Intig neuro exam 1

Tactile meaning

touch

olfactory meaning

smell

auditory meaning

hearing

gustatory meaning

oral

visual

sight

vestibular meaning

balance

proprioceptive meaning

body awareness

two types of sensory systems

sensations vs. preception

5 tasks of sensory systems

transduction

transmission

interference

deduction

follow-up

transduction

convert information into neural signals

transmission

pass information on

interference

when one sensory stimulus negatively impacts the processing or perception of another stimulus

deduction

what and where

follow-up

pay more/less attention

5 qualities of information to endcode

modality

intensity

duration

location

5 factors that can influence success or failure

fatigue

adaptation

sensitization 

overlap/ redundancy

damage/ overload

What ganglion carries sensory input from the face?

Trigeminal ganglia

What ganglion carries sensory input from the body?

Dorsal root ganglia

What sensations are carried through trigeminal ganglia?

Mechanical sensation (touch/pressure) and pain/temperature for the face

What sensations are carried through dorsal root ganglia?

Mechanical sensation and pain/temperature for the body.

Where do pain and temperature pathways typically cross (decussate)?

Early — in the spinal cord (body) or brainstem (face).

Where do mechanical sensation pathways usually cross?

Later — in the brainstem/medulla.

What is the “hub” that relays all sensory information to the cortex?

The thalamus.

Where in the brain do sensory signals ultimately go?

The primary somatosensory cortex (parietal lobe).

What is the overall order of sensory transmission?

Receptor → Ganglion → Spinal cord/Brainstem → Thalamus → Somatosensory cortex.

Which nervous system houses sensory receptors and ganglia?

Peripheral nervous system (PNS).

Which nervous system processes signals in the spinal cord, brainstem, and brain?

Central nervous system (CNS).

In what form do all sensory fibers transmit nerve impulses?

Action potentials.

Do all sensory receptors respond equally to all stimuli?

No — different sensory receptors have different sensitivities to specific types of stimuli.

What is the initial electrical change caused when a sensory receptor is activated?

A receptor potential (change in membrane potential).

What type of neurons are dorsal root ganglia (DRG) cells?

Pseudo-unipolar neurons.

Where can an action potential in a dorsal root ganglion (DRG) neuron begin?

In the distal process in the periphery.

Does the action potential in a DRG neuron stop at the cell body?

No — it bypasses the cell body and continues along the proximal axon to the dorsal horn of the spinal cord.

Where do DRG axons synapse in the CNS?

In the dorsal horn of the spinal cord.

What are the three main types of sensory fibers shown here?

• Nociceptors (Aδ/C fibers) → pain

• Proprioceptors (Aα fibers) → body position

• Mechanoreceptors (Aα/Aβ fibers) → touch/pressure

What can the distal section of a sensory axon be?

Either a bare nerve ending or encapsulated by a receptor structure.

What do dorsal root ganglia (DRG) contain?

The sensory neurons of the somatosensory system.

Where are DRG located?

Along the spinal cord at cervical, thoracic, lumbar, and sacral levels.

What is the difference between dorsal and ventral roots?

Dorsal root = sensory input; Ventral root = motor output.

What higher brain structures do sensory signals from DRG ultimately reach?

Thalamus → somatosensory cortex.

What do Aα and Aβ fibers carry, and what are their properties?

Large, myelinated; carry proprioception (muscle spindle) and discriminative/light touch.

What do Aδ fibers carry, and what are their properties?

Medium, lightly myelinated; carry innocuous temperature, itch, and sharp/mechanical/thermal/chemical pain.

What do C fibers carry, and what are their properties?

Small, unmyelinated; carry innocuous temperature, itch, and slow/dull mechanical/thermal/chemical pain.

What do Meissner corpuscles detect, and how do they adapt?

Light touch; rapidly adapting.

What do Merkel cells (cell–neurite complexes) detect, and how do they adapt?

Sustained pressure; slowly adapting.

What do Ruffini endings detect, and how do they adapt?

Deep tension/stretch; slowly adapting.

What do Pacinian corpuscles detect, and how do they adapt?

Vibration/deep pressure; rapidly adapting.

Where do mechanosensitive nerve endings send signals from the body and face?

Body → dorsal root ganglia; Face → trigeminal ganglia.

What do touch receptors transduce mechanical stimuli into?

Action potentials.

What two key properties vary among touch receptors?

adaptation and receptive field

What kinds of sensory info can touch receptors encode?

Gentle touch, shape, texture, vibration, and painful stimuli.

What do slowly adapting afferents convey?

Spatial attributes such as size and shape of a stimulus.

What do rapidly adapting afferents convey?

Changes in ongoing stimulation (dynamic qualities), encoded in bursts of action potentials.

What does deformation of dorsal root ganglion (DRG) endings do?

Lowers the threshold needed to evoke an action potential.

