Donette Steele, M.A. / Clinical Psychology

The Body Senses and Movement

 

Proprioception and the Vestibular Sense

         Proprioception – sense of the position and movement of our limbs and body

       sensitive to tension in muscles and angles of limbs at joints

       helps maintain posture, move limbs and grasp objects

         Vestibular sense – maintains balance through head position and movement

       semicircular canals of inner ear responsive to rotational movement

>     at base is cupula which has hair cells protruding into it

>     hair cells bend during acceleration causing depolarizations or hyperpolarizations (depending on direction)

 

The Vestibular Sense

         Utricle and saccule monitor head position

       receptors covered with gelatinous mass embedded with calcium carbonate crystals (otoliths)

       when head is tilted or moved the gelatinous mass with otoliths shifts bending cilia of the receptors (depolarizations; hyperpolarizations)

       utricle for horizontal; saccule for vertical

       responds to acceleration – not steady speed movement

 

The Skin Senses

         Touch, warmth, cold and pain

         Receptors are free nerve endings or encapsulated endings

         Encapsulated endings detect touch

       Messner's corpuscles and Merkel's discs are located in superficial layers of skin and give brief vs. sustained responses, respectively

>     texture, detail, movement

 

Receptors of the skin

The Skin Senses, continued

         Pacinian corpuscles and Ruffini endings are deeper in skin

       detect stretching

         Free nerve endings detect warmth, cold and pain

         Some areas (lips, face, fingers) have more receptors, therefore more sensitive

         Are separate pathways for the different skin and body senses

       body divided into dermatomes – distinct areas served by one spinal nerve

         Information from skin senses travels to somatosensory cortex of parietal lobe

 

Dermatomes of the human body

Brain Areas for Skin Senses

         Primary somatosensory (S-I) cortex contains a map of the body with different areas differentially sensitive (large areas of brain for small area of body – lips)

         Cells arranged in columns – single column responds to one area of body and one skin sense

         Some cells are feature detectors for shape, orientation, texture, movement, etc.

 

Brain Areas for Skin Senses, continued

         Secondary somatosensory cortex (S-II) receives input from right and left S-I (S-I is more lateralized)

       connects to temporal lobe and hippocampus – determines whether stimulus will be remembered

         Posterior parietal cortex combines input from various different sensory modalities

       integrates the body with the world

       coordinates sensory information and motor behavior

 

The somatosensory and posterior parietal areas

Pain

         Three types of pain receptors

       thermal – respond to extreme heat and cold

       mechanical – respond to extreme pressure and cutting

       polymodal – respond to all of the above plus chemicals released

>     chemicals include bradykinin, histamine, prostaglandins,

 

Pain, continued

         Two types of pain fibers

       large, myelinated A-delta fibers – rapid transmission – sharp pain

       small, lighly or even unmyelinated C fibers – slower transmission – dull, throbbing pain

         Pain neurons in spinal cord release gultamate and substance P

 

Pain Relief

         Gate control theory

       a neural gate exists for pain perception – when open, feel pain; when closed; pain perception decreased

       emotion, distraction and counterirritation may work by closing the gate

>     use of transcutaneous electrical nerve stimulation to decrease pain

 

Pain Relief, continued

         Endorphins

       neurotransmitter/hormone that acts at opiate receptors – reduces pain

       stress, acupuncture & vaginal stimulation can also release endorphins

       released by periaqueductal gray (PAG) and activate PAG neurons that travel down spinal cord inhibiting release of substance P

 

Phantom Pain

         Amputees report vivid experiences of missing limbs – including pain

         Originally thought to be due to nerve fibers that used to connect limb to brain

         May be due to the brain tissue originally relegated to the missing limb being taken over by new functions (for arm it is usually the face)

 

Muscles

         Three types of muscles

       skeletal/striated – move body and limbs

       smooth muscles – internal organs, digestion

       cardiac muscles – heart

         Made up of many muscle fibers

         Muscle fibers innervated by neurons at neuromuscular junction

       acetylcholine is the neurotransmitter at all neuromuscular junctions

         Limbs have antagonistic pairs of muscles for flexion and extension

 

