Module 11 How Does the nervous System Respond to Stimulation and Produce Movement? Flashcards
Neuroprosthetics
-Field that develops computer-assisted device to replace lost biological function
Motor Sequence
-Movement modules preprogrammed by the brain and produced as an unit`
Locked-in syndrome
Condition in which a patient is aware and awake but cannot move or communicate verbally muscles except the eyes
Cerebral Palsy (CP)
-Group of disorders that result from brain damage acquire perinatally (at of near birth)
Quadriplegia
-Paralysis of the legs and arms due to spinal cord injury
Paraplegia
-Paralysis of the legs due to spinal cord injury
Scratch Reflex
-Automatic response in which an animal’s hind limb reaches to remove a stimulus from the surface of its body
Homunculus
-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
Position-point theory
-Idea that the motor cortex allows an appropriate part to be moved to a point in space
Constraint-induced therapy
-Procedure in which restraint of healthy limb forces a patient to use an impaired limb to enhance recovery of function
Corticospinal tract (Pyramidal Tract)
-Bundle of nerve fibers directly connecting the cerebral cortex to the spinal cord, branching at the brainstem into an opposite-site lateral tract that informs movement of limbs and digits and a same-side anterior tract that informs movement of the trunk
Hyperkinetic Symptom
-Excessive involuntary movement, as seen in Tourette Syndrome
Hypokinetic Stmptom
-Paucity of movement, as seen in Parkinson disease
Glabrous Skin
-Skin that does not have hair follicles but contains larger numbers of sensory receptors than do hairy skin areas
Nociception
-Perception of pain, temperature, and itch
-Hapsis
-Perceptual ability to discriminate objects on the basis of touch
Proprioception
-Perception of the position and movement of the body, limbs, and head
Rapidly adapting receptor
-Body sensory receptor that responds briefly on the onset of a stimulus on the body
Deafferentation
-Loss of incoming sensory input; usually due to damage to sensory fibers; also loss of any afferent input to a structure
Posterior Spinothalamic tract
-Pathway that carries fine-touch and pressure fiber toward the brain
Ventrolateral Thalamus
-Part of the thalamus` that carries information about body senses to the somatosensory cortex
Anterior Spinothalamic Tract
-Pathway from the spinal cord to the thalamus that carries information about pain and temperature toward the brain
Monosynaptic Reflex
-Reflex requiring one synapse between sensory input and movement
Pain Gate
-Hypothetical neural circuit in which activity in fine-touch and pressure pathways diminishes the activity in pain and temperature pathways
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 (female sexual behavior) and play an important role in the modulation of pain
Referred Pain
-Pain that arises in one of the internal organs but is felt on the surface on the body
Vestibular System
-Somatosensory system comprising a set of receptors in each inner ear that respond to body position and to movement of the head
Meniere disease
-Disorder of the middle ear resulting in vertigo and loss of balance
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
How Does the Nervous System Respond to Stimulation and Produce Movement?
- Hierarchy of Movement Control
- Motor System Organization
- Basal Ganglia, Cerebellum and Movement
- Organization of the Somatosensory System
- Exploring the Somatosensory Cortex
Hierarchy of Movement Control
-Major components of the motor system:
~Cerebrum (forebrain): conscious control of movement
~Brainstem: automatic movements
~Spinal cord: automatic movements
-With impaired brainstem or spinal-cord function, the forebrain can imagine movements but can no longer produce them.
-Other regions of the motor system:
~Subcortical basal ganglia helps to produce the appropriate amount of force for grasping.
~The cerebellum helps to regulate the timing and accuracy of movement.
Relating the Somatosensory and Motor Systems
-Afferent somatosensory information travels from the body inward via the somatic nervous system.
-Movement information travels out of the central nervous system via a parallel, efferent motor system.
-Information coming from sensory receptors comes into the CNS via dorsal root fibers.
-Fibers leaving the spinal cord’s ventral side carry information out from the spinal cord to the muscles.
~They, too, bundle together as the fibers exit the spinal cord, forming a ventral root.
-Spinal Segments and Dermatomes
~Each spinal segment corresponds to a region of body surface called a dermatome.
-Layering in the Neocortex
~Layer IV (afferent) is relatively thick in the sensory cortex but relatively thin in the motor cortex.
