Bellwork: If you were to cut yourself, how can your brain tell how serious the injury is?

Chapter 31: The Nervous System Section 31.1: The Nervous System

What are the main functions of the Nervous System? The Nervous System collects information about the body’s internal and external environment It processes this information It finally responds to this information The Nervous system is divided into two parts Peripheral Nervous System – nerves and supporting cells Central Nervous System – brain and spinal chord

What does a neuron do? What are the three different types? A neuron transmits nervous system impulses 3 types – sensory, motor and interneurons. Although there are many different shapes and sizes of neurons they all share certain features Dendrites: Receive impulses from other neurons, and carry impulses to the cell body Axon: The long fiber that carries the impulse away from the cell body Neurons may have dozens of dendrites, but only one axon Nerve – cluster of axons and dendrites Myelin Sheath – surrounds a single, long axon has many gaps called nodes Impulse travels faster with a myelin sheath

How is meant by resting potential? Neurons have a charge or electrical potential across their cell membranes The inside has a voltage of -70 millivolts compared to the outside This difference is known as the resting potential Active transport pumps Na+ ions out and K+ ions into the cell K+ ions can easily leave the cell through ungated channels This will happen due to diffusion, and the inside become negatively charged

How does a nerve impulse actually begin? A large enough stimulus is required to start a nerve impulse A neuron can be stimulated by either another neuron or by the environment The impulse itself is actually a sudden reversal of the resting potential. Gated Sodium cannels are open, allowing Na+ ions into the cell Inside becomes positive, reversing the resting potential This reversal is called a nerve impulse, or action potential Once the impulse passes, the Na gates close, and K+ channels open, allowing K+ to flow out - resting potential is restored Na –K pump keeps working, ensuring that the axon will be ready for more action potentials A nerve impulse is self propagating, the flow of ions causes the Na channels to open Allows rapid movement of impulse along the axon

Are there different levels of nervous impulse? No, a nervous impulse is an all or nothing response Not all stimuli are capable of starting an impulse – they must meet the threshold Our brain doesn’t rely on the strength of an impulse to determine the amount of pain, or the how hard you are pushing… This instead relies on the number action potentials A weak stimulus is typically 3 or 4 action potentials per second A strong stimulus might produce 100 per second

What is a synapse? At the end of each neuron is an an axon terminal This marks where the impulse may be passed to another cell The point at which a neuron passes an impulse to another cell is called a synapse Synaptic cleft separates axon terminal from adjacent cell Axon terminal contains neurotransmitters These are chemicals that transmit an impulse across a synapse to another cell They are released from the axon, diffuse across the synaptic cleft and bind to receptors on the membrane of the receiving cell If the stimulation exceeds the cell’s threshold, a new impulse begins Once they have done their job, the neurotransmitters are broken down by enzymes in the synaptic cleft, or taken up and recycled by axon terminal

Key Concepts What are the main functions of the nervous system? What is the difference between the peripheral nervous system and central nervous system? What are the three types of neurons? What is an action potential? How is it generated? How do impulses travel between neurons?

The Central Nervous System Section 31.2

Where does the body process information that it receives? The control point of the central nervous system is the brain The brain can be divided into a number of major areas Cerebrum, Cerebellum and brain are all responsible for processing and relaying information The brain is constantly changed by its interactions with the environment Sensory experience changes many of the patterns of neuron connections Stem cells in the brain produce new neurons throughout life The brain is constantly reacting and changing to the world around it

What is the role of the spinal cord? The spinal cord is the main communication link between the brain and the rest of the body Like a major telephone line, carrying thousands of signals at once 31 pairs of spinal nerves branch out from the spinal cord, connecting the brain to different parts of the body Some kinds of information, such as reflexes, are processed directly in the spinal cord Remember, a reflex is a quick automatic response to a stimulus

What are the five key parts of the brain? Cerebrum: Responsible for the voluntary or conscious activities of the body. Also site of intelligence, learning and judgment Divided into two hemispheres, connected by corpus callosum ( a small band of tissue) Each hemisphere deals with opposite side of the body Hemispheres are also divided into lobes, which are associate with different functions Cerebral cortex – outer layer, made of densely packed nerve cell bodies called gray matter White matter – inner layer of cerebrum. Color comes from bundles of axons with myelin sheaths, and connect different areas of the brain

The other parts of the brain Cerebellum: second largest region, receives information about muscle and joint position, and sensory input. Cerebellum does not send commands to muscles, but coordinates and balances action of muscles When beginning any activity involving muscle co-ordination, the cerebellum learns the movements and coordinates the necessary action Thalamus and Hypothalamus: Thalamus receives information from sensory receptors, and relays information to the cerebrum for further processing. Hypothalamus control center for recognition and analysis of hunger, thirst, fatigue, anger and body temperature, whilst also coordinating the nervous and endocrine systems Limbic System: Linked to emotion, behavior and memory, and the brains pleasure center Brain Stem: Connects brain and spinal cord. Divided into three – the midbrain, the pons and the medulla oblongata. All regulate the flow of information between the brain and the rest of the body. Has the job of keeping the body functioning when are unconscious or asleep (controls heart rate, breathing, swallowing etc….)

How do drugs change the brain and lead to addiction? Virtually every addictive substance (both legal and illegal) affect brain synapses Although the chemistry of each drug is different they all produce changes in in one particular group of synapses, which use the neurotransmitter dopamine, and are associated with the brain’s pleasure and reward centers Any activity that brings us pleasure stimulates neurons in the hypothalamus and limbic system to release dopamine, which acts on other neurons across these synapses, producing a sensation of pleasure and wellbeing Different drugs affect dopamine production in different ways – some flood the brain with dopamine producing an instant high ,some keep dopamine present the longer, some stimulate dopamine production in other parts of the brain The problem is that the brain reacts to excessive dopamine by reducing the number of receptors for the neurotransmitter. This means that normal activities (such as smelling amazing food) will no longer produce the same dopamine levels The drug user requires increased amounts of the drug to produce the same effect or “high”. This begins a vicious circle of addiction that is difficult to break

Key concepts What are the three major regions of the brain? What is the role of the spinal cord? How do reflexes protect the body from injury? What affect does drug use have on the brain? Why do many drug uses begin to take more and more of the drug they abuse?

Bellwork: