The nervous system has 3 main functions: sensory input, integration, and motor output. It is divided into the central nervous system (CNS; brain and spinal cord) and peripheral nervous system (PNS). The PNS has sensory and motor divisions. The motor division is further divided into somatic and autonomic systems. Nervous tissue contains neurons and supporting cells like neuroglia. Neurons have dendrites, axons, and may be covered by a myelin sheath. Information passes between neurons at synapses. The brain is divided into the cerebrum, diencephalon, brain stem, and cerebellum. The special senses of smell, taste, vision, and hearing involve specialized receptors and

1. The Nervous
System
Chapters 11, 12, and 16

2. Introduction
 The nervous system is the master
controlling and communicating system of
the body.
 It has 3 functions
1. Sensory Input – monitors changes
inside/outside body
2. Integration – processes and interprets and
decides what to do
3. Motor Output – activates the response

3. Organization
 Very highly integrated system
 Divided into two parts:
 CNS (Central Nervous System) – consists of
brain and spinal cord; command center;
interprets sensory information and dictates
responses
 PNS (Peripheral Nervous System) – parts of
nervous system outside the CNS;
communication link for the body to the CNS

4. PNS
 The PNS has 2 subdivisions:
1. Sensory (afferent) Division – consists of nerve
fibers that convey impulses to the CNS from
the sensory receptors around the body
2. Motor (Efferent) Division – transmits impulses
from the CNS to the body

5. The Motor Division
 The Motor Division (Efferent) is also
divided into 2 subdivisions:
1. Somatic nervous system – conducts impulses
from CNS to skeletal muscle; AKA voluntary
nervous system
2. Autonomic nervous system – regulates activity
of smooth and cardiac muscle and glands; AKA
involuntary nervous system
a. Sympathetic
b. Parasympathetic

6. Nervous Tissue
 Two principal types of cells:
1. Neurons – excitable nerve cells that transmit
electrical signals
2. Supporting cells

7. Supporting Cells
 Supporting cells, neuroglia (glial cells),
each have a unique function, but in general
serve as a helper, or link, for the neurons.

8. Neurons
 There are billions of neurons, nerve cells.
 Special characteristics of neurons:
1. Extreme longevity – can live for over 100 years
2. Amitotic – Cannot replace themselves if
destroyed
3. High metabolic rate – required lots of oxygen
and glucose

9. Neurons (con’t)
 Typically large, complex cells.
 Have one large body and several slender
processes (arms)
 Processes are
 Dendrites – short, tapering, branching
processes; input source
 Axons – one per neuron; conducting source
(generates nerve impulses and transmits it)

10. Myelin Sheath
 Myelin protects and insulates fibers from
one another.
 Also, it increases the speed of transmission
of the nerve impulses.
 Myelin sheaths are only associated with
axons.

11. Synapse
 A synapse is a unique junction that
mediates information transfer from one
neuron to the next or from a neuron to an
effector cell – it’s where the action is!
 There are two varieties of synapses:
 Electrical
 Chemical

12. Synesthesia
What is it??

13. The Brain

14. The Brain
 About 2 fistfuls large
 For average adult male, brain is 1600 g,
and for the female about 1450 g.
 This is in terms of brain weight per body
weight. Males and females have equivalent
brain sizes.

15. Parts of the Brain
 We will use the medical scheme for brain
regions:
1. Cerebral hemispheres
2. Diencephalon
3. Brain stem (midbrain, pons, and medulla)
4. Cerebellum

17. The Cerebral Hemispheres
 Form the superior part of the brain.
 They account for 83% of the brain’s mass.
 Elevated ridges of tissue are the gyri, and
the grooves are the sulci.
 Each hemisphere has 3 basic regions:
 Gray matter
 White matter
 Basal nuclei

18. Cerebral Cortex (Gray matter)
 Where the conscious mind is found.
 Enables us to be aware of ourselves and our
sensations, to communicate, remember, and
understand, and to initiate voluntary movements.
 Although the two hemispheres are equal in size,
they are not entirely equal in function.
 No part of the cortex works alone. Conscious
behavior requires the entire cortex.
 It is also contralateral, meaning that the left part
controls the right side of the body, vice versa.

19. Cerebral White Matter
 Under the gray matter
 Responsible for communication between
cerebral areas and between the cerebral
cortex and lower CNS centers.

20. The Diencephalon
 Forms the central core of the forebrain and
is surrounded by the cerebral hemispheres.
 Made of 3 structures:
 Thalamus
 Hypothalamus
 Epithalamus

21. The Thalamus
 Makes up 80% of the diencephalon.
 Afferent impulses from all senses and all
parts of the body converge on the
thalamus.
 It sorts out and edits information.

22. The Hypothalamus
 Located below the thalamus.
 Even though small, it is the main control center of
the body and maintains homeostasis.
 Maintains homeostasis as:
 Autonomic control center
 Center for emotional response
 Body temperature regulation
 Regulation of food intake
 Regulation of water balance and thirst
 Regulation of sleep-wake cycles
 Control of endocrine system functioning

23. The Epithalamus
 Most dorsal portion of the diencephalon.
 Secretes the hormone, melatonin, which
induces sleep.
 Also, regulate the sleep-wake cycle and
some moods.

