Somatic Sensory and Motor SystemsSomatosensory NeuronsHow do mechanoreceptors detect touch?Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14SummarySomatic Sensory and Motor SystemsSomatosensory•What are the various types of somatosensory neurons and what do they look like?•Mechanoreceptors:–How do they detect touch?–How is that information organized?Somatic Motor- Motor Neurons•What is a neuromuscular junction?–How many neurons innervate a single muscle fiber?–How many muscle fibers does a single neuron innervate?•How are alpha motor neurons arranged in the spinal cord?Somatosensory NeuronsHow do mechanoreceptors detect touch?Endings and their location in the skinWhat are rapidly adapting mechanoreceptors good at detecting?What are slowly adapting mechanoreceptors good at detecting?AdaptationHow do mechanoreceptors detect touch?Receptive Fields- the region of a sensory surface that, when stimulated, changes the membranepotential of a neuronHow do mechanoreceptors detect touch?We are going to measure our own mechanoreceptor receptive fields on our fingertips, lower fingers, palms, forearms, and backs using a 2-point discrimination test. Predictions:Which body part do you think will have the smallest receptive field?Which body part do you think will have the largest receptive field?Do you think the size of the receptive field on your palm will be much different than your lower finger? Forearm?Experiment:Place 1 or both ends of the bent paperclip on your blinded partner’s skin and ask your partner if it was 1 point or 2. The smallest distance between the 2 ends (measured with your ruler) at which they can tell there are 2 points at least 3 times is the approximate size of their receptive field for that part of the body. Fingertip:_________________________ Lower Finger:______________________ Palm:_____________________________ Forearm:__________________________ Back:______________________________How is mechanoreceptor information organized?Spinal Segments: Dermatomes:Dorsal Column–Medial Lemniscal PathwayHow is mechanoreceptor information organized?Somatotopy (Homunculus) Columnar OrganizationHow is mechanoreceptor information organized?Cortical Plasticity“Use It or Lose It”Alpha Motor NeuronsFlexor- Muscle that creates a smaller joint angle when it contractsExtensor- Muscle that creates a larger joint angle when it contractsSynergists- Muscles that work together when they contractAntagonists- Muscles that work against each other when they contractRostral-Caudal Organization:Dorsal-Ventral and Medial-Lateral Organization:SummarySomatosensory•Somatosensory neurons (proprioceptors, mechanoreceptors, and nociceptors) are unipolar neurons with cell somas in the dorsal root ganglia and enter the spinal cord through the dorsal root•Mechanoreceptors have different endings and locations in the skin that give them specialized properties and the size of the receptive fields depends on the area of skin that their endings are located•Mechanoreceptor info:–Is divided by dermatomes as it enters the spinal cord–Is arranged somatotopically –Slow and fast adaptation information is segregated in the primary somatosensory cortexSomatic Motor- Motor Neurons•Each alpha motor neuron innervates many muscle fibers, although each muscle fiber is only innervated by one neuron•The ventral spinal cord is somatotopically arranged:–MNs innervating flexors are dorsal to MNs innervating extensors–MNs innervating distal muscles are lateral to MNs innervating proximal muscles–The MNs in the rostral parts of the spinal cord innervate rostral muscles and vice