Coordinates voluntary and involuntary actions of the body and transmits signals between different parts of the body.
Together with endocrine system controls and integrates activities of the body.
Nervous system allows us to perceive, understand, and respond to our environment.
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Nervous System Overview.pptx
1. Nervous System
Dr. Rabia Inam Gandapore
Assistant Professor
Head of Department Anatomy
(Dentistry-BKCD)
B.D.S, M.Phil. Anatomy,
Dip.Implant, CHPE, CHR, Dip. Implant
2. Nervous System
Coordinates voluntary and involuntary
actions of the body and transmits signals
between different parts of the body
Together with endocrine system controls
and integrates activities of the body
Nervous system allows us to perceive,
understand, and respond to our
environment
3. Components of Nervous System
Divided into 2
1. Central nervous system
Brain
Spinal cord
2. Peripheral nervous system
12 pairs of cranial nerves
31 pairs of spinal nerves and their associated ganglia
Divided into 2 main components (functionally)
a. Somatic nervous system
Controls voluntary activities
b. Autonomic nervous system
Controls involuntary activities
6. Cellular Components of the Nervous
System
Comprised of two different types of cells:
1. Nerve cells (neurons): form functional
basis of nervous system, transmits signals
as electrical or chemical signals
2. Glial cells: provide functional and
structural support for neurons.
Example: Schwann cell: produces lipid
sheath of peripheral neurons
7. Central Nervous System (CNS)
Composed of nerve cells (neurons) & processes (dendrites: Short & Axons: Long)
Supported by specialized tissue called neuroglia (outnumber neurons by 10-50 times)
Interior of the CNS is organized into:
Gray matter (nerve cells, dendrites and synaptic contacts embedded in neuroglia)
White matter (nerve fibers- axon embedded in neuroglia)
Cell bodies of neurons are often grouped together in discrete areas termed as nuclei
Embryologically: CNS is derived from the neural tube
8. Nerve cell/ Neuron
Gray matter substantia grisea is
where the processing is done (cell
bodies, dendrites, axon terminals for
synapses) and the white matter
substantia alba is the channels of
communication (Nerve fibers-axons)
9. Neuronal Structure
Different types, sizes of neurons found in nervous system
Neurons are post-mitotic cells and, with few exceptions, are not replaced when lost
All contain the same key structural components
1. Cell body
2. Dendrites,
3. Axon
4. Axon terminals
10. 1. Cell Body/ perikaryon/ soma
Soma is central mass of cytoplasm, Holds the nucleus
Site of protein synthesis, which occurs on small granules
of rough endoplasmic reticulum called nissl substance
In the nervous system, many neuronal cell bodies can
group together to form a distinct structure.
a) CNS: this is known as a nucleus (clustered into nuclei,
columns or layers , dispersed within grey matter)
b) PNS: as a ganglion
11.
12. Plasma membrane of the soma is unmyelinated
Cytoplasm is rich in rough and smooth endoplasmic reticulum and free
polyribosomes that congregate in large groups associated with the RER, many
mitochondria and moderate numbers of lysosomes.
These aggregates of RNA-rich structures are visible by light microscopy as
basophilic Nissl (chromatin) bodies or granules
More obvious in large, highly active cells such as spinal motor neurons
The apparatus for protein synthesis (including RNA and ribosomes) occupies
the soma and dendrites but is usually absent from axons.
13. Contacts of Soma
Contacted by inhibitory and excitatory axo-somatic
synapses
Very occasionally, somasomatic and dendrosomatic
contacts may be made
Non-synaptic surface is covered by astrocytic or
satellite, oligodendrocyte processes
Various trans-membrane channel proteins and
enzymes are located at the surfaces of neurons, where
they are associated with ion transport
14.
15. 2. Dendrites
Dendrites are highly branched, usually short
processes that project from the soma/ body
Dendritic trees may be expanding and contracting
as traffic of synaptic activity varies through afferent
axo-dendritic contacts.
Extend outwards, receiving input from the
environment and from other neurons
16. 3. Axons
A long, thin structure that conducts action potentials (the nerve impulse)
Neurons have many dendrites, most cells only have one axon
Axon is coated in myelin – a layer of insulating lipid. Myelin is formed by cells
wrapping themselves around the nerve axon
a) CNS: this is performed by oligodendrocyte cells
b) PNS: Schwann cells
There are gaps ,nodes of Ranvier, between the myelin sheaths formed by different
cells. They allow for saltatory conduction of impulses
17.
