Nervous System and Cranial Nerves Flashcards

Overview of the Nervous System

• The nervous system has complex pathways for carrying sensory information from the periphery (skin) to the brain.

• Key topics include the peripheral nervous system, the somatosensory pathways, and motor pathways.

Somatosensory Pathways

Dorsal Column Medial Lemniscus System

• Function: Carries touch and proprioception information.

  • First Order Neurons: Detect stimuli in the periphery (skin), enter the spinal cord via the dorsal root.

  • Second and Third Order Neurons: Located in the spinal cord and brain, respectively.

  • Gracilis vs. Cuneatus: Gracilis carries information from the lower body; cuneatus from the upper body.

Anterolateral System

• Function: Carries pain and temperature information.

  • First Order Neuron: Detects stimulus (pain/temperature) and enters spinal cord through the dorsal root.

  • Second Order Neuron: Located in the dorsal horn of the spinal cord; immediately synapses.

  • Decussation: Crossing over occurs in the spinal cord before ascending to the thalamus.

  • Paths: Travels via the spinothalamic tract to the thalamus and then to the primary somatosensory cortex (S1).

Primary Somatosensory Cortex (S1)

• Location: Postcentral gyrus of the brain.

• Body Mapping: Area of cortex dedicated to body regions correlates with sensitivity, not size.

  • Example: Large areas for hands and lips due to higher sensitivity; smaller for less sensitive areas such as the trunk.

Motor Pathways

Corticospinal Tract

• Function: Carries motor commands to peripheral muscles.

  • Decussation: Occurs at the medulla's pyramids.

  • Synapse: Lower motor neurons in the ventral horn of the spinal cord synapse on muscles.

Organization of Primary Motor Cortex (M1)

• Located in the precentral gyrus.

• Functions similarly to S1, reflecting how finely motor control is required in different body regions.

Basal Nuclei & Cerebellum Functions

• Basal Nuclei: Groups of nuclei that modulate voluntary movement (gas for voluntary; brakes for involuntary).

• Cerebellum: Monitors movements, calculates discrepancies between intended and actual movements (motor error), and facilitates motor learning.

Spinal Nerves and Cranial Nerves Overview

Spinal Nerves

• Total: 31 pairs of mixed spinal nerves (both sensory and motor).

• Roots: Dorsal (sensory) and ventral (motor) roots combine to form spinal nerves.

Cranial Nerves

• Total: 12 pairs; can be sensory, motor, or both.

• Learning Focus: Name, function, and whether each nerve is sensory, motor, or both.

  • Key Cranial Nerves:

  • II (Optic): Vision.

  • III (Oculomotor), IV (Trochlear), VI (Abducens): Eye movement.

  • V (Trigeminal): Sensation in the face, motor functions in facial muscles.

  • VIII (Vestibulocochlear): Hearing and balance.

  • IX (Glossopharyngeal): Taste and motor functions of the throat.

  • XI (Accessory): Motor control of neck muscles.

  • XII (Hypoglossal): Motor control of the tongue.

Important Terminology

• Decussation: The crossing over of nerve fibers from one side to another.

• Somatotopy: Organization of the brain that relates to the body, where adjacent body parts are represented adjacently in the brain's cortex.

• Sensory and Motor Functions: Recognize the distinction within cranial nerves for learning purposes (e.g., sensory, motor, or both).