b and b3 lec ppt_ch11

An Introduction to Brain and Behavior Third Edition

CHAPTER

How Does the Nervous System Respond to Stimulation and

Produce Movement?

11

PowerPoints prepared by: Paul Smaldino, UC Davis, Department of Psychology

Bryan Kolb & Ian Q. Whishaw

Kolb & Whishaw, An Introduction to Brain and Behavior, Third Edition - Chapter 11

How Does the Nervous System Respond to Stimulation and Produce Movement?

• Hierarchical Control of Movement

• Organization of the Motor System

• The Motor Cortex and Skilled Movements

• The Basal Ganglia and the Cerebellum

• Organization of the Somatosensory System

• Exploring the Somatosensory Cortex


Hierarchical Control of Movement

• Components of Hierarchy– Neocortex, brainstem, and spinal cord

– Normally functions as a whole

• Hughlings-Jackson (19th Century)– Conceived of nervous system as organized in

successive layers, with higher levels controlling complex behavior by acting through lower levels

– Adapted from evolutionary theory


Hierarchical Control of MovementThe Forebrain and Initiation of Movement

• Motor Sequence– Movement modules preprogrammed by the

brain and produced as a unit

– Karl Lashley (1950s)

• Frontal Lobes – Prefrontal Cortex: Planning of movements

– Premotor Cortex: Organizes motor sequences

– Primary Motor Cortex: Produces specific movements


Animals with damage to the premotor cortex cannot put motor sequences together


Measuring cerebral blood flow while performing various motor tasks


Hierarchical Control of MovementThe Brainstem and Species-Typical Movement

• Species-Typical Behavior– Actions produced by every member of a

species (e.g., hissing in cats)

• Hess (1950s) – Stimulating different areas within the

brainstem produced different species-specific behaviors

• Brainstem performs other behaviors as well (e.g., survival-related behaviors)


Hierarchical Control of MovementThe Brainstem and Species-Typical Movement

• Cerebral Palsy– Group of brain disorders that result from brain

damage acquired perinatally

• Autism Spectrum Disorder (ASD)– Range of cognitive symptoms that characterize

autism; severe symptoms include greatly impaired social interaction, a bizarre and narrow range of interests, marked abnormalities in language and communication, and fixed repetitive movements


Hierarchical Control of MovementThe Spinal Cord and Execution of Movement

• Quadriplegia– Paralysis of the legs and arms due to spinal

cord injury

• Paraplegia– Paralysis of the legs due to spinal cord injury

• Spinal Cord Reflexes– Movements that depend on the spinal cord

alone


Hierarchical Control of MovementThe Spinal Cord and Execution of Movement

• Scratch Reflex– Automatic response in which an animal’s hind

limb reaches to remove a stimulus from the surface of the body


Organization of the Motor SystemThe Motor Cortex

• 1870: Fritsch and Hitzig– Electrical stimulation of a dog’s cortex produced

movement of mouth, limbs, and paws

• 1930s: Wilder Penfield– Used electrical stimulation to map the cortices of

human patients who were about to undergo neurosurgery

– Confirmed the role of primary motor cortex in producing movement in humans



• Homunculus (little person)– Representation of the human body in the sensory

or motor cortex; also any topographical representation of the body by a neural area

• Topographic Organization– Neural spatial representation of the body or areas

of the sensory world perceived by a sensory organ

– The parts of the motor cortex that control the hands, fingers, lips, and tongue are disproportionately larger than parts of the motor cortex that control other areas


NOTE: More recent research suggests that there are as

many as 10 motor homunculi in the primary motor cortex

and supplementarymotor cortex.



