INTRODUCTION DEFINITION The system which controls the sensory
and motor functions of the body is called nervous system.
CLASSIFICATION Nervous system can be classified in two ways 1.
Anatomically (according to the structure) 2. Functionally
(according to the function)
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Anatomically Nervous system is divided into 1 Central nervous
system Brain (Cerebrum,Cerebellum, Brainstem ) midbrain, pons,
medulla oblongata Spinal cord 2. Peripheral nervous system 12 pairs
of cranial nerves 31 pairs of spinal nerves 2 sympathetic
trunks
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Cranial nerves These nerves arise from brain within the cranial
cavity and supply the face,its parts, digestive system, respiratory
system and heart. Spinal nerves These nerves arise from the spinal
cord and control the functions of rest of the body.
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Functionally Nervous system can be classified into 1. Somatic
nervous system Controls the voluntary function of the body like
moving the arms, blinking the eyes etc 2. Autonomic nervous system
Controls the involuntary activities of the body like heart beating,
movement of the digestive tract etc Autonomic nervous system
further divides into a. Sympthatic nervous system (works in danger)
b. Parasympathetic nervous system (works in normal life)
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Functional unit of nervous system o Neuron is the functional
unit of the nervous system. All the functions of nervous system
depends on the neuron. o Neuroglia (supporting cells) Astrocytes
Ependymal cells Microglial cells Oligodendrocytes Definition It is
defined as 1. The cell which carries the messages from the brain
and spinal cord to the rest of the body or 2. The cell which
transmits the nerve impulses.
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Anatomy of a Neuron Each neuron contains: - Cell body with
nucleus - Cell body with nucleus - Dendrites : fibers that receive
messages from other neurons - Dendrites : fibers that receive
messages from other neurons - Axons : fibers that send messages to
other neurons - Axons : fibers that send messages to other
neurons
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Neurons do NOT touch; there is a gap between them called a
synapse Neurons do NOT touch; there is a gap between them called a
synapse Messages are sent across the synapses by special chemicals
called neurotransmitters Messages are sent across the synapses by
special chemicals called neurotransmitters
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TYPES OF NEURONS INTERNEURON- located entirely within
CNS,integrates functions in CNS Sensory (from sensory receptor to
CNS) Motor (from CNS to effector organ)
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Sensory (Afferent) vs. Motor (Efferent) e.g., skin e.g., muscle
sensory (afferent) nerve motor (efferent) nerve Neurons that send
signals from the senses, skin, muscles, and internal organs to the
CNS Neurons that transmit commands from the CNS to the muscles,
glands, and organs
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The Nervous System: Anatomy and Physiology In unmyelinated
axons, electrical signals propagate along the entire axon membrane.
Myelinated nerves are surrounded by a myelin sheath, manufactured
by Schwann cells. Narrow gaps between these cells are the nodes of
Ranvier.
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Neurologic Structures A neuromuscular junction is the
connection between a motor neuron and a muscle fiber. A motor end
plate formed by specialized muscle fiber membranes
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The Central Nervous System Meninges Tough membranes, enclose
entire CNS Dura mater: outer, toughest layer Arachnoid: second
layer Pia mater: innermost layer In between cerebrospinal fluid
(CSF)
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Physiology of Sensation Ability to gather and process
information about the body and the external environment is
important Generated and transmitted by sensory receptors Message is
processed and: Brought to conscious thought Generates an automatic
response (reflex) Discarded as unimportant
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General Senses Monitored by receptors in different tissues
Nociceptors monitor pain. Mechanoreceptors monitor physical
properties. Proprioceptors track position in space. Baroreceptors
measure changes in pressure. Chemoreceptors measure chemicals in
the body.
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Special Senses Sense of taste Taste receptors respond to sweet,
salty, sour, and bitter
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Special Senses Sense of smell Upper nasal cavity contains
olfactory receptors
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Special Senses Sense of sight Eyeball is the source of
information the brain processes into pictures Image is brought into
focus by altering shape and thickness of the lens Distortion of the
lens causes difficulty focusing on an object.
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Special Senses Sense of hearing External ear collects sounds
into the ear canal Sound waves travel through the ear canal to the
tympanic membrane or eardrum.
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Special Senses Sense of balance Vestibular system is contained
within the inner ear. Composed of fluid-filled sacs (otoliths) and
fluid-filled passageways (semicircular canals) Structures are used
by the CNS to collect information about movement and
orientation.