18. Originates either from the soma or from the proximal segment of a dendrite, at a
specialized region called the axon hillock which is free from Nissl granules
The axonal membrane (axolemma) is undercoated at hillock by a concentration of
cytoskeletal molecules i.e spectrin and actin fibrils
Spectrin and actin fibrils helps in anchoring numerous voltage-sensitive channels to
the membrane
Nodes of Ranvier are specialized constricted regions of myelin-free axolemma where
action potentials are generated and where an axon may branch
19. Axonal Ion Channels
Density of sodium channels in the axolemma is highest at the nodes of Ranvier
and very low along internodal membranes.
Sodium channels are spread more evenly within axolemma of unmyelinated axons.
Fast potassium channels are also present in the paranodal regions of myelinated
axons.
20.
21. Neuronal Skeleton
A prominent feature of neuronal cytoplasm
Gives shape, strength and rigidity to the dendrites and axons.
Neurofilaments (the intermediate filaments of neurons) and
microtubules (motor protein call kinensin; transportation via
axon) are abundant
Bundles of neurofilaments constitute neurofibrils
Some axons are almost filled by neurofilaments.
Dendrites usually have more microtubules than axons.
22. Kinesin protein and transport, enzyme,
neurotransmitter, membrane protein etc.
Dynein protein
transports dead
mitochondria, nerve
growth factors,etc.
23. 4. Axon Terminals
Most distal part of the axon
In here neuron sends chemical signals to other
cells – usually via neurotransmitter release ( hence
contain large number of mitochondria
Reuptake of neurotransmitters
The terminals of an axon are unmyelinated
Neuron
24. Pattern of axonal termination
Vary considerably
Single axon may synapse with one neuron
Example: climbing fibres ending on
cerebellar Purkinje neurons
More often, synapses with many
Example: Cerebellar parallel fibres
25. How dendrites are different from axons
Represent afferent neuron
Receive both excitatory and
inhibitory axo-dendritic contacts
May also make dendrodendritic and
dendrosomatic connections
Synapses occur either on small
projections called dendritic spines or
on the smooth dendritic surface
26. Coverings of the nerves
In PNS: axons of neurons are grouped together to form nerves
The axons are enclosed by several connective tissue layers:
Endo-neurium: Surrounds the axon of an individual neuron.
Peri-neurium: Surrounds a fascicle, which is a collection of neurons.
Epi-neurium: Surrounds the entire nerve, which is formed by a collection of fasicles
Contains numerous small blood vessels, which supply the nerve fibres
Epineurium appears on the nerve as it exits the intervertebral foramen
Created by the fusion of arachnoid and pia mater, which are layers of the meninges
27.
28. Classification of Neurons (Structural)
1. Structural classification of neurons
Unipolar: cell body is at one end of a single un-branched axon,& no dendrites.
Example: cochlear nucleus of brain
Pseudounipolar: axon (not distinguished) with two branches (peripheral &
central process) from the cell body. Example: Sensory neurons, Dorsol root
ganglion, Cranial nerve 5 (trigeminal ganglion)
Bipolar: have two processes arising from a central cell body – typically one
axon and one dendrite. Example: found in retina, olfactory nerves, inner ear.
Multipolar: They have one axon and many dendrites, with a cell body displaced
to one side of the axon. Example: Motor Cortex neurons , cerebellum
30. 2. Functional Classification of Neurons
3 types:
1. Sensory (afferent): Towards CNS
Viscera to CNS: 1. General Visceral (lungs, heart, GIT), 2. General Somatic (skin, skeletal
muscle, joints), 3. Special Sensory ( vision & hearing), 4. Special Viscera (Smell, Taste)
2. Intermediate- Interneurons: Between sensory & motor (Motor Pathway: Motor cortex
down to neurons in spinal cord (lower motor neurons) and goes to skeletal muscles,
Sensory Pathway: Sensory receptors from skin or muscle to neuron (Nucleus gracilis) in
spinal cord and then to another neuron (Thalamus nuclei) and final to the cerebral cortex
(motor neuron))
3. Motor (efferent): Away from CNS to Effector Organ
1. General Visceral (smooth muscle in bronchi, cardiac muscle, gland- ANS), 2. General
Somatic (Skeletal Muscle). 3. Special Visceral (Muscles of Head & neck cranial nerves
5T,7F,9G,10V)
31.
32. There are key structural differences between these three types:
1. Sensory nerves: small axons and pseudo-unipolar structure.
2. Motor nerves: larger axons and multipolar structure.
3. Intermediate neurons: central cell body and many dendrites.
Sensory and motor nerves are located within the PNS, whereas
intermediate nerves are found in the CNS.
