Neural Control

Chapter 33 Part 2

33.6 A Smorgasbord of Signals

Different types of neurons release different

neurotransmitters; Parkinson’s disease involves

dopamine-secreting neurons and motor control

Fig. 33-13a, p. 562

Fig. 33-13b, p. 562

Fig. 33-13c, p. 562

Major Neurotransmitters

and Their Effects

The Neuropeptides

Neuromodulators

• Neuropeptides made by some neurons that

influence the effects of neurotransmitters

• Substance P enhances pain

• Enkephalins and endorphins are pain killers

33.7 Drugs Disrupts Signaling

Psychoactive drugs exert their effects by

interfering with the action of neurotransmitters

• Stimulants (nicotine, caffeine, cocaine,

amphetamines)

• Depressants (alcohol, barbiturates)

• Analgesics (narcotics, ketamine, PCP)

• Hallucinogens (LSD, THC)

PET Scan: Effects of Cocaine

Signs of Drug Addiction

33.2-33.7 Key Concepts

How Neurons Work

Messages flow along a neuron’s plasma

membrane, from input to output zones

Chemicals released at a neuron’s output zone

may stimulate or inhibit activity in an adjacent

cell

Psychoactive drugs interfere with the information

flow between cells

33.8 The Peripheral Nervous System

Peripheral nerves carry information to and from

the central nervous system

Nerves are bundled axons of many neurons

Each axon is wrapped in a myelin sheath that

increases transmission speed

Nerve Structure and Function

Nerve Structure and Function

Nerve Structure and Function

Nerve Structure and Function

Fig. 33-15a, p. 564

myelin

sheath

axon

blood vessels

nerve fascicle (a

number of axons

bundled inside

connective tissue)

the nerve’s outer

wrapping

Fig. 33-15b, p. 564

unsheathed node axon

b “Jellyrolled” Schwann

cells of an axon’s myelin

sheath

Fig. 33-15c, p. 564

Na+

action potential resting potential resting potential

Fig. 33-15d, p. 564

K+Na+

resting potential restored action potential resting potential

Animation: Nerve structure

Animation: Ion flow in myelinated axons

Divisions of

the Peripheral Nervous System

Somatic nervous system

• Conducts information about the environment to

the central nervous system (involuntary)

• Controls skeletal muscles (voluntary)

Autonomic nervous system

• Conducts signals to and from internal organs and

glands

Divisions of

the Autonomic Nervous System

The two divisions of the autonomic nervous

system have opposing effects on effectors

Sympathetic neurons are most active in times

of stress or danger (fight-flight response)

Parasympathetic neurons are most active in

times of relaxation

Divisions of

the Autonomic Nervous System

Fig. 33-16, p. 565

eyesoptic nerve

midbrain

salivary glandsmedulla

oblongata

cervical

nerves (8

pairs)

heartvagus

nervelarynx

bronchi lungs

stomach

liver spleen

pancreas

thoracic

nerves

(12 pairs)

kidneys

adrenal glands

small intestine

upper colon (all ganglia

in walls of

organs)lower colon

rectum

lumbar

nerves (5

pairs)

(most ganglia

near spinal

cord)

bladder sacral

nerves (5

pairs)uterus pelvic

nerve

genitals

Animation: Autonomic nerves

33.9 The Spinal Cord

Spinal cord

• Runs through the vertebral column and connects

peripheral nerves with the brain

• Serves as a reflex center

Central nervous system (CNS)

• The brain and spinal cord

Protective Features

Meninges

• Three membranes that cover and protect the

CNS

Cerebrospinal fluid

• Fills central canal and spaces between meninges

• Cushions blows

White Matter and Gray Matter

White matter

• Bundles of myelin-sheathed axons (tracts)

• Outermost portion of spinal cord

Gray matter

• Nonmyelinated structures (cell bodies, dendrites,

neuroglial cells)

Reflex Pathways

Reflex

• An automatic response to a stimulus

• Stretch reflex, knee-jerk reflex, withdrawal reflex

Spinal reflexes do not involve the brain

• Signals from sensory neurons enter the cord

through the dorsal root of spinal nerves

• Commands for responses go out on the ventral

root of spinal nerves

Stretch Reflex

Fig. 33-18, p. 567

A Fruit being loaded into a bowl puts weight on an arm muscle and stretches it. Will the bowl drop? NO! Muscle spindles in the muscle’s sheath also are stretched.

