3A: Somatosensory Disorders

Question 1

Cutaneous senses

Answer 1

perception of touch and pain from stimulation of the skin

Question 2

Proprioception

Answer 2

ability to sense position of the body and limbs

Question 3

Kinesthesis

Answer 3

ability to sense movement of body and limbs

Question 4

Skin

Answer 4

the largest organ in the body both in surface and in weight. The skin provides protection, regulation of body temperature and water loss, and sensation.

Question 5

Epidermis

Answer 5

the outermost, protective layer of the skin, composed mostly of dead cells

Question 6

Basement membrane

Answer 6

immediately below the epidermis is the basement membrane, a specialized structure that lies between the epidermis and dermis. It includes various protein structures liking the basal layer of keratinocytes (skin cells) to the basement membrane and the basement membrane to the underlying dermis. Once skin cancer cells cross this boundary, they can begin to spread through the body through the vascular system of the dermis.

Question 7

Dermis

Answer 7

the middle layer of skin below the epidermis that forms the true skin, containing blood capillaries, nerve endings, sweat glands, hair follicles, and other structures.

Question 8

Subcutaneous tissue

Answer 8

the deepest layer of the skin, made up of vessels, fat, and connective tissue.

Question 9

Hairy skin

Answer 9

most of our skin has hair. The primary somatosensory receptor in hairy skin is the follicle receptor, which is a mechanoreceptor triggered by distortion of the hair shaft.

Question 10

Glabrous skin

Answer 10

hairless skin (ex. palms, soles, lips, labia, penis); contains more specialized types of mechanoreceptors

Question 11

Mechanoreceptor

Answer 11

a sensory receptor that responds to mechanical pressure or distortion via mechanotransduction: movement of the cell membrane physically pulls open/pushes closed ion channels in the membrane, leading to changes in cell signaling.

Question 12

Slowly adapting fibers (SA)

Answer 12

fire continuously as long as pressure is applied to provide detailed/high acuity tactile info; found in Merkel’s disks (upper dermis) and Ruffini cylinders (lower dermis)

Question 13

Rapidly adapting fibers (RA)

Answer 13

fire at onset and offset of stimulation to provide info about the start of a sensation; found in Meissner’s corpuscles (upper dermis) and Pacinian corpuscles (lower dermis)

Question 14

Acute nociceptive pain

Answer 14

-Part of a rapid warning relay instructing the motor neurons of the central nervous system to minimize detected physical harm. It is mediated by nociceptors, on A-δ and C fibers.
-these nociceptors are free nerve endings that terminate just below the skin, in tendons, joints, and in body organs. They serve to detect cutaneous pain, somatic pain and visceral pain.
-nociceptors are specialized for heat, chemicals, severe pressure, and cold. Hot and cold sensations are carried via thermoreceptors.
-threshold of eliciting receptor response must be balance to warn of damage but not be affect by normal activity.

Question 15

Chronic inflammatory pain

Answer 15

-inflammatory nociceptive pain is associated with tissue damage and the resulting inflammatory process
-it is adaptive in that it elicits physiologic responses that promote healing

Question 16

Chronic inflammatory pain

Answer 16

-inflammatory nociceptive pain is associated with tissue damage and the resulting inflammatory process
-it is adaptive in that it elicits physiologic responses that promote healing

Question 17

Chronic neuropathic pain

Answer 17

-neuropathic pain is produced by damage to the neurons in the peripheral and central nervous systems and involves sensitization of these systems.
-In peripheral sensitization, there is an increase in the stimulation of peripheral nociceptors that amplifies pain signals to the central nervous system.
-In the central sensitization, neurons that originate in the dorsal horn of the spinal cord become hyperstimulated, increasing pain signals to the brain and thereby increasing pain sensation.

Question 18

Spinal cord

Answer 18

a long, thin, tubular bundle of nervous tissue and support cells (like glia) that extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column. The brain and spinal cord together make up the CNS. In contrast to cortex, gray matter is in the inside of the spinal cord and is surrounded by white matter. The spinal cord has three major functions: as a conduit for motor information, which travels down the spinal cord, as a conduit for sensory information in the reverse direction, and finally as a center for coordination certain reflexes.

Question 19

Vertebral column

Answer 19

bony structure made of multiple vertebrae that protects the relatively shorter spinal cord. Spinal nerves project through small openings in the vertebral bones.

Question 20

Dorsal root ganglion

Answer 20

the sensory nerves of the peripheral nervous system have their cell bodies in the dorsal rot ganglion. These cells have projections that carry information from the peripheral sensory receptors-peripheral nerve- and also projections that carry information into the spinal cord- dorsal root.

