The Central Nervous System - The Brain

The Brain

• The brain is responsible for interpreting incoming impulses and deciding on a response.
• Grey matter: composed of cell bodies and dendrites.
• White matter: composed of axons.
• The skull protects the brain.
• The brain is surrounded by three layers of membranes called the meninges.
  • Cerebrospinal fluid (CSF) is found between these membranes, protecting the brain.
  • Meningitis is an infection of the meninges, caused by either a viral or bacterial infection.

Structure of the Brain

• The brain is composed of outer grey matter and inner white matter.
• It is divided into three main parts:
  1. Forebrain: Includes the cerebrum, hypothalamus, thalamus, pituitary gland, and pineal gland.
  2. Midbrain: A small part of the brain containing optic lobes, which control eye movements. It connects the forebrain with the hindbrain.
  3. Hindbrain: Includes the cerebellum and medulla oblongata.

Parts of the Brain

Part	Function
Cerebrum	• Made of two hemispheres, connected by the corpus callosum (bundle of nerves). • Controls thought, logic, will, intelligence, memory, and activities connected with sense organs (e.g., speech, vision, hearing), plus motor control. • The right hemisphere controls the left side of the body and vice versa.
Thalamus	• Receives sensory messages and directs them to the correct area in the cerebrum. • Controls emotional states such as pain and pleasure.
Hypothalamus	• Regulates the internal environment (homeostasis) by monitoring osmoregulation, appetite, thirst, body temperature, heart rate, blood pressure, breathing etc. • Assists the pituitary gland in hormone regulation.
Cerebellum	• Located at the back of the head. • Controls balance and muscular coordination. • Affected by alcohol.
Medulla oblongata	• Located where the spinal cord enters the brain. • Controls involuntary muscles involved in breathing (diaphragm), heart rate, swallowing (peristalsis), coughing and sneezing. • Detects carbon dioxide levels in the blood.
Pituitary	• Known as the master hormone gland. • Controlled by the hypothalamus.
Pineal body	• Controls sleep/wake cycles by secreting melatonin.
Olfactory lobes	• Responsible for the sense of smell.

The Spinal Cord

• The spinal cord carries messages to and from the brain.
• The spinal cord has 31 pairs of spinal nerves, which carry messages to and from different areas of the body.
• Before entering the spinal cord, each spinal nerve divides into a dorsal root and a ventral root.
  • Dorsal roots carry sensory neurons into the spinal cord.
  • Ventral roots carry the axons of motor neurons away from the spinal cord.
• The dorsal root is at the back of the spinal cord, and the ventral root is at the front of the spinal cord.
• Every dorsal root has a dorsal root ganglion, which holds the cell bodies of sensory neurons.

Sections of the Spinal Cord

1. Outer section (White Matter):

• Contains axons covered in a myelin sheath, which allows for faster impulse transmission.

2. Inner section (Grey Matter):

• Contains cell bodies, dendrites, and interneurons.
• Includes the central canal, filled with cerebrospinal fluid. This helps cushion and protect the spinal cord.