Chapter 11: How Does the Nervous System Respond to Stimulation and Produce Movement?

Question 1

How does the nervous system respond to stimulation and produce movement?

Answer 1

-Hierarchy and parallel movement control
-Motor system organization
-Basal ganglia, cerebellum, and movement
-Somatosensory system receptors and pathways
-Exploring the somatosensory cortex

Question 2

Hierarchy and parallel movement control

Answer 2

-Major components of the motor system
-Cerebrum (forebrain):conscious movement control
-Brainstem: Direct movements
-Spinal cord: Direct movements
-Subcortical basal ganglia: Produce appropriate amount of force for grasping
-Cerebellum helps regulate the timing and accuracy of movement

Question 3

Impaired brainstem or spinal cord

Answer 3

-The forebrain can imagine movements but no longer produce them
-Information can no longer be sent to the cerebrum (conscious control of movement)

Question 4

Sequentially organized movement

Answer 4

1) Visual information required to locate target
2) Frontal-lobe motor areas plan the reach and command the movement
3) Spinal cord carries information to the hand
4) Motor neurons carry message to the muscles of the hand and forearm
5) Sensory receptors on the fingers send message to the sensory cortex saying the cup was grasped
6) Spinal cord carries info to brain
7) Basal ganglia judge grasp force and cerebellum corrects movement errors
8) Sensory cortex receives message that cup has been grasped

Question 5

Afferent VS efferent

Answer 5

-Afferent = sensory= inward somatic nervous system
-Efferent = motor = outward from CNS via parallel system

Question 6

Spinal segments

Answer 6

-Each spinal segment corresponds to a region of body surface called a dermatome
-Dermatomes are slices/segments

Question 7

Specific segments

Answer 7

Cervical: C1-C8
-Thoracic: T1-T12
-Lumbar: L1-L5
-Sacral nerves: S1-S5

Question 8

Layering in neocortex

Answer 8

-Layer IV (afferent) is thick in sensory cortex and thin in motor cortex
Layer V (efferent) is thick in motor and thin in sensory cortex

Question 9

Lashley

Answer 9

-We perform skilled movements too quickly to rely on feedback about one movement before shaping the next
-Time spent is too long for effective action
-Argued that movements must be performed as motor sequences held in readiness while the ongoing is under way
-Motor sequence

Question 10

Motor sequence

Answer 10

Movement modules are preprogrammed by the brain and produces as a unit

Question 11

Initiating a motor sequence

Answer 11

-Mastering sequences of action
1) Prefrontal cortex (front): Plans the complex behavior
2) Premotor cortex (Middle): Produces appropriate complex movement sequences
3) Primary motor cortex (Back): specifies how each behavior is carried out

Question 12

Primary motor cortex

Answer 12

-Specializes in producing focal skilled movements such as those of the arms, hands and mouth
-People with damage to the M1 have difficulty reaching and shaping their fingers to perform various hand grasps

Question 13

Experimental evidence for the hierarchical and parallel movement control

Answer 13

-Frontal lobe regions in each hemisphere that plan, coordinate and execute precise movements are hierarchically related
-Prefrontal formulates plan and instructs premotor to organize and the primary motor executes the function

Question 14

Species typical behavior

Answer 14

-Actions produces by every member of a species
-Automatically coded

Question 15

Hess

Answer 15

-Stimulated different areas within the brainstem to produce different species-specific behaviors
-Some sites produced head turning, others produced walking or running and others elicited displays of aggression or fear

Question 16

Brainstem

Answer 16

-organizes many adaptive movements
-Maintains posture, standing, coordinating limb movements, swimming, walking, grooming fur, making nests

Question 17

Cerebral palsy

Answer 17

-Voluntary movements are difficult to make, whereas conscious behavior controlled by the cortex may remain intact
-Caused by brainstem trauma

Question 18

Locked in syndrome

Answer 18

-Condition in which a patient is aware and awake but cannot move or communicate verbally because of complete paralysis of nearly all voluntary muscles except eyes
Due to brainstem damage, MS or demyelination
-No afferent or efferent movements
-

Question 19

Quadriplegia

Answer 19

-Paralysis and loss of sensation in the legs and arms due to spinal cord injury

Question 20

Paraplegia

Answer 20

Paralysis and loss of sensation confined to legs and lower body due to spinal cord injury