33. Neurotransmitters
Two Classes
A. Excitatory neurotransmitters
Cause depolarization of post-synaptic membrane
Promote action potentials
B. Inhibitory neurotransmitters
Cause hyperpolarization of post-synaptic membranes
Suppress actions potentials
34. The effect of a
neurotransmitter on a
postsynaptic membrane
depends on the
receptor, Not on the
neurotransmitter
For example,
Acetylcholine (ACh)
: promotes action
potentials, But
inhibits cardiac
neuromuscluar
junctions
35. Neurotransmitters
Asymmetric synapses (Excitatory) with relatively
small spherical vesicles are associated with
acetylcholine (ACh), glutamate, serotonin
(5hydroxytryptamine, or 5-HT) and some amines.
Those with dense-core vesicles include many
peptidergic synapses and other amines (e.g.,
noradrenaline, adrenaline, dopamine)
Symmetric synapses ( Inhibitory) with flattened or
pleomorphic vesicles contain either gamma-
aminobutyric acid (GABA) or glycine
36. Neurotransmitters
50 neurotransmitters other than Ach, including: Biogenic amines, Amino
acids, Neuropeptides, Dissolved gases
Important Neurotransmitters
Norepinephrine (NE): Released by adrenergic synapses, Excitatory
and depolarizing effect. Widely distributed in brain and portions of ANS
Dopamine: A CNS neurotransmitter, May be excitatory or inhibitory
Involved in Parkinson's disease and cocaine use
Serotonin: A CNS neurotransmitter Affects attention & emotional states
37. Difference between neurotransmitter and
neuromodulator
Neuronal Responses to injuries Axons respond differently to injury,
depending on whether the damage occurs in the CNS or PNS.
38. Receptors for Neurotransmitters
1. Cholinergic receptors for ACh : Named after drugs that bind to them and mimic
ACh effects. Two types of receptors bind ACh
1. Nicotinic: Found on Motor end plates of skeletal muscle cells, All ganglionic
neurons (sympathetic and parasympathetic), Hormone-producing cells of the adrenal
medulla, Effect of ACh at nicotinic receptors is always stimulatory
2. Muscarinic: Found on All effector cells stimulated by postganglionic cholinergic
fibers, The effect of ACh at muscarinic receptors can be either inhibitory or excitatory,
Depends on the receptor type of the target organ
39.
40. 2. Adrenergic receptors for NE: Effects of Norepinephrine depend on which
subclass of receptor predominates on the target organ. Two types
1. Alpha (subtypes 1, 2)
2. Beta (subtypes 1, 2 , 3)
41.
42. Classification of Glial cells
CNS Glia PNS Glia Basic Function
Astrocyte Satellite Cell Support
Oligodendrocyte Schwann Cell Insulation , Myelination
Microglia Immune surveillance & phagocytosis
Ependymal Cell Creating CSF
45. Brain (Encephalon)
Lies within the cranium
Receives information & controls activities of
trunk and limbs via spinal cord
Brain is divided into major regions based on:
Ontogenetic growth (morphological)
Phylogenetic principles (evolutionary)
Principal division from spinal cord to higher up:
Hindbrain or rhombencephalon
Midbrain or mesencephalon
Forebrain or prosencephalon
48. Brain stem: lies over the basal portions
of the occipital and sphenoid bones
Medulla ablongata: is the most caudal
part of the brain stem. Continuous with
the spinal cord below the level of foramen
magnum
Pons: lies rostral to the medulla and is
distinguished by the mass of transverse
fibers which connect it to cerebellum
49. Cerebellum
Cerebellum “little brain”
Role in motor control, with cerebellar dysfunction often presenting with motor signs
Active in coordination, precision, timing of movements, and in motor learning
Anatomical Location
Located at the back of the brain, immediately inferior to the occipital and temporal
lobes, and within the posterior cranial fossa
Separated from these lobes by the tentorium cerebelli, a tough layer of dura mater
Lies at the same level of and posterior to the pons, from which it is separated by the
fourth ventricle
50.
51.
52. Anatomical Structure of Cerebellum
Consists of two hemispheres which are connected by the vermis, a narrow midline
area
Grey matter: located on the surface of the cerebellum. Tightly folded, forming the
cerebellar cortex.
White matter: located underneath the cerebellar cortex. Embedded in the white
matter are the four cerebellar nuclei (Dentate, emboliform, globose, and fastigi
nuclei).
3 subdivisions: Anatomical lobes, zones and functional divisions
53.
