Midterm 1 - Somatosensory & Motor Systems Flashcards
Various Senses
- Pain
- Touch/Pressure
- Temperature
- Vibration
Two Basic Types of Sensory Receptors & Role
Sensory Transduction = Sensory receptors turn stimuli into a message the brain can understand.
- Free Nerve Endings - Pain receptors. Lightly myelinated.
- 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).
Dermatomes
Provide a map of the body such that information gets to the brain in a very conserved order.
Somatosensory Pathway
(Visual)
Somatosensory Pathway
(Verbal)
- 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.
Dorsal Columns
+
How Axons Are Added to Dorsal Column & Order is Preserved
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.
Somatotopy
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).
Somatosensory Cortex
Just caudal to central sulcus.
Somatotopy of Somatosensory Cortex
Somatotopy of Somatosensory and Motor Systems Compared
(Visual)
Two-Point Discrimination Test
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!
Somatosensory System vs. Motor System
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.
Motor System
(Overview)
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.
Neuromuscular Junction
(Overview Picture)
Neuromuscular Junction Description
Where the axons of motor neurons synapse directly on muscle fibers.
Neurotransmitter at Neuromuscular Junction
- 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).
2 Types of Motor Neurons in Ventral Horn
- Alpha - Synapse on extrafusal muscle fibers.
- Gamma - Synapse on intrafusal muscle fibers.
Tendon v Ligament
- Tendon - Connects muscle to bone.
- Ligament - Connects muscle to muscle.
Extrafusalmuscle Fibers
Force exerted by contraction.
Innervated by alpha motor neurons and generate tension by contracting, thereby allowing for skeletal movement.
Intrafusal Muscle Fibers
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.
Golgi Tendon Organ (GTO)
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).
NMDA Receptor
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).
Motor Cortices
(Picture)
Motor System Pathway
(Visual)
Motor Homunculus
Motor homunculus is laid out just like the somatosensory homunculus (muscle control of face near bottom).
Motor Pathway
Overview
- Reasons for/thoughts re movement generated in PFC
- Information from PFC goes to the striatum (caudate and putamen)
- 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.
- Corticospinal cord that carries this information from M1 through the medulla/pyramids.
- Plan sent to cerebellum for refinement
- Plan goes down spinal chord and synapses on the motor neurons in the ventral horn.
- Motor neurons send axons to the muscle
- Muscle fibers activated.
Medulla/Pyramids
Where motor axons in the corticospinal tract cross/decussate.
***Remember, left cortex works right side of body.
Cerebellum
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.
Alcohol, GABA & the Cerebellum
Cerebellum works primarily on GABA and if a person takes a GABA agonist (e.g., alcohol, the cerebellum will be shut down).
Cerebellum & Synaptic Plasticity
Through synaptic plasticity, the cerebellum learns to refine motor movements (e.g., Kobe Bryant cerebellum’s = Einstein’s astrocytes!).
Basal Ganglia
(Coronal Section)
Basal Ganglia:
Internal Capsule
Band of myelinated fibers that separates caudate, putamen, globus pallidus.
Pathway of Thoughts in PFC to Basal Ganglia
- PFC
- Caudate
- Putamen
- Globus Pallidus
- Subthalamic Nucleus
- Thalamus
- Motor cortices
Basal Ganglia Is Responsible For …?
This system is responsible for starting and stoppin movement.
NTs and Pathway of NTS Involved With Basal Ganglia
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.
Parkinson’s
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.
Cocaine
Dopamine re-uptake inhibitor.
Theoretically could be used to treat Parkison’s but the therapeutic window is so short.
Subthalamic Nucleus and Parkinson’s
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.
Huntington’s Chorea Disease
Movement disorder where person can’t stand still and does dance like movements.
Degeneration of caudate.
Genetically inherited.
