Biology 30 The Nervous System Chapter 11 and 12 Intro Animation

In the Biology 20 course, you studied some of the major body systems in the context of achieving homeostasis. Homeostasis: the process by which a constant internal environment is maintained despite changes in the environment. Examples? The current unit builds on that knowledge by investigating the control mechanisms that keep all of these systems working together in balance.

The Nervous & Endocrine System Though many organ systems play a role in regulating the body, the two main systems are the endocrine system and the nervous system. The endocrine and the nervous system sometimes determine how other systems do their jobs. Endocrine System: hormones Nervous System: electrical messages

The Nervous System -an elaborate communication system that contains more than 100 billion nerve cells in brain alone -monitors the internal and external environment, integrates all of these inputs, and orchestrates a coordinated response to any changes. For Example: nerve cells detect external environmental stimuli (smells, light intensity, pressure, etc.) and relays the information to the brain. internal nerve cells also tell the brain about breathing rate, heart rate, blood pressure -if environmental conditions change, the nervous system quickly lets the body adjust to those changes -complex nerve connections in the brain allow us to think, reason, remember, show various emotions, etc.

Central Nervous System- See p. 367 Central Nervous System- Peripheral Nervous System- Somatic Nervous System: Autonomic Nervous System:

Nervous System Function • to maintain homeostasis • it controls all of the bodies activities • 3 major functions: 1. Sensory input – moves signals form our various sense organs to the brain 2. Integration – interpretation of those signals and the formation of an appropriate response. 3. Motor output – conduction of signals to the body’s muscles and glands

Neuron Types 3 Types of Neurons Caption: Wearable computing. Male researcher using the prototype fingernail touch sensor he has developed. This affective computer detects each touch of the finger by the change it causes in the colour of the blood capillaries below the nail. Such a system could be used for buttonless controls, for example for a computer. By resting on the fingernails, the sensors do not interfere with the natural sense of touch. Affective computers provide feedback about the wearer's physical state or behaviour. This sensor was created at the Media Lab of the Massachusetts Institute of Technology (MIT), USA. 3 Types of Neurons 1. Sensory neurons : Carry information from the environment to the CNS for processing (ex. Eyes responding to light). 2. Interneurons : Link or connect neurons together in the CNS. They carry impulses within the CNS (found predominantly in the brain and spinal cord). They interpret the sensory information and connect neurons to outgoing motor neurons. 3. Motor neurons : Carry information from the CNS to the body effectors (muscles and glands because they are what cause things to happen)

Anatomy of a Nerve Cell 2 Types of cells found in the nervous system: Neurons and Glial Cells Neuron (nerve cell) - the fundamental structural unit of the nervous system that enables us to receive information, process it, and produce action. a “bundle” of neurons forms a nerve Glial cells - (“glue”) are non-conducting cells that help the neurons out, tying them together and providing support (nourish and remove wastes). Largest concentration found in the brain

Nerves are composed of neurons Individual neurons Nerve

Neuron Structure dendrites - the branching structure of a neuron that receives messages (attached to the cell body) axon - the long extension of a neuron that carries nerve impulses away from the body of the cell. axon terminals - the hair-like ends of the axon cell body - the cell body of the neuron; it contains the nucleus (also called the soma) myelin sheath - the fatty substance that surrounds and protects some nerve fibers made up of many cells Node of Ranvier - one of the many gaps in the myelin sheath - this is where the action potential occurs during saltatory conduction along the axon Schwann's cells - cells that produce myelin - they are located within the myelin sheath.

The Basic Neuron The 3 basic parts to a neuron: cell body, axon, and dendrites.

Glial Cells

Myelin Sheath -a white fatty, protein covering on the axon -formed by special glial cells called Schwann cells -acts as insulation for neurons to prevent loss of charged ions from the nerve cell -in between parts of the myelin sheath are nodes of Ranvier -nerve impulses “jump” from node to node, speeding up nerve impulse Transmission; therefore, nerve impulses move faster along a myelinated nerve.

Myelinated vs. Unmyelinated Nerve transmission

Types of Nerves 1. Myelinated Nerves are covered with a myelin sheath make up the white matter of the brain and spinal cord the myelinated neurons located outside the central nervous system are covered with a membrane called a neurilemma the neurilemma promotes regeneration of damaged axons or dendrites 2. Unmyelinated Nerves have no myelin sheath make up the grey matter in the brain and spinal cord Lack neurilemma resulting in permanent damage

Multiple Sclerosis An auto-immune disease in which the immune system attacks and destroys the myelin sheath around surrounding axons. Results in a progressive loss of signal, muscle control, and brain Function What it is like to have MS

The Reflex Arc Reflex arc- a neural pathway through the spinal cord that provides the framework for a reflex action (an involuntary, unconscious action) A reflex arc does not require coordination by the brain Contains 5 essential components: --Stimulus 1. the sensory receptor 2. the sensory neuron 3. the interneuron 4. the motor neuron 5. the effector (muscle or gland etc) --Response

Draw Reflex arc When the patellar tendon is tapped, (1)sensory neurons detect the stretching and send a signal (2) to the CNS (in this case, the spinal cord). The information goes to a motor neuron (3) and to an interneuron (4). The motor neuron stimulates the contraction of the quadriceps muscle which extends the leg, while the interneuron sends an inhibitory signal to the flexor muscle. Reflexes are a protective mechanism for the body

Examples of Reflexes 1. Knee jerk 2. Pupillary – a light shone in one eye sends a nerve impulse to the CNS (brain in this case). A connection is made with interneurons and then motor neurons, one going to each eye. The motor neurons stimulate the pupillary muscles to contract, and the pupils get smaller.

Reflexes In general the following characteristics are used to describe reflex actions. They are: involuntary – mostly unaware of them until after the brain has registered what has occurred purposeful and adaptive – most are essential to our survival predictable – a specific given stimulus will continue to produce the same result have a measurable reaction time – although extremely quick, do not occur instantaneously The more complex the reaction, the longer the reaction time Physiological conditions can affect reaction time (fatigue, drugs) Occur more rapidly in different people

Check Your Understanding Differentiate between the PNS and the CNS. Describe the function of the following parts of a neuron: dendrites, myelin sheath, Schwann cells, cell body, and axon. What is the relationship between the speed of a nerve impulse and the size of the axon along which it travels? What is the difference between gray and white matter? Name the essential components of a reflex arc and the function of each. What are the nodes of Ranvier? What the benefit of having an axon covered by neurillemma?