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