Biology 12 Ms. Kim Lesson 11: Nervous System

Main Point Notes Organization of the Nervous System

______________________ : complex network of nerves and cells that carry messages to and from the brain and spinal cord to the body 2 functional systems:

• ___________________________(CNS) • Brain and spinal cord

• ___________________________(PNS) • Nerves that carry information between organs and CNS

Peripheral Nervous System

• Sensory (_____________) nerves à relay information about environment to

CNS a) Somatic b) Autonomic

• Motor (_____________) nerves à initiate an appropriate response

• Somatic system à skeletal muscle, skin, sensory organs (voluntary)

• Autonomic system à internal organ control i.e. smooth muscles and glands

(involuntary)

Learning Goals:

1. How is the nervous system divided? 2. What are the components of a neuron? 3. How does a neural circuit work? 4. What is a reflex arc? 5.

Biology 12 Ms. Kim

a) Sympathetic à nerve cells that prepare body for stress (“fight or flight”) b) Parasympathetic à nerve cells that return the body to a normal state

after stress (“rest or digest”)

Neuron (nerve cell)

A neuron is a specialized nerve cell that is the functional unit of the nervous system:

• Specialized nerve cell that is the ______________________ of the nervous system • Allows organisms to ____________ and ____________ to both internal and

external stimuli 3 main parts:

1. Dendrites – ___________ information à Cell body

2. Cell body – information is transmitted ___________ from the body à axon

3. Axon – information is sent along the axon à _____________________________ Overall:

1. Cell body • Contains _____________ and most cell organelles

2. Dendrites • Highly branched projections that receive signals and transmits them

towards the _______________ 3. Axons

• Conducts signals towards another neuron or an effector 4. Axon terminal

• Enables the signals to the transmitted from one neuron to another or an effector

5. Nucleus • Organelle where __________ is stored

6. Schwann cells • A glial cell; form tightly wrapped layers of plasma membrane called

myelin sheath • Glial cells: Contains nucleus and most cell organelles; do not conduct

signals; provide ____________ and ___________ to neurons 7. Myelin sheath

• ____________________ that acts as electrical insulators and help increase speed of impulses

8. Nodes of Ranvier • Gap between Schwann cells which expose the axon directly to

________________________________

Biology 12 Ms. Kim Reflex Arc

• Simplest nerve circuit pathway • Quick reaction using a neural

circuit through the spinal cord • Does not involve the brain

• Though interneurons connected to reflex circuits also send signals to the brain, making an individual aware of the stimulus that caused the reflex

Neural Circuit

Consists of 5 components:

1. Receptor

• Detection of _____________ by sensory receptors on afferent neurons

2. Afferent neuron (sensor) • Transmission (movement) of a

message along afferent neurons to __________________ 3. Interneuron

• Interpretation of neural messages in the ____________ and determination of the appropriate response

4. Efferent neuron (motor) • Efferent neurons transmit response signals from interneurons to _____________

5. Effector • Transmission of neural message to effectors (i.e. skeletal muscles, glands,

organs), where appropriate _________________ occurs

Questions

1. Explain the difference between afferent and efferent neurons - Afferent neurons receive signals from sensory receptors - Efferent neurons transmit neural messages to effector tissues

Biology 12 Ms. Kim

2. Explain why reflex occurs without the need for the brain to process this information - Reflexes occur without the need for the brain to process information because processing by the brain

requires more time, possible resulting in damage or injury to the body

3. Explain the difference between the central nervous system and the peripheral nervous system - The CNS consists of the brain and spinal cord, made of interneurons - The PNS communicates with the CNS and contains afferent (sensor) and efferent (motor) neurons

4. In what order does an impulse travel along a reflex arc? - The neural circuit travels from the receptor to the afferent neuron then to the interneuron in the spinal

cord, and then the impulse travels from the efferent neuron to the effector

5. Match the following words to their brief description and then label the neuron diagram below

D Dendrite A The long extension of a neuron that carries nerve impulses away from the cell body

C Cell body B Hair-like ends of the axon; they are the points of connection that enable the signals to be transmitted from one neuron to the next neuron or a regulator

H Nucleus

C The body of a neuron that contains the nucleus

A Axon D The branching structures of a neuron that receive information (the electrochemical impulse) from sensory receptors or from other nerve cells

E Myelin sheath

E The fatty protein that surrounds and protects the axon

G Schwann cells F The gaps between the myelin sheath that speed up the movement of the nerve impulses

F Nodes of Ranvier G Cells that produce myelin and are located within the myelin sheath

B Axon terminal

H The organelle of the neuron where the DNA is stored

Additional Reading (Nelson 2003) Read: pg. 412-417 Next Class Lesson 12: Action Potential (pg. 418-422)