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3 types of somatosensation
(types of somatosensation) Exteroceptive
-perception of stimuli applied to the skin
(types of somatosensation) Proprioceptive
-perception of joints, muscles, and balance. Important for knowing where your body is in space
(types of somatosensation) Interoceptive
internal signals such as body temp and blood pressure
4 types of receptors in exteroceptive system
- - free nerve endings
- *temp, pain
(types of receptors ext. sys.) Free nerve endings
nerve endings on skin
*pick up information on temp, pain, etc.
(types of receptors ext. sys.) Pacinian (3)
-respond to displacement of the skin (pressure)
-best suited for sensing suddent change
(types of receptors ext. sys.) Ruffini
-best suited to signal gradual changes in skin stretch
(types of receptors ext. sys.) merkel
-best suited to singla gradual changes in skin indentation
processes from the exterocepticve receptors gather and roject to the...
spinal cord where they enter via dorsal root ganglion.
area of skin that is served by the dorsal root ganglion
-orderly entry of dermatomes into the spinal cord
-topography is maintained all the way to the cortx just like in the viual and auditory systems
From the skin to the brain steps
1. info enters via dorsal root ganglion
2. information projects to and synapses on to cells of dorsal column nuclei
- 3. CONTRALATERAL projection to ventral posterior nucleus of the thalamus
- 4. then arrives at primary somatosneory cortex
Thalamus has stops for 4/5 follwing senses...
lateral geniculate nucleus
-located in occipital
medial geniculate nucleus
-located in temporal
ventral posterior medial nucleus
-located in frontal
ventral posterior nucleus
-located in parietal
where is the somatosensory located?
-in the parietal lobe
-posterior to the central sulcus
what is homunculus?
The rceptive fieldsin homunculus vary...
-representations vary per body part, some are more sensitive than others
*receptive fields are much larger on our trunks than hands.
- brain structures can change to better cope with the environment
- *constant stimulation can change the pattern of nuerons
limb is lost, individual still feel sensations in that limb for days, months, and even years to come
Cause of phantom limbs
-representation of the limb in somatosensory cortex is still present
Therefore, because the limb is no longer in use, adjacent areas of somasensory cortex might take over (plasticity)
Damage to somatosensory cortex
- -damahe to large portions or parietal cortex include primary and secondary leads to asomatognosia
- *failure to recognize a body part as belonging to oenself
- -can also result in contralateral neglect
- *people fail to address their other side of body affected
whats sensory feedback?
- sensory systems interact with motor systems to guide appropriate motor behavior
- *when we make a movement, all the following in used report back to evaluate how effective the movement was
(sensorimotor association cortex) to make effective movements...
- -we must know where our limbs are realtive to our body
- *starting point
-we must know location of the object we wish to target for grasping
Posterior parietal association cortex
-receives input from visual, auditory, and somatosensory systems
-sends info to secondary motor cortex and other areas of association cortex involved in movement
Secondary motor complex
-receives information from sensorimotor association cortex
-sends information to primary motor cortex
-involved in planning of motor sequences
*stimulation of secondary motor cortex evokes complex movements that involve both sides of the body
Secondary motor complex continued...
-neurons in this morter cortex begin responding before movement has been initiated
- - some regions have bimodal responses.
- *they respond to visual stimuli in addition to being involved in movements
Primary motor cortex
-individual areas of primary motor cortex control
the movement of specific muscle groups
- -it also receives 'feedback' from somatosensory system via somatosensory cortex as well as receptors in muscles and joints so that movements can be completed or modified
- *throwing darts at bullseyes
Location of primary motor cortex
-located in the frontal lobe
*just anterior to the central sulcus
pic of primary somatosensory
pic of primary motor complex
(descending motor pathways) dorsolateral pathways
cross the middle line
(descending motor pathways) ventromedial pathways
does not cross the midline
muscles are composed of many...
individual muscle fibers
2 types of muscle fibers
-slow twitch and fast twitch
(types of muscles) Fast twitch
contract faster but exhaust
(types of muscles) Slow twitch
contract more slowly but can contract more often
(muscles and motor unit) a single motor nueron of the spinal cord innervates...
a fixed number of muscle fibers
(muscles and motor unit) motor nueron and the fibers it innervates is referred to as...
(muscles and motor unit) when motor nueron fires an action potential...
all the fibers it contacts will contract
(muscles and motor unit) motor nueron realeases acetylcholine...
which causes the muscle to contract
what are the neural elements that talk to muscles and get them to contract?
spinal motor nuerons
none of the systems innervate muscles directly...
they either directly or undirectly innervate neurons of the ventral horns of spinal cord