Copyright 2010, John Wiley & Sons, Inc. Chapter 15 Sensory, Motor and Integrative Systems.

Copyright 2010, John Wiley & Sons, Inc.

Chapter 15Sensory, Motor and Integrative Systems


Chapter 15: Sensory, Motor and Integrative SystemsThe work of the nervous system requires that information be

collected, processed, and acted upon:

Sensory systems respond to stimuli by sending signals to the CNS

Integrative systems (within the CNS) process and evaluate the sensory information in a process called integration

Motor systems carry signals from the CNS to effectors, and makes sure that motor output is coordinated for efficient responses


Sensory Information: Basic Terminology Some terms used to describe sensory information

Sensory modality refers to the type of sensation (touch, vision, etc.)

The special senses include five key types of sensory input, all originating in the head (smell, taste, vision, hearing, and balance)

The general senses include input from throughout the body Somatic senses (input from skin and musculoskeletal system) Visceral senses (input from internal organs)

Sensation - conscious or subconscious awareness Perception - awareness plus interpretation of sensory

information


The Process of Sensation■ Four events typically involved when a sensation happens

1.A sensory receptor is stimulated

2.The sensory receptor transduces the sensory stimulus – creating a graded potential in response to a specific type of stimuli

3.The sensory neuron creates one or more nerve impulses which travel toward the CNS

4.Integration of the sensory input occurs in specific regions of the CNS


Three Structural Classes of Sensory Receptors ■ Sensory receptors vary structurally in how the stimulus is received—by free nerve endings, by encapsulated nerve endings, or by specialized sensory receptor cells


Three Structural Classes of Sensory Receptors


Classification of Sensory Receptors Classification by

location (at the body surface, inside the body, in muscles and joints)

Classification by the type of stimulus (light, heat, etc)


Sensory Receptors: Adaptation Most sensory receptors adapt to a constant stimulus, by

decreasing their response and sending fewer action potentials to the CNS Rapidly adapting receptors decrease their responses quickly.

These receptors help the nervous system monitor changes in the environment

Slowly adapting receptors decrease their responses slowly, and continue to send action potentials as long as the stimulus lasts. These receptors help monitor tension in postural muscles, pain, and blood chemistry


Somatic Sensations

Somatic (“of the body”) sensations arise from body surfaces, muscles and joints Tactile sensations

Thermal sensations

Pain

Proprioception

Somatic sensations arising from the skin are known as cutaneous sensations


Somatic Sensations


Tactile Sensations

Tactile receptors in the skin include Corpuscles of touch (also called Meissner corpuscles)

Hair root plexuses

Mechanoreceptors Merkel discs Ruffini corpuscles

Lamellated corpuscles also called Pacinian corpuscles)

Free nerve endings


Tactile Sensations


Thermal Sensations

We have two different classes of thermal receptors located in the dermis Cold receptors respond to low temperatures (10–40 C)

Warm receptors respond to a higher temperature range

(32–48C)

Temperatures outside of the ranges above primarily stimulate nociceptors (pain)


Pain Pain sensations (or just “pain”) is how we learn about

things that are harmful. Pain serves a protective function, since it motivates us to avoid harmful stimuli

Nociceptors are free nerve endings found everywhere in the body (except the brain). Nociceptors have several unusual properties

Nociceptors are activated by multiple types on stimuli

Many chemicals can stimulate nociceptors, and/or sensitize them to other stimuli - in this way pain plays a major role in inflammation

Nociceptors adapt poorly, allowing pain to continue


Types of Pain Painful sensations can be described by how quickly

they appear, and by where in the body they originate

Fast pain is perceived rapidly (< 0.1 second). Fast pain includes acute, sharp, and prickly sensations.

Slow pain is perceived more slowly (after 1 second or more), and gradually increases in intensity. Slow pain includes chronic, burning, aching, and throbbing sensations.