54. 1. Lobes and fissures of Cerebellum
Anatomical Lobes
3 anatomical lobes
Anterior lobe,
Posterior lobe
Flocculonodular lobe
Lobes are divided by two fissures
1. Primary fissure
2. Posterolateral fissure
55. 2. Zones of the Cerebellum
3 cerebellar zones
Midline of cerebellum is vermis
Either side of the vermis is the intermediate zone
Lateral to the intermediate zone are the lateral hemispheres
There is no difference in gross structure between the lateral
hemispheres and intermediate zones
56. Vasculature of Cerebellum
Arterial Supply:
Superior cerebellar artery (SCA) branch of basilar artery
Anterior inferior cerebellar artery (AICA) branch of basilar artery
Posterior inferior cerebellar artery (PICA) branch of the vertebral artery
Venous drainage: superior and inferior cerebellar veins, drain into the superior
petrosal, transverse and straight dural venous sinuses
57.
58. 2. Midbrain/Mesencephalon
Short segment of brainstem lying rostral to the pons
Associated with vision, hearing, motor control, sleep awake, arousal & temperature
regulation
Located below cerebral cortex and above hindbrain, placing it center of brain
Comprises of:
Tectum
Cerebral aqueduct
Cerebral peduncles
Several nuclei and fasciculi
Caudally it adjoins pons and cerebellum, rostrally it adjoins thalamus and
hypothalamus
62. Forebrain Conti..
Diencephalon: completely embedded in cerebrum & largely hidden from exterior
Human cerebrum constitutes the major part of the brain
Occupies the anterior cranial fossae and is directly related to the cranial vault
Consists of 2 cerebral hemispheres
Surface of each hemisphere is convoluted into a complex pattern of ridges called
gyri and furrows known as sulci
Internally each hemisphere has an outer layer of grey matter- cerebral cortex
Beneath which lies a thick mass of white matter
63. Sulci and Gyri
Sulci: (Furrows)
Central sulcus: groove separating frontal and parietal lobes
Lateral sulcus: groove separating frontal and parietal lobes from temporal lobe
Lunate sulcus: groove located in the occipital cortex
Gyri: (Ridges)
Precentral gyrus: ridge directly anterior to central sulcus, location of primary motor
cortex
Postcentral gyrus: ridge directly posterior to central sulcus, location of primary
somatosensory cortex
Superior temporal gyrus: ridge located inferior to lateral sulcus, responsible for the
reception and processing of sound
67. Cerebral Hemisphere
1. Frontal lobe: (premotor cortex, frontal eye field, motor speech area)
Occupies area anterior to central sulcus and superior to lateral sulcus
2. Parietal lobe: (primary somesthetic area)
Occupies area posterior to the central sulcus and superior to lateral
sulcus
3. Temporal lobe: (primary auditory area)
Occupies the area inferior to the lateral sulcus
4. Occipital lobe: (primary visual area)
Occupies the small area behind the parieto-occipital sulcus
68.
69. Vasculature of the Cerebrum
Arterial Supply:
Anterior Cerebral Arteries: branches of internal carotid arteries, supplying the
antero-medial aspect of the cerebrum
Middle Cerebral Arteries: continuation of internal carotid arteries, supplying most of
lateral portions of cerebrum
Posterior Cerebral Arteries: branches of vertebral arteries, supplying both medial
and lateral sides of cerebrum posteriorly
Venous drainage:
small cerebral veins , empty into dural venous sinuses – endothelial lined spaces
between outer and inner layers of dura mater
70.
71. Internal capsule is an important component of cerebral white matter
Contains nerve fibers which pass to and from cerebral cortex and lower levels of
neuraxis
Several large nuclei of grey matter called basal ganglia, are partly embedded in
the subcortical white matter
Corpus callosum midline commissure that links the corresponding regions of the
two sides of the brain via fibers passing through it
Basal Ganglia is group of subcortical nuclei responsible primarily for motor
control, motor learning, executive functions and behaviors, and emotions.
76. Ventricular System
Interconnected cavities in the brain
choroid plexus are present, secrete cerebrospinal fluid which fills the ventricles
Parts: Lateral ventricles ,3rd ventricle & 4th ventricle
Lateral ventricles: Large cavities located on each side of the cerebral
hemisphere. Communicates caudally with 3rd ventricle via a small aperture
3rd ventricle: Caudal end of lateral ventricles opens into a narrow slit-like midline
cavity called 3rd ventricle, Bounded laterally by diencephalon, Continuous caudally
with 4th ventricle with a narrow channel called cerebral aqueduct, which passes
through the midbrain
77.
