Better Neuro Flashcards

What is the Sensorimotor system, and why is it important

• Network of sensory, motor, and CNS components that work together to integrate sensory input and motor output to facilitate interaction with the environment

• Integrating sensory signals – such as touch, balance, vision – to guide precise motor behavior

• Planning, executing, and controlling movements

Sensory neuron

excitatory, afferent, respond to sensory stimuli (such as touch, light, odor, sound, etc.)

Motor Neurons

excitatory, efferent, Contact muscles or glands to give “motor instructions”

Relay interneurons

inhibitory, receive input and send input between neurons – integrate signals

Which brain regions are involved in the Sensorimotor system

Cortical regions (“sensorimotor cortex”): Cerebellum, basal ganglia, thalamus, Brainstem, spinal cord
Plan and execute movements; Process tactile inputs (touch, pain, temperature); Process visual inputs; Process auditory inputs

Somatosensation

The body's collection of general senses that convey information about physical contact, temperature, pain, and body position
There are multiple types of sensory nerve fibers & different tactile receptors on the skin

Mechanoreceptors

Detect touch, vibration, pressure, stretch

Thermoreceptors

Free nerve endings that sense changes in skin temperature

Nociceptors

Free nerve endings that respond to pain

Pruriceptors

Specialized free nerve endings that trigger itch

Touch receptors

vary in type and density throughout the skin, they determine the ability to feel fine details and pinpoint where touch occur

Free nerve endings detect…

touch, pain, itch, and temperature

Merkel’s disc

touch receptor, Fine texture

Meissner’s corpuscle

touch receptor, Light touch

Hair follicle receptor

touch receptor, Light touch

Pacinian (or lamellated) corpuscle

touch receptor, vibration and pressure

Ruffini corpuscle

touch receptor, skin stretch

Receptive field

region of a sensory space that varys in size

Regions with sensory neurons that have smaller receptive fields are more sensitive – for better discrimination between 2 points and more precise localization
Larger receptive field = less precise localization; Smaller receptive field = more precise localizatio

Transient Receptor Potential (TRP) channels

a family of ion channels expressed on free nerve endings
- C-fibers (slow, unmyelinated) carry signals from TRPM8 receptors – signaling cool temperature
- A-delta fibers (larger, myelinated) carry signals from TRPV2 – signaling high noxious heat/pain

Pain and temperature use the same pathway

Somatosensory transmission

• Stimuli activate sensory receptors on the skin → receptors generate graded potentials (or receptor potential)

• If the potential reaches the neuron's threshold, an action potential is generated

  • Action potential is an all-or-none event (occurs at full amplitude or not at all)

• A single neuron can convey stimulus intensity by changing the frequency of its action potentials; Stronger stimulus = more action potential fired

• Multiple neurons can act in parallel; Stronger stimulus = more neurons are recruited

• Different neurons respond to different stimulus intensity ranges (range fractionation); Some respond to weaker stimuli; some respond to stronger (divide and conquer)

• Information about duration is carried by the pattern of receptor and sensory neuron activity over time

  • Different receptors differ in how their responses change during continued stimulation

Phasic receptors

rapidly adapting

Tonic receptors

slowly adapting

Dorsal column (Somatosensory Pathway)

for touch, vibration; Cross over at the medulla, ends in the primary somatosensory cortex

Spinothalamic tract (Somatosensory Pathway)

for pain, temperature; Cross over upon entering, ends in the primary somatosensory cortex

The primary somatosensory cortex location

Located in the postcentral gyrus

The primary somatosensory cortex location

Located in the postcentral gyrus

The primary somatosensory cortex

Receives touch info from the opposite side of the body (contralateral)

• Information from different body regions inputs different parts of S1

• Information from more sensitive body regions take up larger portions of S1

Homunculus

cortical map of body regions that are prioritized in S1 (the primary somatosensory cortex)

The somatosensory cortex’s ability to reorganize

The somatosensory cortex can reorganize its maps in response to sensory loss, peripheral nerve injury, or training, though the extent of this neuroplasticity varies depending on the type and timing of the event.

