unipolar neurons
• Multipolar neurons
13
Classification of Neurons: Structural Differences
• Bipolar neurons
• Two processes
• Eyes, ears, nose
• Unipolar neurons
• One process
• Ganglia of PNS
• Sensory
• Multipolar neurons
• 99% of neurons
• Many processes
• Most neurons of
CNS
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dendrites
Axon Axon
AxonDirection
of impulse
(a) Multipolar
Central
process
Peripheral
process
(c) Unipolar(b) Bipolar
15
Classification of Neurons: Functional Differences
• Sensory Neurons
•Afferent
• Carry impulse to CNS
• Most are unipolar
• Some are bipolar
• Interneurons
• Link neurons
•Aka association neurons
or internuncial neurons
• Multipolar
• Located in CNS
• Motor Neurons
• Multipolar
• Carry impulses away from CNS
• Carry impulses to effectors
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Central nervous system Peripheral nervous system
Cell body
Interneurons
Dendrites
Axon
Axon
Sensory (afferent) neuron
Motor (efferent) neuron
Cell body
Axon
(central process)
Axon
(peripheral process)
Sensory
receptor
Effector
(muscle or gland)
Axon
terminal
16
Types of Neuroglial Cellsin the CNS
2) Astrocytes
• CNS
• Scar tissue
• Mop up excess ions.
• Induce synapse formation
• Connect neurons to blood vessels
•Part of Blood Brain Barrier
3) Oligodendrocytes
• CNS
• Myelinating cell
4) Ependyma or ependymal
• CNS
• Ciliated
• Line central canal of spinal
cord
• Line ventricles of brain
1) Microglia
• CNS
• Phagocytic cell
18
Types of Neuroglial Cells
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Microglial cell
Axon
Oligodendrocyte
Astrocyte
Capillary
Neuron
Myelin
sheath (cut)
Node of
Ranvier
Ependymal
cell
Fluid-filled cavity
of the brain or
spinal cord
19
Types of Neuroglial Cellsin the PNS
1) Schwann Cells
• Produce myelin found on peripheral myelinated neurons
• Speed up neurotransmission
2) Satellite Cells
• Support clusters of neuron cell bodies (ganglia)
21
Regeneration of A Nerve Axon
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
AxonSite of injury Schwann cells
(a)
(b)
(c)
(d)
(e)
Changes
over time
Motor neuron
cell body
Former connection
reestablished
Schwann cells
proliferate
Schwann cells
degenerate
Proximal end of injured axon
regenerates into tube of sheath cells
Distal portion of
axon degenerates
Skeletal
muscle fiber
22
General Functions of the Nervous System
• The three general functions of the nervous system:
• Receiving stimuli = sensory function
• Deciding about stimuli = integrative function
• Reacting to stimuli = motor function
23
Functions of Nervous System
• Sensory Function
• Sensory receptors gather information
• Information is carried to the CNS
• Integrative Function
• Sensory information used to create:• Sensations
• Memory
• Thoughts
• Decisions
• Motor Function
• Decisions are acted upon
• Impulses are carried to effectors
24
Myelination of Axons
• White Matter
• Contains myelinated
axons
• Considered fiber tracts
• Gray Matter
• Contains unmyelinated
structures
• Cell bodies, dendrites
Dendrite
Node of Ranvier
Myelinated region of axon
Axon
(a)
Unmyelinated
region of axon
Neuron
cell body
Neuron
nucleus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(c)
Enveloping
Schwann cellSchwann
cell nucleus
Unmyelinated
axon
Longitudinal
groove