Reflex Arc and Nervous System Overview

Reflex Arc Components
  • Receptor:
    • Site of stimulus action.
  • Sensory Neuron:
    • Transmits afferent (sensory) impulses to CNS.
  • Integration Center:
    • Sensory neuron synapses with other neurons to process information and relay the signal to a motor neuron.
    • Can be monosynaptic or polysynaptic.
  • Motor Neuron:
    • Conducts efferent impulses from the integration center to the effector organ.
  • Effector:
    • Muscle fiber or gland cell that responds to efferent impulses by contracting or secreting.
  • Reflex Arc:
    • Neural pathway that exists for rapid, involuntary responses.
Neural Pathway
  • Definition:
    • Series of connected neurons sending signals/electrical impulses within the brain.
Brachial Plexus
  • Definition:
    • Network of interlacing nerves found in the upper arm area.
  • Major Nerves:
    • Axillary, Musculocutaneous, Radial, Median, Ulnar.
Nerve Functions
  • Axillary Nerve:
    • Innervates deltoid, teres minor, and skin/joint capsule of shoulder.
  • Musculocutaneous Nerve:
    • Innervates biceps brachii, brachialis, and skin of lateral forearm.
  • Radial Nerve:
    • Innervates all extensor muscles, supinators, and posterior skin of the limb.
  • Median Nerve:
    • Innervates skin, most forearm flexors, wrist/finger flexors, and thumb opposition muscles.
  • Ulnar Nerve:
    • Supplies flexor carpi ulnaris, flexor digitorum profundus, most intrinsic hand muscles, skin of medial hand, and wrist/finger flexion.
Lumbar and Sacral Plexus
  • Lumbar Plexus:
    • Arises from L1-L4; innervates thigh, abdominal wall, and psoas muscle.
    • Major nerves: femoral and obturator.
  • Sacral Plexus:
    • Arises from L4-S4; innervates buttocks, perineum, lower limbs, and pelvic structures.
    • Major nerve: sciatic nerve (longest and thickest nerve, innervates hamstrings, adductor magnus, and most muscles in leg and foot).
Sensory and Motor Information Pathways
  • Sensory Information: Travels to spinal cord via the dorsal root.
  • Motor Information: Travels away from spinal cord via the ventral root.
Types of Receptors
  • Proprioceptors:
    • Inform brain of body movements via stretch response in muscles, tendons, joints, etc.
  • Exteroceptors:
    • Sense external stimuli through receptors in skin for touch, pressure, pain, and temperature.
  • Interoceptors (Visceroceptors):
    • Sensitive to internal stimuli; not always conscious awareness (may cause discomfort).
Cranial Nerves
  • Olfactory Nerve (I):
    • Smell (sensory).
  • Optic Nerve (II):
    • Vision (sensory).
  • Oculomotor Nerve (III):
    • Eye movement (motor).
  • Trochlear Nerve (IV):
    • Eye movement (motor).
  • Trigeminal Nerve (V):
    • Mixed (largest; div. into ophthalmic, maxillary, and mandibular branches).
  • Abducens Nerve (VI):
    • Eye movement (motor).
  • Facial Nerve (VII):
    • Taste and facial expressions (mixed).
  • Vestibulocochlear Nerve (VIII):
    • Hearing and balance (sensory).
  • Glossopharyngeal Nerve (IX):
    • Taste, swallowing, and blood pressure (mixed).
  • Vagus Nerve (X):
    • Regulates autonomic functions (mixed).
  • Accessory Nerve (XI):
    • Motor for neck muscles (mixed).
  • Hypoglossal Nerve (XII):
    • Tongue movement (motor).
Meninges and CNS Protection
  • Meninges:
    • Protective coverings of CNS; contain CSF, protect blood vessels, enclose venous sinuses.
  • Layers:
    • Dura Mater: Outermost and strongest layer.
    • Arachnoid Mater: Middle web-like layer.
    • Pia Mater: Thin inner layer.
  • Subarachnoid Space:
    • Contains CSF and large blood vessels of the brain.
Cerebrospinal Fluid (CSF)
  • Function:
    • Bathe the brain, act as a shock absorber, transport nutrients, waste products, and chemical messengers.
  • Ventricles:
    • CSF-filled cavities lined by ependymal cells.
Brain Structure
  • Cerebrum:
    • Largest part of the brain; responsible for voluntary activities.
  • Cerebellum:
    • Coordinates movement output and balance.
  • Brain Stem:
    • Includes midbrain, pons, medulla oblongata; controls vital functions.
Functional Areas in Brain Lobes
  • Frontal Lobe:
    • Reasoning, planning, movement, emotions.
  • Parietal Lobe:
    • Sensory input for touch and body position.
  • Occipital Lobe:
    • Visual processing.
  • Temporal Lobe:
    • Auditory processing and language.