~Layer V (efferent) is relatively thick in the motor cortex and relatively thin in the sensory cortex.
Forebrain and Initiation of Movement
-Lashley (1951)
~After we act, we wait for feedback about how well the action has succeeded, then we make the next movement accordingly.
~Movements must be performed as motor sequences, with one sequence held in readiness while an ongoing sequence is being completed.
~As one sequence is being executed, the next sequence is being prepared so that it can follow the first smoothly.
Initiating a Motor Sequence
-Motor Sequence
~Movement modules preprogrammed by the brain and produced as a unit
-Frontal Lobes
~Prefrontal Cortex: plans complex behavior
~Premotor Cortex: produces the appropriate complex movement sequences
~Primary Motor Cortex: specifies how each movement is to be carried out
Mirror Neurons
-Allow us to produce movement sequences and also to observe, understand, and copy the movement sequences of others.
-Function in premotor cortex:
~They discharge when we perform an action such as reaching for food.
~They discharge when we observe another individual performing a movement, even though we may be making no movement at all.
~They can also discharge if we simply think about performing the movement.
Experimental Evidence for the Movement Hierarchy
-Frontal lobe regions in each hemisphere that plan, coordinate, and execute precise movements are hierarchically related.
~Prefrontal cortex formulates a plan of action.
~Prefrontal cortex instructs premotor cortex to organize the appropriate sequence of behaviors.
~Primary motor cortex executes the movements.
Brainstem and Species-Typical Movement
-Species-Typical Behavior
~Actions produced by every member of a species (e.g., hissing in cats)
-Hess (1950s)
~Stimulated different areas within the brainstem to produce different species-specific behaviors
~Some sites produced head turning, others produced walking or running, and still others elicited displays of aggression or fear.
-Brainstem organizes many adaptive movements
~Maintaining posture, standing upright, coordinating movements of the limbs, swimming and walking, grooming the fur, and making nests
-Cerebral palsy
~Voluntary movements become difficult to make, whereas conscious behavior controlled by the cortex may remain intact
~Caused by brainstem trauma
Spinal Cord and Execution of Movement
-Quadriplegia
~Paralysis and loss of sensation in the legs and arms due to spinal cord injury
-Paraplegia
~Paralysis and loss of sensation confined to legs and lower body due to spinal cord injury
-In humans and other animals with a severed spinal cord, spinal reflexes still function even though the spinal cord is cut off from communication with the brain.
~Paralyzed limbs may display spontaneous movements or spasms.
~The brain can no longer guide the timing of these automatic movements.
Motor System Organization
-Motor Cortex
-What properties of the motor system allow versatility in carrying out skilled movements?
-Fritsch and Hitzig
~Discovered they could electrically stimulate the neocortex of an anesthetized dog to produce movements of the mouth, limbs, and paws on the opposite side of the dog’s body
-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
Mapping the Motor Cortex
-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.
-The motor homunculus maps the association of the cortex with body members
-Because of the fine motor skills found in hands, lips, and face, they are represented as being larger on the homunculus.
-A part of the body with lower motor ability is represented to appear smaller.
Homuncular Man
- Distortions illustrate the fact that extensive areas of the motor cortex allow precise regulation of the hands, fingers, lips, and tongue.
- Areas of the body over which we have much less motor control have a much smaller representation in the motor cortex.
Modeling Movement
-Michael Graziano (2006)
~Recent experiments suggest that the motor cortex represents not muscles, but rather a repertoire of fundamental movement categories.
-Studies on humans using MRI suggest that the human motor cortex is organized in terms of functional movement categories.
~Motor cortex maps appear to represent basic “types” of movement that learning and practice can modify.
~The motor cortex encodes not muscle twitches but a “lexicon,” or dictionary, of movements.
~The motor cortex represents the repertoire of movements that each species of animal can make.
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 muscle
-Studies using human participants reveal a number of situations in which motor-cortex neurons are active at the same time that no movement occurs.
-Flexible properties of motor neurons probably underlie our ability to imagine movements and also allow them to control brain-computer interfaces.