Michael Graziano (2006)

• Electrical stimulation in conscious non-human primates elicits recognizable actions– The movement categories have the same end

regardless of the location of the monkey’s limb or its ongoing behavior

• The motor cortex represents three types of organization:– The part of the body that is to be moved, the spatial

location to which the movement is directed, and the movement’s function


Organization of the Motor SystemCorticospinal Tracts

• Corticospinal Tract– Bundle of nerve fibers directly connecting the

cerebral cortex to the spinal cord

– Branches at the brainstem into opposite-side lateral tract that controls movement of limbs and digits, and a same-side ventral tract that informs movement of the trunk

– Also called the pyramidal tract


Organization of the Motor SystemCorticospinal Tracts

• Lateral Corticospinal Tract– Branches at the brainstem level, crossing over to

the opposite side of the brain and spinal cord

– Moves the digits and limbs on the opposite side of the body

• Ventral Corticospinal Tract– Remains on the same side of the brain and spinal

cord

– Moves the muscles of the midline body (trunk) on the same side of the body


Organization of the Motor SystemMotor Neurons

• Two kinds of neurons located in the spinal column’s ventral horns– Interneurons project to motor neurons– Motor neurons project to muscles of the body

• Laterally located motor neurons project to the muscles that control the fingers and hands

• Intermediately located motor neurons project to muscles that control the arms and shoulders

• The most medially located motor neurons project to muscles that control the trunk


Organization of the Motor SystemControl of Muscles

• Limb muscles are arranged in pairs– Extensor

• Moves (extends) the limb away from the trunk

– Flexor• Moves the limb toward the trunk

• Connections between interneurons and motor neurons ensure that the muscles work together so that, when one muscle contracts, the other relaxes


The Motor Cortex and Skilled Movement

• Characteristics of motor cortex neurons (Evarts, 1968)– Planning and initiating movements

• Discharge before and during movements

– Code force of movements• Neurons increase their rate and duration of firing in

response to heavier weights

– Simple coding of movement direction• Flexor versus extensor muscles


The Motor Cortex and Skilled MovementControl of Skilled Movements in Nonhuman

Species

• Evolution has imbued each species with a cortical representation consistent with the appropriate sensorimotor demands of the animal


The Motor Cortex and Skilled MovementHow Motor-Cortex Damage Affects Movements

• Nudo and colleagues (1996)– Damaged part of motor cortex that controlled the

hand in monkeys – Without rehabilitation:

• The hand area of the motor cortex became smaller whereas the elbow and shoulder area became larger

• Monkeys lost most ability to move the hand

– With rehabilitation:• The hand area of the motor cortex retained its size• Monkeys retained some ability to move hand


The Basal Ganglia and the CerebellumThe Basal Ganglia and Movement Force

Basal Ganglia• Collection of subcortical nuclei within the forebrain

• Receives input from – All areas of the neocortex and limbic cortex

– The nigrostriatal dopaminergic system

• Project back to the motor cortex and substantia nigra

• Allow us to adjust the force of our movements



• Damage to the basal ganglia can produce two main types of motor symptoms

• Hyperkinetic Symptom– Symptom of brain damage that results in excessive

involuntary movements, as seen in Tourette’s syndrome

• Hypokinetic Symptom– Symptom of brain damage that results in a paucity

of movement, as seen in Parkinson’s disease



Volume Hypothesis• The internal globus pallidus acts like a volume

dial and projects to the thalamus, which projects to the motor cortex

• Two pathways within the basal ganglia– Direct

• Inhibitory: Too much activity leads to overactivity in the thalamus and amplified force of movement

– Indirect• Excitatory: Too much activity leads to underactivity in the

thalamus and reduced force of movement


The Basal Ganglia and the CerebellumThe Cerebellum and Movement Skill

Cerebellum

• Flocculus– Small but dense lobe involved in eye movements and

balance

• Two hemispheres– Homuncular organization

– Lateral parts • Controls movement of limbs, hands, feet, and digits

– Medial parts• Controls movement of face and midline of body


The Basal Ganglia and the CerebellumThe Cerebellum and Movement Skill

Two Main Motor Functions

1) Timing

• Movements and perceptions

2) Maintaining Movement Accuracy

• Error Correction – Compares intended movement with actual

movement and makes the necessary adjustments accordingly


Organization of the Somatosensory System

Somatosensory System

• Tells us what the body is up to and what’s going on in the environment by providing bodily sensations such as:– Touch, temperature, pain, position in space, and

movement of the joints

• Allows us to distinguish between what the world does to us and what we do to it

