The cerebral cortex has four lobes, each is specialized for different activities.

• The lobes and some of their functions:– Occipital lobe- initial processing of visual input

– Temporal lobe - primary auditory cortex, integration of multiple sensory inputs, Wernicke’s area

– Parietal lobe - somatosensory processing. Each region of parietal cortex receives somesthetic and proprioceptive input from a specific body area, mostly from the opposite side of the body.

– Frontal lobe - voluntary motor activity, speaking ability (Broca’s area), and elaboration of thought. Stimulation of different areas of its primary motor cortex moves different body regions.

Frontallobe

Central sulcus

Parietallobe

Parietooccipitalnotch

Occipitallobe

Cerebellum

Brain stem

Temporallobe

Lateralfissure

Occipital lobe

Primary visual cortex

Wernicke’s area

Temporal lobe

Primary auditory cortex

Centralsulcus

Somatosensory cortex

Posterior parietal cortex

Wernicke’s area

Parietal lobe

Lefthemisphere

Cross-sectional view

Temporal lobe

Sensory homunculus

Primary motor cortex

Centralsulcus

Broca’s area

Frontal lobe

Premotor cortex

Lefthemisphere

Cross-sectional view

Temporal lobe

Motor homunculus

Centralsulcus

Parietal-temporal-occipitalassociation cortex

Limbic association cortex

Prefrontal association cortex

Association areas of the cortex carry out many higher functions:Association Areas of the Cerebral Cortex

planning for voluntary activity, decision-making,

creativity, and developing

personality traitsintegrates somatic,

auditory, and visual sensations from these three

lobes

involved with motivation, emotion, and

memory

Sensory input

Primary sensory areas(somatosensory, 1o visual, 1o auditory cortices)

Higher sensory areas

Association areas

Higher motor areas

Primary motor areas

Motor output

Fundamentals of Sensory Systems

A. General Concepts in Sensation and PerceptionFunction of sensory systemsVisceral versus sensory afferentsSensation versus perceptionPsychophysics

B Receptor Structure and FunctionSpecific for particular forms of energyVary across sensory systemsPerform common function (transduction) in unique waysSites of convergence and divergence

C. Peripheral OrganizationLabeled Line PrincipleTopographic projectionsMechanisms to enhance contrast sensitivity

• Central ProcessingIncludes sensory cortex and association areasResponse Maps and Plasticity

Variable perceptions from the same visual inputDo you see two faces in profile, or a wine glass?

Do you “see” a white square that is not really there?

Receptor Morphologies Reflect Specialized Functions

PhotoreceptorsMechanoreceptorsThermoreceptorsOsmoreceptorsChemoreceptorsNociceptors

CATEGORIES OF RECEPTORS

Receptor Potentials are GRADED

Generator potential: SomatosensoryReceptor potential: Auditory/Visual

Stimulus off

Slowly adapting

Stimulus on

Time

Receptorpotential(mV)

Stimulusstrength

Tonic ReceptorsMuscle Stretch, Proprioception

Stimulus off

Rapidlyadapting

Stimulus on

Time

Receptorpotential(mV)

Stimulusstrength

Off response

Phasic Receptorsskin touch

Doctrine of Specific Energyor

Labeled Line Principle

“Phantom”

Pain

Coding of Sensory Information

Stimulus Property Coding Mechanism

Stimulus Modality Distinguished by the type of receptor activated (what) and the specific pathway that transmits

this information to a particular area of (sensory)cerebral cortex

Stimulus Location Distinguished by location of activated receptive (where) field, and the pathway that is activated to

transmit this information to the area ofcerebral cortex representing that location.

Stimulus Intensity Distinguished by the frequency of action (how much?) potentials and the number of receptors

activated.

Receptor endingsof afferent neurons

Receptive fieldson skin surface

Receptive Field Size Determines Acuity

Sensory homunculus

Stimulated less Stimulated less

Stimulated most

Receptorpathways

Skin surface

Frequencyof action

potentials

Baselinelevel ofactivity

Location on skin

Mechanisms To

Enhance Acuity

Transmissionstopped

Lateralinhibition

Frequencyof action

potentials

Baselinelevel ofactivity

Area of sensation on skin

Transmissionstopped

Transmission continues

Center/Surround Organization of Receptive Fields

Sensory Pathways: CNS

Primary Sensory and Association Areas of Cerebral Cortex

Practical Applications