3. What is nervous system?
• Your nervous system is your body's command
center. Originating from your brain, it controls
your movements, thoughts and automatic
responses to the world around you. It also
controls other body systems and processes,
such as digestion, breathing and sexual
development (puberty).
4. NERVOUS SYSTEM DIVISIONS
The nervous system has two divisions. The central
nervous system (CNS) consists of the brain and
spinal cord. The peripheral nervous system (PNS)
consists of cranial nerves and spinal nerves. The
PNS includes the autonomic nervous system (ANS).
5.
6.
7. The peripheral nervous system relays
information to and from the central nervous
system, and the brain is the center of activity
that integrates this information,initiates
responses.
8. NERVE TISSUE
• Nerve cells are called neurons, or nerve
fibers. Whatever their specific functions, all
neurons have the same physical parts.
• The cell body contains the nucleus and is
essential for the continued life of the neuron.
9. • Dendrites are processes (extensions) that
transmit impulses toward the cell body.
• The one axon of a neuron transmits impulses
away from the cell body. It is the cell
membrane of the dendrites, cell body, and
axon that carries the electrical nerve impulse.
10. • In the peripheral nervous system, axons and
dendrites are “wrapped” in specialized cells
called Schwann cells.
• These layers are the myelin sheath; myelin is a
phospholipid that electrically insulates
neurons from one another. Without the
myelin sheath, neurons would short-circuit,
just as electrical wires would if they were not
insulated.
11.
12.
13. SYNAPSES
• Neurons that transmit impulses to other
neurons do not actually touch one another.
The small gap or space between the axon of
one neuron and the dendrites or cell body of
the next neuron is called the synapse.
14.
15. • Within the synaptic knob (terminal end) of the
presynaptic axon is a chemical
neurotransmitter that is released into the
synapse by the arrival of an electrical nerve
impulse.
• The neurotransmitter diffuses across the
synapse, combines with specific receptor sites
on the cell membrane of the postsynaptic
neuron, and there generates an electrical
impulse that is, in turn, carried by this
neuron’s axon to the next synapse, and so
forth.
16.
17. TYPES OF NEURONS
• Neurons may be classified into three groups:
sensory neurons, motor neurons, and
interneurons.
• Sensory neurons (or afferent neurons) carry
impulses from receptors to the central
nervous system. Receptors detect external or
internal changes and send the information to
the CNS in the form of impulses by way of the
afferent neurons.
18. • The central nervous system interprets these
impulses as a sensation.
• Sensory neurons from receptors in skin,
skeletal muscles, and joints are called somatic;
those from receptors in internal organs are
called visceral sensory neurons.
19.
20. • Motor neurons (or efferent neurons) carry
impulses from the central nervous system to
effectors.
• The two types of effectors are muscles and
glands. In response to impulses, muscles
contract or relax and glands secrete. Motor
neurons linked to skeletal muscle are called
somatic; those to smooth muscle, cardiac
muscle, and glands are called visceral.
21.
22. • Interneurons are found entirely within the
central nervous system. They are arranged so
as to carry only sensory or motor impulses, or
to integrate these functions.
23. NERVES AND NERVE TRACTS
• A nerve is a group of axons and/or dendrites
of many neurons, with blood vessels and
connective tissue.
• Sensory nerves are made only of sensory
neurons.
• Motor nerves are made only of motor
neurons; autonomic nerves are motor nerves.
24. • A mixed nerve contains both sensory and
motor neurons. Most of our peripheral
nerves, such as the sciatic nerves in the legs,
are mixed nerves.
• The term nerve tract refers to groups of
neurons within the central nervous system.
All the neurons in a nerve tract are concerned
with either sensory or motor activity.
25. THE SPINAL CORD
• The spinal cord transmits impulses to and
from the brain and is the integrating center for
the spinal cord reflexes.
• the spinal cord extends from the foramen
magnum of the occipital bone to the disc
between the first and second lumbar
vertebrae.
• Ascending tracts carry sensory impulses to the
brain.
• Descending tracts carry motor impulses away
from the brain.
26.
27.
28. SPINAL NERVES
• There are 31 pairs of spinal nerves, those that
emerge from the spinal cord. The nerves are
named according to their respective
vertebrae: 8 cervical pairs, 12 thoracic pairs, 5
lumbar pairs, 5 sacral pairs, and 1 very small
coccygeal pair
29. • In general, the cervical nerves supply the back
of the head, neck, shoulders, arms, and
diaphragm (the phrenic nerves).
• The first thoracic nerve also contributes to
nerves in the arms. The remaining thoracic
nerves supply the trunk of the body.
• The lumbar and sacral nerves supply the hips,
pelvic cavity, and legs
30.
31.
32. SPINAL CORD REFLEXES
• A reflex is an involuntary response to a
stimulus, that is an automatic action
stimulated by a specific change of some kind.
• Spinal cord reflexes are those that do not
depend directly on the brain.
33. Reflex Arc
• A reflex arc is the pathway that nerve impulses
travel when a reflex is elicited, and there are
five essential parts:
34. 1. Receptors—detect a change (the stimulus)
and generate impulses.
2. Sensory neurons—transmit impulses from
receptors to the CNS.
3. Central nervous system—contains one or
more synapses (interneurons may be part of the
pathway).
4. Motor neurons—transmit impulses from the
CNS to the effector.
