Chapter 25 Nervous Control (sec. 2 up to pg. 719 & sec 1) Unit 17: Nervous Control 300 Chapter 25 Nervous Control (sec. 2 up to pg. 719 & sec 1) How do we see unity within diversity in relation to nervous control??? How does form follow function??? Kid’s Health website http://kidshealth.org/PageManager.jsp?lic=1&article_set=59295&cat_id=20607

The Role of the Nervous System What is the nervous system? a system that lets an animal detect changes & respond to them nerve cells, sense organs, & brain Which characteristic of life is an organism’s nervous system related to? response to stimuli Most animals can quickly detect changes that take place around them. Usually, they respond quickly… A response is the action of an organisms b/c of a change in its environment. Receives information from internal and external stimuli – and responds (by sending a message to an “effector” such as a muscle or gland)

Comparison of Nervous Systems

Nervous Systems in Unicellular Organisms Euglena light-sensitive structure under the “eye-spot” allows Euglena to swim in direction of light Paramecium can respond to obstacles in path turns 30 & moves forward again… Continues to do this until passes object seems to be under chemical control

Nervous Systems in Invertebrates radially symmetrical organisms have no center for nervous control many short neurons form nerve net no definite nerve pathways ex. Hydra bilaterally symmetric animals have a primitive control center(s) (ganglia) & specific nerve pathways ex. Planaria

Nervous Systems in Invertebrates other bilaterally symmetric animals also have brains ex. earthworm cerebral ganglia (slightly larger ganglia) ex. grasshopper brain divided into specialized areas protocerebrum deutocerebrum In arthropods such as the grasshopper, the brain is divided into specialized areas, including the protocerebrum (controlling vision) and the deutocerebrum (processing antenna signals). The stomatogastric system regulates digestion.

Nervous System in Fish lateral line system electrical sense can sense the slightest movements (vibrations) in water electrical sense Ampullae of Lorenzini sense changes in electrical fields Being highly complex life forms fish need a brain and a nervous system to control their body's actions. The nervous system of fish, much like ours, is composed of a central co-ordinating brain, a spinal cord and many, many nerves. The Brain:- Generally speaking fish have small brains in relationship to their overall body weight. Elasmobranchs (Sharks and Rays) in general have a slightly larger brain for the same body mass as Teleosts (Bony Fish), however there is great variety within the teleosts scientists have learned something quite surprising about the Elephantnose Fish (Gnathonemus petersii).

The Human Nervous System The human nervous system is divided into 2 main parts. 1. central nervous system (CNS)… Which includes the… brain spinal cord 2. peripheral nervous system (PNS)… Which includes the… body nerves CNS serves as control centers… info brought from PNS analyzed by means of interneurons in the CNS & impulses then carried to appropriate effectors by motor neurons of PNS PNS sensory & motor neurons connected to the CNS…. Info about animal’s environment gathered by receptors & brought to CNS by sensory neurons

What do the 3 Major Parts of the Brain Do? What does the cerebrum control? speech, reasoning, emotions What does the cerebellum control? balance, posture, muscle tone What does the medulla control? involuntary actions of internal organs heart rate, breathing rate, peristalsis, etc. cerebrum cerebellum medulla (brain stem) spinal cord Cerebrum… sensory inputs are interpreted & motor impulses started Cerebellum… coordinates impulses sent out from cerebrum think of Belle dancing w/ the Beast…. Her balance, posture, muscle tone…. Medulla oblongata… part of brain stem… controls involuntary actions of internal organs (heart rate, breathing rate, peristalsis, etc.)You’d be dull & lifeless w/o it

Nerve Tissue What is a nerve? many neurons bundled together can be compared to a cable bundle of neurons Different types of neurons differ in structure & direction in which they carry impulses Can be compared to a cable… made of many wires bunched together, thick

Nerve Tissue What is a neuron? specialized cell that transmits nerve impulses (carries messages) through the body can compare to electrical wires Different types of neurons differ in structure & direction in which they carry impulses the main part of the nervous system can be compared to electrical wires: very thin & long, carry messages & have a covering of insulation around them, usually connect 2 things

