2. Content
o Introduction of nervous system
o Organization of nervous system
o Nervous tissue
o Neurons and its types
o Supporting cells
o Ascending tract and descending tract
o Reflex
3. Introduction
Nervous system is:
A physically connected network of cells, tissues and organs
that allow us to communicate with and react to the
environment and perform life activities.
Master controlling and communicating system
Has two main division
Central nervous system
Peripheral nervous system
4. FOUR PRIMARY FUNCTIONS OF
NERVOUS SYSTEM
Sensing the world
Vision, Hearing, Smell,
Taste, Touch
Transmitting information
Processing information
Producing a response
5. Organization
A. Central Nervous System (CNS)
▫ Brain & spinal cord
▫ Integrative and control centers
-Receives, interprets and sends signals to PNS
B. Peripheral Nervous System (PNS)
▫ Nerves (31 pairs of spinal nerves,12 pairs of cranial nerves)
▫ Communication lines between CNS and rest of body
▫ Two Divisions:
1. Sensory (afferent) Division: Sensory receptors --
CNS
2. Motor (efferent) Division: CNS -- effectors (muscles &
glands)
6. Motor Division
Somatic nervous system (voluntary)
- control skeletal muscles
Autonomic nervous system (ANS) (involuntary)
– regulate smooth muscles, cardiac, glands
▫ Subdivisions:
o Sympathetic :
o “Fight or Flight”
o Activated during emergencies, exercise or vigorous physical activity
o Revs up body to respond to situations that upset homeostasis
o Parasympathetic:
o “Rest & Digest”
o Reduces energy use
o Promotes:
o Storage of energy
o Elimination of wastes
o Homeostasis
7.
8.
9.
10. The mammalian brain is
highly complex, containing
many specialized regions that
carry out specific functions.
Generally, the brain is divided
into:
Hindbrain
Midbrain
Forebrain
THE COMPLEX BRAIN
12. Midbrain
Located between the hindbrain and forebrain.
All sensory and motor information that travels
between the forebrain and the spinal cord
passes through the midbrain
making it a relay station for the central nervous
system.
the “traffic cops” of the brain.
Filters sensory input, which allows us to
concentrate.
Filtering can be affected by higher thoughts.
13. Forebrain
Thalamus:
relay station channeling
sensory information.
Limbic system:
basic emotions, drives, and
behaviors.
Cortex:
higher thought
14. Limbic system
Hypothalamus:
Master controller of the
endocrine system.
Amygdala:
sensations of pleasure or
fear, recognition of fear
in others.
Hippocampus:
formation of memories.
Damage to these areas can lead to
amnesia or emotional disturbances
“controls: emotions and memories”
15. Cortex
Various areas :
control
sensory
processing
motor control,
thought,
memory.
Top layer of the brain
Stores: experiences and/or learning
behavior & emotion
Sensory info
concerning touch
vision
memory &
emotion, speech
and hearing
16. Spinal cord
Grey matter
mostly made up of cell bodies of neuron
White matter
composed of nerve fibers ( ascending and descending tracts )
embedded in neuroglial cells
17.
18. Nervous Tissue
1. Neurons (nerve cells)
• Functional unit of the nervous system
• Transmit message
Anatomy:
Cell body – contains nucleus; metabolic center
Dendrite – fiber that conveys messages toward cell body
Axon – conduct nerve impulses away from the cell body
Axon terminals – end of axon; contain neurotransmitters&
release them
Synaptic cleft/synapse – gap between neurons
22. Myelin
Whitish, fatty material that covers nerve fibers to
speed up nerve impulses
Schwann cells
Surround axons and form myelin sheath
Myelin sheath
• Tight coil of wrapped membranes
Nodes of Ranvier
Gaps between Schwann cells
23. • Ganglia: collections of cell bodies
• Bundles of nerve fibers = tracts (CNS) or nerves (PNS)
• White matter
• Dense collections of myelinated fibers
• Gray matter
• Unmyelinated fibers & cell bodies
• (nerve cell bodies, dendrites, axon terminals, bundles of
unmyelinated axons and neuroglia (gray color)
24. Dendrites receive signals.
The cell body integrates
signals.
The axon transmits action
potential. The myelin
sheath makes the signal
travel faster.
Synaptic terminals
transmit signals.
The Neuron
25. Neurons
Neuron Function
Irritability:
ability to respond to stimulus & convert
to nerve impulse
Conductivity:
transmit impulse to other neurons,
muscles, or glands
Classification of Neuron
Functional Classification
Structural Classification
26. 1. Functional Classification:
Direction nerve impulse is traveling
Sensory
neurons
Motor
neurons
Interneurons
carry impulses from
sensory receptors to
CNS
carry impulses from
CNS to muscles &
glands
connect sensory &
motor neurons
Vision, hearing,
equilibrium, taste,
smell, pain,
pressure, heat
27. 2. Structural Classification:
Processes extending from cell body
Multipolar Bipolar Unipolar
1 axon, several
dendrites
1 axon, 1 dendrite 1 process
Most common
(99%)
Rare
Short with 2
branches (sensory,
CNS)
Eg. Motor
neurons,
interneurons
Eg. retina, nose,
ear
Eg. PNS ganglia
28.
29. Nerve Impulses
Cell membrane at rest = polarized
Na+outside cell, K+inside cell
Inside is (-) compared to outside
Stimulus ---excited neuron (Na+rushes in)--
becomes depolarized
Depolarization activates neuron to transmit an
action potential (nerve impulse)
All-or-none response
Impulse conducts down entire axon
K+ diffuses out ---repolarization of membrane
Na+/K+ ion concentrations restored by sodium-
potassium pump (uses ATP)
Exciting a Neuron
30. Synapse
Neurons usually do not connect
directly to one another. A gap
called a synapse controls the
transmission of signals.
