Vocab Terms Chapter 2

Sensory neurons

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

Motor neurons

excitatory, contact muscles or glands to give “motor instructions”

Relay interneurons

inhibitory, receive input and send input between neurons, they integrate signals (mostly in CNS)

Afferent, efferent

Sensory neurons are _____ , they carry signals TOWARDS the CNS

Motor neurons are ______, they carry signals AWAY from the CNS

Sensorimotor pathway structures

Spinal nerve, Dorsal root, Ventral root, Dorsal root ganglion

Mechanoreceptors

Detect touch, vibration, pressure, stretch

Thermoreceptors

Free nerve endings specialized to detect temperature changes.

Nociceptors

Specialized free sensory nerve endings that detect pain.

Pruriceptors

Specialized free nerve endings that trigger itch

Touch receptor type and relationship with density

The type and density of touch receptors vary throughout the skin, they determines the ability to feel fine details and pinpoint where touch occur

Free nerve endings

can be utilized to detect crude touch, pain, itch, and temperature

Merkel’s discs detect

Fine texture

Meissner’s corpuscles detect

Light touch

Hair follicle receptors detect

Light touch

Pacinian (lamellated) corpuscles detect

deep pressure and vibration

Ruffini corpuscles detect

Skin stretch

C-fibers

slow, unmyelinated, they carry signals from TRPM8 receptors and signal cool temperature

A-delta fibers

larger, myelinated, they carry signals from TRPV2, signaling high noxious heat/pain

Action potential

an all-or-none event (occurs at full amplitude or not at all)

Stimulus intensity encoding

A single neuron can convey stimulus intensity by changing the frequency of its action potentials.

The stronger stimulus = more action potential fired, with multiple neurons be being able to act in parallel
• Stronger stimulus indicates that more neurons are recruited

Range fractionation

Different neurons respond to different stimulus intensity ranges, some respond to weaker stimuli; some respond to stronger (divide and conquer)

Stimulus duration encoding

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 tract

for touch and vibration, ascending, they cross over at the medulla

Spinothalamic tract

for pain, temperature, ascending, Cross over upon entering the spinal cord

Somatosensory homunculus

cortical map of body regions that are prioritized in the somatosensory cortex

Congenital insensitivity to pain

caused by loss-of-function mutation in sodium channels (NaV 7.1) found in pain fibers in dorsal root ganglia leading to the inability to feel pain

Congenital hypersensitivity to pain

gain-of-function mutation in sodium channels (NaV 7.1) found in pain fibers in dorsal root ganglia, leading to the constant feeling of severe burning pain

Nociceptive pain

pain caused by damage to body tissue

Neuropathic pain

pain caused by nerve damage or disease

Nociplastic pain

pain caused by nervous system processing changes

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

Brainstem in motor control

Integrates motor commands from higher brain regions and relays signals to the spinal cord.

Spinal cord in motor control

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

Prefrontal cortex

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

Posterior parietal cortex

Integrates sensory information to plan movement

Primary motor cortex

(M1) - initiates and executes motor commands, located in the precentral gyrus

Nonprimary motor cortex

plans motor commands

Premotor cortex

plans movement using external sensory information

Supplementary motor area

plans learned and complex sequences of behavior

Basal ganglia

consists of the caudate nucleus, putamen, globus pallidus, substantia nigra, and subthalamic nucleus

used to modulate motor actions by controlling the amplitude and direction of movement

It is Important for:

• Initiating/ending a movement

• Fine-tuning for smooth movement (avoid jerks)

• Movements performed by memory (biking, tying shoes, etc.)

Cerebellum

contains Purkinje cells, which only send inhibitory messages, letting it modulates motor actions through inhibition

It is important for:

• Fine-tuning and error correction of movements

• Motor learning (“muscle memory”)

Pyramidal tract

for voluntary movement, originating from the primary motor cortex

it has 2 tracts:

• Corticospinal tract – for skeletal muscle movement

• Corticobulbar tract – for face, head, neck movement

Extrapyramidal tract

for involuntary movement, originating from the brainstem (pons, medulla, midbrain)

It has 4 tracts:

• Rubrospinal tract – for fine movement

• Reticulospinal tract – for tone control and automate breathing

• Vestibulospinal tract – for balance and posture

• Tectospinal tract – for head-eye-body coordination, saccades

Corticospinal tract

For skeletal muscle voluntary movement

Cortex → Spinal cord → Spinal nerves → Muscles

Corticobulbar tract

For face, head, neck voluntary movement

Cortex → Brain stem → Cranial nerves → Muscles

Upper motor neurons

Originate in the cortex, they travel down to brain stem or spinal cord, where it synapses onto lower motor neurons.

• Use glutamate as their primary neurotransmitter

Lower motor neurons

Originate in the brainstem or spinal cord (ventral horn), where they project directly to muscles or glands

• Use acetylcholine as their primary neurotransmitter

• 3 subtypes: alpha, gamma, beta

Skeletal muscles

type of muscle that move bones and enable voluntary body movements, composed bundles of muscle fibers (individual muscle cells)

Motor neuron innervation

A single motor neuron branches to control many muscle fibers, with 1 motor neuron being able to 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

Muscle contraction

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

Proprioceptors

There are sensory receptors in muscles that detect muscle changes

Muscle spindles

detect changes in muscle length (stretching!)