Different Types of Neurons What are the types of neurons involved in the pathway of impulses? sensory neurons transmit incoming impulses (stimuli) from receptors to control center interneurons transfer impulses within control centers (brain & spinal cord) from sensory to motor neurons motor neurons transmit outgoing impulses from control center to effectors muscles, glands, organs Sensory neuron Motor neuron interneuron Stimulus response interpretation Different types of neurons differ in structure & direction in which they carry impulses Sensory neurons transmit incoming impulses from receptors to a coordination center where impulses are interpreted Interneurons transfer impulses from sensory to motor neurons (in brain & spinal cord) Motor neurons once incoming impulses have been analyzed, the brain or spinal cord will send out a response… motor neurons transmit outgoing impulses to effectors

Neuron Structure What are the main parts of a neuron? dendrites receive impulses & move them toward cell body cell body (soma) nucleus, organelles, & cytoplasm axon carries impulses away from cell body towards end branch terminal buttons/end branch of axon help send impulses to next neuron or effector (muscle, organ, gland) Terminal buttons/ end branch of axon dendrites highly branched fibers; receive impulses from end brush of previous neuron; conduct impulses toward cell body cell body portion of neuron that most resembles other types of cells…. contains nucleus & cytoplasm Axon long, narrow portion of cell; carries impulses away from cell body… to terminal buttons/end branch of axon (end of axon that divides into many filaments… then impulse travels to dendrites of next neuron or to effector). Axons are often covered with myelin sheath (insulating lipid material). Myelin allows impulse to move very rapidly… consists of many layers… made of Schwann cells wrapping around & around axon… Schwann cells help provide nourishment to the axon & aids in axon regeneration. Between Schwann cells the axon is left uncovered. These bare areas are called nodes of Ranvier & help transport impulses quickly b/c the impulse is able to move from node to node instead of continuously along membrane.

Neurons What are the other parts of a neuron? myelin sheath fatty layer surrounding axon that protects it & allows impulses to move quickly Schwann cells make myelin Nodes of Ranvier sections of axon between Schwann cells not covered in myelin sheath help transport impulses quickly dendrites highly branched fibers; receive impulses from end brush of previous neuron; conduct impulses toward cell body cell body portion of neuron that most resembles other types of cells…. contains nucleus & cytoplasm Axon long, narrow portion of cell; carries impulses away from cell body… to terminal buttons/end branch of axon (end of axon that divides into many filaments… then impulse travels to dendrites of next neuron or to effector). Axons are often covered with myelin sheath (insulating lipid material). Myelin allows impulse to move very rapidly… consists of many layers… made of Schwann cells wrapping around & around axon… Schwann cells help provide nourishment to the axon & aids in axon regeneration. Between Schwann cells the axon is left uncovered. These bare areas are called nodes of Ranvier & help transport impulses quickly b/c the impulse is able to move from node to node instead of continuously along membrane.

Neurons dendrites terminal buttons (end branch) nucleus cytoplasm cell body (soma) axon terminal buttons (end branch) cytoplasm nucleus dendrites myelin sheath nodes of Ranvier cell body (soma) terminal buttons/ end branch of axon Dendrites Direction of impulse dendrites highly branched fibers; receive impulses from end brush of previous neuron; conduct impulses toward cell body cell body portion of neuron that most resembles other types of cells…. contains nucleus & cytoplasm Axon long, narrow portion of cell; carries impulses away from cell body… to terminal buttons/end branch of axon (end of axon that divides into many filaments… then impulse travels to dendrites of next neuron or to effector). Axons are often covered with myelin sheath (insulating lipid material). Myelin allows impulse to move very rapidly… consists of many layers… made of Schwann cells wrapping around & around axon… Schwann cells help provide nourishment to the axon & aids in axon regeneration. Between Schwann cells the axon is left uncovered. These bare areas are called nodes of Ranvier & help transport impulses quickly b/c the impulse is able to move from node to node instead of continuously along membrane.

