Central and Peripheral Nervous System Overview

Central Nervous System (CNS)

• Consists of the brain and spinal cord
• Responsible for processing and coordinating information
• Divided into three main parts:
  • Autonomic nervous system
  • Peripheral nervous system
  • Central Nervous System

Peripheral Nervous System (PNS)

• Includes all nerves outside the spinal cord
• Carries motor impulses to muscles
• 12 pairs of cranial nerves:
  • Olfactory nerve: Sensory, responsible for smell.
  • Optic nerve: Sensory, responsible for vision.
  • Oculomotor nerve: Motor, responsible for eye muscle movement.
  • Trochlear nerve: Motor, responsible for eye muscle movement.
  • Trigeminal nerve: Both, responsible for sensory functions of the face and motor functions of the jaw muscles.
  • Abducens nerve: Motor, responsible for eye muscle movement.
  • Facial nerve: Both, responsible for sensory functions of the tongue and motor functions of the facial muscles.
  • Vestibulocochlear nerve: Sensory, responsible for hearing and balance.
  • Glossopharyngeal nerve: Both, responsible for sensory functions of the tongue and motor functions of the throat muscles.
  • Vagus nerve: Both, responsible for motor functions of the heart, lungs, and digestive system.
  • Accessory nerve: Motor, responsible for controlling the trapezius and sternocleidomastoid muscles.
  • Hypoglossal nerve: Motor, responsible for controlling the tongue muscles.
• 31 pairs of spinal nerves:
  • 8 Cervical
  • 12 Thoracic
  • 5 Lumbar
  • 5 Sacral
  • 1 Coccygeal

Nerve Cells

• Fundamental unit of nervous system tissue
• Types:
  • Motor neurons: Carry signals from CNS to muscles and glands (efferent).
  • Sensory neurons: Carry signals from the periphery to the CNS (afferent).
  • Interneurons: Connect neurons within the CNS.

Neuron Structure

• Cell body: Contains most cell organelles.
• Dendrites: Receive impulses and transmit them towards the cell body.
• Axon: Conducts impulses away from the cell body.
• Terminal: Distal end of the axon, where neurotransmitters are released.
• Myelin sheath: Fatty sheath that surrounds the axon, increasing the speed of pulse conduction.
• Node of Ranvier: Gaps in the myelin sheath.

White Matter

• Contains myelinated fibers, found in CNS and PNS
• Major tracts in the CNS

Gray Matter

• Contains unmyelinated fibers
• Includes the cerebral cortex and the central portion of the spinal cord.
• H/Butterfly shape in spinal cord

Synapse

• Space between neurons
• Site of communication between neurons

Brain Protection

• Three levels of protection:
  • Skull and vertebrae
  • Meninges (dura mater, arachnoid, pia mater)
  • Cerebrospinal fluid

Cerebrum

• Largest portion of the brain
• Responsible for mental functions: speech, learning, personality, etc.
• Divided into four lobes:
  • Frontal lobe: Anterior portion, responsible for personality, rational thought, decision-making, and motor movement.
  • Parietal lobe: Between the frontal and occipital lobes, controls sensory and gross sensation, touch and pressure, determines weight, size, and shape.
  • Temporal lobe: Under the frontal and parietal lobe, responsible for behavior, hearing, language reception, understanding, and memory.
  • Occipital lobe: Posterior portion, responsible for vision, recognition of size, shape, and color.

Other Brain Structures

• Thalamus: Relay center for body sensations, pain perception.
• Hypothalamus: Controls hormone function, behavior, and temperature regulation.
• Basal ganglia: Coordinates motor movement.
• Brain stem: Located below the cerebrum, controls heart rate and respiration.
  • Midbrain: Controls visual reflexes.
  • Pons: “Bridge” between the midbrain and medulla oblongata.
  • Medulla oblongata: Controls respiration, blood pressure, and heart rate.
• Cerebellum: Controls muscle coordination, tone, and posture.
• Corpus callosum: Connects the right and left cerebral hemispheres.

Spinal Cord

• Connects the brain to the body
• 17 inches long
• Conus medullaris: End of the spinal cord, cone-shaped.
• Cauda equina: Collection of nerve roots (L2-S5).

Autonomic Nervous System

• Controls visceral structures (digestion, reproduction, cardiovascular and respiratory systems).
• Divided into two branches:
  • Sympathetic: “Fight or flight” response, increases heart rate, blood pressure, and breathing.
  • Parasympathetic: Conserves energy, decreases heart rate, blood pressure, and breathing.

Dermatomes

• Area of skin supplied by the sensory fibers of a spinal nerve.

Myotomes

• All the muscles that receive motor innervation from a specific spinal cord segment.

Plexus

• Network of nerves that branch and combine to form peripheral nerves.
• Three major plexuses:
  • Cervical (C1-C4)
  • Brachial (C5-T1)
  • Lumbosacral (L1-S3)