Golgi tendon organs

detect muscle tension

Pain withdrawal reflex

polysynaptic, Pain receptors in skin detect heat, a sensory neuron carries the information to interneurons in the spinal cord, bypassing the brain, leading to interneurons trigger reflex by instructing motor neurons to contract flexors and relax extensors

The brain receives information about pain afterward

Patellar reflex

also known as the knee-jerk 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, characterized by the 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

Motor cortex damage

Can be due to: Stroke, traumatic injury, tumors

Symptoms:

• Hemiparesis – weakness on one (opposite) side of the body

• Loss of fine motor skills – trouble writing, buttoning a shirt, etc.

• Overactive reflexes

• clonus (rapid involuntary muscle contractions)

• 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

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 injury

can result in flaccid paralysis where reflexes, sensation, and muscle strength below the level of injury are lost

Myasthenia gravis

Autoimmune disorder where patient develops antibodies against their own ACh receptors

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

Outer ear

captures sound and transfer them inward

Pinnae

Visible out flaps of ear; captures sound waves

Ear canal

Guides sound waves deeper toward eardrum

Middle ear

concentrates and amplifies sound waves

Eardrum

also known as the tympanic membrane, a thin membrane that vibrates when incoming sound waves hit it

Ossicles

includes the malleus, incus, and stapes, the 3 smallest bones of the body.

they connect eardrum to the oval window (of the cochlea), concentrating and amplifying signals to the inner ear

Eustachian tube

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

Inner ear

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

Cochlea

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

Cochlear hair cells

Tiny sensory cells inside the cochlea; bend from fluid waves and turn movement into electrical signals, they synapse with auditory nerve endings

Auditory nerve

also known as CN8, or the vestibulocochlear nerve, carries the electrical signals to the brain for interpretation

Vestibular system

also known as semicircular canals, detect head rotation and maintain balance

Spiral ganglion neurons

synapse with hair cells – a type of sensory neuron that transmit auditory signals to the brain (via the auditory nerve)

Stereocilia movement toward the kinocilium

Tip links pull MET channels OPEN → K+ ions flow into hair cell, depolarizing membrane → Membrane depolarization leads to opening of voltage-gated Ca2+ channels → Influx of Ca2+ leads to synaptic release of neurotransmitters (glutamate) → Neurotransmitters are detected by receptors on auditory sensory neuron

Stereocilia movement away from the kinocilium

All tension in tip links is gone; results in closure of any MET channels that were open at rest → K+ ions stop flowing into hair cell; membrane hyperpolarizes → No opening of voltage-gated Ca2+ channels, no neurotransmitter release

Semicircular canals

3 fluid-filled tubes, these canals are oriented in 3 planes of head movement

Ampulla

enlarged chamber at the base of the canal, contains specialized sensory receptors that detect rotation and angular acceleration

Utricle and saccule

2 bulbs, specialized receptors in the bulbs provide acceleration and deceleration signals

Vestibular signaling

Head movement initiates fluid movement in the semicircular canal, which deflects stereocilia in the ampulla, this excites CN8, or the vestibulocochlear nerve, which transmits the signal to the vestibular nuclei in the brainstem (most) or directly to the cerebellum

Vestibulo-ocular reflex

movement sensation causes eyes to move in opposite direction to stabilize images

Primary auditory cortex

A1, processes basic sound detection

Secondary auditory cortex

processes complex sounds (speech, music, spatial location, etc.)

Place coding

Different frequencies maximally activate different locations along the cochlea (cochlear tonotopy) – the auditory cortex encodes pitch based on where activity is occurring

• Low pitch sound – highest activity near apex

• High pitch sound – highest activity near base

Temporal coding

For lower frequencies, neurons can synchronize their firing to the timing of the sound wave (phase-locking)

Volley principle

For higher frequencies that are too high for any single neuron to fire every cycle, each neuron only fires at a certain point in the cycle, though it does not respond to each cycle

Interaural intensity differences

different loudness at the two ears

Interaural timing differences

different arrival times for sound at the ears

Auditory ventral stream

Identifies what the sound is, which is important for sound intensity, speech recognition, meaning. It projects to anterior temporal regions

Auditory dorsal stream

Identifies where the sound and how to interact with it which is Important for sound localization, spatial processing, and sensorimotor integration. It Projects toward posterior temporal and parietal regions.

Conduction deafness

disorders of outer or middle ear that prevent sounds from reaching the cochlea

Sensorineural deafness

from cochlea or auditory nerve lesions

Central deafness

caused by brain lesions

Papillae

bumps on the tongue that contain taste buds

Fungiform papillae

Near the tip and sides

Circumvallate papillae

Large, arranged in a V-shaped row near the back