The document discusses the nervous system, including its structural and functional organization. It can be divided into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system (PNS), which includes nerves that connect to the CNS. The nervous system uses neurons and glial cells to transmit signals. Neurons transmit signals through electrical or chemical synapses to control and coordinate functions of the body.

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Ivano-Frankivsk National Medical
University
The Department of Human anatomy
The Nervous
System
Prepared by PhDPrepared by PhD
Tetyana Knyazevych - ChornaTetyana Knyazevych - Chorna

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The Nervous System
 The body’s primary communication and
control system.
 Can be divided according to:
 Structural categories
 Functional categories.

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Nervous System: Structural
Organization
Structural subdivisions of the nervous system:
 Central nervous system (CNS)
 brain and spinal cord
 Peripheral nervous system (PNS)
 cranial nerves (nerves that extend from the brain)
 spinal nerves (nerves that extend from the spinal cord)
 ganglia (clusters of neuron cell bodies (somas) located
outside the CNS)

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 The central nervous system forms from the
embryonic neural tube that developes from
ectoderm.
 The neural plate gives rise to neural groove,
that later form the neural tube.
Development

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Spinal Cord Development
 The cranial (superior) part of the neural
tube expands and develops into the
brain.
 The caudal (inferior) part of the neural
tube forms the spinal cord.

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Nerve Cells
 Nervous Tissue
 Two distinct cell types

Neurons
 excitable cells
 initiate and transmit nerve impulses

Glial cells
 nonexcitable cells
 support and protect the neurons

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Characteristics of Neurons
 Neurons have a high metabolic rate.
 Neurons have extreme longevity.
 Neurons typically are non-mitotic.

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Neuron Structure
 Neurons come in all shapes and sizes
 All neurons share certain basic structural features.
 typical neuron:
 Cell body (soma, perikaryon)
 Dendrites
 Axon

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Classifications of Neurons
 Neurons vary widely in morphology and
location.
 classified based on

structure

function.
 Structural classification: number of processes
extending from the cell body.
 unipolar neuron has a single process
 bipolar neurons have two processes
 multipolar neurons have three or more processes

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Functional Classification
 Sensory afferent neurons: receptor to CNS
 Motor efferent neurons: CNS to effector
 Interneurons (association neurons): facilitate
communication between sensory and motor neurons.

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Glial Cells
 Also called neuroglia
 Occur within both the CNS and the PNS.
 are smaller than neurons
 are capable of mitosis.
 do not transmit nerve impulses.
 Glial cells
 physically protect neurons
 help nourish neurons
 provide a supporting framework for all the nervous tissue.
 Glial cells far outnumber neurons.
 Glial cells account for about half the volume of the
nervous system.

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Glial Cells of the PNS
 Satellite cells:
 Flattened cells
 Cover somas in ganglia
 Separate soma from surrounding tissue
fluid

Regulate exchange.
 Neurolemmocytes (Schwann cells)
 Myelination in the PNS

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Myelination
 Process by which part of an axon is
wrapped with a myelin sheath
 Forms a protective fatty coating
 Has a glossy-white appearance.
 The myelin sheath:
 supports the axon
 protects the axon
 insulates an axon

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Myelination
 No change in voltage can occur across the
membrane in the insulated portion of an axon.
 Voltage change occurs at the nodes
 Neurolemmocytes: form myelin sheaths in PNS
 Oligodendrocytes: form myelin sheaths in the CNS

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Mylenated vs. Unmylenated
Axons
 myelinated axon
 nerve impulse “jumps” from neurofibril node to neurofibril
node
 known as saltatory conduction
 requires less energy (ATP) than does an unmyelinated axon
 unmyelinated axon
 nerve impulse must travel the entire length of the axon
 known as continuous conduction
 nerve impulse takes longer to reach the end of the axon
 Using continuous conduction, unmyelinated axons conduct
nerve impulses from pain stimuli
 A myelinated axon produces a faster nerve impulse.

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Structure of a Nerve
 A nerve is a cable-like bundle of parallel axons.
 three connective tissue wrappings
 Endoneurium

delicate layer of loose connective tissue
 Perineurium

a cellular and fibrous connective tissue layer

wraps groups of axons into fascicles
 Epineurium - a superficial connective tissue covering

This thick layer of dense irregular fibrous connective tissue

encloses entire nerve

provides support and protection

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Nerves
 Nerves are organs of the PNS.
 Sensory (afferent) nerves convey sensory information
to the CNS.
 Motor (efferent) nerves convey motor impulses from
the CNS to the muscles and glands.
 Mixed nerves: both sensory and motor
 Axons terminate as they contact other neurons,
muscle cells, or gland cells.
 An axon transmits a nerve impulse at a specialized
junction with another neuron called synapse.

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Synapses
 Presynaptic neurons
 transmit nerve impulses toward a synapse.
 Postsynaptic neurons
 conduct nerve impulses away from the synapse.
 Axons may establish synaptic contacts with
any portion of the surface of another neuron
 except those regions that are myelinated.

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Types of synapses: based on contacts
 axodendritic
 axosomatic
 axoaxonic

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Main types of synapses
 Electrical synapses
 Gap junctions
 Chemical synapses
 Use neurotransmitters

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Electrical Synapses
 Electrical synapses are not very common in
mammals.
 In humans, these synapses occur primarily between
smooth muscle cells where quick, uniform innervation
is essential.
 Electrical synapses are also located in cardiac
muscle.

