Reflexes and Spinal Cord - Nervous System Lecture PDF

Nervous System, Cont. Chapter 13 Reflexes, spinal cord, spinal tracts Objectives Describe the basic components of a reflex arc Describe the different types of reflex arc Describe the functional anatomy of a muscle spindle Explain how and where signals are sent to and from...

Nervous System, Cont. Chapter 13 Reflexes, spinal cord, spinal tracts Objectives Describe the basic components of a reflex arc Describe the different types of reflex arc Describe the functional anatomy of a muscle spindle Explain how and where signals are sent to and from the CNS, including spinal tracts Spinal Cord Conduction Up = Sensory Down = Motor Neural integration Grey matter E.g., bladder control Locomotion Central pattern generators E.g., repetitive sequences w/ walking Reflexes Reflexes Stimulus  receptor Action  Effector Spinal Reflexes Fast Few neurons Involuntary Require stimulation Very predictable  Polysynap Components tic 1. Sensory Receptor 2. Sensory Neuron 3. Integration Monosynaptic Center 4. Motor Neuron 5. Effector Organ Muscle Spindle Stretch receptors Muscle spindles Higher density in muscles involving fine motor control Proprioception Sensory input Muscle length Movement Motor output Contractions Coordinate movement Regulate posture Corrective reflexes Muscle Spindle Intrafusal fibers Located near ends of muscle Few sarcomere at ends Gamma motor fibers Keeps fibers taunt Sensitivity during muscle shortening Primary sensory fibers Length & Rate Responsive to quick movements Secondary sensory Length Sensory fibers synapse? Extrafusal fibers Muscle Spindle Subconscious monitoring Posture Movement control Corrective reflexes Stretch reflex Contraction Posture/stabilization Equilibrium Synergists Antagonists Extensors Flexors Stretch Reflex Mediated by brain Spinal cord component Stronger if sudden stretch Depend on reciprocal inhibition Flexor Reflex Injurious stimulus Polysynaptic Flexor contraction Weight bearing systems Ipsilateral & contralateral Extension of opposite limb  Contralateral Reflex Arc Developmentally Dynamic Reflexes Palmar grasp reflex Until 5-6 months Moro reflex “Startle reflex” Until ~3-4 months k1.co sg HY be sY Rooting reflex = r tu Until ~4 months ?v you Sucking reflex tch w. e0 /wa //ww Plantar reflex m. ps: Babinski’s sign ht t Under a year Walking/Stepping reflex Integrates ~5-6 months Frontal release signs – adults Parachute reflex Released from inhibition Begins 6-7 months  present in adult Frontal lobe disorders Stop and think… What is the purpose of gamma motor nerve fibers? In order of stimulus perception to an output action, what are the main components of a reflex arc? Why do some reflexes exist only in infants and not in healthy adults? Spinal Tracts Ascending Tracts Sensory signals upwards Signals through 3 neurons 1.First order Stimulus  SC (or brainstem) 2.Second order SC or brainstem  thalamus (gateways, relay center) 3.Third order Thalamus  cerebral  Ascending Tracts 1. Leg/trunk sensation and position Arm sensation and 1 position 2. Muscle feedback (balance, position) 2 3 3. Sensation (light touch, pain, temperature, pressure) Path to CNS Decussation E.g., cuneate fasciculus Spinothalamic Fasciculi: medulla Spinothalamic: SC Spinoreticular: SC Ant. spinocerebellar: SC Post. Descending Tracts 1. Fine limb movement 1 2. Limbs, posture control 2 3. Turning head reflex 1 3 4 4. Limbs, posture control 5 5 5. Respond to tilt, keep balance Path from CNS E.g., corticospinal tracts Lat. corticospinal: medulla Ant. corticospinal: SC Tectospinal: midbrain Reticulospinal: none Lat. vestibulospinal: none Med. vestibulospinal: Stop and think… A patient was recently involved in a car accident on the safest road in Lafayette, Pinhook Rd. The patient received a blow to the upper back region during the accident and is unable to feel positional sensation in his left arm & hand. What is a plausible structure that may have been damaged? What part of the brain would you expect is not receiving normal signals? What tract relays temperature information from the skin through the CNS? What tract carries motor information to your hand after holding it over a flame? Next: Nervous System, Cont. Chapters 14 & 15 The Brain