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

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

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.

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!

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

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

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. 12.2 , Page. 392

CNS

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

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.

Worksheet: Phineas Gage Video: Phineas Gage http://www.youtube.com/watch?v=c6kRP41ygrI

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

http://www.brainline.org/multimedia/interactive_brain/the_human_brain.html?gclid=CLn4gvuCq7ICFTN0Mgod4WAAIA

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

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. 12.12, P. 400

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

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

Damage to the cerebellum video http://www.youtube.com/watch?v=5eBwn22Bnio

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

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.

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

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.

http://www.youtube.com/watch?v=6Zd6IEC-eKs&feature=related

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

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)

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.

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.

Spinal Cord Anatomy http://www.spineuniverse.com/anatomy/spinal-anatomy-animation Worksheet: Spinal Cord Injuries

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)

The Nervous System Simplified Video: http://www.youtube.com/watch?v=sq9qfSusNmA

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)

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. http://www.youtube.com/watch?v=jdJpLvSTZMU

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

Fight or Flight Response http://www.youtube.com/watch?v=m2GywoS77qc

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.

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