The nervous system is a highly organized network of billions of nerve cells that functions as the control center of the body. It has two main parts - the central nervous system comprising the brain and spinal cord, and the peripheral nervous system outside these areas. The peripheral nervous system is further divided into the somatic and autonomic systems. The somatic system controls skeletal muscles and sensation, while the autonomic system regulates involuntary functions through the sympathetic and parasympathetic divisions, which work antagonistically to maintain homeostasis. Neurotransmission occurs via the release of chemical messengers called neurotransmitters at synaptic junctions.

2. The Nervous System

3. The Nervous System
• A network of billions of nerve cells
linked together in a highly organized
fashion to form the rapid control
center of the body.

6. • Functions include:
– Integrating center for homeostasis, movement,
and almost all other body functions.
– The mysterious source of those traits that we
think of as setting humans apart from animals

7. Basic Functions of the Nervous System
1. Sensation
• Monitors changes/events occurring in and outside the
body. Such changes are known as stimuli and the cells
that monitor them are receptors.
2. Integration
• The parallel processing and interpretation of sensory
information to determine the appropriate response
3. Reaction
• Motor output.
– The activation of muscles or glands (typically via the release
of neurotransmitters (NTs))

9. Neurons• The functional and structural unit
of the nervous system
• Specialized to conduct information from one part of the
body to another
• There are many, many different types of neurons but most
have certain structural and functional characteristics in
common:
- Cell body (soma)
- One or more
specialized, slender
processes
(axons/dendrites)
- An input region
(dendrites/soma)
- A conducting
component (axon)
- A secretory (output)
region (axon terminal)

11. Neuron structure

12. Classification of neurons
Structural classification based on number of
processes coming off of the cell body:

13. Anaxonic neurons
• no anatomical clues to
determine axons from
dendrites
• functions unknown

14. Bipolar neuron
• two processes coming off
cell body – one dendrite &
one axon
• only found in eye, ear &
nose

15. Unipolar (pseudounipolar) neuron
• single process coming off cell
body, giving rise to dendrites (at
one end) & axon (making up rest
of process)

16. Multipolar neuron
• multiple dendrites & single
axon
• most common type

18. Classification of neurons
Functional classification based on type of information &
direction of information transmission:
• Sensory (afferent) neurons –
• transmit sensory information from receptors of PNS towards the CNS
• most sensory neurons are unipolar, a few are bipolar
• Motor (efferent) neurons –
• transmit motor information from the CNS to effectors
(muscles/glands/adipose tissue) in the periphery of the body
• all are multipolar
• Association (interneurons) –
• transmit information between neurons within the CNS; analyze inputs,
coordinate outputs
• are the most common type of neuron (20 billion)
• are all multipolar

20. Divided into Two Parts:
Central (CNS)
Peripheral (PNS)

21. Organization of the
Nervous System
• 2 big initial divisions:
1. Central Nervous System
• The brain + the spinal cord
– The center of integration and control
2. Peripheral Nervous System
• The nervous system outside of the
brain and spinal cord
• Consists of:
– 31 Spinal nerves
» Carry info to and from the spinal
cord
– 12 Cranial nerves
» Carry info to and from the brain

23. Peripheral Nervous System
Skeletal
(Somatic)
Sympathetic Parasympathetic
Autonomic
Peripheral Nervous System

24. Peripheral Nervous System
• Responsible for communication btwn the CNS and the
rest of the body.
• Can be divided into:
– Sensory Division
• Afferent division
– Conducts impulses from receptors to the CNS
– Informs the CNS of the state of the body interior and exterior
– Sensory nerve fibers can be somatic (from skin, skeletal muscles or joints)
or visceral (from organs w/i the ventral body cavity)
– Motor Division
• Efferent division
– Conducts impulses from CNS to effectors (muscles/glands)
– Motor nerve fibers

25. Sensory (Afferent) vs. Motor (Efferent)
e.g., skin
e.g., muscle
Gray’s Anatomy 38 1999
sensory (afferent) nerve
motor (efferent) nerve
Neurons that send signals from the senses,
skin, muscles, and internal organs to the CNS
Neurons that transmit commands from the
CNS to the muscles, glands, and organs

26. The Withdrawal Reflex

27. Motor Efferent Division
• Can be divided further:
– Somatic nervous system
• VOLUNTARY (generally)
• Somatic nerve fibers that conduct impulses from the
CNS to skeletal muscles
– Autonomic nervous system
• INVOLUNTARY (generally)
• Conducts impulses from the CNS to smooth muscle,
cardiac muscle, and glands.

