Science

1. Nervous System
Functions of the Nervous System
• Sensory input – gathering information
To monitor changes occurring inside and outside the body
Changes = stimuli
• Integration
To process and interpret sensory input and decide if action is needed
Functions of the Nervous System
Motor output
A response to integrated stimuli
The response activates muscles or glands
Structural Classification of the Nervous System
• Central nervous system (CNS)
Brain
Spinal cord
• Peripheral nervous system (PNS)
• Cranial nerves
Spinal nerves
Functional Classification is concerned only with PNS
1-Sensory (afferent) division
Nerve fibers that carry information to the central nervous system
Functional Classification of the Peripheral Nervous System
2-Motor (efferent) division
Nerve fibers that carry impulses away from the central nervous system ( to Muscles &Glands)
Motor (efferent) division has two subdivisions
1-Somatic nervous system =
voluntary, it controls skeletal muscles
N. B. skeletal muscle reflexes are involuntary
2-Autonomic nervous system = involuntary, it controls smooth
&cardiac muscles &glands This also is divided into sympathetic & parasympathetiuc

2. Organization of Nervous System
Histology of Nervous Tissue
• Despite the complexity of the nervous system, there are only two functional cell types
• Neurons - excitable nerve cells that transmit electrical signals
• Neuroglia (glial) cells - supporting cells
Histology of CNS Tissue - Neuroglia
• Neuroglia - 4 types in the Central NS
1-Astrocytes
• star shaped with many processes
• connect to neurons; help anchor them to nearby blood capillaries
• control the chemical environment of the neurons 2-Microglia
• oval with thorny projections
• monitor the health of neurons
• if infection occurs, they change into macrophages (eating viruses, bacteria and
damaged cells)
Histology of CNS Tissue - Neuroglia
• Neuroglia - 4 types in the Central NS
Astrocytes

3. • star shaped with many processes
• connect to neurons; help anchor them to nearby blood capillaries
• control the chemical environment of the neurons Microglia
• oval with thorny projections
• monitor the health of neurons
• if infection occurs, they change into macrophages
(eating viruses, bacteria and damaged cells)
Histology of CNS Tissue - Neuroglia
• Neuroglia - 4 types in the CNS (continued)
Ependymal cells
• range in shape from squamous to columnar; many are ciliated
• line the dorsal body cavity housing the brain and spinal cord
• form a barrier between the neurons and the rest of the body
Nervous Tissue: Neurons
Oligodendrocytes
• have few processes
• line up along neurons and wrap themselves around axons
• form the myelin sheath – an insulating membrane

4. Histology of PNS Tissue - Neuroglia
• Neuroglia - 2 types in the Peripheral NS
Satellite cells
• surround neuron cell bodies in the periphery
• maintain the extracellular environment Schwann cells (neurolemmocytes)
• surround axons/dendrites and form the myelin sheath around larger nerve fibers in the
periphery
• similar to oligodendrocytes in function - insulators
Neurons = nerve cells
Cells specialized to transmit messages
Major regions of neurons
Cell body – nucleus and metabolic center of the cell
Processes – fibers that extend from the cell body
Neuron Anatomy
Extension outside of the cell body
 Dendrites
Conducts impulses towards the cell body
 Axon
Conduct impulses away from the cell body
Nerve Fiber Coverings
Most long nerve fibers are covered with a whitish fatty material called myelin with waxy appearance. It
insulates the fiber and increases transmission rate.
-Axon outside CNS are wrapped by Schwann Cells.
Axon and Nerve Impulses
Axons end in axonal terminals

5. Axonal terminals contain vesicles with neurotransmitters
Axonal terminals are separated from the next
neuron(neuroneural junction) by a gap called Synaptic cleft
(Synapse)
Functional Classification of Neurons 1-Sensory (afferent) neurons
Carry impulses from the sensory receptors
Cutaneous sense organs
Proprioceptors – detect stretch or tension in muscles and tendons and joints
2-Motor (efferent) neurons
Carry impulses from the central nervous system to muscles and glands ,their cell bodies are
always in CNS
Functional Classification of Neurons
3-Interneurons (association neurons)
Their cell bodies are always found in CNS
Connect sensory and motor neurons in neural pathways
Neuron Classification
Structural Classification of Neurons
Multipolar neurons – many extensions from the cell body

6. Structural Classification of Neurons
Bipolar neurons – one axon and one dendrite
Figure 7.8b
Structural Classification of Neurons
Unipolar neurons – have a short single process leaving the cell body which is very short ,divides almost
immediatly
Functional Properties of Neurons
• Irritability – ability to respond to stimuli
• Conductivity – ability to transmit an impulse
Reflex Arc
The plasma membrane at rest is polarized
Fewer positive ions are inside the cell than outside the cell
• Reflex – rapid, predictable, and involuntary responses to stimuli
• Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector
• Ref. arch have a minimum 5 elements

7. Types of Reflexes and Regulation
• Autonomic reflexes eg.
Salivary gland secretion
Heart and blood pressure regulation
Changes in size of the pupil
• Digestive system regulation
• Somatic reflexes
Activation of skeletal muscles
REGIONS OF BRAIN
Central Nervous System (CNS)
• CNS develops from the embryonic neural tube
By the fourth week the anterior end begins to expand and brain formation begins, The rest of the
tube becomes the spinal cord

8. The central canal
becomes enlarged in
4 regions of the brain
to form ventricles the
ventricles:-Four
chambers within the
brain
-Filled with
cerebrospinal fluid
• Cerebral hemisphere
• Diencephalon
• Brain stem
• Cerebellum