Question 21

Reflexes

Answer 21

-humans/animals with 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
-Brain can no longer guide the timing of these reflexes

Question 22

Motor cortex

Answer 22

-Fritsch and Hitzig: Discovered they could electrically stimulate the neocortex of anesthetized dog to produce movement in mouth, limbs and paws on opposite side of dog body
-Wilder penfield: Used electrical stimulation to map the cortices of human patients undergoing neurosurgery. Confirmed role of primary motor cortex in producing movements

Question 23

Homunculus (little person)

Answer 23

Representation of the human body in the sensory or motor cortex, also any topographical representation of the body by a neural area

Question 24

Topographic organization

Answer 24

-Neural spatial representation of the body or areas of the sensory world perceived by a sensory organ
-Parts of motor cortex that control hands, fingers, lips and tongue are disproportionately larger than parts of the motor cortex that control other areas

Question 25

Penfields hommunculus

Answer 25

-Maps association of cortex with body members -Smaller motor ability looks smaller

Question 26

Modelling movement

Answer 26

-Early idea: Each part of homunculus controls muscles in that part of the body -Recent studies: Motor cortex represents not muscles but rather a repertoire of fundamental movement categories -Used MRI, human motor cortex is organized in terms of functional movement categories. Represents basic types of movements

Question 27

Characteristics of motor cortex neurons

Answer 27

-Planning and initiating movements, discharge before and after movements -Coded 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

Question 28

Nudo

Answer 28

-Damaged part of motor cortex that controlled hand in moneys -Without rehabilitation: The hand area of cortex became smaller, elbow and shoulder became larger. No longer able to move hand -With rehabilitation: Hand area retained size and ability to move

Question 29

Corticospinal tract

Answer 29

-Main efferent pathways from 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 large bumps (pyramid tracts)

Question 30

Lateral Corticospinal tract

Answer 30

-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

Question 31

Ventral (anterior) Corticospinal tract

Answer 31

-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

Question 32

2 neurons in spinal columns ventral horns

Answer 32

-Interneurons project to motor neurons -Motor neurons project to muscles of the body -Laterally located motor neurons project to the muscles that control fingers and hands -Intermediately located motor neurons project to muscles that control arms and shoulders -Most medially located motor neurons project to muscles that control the trunk -Control of enteric nervous system

Question 33

Limb muscles

Answer 33

-Extensor: Moves (extends) limb away from trunk -Flexor: Moves limb towards trunk -Connections between the interneurons and motor neurons ensure that the muscles work together so that when one muscle contracts, the other relaxes

Question 34

Basal ganglia

Answer 34

-Receives input from all areas of neocortex and allocortex including motor cortex. Also the nigrostriatal dopaminergic system from substantia nigra -Project back to the motor cortex and substantia nigra -serves a wide range of functions, including association or habit learning, motivation, emotion and motor control

Question 35

Anatomy of basal ganglia

Answer 35

-Nuclei forming the basal ganglia include caudate nucleus and putamen. Together they form striatum (stripes), subthalamic nucleus, globus pallidus. -Neocortical and allocortical loops likely participate in selecting and producing skilled movements for learned actions and emotional expression

Question 36

Damage to basal

Answer 36

-Hyperkinetic symptom: Damage to the caudate putamen may cause unwanted writhing and twitching movements called dyskinesias; seen in huntington and tourettes -Hypokinetic symptom: Damage to the basal ganglia may result in loss of motor ability, leading to rigidiy and difficult initiating and producing movement; seeing in parkinsons

Question 37

Volume control theory

Answer 37

-Globus pallidus internal acts like a volume control on motor cortex -Turned up = blocked movement and turned down = allows movement

Question 38

2 pathways for basal ganglia

Answer 38

Direct: When activated, the globus pallidus is inhibited and the pathway is freed to produce movement -Indirect: When activated the globus pallidus internal is activated and inhibits the thalamus, blocking movement -Thalaus = endpoint

Question 39

Volume hypothesis

Answer 39

-Recordings made from the globus pallidus cells show excessive activity -If globus pallidus or subthalamic nucleus is partially surgically destroyed in parkinson patients, muscular rigidity is reduced and normal movement is improved -Deep brain stim. of globus inactivates in freeing the movement