28. Somatic System
• Nerves to/from spinal cord
– control muscle movements
– somatosensory inputs
• Both Voluntary and reflex
movements
• Skeletal Reflexes
– simplest is spinal reflex arc
Muscle
Motor
Neuron
Interneuron
Skin receptors
Sensory
Neuron
Brain

30. Autonomic System
• Two divisions:
– sympathetic
– Parasympatheitic
• Control involuntary functions
– heartbeat
– blood pressure
– respiration
– perspiration
– digestion
• Can be influenced by thought and emotion

31. Autonomic Nervous System
• Can be divided into:
– Sympathetic Nervous
System
• “Fight or Flight”
– Parasympathetic
Nervous System
• “Rest and Digest”
These 2 systems are antagonistic.
Typically, we balance these 2 to keep ourselves in a
state of dynamic balance.
We’ll go further into the difference btwn these 2
later!

32. Sympathetic
• “ Fight or flight” response
• Consists of thoracic nerves
(T1-T12) and three lumber
nerves (L1-L3) so called
thoracico-lumber nerve.
• Release adrenaline and
noradrenaline
• Increases heart rate and
blood pressure
• Increases blood flow to
skeletal muscles
• Inhibits digestive functions
CENTRAL NERVOUS SYSTEM
Brain
Spinal
cord
SYMPATHETIC
Dilates pupil
Stimulates salivation
Relaxes bronchi
Accelerates heartbeat
Inhibits activity
Stimulates glucose
Secretion of adrenaline,
nonadrenaline
Relaxes bladder
Stimulates ejaculation
in male
Sympathetic
ganglia
Salivary
glands
Lungs
Heart
Stomach
Pancreas
Liver
Adrenal
gland
Kidney

33. Parasympathetic
• “ Rest and digest ” system
• Consists of four cranial
nerves (III,VII,IX,X) and
three sacral nerve(S3-S5)
so called cranio-sacral
nerve.
• Calms body to conserve
and maintain energy
• Lowers heartbeat,
breathing rate, blood
pressure
CENTRAL NERVOUS SYSTEM
Brain
PARASYMPATHETIC
Spinal
cord
Stimulates salivation
Constricts bronchi
Slows heartbeat
Stimulates activity
Contracts bladder
Stimulates erection
of sex organs
Stimulates gallbladder
Gallbladder
Contracts pupil

34. Comparison of Somatic and
Autonomic Systems
Figure 14.2

37. Summary of autonomic
differences
Autonomic nervous system controls physiological arousal
Sympathetic
division (arousing)
Parasympathetic
division (calming)
Pupils dilate EYES Pupils contract
Decreases SALVATION Increases
Perspires SKIN Dries
Increases RESPERATION Decreases
Accelerates HEART Slows
Inhibits DIGESTION Activates
Secrete stress
hormones
ADRENAL
GLANDS
Decrease secretion
of stress hormones

40. Neurohumoral transmission
• Neurohumoral transmission implies that
nerves transmit their message across
synapses and neuroeffector junctions by
the release of humoral (chemical)
messenger.

41. • Junction transmission was thought to be electrical but observation
by elliott (1905) to suggest that sympathetic nerves functioned by
the release of an adrenaline like substances…
• Dixon (1907) to propose parasympathetic's released a muscarine
like chemical..
• Vagusstoff was found in1926 to be acetyl choline which
charecterised as parasyphathetic.
• Noradrinaline in 1946 by von euler.
• Many humoral transmitters like, Dopamine, 5-HT, GABA,
Purines, peptides etc..

42. Postjunctionally acting Neurohumoral transmitter
substance must fulfill the following criteria

43. 43
STEPS IN NEUROHUMORAL
TRANSMISSION
1) Synthesis of Neurotransmitter
2) uptake into storage vesicle
3) Release of neurotransmitter
4) Binding to receptor
5) Removal of Neurotransmitter
6) Metabolism
R.E.B, 4MedStudents.com, 2003

44. 44

45. Sympathetic Transmission

46. Parasympathetic Transmission

47. Co-transmission
• One neuron-one transmitter is simplification.
• Most peripheral and central neurons to release more
than one active substance when stimulated.
• In ANS, Primary neurotransmitter Ach and NA,
neurons found to elaborate purine(ATP, adenosine),
peptides (Vasoactive intestinal peptide or VIP,
neuropeptide-Y or NPY, Substance-P,
Enkephalines, somatostatines etc..), nitric oxide and
prostaglandines as co-tranamitters.