Nervous system: is the system of communications,the aim of
communications is to keep body homeostasis, N.S does its functions
through a special steps: 1. Detection of the changes 2. Evaluation
of the information 3. Responding property Classification of the
nervous system: we can classify N.S according to its location or
according to its functions.
Slide 3
1. Location of the NS: there are two types: a. central
NS.(CNS)which is formed of the brain and the spinal cord. b.
perpheral NS. (PNS) or the nerve, they are the axons of two types
of neurons: 1. cranial nerves where their cell bodies are present
in the brain, they are 12 nerve. 2. spinal nerves: their cell
bodies are present in the spinal cord.
Slide 4
Afferent and efferent fibers: afferent: are all the incoming
sensory fibers from periphery to the central nervous system.
Efferent: are the outcoming motor fibers, carrying the orders from
the CNs to the periphery. 2. according to the function: there are
two types: a. somatic NS: which controls the skeletal muscles, one
type is ordering the muscle movements (efferent), and the other is
carrying the sensory impulses (afferent). b. autonomic NS: which is
the system of viscera and is formed of two divisions. - Sympathetic
system: is the system of fight and flight - Parasympathetic NS. The
system of autonomic activity of the viscera
Slide 5
The nervous system is the most highly developed and perhaps the
most important of all the system of the body. Not only does it
correlate the activities of the other system but also in the brain
is situated the site of conciousness, thought, memory, speech and
the will to carry out purposeful actions. These factors all
contribute to the formation of the personality of the individual.
The basic unit of the nervous system is the individual nerve cell,
or neuron
Slide 6
. Neurons can be devided into three functional classes: 1.
Afferent (sensory)neurons afferent neurons transmit information
into the central nervous system from receptors at their peirpheral
ending. They are mostly (that is, the cell body and the long
peirpheral process of the axon) outside the central nervous system,
only the short central process of the axon enters the central
nervous system. Afferent neurons have no dendrites.
Slide 7
1. Efferent (motor) neurons efferent neurons transmit
information out of the central nervous systemto effector cells,
particularly muscles, glands. They are mostly (that is, the cell
body, dendrites, and a small segment of the axon) in the central
nervous system, most of the axon is outside the central nervous
system.
Slide 8
3. Interneurons (connecting neurons) interneurons function as
integrators and signal changers. They integrate groups of afferent
and efferent neurons into reflex circuits. They lie entirely within
the central nervous system, and account fo 99% of all neurons.
Slide 9
Neurons have two characteristics: 1. Excitability ability of
the plasma membrane to generate action potential, if a strong
enough stimulus affect on it. 2. Conductivity the ability of the
neuron to move the action potential from point to the next to it
point. Conduction velocities range from about 0.5 m/s for
unmyelinated fibers to about 100 m/s for myelinated fibers.
Slide 10
Action potential propagation once generated, one particular
action potential does not travel along the membrane. Rather, the
local current produced by one action potential serves as the
stimulus that depolarizes the adjacent membrane to its threshold
potential. The new action potential then produces local currents of
its own, which depolarize the region adjacent to it, producing yet
another action potential at the next site, and so on to cause
action potential a propagation along the length of the membrane.
The velocity with which an action potential propagates along a
membrane depends upon fiber diameter and whether or not the fiber
is myelinated.
Slide 11
Slide 12
Slide 13
Slide 14
The larger the fiber diameter, the faster the action potential
propagates. In the myelinated fiber action potentials occur only at
the nodes of ranvier where the myelin coating is interrupted and
the concentration of sodium channels is high. Thus, action
potentials literally jump from one node to the next as they
propagate along a myelinated fiber, and for this reason such
propagation is called saltatory conduction.
Slide 15
Propagation via saltatory conduction is faster than propagation
in nonmyelinated fibers of the same axon diameter. If the fiber
continuity is disrupted the action potential will not transmitted.
Action potential normally transmitted only in one direction.
Slide 16
synapsis Neurons are connected with each other and from chains
of neurons, the axon of one cell extending to the dendrite or body
of another cell. The point at which an impulse (action potential)
passes from an axon of one neuron to the dendrite or cell body of
another is called a synapse
Slide 17
Slide 18
The signal from a presynaptic to a postsynaptic neuron is the
neurotransmitter stored in synaptic vesicles in the presynaptic
axon terminal. Depolarization within the terminal, which raises the
calcium concentration within the terminal, causes the release of
neurotransmitter into the synaptic cleft. The neurotransmitter
diffuses across the synaptic cleft and binds to receptors on the
postsynaptic cell, the activated receptors usually open ion
channels. In the synapses the propagation is slower than in the
fibers, and may even be delayed in them
Slide 19
Synaptic effectiveness are influenced by presynaptic and
postsynaptic events, drugs, and diseases. Neurotransmitters are
chemical substances, released from axon terminals of presynaptic.
