Lecture 9

Question 1

Dorsal “where” pathway

Answer 1

From V1/V2, go to… MT (aka V5)
* Motion perception involves a variety of brain areas, but processing in
the dorsal stream is very important

• middle-temporal cortex (MT) responsible for processing of stimuli
  moving in a particular direction.

Question 2

middle-temporal cortex (MT)

Answer 2

responsible for processing of stimuli
moving in a particular direction.

Question 3

Motion blindness-

Answer 3

refers to the inability to determine
the direction, speed and whether objects are moving
– Likely caused by damage in area MT

Question 4

Association areas are the ultimate
targets of sensory processing in cortex

Answer 4

Association cortical areas, such as the posterior parietal cortex
and prefrontal cortex, are the regions that receive convergent
sensory and motor information from other cortical areas

Question 5

Hierarchy of Movement Control - Spinal cord

Answer 5

controls skeletal
muscles in response to sensory info.

Question 6

Hierarchy of Movement Control - Brainstem

Answer 6

transmits motor commands
from higher levels to spinal cord; also
relays sensory information

Question 7

Hierarchy of Movement Control - Primary Motor Cortex (M1)

Answer 7

initiates much of the main commands for action

Question 8

Hierarchy of Movement Control - nonprimary motor cortex

Answer 8

higher order cortical region; provides additional source of motor information, relayed mostly through M1

Question 9

Hierarchy of Movement Control - Cerebellum and basal ganglia

Answer 9

modulate activities of these hierarchically organized
control systems; often thalamus is involved; involves circuit loops through and back to cortex

Question 10

3 types of muscles -Cardiac muscles –

Answer 10

Cardiac muscles – are heart muscles that have properties of skeletal and smooth muscles
***Controlled by autonomic nervous system

Question 10

3 types of muscles - Smooth Muscles

Answer 10

Smooth muscles – control the digestive system and other organs
***Controlled by autonomic nervous system

Question 11

3 types of muscles -

Answer 11

Skeletal/ striated muscles – control movement of the body in relation to the environment

Question 12

Movement requires the alternating contraction of opposing sets of muscles called …….

Answer 12

antagonistic muscles

flexor muscle - is one that flexes or raises an appendage

extensor muscle - is one that extends an appendage or straightens i

Question 13

neuromuscular junction -

Answer 13

synapse between a motor neuron axon and a muscle fiber; very similar to neuronal synapse

Question 14

Motor unit –

Answer 14

motoneuron and all the muscle fibers that it innervates

Question 15

Low ratio of motoneurons-to-fibers

Answer 15

–allows for fine motor control in
smaller muscles (e.g., eye is 1:3)

Question 16

*High ratio of motoneurons-to-fibers

Answer 16

– less fine, or gross
control; usu. large muscles
(e.g., leg may be 1:200)

Question 17

Each muscle fiber receives innervation from only one …..

Answer 17

motoneuron,
But one motoneuron may innervate multiple fibers

Question 18

2 types of skeletal muscle fibers - Extrafusal muscle fibers

Answer 18

Extrafusal muscle fibers – do all the “work” of the muscle
-receive input from alpha motor neurons

Question 19

2 types of skeletal muscle fibers - Intrafusal muscle fibers

Answer 19

Intrafusal muscle fibers – contained within muscle spindles
-these are sensory detectors that inform the muscle how much to contract
-receive input from gamma motor neurons

Question 20

Two major kinds of proprioceptive receptors that convey
the state of the muscles and joints to the brain:

Answer 20

1) Muscle spindle
2) Golgi tendon organ

Question 22

Golgi Tendon Organ (GTO)

Answer 22

• Sensory nerve endings that innervate tendons
• Monitors muscle tension, usually via contractions of the muscle
• GTO detects overloads – strong stimulation of GTO inhibits alpha
  motoneurons, preventing tearing and damage

Question 23

For all other muscles, brain controls activity through connection with
motoneurons in spinal cord
* For this, there are 2 major pathways/ systems:…..

Answer 23

pyramidal and
extrapyramidal motor system

Question 24

Pyramidal System

Answer 24

* a.k.a. – corticospinal system – describes a descending motor pathway originating from the primary motor cortex (M1) * Controls movement in peripheral areas (hands and feet) * axons extend from one side of the brain contralaterally to the spinal cord and control opposite side of the body

Question 25

M1 – Primary motor cortex

Answer 25

primary motor cortex/ M1 - located in the precentral gyrus of the frontal lobe * Neurons in M1 generate APs that project to alpha MNs in the spinal cord that control the muscles * M1 mediates fine voluntary movements, especially of the hands and feet * M1 also is important not only for controlling muscles but also for executing behaviors

Question 26

Premotor cortex - guided by external stimuli

Answer 26

– Involved in learning and executing movements that are guided by sensory information

Question 27

Supplementary motor cortex (SMC) -

Answer 27

key for initiating movement sequences that are internally driven – Important for planning a behavior to carry out a sequence of movements in a particular order – SMC is active seconds before the movement occurs

Question 28

Extrapyramidal systems

Answer 28

1) Reticulospinal tract – runs from reticular formation in brain stem to spinal cord -controls muscles responsible for postural movements (i.e., core, legs) 2) Rubrospinal tract – runs from the red nucleus (rubro = red) to the spinal cord -controls flexor movements of arms -receives input from M1 and cerebellum -pathway is less important in humans than in other mammals, since corticospinal is stronger 3) Vestibulospinal tract (not shown in diagram) – also originates in brain stem  important for head stabilization and relevant postural adjustments, coordinates head and eye movements  receives information from the vestibular system! SUMMARY: the extrapyramidal systems modulate activity; prevent erratic movements, maintain muscle tone and postural stability

Question 29

Basal ganglia (BG) –

Answer 29

collection of subcortical nuclei that influence movements * BG receives cortical sensory information and outputs to M1 (with some descending projections) * BG consists of several intrinsic structures that form a circuit loop whereby information is processed and refined in an iterative manner

Question 30

3 Parts of the Basal ganglia/Important associated regions:

Answer 30

1)Caudate nucleus 2) Putamen 3) Globus pallidus 2 Important associated regions: 1) Subthalamic nucleus 2) substantia nigra striatum

Question 31

Basal Ganglia - Caudate nucleus and putamen

Answer 31

Caudate nucleus and putamen receive input from the M1 (and other cortical areas) * Send inhibitory projections to the globus pallidus

Question 32

Basal Ganglia - Globus pallidus

Answer 32

Globus pallidus connects to the thalamus and inhibits it, in turn inhibiting M1 and Suppl motor cortex

Question 33

Parkinson’s Disease

Answer 33

Dopamine normally modulates the caudate-putamen, so when substantia nigra (SN) neurons degenerate, this can lead to overactivity in the BG circuit that produces rigidity and difficulty moving * When >90% of SN dopamine cells die, one sees the onset of Parkinson’s symptoms

Question 34

Cerebellum

Answer 34

Generally speaking, the cerebellum is associated with coordination, precision of movement, and timing * Recent evidence suggests a role in attention, language, and even emotional control

Question 35

Cerebellum parts;

Answer 35

Parallel fibers – are granule cell axons that collect input from: the spinal cord, each of the sensory systems, and cortex * Parallel fibers project to the cerebellar cortex where they make synapses with Purkinje neurons * Purkinje neurons inhibit deep cerebellar nuclei (DCN) * The net effect of Purkinje cell activation is inhibition of targets and output, producing finer control of feedback and motor function