Midterm 1 - Somatosensory & Motor Systems

Question 1

Various Senses

Answer 1

1. Pain
2. Touch/Pressure
3. Temperature
4. Vibration

Question 2

Two Basic Types of Sensory Receptors & Role

Answer 2

Sensory Transduction = Sensory receptors turn stimuli into a message the brain can understand.

1. Free Nerve Endings - Pain receptors. Lightly myelinated.
2. Encapsulated Nerve Endings - Heavily myelinated. Covers larger surface area. When send sensory information to the brain it is transmitted in a pattern consistent with the way the receptors are laid out in the body (dermatomes).

Question 3

Dermatomes

Answer 3

Provide a map of the body such that information gets to the brain in a very conserved order.

Question 4

Somatosensory Pathway

(Visual)

Answer 4

Question 5

Somatosensory Pathway

(Verbal)

Answer 5

• Sensory information from free nerve endings and encapsulated nerve endings enter the spinal cord via the dorsal root ganglion.
• The information either
  
  • Goes up dorsal columns (fine touch, precisely localized information, proprioception, other sensory information)
  • OR crosses and goes up the spinothalamic tract to the ventral posterior nucleus (VPN) of the thalamus (pain, touch, temp).
• Information then goes to S1.

Question 6

Dorsal Columns

+

How Axons Are Added to Dorsal Column & Order is Preserved

Answer 6

Get heavier and more myelinated as you go up the brain (because there’s more input built up as you go higher).

We know where the axons are coming from because they’re being added to the outside.

By the time you get to S1, there’s a map of the body laid out in the brain.

Question 7

Somatotopy

Answer 7

Map of the body in the brain (“homunculus” - little man).

Somatosensory homunculus is laid out in S1 and there are some regions that are overrepresented (e.g., fingers, face, lips).

Question 8

Somatosensory Cortex

Answer 8

Just caudal to central sulcus.

Question 9

Somatotopy of Somatosensory Cortex

Answer 9

Question 10

Somatotopy of Somatosensory and Motor Systems Compared

(Visual)

Answer 10

Question 11

Two-Point Discrimination Test

Answer 11

Can you discriminate distance between 2 points?

There are different densities of receptors at different locations in the body. Discrimination is the worst in the middle of the back, whereas there’s a lot of information coming from the face!

Question 12

Somatosensory System vs. Motor System

Answer 12

Somatosensory

• Starts in the dermatomes and goes to the brain.

Motor

• Starts in the brain and goes down the ventral spinal cord to the muscles.

Question 13

Motor System

(Overview)

Answer 13

Info travels from the brain down the corticospinal tract and synapses on motor neurons (2 types) in the ventral horn of the spinal cord. These motor neurons send axons that go to (synapse on) and work the muscles.

Question 14

Neuromuscular Junction

(Overview Picture)

Answer 14

Question 15

Neuromuscular Junction Description

Answer 15

Where the axons of motor neurons synapse directly on muscle fibers.

Question 16

Neurotransmitter at Neuromuscular Junction

Answer 16

• ACh is the only NT released at this junction.
• When ACh is released, it synapses on ACh post-synaptic receptor sites and then acetylcholinesterase (enzyme) immediately degrades ACh so that it gets out of binding site (want muscle to be able to fire again).

Question 17

2 Types of Motor Neurons in Ventral Horn

Answer 17

1. Alpha - Synapse on extrafusal muscle fibers.
2. Gamma - Synapse on intrafusal muscle fibers.

Question 18

Tendon v Ligament

Answer 18

1. Tendon - Connects muscle to bone.
2. Ligament - Connects muscle to muscle.

Question 19

Extrafusalmuscle Fibers

Answer 19

Force exerted by contraction.

Innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement.

Question 20

Intrafusal Muscle Fibers

Answer 20

Innervated by gamma motor neurons.

These fibers are a proprioceptor that detect the amount and rate of change of length in a muscle.

Fine-tuned motor movement.

Has stretch receptors.