Congenital insensitivity to pain

loss-of-function mutation in sodium channels, found in pain fibers in dorsal root ganglia; Inability to feel pain

Congenital hyper to pain

gain-of-function mutation in sodium channels, found in pain fibers in dorsal root ganglia; Constant feeling of severe burning pain

Nociceptive Chronic Pain

Pain from damage to body tissue

Neuropathic Chronic Pain

Pain from nervous system processing changes

Nociplastic Chronic Pain

Pain from changes in the nervous system

Hypersensitivity to touch

stimulus avoiders, distressed by having face/hair washed or nails cut; Picky eater, only eats certain textures; Refuses to walk barefoot on grass or sand; toe walks

Hyposensitivity to touch

stimulus seekers, Craves touch; touches everything and everyone; Hurts other children or pets while playing; May pinch, bite, or bang own head

Characteristics of the Cortex neuromuscular system

plans, initiates, and executes motor commands

Characteristics of the Basal ganglia and cerebellum in the neuromuscular system

modulate motor actions

Characteristics of the Brainstem in the neuromuscular system

integrates motor commands; sends signals to spinal cord

Characteristics of the spinal cord in the neuromuscular system

sends signals from brain to skeletal muscles (or responds directly to sensory inputs for reflexes)

Characteristics of the skeletal system and muscles in the neuromuscular system

power movement

Prefrontal cortex in motor control

Long-term movement planning; decides if or when a movement should occur

Posterior parietal cortex in motor control

Integrates sensory information to plan movement

Primary motor cortex (M1) in motor control

initiates and executes motor commands

Nonprimary motor cortex in motor control

plans motor commands

Premotor cortex in motor control

plans movement using external sensory information

Supplementary motor area in motor control

plans learned and complex sequences of behavior

Basal ganglia; Caudate nucleus, putamen, globus pallidus, substantia nigra, subthalamic nucleus in motor control

Modulate motor actions by controlling the amplitude and direction of movement

Important for: Initiating/ending a movement; Fine-tuning for smooth movement (avoid jerks); Movements performed by memory (biking, tying shoes, etc.)

Cerebellum in motor control

contains Purkinje cells, which only send inhibitory messages; Modulates motor actions through inhibition

Important for: Fine-tuning and error correction of movements; Motor learning (“muscle memory”)

Brainstem in motor control

Integrates motor commands from higher brain regions and sends signals to spinal cord (“relay center”)

The steps of executing a motor plan

1)What is current state of the body?

2) Should I move?

3) Select a movement plan

4) Load the plan

5) Execute the plan

6) Feedback on how the plan is going; Need to change it?

Pyramidal tracts include:

Corticospinal tract and Corticobulbar tract, with both originating from the primary motor cortex, and are used for voluntary movement

Corticospinal tract

Pyrimidal Tract, for skeletal muscle movement, Cortex → Spinal cord (spinal nerves) → Muscles

Corticobulbar tract

Pyrimidal Tract, for face, head, neck movement, Cortex → Brain stem (cranial nerves) → Muscles

Extrapyramidal tract involves

The Rubrospinal tract, Reticulospinal tract, Vestibulospinal tract, Tectospinal tract

The Rubrospinal tract

Extrapyramidal, for fine movement

Reticulospinal tract

Extrapyramidal, for tone control and automate breathing

Vestibulospinal tract

Extrapyramidal, for balance and posture

Tectospinal tract

Extrapyramidal, for head-eye-body coordination, saccades

Upper motor neurons

Originate in the cortex; Travel down to brain stem or spinal cord – where it synapse onto lower motor neurons; Use glutamate as their primary neurotransmitter

Lower motor neurons

Originate in the brainstem or spinal cord (ventral horn); Project directly to muscles or glands; Use acetylcholine as their primary neurotransmitter; 3 subtypes: alpha, gamma, beta

How skeletal muscles facilitate movement

Skeletal muscles are a type of muscle that move bones and enable voluntary body movements

• Skeletal muscles are composed bundles of skeletal muscle fibers (individual muscle cells)

  • Each muscle fiber is innervated by a single motor neuron

  • A single motor neuron branches to control many muscle fibers

  • 1 motor neuron can innervate 10s to 1000s of muscle fibers

  • 1 neuron innervating few muscle fibers – precise, fine movement

  • 1 neuron innervating many muscle fibers – large and powerful movement

Neuromuscular junction

Synapse between a motor neuron and a muscle fiber

Depolarization of the muscle cell membrane triggers

an action potential that causes the release of Ca2+ ions needed for protein filaments within the muscle to slide and contract

How sensory feedback guides muscle actions

The brain constantly receives information about the length, tension, and angle of muscles and uses this to adjust their activity

• There are sensory receptors (proprioceptors) in muscles that detect muscle changes

• The brain processes this information – compares it with the intended movement and determines whether it needs to contract or relax more – and generates motor commands to adjust muscle activity accordingly

How do Muscle spindles guide muscle actions with sensory feedback?

detect changes in muscle length (stretch), sensory neurons attached to these receptors carry this information back to the brain

How do Golgi tendon organs guide muscle actions with sensory feedback?

detect muscle tension, sensory neurons attached to these receptors carry this information back to the brain

Cortical homunculus

Different regions (and sizes of regions) within the motor cortex control the movement of specific body parts

Primary motor cortex reside within

the precentral gyrus

Primary somatosensory cortex reside within

the postcentral gyrus

Which sensory signal bypasses the thalamus and can be transmitted directly to the cortex?

