Unit Three:
Nervous Control Chapter Five:
Nervous System
5.1 Introduction
• Genetic material has control over all systems of the organism.
• Hormonal or chemical control in coordination with the nervous system comes next in levels of controlling all aspects of the organism.
• Nervous system is responsible for the property of life called irritability, the ability of cells or whole organisms to respond in certain way to external and internal environmental stimuli.
• Communication within the nervous system as well as to and from the body and nervous system occurs through neurons,
5.2 Functions of The Nervous System
•
Signals are conducted in the neurons by electrochemical currents that can travel at speeds of more than 100 m/s in vertebrates, and up to 0.5 m/s in invertebrates.
•
The nervous system has three main functions:
Detection (sensory reception, sensory input).
Integration (interpretation and processing).
Response (decision making, motor output).
5.3 Anatomical and Functional
Organization of The Nervous System
• In human and higher vertebrates, the nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord, while the PNS consists of all nervous tissue outside of the CNS.
• The PNS has two divisions: the voluntary or somatic division, and the involuntary or autonomic division (ANS).
• The latter has two parts, the sympathetic and para-
Prepared by Prof. Nabih A. Baeshen 5
Central Nervous System (CNS)
Brain Spinal Cord
Integrative and control centers
Peripheral Nervous System (PNS)
Motor (efferent) division Sensory (afferent) division
Autonomic Nervous System (ANS) Motor innervation of smooth muscle, cardiac muscle, and glands
Somatic Nervous System
Motor innervation of all skeletal muscles
Parasympathetic division
Sympathetic division Visceral Sensory
General: Stretch, pain, temperature, chmical changes, and irritation in viscera; nausea and hunger
Special: Taste, smell Somatic Sensory
General: Touch, pain, pressure, vibration,
temperature, and proprioception in skin, body wall, and limbs
Special: Hearing, equilibrium, vision
Nervous System
Fig. 5-1. Anatomical and Functional
5.4 The Brain: Divisions and Functions
• The brain in most animals is swollen part contained within the head, at the superior end of the spinal cord:
o The primary control center for all internal and external life processes.
o The center of intellect, thought and learning in higher vertebrates such as human.
• The brain is usually divided into three to five sections, depending on its complexity in different organisms as demonstrated by the human brain (Fig. 5-2) (Table 1-1) .
Prepared by Prof. Nabih A. Baeshen Fig. 5-2. Structural Parts of The Human 7
Parts Principle Functions
Forebrain
Cerebrum
Seat of intelligence, confers sophisticated
imagination, memory, and reasoning in humans that is considered unique among the Animal
Kingdom.
Thalamus Relay station that directs sensory and other information to the brain
Hypothalamus
Regulates body temperature, appetite, fat metabolism, and certain emotions;
Controls pituitary gland and in coordination with it maintains homeostasis
Brain Stem
Midbrain
Involved in vision and auditory integration, conducts sensory information to hire brain centers
Hindbrain
Pons
Connects various parts of brain with one another;
controls breathing, sleeping and generating dreams
Cerebellum Responsible for coordinating movement and balance
Controls heartbeat, respiration, blood pressure,
Table 1-1 : Functions of The Brain Structural Parts
• The functions of structural parts of human brain are as follows:
• The cerebrum considered the seat of intelligence.
o Confers sophisticated imagination, memory, and reasoning in humans that is considered unique among the Animal Kingdom.
• The thalamus which can be considered a relay station that directs sensory and other information to the brain.
• The hypothalamus responsible for maintaining homeostasis.
• The midbrain involved in vision and auditory integration, conducts sensory information to hire brain centers.
• Brain Stem sends information from and to other brain centers, involve in homeostasis and body movement coordination.
• The medulla oblongata, through which sensory and motor tracts pass.
• The cerebellum responsible for coordinating movement and balance.
• The pons controls breathing and generating dreams.
5.5 Brain Cranial Nerves and Spinal Nerves
• Twelve cranial nerves are associated with the brain that innervates mostly the head and neck.
o Some of the cranial nerves are sensory (afferent nerves)
o Some are motor (efferent nerves).
o Some others consisted of both types.
o For example: vagus nerve is connected to medulla oblongata and branches into pharynx and larynx and to most of the eternal organs (Fig. 5-3).
Fig. 5-3. Ventral View of The Human Brain Showing Twelve Pairs of Cranial Nerves, Notice The Vagus Nerve
• The long cylindrical spinal cord forms the second part of the CNS.
• Spinal nerves emerge from the cord at every vertebra of the vertebral column (Fig. 5-4).
• In a cross section, the spinal cord has an outer region called white matter represents axons of the neurons that travel to and from the brain.
• An inner region (butterfly-shaped) called gray matter represents dendrites and the cell bodies of interneurons and motor neurons.
• The cell bodies of the sensory neurons are outside the cord in the dorsal root ganglion.
