Chapter 38

Nervous System

Learning Objectives

Describe the evolution of nervous system List the functions and location of the cerebrum,

thalamus, hypothalamus, midbrain, cerebellum, pons, medulla oblongata, basal nucleii, amygdala and hippocampus of the limbic system

Differentiate the somatic and autonomic systems

Diagram the spinal reflex circuit Differentiate functions of the left and right

hemisphere

Learning Objectives

Diagram the lobes of the cerebrum according to function and anatomy

Discuss the process of memory Debate the existence of consciousness Explain the various types of neurological

disorder incidence and symptoms

Invertebrate Nervous Systems (1)

Simplest nervous systems: The nerve nets of cnidarians

Echinoderms have modified nerve nets, with some neurons grouped into nerves

Invertebrate Nervous Systems (2)

Flatworms, arthropods, and mollusks have a simple central nervous system (CNS)Ganglia in the head region (brain)

Peripheral nervous system (PNS) Nerve cords from central ganglia to rest of body

Fig. 38.1c, p. 869

c. Planarian (flatworm)

Eyespot

Ganglia

Longitudinal nerve cords

Fig. 38.1d, p. 869

d. Arthropod (grasshopper)

Dorsal ganglia

Ventral ganglion

Ganglia of ventral nerve cord

Fig. 38.1e, p. 869

e. Mollusk (octopus)

Ganglia associated with internal organs

Optic lobe

Frontal lobes

Lobed brain

Eye

Chordate Nervous Systems

CNS Large brain located in the headHollow spinal cord

PNS All the nerves and ganglia connecting CNS to the

rest of the body

Development in Vertebrates

Vertebrate embryoAnterior end of neural tube develops into brain Rest develops into spinal cord

Embryonic brain enlarges into forebrain, midbrain, and hindbrainDevelop into adult structures

Fig. 38.2a, p. 870

Regions in 4-week embryo

Regions in 5-week embryo

Regions in adult

Functions in adultNeural tube

Telencephalon Telencephalon (cerebrum)

Higher functions, such as thought, action, and communication

Forebrain Diencephalon ThalamusCoordinates sensory input and relays it to cerebellum

Hypothalamus Center for homeostatic control of internal environment

Midbrain Mesencephalon Midbrain Coordinates involuntary reactions and relays signals to telencephalon

Hindbrain Metencephalon CerebellumIntegrates signals for muscle movement

Pons Center for information flow between cerebellum and telencephalon

MyelencephalonMedulla oblongata

Controls many involuntary tasks

Fig. 38.2e, p. 870

Hemisphere of cerebrum

Hypothalamus

Thalamus

Brain stem: Midbrain

Cerebellum

Spinal cord Central canal

Adult brain regions

Pons

Medulla oblongata

The Peripheral Nervous System

Somatic system controls skeletal musclesVoluntary body movements Involuntary muscle contractions that maintain

balance, posture, muscle tone

Autonomic system controls involuntary functions Sympathetic systemParasympathetic system

Fig. 38.4, p. 872

Parasympathetic Division Sympathetic Division

Constricts pupil; adjusts eye for near vision

EyesDilates pupil; adjusts eye for far vision

Optic nerveEyes

Cranial nervesStimulates secretion

Salivary glands Salivary

glands Inhibits secretion

Vagus nerveDecreases

heart rate Heart Heart Increases heart rate

Constricts bronchioles (airways)

LungsLungs Dilates

bronchiolesStimulates stomach activity

StomachStomach Inhibits stomach

activityInhibits glucose release

LiverLiver

Stimulates glucose release

Stimulates activity

IntestinesIntestines Inhibits activity

Stimulates contraction (emptying)

Bladder Bladder Relaxes bladder muscles

Stimulates penile or clitoral arousal

Chain of sympathetic

ganglia

Genitals GenitalsInhibits penile or clitoral arousal

Spinal nerves

The Spinal Cord

Carries signals between the brain and the PNS

Its neuron circuits control reflex muscular movements and some autonomic reflexes

Fig. 38.5, p. 873

1 A pain receptor in the finger stimulates an afferent neuron.

2 The afferent neuron transmits the impulses to the spinal cord.

3 Interneurons integrate the information. Interneuron

connections leading to brain

Integrating interneurons in spinal cord

Stimulus Ganglion

Spinal nerve

Central canal

Gray matter

White matter

Response Biceps muscle (flexor) contractsHand

withdrawn

4 One efferent neuron stimulates the flexor muscle to contract.

Effector5 The other efferent neuron sends inhibitory signals that keep the extensor muscle from contracting.6 The flexor contracts,

withdrawing the hand from the pain.

Triceps muscle (extensor) relaxes

Major Brain Structures

Cerebrum

Brain stemMedulla Pons Midbrain

Thalamus and hypothalamus

Structures of the Cerebrum

Right and left cerebral hemispheresConnected by corpus callosum

Cerebral cortex Thin gray matter covering core of white matter

Basal nucleiCollections of gray matter deep in telencephalon

Protecting the CNS

Cerebrospinal fluid provides nutrients and cushions the CNS

A blood-brain barrier allows only selected substances to enter the cerebrospinal fluid

Fig. 38.6, p. 874

Layer of cerebrospinal fluid between meninges

Ventricles

Central canal of spinal cord

Cerebral cortex (gray matter)

White matter

Corpus callosum

Basal nuclei (gray matter)