At most synapses, the signal is transmitted from one neuron to
another by neurotransmitters. These chemical messengers diffuse
across an extracellular gab to the cell opposite the terminal.
Neurotransmitters bind to receptors on the plasma membrane of the
postsynaptic cell. The result of the binding of neurotransmitter to
receptor is the causing of the action potential
Slide 20
Neurotransmitter binding to the receptor is a transient event,
and the ion channels in the postsynaptic membrane return to their
resting state when the neurotransmitter is no longer bound. Unbound
neurotransmitters are removed from the synaptic cleft when they
enzymatically transformed into ineffective substances.
Slide 21
Control systems In order to synchronize the functions of the
trillion of cells of the human body, two control systems exist.
One, the endocrine system, a collection of blood- borne messengers,
that works slowly, and for long term. The other is the nervous
system, which is a rapid and short term control system. Together
they regulate many internal functions and organize and control the
activities we know as human behavior.
Slide 22
Parts of nervous system The various structures of the nervous
system are intemately interconnected, but for convenience they are
divided into: 1. Central nervous system (CNS) 2. Peripheral nervous
system 3. Autonomic nervous system
Slide 23
Central nervous system central nervous system composed of the
brain and spinal cord. Inside the skull and vertebral column, the
brain and spinal cord are enclosed in and protected by the
meninges. Spinal cord Spinal cord is divided into two areas:
central gray matter, which contains nerve cell bodies and
dendrites, and white matter, which surrounds the gray matters and
contains myelinated axons organized into ascending (sensory) or
descending (motor)tracts. The axons of the afferent and efferent
neurons from the spinal nerves
Slide 24
Slide 25
Function of the spinal cord The main functions of the spinal
cord are: 1. The spinal cord communicates through nerve fibers, its
nervous pathways, with various parts of the brain and through
spinal nerves with organs. The spinal cord contains two kinds of
nervous pathway: ascending (sensory) and descending (motor). The
spinal nerve also contain two types of nerve fiber sensory and
motor. Nerve impulses are transmitted to spinal cord from the
periphery, from organs, along sensory fibers of the spinal nerves,
then conducted along the ascending nervous pathways to brain.
Slide 26
Nerve impulses are transmitted from the brain to the spinal
cord along the descending pathways and thence along motor fibers of
the spinal nerves to the periphery, the organs. These impulses
alter the state of various organs
Slide 27
2. Reflex activity the spinal cord contains the reflex centers
of various functions. Reflex is an involuntary, unpremeditated,
unlearned built in response to astimulus. Examples of such reflexes
include pulling ones hand away from a hot object or shutting ones
eyes as an object rapidly approaches the face. The pathway
mediating a reflex is known as the reflex arc.
Slide 28
A stimulus is a detectable change in the internal or external
environment, such as a change in temperature, or blood pressure. A
receptor detects the environmental change. A stimulus acts upon a
receptor to produce a signal that is relayed to an integrating
center. The pathway traveled by the signal between the receptor and
the integrating center is known as the afferent pathway (the
general term afferent means to carry to in this case, to carry to
integrating center).
Slide 29
An integrating center often receives signals from many
receptors, some of which may be responding to quite different types
of stimuli. Thus, the output of an integrating center reflects the
net effect of the total afferent input, that is, it represents an
integration of numerous bits of information. The output of an
integrating center is sent to the last component of the system, a
device whose change in activity constitutes the overall response of
the system.
Slide 30
This component is known as an effectors. The information going
from an integrating center to an effector is like a command
directing the effector to alter its activity. The pathway along
which this information travels is known as the efferent pathway
(the general term efferent means to carry away from , in this case,
away from the integrating center).
Slide 31
Characteristics of reflexes: 1. Many reflexes are protective in
character. 2. Reflexes are designed to obtain the quickest possible
motor response 3. Some reflexes are concerned with automatic
control of functions which do not require the supervision of
consciousness. 4. Reflexes are specific: each stimulus has its own
response. 5. Most reflexes are subject to alteration by
learning.