78. Ventricular System conti..
4th ventricle:
Cavity of rhombencephalon expands to form 4th ventricle
lies dorsal to pons and upper half of medulla
Rostrally: connected to 3rd ventricle via cerebral aqueduct
Caudally: it is continuous with a canal in the caudal medulla and through this
with the central canal of the spinal cord
It is continuous with sub arachnoid space through 3 openings in its roof
(Foramina of Luschka and of Magendie)
80. Meninges of the Brain
Membranous coverings of brain and spinal cord
3 layers of meninges:
Dura, Arachnoid & Pia mater
Two major functions:
Provide a supportive framework for the cerebral
and cranial vasculature
Acting with cerebrospinal fluid to protect the
CNS from mechanical damage
81. Dura Mater
Outermost layer of the meninges, lying directly underneath the bones of the skull
and vertebral column
It is thick, tough and inextensible
Within the cranial cavity, the dura contains two connective tissue sheets:
1. Endosteal layer: Lines the inner surface of the bones of the cranium.
2. Meningeal layer: Lines the endosteal layer inside the cranial cavity and the only
layer present in the vertebral column
Between these two layers, the dural venous sinuses are located
They are responsible for the venous vasculature of the cranium, draining into the
internal jugular veins
82. In some areas within skull, meningeal layer of dura mater folds inwards as dural
reflections
They partition the brain, and divide the cranial cavity into several compartments.
Example: tentorium cerebelli divides the cranial cavity into supratentorial and
infratentorial compartments.
Dura mater vasculature: middle meningeal artery and vein
Innervation: trigeminal nerve (V1, V2 and V3)
83.
84. Arachnoid Mater
Middle layer of the meninges, lying directly underneath the dura mater
Consists of layers of connective tissue, is avascular, and does not receive any
innervation
Underneath the arachnoid is a space known as the sub-arachoid space,
Contains cerebrospinal fluid, which acts to cushion the brain
Small projections of arachoid mater into the dura (known as arachnoid
granulations) allow CSF to renter the circulation via the dural venous sinuses
85.
86. Pia Mater
Located underneath the sub-arachnoid space
Thin & tightly adhered to surface of brain and spinal cord
Only covering to follow contours of brain (the gyri and fissures)
Highly vascularised, with blood vessels perforating through the membrane to
supply the underlying neural tissue
88. Spinal Cord
Lies within the vertebral column, in the upper 2/3rd of the vertebral canal
Extends from upper border of atlas vertebra to the junction between first and 2nd
lumbar vertebrae
Continuous rostrally with medulla ablongata of the brain stem
It narrows caudally to conus medullaris (L1, L2), whose apex is attached to
connective tissue filament filum terminale
Cauda Equina (L2, Co1): Nerves go down as bunch /bundle (Horsetail)
Cervical enlargement (C5-T1), more grey matter in ventral grey horn of spinal cord
(Supply Skeletal muscle of upper Limbs)
Lumbar enlargement (L2-S3): Ventral grey matter-Skeletal muscles of lower limbs
89.
90. Terminates at L1 or L2
C1
Spinal cervical nerves 8
(Above Vertebrae)
91. Receives afferent inputs and controls the
functions of the trunk and limbs
Afferent and efferent connections
between periphery and spinal cord travel
via segmentally arranged spinal nerves
Consists of central core of grey matter
surrounded by white matter
Grey matter has a characteristic “H” or
butterfly shape
92. White Matter
White matter decrease C1-C01), Grey matter Increase (C1-Co1)
White matter: Sensory (Ascending), Motor (Descending) tracts
White matter more in cervical and less in coccygeal (sensory information from tail
bone) because the sensory information ascends up from co1 medially (midline
portion of dorsal column) up to the cerebral cortex , followed by sacral (genital
area), Lumber ,thoracic (trunk), and cervical (Neck,Limbs) more laterally.
Same concept with the descending pathway(motor) and information exit out at ever
portion of spinal cord. The more information is received at the cervical region of the
spinal cord that’s why white matter is more in cervical region. Hence grey matter
(ventral grey horn) thickens at Co1.
93.
94. Grey matter has projections:
1. Dorsal horn: Neurons=Sensory Function
2. Ventral horn: Neurons= Motor activity
3. Intermediate horn: Small lateral horn is additionally present,marks location of cell
bodies of preganglionic sympathetic neurons
Central canal: a vestigial component of ventricular system lies in center of spinal
grey matter and runs the length of the cord
White matter: consists of ascending and descending tracts that link spinal cord
segments to one another and spinal cord to brain
97. Spinal cord cross-section
Axon appear white due to myelin sheath (White Matter), while dendrites are
unmyelinated and give grey color (Grey matter).