ThalamusVentricles

Right cerebral hemisphere

Left cerebral hemisphere

Functions of the Brain Stem

Gray-matter centers in pons and medulla control involuntary functions

Centers in midbrain coordinate responses to visual and auditory sensory inputs

Reticular formation Receives sensory inputs from the bodySends outputs to cerebral cortex that help maintain balance,

posture, muscle toneRegulates states of wakefulness and sleep

Fig. 38.8, p. 875

Midbrain

PonsCerebellum

Reticular formation

Medulla

Fig. 38.7, p. 875

Front of brain

Functions of the Cerebellum

Integrates sensory inputs to coordinate body movementsPositions of muscles and jointsVisual and auditory information

The Telencephalon’s Subcortical Gray-Matter Centers Thalamus

Receives, filters, and relays sensory and motor information to/from regions of cerebral cortex

Hypothalamus Regulates basic homeostatic functions of body Contributes to endocrine control of body functions

Basal nuclei Affect fine-tuning of body movements

The Limbic System

StructuresParts of thalamus, hypothalamus, basal nuclei Amygdala and hippocampus

FunctionsControls emotions Influences basic body functions controlled by

hypothalamus and brain stem

Fig. 38.9, p. 876

Cerebrum

Thalamus Gathers sensory information before distribution to higher areas

Basal nuclei

Olfactory bulbs

Hypothalamus Amygdala Controls emotions, activates “fight or flight” self-preservation reactions

Hippocampus Involved mainly with memory

The Cerebral Cortex

Primary somatosensory areas Register information on touch, pain, temperature,

and pressure from all parts of the bodyRight cerebral hemisphere receives sensory

information from left side of body and vice versa Primary motor areas control voluntary

movements of skeletal muscles

Fig. 38.11, p. 878

Front

Primary somatosensory area of left hemisphere

Primary motor area of left hemisphere

Back

Cross-sectional view Cross-sectional view

Left hemisphere

Lefthemisphere

Association Areas of Cerebral Cortex Integrate sensory information and formulate

responses passed on to primary motor areas Wernicke’s area

Integrates visual, auditory, other sensory information into comprehension of language

Broca’s area Coordinates movements of lips, tongue, jaws,

other structures to produce sounds of speech

Fig. 38.10, p. 877

General motor association area

Primary motor area

Frontal Association area(planning,personality)

Primary somatosensory area

General sensory association area

Parietal lobeFrontal

lobeTaste

Wernicke’s area (understanding language)

Visual association area

SmellTemporal lobe

Occ

ipita

l lo

be

Broca’s area (expressing language)

Primary visual cortex (visual input)

Auditory area (hearing input)

Auditory association area

Facial recognition area (on inner side of cortex)

Cerebellum

Brain stem

Lateralization of the Cerebral Hemispheres Left hemisphere functions

Spoken and written language, abstract reasoning, precise mathematical calculations

Right hemisphere functionsNonverbal conceptualizing, mathematical estimation, intuitive

thinking, spatial recognition, artistic and musical abilities

Equal functionsLong-term memory and consciousness

Memory

Storage and retrieval of a sensory or motor experience or thought

Short-term memory involves temporary storage of information

Long-term memory is essentially permanent

Learning

Modification of a response through comparisons made with information or experiences stored in memory

Consciousness

Awareness of ourselves, our identity, and our surroundings

Varies through states from full alertness to sleep

Controlled by the reticular activating system

Fig. 38.13, p. 882

Awake (beta waves)

Eyes closed, relaxed (alpha waves)

Dozing (theta waves)

Deep sleep (delta waves)

Time (sec)

Major Diseases of the Brain

Autism Spectrum Disorder ADHD Alzheimer’s Disease/Dementia Schizophrenia

Autism Spectrum Disorder

In 2006, 1% or one child in every 110 was classified as having an ASD

Males: 1:70; females: 1:315. Increased 57% from 2002

(Rice, December 18, 2009 / 58(SS10);1-20).

ASD

People with autistic disorder usually have significant language delays, social and communication challenges, and unusual behaviors and interests

People with Asperger syndrome usually have some milder symptoms of autistic disorder.  They might have social challenges and unusual behaviors and interests.  However, they typically do not have problems with language or intellectual disability.

ADHD

4.5 million children 5-17 years of age have ever been diagnosed with ADHD as of 2006.

3%-7% of school-aged children suffer from ADHD. Some studies have estimated higher rates in community samples

Boys (9.5%) are more likely than girls (5.9%) to have been diagnosed with ADHD. Diagnosis of ADHD increased an average of 3% per year from 1997 to 2006

(http://www.cdc.gov/ncbddd/adhd/data.html)

Types of ADHD

Predominantly Inattentive Type: Lack of organization or finish a task, Unable to pay attention to details, or to follow instructions or conversations. Easily distracted or forgets details of daily routines.

  Predominantly Hyperactive-Impulsive Type: fidgets and talks a lot. hard to sit still for long (e.g., for a meal or while doing homework). Smaller children may run, jump or climb constantly. Feels restless and has trouble with impulsivity. May interrupt others a lot, grab things from people, or speak at inappropriate times  Combined Type: Symptoms of the above two types are equally present in the person

Alzheimer’s Disease/Dementia

About 5% ages 65-74 year old About 50% over 80 years old An estimated 5 million Americans have Alzheimer’s

disease. This number has doubled since 1980 It is expected to be as high as 13.4 million by 2050 Individuals with Alzheimer’s disease make up less than

13 percent of the Medicare population, yet they account for 34 percent of Medicare spending.*

How old will you be in 2050? Who is paying the bill?

Schizophrenia

Affects 1.1 percent of the population Onset usually after age 18 Later in women Often addicted to nicotine and other

substances Genetically linked

Symptoms

Positive: Hallucinations (voices are common) Delusions (religious or alien, or authority) Thought disorders Movement disorders Negative: Absence of pleasure, planning, enjoyment (affect),

speaking, etc. Cognitive defects: Little understanding, trouble focusing, and little memory