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CNS (The Brain and Spinal Cord)
The Spinal Cord
• carries messages from sensory nerves to the brain and motor nerve
messages from the brain to organs, muscles and glands.
• it contains two types of tissue:
• grey matter - non-myelinated interneurons
• white matter - myelinated neurons (motor and sensory)
• the interneurons are arranged in tracts which connect the spinal cord to
the brain.
• the dorsal tract brings sensory information into the spinal cord and the
ventral tract carries motor information from the spinal cord to the
muscles, organs and glands.
• the brain and spinal cord are protected by protective membrane, the
meninges and surrounded by cerebrospinal fluid.
The Brain
• the major components of the brain are:
• cerebrum - responsible for complex behaviour and intelligence, it
interprets sensory input and starts motor impulses.
• it consists of two hemispheres, each of which has 4 lobes:
• frontal - motor control for movement of voluntary muscles
• temporal - sensory areas for visual processing and hearing
• parietal - sensory areas for touch and temperature sense
• occipital - sensory areas for vision
• the surface of the cerebrum (the cerebral cortex) is made of grey matter
and is highly folded, increasing surface area.
• corpus callosum - a bundle of nerves which connects the left and right
hemispheres of the brain
• below the cerebrum is the thalamus, which sorts sensory information
and directs it to the correct part of the cerebrum.
• below the thalamus, is the hypothalamus, the control centre for the
Autonomic Nervous System.
• it controls hunger, body temperature, aggression and other aspects of
behaviour and metabolism.
• the hypothalamus controls the endocrine hormone system because attached
to it is the pituitary gland.
• the pituitary gland produces hormones that control many of the endocrine
glands.
• the midbrain is a short segment of the brainstem involved in hearing and
visual reflexes.
• the cerebellum is part of the hindbrain that controls muscle coordination, it
contains 50% of the neurons in the brain. Most of the physical skills we learn
are eventually taken over by the cerebellum so that we don’t have to
concentrate on them.
• the medulla oblongata joins the spinal cord to the cerebellum, it controls
involuntary muscle action (breathing movements, heart rate).
• the pons contains bundles of axons traveling between the cerebellum and
the rest of the CNS, it helps the medulla to regulate breathing rate.