STIMULUS

Biceps stretches.

B Stretching stimulates sensory receptor endings in this muscle spindle. Action potentials are propagated toward spinal cord.

C In the spinal cord, axon terminals of the sensory neuron release a neurotransmitter that diffuses across a synaptic cleft and stimulates a motor neuron.

D The stimulation is strong enough to generate action potentials that self-propagate along the motor neuron’s axon.

E Axon terminals of the motor neuron synapse with muscle fibers in the stretched muscle.

F ACh released from the motor neuron’s axon terminals stimulates muscle fibers.

RESPONSEBiceps contracts.

G Stimulation makes the

stretched muscle contract.

Ongoing stimulations

and contractions hold the bowl steady.

muscle

spindle

neuromuscular

junction

Animation: Stretch reflex

33.8-33.9 Key Concepts

Vertebrate Nervous System

The central nervous system consists of the brain

and spinal cord

The peripheral nervous system includes many

pairs of nerves that connect the brain and spinal

cord to the rest of the body

The spinal cord and peripheral nerves interact in

spinal reflexes

33.10 The Vertebrate Brain

The brain is the body’s main information

integrating organ, part of the CNS

During development, the brain is organized as

three functional regions: forebrain, midbrain and

hindbrain

Hindbrain and Midbrain

The hindbrain includes the medulla oblongata,

the pons, and the cerebellum

The midbrain in mammals is reduced

The brain stem (pons, medulla, and midbrain) is

involved in reflex behaviors

The Forebrain

Cerebrum

• Main processing center in humans

• Evolved as an expansion of the olfactory lobe

Thalamus and hypothalamus

• Important in thirst, temperature regulation, and

other responses related to homeostasis

Development of the Human Brain

Fig. 33-19 (a-c), p. 568

Fig. 33-19 (a-c), p. 568

forebrain midbrain

hindbrain

Protection at the Blood-Brain Barrier

Blood-brain barrier

• Protects the CNS from harmful substances

• Tight junctions form a seal between adjoining

cells of capillary walls

• Some toxins (nicotine, alcohol, caffeine, mercury)

are not blocked

The Human Brain

Cerebellum

• Has more interneurons than other brain regions

• Involved in balance, motor skills and language

Cerebrum

• Divided into two hemispheres, coordinated by

signals across the corpus callosum

• Each hemisphere deals with the opposite side of

the body

Major Brain Regions of Vertebrates

Fig. 33-20a, p. 569

olfactory

lobe

forebrain

midbrain

hindbrain

FISH AMPHIBIAN REPTILE BIRD

shark frog alligator goose

Fig. 33-20b, p. 569

Fig. 33-20b, p. 569

corpus

callosum

hypothalamus thalamus pineal

gland

locationpart of

optic

nerve

midbrain

cerebellum

pons

medulla oblongata

Animation: Sagittal view of a human

brain

33.11 The Human Cerebrum

Each cerebral hemisphere is divided into frontal,

temporal, occipital and parietal lobes

Cerebral cortex

• Outermost gray matter of the cerebrum

• Controls voluntary activity, sensory perception,

abstract thought, language and speech

• Distinct areas receive and process signals

Lobes of the Brain

Fig. 33-21, p. 570

frontal lobe

(planning of

movements,

aspects of

memory,

inhibition of

unsuitable

behaviors)

primary

motor

cortex

primary

somatosen

sory cortex

parietal

lobe

(visceral

sensations)

Wernicke’s

area

Broca’s area

temporal lobe (hearing,

advanced visual processing)

occipital lobe

(vision)

