Overview
This lecture introduces the structure and function of the peripheral and central nervous systems, directional and anatomical terminology, vascular and cerebrospinal fluid systems, and cranial nerves.
Directional and Anatomical Terms
- Medial means toward the midline; lateral means away from the midline.
- Dorsal refers to the top or back (depending on context); ventral refers to the bottom or front.
- Anterior means toward the nose; posterior means toward the tail/butt.
- Rostral is toward the nose; caudal is toward the tail.
- Hypo- means below; supra- means above.
Nervous System Organization
- The nervous system is divided into the central (CNS, brain and spinal cord) and peripheral (PNS) nervous systems.
- The PNS includes the somatic (voluntary movement) and autonomic (involuntary processes) systems.
- Afferent neurons bring sensory information to the CNS; efferent neurons carry commands away ("SAME DAVE" mnemonic: Sensory=Afferent, Motor=Efferent; Dorsal=Afferent, Ventral=Efferent).
- The autonomic system is divided into sympathetic (fight or flight) and parasympathetic (rest and digest) branches.
Spinal Cord and Meninges
- The spinal cord relays messages between body and brain and controls some reflexes.
- Spinal cord has gray matter (cell bodies) centrally, white matter (axons) peripherally.
- Regions: cervical, thoracic, lumbar, sacral, and coccygeal.
- Cauda equina: nerve bundle at lumbar end; site for lumbar puncture (spinal tap).
- Meninges: dura mater (tough outer), arachnoid mater (web-like, middle), pia mater (delicate inner covering).
- Meningitis is inflammation of the meninges, can be life-threatening.
Cerebrospinal Fluid (CSF) and Ventricles
- CSF cushions brain and spinal cord, removes waste, and maintains environment.
- Produced by choroid plexus in ventricles; circulates through subarachnoid space and central canal, reabsorbed via dural sinuses.
- Four ventricles: two lateral ventricles, third ventricle (center), fourth ventricle (near cerebellum).
- Monroe foramina connect each lateral ventricle to the third; cerebral aqueduct links third to fourth.
Cerebral Blood Supply
- Blood supplied by carotid (internal and external) and vertebral arteries.
- Internal carotid forms anterior and middle cerebral arteries; vertebral forms basilar artery, then splits into posterior cerebral arteries.
- Circle of Willis is a safety loop ensuring continued blood flow if blockage occurs.
Cranial Nerves
- There are 12 pairs; numbered I-XII; control sensory and motor functions mostly for head and neck.
- I: Olfactory—smell; II: Optic—vision; crossing at optic chiasm sorts left/right visual fields.
- III, IV, VI: Eye movement (III: up/down/in, IV: rotation, VI: outward).
- V: Trigeminal—facial sensation and chewing.
- VII: Facial—facial expression, taste (front 2/3 tongue), stabilizes stapes; damage causes Bell’s palsy.
- VIII: Vestibulocochlear—hearing and balance.
- IX: Glossopharyngeal—taste (back 1/3 tongue), gag/swallow reflex, stimulates parotid gland.
- X: Vagus—most parasympathetic control; innervates organs from brainstem to colon.
- XI: Accessory—neck and shoulder movement.
- XII: Hypoglossal—tongue movement.
Key Terms & Definitions
- Central Nervous System (CNS) — brain and spinal cord.
- Peripheral Nervous System (PNS) — nerves outside CNS.
- Afferent Neurons — carry sensory info to CNS.
- Efferent Neurons — carry motor commands from CNS.
- Sympathetic Nervous System — activates body’s fight/flight response.
- Parasympathetic Nervous System — calms body, rest/digest.
- Meninges — protective coverings of brain/spinal cord (dura, arachnoid, pia).
- Cerebrospinal Fluid (CSF) — fluid that cushions and nourishes CNS.
- Ventricles — interconnected cavities in the brain containing CSF.
Action Items / Next Steps
- Review assigned readings on nervous system anatomy.
- Memorize cranial nerve functions and numbers for exam.
- Prepare for next week’s lecture on brain regions and functions.