Slide 32
Anatomically, the brain is composed of four subdivisions:
cerebrum, diencephalon, brainstem, and cerebellum. The cerebrum and
diencephalons together constitute the forebrain. The brainstem
consists four interconnected cavities, the cerebral ventricles,
which are filled with circulating cerebrospinal fluid. Brainstem
brainstem is composed midbrain, pons, and medulla oblongata. The
brain
Slide 33
Function of the midbrain : 1. Regulation of the cerebrospinal
fluid circulation. 2. The gray matter forms the nuclei of third and
fourth cranial nerves. 3. Joins the cerebral hemispheres above to
the pons below. Function of the pons: 1. It acts a bridge between
the two lobes of the cerebellum. 2. Nerve fibers pass up and down
between the midbrain above and the medulla oblongata below. 3. The
gray matter forms the nuclei of the 5 th,6 th,and 7 th cranial
nerves.
Slide 34
Function of medulla oblongata: 1. Connects the brain with the
spinal cord. 2. Contains fibers passing from spinal cord,
forebrain, and cerebellum. 3. It contains also collection of gray
matter known as vital centers. The most important of these are: a.
the respiratory center which controls the rate and depth of
respiration. b. the vasomotor center which controls the caliber of
the blood vessels.
Slide 35
c. the cardiac center which influences the rate of the heart.
d. special centers such as the swallowing, vomiting centers,
centers for the movement of the stomach and the secretion of saliva
and gastric juice. 4. The gray matter forms the nuclei of 9 th, 10
th, 11 th.12 th, cranial nerves.
Slide 36
cerebellum Function of the cerebellum 1. Coordinates movements,
including those for posture and balance. 2. participates in some
forms of learning. 3. it helps to maintain balance and
equilibrium.
Slide 37
cerebrum The cerebrum consists of the right and left cerebral
hemispheres. Functions of the cerebral hemispheres: 1. Contain the
cerebral cortex, which participates in perception, the generation
of skilled movements, reasoning, learning, and memory. 2. Contain
subcortical nuclei, which participata in coordination of
skeletal-muscle activity. 3. Contain interconnecting fiber
pathways
Slide 38
Diencephalon (between brain) Diencephalon contains two major
parts: the thalamus and hypothalamus. Functions of thalamus 1. Is a
synaptic relay station for sensory pathways on their way to the
cerebral cortex. 2. Participates in control of skeletal-muscle
coordination 3. Plays a key role in awareness.
Slide 39
Function of hypothalamus: 1. Regulates the anterior pituitary
gland. 2. Regulates water balance. 3. Participates in regulation of
autonomic nervous system. 4. Regulates eating and drinking
behavior. 5. Regulates reproductive system. 6. Reinforces certain
behaviors. 7. Generates and regulates circadian rhythms. 8.
Regulates body temperature. 9. Participates in generation of
emotional behavior.
Slide 40
The physiology of the brain The brain is the control center of
the whole human body. Physiologically it may be divided into the
higher centers which are the seat of consciousness, mind, memory
and will; and the lower centers which control many important
unconscious acts. The higher centers are situated in the cerebral
hemispheres while the lower ones are found in the cerebellum and
brainstem as well as in the basal ganglia of the cerebrum.
Slide 41
The following mechanisms enable the brain to exercise this
power of control: 1. It receive sensory or afferent impulses from
all parts of the body, through the sensory pathway. 2. It is able
to send out motor or afferent impulse from all parts of the body,
through the motor pathway, which has two tracts:
pyramidal(corticospinal) tract, which may be two kinds : straight
or crossed, and extrapyramidal tract.
Slide 42
3. There is a complicated system of connection between all
parts of the brain with each other. Projection fibers transmits the
impulse from the brainstem to the cerebral cortex. Association
fibers which are situated in the cerebral cortex transmits the
impulse from one area to another within the same hemisphere.
Commissural fibers transmit the impulse from one hemisphere to
another one (from right to the left for example)
Slide 43
Functional regions All areas of the cortex are interconnected
and the activity of each depends on the state of the entire cortex.
however, the different regions differ in function and structure.
These areas are: 1. The motor cortex area the motor cortex area is
located in the frontal lobe from the cell of this area, voluntary
motor impulses arises and are transmitted to the various groups of
muscles in the body are represented in this area. The right
cerebral hemisphere controls the left side of the body and vice
versa