Plasticity in the Motor Cortex
-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
Corticospinal Tracts
-Corticospinal Tracts
~Main efferent pathways from the motor cortex to the brainstem to the spinal cord
~Axons descend into the brainstem, sending collaterals to a few brainstem nuclei, and eventually emerge on the brainstem’s ventral surface where they form a large bump on each side (pyramidal 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
Motor-Tract Organization
- Coriticospinal tracts originate in the neocortex and terminate in the spinal cord.
- Within the spinal cord, corticospinal fibers make synaptic connections with both interneurons and motor neurons.
- Motor neurons carry all nervous system commands out to the muscle
Motor 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.
-Neurons of the motor homunculus in the left-hemisphere cortex control the trunk on both sides of the body and the limbs on the body’s right side.
-Neurons of the motor homunculus in the right-hemisphere cortex control the trunk on both sides of the body and the limbs on the body’s left sid
Control 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 relaxe
Basal Ganglia and Movement Force
-The Basal Ganglia:
~Receive input from
*All areas of the neocortex and limbic cortex, including motor cortex
*The nigrostriatal dopaminergic system from the substantia nigra
~Project back to the motor cortex and substantia nigra
~Subserve a wide range of functions, including association or habit learning, motivation, emotion, and motor control
How the Basal Ganglia Control Movement Force
-Damage to the basal ganglia can produce two main types of motor symptoms
-Hyperkinetic Symptom
~When damage to the caudate putamen causes unwanted writhing and twitching movements called dyskinesias; seen in Huntingon’s and Tourette’s
-Hypokinetic Symptom
~When damage to the basal ganglia results in a loss of motor ability, leading to rigidity and difficulty initiating and producing movement; seen in Parkinson’s
-Volume Hypothesis
~The internal globus pallidus (Gpi) acts like a volume control on the motor cortex.
*If it is turned up, movement is blocked; if it is turned down, movement is allowed.
~Two pathways within the basal ganglia
*Direct
**When activated, the GPi is inhibited and the pathway is freed to produce movement.
*Indirect
**When activated, the GPi is activated and inhibits the thalamus, thus blocking movement.
Cerebellum and Movement Skill
-Anatomy of the 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
How the Cerebellum Improves Movement Control
-Two Main Motor Functions
~Timing
*Movements and perceptions
~Maintaining Movement Accuracy
*Error Correction
**Compares intended movement with actual movement and makes the necessary adjustments accordingly
-Cortex sends motor instructions to the spinal cord
-Copy of same instructions is sent to the cerebellum
-Sensory receptors code the actual movement and send a message about it back to the cerebellum.
-Cerebellum has information about both versions of the movement—what you intended to do and what you actually did—and can calculate the error and tell the cortex how to correct the movement.
Organization of the 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
-Has a closer relationship with movement than the other senses do
Somatosensory 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.
Classifying Somatosensory Receptors
-Nocioception
~Perception of pain, temperature and itch
~Free nerve endings activated by chemicals
-Hapsis
~Perceive fine touch and pressure, and identify objects that we touch and grasp
~Activated by mechanical stimulation of the hair, tissue, or capsule
-Proprioception
~Perception of the location and movement of the body
~Sensitive to the stretch of muscles and tendons and the movement of joints
Duration of Receptor Response
-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
Dorsal-Root Ganglion Neurons
- 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.
Dorsal-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, temperature and itch information
~Small axons with little or no myelination (slo
Disruption of Dorsal-Root Ganglion Function
-Local anesthetics block pain perception but also the ability to move facial muscles properly
-Deafferentation
~Loss of incoming sensory input usually due to damage to sensory fibers; also loss of any afferent input to a structure
Disruption of Body Awareness
-Movement abnormalities result from selective damage to neurons that carry proprioceptive information
~“Proprioception is like the eyes of the body, the way the body sees itself. And if it goes… it’s like the body’s blind.” (Sacks, 1998, p 46)
Somatosensory Pathways to the Brain
- The haptic-proprioceptive axons for touch and body awareness ascend the spinal cord ipsilaterally.
- Nocioceptive (pain, temperature, itch) nerve fibers synapse with neurons whose axons cross to the contralateral side of the spinal cord before ascending to the brain.
Dorsal Spinothalamic Tract
-Carries haptic and proprioceptive information
~Axons from the dorsal-root ganglion neurons enter the spinal cord and ascend ipsilaterally synapsing in the dorsal column nuclei.
