chapter 16: sensory, motor, and integrative systems

Copyright 2009, John Wiley & Sons, Inc.

Chapter 16:

Sensory, Motor,

and Integrative Systems

Sensation

Conscious and subconscious awareness of

changes in the external or internal

environment.

Components of sensation: Stimulation of the

sensory receptor → transduction of the

stimulus → generation of nerve impulses →

integration of sensory input.



Classification of Sensory Receptors

General senses: somatic and visceral.

Somatic- tactile, thermal, pain and

proprioceptive sensations.

Visceral- provide information about conditions

within internal organs.

Special senses- smell, taste, vision, hearing

and equilibrium or balance.

Types of Sensory Receptors

Free nerve endings: pain and

thermoreceptors.

Encapsulated nerve endings: pacinian

corpuscles.

Separate cells: hair cells, photoreceptors and

gustatory receptor cells.


Generator Potential and Receptor

Potential Generator potential is produced by free nerve

endings, encapsulated nerve endings, and

olfactory receptors. When it reaches a

threshold, it triggers one or more nerve

impulses in the axon of a first-order sensory

neuron.

Receptor potential triggers the release of

neurotransmitter → postsynaptic potential →

action potential.


Sensory Receptors and their Relation-

ship to First-Order Sensory Neurons



Based on the Location

Exteroceptors

Interoceptors

Proprioceptors



based on the type of Stimulus Mechanoreceptors

Thermoreceptors

Nociceptors

Photoreceptors

Chemoreceptors

Osmoreceptors


Adaptation of Sensory Receptors

Rapidly adapting receptors: receptors that

detect pressure, touch and smell.

Slowly adapting receptors: receptors that

detect pain, body position, and chemical

composition of the blood.


Somatic Sensations

Sensory receptors in the skin (cutaneous

sensations), muscles, tendons and joints and

in the inner ear.

Uneven distribution of receptors.

Four modalities: tactile, thermal, pain and

proprioceptive.


Sensory Receptors in the Skin


Tactile Sensations

Include touch, pressure, vibration, itch and

tickle.

Tactile receptors in the skin are Meissner

corpuscles, hair root plexuses, Merkel discs,

Ruffini corpuscles, pacinian corpuscles, and

free nerve endings.


Meissner Corpuscles or Corpuscles of

Touch Egg-shaped mass of dendrites enclosed by a

capsule of connective tissue.

Rapidly adapting receptors.

Found in the dermal papillae of hairless skin

such as in the fingertips, hands, eyelids, tip of

the tongue, lips, nipples, soles, clitoris, and

tip of the penis.


Hair Root Plexuses

Rapidly adapting touch receptors found in the

hairy skin.

Free nerve endings wrapped around hair

follicles.

Detect movements on the skin surface that

disturb hairs.


Merkel Discs or Tactile Discs

Also known as type I cutaneous

mechanoreceptors.

Slowly adapting touch receptors.

Saucer-shaped, flattened free nerve endings.

Found in the fingertips, hands, lips, and

external genitalia.


Ruffini Corpuscles

Also called as type II cutaneous

mechanoreceptors.

Elongated, encapsulated receptors.

Located deep in the dermis and in ligaments

and tendons.

Found in the hands, and soles.


Pacinian or Lamellated Corpuscles

Large oval structure composed of a

multilayered connective tissue capsule that

encloses a dendrite.

Fast adapting receptors.

Found around joints, tendons, and muscles;

in the periosteum, mammary glands, external

genitalia, pancreas and urinary bladder.


Thermal Sensations

Thermoreceptors are free nerve endings.

Two distinct thermal sensations:

cold receptors-

warm receptors-


Pain Sensations

Protective.

Sensory receptors are nociceptors.

Free nerve endings.

Two types of pain: fast and slow.

Fast pain: acute, sharp or pricking pain.

Slow pain: chronic, burning, aching or

throbbing pain.


Referred Pain

Pain is felt in or just deep to the skin that

overlies the stimulated organ or in a surface

area far from the stimulated organ.


Distribution of Referred Pain


Proprioceptive Sensations

Receptors are called proprioceptors.

Slow adaptation.

Weight discrimination.

Three types: muscle spindles, tendon organs

and joint kinesthetic receptors.


Muscle Spindles

Interspersed among most skeletal muscle

fibers and aligned parallel to them.

Measure muscle stretching.

Consists of intrafusal muscle fibers-

specialized muscle fibers with sensory nerve

endings and motor neurons called gamma

motor neurons.

Extrafusal muscle fibers- surrounding muscle

fibers supplied by alpha motor neurons.


A Muscle Spindle and a Tendon

Organ


Tendon Organs

Located at the junction of a tendon and a

muscle.

Protect tendons and their associated muscles

from damage due to excessive tension.

Consists of a thin capsule of connective

tissue that encloses a few tendon fascicles.


Joint Kinesthetic Receptors

Found within or around the articular capsules

of synovial joints.

Free nerve endings and Ruffini corpuscles in

the capsules of joints respond to pressure.

Pacinian corpuscles respond to acceleration

and deceleration of joints during movement.


