Key Concepts in Reflexes and Nervous System Function

Overview of Motor Activity

• Importance of motor endings in communication between nerves and effectors (muscle/gland)
• Types of effectors: skeletal muscle, smooth muscle, cardiac muscle, and glands

Nervous System Types

• Somatic Motor Nervous System:
• Targets skeletal muscle through neuromuscular junction (NMJ)
• Defined by direct nerve to muscle communication
• Autonomic Nervous System:
• Targets visceral muscles and glands with diffuse effects
• Neurotransmitters include acetylcholine, norepinephrine, and epinephrine

Levels of Motor Control

• Different levels: spinal cord, brainstem, and higher brain areas (cerebrum, cerebellum, basal nuclei)
• Reflexes are immediate responses at the level of the spinal cord

Reflexes

• Two main types: intrinsic (inborn) and acquired
• Intrinsic: automatic, e.g., posture regulation
• Acquired: learned, e.g., driving
• Reflex Arc Components:
• Receptor, Sensory Neuron, Interneuron, Motor Neuron, Effector

Types of Reflexes

• Stretch Reflex:
• Monosynaptic: contraction of muscle that was stretched
• E.g., patellar reflex
• Reciprocal inhibition involved (agonist muscle contracts, antagonist relaxes)
• Tendon Reflex:
• Polysynaptic: relaxes the muscle of the tendon that was stimulated
• Reciprocal activation involved (agonist muscle relaxes, antagonist contracts)
• Withdrawal Reflex:
• Polysynaptic: automatic withdrawal from painful stimulus
• Crossed Extensor Reflex:
• Polysynaptic: shifts weight to opposite limb during withdrawal
• Superficial Reflexes:
• E.g., plantar reflex (Babinski test) and abdominal reflex

Development of the Nervous System

• From ectoderm germ layer
• Aging affects sensory receptors and reflex efficiency

Comparing Somatic and Autonomic Systems

• Effector types differ (skeletal in somatic; smooth/cardiac in autonomic)
• Pathways and neurotransmitters also differ
• Somatic: one neuron, acetylcholine only
• Autonomic: two neurons (preganglionic and postganglionic); varied neurotransmitters
• Sympathetic: norepinephrine/epinephrine; Parasympathetic: acetylcholine

Functioning of the Autonomic Nervous System

• Dual innervation: sympathetic (fight or flight) vs. parasympathetic (rest and digest)
• Balance of systems maintains homeostasis and responds to stimuli
• Impact of stress and learned responses on reflexes and behaviors