Olfaction

Which of the following cells can fire action potentials? Select all that apply.

- Cochlear hair cells

- Taste receptor cells

- Olfactory receptor neurons

- Mitral cells

- Photoreceptors

- Retinal ganglion cells

Retinal ganglion cells and Olfactory receptor neurons

nformation from more sensitive body regions take up larger portions of the…

the primary somatosensory cortex (S1)

The motor cortex’s ability to reorganize

The motor cortex can reorganize (just like how somatosensory cortex can)

ex: Professional musicians have larger motor cortex and larger finger map

Pain withdrawal reflex

polysynaptic

• Pain receptors in skin detect heat

• sensory neuron carries the information to interneurons in the spinal cord, bypassing the brain

• Interneurons trigger reflex by instructing motor neurons to contract flexors and relax extensors

• Brain receives information about pain afterward

Knee jerk (patellar reflex)

monosynaptic

• A tap on the patellar tendon stretches the quadriceps muscles; muscle spindles detect the stretch

• A sensory neuron carries the information directly to motor neurons in the spinal cord, causing muscles to contract

• At the same time, a branch of the sensory neuron stimulates an interneuron in the spinal cord, that blocks the motor neurons controlling the opposite muscle, thereby relaxing hamstrings

Amyotrophic lateral sclerosis (ALS)

Also known as Lou Gehrigs’s disease, Degeneration of motor neurons, and consequently, loss of control of target muscles

Symptoms: Limb weakness; Muscle twitching or stiffness; Loss of motor controls; Respiratory issues; Swallowing issues; Eventually, death from respiratory failure 2-5 years after diagnosis

Damages to motor cortex include

Stroke, traumatic injury, tumors

Hemiparesis

weakness on one (opposite) side of the body

Symptoms: Loss of fine motor skills – trouble writing, buttoning a shirt, etc.; Overactive reflexes – clonus (rapid involuntary muscle contractions) and spasticity (prolonged involuntary muscle contractions); Speech issues

Parkinson’s disease

Caused by degeneration of dopamine cells in the substantia nigra, which project to the basal ganglia

Symptoms: Tremors; Bradykinesia; Shuffling gait; Postural instability (Lecture 8, slide 48)

Cerebellar ataxia

Caused by damage to the cerebellum caused by stroke, tumors, head injuries, or inherited factors.

Symptoms: Unsteady fair, clumsy walking; Poor coordination; Tremors; Speech issued; Eye movement issues (nystagmus)

Spinal cord injuries can result in

flaccid paralysis – reflexes, sensation, and muscle strength below the level of injury are lost

Myasthenia gravis

Autoimmune disorder where patient develops antibodies against their own ACh receptor

Symptoms: Weakness of the eye muscles; Drooping of one or both eyelids; Blurred or double vision; Changes in facial expressions; Difficulty swallowing; Shortness of breath; Impaired speech; Weakness in the arms, hands, fingers, legs, and neck

The outer ear…

captures sound and transfer them inward

Pinnae

Visible outer flaps of ear; captures sound waves

Ear canal

Guides sound waves deeper toward eardrum

The outer ear consists of..

the pinnae and ear canal

The middle ear…

The middle ear consists of…

the Eardrum (tympanic membrane), the Ossicles and the Eustachian tube

Eardrum

known as the tympanic membrane, Thin membrane that vibrates when incoming sound waves hit it

Ossicles consists of…

malleus, incus, and stapes

The ossicles connect the

eardrum to the oval window

The purpose of the ossicles are to…

concentrates and amplifies signals to the inner ear

Eustachian tube

A small passage connecting the middle ear to the back of the throat to balance air pressure

The inner ear…

converts sound vibrations into electrical signals and detect head movements to maintain balance

The inner ear consists of…

The Cochlea, Hair cells, Auditory nerve, and the Vestibular system

Cochlea

snail-shaped, fluid-filled chamber that receives the mechanical sound vibrations

Hair cells

Tiny sensory cells inside the cochlea; bend from fluid waves and turn movement into electrical signals

Auditory nerve

Also known as the vestibulocochlear nerve, or CN-8 Carries the electrical signals to the brain for interpretation

Vestibular system (semicircular canals)

Detect head rotation and maintain balance