Spinal cord cross-section:
1. Posterior median sulcus
2. Grey matter: Dendrites, Synapses
3. Posterior (dorsal) grey horn: Sensory Neurons
4. White matter: Axons
5. Anterior median fissure
6. Intermediate zone : Visceral motor function (smooth, cardiac, glands-Sympathetic
& Para-Sympathetic)
98. 7. Anterior (ventral) grey horn: Motor Neurons-somatic (skeletal muscle) motor neurons,
CNS= nuclei
8. Lateral grey horn: T1 to L2, Pre-ganglionic motor neurons of the sympathetic nervous
system, Comes out of intermediate zone only at T1 to L2
9. Dorsal (posterior) white column or funiculus: Ascending tracts- Somatic-Sensory
Information, Visceral sensation
10. Lateral white column or funiculus: Ascending (Sensory) & Descending (Motor) tracts
11. Ventral (anterior) white column or funiculus: Ascending (Sensory) & Descending
(Motor) tracts
12. Anterior white Commissure: crossing of fibers occurs, when fibers come in dorsal
horn and has to go to opposite side, it cross this structure
13. Grey Commissure: Connection 2 side (Dorsal, ventral and intermediate zone)
together in middle.
99. Axon bundles in CNS is called tracts
Cell bodies with Dendrites bundles in horn in the CNS is called nuclei
Ganglia: group of cell bodies in PNS
Spinal Nerve
Dorsal Root
Ventral Root
Spinal Nerve splits and one go towards back is called dorsal rami (Supply: Bac;, neck,
vertebra , Anterio-lateral supply of limbs are called ventral rami (Supply: Anterior
trunk,Lateral trunk, Limbs)
White and grey rami communicans and connected to a ganglia
Spinal Nerve
100.
101. Sensory Information from dorsal or ventral rami will move through the spinal nerve,
go in dorsal root and enter the dorsal root ganglia. It then enter the posterior grey
horn (sensory neurons) and inter-neuronal synapse occur. It activate somatic motor
neuron present in the ventral grey horn and enter ventral root and then enter spinal
nerve and go to dorsal rami (back) or go to ventral rami (trunk, Limbs)
102.
103.
104. Spinal Dorsal Horn
Involved in the processing and transmission of sensory information to the brain
The circuitry involved is complex and still poorly understood
106. Functions of the Spinal Dorsal Horn
Transmits/modifies inputs that it receives from primary afferents
•Local interneurons
•Descending axons
Provides outputs to
•Brain (projection neurons)
•Spinal circuits involved in Reflexes,
•Autonomic functions
Melzack & Wall (1965) Science 150 971-‐-979
107. Overview of Ascending Sensory
Pathways
Responsible for the transmission and interpretation of sensory modalities
(special and general senses)
Special senses:
Olfaction
Vision
Taste
Hearing Vestibular function
General senses: Touch,Thermal sensation, Pressure, Proprioception,
Vibration, Pain
108.
109. Ascending Pathway conti…
Stimuli from the external and internal environments activate a diverse range of
receptors in the skin, viscera, muscles, joints and tendons
Afferent impulses from the trunk and limbs are conveyed to the spinal cord in
spinal nerves while those from head are carried to brain in cranial nerves
Ascending pathways in general consists of a sequence of 3 neurons that extend
from peripheral receptor to the contralateral cerebral cortex
They are referred to as:
Primary (first order) o Secondary (second order) o Tertiary (third order)
110. 1. Tract of Lissauer
White matter tract
Ascending & descending pathway
Pain & temperature pathway
Example; T1-T3 = Receptors picks pain & temperature sensation
and go through sensory neuron to posterior grey horn but NO, it
enter the tract instead on posterior grey horn and allows to ascend
1 or 2 spinal cord segments , it will not synapse in the posterior
grey horn at T3 instead synapse at T1 level. It will than crossover
and ascends up via the Spinothalamic tract.
