Lecture 9: Touch and Sensory

imma touch you

What results in perception?

The cerebral cortex analyzes the sensory information

Tactile sensation includes

• Touch

• Vibration

• Pressure

• Proprioception

Pain and Temperature sensation includes

• Pain

• Itch

• Warm and Cool

What is the “3-neuron pathway”?

The pathway of perception

Reflexes are…

Immediate responses to stimuli

Axons conduct

Action potentials

Cell body (nuclei) synapses

Integrate activity

Cell Body and Axon of path 1

Dorsal Root ganglion, Spinal cord

Cell body and Axon for pathway 2

Spinal cord/brainstem, decussates on CNS

Cell body and axon of pathway 3

Thalamus, Internal capsule Corona Radiata synapses

Nerve endings of neuron #1 are modified to what ?

Transduce sensory stimuli

Different types of receptors respond to…

Different types of tactile stimuli

Meissner’s corpuscle responds to

Touch, low frequency vibration

Merkel Disk responds to

Touch

Pacinian corpuscle responds to

High frequency vibration

Ruffini ending responds to

Pressure

Hair folicle responds to

Bending

Muscle spindles golgi tendon organs responds

Proprioception

Receptors vary in

• Shape

• Position in skin/body

• Density many more on fingers and face

• Physiological properties

Muscles spindles respond to…

Muscle stretch

Nerve endings contain

mechanosensitive ion channels

Membrane is deformed

The axon is depolarized and action potentials are conducted along a pathway

Axons conducting tactile information are ____ and ____ fibers

Large, myelinated

Axons conducting pain/temperature information are small ______ or small ________ fibers

myelinated, myelinated

A tactile stimulus at my finger would travel to my spinal cord in about _____

8msec

A pain stimulus at my finger would travel to my spinal cord in about _____

1sec

Dermatomes

The spinal nerve from each spinal cord segment supplies a specific region of body surface

Body dermatomes are key to identifying what?

Sensory deficits

Lower body dermatomes are below __ and axons enter through _

T6, Fasciculus gracilis

Upper body dermatomes are at/above __ and enter what?

T6, enters fascilcus cuneatus

Fasciculus gracilis and fasciculus cuneatus travel the length of what? On which side?

The spinal cord and dorsal (posterior) surface

Sensory info enters the spinal cord, it is used for

Reflexes

What is the basis of stretch reflexes?

Spinal cord

Axons make local connections in what? And then onto what?

Spinal cord, onto the motoneurons before continuing to cortex

Tactile Sensory Pathway FIRST HALF

Dorsal root ganglion → Dorsal root → Fasciculus Gracilis → Nucleus Gracilis → THE CHECKPOINT

Tactile Sensory Pathway

Medial Lemniscus → VPL → Internal Capsule → Corona Radiata → Postcentral Gyrus

Nucleus Gracilis and Cuneatus are in the ____ ____ on the what surface?

Caudal medulla the dorsal surface

What are the two bumps on the caudal medulla?

The nucleus gracilis and cuneatus ON THE DORSAL SURFACE

The axon of neuron 3 travels through the _________ and then to _______ to reach the ______

Internal capsule, corona radiata, Postcentral gyrus

The internal capsule is between these 3 structures

Thalamus, caudate nucleus, and lentiform nucleus

What is the corona radiata?

The radiating crown

Beyond the internal capsule, axons spread out into what?

The corona radiata then to the cortex

Neuron 3 terminates in the _______ and _______

Postcentral Gyrus, Paracentral Lobule

What is the highlighted area?

The postcentral gyrus

What is this highlighted area?

Paracentral lobule

Cortex, in relation to sensory, is for

Somatotopic orientation

Posterior part of paracentral lobule is responsible for

Sensory information from the leg and foot

Vitamin B12 deficiency and Tabes Dorsalis are examples of…

Disorders involving demylination of axons in the fasciculus gracilis and cuneatus

Tactile Pathway Part 1

Dorsal Root Ganglion → Dorsal Root → Fasciculus Gracilis/Cuneatus

Tactile Pathway Part 2

Nucleus Gracilis/Cuneatus → Medial Lemniscus

Tactile Pathway Part 3

VPL → Internal Capsule → Corona Radiata → Paracentral Gyrus/Paracentral Lobule