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Chemical Synapses
 Most numerous type of synapse
 Facilitates interactions
 between neurons
 between neurons and effectors.
 These are cell junctions
 Presynaptic membrane:
 releases a signaling molecule called a neurotransmitter,
such as acetylcholine (ACh).
 Other types of neurons use other neurotransmitters.
 Postsynaptic membrane:
 Contains receptors for neurotransmitters

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The Spinal Cord
 Link between the brain and the body.
 Exhibits some functional independence from
the brain.
 The spinal cord and spinal nerves serve two
functions:
 pathway for sensory and motor impulses
 responsible for reflexes

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Structure of the Spinal Cord
 Typical adult spinal cord
 ranges between 42 and 45 centimeters (cm) (16 to
18 inches) in length.
 In cross section
 roughly cylindrical
 slightly flattened both posteriorly and anteriorly.
 External surface has two longitudinal
depressions:
 the posterior (dorsal) median sulcus
 the anterior (ventral) median fissure

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Regions of the Spinal Cord
 The cervical region
 continuous with the medulla oblongata
 contains neurons whose axons form the cervical spinal
nerves (8)
 The thoracic region
 attached to this region are the thoracic spinal nerves (12)
 The lumbar region
 contains the neurons for the lumbar spinal nerves (5)
 The sacral region
 contains the neurons for the sacral spinal nerves (5)
 The coccygeal region
 one pair of coccygeal spinal nerves arises from this region

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Structure of the Spinal Cord
 The spinal cord is shorter than the vertebral canal
that houses it.
 Conus medullaris:
 tapered inferior end of the spinal cord
 marks the official “end” of the spinal cord proper.
 Cauda equina
 Inferior to conus medularis
 nerve roots (groups of axons) that project inferiorly from the
spinal cord.
 Filum terminale
 Within the cauda equina
 thin strand of pia mater
 helps anchor the conus medullaris to the coccyx.

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Structure of the Spinal Cord
 The spinal cord is associated with 31 pairs of spinal
nerves
 Connect the CNS to:
 receptors
 effectors (muscle and glands)
 Each side of the spinal cord contains:
 8 cervical nerves (called C1–C8)
 12 thoracic nerves (T1–T12)
 5 lumbar nerves (L1–L5)
 5 sacral nerves (S1–S5)
 1 coccygeal nerve (Co1)

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Arrangement and Functions of
the Spinal Meninges
 Are continuous with the cranial meninges.
 Structures that encircle the spinal cord, listed from
superficial to deep are:
 vertebra
 epidural space
 dura mater
 subdural space
 arachnoid
 subarachnoid space
 pia mater

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Location and Distribution of
Gray Matter
 In the spinal cord, it is centrally located.
 Its shape resembles a letter H or a butterfly.
 The gray matter may be subdivided into the following
components:
 anterior horns
 lateral horns
 posterior horns
 the gray commissure

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Location and Distribution of
White Matter
 The white matter of the spinal cord is
external to the gray matter.
 Three regions.
 Composed of tracts

Ascending

Descending
 A posterior funiculus:

lies between the posterior gray horns and the
posterior median sulcus.

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Location and Distribution of
White Matter
 Lateral funiculus.
 Anterior funiculus
 between the anterior gray horns and the
anterior median fissure.
 The anterior funiculi are interconnected
by the white commissure.

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Reflexes
 A reflex is a response:
 Rapid, automatic
 involuntary reactions of effectors to a stimulus.
 Properties.
 a stimulus

required to initiate a response to sensory input
 a rapid response

requires that few neurons be involved

synaptic delay be minimal
 an automatic response occurs the same way every time
 An involuntary response requires no intent or pre-awareness of
the reflex activity.
 Reflexes usually can not be suppressed.
 Awareness of the stimulus occurs after the reflex action
 in time to correct or avoid a potentially dangerous situation.

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Components of a Reflex Arc
 The neural “wiring” of a single reflex.
 Always begins at a receptor in the PNS
 Sensory afferent
 Communicates with the CNS.
 May involve interneurons
 Ends at a peripheral effector (muscle or
gland)
 Motor efferent

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Ipsilateral and Contralateral
Reflex Arcs
 Ipsilateral:
 both the receptor and effector organs of the reflex
are on the same side of the spinal cord.
 Contralateral
 the sensory impulses from a receptor organ cross
over through the spinal cord to activate effector
organs in the opposite side

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Monosynaptic Reflexes
 The simplest of all reflexes.
 No interneurons.
 The patellar (knee-jerk) reflex is a
monosynaptic reflex
 physicians use to assess the functioning of the
spinal cord.
 tap the patellar ligament with a reflex hammer
 muscle spindles in the quadriceps muscles are
stretched.
 Produces a noticeable kick of the leg.

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Polysynaptic Reflexes
 Have more complex neural pathways
 exhibit a number of synapses
 involve interneurons within the reflex arc.
 Has more components
 more prolonged delay between stimulus and response.

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Stretch Reflexes
 Monosynaptic reflex that monitors and regulates
skeletal muscle length.
 When a stimulus results in the stretching of a muscle,
that muscle reflexively contracts.
 The patellar (knee-jerk) reflex is an example of a
stretch reflex.
 The stimulus (the tap on the patellar tendon) initiates
contraction of the quadriceps femoris muscle and
extension of the knee joint.

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Golgi Tendon Reflex
 Prevents skeletal muscles from tensing excessively.
 Golgi tendon organs are nerve endings located within
tendons near a muscle–tendon junction.
 activation of the Golgi tendon organ signal interneurons in
the spinal cord, which in turn inhibit the actions of the motor
neurons
 The associated muscle is allowed to relax, thus
protecting the muscle and tendon from excessive
tension damage.

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Reflex Testing in a Clinical
Setting
 Reflexes can be used to test specific muscle groups
and specific spinal nerves or segments of the spinal
cord.
 Consistently abnormal reflex response may indicate
damage to the nervous system or muscles.
 A reflex response may be normal, hypoactive, or
hyperactive.

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Thank you for attention!