Antagonistic muscles of the upper arm

Muscles and the Spinal Cord

         Spinal cord coordinates reflexes

       stretch reflex – patellar tendon reflex

       patellar tapped – stimulates muscle spindles in muscle – sends signal to spinal cord which sends signal to extensor muscle

       allows maintenance of balance

         Golgi tendon organs act to inhibit muscle – safety mechanism

         Spinal cord contains central pattern generators that can be used without the brain

       produce rhythmic pattern of motor activity (walking)

 

The patellar tendon reflex, an example of a stretch reflex

Brain Areas and Movement

         Motor cortex contains primary motor cortex and two secondary motor areas

       supplemental motor area and premotor cortex

       other secondary motor areas are in cingulate cortex

       greater amounts of brain tissue are dedicated to certain areas than others

>     finer motor control (fingers)

 

Brain Areas and Movement, continued

         The prefrontal cortex

       receives input from posterior parietal lobe for motor planning

       is activated before actual movement in monkeys during a delayed-match-to-sample task

         The premotor cortex

       begins programming a movement by integrating information needed for that movement

>     cells respond to both visual and body information

 

Brain Areas and Movement, continued

         The supplemental motor area

       responsible for assembling movement sequences

       coordinates sequencing between sides of body

         The primary motor cortex

       execution of voluntary movements

       refines direction, force and precision of movements

       receives direct input from somatosensory cortex and posterior parietal lobe as well as secondary motor areas

 

Brain Areas and Movement, continued

         Basal ganglia (caudate nucleus, putamen & globus pallidus)

       smooth movements via connections to thalamus

       receives input from motor (primary & secondary) & somatosensory areas

       damage leads to postural abnormalities and involuntary movements

       coordinates complex sequences of movements and the learning of movement sequences

       implicated in Parkinson's and Huntington's disease

 

The basal ganglia

Brain Areas and Movement, continued

         Cerebellum

       refines movements, maintains balance, controls certain eye movements

       receives input from vestibular system

       programs order and timing of complex movements

>     keeps smooth and coordinated

       necessary for learning motor skills

       also has functions in non-motor learning, attention and speed & time judgments concerning auditory and visual stimuli

 

Disorders of Movement

         Parkinson's disease

       motor tremors, rigidity, loss of balance and coordination, difficulty initiating movements

       caused by deterioration of dopamine-secreting neurons in the substantia nigra of brain stem (sends signal to part of basal ganglia)

       cause of the degeneration is unclear

>     genetic mutations can lead to build up of certain proteins that can lead to abnormal clumps in neurons (Lewy bodies)

 

Disorders of Movement, continued

         Parkinson's disease

       industrial chemicals, herbicides and pesticides also implicated

       disease rate lower in coffee drinkers and smokers

         Treatments for Parkinson's disease

       levodopa (L-dopa)

       embryonic stem cell transplantation

       surgery: thalamotomy and pallidotomy

       electrical stimulation of globus pallidus and cerebellum

 

Disorders of Movement, continued

         Huntington's disease

       begins with jerky movements, then involuntary movements such as fidgeting, limb movement, writhing and facial grimacing

       also involves depression, personality changes, impaired judgement, and cognitive impairment

       degeneration in striatum of basal ganglia and cortex

 

Disorders of Movement, continued

         Huntington's disease

       probably caused by build up of huntingin

       is a single-gene disorder

         Treatments for Huntington's disease

       fetal striatum cell transplantation

 

Disorders of Movement, continued

         Myasthenia gravis (MG)

       extreme muscular weakness caused by reduced acetylcholine receptors

       acetylcholinesterase inhibitors are effective temporarily (increase levels of acetylcholine at neuro-muscular junctions)

       thymectomy can be effective as many patients have tumors on thymus gland

 

Disorders of Movement, continued

         Muscular sclerosis (MS)

       deterioration of myelin in central nervous system

       slowing or elimination of neural responses; desynchronization of neural impulses

       patient experiences muscular weakness, impaired coordination, urinary incontinence and visual problems

       immune system attacks the person's own myelin; may be due to earlier viral infections

 

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