9. Figure 7.1
GRAY MATTER
-Outer layer composed mostly of neuron
BASAL NUCLEI
-Internal islands of gray matter
WHITE MATTER
-fiber tracts inside the gray matter
-ex: corpus callosum connects hemispheres
The surface is made of ridges (gyri) and grooves
(sulci)
Specialized Area of the Cerebrum
Cerebral areas involved in special senses
Gustatory area (taste)
Visual area
Auditory area
Olfactory area
Specialized Area of the Cerebrum
Interpretation areas of the cerebrum
Speech/language region
Language comprehension region
General interpretation area
Cerebral Hemispheres (Cerebrum)
Paired (left
and right)
superior parts
of the brain
Include more
than half of
the brain
mass

10. Diencephalon
• Sits on top of the brain stem
Enclosed by the cerebral heispheres
Made of three parts
Thalamus
Hypothalamus
Epithalamus
Thalamus
• Surrounds the third ventricle
The relay station for sensory impulses
(except olfaction)
Transfers impulses to the correct part of the cortex for localization and interpretation
Hypothalamus
• Under the thalamus
Important autonomic nervous system center
Helps regulate body temperature
Controls water balance
Regulates metabolism
Hypothalamus
• An important part of the limbic system
(emotions)
The pituitary gland is attached to the hypothalamus
Epithalamus
• Forms the roof of the third ventricle
Houses the pineal body (an endocrine gland)
Includes the choroid plexus – forms cerebrospinal fluid
Brain Stem
• Attaches to the spinal cord
Parts of the brain stem
Midbrain
Pons
Medulla oblongata

11. Midbrain
• Mostly composed of tracts of nerve fibers
Has two bulging fiber tracts – cerebral peduncles
Has four rounded protrusions – corpora quadrigemina
Reflex centers for vision and hearing
The bulging center part of the brain stem
Mostly composed of fiber tracts
Includes nuclei involved in the control of breathing
Medulla Oblongata
• The lowest part of the brain stem
Merges into the spinal cord
Includes important fiber tracts
Contains important control centers
Heart rate control
Blood pressure regulation
Breathing
Swallowing
Vomiting
Reticular Formation
• Diffuse mass of gray matter along the brain stem
Involved in motor control of visceral organs
Reticular activating system plays a role in awake/sleep cycles and consciousness
Cerebellum
• Two hemispheres with convoluted surfaces
Provides involuntary coordination of body movements
BLOOD BRAIN BARRIER
• Includes the least permeable capillaries of the body
Excludes many potentially harmful substances
• Useless against some substances
Fats and fat soluble molecules
Respiratory gases
Alcohol
Nicotine

12. Anesthesia
Slight brain injury
No permanent brain damage
TRAUMATIC BRAIN INJURIES
• Concussion
Slight brain injury
No permanent brain damage
• Contusion
Nervous tissue destruction occurs
Nervous tissue does not regenerate
• Cerebral edema
Swelling from the inflammatory response
May compress and kill brain tissue
Cerebrovascular Accident (CVA)
• Commonly called a stroke
The result of a ruptured blood vessel supplying a region of the brain
Brain tissue supplied with oxygen from that blood source dies
Loss of some functions or death may result
Alzheimer’s Disease
• Progressive degenerative brain disease
Mostly seen in the elderly, but may begin in middle age
Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons
Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death
Mixed nerves – both sensory and motor fibers
Afferent (sensory) nerves – carry impulses toward the CNS
Efferent (motor) nerves – carry impulses away from the CNS
CLASSIFICATION OF NERVES
• 12 pairs of nerves that mostly serve the head and neck
Numbered in order, front to back
Most are mixed nerves, but three are sensory only

13. CRANIAL NERVES
I Olfactory nerve – sensory for smell
II Optic nerve – sensory for vision
III Oculomotor nerve – motor fibers to eye muscles
IV Trochlear – motor fiber to eye muscles
nerve – sensory for the face; motor fibers to chewing muscles
VI Abduces nerve – motor fibers to eye muscles
VII Facial nerve – sensory for taste; motor fibers to the face
VIII Vestibulocochlear nerve – sensory for balance and hearing
IX-fibers to the pharynx
X Vagus nerves – sensory and motor fibers for pharynx, larynx, and abdominal viscera
XI Accessory nerve – motor fibers to neck and upper back
XII Hypoglossal nerve – motor fibers to tongue
Spinal Nerves
• There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs
Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord
Spinal nerves are named for the region from which they arise
AUTONOMIC NERVOUS SYSTEM
• The involuntary part of the peripheral nervous system
Consists of motor nerves only
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• Divided into two divisions
Sympathetic division
Parasympathetic division
• The involuntary part of the peripheral nervous system
Consists of motor nerves only
• Divided into two divisions
Sympathetic division
Parasympathetic division
Differences Between Somatic and
Autonomic Nervous Systems
• Nerves
Somatic – one motor neuron
Autonomic – preganglionic and postganglionic nerves
• Effector organs
Somatic – skeletal muscle
Autonomic – smooth muscle, cardiac muscle,and glands
Differences Between Somatic and
Autonomic Nervous Systems
• Nerurotransmitters
Somatic – always use acetylcholine
Autominic – use acetylcholine, epinephrine, or norepinephrine

15. Sympathetic – “fight-or-flight”
Response to unusual stimulus
Takes over to increase activities
Remember as the “E” division = exercise, excitement, emergency, and embarrassment
Parasympathetic – housekeeping activities

16. Conserves energy
Maintains daily necessary body functions
Remember as the “D” division - digestion, defecation, and diuresis
Development Aspects of the Nervous System
• The nervous system is formed during the first month of embryonic development
• Any maternal infection can have extremely harmful effects
• The hypothalamus is one of the last areas of the brain to develop
Development Aspects of the
Nervous System
• No more neurons are formed after birth, but growth and maturation continues for several years
• The brain reaches maximum weight in
Young adults