Neuro

Question 1

Reflexes

Answer 1

• Monosynaptic: Single synapse between afferent and efferent neurons. Polysynpatic: Two or more synapses
• Stretch reflex: Subconscious level, stimulus: passive stretch by applied load -> active contraction of muscle. monosynaptic connection to motorneurons. stabilizing posture
• Golgi Tendon Reflex: Polysynaptic pathway. GTO afferents synapse on interneurons in intermediate zone of spinal cord. Inhibit motorneurons of same muscle. Stimulus: active tension in muscle, response: relaxation/reduction of tension. Acts simultaneously with stretch reflex to stabilize posture
• Flexion Withdrawal Reflex: Nociceptor afferents synapse on interneurons in superficial dorsal horn. Stimulus: injury of limp, Response: flexion of joints proximal to stimulus
• Patellar Tendon Reflex: Tap on patellar tendon -> stretch quads -> contract quad. Inhibit hamstring contraction
• Cross Extension Reflex: Contralateral extension for increased postural support, commisural interneurons carry signal to contralateral spinal cord
• Extensor Thrust Reflex: Mechanoreceptors project to intermediate zone interneurons -> extensor motoneurons. Stimulus: pressure on sole of foot, Response: activation of leg extensor. Operate only during stance
• Vestibule-Spinal Reflex: Otolith afferent activate lateral vestibulo-spinal tract: ipsilateral projection extensor motor nuclei, Stimulus: downward deviation of head on one side -> activate otolith afferent, Response: downhill limbs extend

Question 2

CPG(Central Pattern Generator)

Answer 2

• CPGs located in spinal cord and brainstem
• Leg Step Cycle: Flexor burst drives flexor burst motor nuclei, Extensor burst generator drives extensors. Mutually inhibit another
• Flexor burst build up of inhibition stops burst of action potential -> end activation of flexor motorneurons. Reciprocal inhibition ceases -> extensor network active
• Regulated by sensory feedback: eg. heel strike
• E3 phase stops and disinhibition flexor burst if leg is not bearing weight, hip extended, opposite leg in stance
• Arm swing flexion phase synchronous with contra-lateral flexion in leg
• Postural CPGs in reticular formation to coordinate upper body motion with spinal step cycles
• Postural maintenance organized in reticular formation of pons and medulla -> relies on somatosensory, vestibular, visual

Question 3

CMA(Corticol Motor Areas)

Answer 3

• Rubrospinal cells within red nucleus activate localized synergies in distal limbs. Rubrospinal crosses midline and ends up in intermediate zones
• Single motor nuclei represented in columns at many loci.
• Precision grip: particular neuron in motor cortex very active. Power grip: particular neuron in motor cortex is not active
• Premotor cortex processes sensory inputs, especially visual and auditory for cueing movement phases
• Sensorimotor cues: Environmental cues that trigger motor reactions. Premotor cortex selects appropriate response synergies
• Supplementary Motor Area controls bilateral coordination of limbs when different motions done on each side. Process internal volitional signals that drive movements
• Cingulate Motor Area processes emotional, and motivational drive to movements

Question 4

ANS(Autonomic Nervous System)

Answer 4

• Divided into preganglionic(CNS to spinal cord) and postganglionic(CNS to target tissue): Sympathetic and Parasympathetic release Ach -> binds to nicotinic receptors -> para releases norepinephrine -> adrenergic receptor, symp releases Ach -> muscarinic receptor
• Sympathetic: preganglionic neurons originate in thoracolumbar spinal cord, ganglia and short preganglionic neurons to sympathetic chain, long postganglionic neurons from chain to effector neurons
• Parasympathetic: preganglionic neurons originate in spinal cord -> long preganglionic to ganglia near effector organ, short postganglionic from ganglia to effector organs
• Sympathetic: fight or flight, increase heart rate and blood pressure
• Preganglionic sympathetic neurons -> chromaffin cells -> release epinephrine
• Parasympathetic: Relaxed state, decrease heart rate and blood pressure
• Autonomic neurons target smooth muscle, cardiac muscle, varicosities: axon swelling, vesicles filled with NE
• Too bright: parasympathetic via cranial nerve III to iris muscles. Too dark: sympathetic via thoracic cord
• Baroreflex: Cardiovascular center, adjusts blood pressure based on posture, beside respiratory center. NTS send information to VLM. Caudal drops BP, Rostral raises BP and HR
• Periaqueductal Gray functions as coordinator of autonomic behavior
• Diffuse Modulatory System: Cholinergic(sleep-wake cycle), originate in cerebrum/pons, terminate in the hippocampus
  Serotenergic: Mood, behavior. originate in raphe nuclei along brainstem midline, terminate: lower nuclei project to spinal cord, upper nuclei to rest of brain
  Noradrenergic: attention, arousal. originate: pons, terminate: cerebral cortex, thalamus
  Dopaminergic: reward center. Originate: midbrain, Terminate: Cortex
  Histaminergic: sleep-wake control, Originate in posterior thalamus, project throughout forebrain

Question 5

Muscle

Answer 5

• Skeletal muscle: activated by somatic nervous system, contractile filaments in sarcomeres, developed sarcoplasmic reticulum(Ca++ storage). Muscle fiber made up of myofibril.
• Motor Unit Types: Slow twitch oxidative fibers: slowly contracting, for posture. Fast twitch oxidative fiber: fast contraction, for walking. Fast twitch glycolytic fibers: Fast twitch, rapid fatigue, sprinting and jumping
• Botox prevent vesicle release, smooth wrinkles
• Ach-esterase inhibition, continuously cause depolarization -> paralysis
• Thin filament made up of actin, thick filament made of myosin. Troponin holds tropomyosin over myosin binding site on actin -> relax muscle
• Ca++ binds troponin, exposes actin binding site -> muscle contracts
• Myosin release ADP at end of power stroke -> low affinity for actin
• Latent Period: Excitation-contraction occurs, Period of contraction: Intracellular Ca++ levels high -> crossbridge cycling, Period of relaxation: Ca++ levels fall
• Smooth muscle: Internal organs, blood vessels, not arranged in sarcomeres, involuntary control by ANS. no NMJ
• Single unit: Blood vessels, exhibit spontaneous activity. Multi-unit: Large airways, contract when nervous supply stimulated
• Excitation-Contraction: Calcium trigger release of calcium from sarcoplasmic reticulum -> bind to calmodulin -> activate MLCK -> phosphorylate myosin -> crossbridge cycling
• Cardiac muscle: Contractile cells and conductile cells, contractile filaments in sarcomeres, modulated by ANS. AP duration 300ms in ventricles. Increase force of contraction by increase muscle length
• Systole: Increased cytosolic Ca++, Diastole: Removal of Ca++ from cytosol allow for relaxatio