Question 21

Ventral root

Answer 21

is the motor nerve exiting the spinal cord to innervate muscle fibers

Question 22

Fascicle

Answer 22

a bundle of neuronal axons surrounded by a connective tissue; a component of a nerve

Question 23

Spinal reflex pathway

Answer 23

A neural pathway that controls a reflex action. As most sensory neurons synapse in the spinal cord before going to cortex, spinal motor neurons can be rapidly activated without waiting for signals to go to/ come from the brain first. Sensory input is sent to the brain while the reflex is being carried out.

Question 24

Posterior columns

Answer 24

a set of somatosensory white matter tracts in the posterior spinal cord that carry information about fine touch, vibration, pressure, and joint position from the spinal cord to the thalamus (and then to S1). Name turns into ‘medial lemniscus’ when tracts reach the brainstem, where the dorsal root ganglion axons then synapse and cross to opposite side. Organized somatotopically.

Question 25

Spinocerebellar tract

Answer 25

a set of somatosensory white matter tracts in the posterior/lateral spinal cord that carries information about joint position and muscle fiber tension from the spinal cord to the cerebellum; projections do NOT cross to opposite side. Organized somatotopically.

Question 26

Lateral spinothalamic tract

Answer 26

a set of somatosensory white matter tracts in the anterior spinal cord that carries information about crude touch and pressure from the spinal cord to the thalamus; dorsal root ganglion axons synapse and cross immediately to opposite side. Organized somatotopically.

Question 27

Thalamus

Answer 27

The sensory ‘relay station’ in the brain (located subcortically) to which all sensory neuronal pathways project prior to entering cortex, except for those involved in olfaction.

Question 28

Primary somatosensory cortex (S1)

Answer 28

A strip of cortex just posterior to the central
sulcus, where the primary control of sensation occurs. S1 contains a somatotopic (body map) representation. S2 is the second somatosensory area located just inferior and
posterior to S1.

Question 29

Somatotopy

Answer 29

is the point-for-point correspondence of an area of the body to a specific point on the central nervous system; somatotopic organization is present in both S1 and M1.

Question 30

Pain matrix

Answer 30

• a number of different areas of the brain involved in pain perception. Signals from nociceptors travel up the spinothalamic pathway and activate many of these areas. New research demonstrates that S1 and S2 are also directly involved in pain perception.

Question 31

Tactile agnosia

Answer 31

A disorder characterized by the inability to identify by touch an object (or specific characteristics of an object, e.g., weight); possibly caused by damage to S1. Much like visual agnosia, but symptoms now apply to touch. Specific tactile agnosias may also arise from damage to higher-order regions of the somatosensory system, including inability to identify an object’s weight or size (but still identify the object with tactile info).

Question 32

Cotard syndrome

Answer 32

The delusional belief that one is dead, does not exist, is putrefying or has lost his/her blood or internal organs (‘walking corpse syndrome’); paradoxical delusions of immortality may also occur (‘I am dead already, so now I can’t be killed’). Associated with depression, schizophrenia, Capgras syndrome, bipolar disorder, migraine, herpes medication (acyclovir). May arise from a disconnection between highorder sensation/face perception(?) and emotional processing of limbic cortex. Treatments may include electro-convulsive shock therapy (ECT).

Question 33

Congenital analgesia

Answer 33

also known as congenital insensitivity to pain (CIP), is a set of rare conditions in which a person cannot feel (and has never felt) physical pain. Condition may be cause by 1) increased endorphins/natural opioids, or 2) mutation in
sodium channel in pain receptors. Causes high risk of serious injury, illness, and death.

Question 34

Insensitivity to pain

Answer 34

means that the painful stimulus is not even perceived: a patient cannot describe the intensity or type of pain.

Question 35

Indifference to pain

Answer 35

means that the patient can perceive the stimulus, but lacks an appropriate response: they do not flinch or withdraw when exposed to pain.

Question 36

Chronic pain

Answer 36

pain that extends beyond the expected period of healing. Affects 1/3 of all Americans, has major impacts on quality of life, and creates a large economic burden on society. Patients are severely undertreated, yet chronic pain affects more people than heart disease, cancer, and diabetes COMBINED. There are affective and emotional effects on pain perception, but chronic pain is NOT ‘all in the patient’s head’.

Question 37

Phantom limb syndrome

Answer 37

A disorder characterized by having sensations in a limb that is no longer attached to the body; mirror therapy or virtual reality may provide some relief. Although phantom pain can be debilitating, the sensation of a phantom limb can actually improve a person’s ability to use a prosthetic.