~Axons from the dorsal column nuclei cross over to the opposite side of the brain and project up 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.
Ventral Spinothalamic Tract
-Carries nocioceptive information
~Axons from the dorsal-root ganglion neurons enter the spinal cord and cross over, synapsing onto neurons on the contralateral side.
~Axons from contralateral spinal cord ascend where they join other axons forming the medial lemniscus, synapsing with neurons in the ventrolateral nucleus of the thalamus.
~Neurons from the thalamus then project to the somatosensory cortex.
Effects of Unilateral Spinal-Cord Damage
-Two separate pathways convey somatosensory information.
~Haptic-proprioceptive
~Nocioceptive
-Loss of hapsis and proprioception occurs unilaterally on the side of the body where the damage occurred, and loss of nocioception occurs contralaterally on the opposite side of the body.
Spinal 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)
Feeling and Treating Pain
-Pain is a fact of life.
~30% of visits to physicians are for pain symptoms, as are 50% of emergency room visits.
~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 situation
Perceiving Pain
-People experience “central pain” in a part of the body that is not obviously injured.
-There are as many as eight different kinds of pain fibers, judging from the peptides and other chemicals released by these nerves when irritated or damaged.
~We may feel itchy when a foreign object is on our body.
~We also frequently feel an itch in the absence of an obvious stimulus.
-Ventral spinothalamic tract is main pain pathway to the brain
-Other pathways may carry pain information from the spinal cord to the brain.
~Reticular formation associated with arousal
~Amygdala associated with emotional responses
~Hypothalamus associated with hormonal and cardiovascular responses
-Cannot simply treat pain by severing the ventral spinothalamic pathway
Responding to Pain
-Gate Theory of Pain (Melzack & Wall, 1965)
~Activities in different sensory pathways play off against each other and so determine whether and how much pain is perceived as a result of an injury.
~Haptic-proprioceptive stimulation can reduce pain perception, whereas the absence of such stimulation can increase pain perception through interactions at a pain gate.
Treating Pain
-Gate theory
~When you stub your toe, you feel pain because the pain pathway to the brain is open.
~Rubbing the toe activates the haptic–proprioceptive pathway and reduces the flow of information in the pain pathway because the pain gate partly closes, relieving the pain sensation.
-Massage, acupuncture, and immersion in warm water may produce pain-relieving effects by selectively activating haptic and proprioceptive fibers to close the pain gate.
-Gate theory
~Interneuron that is the gate uses an endogenous opiate as an inhibitory neurotransmitter
*Opioids relieve pain by mimicking the actions of the endogeneous opioid.
~Electrical stimulation at a number of sites in the brainstem can reduce pain, perhaps by closing brainstem pain gates.
~Perceptions might be lessened through descending pathways from the forebrain and the brainstem to the spinal-cord pain gate.
-Periaqueductal Gray Matter (PAG)
~Electrical stimulation of the PAG suppresses pain.
~PAG neurons produce their pain-suppressing effect by exciting pathways in the brainstem that project to the spinal cord where they inhibit neurons that form the ascending pain pathways.
Referred Pain
-Neurons in the spinal cord that relay pain and temperature messages to the brain receive two sets of signals
~From the body’s surface and internal organs.
-Pain in the heart associated with a heart attack is felt as pain in the left shoulder and upper arm
The Vestibular System and Balance
-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 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
-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
~Refines the construction of perceptions, projects to the frontal cortex
Somatosensory Homunculus
-Penfield’s original studies suggested that there was a single homunculus, just as with the motor cortex.
-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, pressur
Effects of Damage to the Somatosensory Cortex
-Damage to the primary somatosensory cortex impairs:
~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 arm becomes sensitive to the face.
Somatosensory Cortex and Complex Movement
-The somatosensory cortex plays an important role in confirming that movements have taken place.
~Damage does not disrupt plans for making movements, but does disrupt how the movements are performed, leaving their execution fragmented and confused.
-Apraxia
~Inability to complete a plan of action accurately; to make a voluntary movement
-Dorsal visual stream projects to the secondary somatosensory cortex then to the frontal cortex
~Visual information is integrated with somatosensory information to produce unconscious movements
-Secondary somatosensory cortex interacts with the ventral stream by providing conscious haptic information about the identity of objects and completed movement
