The Nervous System

Chapters 11-14

Unit Objectives• List the organs and divisions of the nervous system & describe the generalized

functions of the system as a whole.• Identify the major types of cells in the nervous system and discuss the function

of each.• Identify the anatomical and functional components of a signal. Compare and

contrast the propagation of a nerve impulse along a nerve fiber and across a synaptic cleft.

• Identify the major anatomical components of the brain and spinal cord and briefly comment on the function of each.

• Compare and contrast spinal and cranial nerves.• Discuss the functional characteristics of the two divisions of the autonomic

nervous system

Organs & Divisions of Nervous System

• Central Nervous System (CNS): Brain & Spinal Cord

• Peripheral Nervous System (PNS): Nerves extend to outlying or peripheral parts of the body– Autonomic Nervous System (ANS):

subdivision of PNS regulates automatic or involuntary functions

1. Brainstem

Spinal cord

Brainstem

Medulla OblongataFunction:

-movement-posture-rate of heart contractions-breathing rate-non-vital reflexes

Pons-relays sensory information-regulates breathing

Midbrain

-skeletal reflex center

2. Diencephalon

Spinal cord

Diencephalon

Thalamus-interprets all senses except smell-synapses for voluntary movement

Hypothalamus-controls the autonomic nervous system-coordinates the nervous and endocrine system-controls reactions to threats-controls sleep cycles-involved in sexual responses-controls body temperature

3. Cerebrum- makes up about 7/8 of your entire brain

Divided into 4 lobes

CerebrumThe surface of the

cerebrum is highly folded.

Ridges = gyri

Grooves = sulci

Deep grooves= fissures

They create more surface area.

Why does the cerebrum need more surface area?

4. Cerebellum (little brain)

-quality control center for movement

It fine-tunes the movements called for by the cerebrum. It compares the actual movement with the intended movement and makes corrections, as necessary.

Cerebellum

Cranial Nerves

SPINAL NERVES

The Peripheral Nervous System

• Consists of the nerves that lead into or outward from the brain and spinal cord

-12 cranial nerves

-31 pairs of spinal nerves

Cells of the Nervous System

• Neurons• 3 Main Parts

– Dendrites: conducts impulses to cell body – Cell body– Axon: conducts impulses away from the cell

body

Cells of the Nervous System

• Neurons are classified according to function– Sensory: conduct impulses to the spinal cord &

brain– Motor: conduct impulses away from brain &

spinal cord to muscles & glands– Interneurons: conduct impulses from sensory

neurons to motor neurons

Neuron

Dendrite Axon terminals

Cell body

Node of Ranvier

Schwann’s Cells

Myelin SheathAxon Hillock

Nucleus

1 2

34

5

67

8

Cells of the Nervous System

• Glia: Connective tissue cells of the CNS• 3 Main types

– Astrocytes: star-shaped cells that anchor small blood vessels to neurons

– Microglia: small cells that move in inflamed brain tissue carrying on phagocytosis

– Oligodendrocytes: form myelin sheaths on axons in the CNS

Cells of Nervous System

– Satellite cells- surround and control the

chemical environment of the neuron

– Schwann cells- insulate the neuron, form the myelin sheath

• Nerve impulses have a domino effect• Through a chain of chemical events, the

dendrites pick up an impulse that’s shuttled through the axon and transmitted to the next neuron.

• The entire impulse passes through a neuron in about 7 milliseconds- faster than a lightning strike.

Nerve Impulses

Step 1 Resting Potential

(the nerve fiber is not sending a signal)

• NaK pumps in the cell membrane actively transport 3 Na+ ions out of the cell for every 2 K+ ions pumped into the cell

• The result- the interior of the cell is negatively charged with respect to the exterior- polarization

Step 2 Depolarization

• A threshold stimulus is received. A threshold stimulus is the stimulation level that must be exceeded to elicit a nerve impulse or a muscle contraction

• Sodium Channels in a local region of the membrane open and sodium diffuses inward depolarizing the membrane

• What charge are sodium ions?• +• What will happen to the charge inside of the

neuron?• It will become more +

Step 3Repolarization

• Potassium channels in the membrane open

• Potassium ions diffuse outward, repolarizing the membrane

Step 4Action Potential

• The resulting action potential causes a local bioelectric current that stimulates adjacent portions of the membrane

• The wave of action potential travels the length of the nerve fiber as a nerve impulse

Summary of Nerve Impulse•Nerve impulse summary animation

The Synapse

• A gap called a synapse or synaptic cleft separates the axon of one neuron and the dendrites of the next neuron.

• *Neurons do not touch.• Chemicals carry

messages across

the synapse.

1

2

3

45

67

8

1

2

34

5 6

7

The synapse animation

Neurotransmitters• Excitatory neurotransmitters- lead to changes that generate

an action potential in the postsynaptic neuron

• Inhibitory neurotransmitters- tend to block the changes that cause an action potential to be generated in a postsynaptic neuron.

• Note- If a postsynaptic cell receive both excitatory and inhibitory messages the response of the postsynaptic depends on which message is stronger

Excitatory neurotransmitters

1. Acetylcholine- muscle contractions, memory

2. Serotonin- sleep patterns, sensory perception, mood, temperature regulation, cerebral blood flow

3. Catecholamines (epinephrine, norepinephrine)- mood, temperature regulation, dreaming

Inhibitory Neurotransmitters

1. GABA- calms the brain

2. Dopamine- emotions, subconscious movement of skeletal muscle, separation of real from imagined

3. Endorphins- pain relieving, apatite modulation, associated with runner’s high

Effect of drugs on neurotransmission

When neurons do not communicate normally, the brain does not function normally either.

• Alcohol animationWhy is drinking alcohol dangerous?

• Cocaine animationWhat feeling does dopamine give a person?How does cocaine affect the transmission of dopamine?Why is cocaine addicting?

Autonomic Nervous System

• Motor Neurons that conduct impulses from the central nervous system to cardiac muscle, smooth muscle, and glandular epithelial tissue

• Regulates the body’s automatic functions to maintain or quickly restore homeostasis

Autonomic Nervous System

• Composed of two divisions– Sympathetic Nervous System– Parasympathetic Nervous System

Sympathetic Nervous System

• Serves as the emergency or stress system, controlling visceral effectors during strenuous exercise & strong emotions (anger, fear, hate, or anxiety)

• Group of changes induced by sympathetic control is called fight-or-flight response

Parasympathetic Nervous System

• Dominates control of many visceral effectors under normal, everyday conditions.