12.2 - Nervous System

Organisation of the Human Nervous System

• Central nervous system: Brain and spinal cord.
• Peripheral nervous system: Sensory receptors, 12 pairs of cranial nerves and 31 pairs of spinal nerves.
• Cranial nerves send nerve impulses from and to the brain.
• Spinal nerves send nerve impulses from and to the spinal cord.

Brain

Cerebrum

• Largest and most complex structure at the front of the brain.
• Controls emotions, hearing, sight, personality and voluntary actions.
• Receives, analyses, integrates and correlates information from receptors to produce sensory perception.
• Determines responses and sends instructions to effectors.
• Responsible for higher mental abilities, including learning, memory, linguistic skills and mathematical skills.

Cerebellum

• Coordinates body balance and muscle contraction for body movement.

Hypothalamus

• Maintains homeostasis.
• Regulates body temperature, water balance and blood pressure; senses hunger, thirst and fatigue.
• Connects the nervous system to the endocrine system through the pituitary gland.
• Controls the secretion of some pituitary hormones.

Pituitary Gland

• Located at the base of the hypothalamus.
• Main endocrine gland; secretes hormones that control hormone secretion by other endocrine glands.

Medulla Oblongata

• Located in front of the cerebellum.
• Controls involuntary actions: heartbeat, breathing, food digestion, vasoconstriction, blood pressure, peristalsis, vomiting, coughing, sneezing and swallowing.

Spinal Cord

• Contained within the vertebral column and surrounded by cerebrospinal fluid, which protects and supplies nutrients.
• Grey matter: Butterfly- or H-shaped central region made mainly of cell bodies.
• White matter: Surrounds grey matter; contains myelin-coated axons extending up and down the spinal cord.
• Processes some sensory information and sends responses through motor neurones.
• Controls reflex actions and connects the brain to the peripheral nervous system.

Cross-section of the Spinal Cord

• Dorsal root: Contains sensory neurone axons that send impulses from sensory receptors to the spinal cord.
• Dorsal root ganglion: Contains clustered cell bodies of sensory neurones.
• Ventral root: Contains motor neurones that send impulses from the spinal cord to effectors.
• Spinal nerve: Contains sensory and motor neurones.

Peripheral Nervous System

• Connects sensory receptors and effectors to the central nervous system.
• Somatic nervous system: Regulates voluntary actions.
• Autonomic nervous system: Controls involuntary actions such as heartbeat and blood-vessel contraction.