Question 21

Golgi Tendon Organ (GTO)

Answer 21

Gets feedback from intrafusal muscle fibers (gamma motor neurons) and if there is too much stretch/strain on the muscle the GTO can turn off the muscle.

Attaches to muscle and bone.

Gauges whether there is too much stretch by the rate of muscle firing (not by the length of the muscle).

Works on glutamate and has NMDA receptors (type of glutamate receptor).

Question 22

NMDA Receptor

Answer 22

Type of glutamate receptor on the GTO.

Ex. of NMDA Antagonist = PCP (makes it so the GTO won’t operate and therefore won’t shut down a muscle = SUPER-strength).

Question 23

Motor Cortices

(Picture)

Answer 23

Question 24

Motor System Pathway

(Visual)

Answer 24

Question 25

Motor Homunculus

Answer 25

Motor homunculus is laid out just like the somatosensory homunculus (muscle control of face near bottom).

Question 26

Motor Pathway Overview

Answer 26

1. Reasons for/thoughts re movement generated in PFC 2. Information from PFC goes to the striatum (caudate and putamen) 3. Thoughts sent to (a) supplementary motor cortex, then (b) premotor cortex and then (c) M1 (primary motor cortex/pre-central gyrus) where a plan is generated. 4. Corticospinal cord that carries this information from M1 through the medulla/pyramids. 5. Plan sent to cerebellum for refinement 6. Plan goes down spinal chord and synapses on the motor neurons in the ventral horn. 7. Motor neurons send axons to the muscle 8. Muscle fibers activated.

Question 27

Medulla/Pyramids

Answer 27

Where motor axons in the corticospinal tract cross/decussate. \*\*\*Remember, left cortex works right side of body.

Question 28

Cerebellum

Answer 28

Fine tunes/refines movement via inhibition (GABA, which is inhibitory, is present in cerebellum) then sends the information back down the corticospinal tract. Needed for coordination.

Question 29

Alcohol, GABA & the Cerebellum

Answer 29

Cerebellum works primarily on GABA and if a person takes a GABA agonist (e.g., alcohol, the cerebellum will be shut down).

Question 30

Cerebellum & Synaptic Plasticity

Answer 30

Through synaptic plasticity, the cerebellum learns to refine motor movements (e.g., Kobe Bryant cerebellum's = Einstein's astrocytes!).

Question 31

Basal Ganglia | (Coronal Section)

Answer 31

Question 32

Basal Ganglia: Internal Capsule

Answer 32

Band of myelinated fibers that separates caudate, putamen, globus pallidus.

Question 33

Pathway of Thoughts in PFC to Basal Ganglia

Answer 33

* PFC * Caudate * Putamen * Globus Pallidus * Subthalamic Nucleus * Thalamus * Motor cortices

Question 34

Basal Ganglia Is Responsible For ...?

Answer 34

This system is responsible for starting and stoppin movement.

Question 35

NTs and Pathway of NTS Involved With Basal Ganglia

Answer 35

Dopamine * Substantia Nigra (down in brainstem) makes dopamine and ships it forward via the nigrostriatal pathway to the striatum (caudate + putamen) Parts of the basal ganglia communicate with each other via the release of dopamine.

Question 36

Parkinson's

Answer 36

Cells in the substantia nigra die. As the neurons start to die, other neurons pick up the slack for dopamine production. Therefore, it takes a loss of ~95% of neurons before motor deficits manifest. If there's not enough dopamine to ship to caudate, there will be deficits in terms of starting and stopping movement.

Question 37

Cocaine

Answer 37

Dopamine re-uptake inhibitor. Theoretically could be used to treat Parkison's but the therapeutic window is so short.

Question 38

Subthalamic Nucleus and Parkinson's

Answer 38

This system calms the body at rest. One treatment for LATE-STAGE Parkinson's (where can't move) is a paladotomy (take out subthalamic nucleus). Thus, there will be more movement.

Question 39

Huntington's Chorea Disease

Answer 39

Movement disorder where person can't stand still and does dance like movements. Degeneration of caudate. Genetically inherited.