• It has a closer relationship with movement than the other senses do


Organization of the Somatosensory SystemSomatosensory Receptors and Perception

• Areas with larger numbers of receptors are more sensitive to stimulation than areas with relatively fewer receptors

• Sensitivity to different somatosensory stimuli is a function of the kinds of receptors

• Humans have two kinds of skin– Hairy skin

– Glabrous skin• Skin that does not have hair follicles but contains larger

numbers of sensory receptors than do other skin areas



Three Main Types of Somatosensory Perception

• Nocioception– Perception of pain and temperature

• Hapsis– Perception of fine touch and pressure

• Proprioception– Perception of the location and movement of the

body



• Somatosensory receptors tell us two things about a sensory event: when it occurs, and whether it is still occurring

• Rapidly Adapting Receptor– Body sensory receptor that responds briefly to the

beginning and end of a stimulus on the body

• Slowly Adapting Receptor– Body sensory receptor that responds as long as a

sensory stimulus is on the body


Organization of the Somatosensory SystemDorsal-Root Ganglion Neurons

• Dorsal-Root Ganglion Neuron– The dendrite and axon are continuous and carry

sensory information from the skin to the CNS via the spinal cord

– The tip of the dendrite is responsive to sensory stimulation

– Each spinal cord segment has one dorsal-root ganglion on each side that contains many dorsal-root ganglion neurons

– In the spinal cord, the axons of these neurons may synapse onto other neurons or continue up to the brain


Organization of the Somatosensory SystemDorsal-Root Ganglion Neurons

• Proprioceptive and Haptic Neurons– Carry in formation about location and movement

(proprioception) and touch and pressure (hapsis)

– Large, well-myelinated axons (fast)

• Nocioceptive Neurons– Pain and temperature information

– Small axons with little or no myelination (slow)

• Deafferentation– Loss of incoming sensory input usually due to damage

to sensory fibers; also loss of any afferent input to a structure


Organization of the Somatosensory SystemSomatosensory Pathways to the Brain

1) Dorsal Spinothalamic Tract– Carries haptic and proprioceptive information– Axons from the dorsal-root ganglion neurons enter

the spinal cord and ascend ipsilaterally until they synapse in the dorsal column nuclei (base of brain)

– Axons from the dorsal column nuclei cross over to the opposite side of the brain and project up through the brainstem as part of a pathway called the medial lemniscus

– Axons synapse with neurons located in the ventrolateral nucleus of the thalamus, which projects to the somatosensory cortex and motor cortex



2) Ventral Spinothalamic Tract– Carries nocioceptive information

– Axons from the dorsal-root ganglion neurons enter the spinal cord and cross over right away and synapse onto neurons on the contralateral side

– Axons from contralateral spinal cord then ascend to the brain where they join with other axons forming the medial lemniscus, eventually synapsing with neurons located in the ventrolateral nucleus of the thalamus

– Neurons from the thalamus then project to the somatosensory cortex



• Two Separate Pathways Convey Somatosensory Information– Haptic-proprioceptive

– Nocioceptive

• Because of this arrangement, unilateral spinal-cord damage results in distinctive sensory losses to both sides of the body below the site of injury


Organization of the Somatosensory SystemSpinal Reflexes

• Monosynaptic Reflex– Reflex requiring one synapse between sensory

input and movement

– Example: Knee-jerk reflex

• Other more complex spinal reflexes involve connections among sensory neurons, interneurons, and motor neurons (multisynaptic connections)