5. Effector—performs its characteristic action.
35.
36. THE BRAIN
• The brain consists of many parts that function
as an integrated whole. The major parts are
the medulla,pons, and midbrain (collectively
called the brain stem), the cerebellum, the
hypothalamus, the thalamus,and the
cerebrum.
37.
38. MEDULLA
• The medulla extends from the spinal cord to
the pons and is anterior to the cerebellum.
• Its functions are those we think of as vital (as
in “vital signs”).
• The medulla contains cardiac centers that
regulate heart rate, vasomotor centers that
regulate the diameter of blood vessels and,
thereby, blood pressure, and respiratory
centers that regulate breathing
39. • Also in the medulla are reflex centers for
coughing,sneezing, swallowing, and vomiting.
40.
41. PONS
• The pons bulges anteriorly from the upper
part of the medulla. Within the pons are two
respiratory centers that work with those in the
medulla to produce a normal breathing
rhythm.
42.
43. MIDBRAIN
• The midbrain extends from the pons to the
hypothalamus, Several different kinds of
reflexes are integrated in the
midbrain,including visual and auditory
reflexes.
44.
45. CEREBELLUM
• The cerebellum is separated from the medulla
and pons by the fourth ventricle and is inferior
to the occipital lobes of the cerebrum.
• many of the functions of the cerebellum are
concerned with movement. These include
coordination, regulation of muscle tone, and
the maintenance of posture and equilibrium.
46.
47. HYPOTHALAMUS
• Located superior to the pituitary gland and
inferior to the thalamus, the hypothalamus is
a small area of the brain with many diverse
functions:
• 1. Production of antidiuretic hormone (ADH)
and oxytocin;
• the ADH enables the kidneys to reabsorb
water back into the blood and thus helps
maintain blood volume. Oxytocin causes
contractions of the uterus to bring about labor
and delivery.
48.
49. • 2. Regulation of body temperature by
promoting responses such as sweating in a
warm environment or shivering in a cold
environment
• 4. Regulation of food intake; the
hypothalamus is believed to respond to
changes in blood nutrient levels.
• For example, during a meal, after a certain
duration of digestion, the small intestine
produces a hormone that circulates to the
hypothalamus and brings about a sensation of
satiety, or fullness, and we tend to stop eating.
50. THALAMUS
• The thalamus is superior to the hypothalamus
and inferior to the cerebrum.
• Many of the functions of the thalamus are
concerned with sensation.
• Sensory impulses to the brain follow neuron
pathways that first enter the thalamus, which
groups the impulses before relaying them to
the cerebrum, where sensations are felt.
51.
52. • For example, holding a cup of hot coffee
generates impulses for heat, touch and the
shape of the cup to the thalamus then
transmit to cerebrum, so that the cerebrum
feels the whole and is able to interpret the
sensation quickly.
53. CEREBRUM
• The largest part of the human brain is the
cerebrum, which consists of two hemispheres
separated by the longitudinal fissure that
called corpus callosum.
• the corpus callosum, a band of 200 million
neurons that connects the right and left
hemispheres.
54.
55. • The surface of the cerebrum is gray matter
called the cerebral cortex. Gray matter
consists of cell bodies of neurons, which carry
out the many functions of the cerebrum.
• Internal to the gray matter is white matter,
made of myelinated axons and dendrites that
connect the lobes of the cerebrum to one
another and to all other parts of the brain
56.
57. • In the human brain the cerebral cortex is
folded extensively. The folds are called
convolutions or gyri and the grooves between
them are fissures or sulci
58.
59. • The cerebral cortex is divided into lobes that
have the same names as the cranial bones
external to them.
• Therefore, each hemisphere has a frontal
lobe, parietal lobe, temporal lobe, and
occipital lobe
60.
61. Frontal Lobes
• Within the frontal lobes are the motor areas
that generate the impulses for voluntary
movement.
• The left motor area controls movement on the
right side of the body, and the right motor
area controls the left side of the body. This is
why a patient who has had a cerebrovascular
accident,or stroke, in the right frontal lobe will
have paralysis of muscles on the left side
62.
63. Parietal Lobes
• The general sensory areas in the parietal
lobes receive impulses from receptors in the
skin and feel and interpret the cutaneous
sensations.
• The left area is for the right side of the body
and vice versa.
64.
65. Temporal Lobes
• The olfactory areas in the temporal lobes
receive impulses from receptors in the nasal
cavities for the sense of smell.
• The auditory areas, as their name suggests,
receive impulses from receptors in the inner
ear for hearing.
66.
67. Occipital Lobes
• Impulses from the retinas of the eyes travel
along the optic nerves to the visual areas in
the occipital lobes.
68. MENINGES
• The connective tissue membranes that cover
the brain and spinal cord are called meninges;
the three layers
• The thick outermost layer,made of fibrous
connective tissue, is the dura mater which
lines the skull and vertebral canal.
• The middle arachnoid membrane is made of
web-like strands of connective tissue.
• The innermost pia mater is a very thin
membrane on the surface of the spinal cord
and brain.
72. THE AUTONOMIC NERVOUS SYSTEM
• The autonomic nervous system (ANS) is
actually part of the peripheral nervous system
in that it consists of motor portions of some
cranial and spinal nerves.
• The ANS has two divisions: sympathetic and
parasympathetic. Often, they function in
opposition to each other.