Fig. 5-4. Section of The Spinal Cord Showing The
gray matter contains cell bodies of motor neurons and interneurons white matter
contains myelinated axons
central canal contains
cerebrospinal fluid peripheral nerve
dorsal root contains axons of sensory
neurons
dorsal root ganglion contains cell bodies of
sensory neurons
ventral root
contains axons of motor neurons
peripheral nerve
•
Reflexes are automatic swift responses to certain
stimuli as a result of being injured or harmed.
•
For example: if somebody directed intense light toward your eyes you are automatically get your eye lids shutdown or avoid looking at the light.
•
The pathway taken by the information in a reflex is called a reflex arc as demonstrated in (Fig. 5-5).
•
Thus reflexes help prevent injury or being harmed.
❶
An insect stings the arm skin
❷
Stimulation of pain receptors
❸
A message carried by a sensory
neuron
❹
Message is passed along a rely
neuron
(interneurons)
❺
Message is carried by a motor neuron
❻
The muscle
contracts and moves the hand away of the
source of sting
5.6 Peripheral Nervous System (PNS)
• Referring to (Fig. 5-1) the cranial and spinal nerves, along with sensory receptors in the body, make up the PNS.
• There are different functional types of nerves in the PNS.
• Sensory nerves carry information into the CNS from sensory receptors in the body.
• Sensory receptors may be part of the autonomic nervous system (ANS), in which case they are located in organs or smooth muscle, or they may be associated with senses such as sight or touch.
Central Nervous System (CNS)
Brain Spinal Cord
Integrative and control centers
Peripheral Nervous System (PNS)
Motor (efferent) division Sensory (afferent) division
Autonomic Nervous System (ANS) Motor innervation of smooth muscle, cardiac muscle, and glands
Somatic Nervous System
Motor innervation of all skeletal muscles
Parasympathetic division
Sympathetic division Visceral Sensory
General: Stretch, pain, temperature, chmical changes, and irritation in viscera; nausea and hunger
Special: Taste, smell Somatic Sensory
General: Touch, pain, pressure, vibration,
temperature, and proprioception in skin, body wall, and limbs
Special: Hearing, equilibrium, vision
Nervous
System
•
Motor nerves may activate skeletal muscles, which require a conscious decision (from the cerebrum) for activation.
•
Skeletal muscles are described as voluntary for this reason.
•
Motor nerves in the PNS may also be part of the ANS, in which case their action is involuntary.
•
Autonomic motor neurons may be sympathetic or
para-sympathetic.
•
The two have opposite effects, and the status of the body is usually set by the balance of the two.
•
When the sympathetic division is dominant, the body is activated.
•
When the parasympathetic division dominates, the
body is inactive and involved in maintenance and
restoration (Fig. 5-6).
Fig. 5-6. A
Demonstration of
How Parasympathetic and Sympathetic
Nervous System Regulates the
Functions of The Body Different Organs
Prepared by Prof. Nabih A. Baeshen
5.7 The Neurons are Nerve Cells transmit information as electrical impulses
• The animal nervous system consists of two types of cells:
Neurons are electrically excitable and relay signals known as nerve impulses (Fig. 5-7).
• The glial cells serve a supportive function and do not carry signals. They supply nutrients, protection, and confer immunity.
• Neurons are large, highly specialized, metabolically active cells that are incapable of dividing, although they have some capacity to regenerate and change shape.
22
Prepared by Prof. Nabih A. Baeshen Fig. 5-7. Neuron (Nerve Cell) Structure 23 Structural part Function
Dendrites Receive information from other neurons and
transmit it to the cell body
Cell body Integrate, process and form a response (signal) Axon Transmit signals to
another neuron or an effector (i.e. a muscle) Myelin sheath An insulating material
that speed up the signal Synaptic
terminal
Transmit signals to another neuron or an effector (i.e. a muscle) Schwann cell Wrap around axons to
form the myelin sheath it is a glial cell
Nodes of Ranvier
Gaps formed between the myelin sheaths not coated by myelin sheath therefore capable of generating electrical activity
Functions of Neuron Parts
• The typical neuron is composed of dendrites, a soma (cell body), and an axon with axon terminals.
• The numerous dendrites project from the soma and have been likened to the branches of a tree.
• The soma contains a large nucleus (that contains many nucleoli), many organelles, and large amounts of RNA.
• The single axon extends from the soma as a long, uniform projection that can be as long as one meter.
• The axon ends in an axon terminals, which is a short, branching cytoplasmic extension.
• The axon may be enclosed in a myelin sheath made of Schwann cells, a type of glial cells.
• There is an unsheathed area between two adjacent Schwann cells, collectively called Nodes of Ranvier.
• Neurons may be part of a neural pathway, in which case there may be numerous neurons arranged so that the dendrites and soma of one axon are adjacent to, but not quite in contact with, the axon terminal of the next neuron in the pathway.
• The small space between the axon terminal of one axon and the next axon is called the synaptic cleft.
5.8 Nerve Impulse
•
Nerve impulse is relatively a fast electrochemical
current that moves through a neural pathway as
follows: from the dendrites, through the soma, along
the axon to the axon terminal, then to the synapse and
to the next axon in the path, summarized as follows:
•
In addition to being part of a neural pathway, the dendrites or soma of a neuron may interact with a sensory receptor; in this case, activation of the sensory receptor initiates the nerve impulse in the axon.