Question 40

Mesolimbic DA pathway

Answer 40

-Nucleus accumbens receives projections from dopamine cells of the ventral tegmental area. Compulsions are driven here -Mesolimbic dopamine: Part of a loop that aids our perception of cues signaling reward

Question 41

Anatomy of cerebellum

Answer 41

-Flocculus: Small but dense lobe involved in eye movements and balance -2 hemispheres: Homuncular organization (upper part), 1) Lateral parts: Controls movements of limbs, hands, feet and digits 2) Medial parts: Controls movement of face and midline of body

Question 42

2 main motor functions

Answer 42

1) timing: Movements and perceptions, maintaining movement accuracy 2) Error correction: Compares intended movement with actual movement and makes the necessary adjustments accordingly

Question 43

Damage to the cerebellum

Answer 43

-Cannot adjust and adapt when needed for movement

Question 44

How does the cerebellum improve movement control

Answer 44

-Cortex sends motor instructions to the spinal cord -Copy of these same instructions get sent to the cerebellum -Sensory receptors code actual movement and report to the cerebellum -Cerebellum has both information and can calculate error and tell cortex how to correct the movement

Question 45

Somatosensory system

Answer 45

-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, movement of joints -Allows us to distinguish what the world does and what we do to is -Has a closer relationship with movement than other senses -These receptors tell us two things about a sensory event: When it occurs and whether it is still occuring

Question 46

Somatosensory receptors and perception

Answer 46

-Areas with larger number of receptors are more sensitive than areas with relatively fewer receptors -Sensitivity to different somatosensory stimuli is a function of the kinds of receptors -Hairy skin -Glabrous skin: Skin w/out hair follicles but contains larger numbers of sensory receptors

Question 47

Classifying somatosensory receptors

Answer 47

-Nocioception -Hapsis -Proprioception

Question 48

Nocioception

Answer 48

-Perception of pain, temperature and itch -Free nerve endings activated by chemicals

Question 49

Hapsis

Answer 49

-Perceive fine touch and pressure and identify objects we touch and grasp -Activated by mechanical stimulation (move) of the hair, tissue or capsule

Question 50

Proprioception

Answer 50

-Perception of location and movement of body -Sensitive to the stretch of muscles and tendons and the movement of joints

Question 51

Rapidly vs slowly adapting receptor

Answer 51

-Rapid: Body sensory receptor that responds briefly in the beginning and end of a stimulus on the body -Slow: Body sensory receptors that responds as long as the sensory stimulus is on the body

Question 52

Rapidly adapting receptor

Answer 52

-Haptic receptors that respond to touch (meissner corpuscles), fluttering sensations (Pacinian corpuscles), and to vibration -Rods and cones -Quickly assesses feedback

Question 53

Slowly adapting receptor

Answer 53

-Nocioreceptor (pain) that respond to sharp and dull pain and those that respond to temperature -Merkel's receptors (Steady skin indentation) and hair receptors (Flutter or steady skin indentaation) -Ruffini corpuscles

Question 54

Posterior root ganglion neurons

Answer 54

-The dendrite and axon continuously carry sensory information from skin to the CNS via the spinal cord -Tip of dendrite is responsive to sensory stimulation -Each spinal cord segment has one posterior root ganglion on each side that contains many posterior root ganglion neurons -In the spinal cord, the axons of these neurons may synapse onto other neurons or continue up to the brain

Question 55

Haptic neuron of the posterior root ganglion

Answer 55

1) Posterior root ganglion neurons that carry fine-touch and pressure information 2) they have large myelinated axons whose receptors are located in the skin, muscles and tendons 3) The cell body is located in a posterior root ganglion 4) Fine-touch and pressure axons ascend in the ipsilateral spinal cord, forming the posterior spinothalamic tract

Question 56

Proprioceptive and haptic neurons

Answer 56

-Carry information about location and movement (proprioception) and about touch and pressure (hapsis) -Large and myelinated axons = fast

Question 57

Nocioceptive neurons

Answer 57

-Pain and temperature and itch information -Small axons with little or no myelination (Slow)

Question 58

Disruption of Posterior root ganglion function

Answer 58

-Local anesthetics block pain perception and the ability to move facial muscles properly -Deafferentation

Question 59

Deafferentation

Answer 59

-Loss of incoming sensory input usually due to damage to sensory fibers -Loss of any afferent input to a structure -Numb where damage took place

