Chapter 15 Nervous & Chemical Control (sec. 1 & 2)

 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

 How many parts is the human nervous system divided into?  two ▪ 1. central nervous system (CNS) ▪ brain ▪ spinal cord ▪ 2. peripheral nervous system (PNS) ▪ body nerves

 cerebrum  speech, reasoning, emotions  cerebellum  controls balance, posture, muscle tone  medulla (oblongata)  controls involuntary actions of internal organs ▪ heart rate, breathing rate, peristalsis, etc. cerebrum cerebellum medulla (brain stem) spinal cord

1. Detection of stimulus by sensory receptors 2. Transmission of impulse along nerve (PNS) 3. Interpretation & analysis of impulses in control center (CNS) 4. Transmission of impulse along nerve (PNS) 5. Response by effector  muscle, gland, organ

 What is a nerve?  many neurons bundled together  can be compared to a cable bundle of neurons

 What is a neuron?  specialized cell that transmits nerve impulses (carries messages) through the body  can compare to electrical wires

 What are the main parts of a neuron?  dendrites ▪ receive impulses & move them toward cell body  cell body (soma) ▪ nucleus & 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

 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

cell body (soma) terminal buttons/ end branch of axon Dendrites Direction of impulse

 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, there are 2 different pathways…  sensory receptor to control center  control center to effector (muscle, gland, organ)

 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 impulse cross synapse

 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

 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

 Reflex arc 1. Receptors detect stimulus & are activated 2. Sensory neuron transmits impulse towards spinal cord 3. Impulse crosses synapse to interneuron in spinal cord 4. From spinal cord impulse crosses synapse to motor neuron & leaves spinal cord 5. Impulse activates effectors (muscle, gland, organ) which responds appropriately  Does NOT involve brain Reflex Arc Animation Reflex Arc Animation 2

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

Interneuron = association nerve 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 w/ 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!”