Midterm paper

Module 12 LO3

Reflexes

Dr. Lisa Brinn [email protected]

3. Reflexes

• Spinal cord functions in homeostasis A. Action potential propagation • White matter tracts serve as “highways”

B. Integration of information • Gray matter – receives and integrates incoming

and outgoing information

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Spinal Cord Major Sensory Tracts

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• Sensory Tracts A. Dorsal (posterior) columns

• convey action potentials for touch, pressure, vibration and proprioception

B. Spinothalamic tracts • conveys action potentials for sensing pain, temperature, itch and

tickle a) Lateral spinothalamic tract b) Anterior spinothalamic tract

Sensory Action Potential Propagation

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Sensory Homunculus • A cartoon representation of

the sensory homunculus arranged adjacent to the cortical region in which the processing takes place.

Spinal Cord Major Motor Tracts

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• Motor tracts A. Direct pathway – pyramidal pathway

• convey action potentials to cause voluntary movements of skeletal muscles a) Lateral corticospinal tract b) Ventral corticospinal tract c) Corticobulbar tract

B. Indirect pathway – extrapyramidal pathway • convey action potentials that regulate posture, balance, and muscle tone a) Tectospinal tract b) Vestibulospinal tract c) Rubrospinal tract d) Lateral reticulospinal tract e) Medial reticulospinal tract

Ventral corticospinal tract

Motor Action Potential Propagation

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Motor Homunculus

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• A cartoon representation of the motor homunculus arranged adjacent to the cortical region in which the processing takes place.

Integration of Information • Reflex • Fast, involuntary, unplanned sequence of actions • Occurs in response to stimulus

• Classification • Complexity – monosynaptic or polysynaptic • Development – innate or learned • Effector – somatic or autonomic • Integration center – spinal or cranial

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Monosynaptic X Polysynaptic

A Reflex Arc • Step 1: sensory receptor • Step 2: sensory neuron • Step 3: integration center • Step 4: motor neuron • Step 5: effector