The Pathway of Impulses How do messages move along a neuron? an electrical charge moves along the axon in one direction from dendrites to the end branch of the axon So, what are the 2 pathways that messages follow? sensory receptor to control center (brain/spinal cord) control center to effector (muscle, gland, organ) Virtually all nerve impulses must travel through many neurons before reaching their targets Impulse is transmitted in only one direction nerve impulse or “action potential” results from changes in ion concentration inside/outside neuron plasma membrane

The Pathway of Impulses Do neurons touch each other? No, they are separated by a synapse. small, fluid-filled space between end branch of axon (of one neuron) and dendrites of next neuron So, how do messages get from one neuron to the next? neurotransmitters chemical messengers that help move impulses across a synapse Virtually all nerve impulses must travel through many neurons before reaching their targets Impulse is transmitted in only one direction

How do the PNS & CNS Work Together in Nervous Response? Detection of stimulus by sensory receptors Transmission of impulse along sensory neuron (PNS) Interpretation & analysis of impulses in control center (CNS) Transmission of impulse along nerve (PNS) Response by effector muscle, gland, organ 1. Detection of stimulus by sensory receptors (Ex. touch-sensitive cells in skin or cells that form part of sense organ such as eye or ear) convert input into electrical impulse Ex. Touch hot stove & sense too much heat 2. Transmission of impulse along sensory neurons of PNS to CNS Ex. signal sent along sensory neurons to brain or spinal cord 3. Interpretation & analysis of impulses in interneurons of CNS (brain or spinal cord) Ex. brain or spinal cord interprets & processes signal in interneuron 4. Transmission of impulse from CNS to motor neuron of PNS to effector (muscle, gland, organ) 5. Appropriate response by effectors (Muscles, glands, organs that cause the actual response to the stimulus.) Ex. motor neurons transmit outgoing impulses to the effectors which respond (pull hand away from hot stove)

The Senses Adaptations to sense a variety of stimuli 5 major senses receptor or sense organ sends impulses to particular parts of brain where interpreted then act on info provided 5 major senses vision hearing smell taste pain, pressure, heat, cold touch

Reflexes What is a reflex? involuntary/automatic response to stimuli Involve CNS, but does NOT require conscious control or decision making b/c determined by fixed pathways some through brain (ex. blinking) others through spinal cord (ex. touch cactus & respond) known as reflex arc interneuron

5 Steps of the Reflex Arc & the Initial Response Reflex Arc Animation Reflex Arc Animation 2 What are the 5 steps of the “reflex arc”? Receptors detect stimulus & are activated Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord From spinal cord impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors (muscle, gland, organ) which responds appropriately Does the reflex arc involve the brain? NO! Reflex arc Receptors activated (ex. feel excess heat) Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately (ex. pull hand away) Does NOT involve brain Takes a fraction of a second Saying to help you remember… Receive sensory input; move effectively.

5 Steps of the Reflex Arc & the Initial Response 2. Sensory neuron transmits impulse towards spinal cord 3. Impulse crosses synapse into interneuron in spinal cord where interpreted & analyzed 4. impulse crosses synapse from spinal cord motor neuron & leaves spinal cord 1. Sensory receptor receives stimulus & is activated. 5. Impulse received by effector (which responds appropriately) interneuron Reflex arc Receptors activated (ex. feel excess heat) Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately (ex. pull hand away) Does NOT involve brain Takes a fraction of a second

Reflex Arc Reflex arc Receptors activated (ex. feel excess heat) Sensory neuron transmits impulse towards spinal cord Impulse crosses synapse to interneuron in spinal cord Impulse crosses synapse to motor neuron & leaves spinal cord Impulse activates effectors which respond appropriately (ex. pull hand away) Does NOT involve brain Takes a fraction of a second Interneuron = association nerve

The Secondary Response: After the Reflex Arc Since reflex actions (arcs) don’t involve the brain, how does your brain become aware? Some spinal cord interneurons that receive sensory impulses connect with the brain This path is slower than the reflex arc… So, brain becomes aware of what has happened after your body has already responded. secondary response… You yell, “Ouch!”. & grab thumb, foot, etc….