1. Essentials of Human Anatomy Nervous System I
Chapter 7
Dr Fadel Naim
Ass. Prof. Faculty of Medicine
IUG

2. Introduction
The function of the nervous system, along with the endocrine system, is to communicate
The nervous system is made up of the brain, the spinal cord, and the nerves

3. Functions of Nervous System
Sensory Function
sensory receptors gather information
information is carried to the CNS
Motor Function
decisions are acted upon
impulses are carried to effectors
Integrative Function
sensory information used to create
sensations
memory
thoughts
decisions

4. Organization of the Nervous System
Organized to detect changes in internal and external environments, evaluate the information, and initiate an appropriate response
Subdivided into smaller “systems” by location:
Central nervous system (CNS)
Structural and functional center of entire nervous system
Consists of the brain and the spinal cord
Integrates sensory information, evaluates it, and initiates an outgoing response
Peripheral nervous system (PNS)
Nerves that lie in “outer regions” of nervous system
Cranial nerves—originate from brain
Spinal nerves—originate from spinal cord

6. Divisions of Peripheral Nervous System
Sensory Division
picks up sensory information and delivers it to the CNS
Motor Division
carries information to muscles and glands
Divisions of the Motor Division
Somatic – carries information to skeletal muscle
Autonomic – carries information to smooth muscle, cardiac muscle, and glands

7. Divisions Nervous System

8. Organization of the Nervous System
“Systems” according to the types of organs they innervate
Somatic nervous system (SNS)
Somatic motor division—carries information to the somatic effectors (skeletal muscles)
Somatic sensory division—carries feedback information to somatic integration centers in the CNS

9. Organization of the Nervous System
Autonomic nervous system (ANS)
Efferent division of ANS—carries information to the autonomic or visceral effectors (smooth and cardiac muscles and glands)
Sympathetic division—prepares the body to deal with immediate threats to the internal environment
Parasympathetic division—coordinates the body’s normal resting activities
Visceral sensory division—carries feedback information to autonomic integrating centers in the CNS

10. Organization of the Nervous System
Afferent and efferent divisions
Afferent division—consists of all incoming sensory pathways
Efferent division—consists of all outgoing motor pathways

11. Sensory Division Somatic sensory components: General somatic senses:
touch
pain
pressure
vibration,
temperature
proprioception.
Special senses:
Taste
Vision
Hearing
Balance
smell

12. Sensory Division Visceral sensory components
transmit nerve impulses from blood vessels and viscera to the CNS
visceral senses primarily include:
temperature
stretch (of the organ wall).

13. Motor Division
The somatic motor component (somatic nervous system; SNS):
conducts nerve impulses from the CNS to skeletal muscles
also known as the voluntary nervous system
The autonomic motor component (autonomic nervous system; ANS): internal organs, regulates smooth muscle, cardiac muscle, and glands.
Innervates
Internal organs
Regulates smooth muscle
Regulates cardiac muscle
Regulates glands
also known as the visceral motor system or involuntary nervous system

15. Nerve Cells Nervous Tissue Two distinct cell types Neurons Glial cells
excitable cells
initiate and transmit nerve impulses
Glial cells
nonexcitable cells
support and protect the neurons

17. Characteristics of Neurons
Neurons have a high metabolic rate.
Neurons have extreme longevity.
Neurons typically are non-mitotic.

18. Neuron Structure Neurons come in all shapes and sizes
All neurons share certain basic structural features.
typical neuron:
Cell body (soma)
Dendrites
Axon

19. Neuron Structure – Cell Body
The cell body
the neuron’s control center
responsible for:
receiving
integrating
sending nerve impulses.
Consists of:
Plasma membrane
Cytoplasm
Nucleus with prominent nucleolus
Chromatophobic substance (Nissil bodies): RER
Free ribosomes

20. Cells of the Nervous System
Components of neurons
Dendrites
Each neuron has one or more dendrites, which branch from the cell body
Conduct nerve signals to the cell body of the neuron
Distal ends of dendrites of sensory neurons are receptors

21. Cells of the Nervous System
Components of neurons
Axon
A single process extending from the axon hillock, sometimes covered by a fatty layer called a myelin sheath
Conducts nerve impulses away from the cell body of the neuron

22. Neuron Structure – Axon
Structures
Collaterals
Telodendria (axon terminals)
Synaptic knobs (terminal boutons)
The axon transmits a nerve impulse away from the cell body toward another cell.

24. Classifications of Neurons
Neurons vary widely in morphology and location.
classified based on
structure
function.
Structural classification: number of processes extending from the cell body.
unipolar neuron has a single process
bipolar neurons have two processes
multipolar neurons have three or more processes

25. Classification of Neurons – Structural Differences
Unipolar
one process
ganglia
Bipolar
two processes
eyes, ears, nose
Multipolar
many processes
most neurons of CNS

26. Classification of Neurons – Functional Differences
Sensory Neurons
afferent
carry impulse to CNS
most are unipolar
some are bipolar
Interneurons
link neurons
multipolar
in CNS
Motor Neurons
multipolar
carry impulses away from CNS
carry impulses to effectors

28. Nerves Nerves are organs of the PNS.
Sensory (afferent) nerves convey sensory information to the CNS.
Motor (efferent) nerves convey motor impulses from the CNS to the muscles and glands.
Mixed nerves: both sensory and motor
Axons terminate as they contact other neurons, muscle cells, or gland cells.
An axon transmits a nerve impulse at a specialized junction with another neuron called synapse.

29. Peripheral Nerves Organization – coverings:
Epineurium wraps entire nerve
Perineurium wraps fascicles of tracts
Endoneurium wraps individual axons

30. Repair of Nerve Fibers
Mature neurons are incapable of cell division; therefore, damage to nervous tissue can be permanent
Neurons have limited capacity to repair themselves
Nerve fibers can be repaired if the damage is not extensive, the cell body and neurilemma are intact, and scarring has not occurred

31. Regeneration of PNS Axons
PNS axons are vulnerable to cuts and trauma.
A damaged axon can regenerate
if some neurilemma remains.
PNS axon regeneration depends upon three factors.
amount of damage
neurolemmocyte secretion of nerve growth factors
stimulates outgrowth of severed axons
distance between the site of the damaged axon and the effector organ

34. Repair of Nerve Fibers Wallerian degeneration:
Stages of repair of an axon in a peripheral motor neuron
Following injury, distal portion of axon and myelin sheath degenerates
Macrophages remove the debris
Remaining neurilemma and endoneurium form a tunnel from the point of injury to the effector
New Schwann cells grow in the tunnel to maintain a path for regrowth of the axon
Cell body reorganizes its Nissl bodies to provide the needed proteins to extend the remaining healthy portion of the axon
Axon “sprouts” appear
When “sprout” reaches tunnel, its growth rate increases
The skeletal muscle cell atrophies until the nervous connection is reestablished
In CNS, similar repair of damaged nerve fibers is unlikely

35. THE END