Organization of the Somatosensory SystemFeeling and Treating Pain

• Pain is a fact of life– 36% of patients visiting a physician’s office

complain of chronic pain

– Pain has many causes

• Pain is necessary– The occasional person born without pain

receptors experiences body deformities through failure to adjust posture and acute injuries through failure to avoid harmful situations



• Ventral spinothalamic tract is main pain pathway to the brain

• Other pain pathways from spinal cord to brain– Reticular formation, amygdala, and hypothalamus

– Cannot simply treat pain by severing the ventral spinothalamic pathway



• Pain Gate (Melzack & Wall, 1965)– Hypothetical neural circuit in which activity in fine-

touch and pressure pathways diminishes the activity in pain and temperature pathways

– May be located in the brainstem and cortex in addition to spinal cord

• Could explain how other approaches to pain relief work



• Periaqueductal Gray Matter (PAG)– Nuclei in the midbrain that surround the cerebral

aqueduct joining the third and fourth ventricles

– PAG neurons contain circuits for species-typical behaviors (e.g., female sexual behaviors) and play an important role in the modulation of pain

– Electrical stimulation of the PAG suppresses pain

• Referred Pain– Pain felt on the surface of the body that is actually

due to pain in one of the internal organs


Organization of the Somatosensory SystemThe Vestibular System and Balance

Vestibular system• Somatosensory system that comprises a set

of receptors in each inner ear that respond to body position and to the movement of the head



• Within each ear, there is a vestibular organ that contains:– Three semicircular canals– Otolith organs (utricle and saccule)

• Vestibular organs have two functions– Tell us the position of the body in relation to

gravity – Signal changes in the direction and speed of head

movements



• When the head moves, fluid (endolymph) located within the semicircular canals pushes against hair cells, which causes bending of the cilia located on top of the hair cells

• Bending of cilia leads to receptor potentials in the hair cells and action potentials in the cells forming the vestibular nerve

• The direction in which the cilia are bent determines whether the hair cell becomes depolarized or hyperpolarized



• The utricle and saccule also contain hair cells, which are embedded within a gelatin-like substance that contains small crystals of calcium carbonate called otoconia

• When the head is tilted, the gelatin and otoconia push against the hair cells, which alters the rate of action potentials in cells that form the vestibular nerve


Exploring the Somatosensory Cortex

Two main somatosensory areas in the cortex• Primary Somatosensory Cortex

– Receives projections from the thalamus

– Brodmann’s areas 3-1-2

– Begins the process of constructing perceptions from somatosensory information

• Secondary Somatosensory Cortex– Located behind the primary somatosensory cortex

– Brodmann’s areas 5 and 7

– Continues the construction of perceptions, prjects to the frontal cortex


Exploring the Somatosensory CortexThe Somatosensory Homunculus

• Just as with the motor cortex, Penfield’s original studies suggested that there was a single homunculus

• More recent work suggests that there are four separate somatosensory homunculi– Area 3a: Muscles

– Area 3b: Skin (slow)

– Area 1: Skin (fast)

– Area 2: Joints, pressure


Exploring the Somatosensory CortexEffects of Damage to the Somatosensory Cortex

• Damage to the primary somatosensory cortex results in impairment in:– Sensory thresholds, proprioception, hapsis

(ability to identify objects by touch), and simple movements (e.g., reaching and grasping)

• As with the motor cortex, reorganization following damage is possible– Example: Pons and colleagues (1991)

• Following damage to the arm, the cortex that was devoted to the hand becomes sensitive to the face


Exploring the Somatosensory CortexThe Somatosensory Cortex and Complex Movement

• Apraxia– Inability to make voluntary movements in the

absence of paralysis or other motor or sensory impairment, especially an inability to make proper use of an object


Exploring the Somatosensory CortexThe Somatosensory Cortex and Complex Movement

• Secondary Somatosensory Cortex – Involved in integrating information from the

sensory and motor systems

– Damage does not interfere with movement planning, but disrupts how the movements are performed

• Somatosensory Cortex– Contributes to movement by participating in both

the dorsal and ventral visual streams

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