Somatic Sensory Pathways

First-order neuron(somatic receptor to the

brain stem/spinal cord)

→ second order neuron(brain stem/spinal cord

too the thalamus; decussate)

→ third-order neuron(thalamus to the primary

somatosensory area of the cortex).


Major Somatic Sensory Pathways

The posterior column-medial lemniscus

pathway.

The anterolateral (spinothalamic) pathway.

The trigeminothalamic pathway.

The anterior and posterior spinocerebellar

pathway.


The Posterior Column-Medial

Lemniscus Pathway Conveys nerve

impulses for touch,

pressure, vibration

and conscious

proprioception from

the limbs, trunk, neck,

and posterior head to

the cerebral cortex.


The Anterolateral (spinothalamic)

pathway Conveys nerve

impulses for pain,

cold, warmth, itch,

and tickle from the

limbs, trunk, neck,

and posterior head to

the cerebral cortex.


Trigeminothalamic Pathway

Conveys nerve

impulses for most

somatic sensations

from the face, nasal

cavity, oral cavity and

teeth to the cerebral

cortex.


Mapping of the Primary

Somatosensory Area Mapping of the

postcentral gyrus.

Size of the cortical

region representing a

body part depends on

the sensory impulses

received from that

part.


Somatic Motor Pathways

Upper motor neurons → lower motor neurons

→ skeletal muscles.

Neural circuits involving basal ganglia and

cerebellum regulate activity of the upper

motor neurons.


Organization of the Upper Motor

Neuron Pathways Direct motor pathway- originates in the

cerebral cortex.

Corticospinal pathway: to the limbs and trunk.

Corticobulbar pathway: to the head.

Indirect motor pathway- originates in the

brain stem.


Mapping of the Motor Areas

Located in the

precentral gyrus of

the frontal lobe.

More cortical area is

devoted to those

muscles involved in

skilled, complex or

delicate movements.


The Corticospinal Pathways


The Corticobulbar Pathway


Indirect or Extrapyramidal Pathways

Originate in the brain stem. Include:

Rubrospinal tract

Tectospinal tract

Vestibulospinal tract

Reticulospinal tract


Modulation of Movement from the

Cerebellum

The cerebellum coordinates and

smoothes contractions of skeletal

muscles during skilled movements and

helps maintain posture and balance.


Sagittal

plane

Motor areas of

cerebral cortex

Thalamus

Corrective

feedback

Motor centers in

brainstem

Pons

Pontine nuclei

Direct pathways

Indirect pathways

Signals to lower

motor neurons

Sagittal section through brain and spinal cord

Sensory signals from

proprioceptors in muscles

and joints, vestibular

apparatus, and eyes

Cortex of

cerebellum

1

Sagittal

plane

Motor areas of

cerebral cortex

Corrective

feedback

Pons

Direct pathways

Indirect pathways

Signals to lower

motor neurons





apparatus, and eyes

Cortex of

cerebellum

1

2

Thalamus

Motor centers in

brainstem

Pontine nuclei

Sagittal

plane

Motor areas of

cerebral cortex

Corrective

feedback

Pons

Direct pathways

Indirect pathways

Signals to lower

motor neurons





apparatus, and eyes

Cortex of

cerebellum

1

2

3

Thalamus

Motor centers in

brainstem

Pontine nuclei

Sagittal

plane

Motor areas of

cerebral cortex

Corrective

feedback

Pons

Direct pathways

Indirect pathways

Signals to lower

motor neurons





apparatus, and eyes

Cortex of

cerebellum

1

2

4

3

Thalamus

Motor centers in

brainstem

Pontine nuclei

Integrative Functions of the Cerebrum

Wakefulness and sleep-

Learning and memory-


The role of Reticular Activating

System (RAS) in Awakening Consists of neurons

whose axons project

from the reticular

formation through the

thalamus to the

cerebral cortex.

Increased activity of

the RAS causes

awakening from sleep

(arousal).


Sleep

A state of altered consciousness.

Two components: non-rapid eye movement

(NREM) sleep and rapid eye movement

(REM) sleep.

NREM sleep consists of four stages:

Stage 1-

Stage 2-

Stage 3-

Stage 4-


Learning and Memory

Learning is the ability to acquire new

information or skills through instruction or

experience.

Memory is the process by which information

acquired through learning is stored and

retrieved.


Memory Types

Immediate memory- recall for a few seconds.

Short-term memory- temporary ability to

recall.

Long-term memory- more permanent.

Memory consolidation.



End of Chapter 16

Copyright 2009 John Wiley & Sons, Inc. All rights reserved. Reproduction or translation of this work beyond that permitted in section 117 of the 1976 United States Copyright Act without express permission of the copyright owner is unlawful. Request for further information should be addressed to the Permission Department, John Wiley & Sons, Inc. The purchaser may make back-up copies for his/her own use only and not for distribution or resale. The Publishers assumes no responsibility for errors, omissions, or damages caused by the use of theses programs or from the use of the information herein.

chapter 16: sensory, motor, and integrative systems

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