111. Spinothalamic Tract
1st order neuron:
Primary afferents carrying pain, temp & touch
Peripherally located sensory endings and cells bodies that lie in the dorsal root
ganglia or sensory ganglia associated with cranial nerves
Axons enter the CNS through spinal or trigeminal nerves
Terminate by synapsing on cell bodies of ipsilateral 2nd order neurons
Precise location of termination depends upon the modality they carry
112. 2nd order neuron:
Cell bodies are located either in the dorsal horn or trigeminal sensory nucleus of
the brain stem
Axons decussate and ascend to the ventral posterior nucleus of the contralateral
thalamus as spinothalamic or trigeminothalamic tract
Axons synapse with the cell bodies of 3rd order neurons in thalamus
113. 3rd order neuron:
Axons of third order neuron pass through
the internal capsule to reach cerebral
cortex
They terminate in the post central gyrus
of the parietal lobe, also known as
primary somatosensory cortex
114. Primary afferents carrying propioception
and fine touch
Fibers from trunk and limbs ascend ipsilaterally in the spinal cord as dorsal
column (fasciculus gracilis & fasciculus cuneatus)
They end by synapsing 2nd order neurons in the dorsal column nuclei (nucleus
gracilis and cuneatus) of medulla
2nd order neuron:
Axons of second order decussate in medulla and ascend as medial leminiscus to
VP nucleus of contralateral thalamus to synapse with cell bodies of 3rd order
neuron 3rd order neuron: Axons of these cells pass through internal capsule to
reach cerebral cortex and terminate in the somatosensory cortex
115.
116.
117. Overview of Descending Pathways
Corticospinal fibers/pyramidal tract:
Originates from widespread regions of the cerebral cortex, including primary
motor cortex
These fibers descend through out the length of the brain stem
Majority cross to the contralateral side in the decussation of the pyramids in the
medulla
The continue to descend as the lateral corticospinal tract of the spinal cord
Terminates in association with interneurons and motor neurons of the spinal grey
matter
Take part in control of the fine movements such as movement of hand
118.
119. Fine touch,
Vibration,
proprioreception
Stimulate lower motor
neurons to allow voluntary
muscles of skeletal muscles
Stimulate lower motor
neurons to allow voluntary
muscles of Limb flexors
Proprioception (3D)
Proprioception to inferior olives to
cerebellum (Climbing fibers)
Pain & Temperature
121. Peripheral Nervous System
Consists of cranial and spinal nerves and their associated ganglia
Bundles of axons (nerve fibers) supported by delicate areolar tissue
Specifically composed of
Efferent axons (fibers) of motor neurons situated inside CNS
Cell bodies of sensory neurons grouped together as ganglia
Afferent processes of these sensory neurons
Ganglionic neurons of ANS
Neuronal cells bodies in peripheral ganglia are derived embryologically from
cells that migrate from neural crest
123. Cranial Nerves
12 pairs of cranial nerves
Leave the brain and pass through foramina in the skull
All nerves are distributed in the head and neck except vagus which supplies the
structure of thorax and abdomen
128. Spinal Nerves
31 pairs of spinal nerves
Leave the spinal cord and pass through intervertebral foramina in the vertebral
column
Named according to the region of the vertebral column they are associated with
8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1 coccygeal
129. Structure of a Spinal Nerve
Spinal nerve is connected to spinal cord by 2 roots
1. Anterior root
2. Posterior root
1. Anterior (ventral) root:
Consists of bundles of nerve fibers carrying nerve impulses away from central
nervous system (also called efferent fibers)
Those efferent fibers that innervate skeletal muscles are called motor fibers
Their cells of origin lie in the anterior horn of the spinal cord
130. 2. Posterior (dorsal) root:
Consists of bundles of nerve fibers carrying nerve impulses to CNS
They are also called afferent fibers
They carry information about the sensation of touch, pain, vibration and
temperature, hence also termed as sensory fibers
131.
132. Structure of a Spinal Nerve
Cells bodies are present in a swelling of the posterior root called posterior/dorsal root
ganglion
At each intervertebral foramen, both anterior and posterior root unite to form a spinal
nerve
Spinal nerve is a mixture of motor and sensory fibers
It emerges from foramen and divides into
1. Large anterior ramus (supplies muscle and skin of anterolateral body wall, muscles
and skin of limbs)
2. Smaller posterior ramus (supplies muscle and skin of the back)
Spinal nerves also give a small meningeal branch that supplies the vertebrae and the
coverings of the spinal cord (the meninges)
133.