Types of Pain Superficial somatic pain arises from nociceptors in the skin

Deep somatic pain arises from nociceptors in muscles, joints, tendons, ligaments, and fascia

Visceral pain arises from stimulation of nociceptors in visceral organs


Localization of Pain Fast pain is precisely localized - we know exacty where

the stimulus is Slow pain has a more general localization - we can only

localize the stimulus to a broader region of the body In referred pain, the pain is perceived to arise from

surface tissues that share neural pathways with the visceral source of the pain


Localization of Pain


Proprioception Proprioceptive sensations allow us an awareness of

where our head and limbs are, and where they are going; these sensations are critical for the precise control of body movements

Proprioceptors inform us about several categories of mechanical stimuli

The degree to which muscles are stretched The tension in tendons, and the position of our joints The position and movements of our head

Proprioceptors adapt only slightly, and feedback from propriceptors allows us to adjust our movements to match changing physical challenges


Muscle Spindles Muscle spindles are proprioceptors located within

skeletal muscles

The length of the muscl is monitored

Muscle spindles are involved in the stretch reflex, and help maintain muscle tone

Muscle spindles contain a mechanism for maintaining their own level of tension - this ensures sensitivity at all muscle lengths


Muscle Spindles


Other Proprioceptors Tendon organs are located where tendons meet

muscle The level of tension in the tendon is monitored Excessive tension results in reflexive muscle relaxation,

protecting the muscle from damage

Joint kinesthetic receptors (not shown) are located within and around synovial joint capsules These receptors provide feedback on joint position


Other Proprioceptors


Somatic Sensory “Map” in the Cerebral Cortex The primary somatosensory area is in the postcentral

gyrus of the parietal lobe Body regions are “mapped” to specific regions Extensive sensory input from some regions (e.g., lips,

hands) results in larger cortical regions representing them

The left side of the body maps to the right cerebral cortex, and vice versa


Somatic Sensory “Map” in the Cerebral Cortex


Somatic Motor “Map” in the Cerebral Cortex The primary motor area is in the precentral gyrus of the

frontal lobe

Major region for control of voluntary movements

Larger cortical areas exist for detailed motor control

Just anterior to the primary motor area is the premotor area of the frontal lobe


Somatic Motor “Map” in the Cerebral Cortex


Somatic Sensory Pathways Somatic sensory pathways carry information from the

body to the somatosensory cortex, and to the cerebellum Sets of three neurons carry information along the

pathways First-order neurons carry signals as far as the spinal cord or

brainstem

Second-order neurons carry signals on to the thalamus

Third-order neurons travel from the thalamus to the cerebral cortex

CNS regions where the three neurons synapse with each other are know as relay stations - these include the spinal cord, regions of the brainstem, and the thalamus



Sensory Pathways: The Posterior Column Pathway This pathway carries information from touch, vibration, and proprioceptors First-order neurons travel via the posterior column of the spinal

cord to the medulla oblongata

Second-order neurons cross to the opposite side of the medulla, then ascend via the medial lemniscus to the thalamus

Third-order neurons project from the thalamus to the cerebral cortex


Sensory Pathways:The Posterior Column Pathway


Sensory Pathways: The Anterolateral Pathway

This pathway carries information for pain, temperature, itch, and tickle sensations First-order neurons travel to the spinal cord and synapse in

the posterior gray horn

Second-order neurons cross to the opposite side of the spinal cord, then ascend in the spinothalamic tract to the thalamus

Third-order neurons project from the thalamus to the cerebral cortex


Sensory Pathways:The Anterolateral Pathway


Somatic Sensory PathwaysInteractions Animation

Somatic Sensory Pathways

You must be connected to the internet to run this animation.

http://www.wiley.com/college/jenkins/0470227583/animations/index_15_05_01.html


Sensory Pathways to the Cerebellum The cerebellum helps us maintain our balance and posture, and execute skilled movements - all requiring extensive input from proprioceptors