24. The Brain Stem
 Produce rigidly programmed, automatic behaviors
that are necessary for survival.
 Parts:
 Midbrain – conducts signals b/t high and low brain
centers; visual and auditory reflex
 Pons – relays info from cerebrum to cerebellum;
respiration
 Medulla Oblongata – relays info b/t brain and spinal cord;
heart rate, respiration rate, vomiting, coughing, etc.

25. The Cerebellum
 Cauliflower-like structure
 Continually compares the higher brain’s
intention with the body’s performance and
sends out messages to initiate the
appropriate corrective messages.

26. Protection of the Brain
 Nervous tissue is soft and delicate, and the
neurons can be damage with even the
slightest pressure.
 Meninges – connective tissue membranes
that lie just external to the CNS organs
 Dura Mater (“Tough Mother”) – strongest
 Arachnoid Mater
 Pia Mater (“Gentle Mother”)

27. Cerebrospinal Fluid
 Found in and around the brain and spinal
cord
 Forms liquid cushion that gives buoyancy to
the CNS organs

28. Brain Injuries
 Concussion – slight brain injury; mild and
short-lived symptoms, no permanent
damage
 Contusion – Brain tissue destruction; can
last for hours or a lifetime; patients may
stay conscious or in a coma
 Subdural Hemorrhage – bleeding from
ruptured vessels in the brain

29. The Spinal Cord
 Provides a two-way conduction pathway to
and from the brain
 Lies between the body vertebrae and the
“dural sheath” in what is known as the
epidural space.
 Typically ends at L1

30. Spinal Cord Injuries
 Any localized damage to the spinal cord or spinal
roots leads to some form of functional loss, either
paralysis or paresthesias (sensory loss).
 Cutting the spinal cord at any level results in total
motor and sensory loss in body regions inferior to
the site of damage.
 Damaged b/t T1 and L1 – paraplegia, loss of
feeling/movement in both lower limbs
 Damaged in the cervical region – quadriplegia, loss of
feeling/movement in all four limbs

31. The Special Senses

32. Intro to Special Senses
 The special senses include – smell, taste,
sight, and hearing (Also, equilibrium!)
 Special Sensory Receptors – distinct
receptor cells confined in the head region
and are highly specialized and housed in
complex organs or structures

33. Taste and Smell
 The receptors for taste (gustation) and smell
(olfaction) are classified as chemoreceptors
because they respond to chemicals.
 Taste receptors are excited by food chemicals
dissolved in saliva and smell receptors are
excited by airborne chemicals.
 These receptors complement one another!

34. Taste
 Taste buds, sensory receptors, are found in
the oral cavity.
 ~10,000 taste buds are located on the
tongue and most are found in the papillae,
peglike projections that gives the tongue its
rough feel.

35. Taste (con’t)
 Tastes are grouped as sweet, sour, salty, and
bitter.
 Most taste buds respond to more than one of the
tastes.
 Also, some substances change tastes as they
moved through the mouth (Ex. saccharin)
 Also, our dislike for bitter tastes is to protect us,
since spoiled food and poisons are bitter!
 Also, we have a gag-reflex for revolting foods.

36. How do we taste?
 A chemical must be dissolved in saliva,
diffused into the taste pore, and contact the
gustatory cells.
 Saliva moistens the food and enzymes
digest starch.
 Taste is 80% smell!!

37. Smell
 The olfactory epithelium is located in the
roof of the nasal cavity.
 Air must enter the nasal cavity and turn
sharply to be “smelled,” which is why are
sense of smell is not very strong!
 Humans can distinguish ~10,000 smells!

38. How do we smell?
 Chemicals must be gaseous.
 Must be sufficiently water soluble.
 Must bind to protein receptors in the nasal
passage.

39. Vision
 Vision is our dominant sense – 70% of
sensory receptors are in the eyes!
 Visual receptor cells, photoreceptors, sense
and encode patterns of light and the brain
processes them.

40. Accessories to the Eye
 Eyebrows – shade and protect the eye
 Eyelids – protect and keep the eye lubricated
 Eyelashes – protect the eye by blinking at the
slightest touch (rich with nerves)
 Conjunctiva – mucous membranes
 Lacrimal apparatus – produce tears
 Eye muscles – control the movement of the eye

41. Parts of the Eye
 Sclera – white of the eye
 Cornea – transparent membrane that bends light
 Iris – visible colored part
 Pupil – dark, round part in the center of the eye;
allows light to enter
 Lens – biconvex, transparent structure that
focuses light as it enters
 Retina – contains millions of photoreceptors,
which process light within the brain
 Optic nerve – pathway from retina to the brain

43. Vision Problems
 Diplopia – double vision
 Strabismus – cross-eyed
 Glaucoma – water drainage is blocked and
pressure within the eye builds up,
compressing the retina and optic nerve
 Cataract – clouding of the lens

44. Hearing
 Structure of the ear:
 Outer (External) Ear
 Pinna – shell-like structure on head
 External auditory canal – extends from outside to the
eardrum
 Tympanic membrane (eardrum) – sound makes it vibrate
and vibrations are transferred to tiny bones in the middle ear
 Middle Ear
 Small air-filled cavity
 Filled with the 3 smallest bones in the body, which vibrate
 Inner (Internal) Ear
 Contains fluid that moves and creates sound

45. Clinical Terms
 Neurologist
 Neuropathy
 Neurotoxin
 Rabies
 Shingles
 Encephalopathy
 Neuroses
 Psychoses
 Opthalmology
 Optometrist
 Otalgia