1. Chapter 12 The Nervous System
Biology 3201
Unit I - Maintaining Homeostasis II

2. Interesting Brain Facts
The average adult human brain weighs three pounds, has a texture like firm jelly and is made up of 75 percent water.
Every time your heart beats, your arteries carry 20 to 25 percent of your blood to the brain.
Every time you recall a memory or have a new thought, you create a connection in the brain.
There are 100 billion neurons (nerve cells) in the brain
There are 100,000 miles of blood vessels in the brain. The distance around the world at the equator is 24,900 miles
The average number of thoughts a person has each day is 70,000

5. What makes our brain different?
The ratio of the brain to body mass increases
A large cerebrum, which is involved in higher mental abilities.
Over the past two
million years, the
human brain has
doubled in size.

7. What is the nervous system?
The system made up of your brain, spinal cord, and a network of nerves that thread throughout your body.
It's the control center for your entire body.
Your brain uses information it receives from your nerves to coordinate all of your actions and reactions. Without it, you couldn't exist!

8. Why is the nervous system important?
1.) It maintains homeostasis in living organisms
Homeostasis – The process of maintaining a relatively constant internal environment despite changing external conditions
Ex: when you get too hot,
you sweat

9. 2.) It transmits electrical impulses as a form of communication to and from all parts of the body
3.) Coordinates movement

10. Two Major Parts of the Nervous System
Central Nervous System (CNS)
Made up of the brain and spinal cord
Peripheral Nervous System (PNS)
Made up of all the nerves that lead into and out of the CNS.
See Fig , Page. 392

11. CNS

13. Central Nervous System
This system receives sensory information and begins motor control
This system is extremely important and therefore must be well protected

14. How is the CNS protected?
Bone - skull around the brain and vertebrae around the spinal cord
Protective membranes called meninges surround the brain and spinal cord
Cerebrospinal fluid fills the spaces between the meninges membranes to create a cushion to further protect the brain and spinal cord.

18. Worksheet: Phineas Gage
Video: Phineas Gage

19. The Structure and Function of the Brain
The brain processes information transmitted from the senses so that the body can react to changes in the external and internal environment.
The brain makes up 2% of the body weight but may contain 15% of the blood supply and consumes 20% of the body’s oxygen and glucose.
The functioning of the brain is not entirely understood but it involves neurons and an internal hormone system

22. Parts of the Brain (Figure 12.11 p.399)
Cerebrum
the part of the brain where all information from our senses is sorted and interpreted
Voluntary muscles that control movement and speech are stimulated from this part of the brain
Memories are stored and decisions are made in this region. It is the center of human consciousness

23. The cerebrum is divided into two halves: Right and left hemispheres.
Each hemisphere is covered by a thin layer called the cerebral cortex. This cortex contains over one billion cells.
The cerebrum is also divided into four lobes.
See Fig , P. 400

24. The 4 lobes are:
Frontal Lobe – involved in the control of muscles, helps us reason, think critically and plan.
Temporal Lobe – receives info from our ears
Occipital Lobe – receives info from our eyes
Parietal Lobe – receives info from our skin & skeletal muscles, and is associated with our sense of taste

27. Cerebellum controls muscle coordination
It contains 50% of the brain’s neurons but only makes up 10% of brain volume
It controls our balance. We do not have to think about certain skills as we get older because they are controlled by the cerebellum

28. Damage to the cerebellum video

29. The respiratory center which controls rate and depth of breathing.
Medulla Oblongata
It is attached to the spinal cord at the base of the brain
It controls:
The cardiac center which controls heart rate and force of contractions.
The vasomotor center which adjusts blood pressure by controlling blood vessel diameter.
The respiratory center which controls rate and depth of breathing.
It also contains reflex centers for hiccupping, vomiting , coughing and swallowing.
Damage to this part of the brain is usually fatal

30. Hypothalamus
a complex bundle of tissue that acts as the main control center for the autonomic nervous system.
It enables the body to respond to external threats by sending impulses to various organs via the sympathetic nervous system.
After the threat has passed, it reestablishes homeostasis by stimulating the parasympathetic nervous system.

31. Thalamus – the sensory relay centre.
It receives sensations of touch, pain, heat and cold, as well as information from the muscles
Mild sensations are relayed to the cerebrum
Strong sensations triggers an immediate reaction & sends info to the hypothalamus

32. Midbrain – involved in sight and hearing
Midbrain – involved in sight and hearing. It is a short section of brainstem between the cerebrum and the Pons.
Pons - works with the medulla to regulate breathing rate and has reflex centers involved in head movement. It contains bundles of axons traveling between the cerebellum and rest of CNS.
Corpus Callosum - a series of nerve fibers that connects the left and right hemispheres of the brain.

34. Structure of the Spinal Cord
The function of the spinal cord is to provide communication between the brain and the peripheral nervous system (PNS).
It is protected by vertebrae
Spinal nerves pass through the vertebrae and out to the PNS

36. What does the spinal cord look like?
A cross section of the spinal cord shows:
Central canal which contains cerebrospinal fluid
Grey matter
White matter
See Fig.12.4 (page 393)

37. What is Grey Matter?
Grey matter is made of neural tissue which contains three types of nerve cells or neurons:
Sensory neurons
Motor neurons
Interneurons
Grey matter is located in the center of the spinal cord in the shape of the letter H.

38. What is White Matter? The white matter is found around the grey matter
It contains the myelinated axons of interneurons that carry information to and from the brain.

39. Spinal Cord Anatomy
Worksheet: Spinal Cord Injuries

40. 2. Peripheral Nervous System
Made up entirely of nerves
The PNS is made up of two subsystems:
2a.Autonomic Nervous System (think of an automatic car)
2b.Somatic Nervous System (think of a standard car)

41. The Nervous System Simplified Video:

42. 2a.) Autonomic Nervous System
Not consciously controlled and is often called an involuntary system.
It is made up of two subsystems:
i) Sympathetic Nervous System
(think of speed)
ii) Parasympathetic Nervous System
(think of a parachute)

44. i.) Sympathetic Nervous System
The sympathetic nervous system sets off what is known as a “fight - or - flight” reaction. This prepares the body to deal with an immediate threat.
Stimulation of the sympathetic nervous system causes a number of things to occur in the body:
Heart rate increases
Breathing rate increases
Blood sugar is released from the liver to provide energy which will be needed to deal with the threat.

45. ii.)Parasympathetic Nervous System
The parasympathetic nervous system has an opposite effect to that of the sympathetic nervous system.
It returns the body to its normal state of rest
The parasympathetic system does this by:
Decreasing heart rate
Decreasing breathing rate
A message is sent to the liver to stop releasing blood sugar since less energy is needed by the body

46. Fight or Flight Response

47. 2b.) Somatic Nervous System
The somatic nervous system IS under conscious control.
It is made up of sensory nerves that carry impulses from the sense organs to the CNS.
It is also composed of motor neurons that transmit the commands of the CNS to the muscles.
The somatic nervous system will also involve reflex actions that are not under conscious control.

48. Activity
Create a flow chart to illustrate the division of the nervous system (CNS and PNS)