Question 60

Movement abnormalities

Answer 60

-result from selective damage to neurons that carry proprioceptive information (location/movement of body) -Proprioceptive is like the eyes of the body. Damage here = blindness in body

Question 61

Somatosensory pathways to brain

Answer 61

-Hapic (Fine touch) and proprioceptive (location/body movement) ascend the spinal cord ipsilaterally (the same side of body): Fast (myelin) -Nociceptive (Pain, temperature, itch) nerve fibers synapses with neurons whose axons cross to the contralateral (opposite) side of the spinal cord before ascending to the brain: Slow (Unmyelinated)

Question 62

Posterior spinothalamic tract

Answer 62

-Carries haptic and proprioceptive information -Axons from 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 medial lemniscus -Axons synapse with neurons located in the ventrolateral nuclei of the thalamus, which projects to the somatosensory cortex and motor cortex

Question 63

Anterior spinothalamic tract

Answer 63

-Carries nocioceptive information -Axons from dorsal root ganglion neurons enter the spinal cord and cross over, synapsing onto neurons on the contralateral side -Axons from the contralateral spinal cord ascend where they join other axons forming the medial lemniscus synapsing with neurons in the ventrolateral nuclei of the thalamus -Neurons from the thalamus then project to the somatosensory cortex

Question 64

Unilateral somatosensory damage

Answer 64

-Damage causes loss of fine touch and pressure sensation on SAME side of cut whereas loss of pain and temperature sensation on the OPPOSITE side of the cut

Question 65

Monosynaptic reflex

Answer 65

-Reflex requiring one (mono) synapse between sensory input and movement -Single synapse between afferent (sensory) and efferent (Motor) ex) Knee-jerk reflex, patellar,

Question 66

Complex spinal reflexes

Answer 66

-Involve connections among sensory neurons, interneurons and motor neurons -Multisynaptic connection

Question 67

Perceiving pain

Answer 67

-Central pain felt in area where injury did not occur -8 kinds of pain fibers (judging by the peptides and other chemical released by these nerves when irritated or damaged -Anterior spinothalamic tract = main pain pathway (Pain cannot simply be treated by cutting this pathway)

Question 68

Alternative pain pathways

Answer 68

-Reticular formation: Arousal -Amygdala: Emotions -Hypothalamus: Hormonal and cardiovascular responses

Question 69

Gate theory

Answer 69

-Responding to pain theory -Activities in different sensory pathways play off against each other and so determine whether and how much pain is perceived as result of injury -Haptic-proprioceptive stimulation can reduce pain perception whereas absence of stimulation can increase pain perception

Question 70

Gate theory process

Answer 70

-Stub toe, feel pain because pain pathway to brain is open -Rubbing toe activates haptic-proprioceptive pathway and reduces flow of information in the pain pathway. Pain gate partially closes and relieves pain sensation -Massage, acupuncture, immersion in warm water may produce pain-relieving effects by selectively activating haptic and proprioceptive fibers to close gate.

Question 71

Interneuron gate

Answer 71

-The interneuron that is the gate uses an endogenous opiate as inhibitory transmitter -Opioids relieve pain by mimicking the actions of the endogenous opioid -Electrical stimulation at a number of sites in brainstem can reduce pain, perhaps by closing pain gates -Perceptions might be lessened through descending pathways from the forebrain and the brainstem to the spinal-cord gate

Question 72

Periaqueductal gray matter (PAG)

Answer 72

-Electrical stimulation of PAG suppresses pain (Surgery) -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 pathways

Question 73

Referred pain

Answer 73

-Neurons in the spinal cord that relay pain and temperature messages to the brain receive two sets of signals -From body's surface -From internal organs -Pain in the heart associated with a heart attack is felt as pain in the left shoulder and upper arm

Question 74

Vestibular system and balance

Answer 74

-Within each ear a vestibular organ contains -3 semicircular canals -Otolith organs (utricle and saccule) -Vestibular organs functions: Tell the position of the body in relation to gravity -Signal changes in the direction and speed of head movements

Question 75

Moving head

Answer 75

-Fluid (endolymph) located within the semicircular canals pushes against the hair cells which bends cilia on top of hair cells -Bending of cilia leads to receptor potentials in the hair cells and action potentials in the cells forming the vestibular nerve -Direction in which cilia are bet determines whether cell is depolarized (right) or hyperpolarized (left)