•
The axon terminal may also interact with muscle,
glands, or organs. In this situation, the arrival of the
nerve impulse will have the intended effect on the
structure it is contacting.
• Neurons normally have a voltage across their plasma membrane referred to as the resting potential (positively charged outside and negatively charged inside).
• Neurons when excited by a stimulus it generates nerve impulse which is the nerve impulse is an electrical signal of a general type called an action potential.
Resting Potential
Action Potential
• Action potentials are generated when there a rapid changes in the concentration and movement of monovalent, positive ions (mostly Na+ and K+ so that it becomes positively charged inside and negatively charged outside) that disrupt the resting potential.
• Action potentials (electrical signals or nerve impulses) travel along the axon until reaching the synaptic cleft but cannot cross the cleft.
• The electrical signals can cross through gap junctions between the two neurons in a common arrangement described as chemical synapse.
•
In this case, the action potential results in the release of a chemical neurotransmitter into the synaptic cleft, which crosses the cleft and induces the action potential in the second neuron in the pathway (Fig. 5-8).
•
An example of a neurotransmitter is acetylcholine.
•
Some toxins such as drugs, nicotine, some snake
venoms, and some bacterial toxins bind to
acetylcholine receptors and prevent its action.
Fig. 5-8. Synaptic Transmission
•Some invertebrates do not have nerves, while some of them have nerve nets (Fig. 5-9).
APPENDIX
Acetylcholine نیلوَك لیتِسأ
Action potential طشنلا دھجلا قرف
Afferent دراو
Autonomic division يتاذ مسق
Autonomic motor neurons ةیتاذ ةیكرح باصعأ
Autonomic nervous system (ANS) يتاذلا يبصعلا زاھجلا
Axon يبصع روحِم
Axon terminals يبصعلا روحملا تاياھن
Brain غامد
Brain stem غامدلا عذج
Central nervous system (CNS) يزكرملا يبصعلا زاھجلا
Cerebellum خیخم
خم
Key Terms
Chemical synapse يئایمیكلا سامملا
Control center مكحتلا زكرم
Cranial nerve يمجمج بصع
Cylindrical spinal cord يناوطسلأا يكوشلا لبحلا
Dendrites ةيریجش دئاوز
Detection راعشتسا
Dorsal root ganglion ةيرھظ ةيرذج ةدقع
Efferent رداص
Electrical synapse يئابرھك يبصع سامم
Forebrain يمامأ غامد
Glial cells يبصعلا ءارغلا ايلاخ
Gray matter )ةيدامر( ةیباجنس ةدام
Hindbrain )يفلخلا غامدلا( غامدلا ةرخؤم
Hypothalamus )داھملا( يرصبلا ريرسلا تحت ام
Integration )ةیلقعلا تایلمعلا عباتت بیترت( لماكت
Intellect ءاكذلا
Interneurons ةینیب ةیبصع ايلاخ
Involuntary ةيدارإ لا
Irritability ساسحلاا
Larynx ةرجنح
Learning ملعتلا
Medulla oblongata لیطتسم عاخن
Midbrain يطسو غامد
Motor division يكرح مسق
Motor nerve يكرح بصع
Motor neuron )ةیكرح ةیبصع ةیلخ( يكرح نوبصع
Myelin sheath يعاخن دمغ
Nerve nets ةیبصع تاكبش
Nerves باصعلأا
Nervous system يبصع زاھج
Neuron )نوبصع( ةیبصع ةیلخ
Neurotransmitter يبصع لقان
Nodes of Ranvier. ةيریفنار دقع
Para-sympathetic. يواثبمسریظن
Peripheral nervous system (PNS) يطیحملا يبصعلا زاھجلا
Pharynx موعلب
Pons خیخملا رسج
Reflex arc يساكعنا سوق
Reflexes تاساكعنلاا
Response ةباجتسا
Resting potential )دومھلا نومك( حيرتسملا دھجلا قرف
Schwann cell نافش ةیلخ
Seat of intelligence ءاكذلا زكرم
Sensory division يسح مسق
Sensory nerves ةیسح باصعأ
Sensory neuron ةیسح )نوبصع( ةیبصع ةیلخ
Sensory receptor يسح لبقتسم
Skeletal muscle ةیلكیھ ةلضع
Soma (cell body) ةیبصعلا ةیلخلا مسج
Somatic division يدسجلا مسقلا
Somatic nervous system يدارلإا يبصعلا زاھجلا
Somatic sensory ةيدسج ةیسح
Spinal cord يكوشلا عاخنلا
Spinal nerve يعاخن بصع
Synaptic cleft يبصعلا سامملا ةوجف
Synaptic terminal يبصعلا سامملا فرط
Thalamus يرصب )ريرس( داھم
Thought ركف
Tracts تاراسم
Vagus nerve مھبملا بصعلا
Vertebra ةراقف
Vertebral column يرقف دومع
Visceral sensory يوشح يسح
Voluntary يدارإ
White matter ءاضیبلا ةداملا