134. Nerve Plexuses
Complicated arrangement of nerve fibers at the root of the limbs
Formed by the anterior rami of spinal nerves
1. Upper Limb: Cervical and brachial plexuses
2. Lower Limb: Lumbar and sacral plexuses
137. Autonomic Nervous System
Concerned with innervation of involuntary structures such as heart, smooth muscles
and glands. Represents general visceral motor component
Distributed through out central and peripheral nervous system
Hypothalamus controls ANS and integrates activities of ANS and endocrine system
Activity is regulated at
1.Higher centres of brain stem,
2.Cerebrum
3.Several nuclei of brain stem reticular formation,
4.Thalamus and hypothalamus,
5.Limbic lobe,
6.Prefrontal neocortex & ascending descending pathways that connect these regions
138. Divided into
1.Sympathetic nervous system
2.Parasympathetic nervous system
3.Enteric (neurons are intrinsic to the wall of GIT)
ANS and Somatic differs in
1. Effectors
2. Efferent pathways (and their neurotransmitters)
3. Target organ responses to neurotransmitters
139. Efferent pathways (& neurotransmitters)
Somatic nervous system
A, thick, heavily myelinated somatic motor fiber makes up each pathway
from the CNS to the muscle
ANS pathway is a two-neuron chain
1. Preganglionic neuron (in CNS) has a thin, lightly myelinated
preganglionic axon
2. Ganglionic neuron in autonomic ganglion has an unmyelinated
postganglionic axon that extends to the effector organ
140. Neurotransmitter Effects
Somatic nervous system: All Somatic motor neurons release
acetylcholine (ACh) & Effects are always stimulatory
ANS:
Preganglionic fibers: release Ach
Postganglionic fibers: release norepinephrine or ACh at effectors.
Effect is either stimulatory or inhibitory, depending on type of
receptors
Somatic Nervous System: Skeletal muscles
ANS: cardiac muscles, smooth muscles and glands
141.
142. Realistically both the systems are integrated and are capable of discrete activation
Autonomic neurotransmission:
Preganglionic neurons of both systems and post ganglionic neurons of
parasympathetic system are cholinergic (release acetylcholine “Ach”-
Excitatory). Stimulates post ganglionic fibers
Post ganglionic neurons of sympathetic system are noradrenergic
(norepinephrine-Inhibitory) – Principal co-transmitters: ATP, neuropeptide Y,
substance P . Stimulates the effector organs.
143. Central nervous system (CNS) Peripheral nervous system (PNS)
Motor (efferent) division
Sensory (afferent)
division
Somatic nervous
system
Autonomic nervous
system (ANS)
Sympathetic
division
Parasympathetic
division
146. Sympathetic Nervous System
General features:
Prepares the body for emergency
Accelerates heart rate
Causes constriction of peripheral blood vessels
Inhibits peristalsis of the intestinal tract
Closes sphinchters
147. Sympathetic Nervous System Cont..
Anatomical features:
Sympathetic trunks are 2 ganglionated nerve cords
Extend from the cranial base to the coccyx
Ganglia are joined to spinal nerves by short connecting nerves called grey and white
rami communicantes
Preganglionic axons join the trunk through the white rami communicantes, while
postganglionic axons leave the trunk in the grey rami
Cell bodies of preganglionic sympathetic neurons are located in the lateral horn of the
spinal grey matter
Cell bodies of post ganglionic sympathetic neurons are located mostly in the ganglia of
the sympathetic trunk
157. Parasympathetic Nervous System
General features:
Aims at conserving and restoring body energy
Slows the heart rate
Increases intestinal peristalsis
Opens sphinchters
158. Parasympathetic Nervous System
Anatomical features: (Cranio-sacral)
Preganglionic parasympathetic neuron cell bodies are located in the:
cranial nerve nuclei (3,7,9,10) of the brain stem
In the grey matter of the second to fourth sacral segments of the spinal cord
Post ganglionic parasympathetic neuron cell bodies are sited distant from the CNS
either in :
Discrete ganglia/ terminal ganglia: located near the innervating structure
(target organ)
Or Intramural ganglia: dispersed in the walls (tissues) of the viscera
159.
160.
161. Divisions Origin of
Fibers
Length of
Fibers
Location of
Ganglia
Type of Ganglia
Sympathetic Thoracolumbar
region of the
spinal cord
(T1-L2)-
Intermediate
lateral grey
Horn
Short
myelinated
preganglionic
(Ach) and long
unmyelinated
postganglionic
(NorEpi)
Close to spinal
cord
• Sympathetic Ganglia/
Paravertebral/ Lateral/
Chain
• Collaterals Ganglia/
prevertebral
• Specialized neurons in
anterior of suprarenal gland
Parasympathetic Brain (Cranial
nerve 3,7,9,
10) and sacral
spinal cord
(S2,S3,S4)
(craniosacral)
Long
myelinated
preganglionic
(ach) and short
unmyelinated
postganglionic
(ach)
In visceral
effector organs
• Within tissue of target
organ (intramural ganglion)
• Close to target organ
(Terminal Ganglion)
166. Enteric Nervous System
Consists of ganglionic plexuses localized in the walls of gastrointestinal tract
Contains reflex pathways through which contractions of the muscular coats of
alimentary tract and other GIT functions are controlled
Capable of sustaining local reflex activity independent of CNS