Unit 17: Nervous Control

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

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

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

The Human Nervous System

3 Major Parts of the Brain

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

How do the PNS & CNS Work Together in Nervous Response?1. Detection of stimulus

by sensory receptors2. 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

Nervesbundle of neurons

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)

Neurons

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

Neurons

cell body (soma)

terminal buttons/end branch of axon

Dendrites

Direction of impulse

Neurons

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)

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

impulse cross synapse

The Pathway of Impulses

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

The Pathway of Impulses

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 arc1. Receptors detect stimulus & are

activated2. Sensory neuron transmits

impulse towards spinal cord3. Impulse crosses synapse to

interneuron in spinal cord4. 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

5 Steps of the Reflex Arc & the

Initial Response

Interneuron = association nerve

ReflexArc

The Secondary Response: After the Reflex ArcSince 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!”