Muscle spindle Gamma motor neurons innervate the contractile

• Muscle spindle • Gamma motor neurons innervate the contractile sides of intrafusal muscle fibers • “resets” the 1 a afferents by tightening up if IMF are slackened • 1 a afferent neurons (dorsal root ganglion cell) innervate the noncontractile centers of intrafusal muscle fibers • Responds to changes in IMF length (and therefore extrafusal MF length)

• Prevents over-extension of muscles and protect the joints

• Golgi tendon organ • 1 b afferent neurons winds through the fibers • When muscles contract, fibers are tightened and 1 b afferent terminals are deformed and persistently signals the muscle tension

• Prevents over-contraction of the muscles and protect the tendons

• Saccule & utricle • Signals static head position and translational acceleration • Saccule: vertical acceleration • Utricle: horizontal acceleration

• The constant tug on the otoconia by gravity keeps populations of hair cells persistently depolarized and hyperpolarized, depending on which side of the striola they are located • Signals head positional information • Also sensitive to acceleration

• Semicircular canals signal angular acceleration (change signals only) • The cupula moves in the opposite direction of head turn • Endolymph has higher K+ concentration rather than Na+

• Depolarized on one side of the head, hyperpolarized on the other side

Area 3 b • cortical columns in Area 3 b receives inputs from one class of receptors from a specific area of the body

Projections between structures • • Layer 2/3 > cortex to cortex Layer 4 > thalamus to cortex Layer 5 > cortex to subcortical structures Layer 6 > cortex to thalamus

primary somatosensory cortex: within-region (column) processing the cortical column layer-specific inputs merging RA info. into SA info. ? dynamical into static? Pacinian’s/Meissner’s into Merkl’s? low-resolution into high-resolution?

SA 2’s

Memorize all the receptors! Mechanoreceptors Transient / RA Sustained / SA Superficial Meissner’s corpuscle Merkel disk -Prefer 20 -50 Hz -Low frequency vibrations & slippage -Small receptive field -Prefer 5 -15 Hz -Fine shape discrimination -Smallest receptive field Pacinian corpuscle Ruffini ending -Prefer 60 -400 Hz -High frequency vibrations -Largest receptive field -Direction of skin stretch -Shape of hand/ objects held in hand -Large receptive field Subcutaneous

Memorize all the receptors! Other receptors Transient / RA Sustained / SA Proprioceptive Muscle spindle Golgi tendon organ -Changes in length of muscle -Muscle tension Semicircular canal Saccule & utricle -Angular acceleration of the head -Static position of the head -Translational acceleration Vestibular

True or False: If a region of interest has greater f. MRI BOLD signal, the neurons in that region are firing more action potentials.

True or False: Generally speaking, action potentials come in different sizes and shapes.

Short Answer: Name the region that summates synaptic potentials and “decides” whether to fire an action potential

True or False: Different classes of mechanoreceptive signals are integrated in the thalamus.

True or False: The dorsal column medial lemniscal system crosses contralaterally in the spinal cord before ascending to the brain.

Short Answer: Name the structure that signals translational movement along the vertical axis.

Short Answer: The anterolateral pathway transmits signals from the ____ and ____ modalities of somatosensation.

True or False: Gamma motor neurons innervate the muscles that move your bones.

True or False: The hair cell inside the cupula on the left side of your head depolarizes if you suddenly turned your head to the right.

Short Answer: What happens to the neuronal activity of 1 a afferents if I were to bend your arm inwards from an extended position?

Short Answer: Name 1 hypothesized function of surround inhibition.

Surprise SAT question: MERKEL DISK : PACINIAN CORPUSCLE : : A. B. C. D. E. Hair cell : nociceptor Semicircular canal : utricle Golgi tendon organ : muscle spindle Medial lemniscus : cuneate fasciculus Saccule : Ruffini ending