What do mechanosensitive ion channels do when the membrane is stretched?

They open, allowing ions (like Na⁺) to enter → generator potential → action potential if threshold is reached.

What characterizes high-threshold mechanosensitive channels?

Found in nociceptors (pain receptors), located in smaller DRG, activated by higher pressures.

How do sensory neurons enter the spinal cord?

Through the dorsal roots.

What is a dermatome?

A field of skin innervated by a single dorsal root

What are dermatomes clinically useful for?

Determining the level of a spinal cord lesion.

How does an epidural affect dermatomes?

Blocks sensation across several dermatomes.

What do proprioceptors provide information about?

The position of limbs and the body in space (“receptors for self”).

What are the three main types of proprioceptors?

Muscle spindles, Golgi tendon organs, and joint receptors.

What do proprioceptors provide feedback about?

Muscle length and muscle tension.

What do muscle spindles detect?

Muscle length (they are stretch receptors).

Which motor neurons innervate intrafusal vs extrafusal fibers?

Gamma motor neurons → intrafusal fibers (inside spindle).
Alpha motor neurons → extrafusal fibers (outside spindle).

What do Golgi tendon organs detect, and where are they located?

muscle tension, located at the junction

What are the two types of afferent fibers in muscle spindles, and how do they adapt?

• Group Ia: large, myelinated, rapidly adapting.

• Group II: myelinated, slowly adapting.

What controls the tension of intrafusal fibers in spindles?

Gamma motor neurons (from the ventral horn of the spinal cord).

Which muscles have many spindles vs few spindles?

Many → muscles requiring fine control (extraocular, neck, hand).
Few → large muscles for coarse movements.

What do muscle spindles vs Golgi tendon organs detect?

Muscle spindles → changes in muscle length.
Golgi tendon organs → changes in muscle tension.

What afferent fibers form Golgi tendon organs?

Group Ib afferents.

Where are Golgi tendon organs located?

At the junction between muscle fibers and tendon.

Where do somatosensory pathways relay information from and to?

From skin receptors → primary somatosensory cortex.

Besides the cortex, where else can sensory axons send collaterals?

To the cerebellum and reticular formation.

How many neurons make up a typical somatosensory pathway?

Three: first-order, second-order, and third-order neurons.

Delete

Later

Which tracts carry touch information in the dorsal column?

Fasciculus gracilis (legs, medial) and fasciculus cuneatus (arms, lateral).

What is Lissauer’s tract?

A tract near the dorsal horn where pain/temperature fibers enter before synapsing.

Where are second-order neurons for pain located?

In the dorsal horn of the spinal cord.

What does the lateral funiculus contain?

Corticospinal tract (upper motor neurons) and spinothalamic tract (pain/temp, arm vs leg).

What does “LMN” refer to in the spinal cord cross-section?

Lower motor neurons in the ventral horn.

What sensations are carried by the dorsal column–medial lemniscus pathway?

Fine touch, vibration, and proprioception.

Where do first-order neurons of the DCML travel?

Through the dorsal column (fasciculus gracilis = lower body, fasciculus cuneatus = upper body).

Where do DCML first-order neurons synapse?

In the medulla — gracile nucleus (lower body) and cuneate nucleus (upper body).

What do second-order neurons of the DCML do?

Decussate (cross) in the medulla → ascend as the medial lemniscus → project to the thalamus (VPL).

Where do third-order neurons of the DCML project?

From the thalamus (VPL) to the primary somatosensory cortex (S1).

What sensory modalities does the trigeminothalamic pathway carry?

Touch, vibration, and proprioception from the face.

Where are the cell bodies of the first-order neurons in the trigeminothalamic pathway located?

In the trigeminal ganglion.

Where do first-order trigeminal neurons synapse?

In the principal sensory nucleus of the trigeminal complex (pons).

What structure do the second-order neurons from the trigeminal nucleus form after crossing midline?

The trigeminal lemniscus.

Where do third-order neurons from the VPM project?

To the primary somatosensory cortex (S1) in the parietal lobe.

Which thalamic nucleus processes somatosensory information from the face?

VPM (ventral posterior medial).

Which thalamic nucleus processes somatosensory information from the body?

VPL (ventral posterior lateral).

What sensory modality does the spinocerebellar pathway carry?

Proprioception (muscle length and tension).

What type of sensory receptors send input via this pathway?

Muscle spindles (stretch) and Golgi tendon organs (tension).

Where do proprioceptive afferents from the lower body synapse in the spinal cord?

In Clark’s nucleus (thoracic spinal cord, T1–L2).

Where do proprioceptive afferents from the upper body travel?

To the dorsal column nuclei in the medulla.

Where do these pathways project?

To the cerebellum (via dorsal spinocerebellar tract) and dorsal column nuclei.

Why are projections to the cerebellum important?

They control the timing of muscle contractions.