Animation: Receiving and integrating

areas

Functions of the Cerebral Cortex

Specific areas of the cerebral cortex correspond

to specific body parts or functions

Examples:

• The body is spatially mapped out in the primary

motor cortex of each frontal lobe

• Association areas are scattered throughout the

cortex, but not in motor or sensory areas

The Primary Motor Cortex

Association Areas Integrate Inputs

Fig. 33-23, p. 570

Motor cortex activity

when speaking

Prefrontal cortex activity

when generating words

Visual cortex activity when

seeing written words

Connections With the Limbic System

The cerebral cortex oversees the limbic system

Limbic system

• Governs emotions, assists in memory, correlates

emotional-visceral responses

• Includes the hypothalamus, hippocampus,

amygdala, and cingulate gyrus

Limbic System Components

Fig. 33-24, p. 571

(olfactory

tract)

cingulate gyrus thalamus hypothalamus

amygdala

hippocampus

Making Memories

The cerebral cortex receives information and

processes some of it into memories

Memory forms in stages

• Short-term memory lasts seconds to hours

• Long-term memory is stored permanently

• Skill memory involves the cerebellum

• Declarative memory stores facts and impressions

Stages in Memory Processing

Fig. 33-25, p. 571

Sensory stimuli, as from

the nose, eyes, and ears

Temporary storage in

the cerebral cortexInput forgotten

SHORT-TERM MEMORY

Emotional state, having time

to repeat (or rehearse) input,

and associating the input with

stored categories of memory

influence transfer to long-term

storage

Recall of

stored

input

LONG-TERM MEMORYInput irretrievable

Fig. 33-25, p. 571

Sensory stimuli, as from

the nose, eyes, and ears

Temporary storage in

the cerebral cortex

SHORT-TERM MEMORY

Emotional state, having time

to repeat (or rehearse) input,

and associating the input with

stored categories of memory

influence transfer to long-term

storage

LONG-TERM MEMORYInput irretrievable Stepped Art

Input forgotten

Recall of

stored

input

33.12 The Split Brain

Investigations by Roger Sperry into the

importance of information flow between the

cerebral hemispheres showed that the two

halves of the brains have a division of labor

Typically, math and language skills reside in the

left hemisphere; the right hemisphere interprets

music, spatial relationships, and visual inputs

Visual Information and the Brain

Fig. 33-26, p. 572

Left Half of

Visual FieldRight Half of

Visual FieldCOWBOY COW BOY

pupil

optic

nervesretina

optic

chiasm

corpus

callosum

left

visual

cortex

right

visual

cortex

Animation: Path to visual cortex

Split-Brain Studies

33.13 Neuroglia—

The Neurons’ Support Staff

Neuroglial cells make up the bulk of the brain

The adult brain has four types of neuroglial cells

• Oligodendrocytes make myelin

• Microglia have immune system functions

• Astrocytes secrete various substances, take up

neurotransmitters, assist in immune defenses,

and stimulate formation of the blood-brain barrier

• Ependymal cells line brain cavities

Astrocytes

About Brain Tumors

Unlike neurons, neuroglia continue to divide in

adults, and can be a source of primary brain

tumors (gliomas)

Exposure to ionizing radiation such as x-rays, or

to chemical carcinogens, increases risk

33.10-33.13 Key Concepts

About the Brain

The brain develops from the anterior part of the

embryonic nerve cord

A human brain includes evolutionarily ancient

tissues and newer regions that provide the

capacity for analytical thought and language

Neuroglia make up the bulk of the brain

Animation: Action potential

Animation: Human brain development

Animation: Organization of the spinal

cord

Animation: Primary motor cortex

Animation: Regions of the vertebrate

brain

Animation: Structures involved in

memory

Animation: Synapse function

Animation: Synaptic integration

ABC video: New Nerves

Video: In pursuit of ecstasy

Video: Brain stem

Video: Limbic system dissection