Input to the cerebellum is not consciously perceived Input to the cerebellum travels via two pathways

Posterior spinocerebellar tract Anterior spinocerebellar tract


Sensory Pathways to the Cerebellum


Somatic Motor Pathways Skeletal muscles are innervated by lower motor

neurons, located in either the spinal cord or the brainstem

Axons of lower motor neurons travel via either spinal nerves or cranial nerves to reach the muscles they innervate



Somatic Motor Pathways Many other neurons help determine the activity of lower

motor neurons

Local circuit neurons help control rhythmic activities

Upper motor neurons help maintain muscle tone, posture and balance

Basal nuclei neurons help begin and end movements

Cerebellar neurons helps coordinate the actions of different muscles


Upper Motor Neuron Pathways

Direct motor pathways descend from the cerebral cortex to lower motor neurons

Lateral corticospinal tract

Anterior corticospinal tract

Corticobulbar tract

Indirect motor pathways (not shown) descend from the brainstem


Upper Motor Neuron Pathways


Modulation of Movement by the Basal Nuclei The basal nuclei play a key role in the initiation and

termination of movements: They receive input from various cortical areas They provide feedback to the motor cortex (by way of the thalamus) They also help suppress unwanted movements, and influence

muscle tone

Sagittalplane

Motor areas ofcerebral cortex

Thalamus

Correctivefeedback

Motor centers inbrainstem

Pons

Pontine nuclei

Direct pathways

Indirect pathways

Signals to lowermotor neurons

Sagittal section through brain and spinal cord

Sensory signals fromproprioceptors in musclesand joints, vestibularapparatus, and eyes

Cortex ofcerebellum

1

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

Thalamus


Pontine nuclei

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

3

Thalamus


Pontine nuclei

Sagittalplane


Correctivefeedback

Pons

Direct pathways

Indirect pathways




Cortex ofcerebellum

1

2

4

3

Thalamus


Pontine nuclei


Modulation of Movement by the Cerebellum The cerebellum helps us maintain posture and balance, as well as learn complex motor skills

Four steps in cerebellar activity

1. Monitors intentions for movement

2. Monitors actual movement

3. Compares command signals with sensory information

4. Sends out corrective feedback


Modulation of Movement by the Cerebellum


Integrative Functions: Wakefulness and Sleep Our sleep-wake cycles are connected to a 24-hour

circadian rhythm which originates in the hypothalamus The reticular activating system (RAS) is a diffuse series of

brainstem nuclei that help us transition between sleep and being awake

The state of wakefulness is also referred to as consciousness Sleep is a state of partial unconsciousness from which we can be

aroused


Integrative Functions: Wakefulness and Sleep


Integrative Functions: Learning and Memory Learning is the acquisition of new information or skills - we learn by instruction or experience

Memory is the process of storing and retrieving the information we learn

Memory must involve structural and functional changes in brain neurons

Areas of the brain involved in memory include association areas, the thalamus and hypothalamus, and parts of the limbic system


Integrative Functions: Memory Occurs in Stages Memory occurs in several stages, over distinct time

periods

Immediate memory gives us knowledge of our current surroundings (duration: one to a few seconds)

Short-term memory allows immediate recall of information (duration: seconds to minutes)

Long-term memory allow retrieval of much older information (duration: days to years)


Integrative Functions: Memory Occurs in Stages Memories for complex motor skills are a special

category of long-term memory, and seem to be stored in the basal nuclei and cerebellum in addition to the cerebral cortex

A number of clinical conditions disrupt retention of recent memory, and in the worst cases can result in amnesia


End of Chapter 15

Copyright 2010 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 these programs or from the use of the information herein.

Date post:	20-Jan-2016
Category:	Documents
Upload:	jewel-webster
View:	218 times
Download:	0 times

Copyright 2010, John Wiley & Sons, Inc. Chapter 15 Sensory, Motor and Integrative Systems.

Documents