Depending on the site of the
synapse, they are often referred to
as axodendritic, axosomatic, or
axoaxonic
Types of synapse
Chemical
Neurotransmitter
Electrical
presynaptic
neuron
Post synaptic
neuron
31.
32. Information Transfer Across Chemical
Synapse
Action potential reaches
axon terminal ----
vesicles release
neurotransmitters (NT)
into synaptic cleft
NT diffuse across
synapse
bind to receptors
of next neuron
Transmission of a nerve
impulse =
electrochemical event
34. Spinal cord
Grey matter
mostly made up of cell bodies of neuron
White matter
composed of nerve fibers ( ascending and descending tracts )
embedded in neuroglial cells
35. CENTRAL NERVOUS SYSTEM
integration / processing / modulating
stimulus
receptor neurone
motor / descending tracts
effector organ / response
PNS
transmission
lower motor neurone
sensory / ascending tracts
36. Ascending tract
1st
The ascending tracts transmit sensory information from the sensory
receptors to higher levels of the CNS.
sensory information
exteroceptive sensation
origin:-outside the body e.g. temp, touch, light, sound, chemicals,
mechanical
receptors:- surface layer of skin, mucosa
proprioceptive sensation
origin:-within the body e.g. muscles, joints, tendons
receptors:- deeper layer of skin, tendons, joints, muscle spindles,
ligaments
Information
• conscious sensation
– reach the cerebral cortex
• unconscious sensation
– reach to the areas other than cortex
37. Ascending tract
VPL
1st
2nd
• cross the mid line
• in front of central canal
The pathways consist of thousands of sets of three
neurons: first-order neuron, second-order neuron, and a
third-order neuron.
38. Ascending tract
First order neuron :
cell body in posterior root ganglion
peripheral process connects with sensory receptor ending
central process enter the spinal cord through the posterior root
synapse with second order neuron in spinal gray matter
Second order neuron:
cell body in posterior gray column of spinal cord
axon crosses the midline ( decussate )
ascend & synapse with third order neuron in nucleus of thalamus
Third order neuron:
cell body in the thalamus
give rise to projection fibres to the cerebral cortex, postcentral gyrus (
sensory area )
39.
40. Ascending Tracts of the Spinal
Cord
Lateral Spinothalamic Tract
pain, temperature
Anterior Spinothalamic Tract
touch, pressure
Posterior White Column: Fasciculus
Gracilis and Fasciculus Cuneatus
conscious proprioceptive sense,
discriminative touch, vibratory sense
Posterior Spinocerebellar Tract&Anterior
Spinocerebellar Tract
unconscious information from muscle,
joints, skin, subcutaneous tissues
Spinotectal Tract
Spinoreticular Tract
Spino-olivary Tract
41. Descending tracts
The descending tracts originate from different cortical areas and
from brain stem nuclei.
The descending pathway carry information associated with
maintenance of motor activities such as posture, balance, muscle
tone, and visceral and somatic reflex activity
42. The Descending Tracts
of the Spinal Cord
Corticospinal Tracts
for fine skilled movements
Reticulospinal Tracts
Inhibit or facilitate voluntary
movement; hypothalamus
controls sympathetic, para-
sympathetic outflows
Rubrospinal Tract
Vestibulospinal Tract
Olivospinal Tract
Tectospinal tract
Reflex postural movements concerning sight
Descending Autonomic Fibers
45. Neuron Function
1. Irritability: ability to respond to stimulus &
convert to nerve impulse
2. Conductivity: transmit impulse to other
neurons, muscles, or glands
46.
47. Reflex
Reflex is an action that is performed without conscious thought
as a response to a stimulus.
Rapid, predictable, involuntary responses to stimuli
1. Somatic Reflexes: stimulate skeletal muscles
Eg. jerking away hand from hot object
2. Autonomic Reflexes: regulate smooth muscles, heart, glands
Eg. salivation, digestion, blood pressure, sweating
Reflex arc
It is the nerve pathway involved in a reflex action, including at
its simplest a sensory nerve and a motor nerve with a synapse
between them.
48. Reflex Arc
1) Receptor - reacts to stimulus
2) Sensory Neurons - afferent impulses to CNS
3) Integration centers - synapses in CNS
4) Motor Neurons - efferent impulses from Integration centers to
effector
5) Effector - muscle or glands
49.
50.
51. Reflex Activities
Patellar (Knee-jerk)
Reflex
Pupillary Reflex
Gently tap your quadriceps tendon, which is located immediately
below your knee cap, with a reflex hammer
Optic nerve --brainstem--muscles
constrictpupil
• Useful for checking brain stem
function and drug use
52. Other Reflexes
Stimulus (receptors) Response (effector)
The aroma of your favorite
food
Salivation
A nasty odor Nausea
A bright light shining in your
eye
Pupils get smaller
An insect flying towards your
eye
Blinking
53. Voluntary Reactions
• More neurons and synapses are involved --
longer response times
Reflex = Involuntary Reaction Voluntary Reaction
54.
55. References
Elaine N. Marieb, Human Anatomy and Physiology 9th Edition .
Dr. Henry Gray and Dr. Henry Vandyke Carter , Grays Anatomy for
Students 40th Edition.
Various internet sources.